Polyvinyl chloride applications along with methods for managing its end-of-life items: A review

Abstract

Owing to its unique blend of properties, polyvinyl chloride (PVC) has become one of the most important polymers that have been used in everyday life for many years. Its short- and long-term applications span multiple key industries such as building, electrical/electronic insulation, packaging, and healthcare. These industries produce high volumes of PVC solid items that require responsible management when they reach their end-of-life because they are not biodegradable. Simple and affordable methods of diverting this waste from landfills would contribute positively towards combating environmental problems. However, many approaches have been reported in literature and there is a need to collate for easier comparison. For example, some alternative approaches are highly effective in transforming PVC waste into a range of valuable products but are still associated with secondary pollution. This overview covers different facets of virgin solid PVC (rigid, semi-rigid, and flexible), focusing mainly on its importance, global increase in use, and waste’s recyclability. In addition to the pros and cons of different recycling strategies, the influence of specific factors on the expanding PVC market is also considered albeit briefly. Notably, $>$ 50 % of the world’s annual PVC production and utilization capacity is accounted for by PVC items meant for building applications; these items also drive the growth of the PVC recycling market.

Introduction

Polyvinyl chloride (PVC) is a thermoplastic commonly synthesized via suspension, emulsion, or bulk polymerization of vinyl chloride monomer (VCM) in a closed system.^1,2 This VCM is obtained as an intermediate chemical during the ethylene dichloride dehydrochlorination or acetylene hydrochlorination process.^3–6 The molecular formula of PVC can be written as (H₂C = CHCl)_n, where n represents the number of vinyl chloride repeating units.^4,5,7 Common ingredients for PVC synthesis include water, VCM-soluble initiator, dispersant, and chain transfer agent.^1,2,6 Furthermore, PVC is essentially uncrystallized due to its atactic nature, even though it can become syndiotactic over short-chain segments and adopt the crystalline form.^2,7 Its resins are commercialized in particle sizes between 50 to 250 $\mu$ m, where their molecular weight normally falls between 30,000 and 80,000 g.mol⁻¹, with chlorine (Cl) content making up more than half of the total weight.^2,8,9 High Cl concentration (ca. 57 wt. %) generally gives the finished PVC compound or item superior properties, including excellent durability, longevity, electricity-insulating ability, and thermostability, as well as high resistance to degradation pertaining to impact, flame, UV radiation, biological organisms, certain chemicals, moisture vapor water, oils, alcohols, aliphatic hydrocarbons, and harsh environmental conditions.^10–17 Owing to these properties, as well as its affordability, low maintenance, abrasion resistance, and antifogging, PVC is one of the polymers that is manufactured on a large scale worldwide.^11,14,15,18 It is ranked in the top five plastic polymers in terms of market share and industrial applications.^{1,2,7,8,11,14–18} PVC is, however, susceptible to esters, ketones, as well as aromatic and chlorinated hydrocarbons; hence, its numerous varieties have been developed to date.^19,20 For instance, it can be divided into two primary types: (a). rigid PVC (rPVC, i.e., unplasticized PVC (PVC-U)) and (b). flexible PVC (fPVC, i.e., plasticized PVC), where the typical subtypes or compounds include chlorinated PVC (CPVC or PVC-C), modified PVC (PVC-A or PVC-M), and molecularly oriented PVC (PVC-O). This PVC division is exacerbated by the utilization of functional additives like plasticizers, stabilizers, impact modifying agents, fillers, etc., which are added to the traditional PVC-U formulations to tailor the properties of the final item. Moreover, rPVC is comparatively stiff and has a generally high glass transition temperature ( $T_g$ , ca. 80 $℃$ ), which limits its usability. For instance, rPVC-derived items are often not as useful in $\le$ −30 $℃$ areas of application because when the temperature of an application is −30 $℃$ or less, the rPVC material is significantly brittle, responds weakly to shocks, and is prone to breaking easily, even when subjected to light loads.^21,22 Nonetheless, Pannico et al. ²³ have reported that PVC can be made flexible even at such low temperatures by employing plasticizers, commonly phthalates, which lubricate the motion of chains and reduce crystallinity.

Various PVC compounds and their consumer end items are on the market as low-cost plastics manufactured by several companies. China, Europe, and North America are the three leading regions in the world for the manufacture of PVC compounds and items, accounting for more than 50% of global production capacity annually.^14,24,25 In addition to its low production costs and a multitude of important properties as well as dependability, a wide range of short- and long-term applications of PVC items exist due to its adaptability to the demands of the manufacturer and customer. ¹⁶ These applications, which are based on particular ASTM or ISO standards, cover a wide range of industries, from electrical and building to packaging and healthcare. However, PVC items—especially those intended for building, which make up the bulk ( $>$ 50 %) of global PVC applications—are linked to a variety of environmental problems related to PVC solid waste management.^{8,11,14,16,18,19,26} Before looking into waste though, it is important to note that the production of raw PVC and the additives used to make PVC items are both associated with specific health risks for humans.^{9,13,14,26,27} Fortunately, the latter has received a lot of attention, and safer additives have been developed to be utilized in the production of PVC compounds used in food, beverage, and medical packaging to mitigate potential health risks. On the other hand, during the PVC production process, emissions of hydrogen chloride and dioxins, among other highly harmful and carcinogenic pollutants, remain a concern for the environment.^24,26 The environmental issues of PVC solid waste exist because of the limited-service life of PVC items compared to the centuries it takes for them to degrade, which causes a constant rise in the quantity of PVC waste produced.^14,26 As a result, the effect that PVC has on both the environment and human health ought to be considered at every stage of the material’s life cycle, which is shown in Table 1. There are several methods available for managing PVC solid waste, which is an act essential to creating a more resilient PVC industrial ecology. As illustrated in Table 1, consideration of PVC solid waste recycling and landfilling completes the PVC life cycle. However, the latter is not recommended because burying PVC solid waste is associated with resultant contamination of surface as well as groundwater and soil, thereby endangering the lifeforms.^{8,11,13,18,20,24,26,27}

Table 1.

PVC life cycle stages.^{1,2,4,8,11,24,28}

Stage	Textual description
1. Raw material extraction	Cl and ethylene, the raw ingredients, are obtained from rock salt (via electrolysis) and oil (i.e., natural gas or petroleum), respectively.
2. Polymerization	Raw materials are mixed via a chemical process called chain polymerization.
3. Resin manufacturing	Polymerized PVC is processed to produce resin, which can be powdered or formed into granules.
4. Compounding	Resin is processed in the presence or absence of additives to make several PVC compounds, each having unique properties.
5. Extrusion or molding	PVC compound is extruded or molded to take on the required shape under specified instrumental conditions (temperature, pressure, etc.).
6. Fabrication and manufacturing	Shaped PVC material undergoes further processing and fabrication to create various finished items.
7. Item commercialization and use	Finished items are put to market and utilized for the purpose for which they were designed.
8. Maintenance and repairs	Some items may require maintenance or repairs throughout their lifetime. This may entail repairing damage, swapping out components, or performing other forms of maintenance.
9. Waste	Following their removal from service (for whatever cause) or when their useful life reaches an end, old PVC items are managed according to specific guidelines, which differ by country.
	Recycling: Recyclability of PVC waste items is feasible. Particularly through mechanical recycling, this waste is collected, cleaned, sorted, processed, and the resultant recyclate is used to make new PVC items. In addition to the reduction of PVC waste’s negative impact on the environment, this stage improves sustainability.
	Landfilling: PVC waste can be safely disposed of in a sanitary landfill, though this is not advised in developed countries and is only done as a last option in cases where recycling is not practical and/or economical.

Recycling, generally categorized into mechanical, chemical, energy recovery, and blending recycling, appears to be the most favoured approach for the appropriate management of PVC solid waste materials. An issue with chemical and energy recovery recycling though is that these approaches involve incineration, thereby generating secondary pollution.^11,25–27 Therefore, the mechanical recycling approach is ideal for the PVC life cycle, as it contributes largely to the reduction of frequent need for virgin PVC production processes.^8,11–17 Although mechanical recycling is generally recommended, a recent study by Swinnerton et al. ²⁸ contends that mechanical recycling of PVC solid waste can also cause environmental and occupational health issues. The study analyzed how employing PVC-containing plastic waste to make bricks via the mechanical recycling process may result in the emission of heavy metals, volatile organic compounds (VOCs), and persistent organic pollutants (POPs), all of which are known to contribute to pollution in all three environmental mediums: air, soil, and water. Nonetheless, the primary goal of mechanical recycling, particularly the secondary type, is to “undo” the fusion—i.e., the joining of particles before melting when the original PVC item is manufactured. A resultant recyclate, through open-loop and closed-loop recycling, is then added to a variety of PVC item formulations to either fully or partially replace virgin PVC. For example, over forty recyclers in South Africa as of 2020 grind and pelletize vinyl items so they can be repurposed into new PVC items like shoe soles and flooring, where the footwear industry (40%) continues to be the largest market for PVC recyclate, followed by the building and construction sector (38%) and agriculture (12%). ²⁹

Due to its numerous applications and ability to be recycled through a variety of recycling approaches, PVC is one of the most used and recycled plastics in developed, developing, and least-developed countries.^1,8,14 Therefore, several applications of its solid items and the approaches used to recycle their resultant wastes are discussed in this overview. The most common applications and recycling processes are the main topics of discussion, together with landfilling.

Importance of polyvinyl chloride based on its key properties and applications

Compared with other typical plastics

PVC is considerably inexpensive and has several remarkable properties, of which its adaptability to different environments or working conditions is arguably the key characteristic that sets it apart from other common types of consumer plastics.^19,20,24 Its utilization over other plastics and/or materials means lower handling and operations expenses. For instance, PVC use leads to both the avoidance of unsafe material movements and improper procedures that generally result in expensive maintenance and damage during transport and installation. Thus, the crucial time frame for construction on site is met if PVC is employed. Because it is resistant to chemicals and corrosion, PVC is dependable under a variety of operating settings for an extended period.^23,30–32 It also provides outstanding hydraulic performance, matching the positive impact on infrastructure with its well-known hydraulic flow control.^33,34 Accordingly, the importance of PVC can be illustrated by comparing its fraction to that of other common consumer plastic types, all of which are produced and consumed extensively throughout the world. For instance, compared to polypropylene, acrylonitrile butadiene styrene, polystyrene, and polyethylene, PVC showed the highest global usage in 2022 (Table 2)—a trend that was also noted ca. four decades ago.^{9,10,18–20,30,35,36} It can be deduced from the data in Table 2 that over 70% of PVC was comparatively used globally in the year 2022 alone. Furthermore, the great importance of PVC arises from its ease of extrusion, injection molding, or blow molding into a range of rigid and flexible articles or items, depending on the type of additive added to the resin formulation.

Table 2.

Global consumption volumes of commonly used plastics in 2022 (in 1000 metric tons).^{9,10,18,20,30,35,36}

Polyvinyl chloride	Polyethylene		Polypropylene	Polystyrene	Acrylonitrile butadiene styrene
	Low-density	High-density
55,715	1520	9870	450	15,610	2600
	11,390 (sum)

Processing of polyvinyl chloride

PVC is processed through a series of stages (Figure 1) that convert raw materials into a variety of useful PVC products or items. The end-of-life form of these items can either be used to create new materials that are distinct from the recycled PVC material (indicating open-loop recycling), or they can be connected back to the preparation of raw materials (i.e., closed-loop recycling).^4,11,22,26 First produced from natural gas or crude oil-derived ethylene and sodium chloride electrolysis-derived chlorine, ethylene dichloride (EDC) is typically converted into vinyl chloride monomer (VCM) by a process known as cracking.^3,10,18 The polymer, PVC resin, is then produced by polymerizing VCM using various methods, including bulk, emulsion, and suspension polymerization.^9,11,32 These processes produce different PVC forms, including rigid and flexible varieties, where their molecular weights typically fall into the 3.0 $\times$ 10⁴ g/mol to 1.0 $\times$ 10⁶ g/mol range.^{14,19,22,23,31} They also depend on the intended PVC use; for instance, emulsion polymerization creates a fine, smooth polymer that is appropriate for coatings and adhesives, while bulk polymerization produces high-purity PVC that is frequently used in medical applications. Suspension polymerization, on the other hand, produces PVC in a granular form that is ideal for several uses.^{22,23,31,32,37}

Figure 1.

PVC processing stages: From raw material preparation to end-of-life item recycling.^{3,11,22,37,38}

To enhance its properties like mechanical strength, thermal stability, as well as chemical and flame resistance, PVC resin undergoes the formulation stage and thereafter is mixed (compounded) with specific additives. This compounding process employs equipment like high-speed mixers, ribbon blenders, ploughshare mixers, extruders, ball mills, and/or twin-screw compounders.^22,25,32 The selection of equipment is mostly based on the production scale, the type of additives used in a formulation, and the desired properties of the finished PVC item.^22,32 Common additives include pigments for aesthetic purposes; stabilizers for the prevention of thermal degradation during compounding, processing, and usage; plasticizers for increased flexibility; fillers for improved physical properties while minimizing costs; and flame retardants for improved fire resistance.^37,38

Several important techniques, such as extrusion, injection molding, blow molding, and calendering, are used to process the PVC compound by shaping it into a desired geometry, thereby meeting a wide range of consumer and industrial requirements.^2,17,21–23 For instance, extrusion manufactures continuous forms like pipes, films, profiles, and sheets by heating and forcing the PVC compound through a die, a tool with a unique cross-sectional shape or profile.^21–23 While blow molding is best suited for hollow items like bottles, barrels, and automotive hollow parts, injection molding is used to create various PVC items in large quantities, from small parts to complex shapes, by injecting molten PVC into closed molds under pressure—typically, 500 to 2000 psi, 50 to 1000 psi, and 1000 to 3000 psi range for injection, holding, and molding pressure, respectively.^2,21–23 Shaping and smoothing a PVC compound by passing it through a series of calendering mills or heated rollers—generally, 150°C to 210°C—into items like coated fabrics, as well as thin sheets and films for use as wall coverings and floors, is known as a mechanical process called calendering.^21,23,31

Shaped PVC items are cooled, and they may thereafter go through a finishing step like surface treatment or trimming to enhance their appearance and functionality.^36,38 Quality control is an essential part of the PVC processing stages that ensure that the compounds fulfill industry standards for specific applications.^36–38 Overall, as the accompanying illustration shows (Figure 1), there is a complex interaction between each stage in the processing of PVC. However, notwithstanding the extensive use of PVC, its processing poses environmental challenges, especially regarding the emission of hazardous chemicals during manufacture, processing, recycling, and disposal.^13,14,23 To lessen the environmental footprint, sustainable additives and recycling technologies are being developed as part of continuous efforts to address these ecological concerns.^{13,17,23,27,36–38} Additionally, advances in processing methods and materials are expected to influence the current status and prospect of PVC uses.

Additives

Items made of flexible PVC (fPVC) usually have a plasticizer added as one of the ingredients in a formulation, whereas no plasticizer is added in formulations of rigid PVC (rPVC). Figure 2 shows some of the plasticizers that are widely used in the manufacture of various transparent or coloured fPVC items. The degree of flexibility varies depending on the amount of plasticizer added and the intended application. Lower item costs can be achieved by combining these plasticizers with secondary plasticizers.^37,38 Moreover, phthalates are employed due to their unique compatibility with PVC. They function by lubricating the PVC molecular chains and lowering their crystallinity to create a fPVC material that is resistant to breaking during deformation under conditions where the temperature is below $T_g$ of PVC.^39–43 Nevertheless, these plasticizers have detrimental effects on the health of lifeforms, increasing the risk of cancer and damaging organ systems, particularly the neurological, endocrine, and urinary systems of humans and animals. Thus, phthalates and their related chemicals, such as PVC heat-sensitive stabilizers, bisphenol A (BPA), etc., are prohibited worldwide, with some countries allowing the use of di-isononyl; di-isodecyl; and di-n-octyl phthalates in toys and childcare items that are put in mouths, provided that the amount is kept $\le$ 0.1 wt.%.^44–46 Water and baby bottles, stationery, and items meant for food, beverage, clothing, cleaning, swimming pools, and medical applications are among the products that have discontinued the use of phthalates and harmful stabilizers.^44–47 Instead, they are made with non-toxic plasticizers and stabilizers, all of which offer improved safety and environmental advantages because they do not contain heavy metals or other potentially harmful materials.^44–47 Trimellitates, benzoates, and phosphate esters—which are typically utilized in car interiors, cables, flooring, films, adhesives, and sealants—are additional plasticizers that are a sustainable choice for the manufacture of PVC items over phthalates.^48,49 Table 3 enumerates more additives and details the distinct effects of each on PVC items. Overall, the additives enhance the properties of PVC, increasing its range of applications.

Figure 2.

Commonly utilized phthalate plasticizers in the manufacture of fPVC items.^37,39,44

Table 3.

Common additives that modify various PVC properties.^9,14,50,51

Additive	Example	Resultant effect on PVC
Stabilizers	Lead derivatives, organotin compounds, barium-zinc based, calcium-zinc based, cadmium, as well as organic and miscellaneous types.	Reduce PVC degradation that is usually caused by oxygen, heat, visible light, or UV radiation, thereby maintaining the PVC’s performance and appearance.
Coupling agents or compatibilizers	Polymer- or copolymer-grafted.	Facilitate easy mixing of PVC with other plastics and aids in its recycling. They also increase toughness and bearing strength whilst reducing brittleness.
Flame retardants	Brominated, chlorinated, and silicone-based compounds, as well as antimony trioxide, aluminum trihydroxides, magnesium dihydroxides, and phosphorus-based melamines.	Strengthen the non-flammability of PVC.
Pigments	Titanium dioxide, lead chromate, copper phthalocyanine, diazo, polycyclic, and monoazo compounds.	Give a colour to PVC.
Plasticisers	Phthalate esters, aliphatic dibasic acid esters, benzoate esters, trimellitate esters, polyesters, adipates, citrates, and bio-based.	Lower both the crystallinity and the glass transition temperature ( $T_g$ ) of PVC and make it soft, flexible, and malleable.
Impact modifiers	Methacrylate-butadiene-styrene (MBS) terpolymer, acrylate polymethacrylate copolymer, chlorinated polyethylene (CPE), ethylene vinyl acetate copolymer, and acrylonitrile-butadiene-styrene (ABS) terpolymer.	Enable PVC to be stress-resistant while absorbing shock.
Fillers	Calcium carbonate, talc, titanium dioxide, carbon black, magnesium hydroxide, and barium sulphate.	Bulk up PVC and improve various properties, including dry blend compounding properties.
Lubricants	Metal stearates (calcium, zinc, and lead stearates), paraffin wax, fatty acids, fatty alcohols, and polyethylene wax.	Reduce friction and improve both the flow and processing characteristics.

Polyvinyl chloride compounds

A variety of PVC compounds have emerged from the two main types of PVC (i.e., rPVC and fPVC) due to developments in the PVC application sectors. ²⁴ These, also incorporating specific additives in their formulations, include chlorinated PVC (PVC-C), modified PVC (PVC-M), and molecularly orientated unplasticized PVC (PVC-O) compounds. Production of the former entails chlorinating the traditional unplasticized PVC (rPVC or PVC-U), where the resulting high Cl concentration of ca. 67 wt. % (compared to ca. 57 wt. % in PVC-U) gives the finished item excellent lightweight, longevity, durability, flexibility, corrosion- and flame-resistant, chemical stability, and thermostability ( $>$ 260 $℃$ ). ⁵² Because of these properties, PVC-C is an ideal material for socket-type fittings, pipes, and tubing that are installed generally in compliance with ASTM F438-17, ASTM F441, and ASTM D2846 standard specifications, respectively, and joined using solvent cements that meet ASTM F493-04 specifications. ⁵² PVC-C pipes, particularly, are typically suitable for solar and electric water heaters, as well as for the supply and distribution of hot and cold water in both indoor and outdoor residential, commercial, and industrial settings. ⁵² On the other hand, PVC-M, the most diverse kind of PVC, is typically an alloy or composite material, which is fabricated by mixing PVC-U and an impact modifying agent, with better user-friendliness and more ductility, durability, and impact (fracture) resistance than PVC-U.^52–55 Similarly, particularly in terms of user-friendliness, PVC-M is typically the most versatile type of PVC since it makes onsite work easier by guaranteeing the effectiveness and integrity of the water network and shielding it from hazardous movements, shoddy installations, and harsh weather or environment.^53–55 From this, it is evident that the main application for PVC-M, per ASTM D1785 specification, is in a broad range of industrial, commercial, and residential piping and fittings systems for cold and hot water, sewage, drainage, and irrigation applications.^53–55 Additionally, the PVC-M pipes and integral joints are known to provide incredibly high resistance to crack propagation (i.e., the main reason for fracture when pressurized pipelines are operating).^52–55 This ensures cost and time savings as well as excellent durability, resistance, and service.^53–55 Finally, PVC-O is produced by rearranging the amorphous structure of PVC-U into a more defined layered structure.^52,56–58 To accomplish this rearrangement, PVC is elongated under specific conditions, which causes its molecules to rotate and align in the direction of deformation.^52,56–58 Since this molecular structure’s modification, which is fully visible under an electron microscope, is the outcome of a physical or mechanical process rather than a chemical one, no changes in the standard or already-established PVC formulation are necessary.^56–58 In comparison to PVC-U, the PVC-O is lighter and ductile yet far more resistant to fatigue and impact (almost unbreakable), with high elongation at break ( ${\epsilon }_b$ ) and ultimate tensile strength (UTS) as well as excellent behaviour to external loads and avoidance of crack propagation.^52,56–58 In accordance with ISO 16422 specification, the current common PVC-O application is also piping systems meant to be used subterranean or above ground for pressurized sewage systems, irrigation systems, cold and hot water, as well as for general purposes that require specific performance requirements like impact loads and pressure fluctuations (up to 2500 kPa).^52,56–58 In addition to piping systems, an array of comparable and dissimilar applications exists for both rPVC and fPVC, and these include E&E insulation, packaging, healthcare, automotive, and more.

Polyvinyl chloride applications

Building and construction

Globally, the building and construction sector is certainly one of the most indispensable applications for PVC.^59,60 Because of its excellent performance attributes, PVC has revolutionized the building and construction industry with its various applications. These include water supply and drainage systems (e.g., potable and gravity piping as well as fittings), window and door profiles, wall coverings, flooring, reservoir linings, siding, trim, louvres, roller shutters, roofing, glazing, guttering, downspouts, sheets and panels, awnings, etc.^60,61 Moreover, the extensive use of PVC in building and construction projects of a wide range of scale is attributed to its longevity, durability, insulating capability, fire retardancy, and low maintenance requirements and costs, as well as simplicity of handling, transporting, fabricating, and installing it.^59–61 Fire retardancy property is important in cases where fire safety is a cause for worry; in this instance, the main PVC-made building components include fire-resistant doors, wall coverings, window frames, roofs, and floors. There are also several other advantages to using PVC over competing plastics for building and construction; for example, PVC pipes that minimize leaks and PVC windows that increase insulation can both save water and energy, respectively, in residential, commercial, and industrial buildings.^59,61 The industrial or ASTM standards for building & construction applications, along with their corresponding PVC compounds, are shown in Table 4.

Table 4.

Building & construction applications, along with their corresponding PVC compounds, according to ASTM standards.^31,61,62

Building & construction application	PVC type	ASTM standard
Exterior building items	rPVC and PVC-C	D4216-22
Pressure-rated pipes (standard dimension ratio series) and fittings	rPVC and PVC-C	D2241
Non-pressure-rated pipes and fittings	rPVC and PVC-C	D4396-15
Sewer pipe and fittings	Plastic sewer main (PSM) rPVC	D3034
Gasketed sewer fittings	rPVC	F1336
Interior-profile extrusions	rPVC	D3679-19
Geomembranes (used in residential, commercial, and industrial roofing, basements, and foundations)	fPVC	D7176
Sheet piling	rPVC	D8427-21
Insulating sheeting	fPVC	F1742-03

Even though PVC materials’ manufacturers often guarantee a long service life, ranging from 25 to 300 years (depending on the quality and maintenance), for building applications, these materials may undergo structural changes that result in the loss of their physical and mechanical properties. ⁶³ As a result, unique PVC compounds (i.e., PVC-M) have been developed and are remarkably resistant to the damaging effects of outdoor weather conditions. These compounds are relatively more durable and resistant to environmental factors (especially heat and water); therefore, their standard specifications permit less cautious safety factors than traditional PVC.^52,55,56,58 Window and door frames, roofing materials, outdoor furniture (e.g., sports stadium seats), and other items that are often exposed to various weather and environmental conditions (mild to aggressive) are among the items that benefit from the PVC-M compound properties. Moreover, other manufactured PVC resins offer unique blends with well-selected pigments that are stable for use with PVC in the building and construction industry, expanding the overall PVC applications in this industry.^24,52,62

Electrical and electronic insulation

The initial use of PVC for electrical and electronic (E&E) insulation applications dates back nearly nine decades ago when vinyl’s usage experienced a considerable increase because of the low supply of crosslinked rubber at the time.^64,65 PVC has been preferred for E&E applications due to its ability to be easily extruded—in the presence of additives—to materials of various thicknesses. ⁶⁶ Due to its exceptional properties, PVC is an essential polymer in the E&E industry for cable insulation and conduit systems. In the former, PVC is used to insulate E&E cables, while in the latter, it is used to protect and route E&E wiring. ⁶⁵ It is an ideal choice for both indoor and outdoor E&E installations, particularly for insulating cables, wires, and electronic components, because of its remarkable electrical properties, which include excellent insulation capability, low conductivity, strong polarity, low dielectric constant (low permittivity), and high dielectric strength, contributing to the safety and efficiency of E&E systems. ⁶⁷ Moreover, PVC conduits are less expensive, lighter, and easier to install than metal conduits, which makes them a preferred choice for E&E insulation. PVC insulation prolongs the lifespan of the E&E cables, wires, and electronic components by shielding them from damage that could result from chemical and mechanical activities, as well as cold, hot, wet, and dry conditions.^65,67

ASTM F512-19 is a common standard specification for PVC applications in E&E systems. It covers the dimensional, design, and performance requirements for five different types of smooth-wall PVC conduits as well as fittings for underground electrical power and communication wires and cables. The conventional criteria used to assess such conduits and fittings include extrusion quality, impact resistance and strength, pipe stiffness, and joint tightness. ⁶⁸ Moreover, PVC applications for E&E insulation may be divided into two categories: primary and secondary insulations. ⁶⁹ Primary insulation is applied directly over the wire conductor whilst secondary insulation is applied as a covering over wires having primary insulation.^69,70 PVC-insulated electric wire normally has a rated voltage (300/300 V, 300/500 V, and 450/750 V), number of cores (1 – 5), and nominal cross-section. ⁶⁹ The recent establishment of higher service temperatures (up to 105 $℃$ ) and voltages, which have led to better heat stability and increased resistance to heat distortion, are both attained with suitable heat stabilizers.^{39,41,43,65,70} These stabilizers are necessary not only for the insulation application but also for the development of sheathing for E&E wires, cables, and connectors. ⁶⁵ Calcium zinc-based stabilizers, for example, have been shown to improve heat stability, lessen cable corrosion, and protect against E&E breakdown, all of which contribute to the effective and safe transmission of electricity.^44,46,47,70 These stabilizers are typically added in emulsion form along with plasticizers to achieve sufficient absorption into the PVC resin particles. Another development in the field of E&E insulation applications regarding the use of PVC involves PVC tubing, which is heat-shrinkable and currently being used to create tight skins and sleeves for cables.^71,72 Additionally, PVC-M compound, specifically the one modified with chlorinated polyethylene (CPE), is currently being used as the outer jacket for industrial power or high-voltage cables, whilst other PVC compounds are ideal for low-voltage cables used in keyboards, appliances, computers, entertainment instruments, cords, phone systems, smart devices, automotive, component housings and commercial applications. ⁷³

Packaging

PVC has a long history of usage in the packaging industry.^16,74 The main justifications for this are its remarkable lightweight, clarity (high gloss and transparency), and barrier properties, as well as adaptability in meeting both rigid and flexible packaging requirements.^74–76 PVC packaging materials are easily obtained through calendering or extrusion processes, where flexibility (good stretchability) and clarity, as well as colour, are often formulation dependent. Furthermore, PVC is a preferred option for packaging since it can be conveniently tailored to match specific branding and design specifications. ⁷⁵ Similarly, it can be molded into a wide range of sizes and shapes, which makes it an ideal polymer for developing packaging solutions that meet the needs of particular products.^75,77 The PVC responsiveness to a range of printing and labelling methods makes it possible to showcase appealing branding and product details on the packaging, increasing appeal to consumer products. PVC is also renowned in the packaging sector for its exceptional strength and durability, as well as protection against oxygen, oils, fats, and several other undesirable substances or contaminants.^16,76,78,79 Thus, the packed products are adequately protected throughout transportation and set storage duration. ⁷⁹ Food and beverage, as well as personal hygiene, pharma, and automotive materials, are often packaged in PVC items, which are typically divided into two groups: food packaging items such as thermoformed cups and trays, bottles and their caps, cling films, etc., and non-food packaging items such as containers for cosmetics, detergents, fuel, engine oil, etc.^75,76,79 Accordingly, it is reported that PVC packaging guarantees the product’s protection and proper shelf life and improves the overall shopping experience.^{11,16,76,78,79} One example of the standard specification employed for PVC packaging is ASTM D5416-95, which covers a standard test method for evaluating the abrasion resistance of stretch wraps/films through vibration testing.

Films and bottles are arguably the most common PVC applications regarding packaging. To ensure the safety (and quality) of these PVC items, their manufacturing process is subject to standards and regulations, which may vary by sector and geographic region. For instance, the European Union (EU), including the United Kingdom (UK), has prohibited the use of cadmium-, barium, tin- and lead-based stabilizers, BPA, and phthalate-based plasticizers in PVC resin formulations intended for packaging applications due to their detrimental effects on human health.^44–49 Instead, heat stabilizers based on calcium-zinc and plasticizers like citrates, adipates, and sebacates are frequently used in PVC packaging.^14,50,51,70 As a result, PVC stretch film, water and baby bottles, and similar items are typically compounded with additives that are unlikely to leach harmful substances, to establish safety as well as economic and environmental sustainability. Using non-toxic additives in PVC resin formulations not only ensures human health safety but also benefits the environment because the resultant PVC-based items can be conveniently and safely recycled once their service life has ended.^51,70

Film: There are two types of PVC film: flexible and rigid films. Flexible types are mainly used as shrink, stretch, and pallet films in consumer and industrial products. Due to PVC’s amorphous nature, which allows for easy additives-based processing to improve dimensional stability and isotropic flow—thereby increasing uniform stretchability and reducing shrinkage—the PVC application for flexible films is primarily made possible.^80,81 For both manufacturers and consumers, the thickness of flexible film is a crucial feature; ASTM D6988 is the standard method for determining this thickness. Generally, flexible films allow oxygen to pass through, which is considered favourable for maintaining the red colour of fresh meat.^75,78,79 However, products that require complete protection from exposure to oxygen are often coated with saran or polyethylene to improve oxygen barrier properties.^75,82,83 Furthermore, both wet and dry bulk foods are often packaged in PVC shrink wrap rather than boxes. This is because the latter is not as strong or secure for such products, whereas the former allows for safe and neat transportation of both food and non-food items in both industrial and non-industrial environments. ⁷⁵ The use of flexible films significantly reduces transportation, distribution, and storage costs. This is generally because shrink-wrapped items take up less space than if packed in boxes, and with film-wrapped boxes, there is no risk of products getting lost or damaged during transportation. ⁷⁵ Meanwhile, the use of rigid PVC films in the packaging sector has also increased significantly.^17,24,75,84 Similar to flexible films, the common rigid film applications include food, beverage, E&E, footwear, pharma, building sectors, etc.^80,85 Nevertheless, in contrast to flexible films, rigid films, which possess superior bending strength, printability, and low-temperature impact properties, are often used in thermoforming and vacuum-forming processes to create clamshells, trays, shelves, containers, blisters, and folding boxes. ⁸⁶

Bottles: For more than 50 years, PVC bottles have played an important role in fluid or liquid packaging.^77,87–89 The standard specifications for these bottles are covered in ASTM D2911/D2911M-16. An indisputable advantage of PVC bottles, especially if a plasticizer was included in a formulation, is their superior resistance to shattering under ambient and low temperatures. Apart from its affordability, PVC is ideal for making bottles because of its colour, design, and shape flexibility, which are easily achieved through the low-cost process called blow molding. Typically, the bottles manufactured using pristine PVC can withstand temperatures from 60 to 66 $℃$ .^43,65 Higher filling temperatures pose a risk of distortion during the handling, conveying, and capping of the bottle. Therefore, specific grades of heat stabilizers are employed to manufacture PVC bottles for high-temperature applications. PVC bottles are also suitable for shampoos, oils, and various other products that require prolonged storage. Plasticizers like phthalates can be utilized for bottles intended particularly for use as anti-corrosive and chemical storage containers.^27,90,91

Healthcare

In the realm of healthcare applications, PVC offers numerous advantages that contribute to its widespread use. Applications of PVC in the healthcare sector greatly advance patient care or treatment and make it possible to create medical equipment, implantable devices (like drainage sets), and packaging (e.g., for pharmaceutical drugs) that is reliable and reasonably priced.^92,93 Due to the impact of the Covid-19 pandemic in 2020, the need for PVC in the healthcare sector has since increased significantly.^94,95 Currently, PVC is used in over 30 % of healthcare applications.^16,96,97 Table 5 presents most of the PVC medical applications, which are primarily based on the unique properties of PVC, including sterility, flexibility, smoothness, biocompatibility, non-reactivity, chemical and moisture resistance, lightweightness, transparency, and ability to maintain its integrity under demanding conditions. Sterility, in particular, is essential and refers to the ability of PVC to withstand sterilization processes through steam, radiation, or ethylene oxide; therefore, ensuring patient safety.^97,98 Flexibility is also important, as it makes it easier to handle and install healthcare PVC items, and the smooth surface aids in the reduction of the risk of bacterial adhesion and contamination.^99–101 Moreover, in addition to ensuring reliability and safety, PVC improves accessibility and cost-effectiveness in healthcare delivery.^92,102 The common standard tests, based on specific standard specifications, performed to guide the quality of PVC items used in the healthcare sector are listed in Table 6.

Table 5.

Specific applications of PVC in the medical field.^98,101

Application	Example
Tubing	Ventilator, enteral feeding, and intravenous (IV) tubes.
Bags	Blood, plasma, IV solution or infusion, IV fluid, dialysis, and urine bags.
Mask	Oxygen, anaesthetic, and respiratory face masks.
Gloves	Household and industrial gloves.
Other	Aprons, catheters, films, trays, ducting, mattress covers, shoe covers, implantable and disposable devices, drug delivery, blister packs, and durable containers.

Table 6.

Standard specification-based tests done on PVC items used in the healthcare sector.

Standard specification, ASTM	Standard test
F2256	Adhesion strength
F88	Sealing strength
F2054/F2054M	Bursting strength
D882-12	Tensile properties
F1306	Penetration resistance

Automotive

In today’s automotive sector, there is a growing demand for innovative materials that improve vehicle performance, safety, cost-efficiency, and sustainability, where PVC is one such material that is gaining significant attention.^103,104 It is currently utilized in the manufacture of ca. 12 % of over one thousand plastic parts found in typical modern autos. ¹⁶ The seamless integration of PVC into various automotive applications has mainly been enabled by its performance at both low and high temperatures.^105,106 Along with its many other advantages, PVC is trusted and extensively utilized in the automotive sector because of its exceptional mechanical properties, which prevent expansion cracking and allow it to withstand the intense conditions of the automotive environment.^103,107,108 It has been incorporated into a wide range of automotive exterior and interior parts, including bumpers, protective strips, door panels, window encapsulation, sun visors, cladding, dashboard skins, instrument panels, seals, gaskets, floor coverings, brake lining, upholstery covers/linings, E&E wiring/cable insulations, and more.^103–108 Additionally, PVC is necessary to improve and maintain the appearance of automotive for a longer period because it is one of the thermoplastics with exceptional resistance to most types of damage, including grazes and scratches. ¹⁰⁹ Its sound-absorbing properties, especially its fPVC type, have also made modern cars quieter.^110,111

Other

PVC’s versatility, which comes from its ease of customization to meet requirements, is a crucial characteristic that makes it ideal for a wide range of applications across diverse sectors. Table 7 lists other applications of PVC, where those in the last row have recently received strong attention due to the necessity for inexpensive and fire-resistant clothes, mattresses, and floor coverings.^16,112–117

Table 7.

Additional uses for PVC.^112–117

Application	Example
Agriculture.	Pipes and fittings as well as greenhouse coverings.
Signage and banners.	Signs, decals, and graphics.
Office supplies.	Binders, rulers, folders, computer keyboards, printing materials, and cards (bank, smart, and identity cards).
Toys and sporting.	Inflatable toys, swimming pools, and other recreational items.
Synthetic leather (i.e., “pleather” or “vinyl leather”).	Furniture (patio chairs, and tables) and clothing (life vests, soles, and boots).
Fibres, foams, and coatings.	–

Fibres: PVC is used to fabricate a variety of high-quality synthetic fibre-based items with the required characteristics. The PVC-based fibres, such as Dynel ® (Union Carbide, Unites States), Saran ® (Dow Chem. Corpn., United States), and Vinyon ® (Avtex Fibres Inc., United States) (Figure 3), are highly valued in fibre/textile industry for their cushiony and non-absorbent properties.^118–120 As the demand for fire-resistant fabrics increases for safety reasons, fire resistance is a special attribute of these PVC-based fibres and may contribute to their current and future use.^118,119 Current applications of these fibres include protective clothing and footwear, blankets, curtains, mattress covers, mats, filter fabrics, fishing nets, heavy-duty tarpaulins, synthetic hair, and moldable fabrics.^118,119 Moreover, PVC-based fibres will play an important role in the future in applications such as casual outerwear, headgear, shoe uppers, children’s clothing, hosiery, undergarments, activewear, lawn furniture, industrial fabrics, and upholstery for cars and chairs. ¹¹⁸ This is primarily because these fibres blend easily and perfectly with other fibres, such as nylon, cotton, and metal threads, typically providing the best reinforcement, design, and moisture absorption for the end user’s desires.^118,119

Figure 3.

Repeat units of common PVC-based fibres.^118–120

Foams

PVC foams are typically converted into a lightweight, cushioned material.^121–124 They find applications in several items, including surfboards, flotation devices, and insulation materials.^123,124 They are fabricated and utilized in large quantities for packaging, healthcare, building, automotive, marine, and aerospace sectors.^122–124 Additionally, the excellent wear and tear resistance properties are a key factor for the use of expanded PVC with a knit backing, especially in clothing and furniture applications.^121,123 The dielectric sealing feature of PVC foam sheets allows for quilting properties in these applications and allows the sheets to be attached to other vinyl materials or themselves.^123,124 Most foamed but rigid and lightweight PVC foam sheets typically have a density between 0.1 to 0.4 g.cm⁻³. ¹²¹ Particularly for the building sector, these sheets are used for floors in homes, libraries, hospitals, schools, laboratories, institutions, and offices because of their affordability, practicality (i.e., ease of maintenance), and noiselessness, as well as excellent physical, mechanical, and aging properties.^121–124

Coatings: PVC coatings are predominantly suitable for bending as well as deep and flat drawing in the post-forming of various sheet and plate materials, whose applications are those with surfaces with important visual properties that are susceptible to damage during manufacturing. ¹²² These protect a variety of surfaces, which are metals, plastics, fabrics, etc., and extend their service life. ¹²² Specifically for PVC-coated fabrics, ASTM D4005-92 covers the integrity of the fusion of PVC dispersion coatings. Furthermore, PVC coatings can be customized to specific requirements, providing flexible solutions for different coating requirements. ¹²⁴ They can also reduce the frequency of recoating, which is important in applications where recoating is expensive. Advantages of PVC that allow it to be used in coatings (both during post-forming processes and service) include its excellent durability, adhesion, and waterproofing, as well as resistance to deformation, breaking, chemicals, abrasion, fire, biological degradation, UV radiation, etc.^121,122,124 Another PVC’s advantage regarding coating is that it is extremely versatile in terms of coating technology and formulation, both of which can be designed to meet equipment requirements and application as well as end-use conditions.^121–124 Owing to these advantages, PVC coatings are suitable for wire and cable insulation, automotive interiors and exteriors, as well as household, building, and marine materials and/or equipment.^121–124 Food packaging, drums, pipes, ships, storage tanks, and various industrial maintenance applications (including those exposed to corrosive environments) rely on the durability of PVC coatings (such as coil coatings and strippable coatings).^121,123,124 With coil coating, the finished coating product is typically post-formed onto building exterior components such as siding, gutters, downspouts, awnings, and roof shingles, all of which have warranties of 20 years or more.^121,123,124 In addition to providing a protective layer that improves the lifespan and performance of the underlying materials, PVC coating also improves the aesthetics of the coated surface, giving it a smooth and glossy finish.

Global growth in the utilization of polyvinyl chloride

In recent years, the size of the global PVC market has grown rapidly, where it was estimated to be worth ca. $59.1 billion in 2018, with a compound annual growth rate (CAGR) of 5.96% expected by 2025, reaching ca. $88.83 billion.^125–129 Concordantly, the Business Research Company group ¹³⁰ projected this growth to increase from $89.94 billion in 2023 to $97.4 billion in 2024 at a CAGR of 8.3%. From there, it is anticipated to continue increasing to $133.39 billion in 2028 at a CAGR of 8.2%. Fluctuations can occur, depending on typical factors such as technological advances, industry trends, and the state of the economy.^125,129,130 These data are predictable based on a statistical analysis of past growth and are further confirmed by figures of expected growth for all individual PVC applications.^128–130 This, therefore, suggests that the expected growth is reasonable and that a severe economic slowdown in any of the countries that significantly contribute to the overall PVC market growth size would be required for it to collapse significantly. ¹²⁹

Global PVC utilization is generally examined from an integrated perspective, i.e., from the perspective of product type (rPVC, fPVC, PVC-C, etc.), application (pipes, fittings, profiles, hoses, wires, cables, films, bottles, etc.), and end-user sector (building, packaging, E&E, automotive, healthcare, etc.). ¹²⁸ In light of this, the overall use of PVC has witnessed significant global growth across various sectors over the years.^128–130 The demand for PVC is projected to increase along with the world’s population and economies, setting the material’s production and use to new heights.^125–129 PVC products for the building sector are comparatively the key materials driving the growth of the PVC significance and its market worldwide.^60,128,129 These have grown recently as a result of expanding infrastructure, urbanization, and sustainability requirements.^60,128 This is evidenced in Figure 4, which shows that a significant portion of PVC applications is in the building sector (e.g., profiles (27%) as well as pipe and fitting (22 %)). This has also been corroborated by Sawlani ¹²⁸ who stated that rapid industrialization is driving PVC market growth through notable advancements in building and infrastructure activities.

Figure 4.

The global usage of PVC, categorized into various applications.^16,128,131

The extent to which PVC has grown in importance over the years generally determines how much PVC has been utilized globally. It was reported that ca. forty years ago applications of rPVC were significantly more common than those of fPVC.^7,131 Utilization of rPVC appeared to be more common during this period because PVC was employed primarily in residential building and vinyl record manufacturing, as opposed to now-established and well-known areas, where fPVC has instead saturated the markets.^7,24,131 A lack of knowledge about plasticizers could be another reason why rPVC applications were dominant. Nevertheless, Yousif et al. ⁷ projected that the growth of rPVC applications would encourage the growth of fPVC applications, with the former growing at a rate of 10 to 15% annually and the latter at a rate of 4 to 5% annually.

Verified Market Research group ¹²⁹ recently (as of 2022) reported that the primary driver of the growth in global PVC utilization is the expansion of the packaging sector, which primarily uses fPVC over rPVC. This was also confirmed by other researchers^81,84,85,89 who reported that the demand for fPVC is increasing due to growth in fPVC packaging applications. Moreover, compared to other common plastics, there has been a great likelihood of the overall PVC market expanding rapidly, given the untapped potential of PVC in developing countries as well as the growth of numerous concepts, such as bio-attributed PVC, renewable energy, electric vehicles, highly efficient pumps, and composites.^78,89 The infrastructure, as well as the agriculture, conveyor, and printing roller industrial sectors, are among those where the use of PVC is said to have increased significantly in recent years; consequently, expanding the PVC market.^59,60,115

Sawlani ¹²⁸ recently reported that competitiveness in the PVC sector, with both large and small companies contributing to the market, is an important factor to consider when looking into the growth of PVC utilization globally. These companies compete with each other in the PVC market based on product quality, demand, cost, trade, innovation, import/export, and market presence. ¹²⁸ Their ultimate goal is to increase their respective market positions in PVC manufacturing and supply through strategic alliances, partnerships, and R&D expenditures. ¹²⁸ As a result, global PVC utilization is undoubtedly growing and will continue to do so as long as this competition endures.^125–129 This is rational considering all the advantages that PVC offers. Nonetheless, the PVC sector is not exempt from arguments regarding the growing concerns about long-term health risks associated with pollution, although it is encouraging that companies are investing in R&D to create environmentally friendly PVC that is not only affordable but has a low carbon footprint and is 100% recyclable. ¹²⁸

Insights into the contribution of regions, companies, and products to the growing polyvinyl chloride market

The PVC market has evidently grown over the years; therefore, it is important to comprehend how various regions, companies, and products have contributed to this growth. In general, analyzing regional trends can aid in identifying area/s where PVC demand is highest and potential further growth opportunities exist. Examining the largest PVC manufacturing and/or supplying companies could also shed some insight into the factors driving the growth of the PVC market. Asia-Pacific, North America, Europe, Latin America, and the Middle East and North Africa (MENA) are the five key regions that make up the various segments of the global PVC market.^{14,24,25,128,129} After Asia-Pacific, which accounts for over 65% of global PVC production, the two main PVC-producing regions are North America and Europe.^24,128,129 Asia-Pacific is anticipated to maintain this position and potentially exhibit the highest growth rates globally in the future due to the region’s ever-increasing demand for PVC in the automotive, E&E, and packaging sectors as well as the rapid industrialization and urbanization of densely populated countries like China, India, and Japan.^{14,24,128,129} This is also because these three countries have the largest economies in the Asia-Pacific region, with China producing more PVC than any other country in the world and is relatively the main driver of the expansion of the Asia-Pacific region’s growth market. ¹²⁸ Table 8 lists the largest, and most probably leading, PVC manufacturing and supplying companies situated in the five regions that have been instrumental in augmenting the size of the worldwide PVC market by virtue of their vast PVC production capacities, inventive PVC-oriented product offerings, and expansion of PVC product portfolios to accommodate evolving market demands.^128,129 These long-standing companies sustain the PVC sector by using the strategies mentioned earlier to combat persistent market challenges. ¹²⁸ The products manufactured and supplied by these companies are intended for a wide range of applications, with the main target industries being the building, automotive, E&E, and packaging sectors, which supports the suggestion illustrated earlier in Figure 4.^{14,24,25,128,129}

Table 8.

Largest PVC manufacturers and suppliers (as of 2022).^128,129

Company	Location
Formosa plastics corporation	North America
Teknor apex	North America, Europe, and Asia
Occidental petroleum	North America
Avient corporation	Latin America, the middle East and Africa, and Asia
Axiall, a Westlake company	North America, Europe, and Asia
INOVYN (INEOS group)	Europe and Asia
KEM ONE	Europe
Vinnolit GmbH & Co.KG
Solvay	North America, Latin America, the middle East and Africa, and Asia
China National chemical corporation	Asia
Xinjiang Zhongtai chemical co., ltd
Finolex industries ltd
Reliance industries limited
Shin-Etsu chemical co. Ltd
Orbia	North America
Mexichem compuestos, S.A. de C.V.
SABIC	The middle East and Africa

The ever-increasing demand for PVC-based products in many end-use areas such as healthcare, building, automotive, E&E insulation, and packaging is the main factor driving the expansion of the North American PVC market.^25,128 Among most, if not all, countries in North America, the United States is the largest producer and user of PVC. ¹²⁹ Similar to Japan, the United States exports a range of PVC homopolymer fibres and their final products.^128,129 Although such fibres are also produced in Europe, the overall European PVC market is mainly driven by the accelerating demand for PVC in the architectural and medical sectors. ¹²⁸ Packaging, especially PVC films, is another application driving the growth of the European PVC market.^81,85,89,128 This is largely because other film products such as those made up of polyethylene, polypropylene, and styrene were developed earlier in other countries than they were in Europe.^85,89,129 Compared to other specific countries in Europe, PVC is most commonly produced and consumed in the United Kingdom and Germany. ¹²⁸ Germany, as well as Italy, are manufacturers and exports of the majority of PVC foil.^128,129 Furthermore, the production and export of PVC homopolymer fibre products are a Netherlands specialty; however, export statistics show that the country lags behind the United States and Turkey. ¹²⁸ Similar to Europe, the main growth driver for the PVC market in Latin America is the increasing demand for PVC in the building and healthcare industries. ¹²⁸ Based on these sectors, Brazil dominates both PVC production and consumption in Latin America.^128,129 The PVC growth market in the MENA region is primarily driven by the packaging sector, in addition to the great demand for PVC in the building sector. ¹²⁹ The two major PVC manufacturers and consumers in the MENA region are particularly Saudi Arabia and the United Arab Emirates.^128,129

Sorting, repurposing, and disposing of polyvinyl chloride solid waste

The combination of virgin PVC’s diverse properties gives rise to various uses that make our lives more convenient. However, it is imperative to consider the potential adverse consequences that a PVC item may have once its useful life has elapsed, particularly if improper management is practiced. Among the most significant issues associated with these effects are long-term persistence in the environment, emissions from incineration, and landfill matter. As is the case with most polymers, PVC is a long-lasting material that helps prolong the lifespan of valuable items but poses waste management challenges due to its slow environmental degradation, which exacerbates the persistent problems with plastic pollution.^132–134 Incinerating PVC solid waste carries risks for the environment and human health despite its benefits for energy recovery. Emissions from incinerations produce organic pollutants that can harm ecosystems and human health, such as dioxins, furanes, polychlorinated biphenyls (PCBs), and various other chlorine (Cl) compounds.^26,132,135 Often, complex and expensive technologies are required to control these emissions.^26,135 Additionally, when PVC waste is disposed of in landfills, its hazardous substances like original formulation additives may leak into the soil and water, also endangering both human health and the environment. ¹³² Fortunately, by employing sustainable practices for managing such waste, these negative effects of PVC waste can be minimized.^26,132 This would also lessen opposition to the continued production and use of PVC.^26,132,136

Sorting into a homogeneous PVC solid waste stream is usually done on mixed PVC solid waste to ensure successful and efficient recovery (or recycling) of PVC waste.^11,137,138 This mixed waste is usually composed of different PVC items, compatible and incompatible plastics, as well as non-plastic materials. Sorting, however, is more important when employing mechanical recycling approaches (section 4.1. gives more details). Moreover, contaminants may still be apparent after sorting, including certain amounts of PVC waste items different from the PVC item being recycled (e.g., the presence of window profile scrap during pipe scrap recycling), other plastic types, and non-plastic materials.^11,28,138 This usually results in a type of waste stream called heterogeneous PVC solid waste, which is managed differently from mechanical recycling. Since the wastes from buildings—which are typically large-sized materials—are frequently sorted, the non-plastic materials are usually mineral wastes (concrete, masonry, etc.).^11,137,138 Sorting is primarily necessary to produce PVC recyclates with comparatively high-quality and valued mechanical and physical properties, even though it adds to the overall cost of PVC recovery processes. ¹¹ This, however, pertains only to PVC applications where the inferiority of these properties could be detrimental. Nonetheless, it is imperative that sorting be done both effectively and efficiently since it is a critical aspect of PVC solid waste management. ¹¹ The steps followed to obtain the sorted PVC solid waste-derived recovered material (i.e., PVC recyclate) are listed below^11,137,138:

a. Collection: PVC waste is collected from residences, businesses, or designated collection points.

b. Labelling and identification: Standardized labels or codes are utilized to properly label the waste to facilitate easy identification. This waste is often contaminated; thus, various methods and techniques are employed to identify it (Table 9).

c. Sorting: via three primary methods, viz.: macro, micro, and molecular separation, both homogeneous and heterogeneous PVC solid waste streams are obtained.

d. Quality control: Frequent quality control checks guarantee contamination-free PVC waste as well as the correctness and efficacy of the sorting process.

e. Recycling: Following the sorting process is the transportation of sorted PVC waste to a recycling factory, where commercial PVC recyclates are produced.

Table 9.

Various sorting methods.^{11,14,137,138}

Method type	Subtype
Macro separation	Manual sorting
	Conveyor belts and sorting lines
	Density separation
	Magnetic separation
	Infrared sorting
	Size reduction and screening
	Wind sifting
	Flotation (froth)
	Vibrating screens
	Colour sorting
Micro separation	Near-infrared (NIR) spectroscopy
	Fourier-transform infrared (FTIR)
	X-ray fluorescence (XRF)
	Eddy current separation
	Electrostatic separation
	Selective dissolution
	Cl detection
	Hydrocyclone separation
	Flame retardant detection
	Sieve analysis
	Advanced robotics and AI sorting
Molecular separation	Chemical dissolution and precipitation
	Polymer degradation and separation
	Pyrolysis and gas chromatography
	Mass spectrometry
	Selective functionalization
	Selective adsorption and chromatography
	Biotechnological approaches

In addition to recyclate’s purity and quality, sorting allows for increased PVC waste market acceptance, efficient processing, and compliance with regulations, as well as recovery of valuable materials (e.g., additives) from it while contributing to energy and cost savings.^11,137 Numerous sorting methods—listed in Table 9 along with their corresponding subtypes—that can be combined in a recycling factory to ensure an accurate and effective PVC solid waste sorting are the driving force behind the advantages of sorting PVC solid waste before recycling. However, molecular separation methods are mainly in the research stage and might not be widely applied because of financial constraints, environmental concerns, and technical difficulties associated with them. ¹¹ Thus, to recover PVC for use in the manufacture of new items, macro and micro separation methods are frequently used, followed by the mechanical, chemical, or blending recycling process.^11,137,138 A selection of new PVC items that have been made through these processes is shown in Table 10, along with their corresponding waste sources that are a major concern regarding PVC solid waste. It appears from this that it is far more desirable to produce new PVC items from the waste of their original item.^{11,14,137,138} Additional processes used for PVC waste management are energy recovery and landfilling, albeit they are applied as a last resort since they tend to generate secondary pollution.^11,14,138

Table 10.

Different PVC wastes and the new items derived from them.^11,14,137

Waste type	New item
Household, office, shop, etc. (packaging and non-packaging)	Film, artificial leather, diskettes, sheets, bottles, and trash bags.
Electrical and electronics	Thermoformed sheets and injection molded items
Automotive	Fuel tanks, bumpers, dashboards, interior linings, seats, and batteries.
Building, agriculture, and industry	Pipes, films, cables, flooring, roofing, window and door frames, conveyor belts, dipped, and healthcare items.

Mechanical recycling

Mechanical recycling pertains to recycling activities, whether primary or secondary, that employ mechanical means to recover PVC solid waste.^11,12,15,28 This extensively used method has been considered the most cost-effective and environmentally friendly choice for recovering PVC waste due to its low energy consumption and minimal to no greenhouse gas emissions.^15,35 The mechanical recycling process involves washing and drying PVC waste, and shredding, crushing, grinding, or pulverizing it into small pellets or granulates (i.e., a recyclate). A recyclate then substitutes a virgin PVC compound entirely or in part, followed by melting, re-granulating, and repurposing it into the new molded or extruded plastic items, which are different or similar to the original ones.^12,15,35 An instrument primarily employed for the generation of a recyclate through mechanical recycling is extrusion because of its large-scale, low-cost, and solvent-free nature. ¹² The material’s thermal softening (i.e., melting) is achieved by heating and rotating it using screws in an extruder. Following that, it goes through barrel sections with temperature control to create a fixed cross-section extrudate. ¹² While in the barrel sections, the material normally undergoes chain degradation, i.e., thermo-oxidative and shear-induced chain scission, chain branching, and/or fusion, as a result of the thermal conduction and viscous shearing that occur inside an extruder. ¹² Because of the chain degradation, the PVC chain length is typically shortened, consequently reducing the processability, quality, as well as physical and mechanical properties of the resultant recyclate.^11,12,15 PVC typically has good thermal properties, especially when heat stabilizers are used; therefore, how much it deteriorates throughout the extrusion process mostly depends on the combination of extrusion parameters, such as temperature, screw speed, and residence time. ¹² Conversely, it was recently demonstrated by Du et al. ¹³⁹ that the thermal stability of PVC can be improved by employing a thermal stabilizer ZnAlLa-maleate-LDHs. Using this stabilizer, the authors also improved the plasticizing and mechanical properties of PVC by preventing both the breakdown of C-Cl bonds in PVC and the creation of HCl. The mechanism underlying PVC degradation via mechanical recycling is still not entirely understood but is believed to vary greatly depending on the instrument set parameters, presence of oxygen, original formulation additives, and stabilizers added during the recycling process.^{11,12,14,15,28,35,140} For instance, extrusion at high screw speeds, temperatures, and times increase chain degradation.^12,35,140 Nevertheless, the PVC degradation mechanism based on free radical reactions has been proposed by Schyns et al., ¹² whereas the mechanism presented by Sadat-Shojai et al. ¹¹ is based on “zipper” dehydrochlorination of PVC. According to Schyns et al., ¹² the principal PVC degradation mechanism involves radicals that are formed along the material’s chain as a result of the removal of hydrogen atoms by heat and the production of peroxy radicals caused by oxygen (Figure 5). Because of the shear forces involved, these radicals can generate $\beta$ -scissions of chains, which reduce both chain length and viscosity. ¹² Sadat-Shojai et al., ¹¹ on the other hand, postulated that the basic process of PVC degradation involves the removal of hydrogen chloride (dehydrochlorination of PVC) via a “zipper” mechanism, either at low temperatures and/or in the presence of light. As per Figure 5, this reaction initiates in the first stage with the production of one double bond and proceeds to a very rapid depolymerization reaction that results in a polyene sequence in the main chain. These polyenes absorb heat and/or light, causing PVC to turn brown or fully black (under extreme conditions), which, for certain applications, is changed to “bright” white using titanium dioxide pigments.^11,50,51 If the latter scenario materializes, which generally indicates high polymer degradation levels, the PVC degradation may also exhibit secondary processes during mechanical recycling.^11,12,28 For instance, the interconnected networks, i.e., new fusions (“crosslinks”), could result from the polyene sequences interacting with each other.^{11,12,141,142} The emergence of instabilities in a polymer caused by allyl chlorides adjacent to internal double bonds, tertiary chlorines at branching carbons, oxygen-containing structures, etc., has been associated with the production of these new fusions during mechanical recycling.^11,12,142 Although mechanical recycling aims at reversing the original fusion by heat and shear stress, which is due to the intense mechanical work, Sadat-Shojai et al. ¹¹ reported that the production of these new fusions gradually transforms the original particle structure into a network of entanglements that impact the physical and mechanical properties of the resultant recyclate.

Figure 5.

Generalized PVC degradation occurring through: (a) Hydrogen abstraction caused by extrusion and (b) “zipper” dehydrochlorination.^11,12

Several researchers^{11,12,143–145} have discussed the utility of specific light and heat stabilizers (Table 11) in the mechanical recycling of PVC waste, pointing out that these additives can prevent free radical reactions occurring during extrusion (for the manufacture of new PVC items). When it comes to preventing oxidation during PVC waste recycling as well as the manufacture of recyclate-based new items and their use, the antioxidant (heat) stabilizers are especially helpful. These are usually divided into primary and secondary categories. The former function as “chain-breaking” antioxidants because they scavenge radicals, integrate oxygen with peroxy radicals to generate stable radicals, and shield chains throughout the PVC item lifetime.^12,144 Conversely, secondary antioxidants, which are typically based on phosphorus or sulphur, function as “preventative” antioxidants by breaking down hydroperoxide accelerants into alcohols during the new and waste PVC melt processing.^12,145 Light stabilizers can absorb and release light energy to shield PVC chains from UV-induced deterioration.^12,144

Table 11.

Typical antioxidants and the mechanisms in which they stabilize PVC materials.^12,143–145

Type of antioxidant	Chemical example	Type of stabilization mechanism
Hindered amines	Tetramethylpiperidine, Tinuvin 770	Primary: Continuous cyclization reaction
Phenol-based compounds	Irganox 1010, curcumin, vitamin E	Primary: Donors of hydrogen
Phosphorus-based compounds	Irgafos, PEP 36	Secondary: Breaks down hydroperoxides
Carbon black	–	Breaks down hydroperoxides and functions as a filler with reinforcement

Primary recycling refers to a closed-loop recycling method in which a PVC waste item is reprocessed and the resultant recyclate is used to make another item within the same category (e.g., bottle-to-bottle). Hence, only the homogeneous PVC waste stream is processed by this type of recycling. Accordingly, it is commonly employed in the recycling of pre-consumer residues, where the input waste is limited to a single type of item with minimal to no contaminants; but it can also be used to recycle thoroughly sorted and cleaned post-consumer PVC waste.^{12,15,146,147} Furthermore, the primary recycling method is also believed to be the most significant mechanical recycling method since, apart from conserving fossil fuels while consuming less resources, the resultant recyclate is similar to the original material (virgin PVC resin) in terms of quality and properties.^{11,12,14,15,17,28,35,148} This recyclate can therefore be utilized as feedstock to generate high-value new PVC items.^11,15 Nevertheless, primary recycling is rather infrequent in research due to its stringent requirements for completely clean, sorted, non-degraded, and homogeneous PVC waste.^15,137 Thus, secondary recycling is a primary focus of most PVC life cycle assessment (LCA) research. ¹³⁷ This type of recycling creates new PVC items that are either similar to or different from the original items, e.g., pipe-to-pipe or pipe-to-floor covers, through the utilization of an input waste consisting of either a single type of PVC waste item or a combination of different PVC waste items. ¹⁵ Secondary recycling can also be employed for recycling the contaminated PVC products, e.g., coated fabrics and laminated films, from which separation into a single polymer stream is either too expensive or not technically viable. ¹⁵ Therefore, both closed- and open-loop and heterogeneous PVC waste stream recycling are terms used to describe the secondary recycling processes. ¹⁵ It is important to emphasize that recyclate generated from secondary recycling of heterogeneous PVC waste stream is often restricted to a limited range of applications due to its properties being poorer than those of recyclate derived from primary recycling.^{11,12,14,15,35,146} These secondary recycling-derived recyclate’s applications include trash containers, plastic fencing, certain pipelines, road cones, shoe soles, plant pots, industrial flooring, and other similar applications where high-quality material is not absolutely necessary.^{11,12,15,16,35,149–152} Nevertheless, several researchers^{11,17,19,150,153–156} have reported that, at optimized conditions, the new PVC items with qualities and properties that are comparable to those made up of virgin PVC can be produced with recyclate obtained through secondary recycling. This is devoted to the concept that since there is no chemical reaction occurring during the secondary recycling process, the chemical composition (i.e., polymer structure) of a recyclate remains unchanged. Thus, it can be stated that the foremost factors influencing a recyclate’s ultimate cost and usability are its quality and properties.

Chemical recycling

Chemical recycling—also known as tertiary or feedstock recycling—refers to processes that chemically break down the PVC structure into chemical components that are utilized to generate useful secondary materials.^{11,15,35,157,158} It is an alternative or supplement to mechanical recycling, and thermal cracking (i.e., pyrolysis) is a common example of a chemical process that is typically driven by thermolysis reactions.^12,139,158 Generally, PVC waste is shredded or chipped to make it easier to recycle both before and during chemical processing. Chemical recycling is often carried out using a cement kiln (as an incinerator) or in a specialized reactor (e.g., fluidized bed pyrolysis reactor), where the latter is preferred since it makes it easier to collect the desired products.^{11,137,157,159,160} An additional experiment that is sometimes conducted before chemical recycling is the selective removal of additives from PVC waste by dissolving it in a solvent like tetrahydrofuran (THF).^161,162 This step is important because the heat stabilizers in particular have the potential to adversely affect the thermal processes. ¹³⁹ PVC is usually precipitated by drying the THF solution, which is followed by the chemical recycling operation.^157,161 Furthermore, the amount of research being done on chemical recycling is currently rising, and this is true even though condensation polymers, such as polyethylene terephthalate, are significantly more suitable for chemical recycling than an addition polymer like PVC.^11,161 Chemical recycling has also grown more rapidly because it can efficiently recycle even the heterogeneous PVC waste stream, minimizing the total recycling costs. In terms of environment and energy, however, there are chemical recycling approaches that are less recommended because, while less susceptible to unsorted or contaminated PVC waste, they produce secondary pollution and require more power and energy since their processes necessitate a high processing temperature (>250 $℃$ ) and/or longer reaction duration in order to produce the desired products.^{11,157,158,163} Pyrolysis is a typical example; hence, the existence of alternative methods, such as oxidation (gasification) and depolymerization (methanolysis, glycolysis, hydrolysis, and aminolysis).^{11,15,35,157,158,164–167} Nevertheless, it seems that pyrolysis is the commonly used chemical recycling method for PVC solid waste. This could be a result of the technology’s ability to recycle waste that has not been cleaned and sorted, which lowers recycling expenses.

Blazevska-Gilev et al. ¹⁶⁸ have reported the use of alkaline media (i.e., sodium hydroxide (NaOH) in dimethyl sulfoxide (DMSO)), where they achieved ca. 95 % degree of PVC dehydrochlorination under mild conditions (i.e., at atmospheric pressure and 30 – 80 $℃$ for 1 – 5 h). Yoshioka et al., ¹⁶⁹ on the other hand, employed a 15 M NaOH solution at ca. 260 $℃$ and 5 MPa (partial pressure of oxygen, PaO₂) for 5 h to study the oxidative degradation of fPVC pellets. According to the authors, ¹⁶⁹ the primary products of oxidation, which occurred after dehydrochlorination, were carbon dioxide (CO₂), benzene/carboxylic acid mixture, and oxalic acid. This chemical recycling method, which fully oxidizes PVC-rich plastic waste, is favourable because it avoids the formation of hazardous substances including furanes, dioxins, PCBs, and other Cl-containing compounds. ¹⁶⁹ PVC waste can also be chemically recycled by nucleophilically substituting Cl atoms within its structure. For instance, Kameda et al. ¹⁷⁰ assessed how PVC-U waste undergoes degradation when nucleophiles like iodide, hydroxide, azide, and thiocyanate are used in different types of glycol solvents. The nucleophiles in this case replaced the Cl atoms, aiding in the removal of hydrogen chloride and ultimately causing PVC-U to become dehydrochlorinated. It was demonstrated that when nucleophile content increased, the degree of this dehydrochlorination increased as well, with optimal substitution occurring at the highest concentrations. When diethylene glycol was used in place of ethylene glycol, the dehydrochlorination reaction rate increased. This could be because the former is more compatible with PVC, which increases the nucleophiles’ efficacy of penetrating its particles.^11,170 A comparable study was recently reported by other researchers, ¹⁷¹ where dehydrochlorination was achieved during the chemical modification of PVC to generate a vinyl chloride monomer.

Waste plastic is thermally broken down by pyrolysis in an inert atmosphere at temperatures between 300 and 900 $℃$ to produce a range of products that, when refined, largely comply with established quality standards and regulations.^{11,161,172,173} Similar to mechanical recycling, the predominant product of PVC waste pyrolysis is a polyene material, which undergoes further degradation through the development of aromatics and transforms into materials whose composition is mainly influenced by processing variables like temperature, time, etc.^12,15,172 Typically, the efficiency of this pyrolysis is promoted by employing a variety of catalysts, solutions, and materials, all of which not only target particular reactions but also reduce process temperature, duration, and costs.^172,173 Common products generated from pyrolyzing PVC waste include vinyl chloride monomer, gases, metal concentrate, calcium chloride (used as thaw salt), organic condensate (used as fuel), coke material or refuse-derived fuel (used in facilities such as waste-to-energy plants, cement kilns, or industrial boilers to generate heat and power), etc.^{11,12,15,161,172,173} Yao et al. ¹⁷⁴ pyrolyzed the PVC solid waste at ca. 600 $℃$ for 1 h and produced acid gas hydrogen chloride (HCl), aliphatic and alicyclic hydrocarbons, benzene, naphthalene, diphenyl, phenanthrene, as well as pyrene and their alkyl derivatives. Recently, when they pyrolyzed PVC using a thermogravimetric analyzer (TGA) from ambient temperature to ca. 575 $℃$ with 10 $℃$ /min heating rate, N₂ (purge gas) at 100 mL/min flow rate, and ca. 10 mg sample, Hong et al. ¹⁷⁵ produced gases (e.g., HCl, H₂ and acetylene), as well as char and slag, which most likely comprised many metal stabilizers found in the original PVC formulation. Calero et al. ¹⁷⁶ also recently reported the highest yield values of hydrocarbons, including cyclotetrasiloxane,octamethyl-, naphthalene, naphthalene,2-methyl-, phenanthrene, and 1,10-biphenyl,4-methyl as well as gases such as HCl, CO₂, H₂, oxygen gas, methane (CH₄), carbon monoxide (CO), ethane, ethene, propane, and prop-1-ene, when they pyrolyzed PVC pipe waste at ca. 525 $℃$ for 1 h. Furthermore, the input normally determines the resultant products; for instance, HCl and CH₄ will be more noticeable in the resulting gases with a proportionately higher amount of PVC waste as an input. ¹⁷⁶ In another study, Tukker et al. ¹⁵⁷ reported pyrolysis tests that utilized 100% PVC waste and resulted in the HCl recovery of higher than 90 %, mostly 94–97 %.

Several researchers^11,177,178 have reported that HCl is the core product of PVC waste pyrolysis and is recovered to make vinyl chloride or utilized in other chemical reactions, most commonly membrane electrolysis for the production of Cl. This, in turn, means that an increase in the efficiency of dehydrochlorination (i.e., elimination of HCl) translates to successful chemical recycling of PVC waste. Masuda et al. ¹⁷⁹ evaluated the pyrolysis of PVC waste in the presence of metal oxides and found that the oxides significantly increase the emission of HCl. Ye et al. ¹⁸⁰ also pyrolyzed PVC in the presence of a metal oxide (viz.: iron (II,III) oxide (Fe₃O₄)), and the degree of PVC degradation was used to determine the boundary temperature of ca. 400 $℃$ , which was used for the two stages of the pyrolysis of PVC/Fe₃O₄ mixtures. The primary products obtained upon PVC breakdown and Fe₃O₄ chlorination were solids (polyene, iron (II) oxide, and iron carbide) and gases (HCl, volatiles, and H₂O), where an increase in HCl yield was attributed to the use of Fe₃O₄ in the process. To reduce the temperature and save energy, Zhao et al. ⁴ employed 180 $℃$ to pyrolyze heterogeneous PVC waste for 1 h, but the authors only achieved ca. 40 % dehydrochlorination degree. This was improved by other researchers^{158,181–183} who used organic and inorganic salts (e.g., ionic liquids) or heavy metal catalysts, and achieved higher dehydrochlorination yield (i.e., $>$ 90 %) at $<$ 200 $℃$ for the same reaction time (i.e., 1 h). Similarly, Wu et al. ¹⁴⁰ demonstrated that poly (ethylene glycol) (PEG) causes a significant increase in the PVC dehydrochlorination degree. By pyrolyzing at 210 $℃$ for 1 h, the authors achieved ca. 74% of the dehydrochlorination yield for a mixture of PVC/PEG, while it was as low as ca. 50% for PVC alone.

Although the HCl emission yields through the pyrolysis processes can be optimally achieved, there is an issue with other useful hydrocarbons produced, especially fuel oils. These have been found to contain a significant amount of Cl, and the use of Cl-containing oil releases pollutants into the environment, causes severe corrosion to units, and puts lifeforms in danger.^{162,184–188} As such, methods of lowering Cl are necessary, with $\le$ 0.1 wt.% Cl content considered acceptable for compliance with most specification requirements.^{163,184–188} When it comes to PVC waste-derived oils and gases that are produced through pyrolysis, various petrochemical specifications limit the halogens—which are generally found as chlorinated inorganic or organic compounds—to only $<$ 0.1 wt.% Cl content.^11,14,157 One general approach in which this could be achieved is to chemically recycle (i.e., pyrolyze) plastic waste streams that contain only $<$ 30 wt.% PVC content. ¹¹ However, this would consequently reduce the yield of HCl and other valuable gases and materials; therefore, there exist methods that, when heterogeneous plastic waste with a significantly higher PVC content is recycled, yield products with lower Cl content in the products.

Processing PVC-rich plastic waste with calcium oxide via milling can be a useful means of removing Cl from the intended products.^11,189 Similarly, by utilizing a mechanochemical method that includes co-grinding the alloy and PVC waste, after which the resultant mixture is washed and filtered by a suitable solvent, metals from this waste can be recovered. ¹⁹⁰ Through this co-grinding, all the metal chlorides, with Cl included, that are produced from PVC are extracted. These chlorides are readily soluble in water and easily separated from the pyrolysis-derived hydrocarbons. NaOH and/or calcium carbonate (CaCO₃) can also be used to neutralize pyrolysis-derived HCl; however, this usually produces salts that are Cl-rich and must be disposed of as chemical waste only in landfills designed to handle such waste. ¹¹ As an alternative, these salts can be partially fed into a rotary kiln and treated again to create inert slag, which can then be utilized as a mine filler. ¹⁵⁷ Yuan et al. ¹⁹¹ have developed a thermal dehalogenation approach, claimed to be both more affordable and meets acceptable standards, that can be performed either in a liquid or fluidized bed pyrolysis to minimize the formation of Cl in resultant products. The authors used hot N₂ as a fluidizing gas to fluidize the molten PVC polymer and allow it to make good contact with N₂. Cl extraction (ca. 99.5 wt.%) in the form of HCl was ensured at ca. 300 $℃$ within ca. 1 min after PVC has melted. Another chemical recycling method that is aimed at reducing Cl content in the pyrolysis-derived hydrocarbons involves fast co-pyrolyzing heterogeneous PVC waste and biowaste (i.e., cattle manure).^11,163,192 Comparably, when PVC waste was co-pyrolyzed separately with three constituents (cellulose, hemicellulose, and lignin) of biomass waste in a fixed bed at 600°C^163,193 and 800°C^163,194, a reduction in HCl emission was observed. Kuramochi et al. ¹⁹³ found that while lignin and hemicellulose can significantly reduce HCl emission, where the PVC/hemicellulose mixture released only <5 wt.% Cl content, the cellulose had little to no effect. However, it was discovered by Zhou et al. ¹⁹⁴ that cellulose, like hemicellulose and lignin, can also reduce HCl emission, probably because of the higher temperature employed. A similar chemical recycling approach was reported by Adeniyi et al., ¹⁸⁴ who co-pyrolyzed the Coca-Cola label films/Terminalia ivorensis leaves mixture. According to the authors, the primary benefit of this method—which involved heating the material at ca. 285 $℃$ for 80 min—is its low cost, low energy consumption, and lack of need for sophisticated technical knowledge. Sakata et al. ¹⁸⁵ also conducted a study on the degradation of PVC-containing waste plastics, and from the resultant fuel oils, they catalytically dehalogenated organic chlorine compounds to produce Cl-free hydrocarbons. The authors ¹⁸⁵ proposed using a variety of carbon composites containing iron oxides and CaCO₃. Analogously, Lopez-Urionabarrenechea et al. ¹⁹⁵ conducted an investigation that combined pyrolysis of PVC-containing plastics with catalytic dehalogenation (utilizing ZSM-5 as a catalyst), producing heavy hydrocarbons that are Cl-free. Additionally, the recyclability, depending on the cycles, of organic salts, inorganic salts, or catalysts, used during the thermal cracking process is another benefit of the chemical recycling of PVC waste.^11,14,15,35 Evidently, efficient pyrolysis processes demand high temperatures and, consequently, significant energy, which both contribute to their high cost. This is true even though numerous researches have been offered thus far to address the high energy requirements of pyrolysis. Therefore, the focus of chemical recycling will probably be limited to wastes for which mechanical recycling is not practical.^{11,14,15,28,35} Accordingly, to improve the circular economy of PVC solid waste—especially the heterogeneous kinds—other available recycling approaches are currently being utilized to recycle this waste.

Energy recovery

PVC waste to energy recovery through incineration is a less complicated process, but in terms of pollution, it is as costly as the chemical recycling approach, especially pyrolysis.^15,35,161 This process is known as “quaternary recycling”, though the EU does not view it as a recycling process. ¹⁵ It yields heat or electricity and is typically useful in situations where mechanical processes are hampered by PVC-rich waste’s sorting or separation challenges, inferiority of a polymer’s properties, and high contamination (combustible or incombustible impurities).^15,161 The latter case is generally evident when other materials need to be recovered in addition to energy. For instance, if E&E high-voltage cables are incinerated for energy recovery, the wires and metal components may be recovered after the process, likely in an inert slag. ¹⁵⁷ Moreover, energy can be conveniently recovered using a cement kiln as well as a specialized reactor, albeit the former is recommended because the latter’s incineration process is quite expensive.^34,164 The cement industry is one that often uses plastic solid waste as fuel in kilns to lower energy costs.^15,35,157

Bulk plastic wastes have historically been incinerated to recover energy for use as heat and electricity. ¹⁵⁷ However, as public opposition mounted, this eventually reached a plateau.^11,141 Because of the harmful emissions that are typically a result of subpar equipment, improper incineration conditions, and inorganic ash residues, the public’s opposition to PVC waste being incinerated for energy recovery continues to grow. ¹¹ In essence, the issue of pollutants and harmful substances, released into the atmosphere, is a recurring one related to the process of incineration as a whole. Furthermore, incinerating PVC poses additional issues because, as previously mentioned, the nature of PVC polymer results in HCl production during thermal breakdown.^11,139,141 In addition to its well-known ability to cause equipment to corrode, HCl can undergo wet and dry deposition in the atmosphere and contribute to acid rain formation.^{11,141,149,161} Even though this can be prevented by using particular filters on the pyrolysis reactor, there is still room for improvement in the current energy recovery incinerators to regulate the levels of HCl and other harmful pollutants released into the atmosphere.

Nevertheless, because of the net energy recovered, the practice of incinerating PVC-rich solid waste for energy recovery continues,^{25,35,157,196} even though some of the studies^11,197,198 have indicated that this energy is not high enough to make this PVC waste management approach economically viable. Evidence of the continued PVC waste energy recovery is the fact that most EU, Nordic, and African countries rely on mixed plastic waste incineration to produce electricity.^{14,25,35,157,196} This has been corroborated by Brown et al., ¹⁹⁹ who stated that the main objectives of incineration as a pre-treatment option for disposing of plastic—waste stabilization and bulk reduction with energy recovery where appropriate—remain relevant today. Modern plastic waste incinerators, with a typical capacity of 200 to 1000 ktpy, adhere to the strictest operating regulations, and are equipped with pollution control devices that minimize the emission of pollutants.^{25,35,157,196,199} These incinerators generally have high initial and periodic expenses, but sales of energy help to offset some of these costs, and economies of scale apply. ¹⁹⁹ Furthermore, similar to most hydrocarbon polymers, the overall PVC-rich solid waste has a calorific value of ca. 64 MJ/kg when incinerated under ideal conditions, as opposed to ca. 14 MJ/kg for paper and wood.^11,200 According to research, however, it is not economically feasible to recover energy from incinerating homogeneous PVC waste stream because PVC incineration requires temperatures above 1427 $℃$ to achieve only ca. 41 MJ/kg.^11,197,198 On the contrary, Tukker et al. ¹⁵⁷ have detailed an approach (viz.: BSL Incineration process) designed for a mixture of waste materials with high chlorination levels. The authors noted that for incinerators of this kind of mixture, an optimal specification for the calorific value of its input normally acts as guidance. Accordingly, a calorific value is a crucial predictor of the effectiveness of burning plastic waste and is employed to regulate an incinerator’s incineration temperature for increased safety. ¹⁵⁷ Therefore, the incinerators are typically fed with PVC waste that incorporates other waste streams with a lower caloric value, to obtain a waste stream with an optimal composition. ¹⁵⁷ This is because an incinerator fed exclusively with homogeneous PVC waste (i.e., 100 % PVC solid waste) would, on average, yield excessively high caloric values, thereby compromising the safety of an incinerator. ¹⁵⁷ This pertains to the notion that, in contrast to chemical recycling approaches, where only $<$ 30 % of PVC content can be fed with other plastics into an incinerator for pyrolysis, chlorine concentration plays a major role in the energy recovery through PVC waste incineration processes.^{11,157,192,198} Moreover, Horodytska et al. ³⁵ and Maris et al. ¹⁵ have reported that incinerating mixed plastic wastes is very likely to produce electricity and district heating with efficiency levels above 90%. Though the energy recovery treatments have advantages for the environment in terms of reducing plastic waste and preserving value in the form of energy, they are also inconsistent with the general principle of the circular economy that the end-of-life plastic items should be managed in closed-loop systems to replenish natural systems whilst reducing the overall pollution.^13,25,35,199 Hence, in terms of the circular economy, energy recovery from PVC waste incineration is comparable to the disposal of this waste in landfills. As a result, before considering these plastic waste management approaches, they should be conveniently used where mechanical and chemical recycling processes are not successful due to various challenges; otherwise, the PVC waste should be blended with virgin PVC, other plastics, and/or non-plastic materials to generate a variety of valuable products.^13,35,199 This is a result of the EU not classifying incineration processes and landfilling methods as recycling operations.^13,188,199

Blending

Applications of PVC recyclate when blended with polymeric, elastomeric, non-polymeric, or non-elastomeric materials have further increased interest in PVC solid waste recycling research.^12,125,201 This is considered an innovative strategy, which was originally initiated to alter the conventional methods of managing PVC waste thereby obtaining more sustainable approaches.^201,202 Blending PVC recyclate with another material allows for the ability to modify certain aspects of PVC waste processing characteristics as well as reducing PVC waste pollution and the costs of various products. It is carried out because the resultant blends could create new markets for technically important PVC materials. In essence, blending PVC recyclate with other materials primarily enhances both its various properties and suitability for original and/or novel applications.^15,203,204 This enhancement is typically required because PVC items deteriorate from both service and grinding.^{12,149,150,205} Regardless of their superior properties, PVC items eventually degrade and infrequently find their way into the waste stream as a result of infrastructure improvements or auto repairs. Degradation through grinding is typically associated with the generation of low molecular weight and shorter polymer chains during the size reduction process. However, Fakhri et al. ²⁰⁶ have recently shown that there exist cases, e.g., a mixture of PVC waste, asphalt, and bitumen for road construction, in which the PVC waste is ground solely for size reduction and ease of mixing, without necessitating any prior enhancement of the recyclate’s properties. Shah ²⁰⁷ has corroborated this and added that incorporating PVC waste, which has been mechanically processed into smaller particles or granules, into asphalt mixtures can help create more resilient and sustainable pavements with better rutting, fatigue, and moisture resistance. Nevertheless, to meet the specifications of certain applications, PVC waste is generally ground into a recyclate, which is then blended with the pellet or ground polymeric or elastomeric material via a melt compounding or blending process. Both virgin and recycled polymeric and elastomeric materials are acceptable, but the latter is usually recommended from an economic standpoint, even though doing so may result in less favourable outcomes in terms of compatibility as well as rheological, physical, mechanical, thermal, and electrical properties of the resultant blends.^{12,149,150,203–207} Accordingly, an interfacial modifier (compatibilizing agent) is one of the additives used to create a miscible system of PVC recyclate with a polymeric or elastomeric material.^12,208 This agent generally enhances the degree of interaction, occurring through the interphase, between the material components.

Research on the life cycle analysis (LCA) of PVC has focused on the blending approach because of its versatility for different kinds of waste streams.^{11,12,15,188,209} PVC recyclate’s granulometry (i.e., shape) and size play a significant role in ensuring its usability in the manufacture of various items. ²⁰⁸ While certain grades of PVC recyclates are simply milled (a few millimeters in size, usually below 1 mm), others are micro- and nano-sized. ²⁰⁸ Depending on the intended application, the quantity of contaminants (i.e., rubber, textile materials, metal particles, etc.) present in PVC recyclate can also have a great impact on the quality of the finished item. ²⁰⁸ Fundamentally, the recyclate’s size matters particularly for easy mixing with another material, and higher levels of impurities can be allowed in a recyclate blended with non-polymeric and non-elastomeric material.^15,210 Furthermore, in addition to additives, materials like fillers or fibers are typically added during melt blending to maximize the improvement of the PVC recyclate’s properties and give its blends the features that make them suitable for use as new products in various sectors.^{11,12,14,50,51} As previously highlighted, it is imperative to use a compatibilizer when a material (polymer or elastomer) is not structurally compatible with PVC and if a PVC recyclate contains other polymers that are incompatible with virgin PVC agent. It has been contended, however, that the use of additives, fillers, etc. raises the costs associated with the commercialization of PVC items.^11,14,50,51 This is the point at which PVC waste recyclate is acceptably blended with non-polymeric and non-elastomeric materials, to find markets for PVC waste in areas where lower-cost materials predominate.

A summary of studies on PVC recyclate blends with different virgin and recycled materials can be found in Table 12. These suggest that pipes are recycled more than other PVC solid waste items, primarily for use in the manufacturing of cementitious materials. This phenomenon can be attributed to the abundance of waste pipes as ca. Half of the world’s yearly production of PVC resin is for virgin pipes.^60,128,129 A waste stream consisting entirely of PVC items that are cleaned, sorted, or have very little contamination is also not necessary for cementitious materials. Furthermore, the additives used in the original PVC formulation are not an issue for the manufacture of blends comprising PVC recyclate and a certain material. For instance, researchers^12,199 have suggested that the stabilizers be retained in PVC waste since, in the absence of a stabilizer, PVC would degrade quickly during blending, especially in the case where a material blended with PVC is reactive at temperatures where PVC degrade. This implies that this blending promotes circular sustainability, by avoiding or minimizing the use of additional resources in the process. ¹⁹

Table 12.

Studies on blending PVC solid recyclate with another material.

Source of PVC recyclate and/or its particle size	Material blended with PVC recyclate	Preparation procedure	Primary finding	Intended outcome or application	Study
–	Silane-modified sodium polyacrylate (PAANa)	Compression-molding foaming	Structure and morphology analyses verified the effective grafting of silane coupling agents onto PAANa’s surface, improving its interfacial contact with the recyclate matrix. A resultant substrate had significantly improved water absorption and retention properties. Mechanical properties of a substrate were found to be favorable, such as increased ultimate tensile strength (UTS), compression strength, elastic modulus, and elongation at break ( ${\epsilon }_b)$ .	Producing a plant growth substrate that has a higher capacity to absorb and retain water, as well as improved mechanical properties.	211
1.5–2 mm	Cover face and core of the conveyor belt	Melt blending	Conveyor belt samples with PVC recyclate were found to have a significantly higher capability to withstand extremely high deformations until a break occurs. Accordingly, conveyor belts’ usage of PVC in their manufacturing offers a way to optimize their characteristics and achieve better performances (high mechanical stress resistance) that can be adjusted to various operating environments, including those where the cover face in particular is subjected to accelerated aging processes.	Improving the performance of conveyor belts.	212
Data cables (outer sheath)	Poly (methyl methacrylate) (PMMA) recyclate	Melt blending	Increased PVC recyclate content increased the impact strength and ${\epsilon }_b$ . The blend’s thermal properties showed better thermal stability than those of its constituent recyclates (i.e., PMMA and PVC, individually).	Improving the tensile and thermal properties of PVC recyclate.	213
“E-waste” (IT and communication devices), 3–6 mm	PMMA recyclate and virgin acrylonitrile butadiene rubber (NBR)	Melt blending	The PVC/PMMA blend recyclate’s ${\epsilon }_b$ , toughness, impact, and thermal properties improved with the addition of virgin NBR.	Improving the mechanical performance and thermal properties of PVC/NBR blend recyclate for various applications, including conveyor belt covers, cable jackets (wire and cable insulation), hose cover linings, gaskets, footwear, and cellular products.	214
Pipes	Zinc borate (ZnB) powder	Melt blending and casting process	PVC recyclate/ZnB film composite prepared using melt mixing had manifestly better tensile and tear strengths than those prepared through the casting procedure. However, it was the opposite concerning the ${\epsilon }_b$ data. Moreover, ZnB addition increased the flame propagation of the composites, where the one prepared via the casting method was the most effective. The thermal stability of a PVC recyclate/ZnB composite prepared via melt mixing increased when exposed to a 30 kGy irradiation dose while that prepared via the casting approach decreased.	Films.	215
“E-waste” (building power supply wires), 0.5–5 mm	Styrenic polymers (i.e., acrylonitrile butadiene styrene (ABS) and high-impact polystyrene (HIPS)	Melt blending	All the blends presented similar mechanical properties. Accordingly, the mechanical behavior was independent of the material’s source. Thus, in the cases of PVC/ABS blends and PVC/HIPS blends, more research was concentrated on those of uninterrupted power supply housing and television monitors, respectively, where the PVC/ABS blends outperformed the PVC/HIPS blends in terms of mechanical properties. HIPS recyclate had an insignificant influence on thermal properties, whereas the ABS recyclate improved the PVC recyclate’s thermal stability.	Enhancing the PVC recyclate’s mechanical and thermal properties.	216
–	Virgin NBR, in the presence of maleic anhydride (MAH)	Melt blending	Greater stabilization torque, mixing energy, stress at peak, and stress at 100 % elongation, as well as decreased ${\epsilon }_b$ and swelling index, indicated that MAH enhanced the interfacial adhesion between PVC recyclate and NBR phases in comparison to the PVC recyclate/virgin NBR blend without MAH.	Improving the mechanical properties and swelling behaviour of PVC recyclate/virgin NBR blend, for applications like conveyor belt covers, etc.	217
Tourist bag	NBR waste	Dry blending	Impact strength and % elongation of PVC increased upon blending it with NBR. The breakdown voltage, volume resistivity, UTS, shore hardness, abrasion resistance, and limiting oxygen index of the blends decreased as the plasticizer concentration increased.	Improving the mechanical and electrical properties of PVC recyclate, for applications like wire and cable insulation, etc.	218
–	Virgin NBR, MAH, and fillers (High abrasion furnace carbon black (CB, N330) and CaCO3)	Melt blending	Upon finding out that NBR is incompatible with PVC recyclate, the use of MAH led to the PVC recyclate/NBR blend’ improved dielectric (permittivity ( ${\epsilon }^{\prime }$ ) and dielectric loss ( ${\epsilon }^{″}$ )) and mechanical properties (stress at yield, stress at rupture, strain at yield %, and strain at rupture %). As CaCO3 content was increased in the blend, both ${\epsilon }^{\prime }$ and ${\epsilon }^{″}$ decreased but increased with increased CB content. On the other hand, increased CB content slightly increased the mechanical properties; however, after 10 phr CB, the mechanical properties values followed a leveling-off trend.	Improving the electrical and mechanical properties of PVC recyclate/virgin NBR, for applications like wire and cable insulation, etc.	219
Credit cards	Virgin and recycled styrenic polymers (i.e., styrene acrylonitrile (SAN) and ABS)	Melt blending	Blends with SAN outperformed those with ABS in terms of both thermal and mechanical properties. Although the mechanical properties were significantly affected by styrenic polymers, the data obtained, indicated a high correlation between the type of polymer used (i.e., if SAN or ABS is used) and its origin (i.e., if recycled or virgin).	Improving the mechanical and thermal properties of PVC recyclate.	149
Matting	Virgin natural rubber (NR)	Melt blending and compression molding	Increased PVC recyclate content increased the hardness and tensile modulus of the PVC recyclate/virgin NR blends. ${\epsilon }_b$ increased with increased PVC recyclate loading but decreased significantly after 40 wt.% PVC recyclate loading whilst the UTS decreased only after the 60 wt.% loading. For thermal properties, both the crystallization temperature and melting point of the blends increased as the PVC recyclate loading was increased.	Improving the thermal and mechanical properties of PVC recyclate.	220
0.5–3 mm	Glass recyclate	Melt blending	Alkali-activated cementitious composites outperformed ordinary portland cement-based composites in terms of mechanical properties (i.e., compressive and flexural strengths as well as energy absorption). PVC/glass recyclates enhanced the energy absorption and thermal resistance of the composites. Recyclates also increased the water absorption rate of the composite because of the weak interlock between the PVC and glass aggregates; however, this was subsequently prevented by substituting glass with sand.	Production of composites (lightweight building blocks) comprised of PVC recyclate.	221
Pipes, <5 mm	Natural sand and ordinary portland cement	Physical blending	Upon an increase in PVC recyclate content, the slump value, compressive strength, tensile strength, and modulus of elasticity of the normal concrete decreased.	Production of concrete comprised of PVC recyclate.	222
Pipes, 4 mm	Natural sand and ordinary portland cement	Physical blending	PVC recyclate reduced the density and compression strength of mortars. The flexural strength was likewise reduced by an increase in PVC recyclate loading; however, the failure was gradual, indicating ductility with increased PVC content. When mortars were subjected to hydrochloric, nitric, and sulfuric acids, the mass loss was reduced as the PVC recyclate content increased. Compared to hydrochloric and sulfuric acid solutions, the produced mortars lost less mass in the nitric acid solution.	Improving brittleness, high acid-resistant, and thermal insulating eco-friendly cementitious materials (mortars) comprised of PVC recyclate.	223
Pipes	Commercial bitumen	Melt blending	PVC shreds improved the properties of bitumen and the PVC shred/bitumen blend. Addition of PVC shreds to the bitumen led to improved phase angle and complex modulus values. In contrast to the neat 80/100 bitumen, a blend exhibited superior resistance to permanent deformation. Indirect tensile strength values, to withstand cracking, of the bitumen increased as a result of shreds addition. Shreds also decreased the bitumen’s rutting values and lengthened its fatigue life.	Production of bituminous material (paving material) comprised of PVC recyclate.	224
Pipes	Commercial bitumen	Melt blending	Shear compliance, torque, and dynamic viscosity of bitumen increased when PVC recyclate was added.	Production of bituminous material comprised of PVC recyclate.	225
–	Cellulose acetate (CA)	Phase inversion	Increased CA content enhanced hydrophobicity, porosity, and pure water flux while decreasing contact angle and bovine serum albumin rejection. Thermal stability also improved with increased CA content.	Production of ultrafiltration membrane comprised of PVC recyclate.	201
Pipes (P) and candy wrappers (CW)	Commercial bitumen	Melt blending	Increased contents of P and CW recyclates caused the bitumen’s specific gravity, softening point, and viscosity to increase while its ductility and penetration properties decreased. P recyclate reduced moisture penetration to the contact surface of the stone mastic asphalt (SMA) mixture by a). Increasing the interfacial tension between the bitumen and the recyclate aggregates and b). Improving the quality of the bitumen’s coating on aggregates. The latter, therefore, increased the viscosity, indirect tensile strength, tensile strength ratio index, shear strength, rigidity, creep stiffness, deformation strength, and resistance to fatigue cracks of the SMA mixture. P recyclate-derived SMA mixture had better skid and rutting resistance at high temperatures, in contrast to CW recyclate-derived mixture. P recyclate outperformed the CW recyclate in terms of mechanical properties.	Production of stone mastic asphalt (paving material) comprised of PVC recyclate.	206,207
Pipes	Thermoplastic starch (TPS)	Melt blending	When subjected to tensile loading, the PVC recyclate/TPS blend outperformed the PVC recyclate compound without TPS in terms of balance of flow properties, heat deflection temperature, stiffness, and strength. However, the dielectric strength data showed that the material’s electrical isolation capacity was significantly decreased when PVC recycle was blended with TPS. Moreover, a blend absorbed moisture, where encapsulation of TPS and reduction of glycerol in the formulation were suggested to avoid this matter.	Production of electrical fittings comprised of PVC recyclate.	226
–	Municipal solid waste (MSW) comprised of food and plastic wastes	Co-pyrolysis	Co-pyrolysis of MSW revealed a strong interaction between its constituents, i.e., food and plastic wastes. Moreover, it became apparent that, as the temperature increased, the tar output from co-pyrolysis was lower than that from the separate pyrolysis of the MSW components. As the temperature for co-pyrolysis increased, the char production decreased.	Accelerate the charring process while decreasing the production of nitrogen (N)-containing tar.	227
–	Biomass wastes and heterogenous plastic waste	Co-pyrolysis	Biomass waste increased char yield and reduced HCl emission. A heterogenous plastic waste also increased char yield. Reduction in HCl emission was also observed from blending PVC waste with coal.	Production of N- and Cl-free plastic waste pyrolytic fuels. Reduce the HCl emission during pyrolysis of PVC-rich waste, thereby improving the ecological environment. Production of char through pyrolysis of PVC solid waste.	163,174,184,191,196,228,229

–: not reported.

An investigation into PVC recyclate blended with virgin PVC seems to have been done inadequately, despite Table 12 demonstrating that this recyclate can be effectively blended with various virgin and recycled materials. Blending PVC recyclate with virgin PVC resin is also important, where the latter can enhance the properties of the former.^{12,15,150–152} This approach could be applied to both homogeneous and heterogeneous PVC wastes, although a compatibilizer would be required if a heterogeneous waste stream is considered. ¹² Fumire et al. ²³⁰ carried out a study on PVC recyclate/virgin PVC blends. In this study, the use of PVC recyclate from window frames in the manufacture of foamed PVC pipes was evaluated, and it was discovered that a PVC recyclate with the particle size of <0.8 mm can be used to substitute a substantial amount (up to 50 wt.%) of virgin PVC in a new PVC item formulation. According to the authors, this particle size was the primary factor that contributed to the high-quality item attained, even though new, high-quality pipes typically have a PVC recyclate proportion of $\le$ 10%.^{11,12,15,35,199,230} Nevertheless, there are regulatory restrictions on the use of recyclate whose primary source differs from the product in question. For instance, a recyclate whose source is a PVC window frame is limited to the manufacture of pipes as indicated in Table 13.

Table 13.

Limitations on the use of PVC window frame recyclate for new PVC pipe manufacturing. ²³⁰

Pipe application	Limitation by standards (%)
Not in drinking water pipes	EN-ISO 1452: = 0 wt.
In compact sewage pipes	EN-ISO 1401: <10 wt.
In the core of foam pipes	EN-ISO 13476: $\le$ 100 wt.
In a central compact layer	EN-ISO 13476: $\le$ 100 wt.

Sombatsompop et al. ¹⁵¹ conducted a study that was comparable to that of Fumire et al., ²³⁰ in which the effect of increased PVC pipe recyclate content on the rheological, mechanical, and thermal properties of the two PVC virgin grades was investigated. The melt shear stress and flow index of both grades increased upon adding PVC recyclate. The die swell ratio was not affected by the PVC recyclate loading; however, because of the PVC gelation feature, a change was noted at the highest reaction temperature (210 $℃$ ). Additionally, the blends of PVC recyclate/PVC bottle grade (40/60, wt.%) and PVC recyclate/PVC pipe grade (80/20, wt.%) gave the optimal impact strength. Compared to the first blend, the second blend contains a higher percentage of PVC recyclate, which suggests that utilizing PVC recyclate that is derived from the same material as the product being manufactured produces a high-quality result, as reported by several other researchers.^{11,12,15,35,199,230} Nevertheless, the blends of PVC recyclate/PVC bottle grade (60/40, wt.%) and PVC recyclate/PVC pipe grade (20/80, wt.%) yielded the optimal ultimate tensile strength (UTS). The blends’ densities and hardness showed a strong correlation, i.e., the blends with higher PVC recyclate loadings had higher densities and hardness. It was also found that increasing PVC recyclate loadings shifts (increases) the temperatures of the glass transition, deterioration, and heat deflection. Sombatsompop et al. ¹⁵² also looked at the feasibility of recycling PVC cable and bottle wastes by incorporating their recyclates into different virgin PVC grades at varied loadings. Their findings indicated that different properties of virgin PVC compounds were dependent on varied PVC recyclate loadings. The optimal loadings of PVC recyclates, according to the authors, should be determined by the intended properties and the type of virgin PVC grade that is utilized. Moreover, the individual addition of PVC cable and bottle recyclates enhanced the tensile and impact strength properties of the virgin PVC compounds. Grigoryeva et al. ²³¹ also conducted a study on PVC recyclate/virgin PVC blends, where a recovered polyurethane (PU) foam-backed PVC-sheet ( ${PVC/PU}^r$ ) was identified as a material that could be reused as a plasticizer for virgin PVC resin ( ${PVC}_r$ ) and as a modifier for virgin plasticized PVC ( ${PVC}_p$ ) without any purification and/or fractionation. ${PVC/PU}^r$ was found to decrease ${\epsilon }_b$ and $T_g$ of virgin PVC samples while increasing their UTS. ²³¹

Landfilling

It is important to consider the fact that even the PVC solid items comprised of recycled elastomeric and/or polymeric material eventually become waste. Generally, PVC can be disposed of in sanitary landfills in any kind of waste setting (i.e., homogeneous PVC waste stream, PVC-rich plastic waste alone or mixed with non-polymeric waste materials, etc.). ²³² The landfills are also the least expensive gatekeepers since they can manage PVC waste as part of ordinary municipal solid waste, saving money on costly collection, separation, and/or pre-treatment procedures.^14,15,199 It is evident that the high expenses associated with repurposing and the low expenses associated with landfilling are impeding the development of recycling methods for PVC waste while fostering its disposal in landfills. ¹⁵ The only costs, which are often minimal, associated with landfilling PVC waste are those of shredding and transportation to the landfills. Furthermore, waste generated by PVC waste chemical recycling—particularly that which comes from incineration, e.g., contaminated fly ash, salts, flue gas cleaning residue, etc.—often finds its way to landfills.^{11,15,140,157,233} This forms a fraction of PVC waste, in addition to hospital PVC-rich plastic waste, that is considerably expensive to recycle, regardless of how the PVC recovery process is structured.^14,234 Regulated landfilling emerges as a solution when repurposing such a fraction is not feasible or affordable. Nonetheless, the major concern regarding landfilling has always been whether or not it is an appropriate solution for managing PVC solid waste items.

Nowadays, landfills and deposited waste must adhere to stricter regulations pertaining to the protection of the environment and public health from solid waste pollution. Although landfilling has historically been the least expensive option for managing PVC waste when compared to any recycling approach, it is now becoming more and more difficult and costly, especially for countries with high population densities.^156,199 As the quantity and capacity of sites rapidly decrease, landfill regulations are becoming more stringent.^15,157,199 Accordingly, landfilling is the least desirable choice in the PVC waste management hierarchy (in terms of environment-harming options) since PVC generally does not readily degrade under anaerobic conditions and it poses risks to the environment by its chlorine constituent.^{14,148,149,220,235} It is worth highlighting, however, that this hierarchy differs by country, with some preferring energy recovery over landfilling and others favouring landfilling over energy recovery.^14,17 Additionally, leachate—a liquid that percolates through PVC waste and collects small, dissolved toxic compounds (organotin, organochloride, phthalic, and dioxin compounds)—can contaminate nearby land or water supplies, which is why large landfills these days need thick, wide liners.^199,232,236 As a result, several countries have passed laws prohibiting the disposal of untreated (i.e., raw) waste, which includes non-biodegradable items like plastic. ¹⁹⁹ To date, however, there is no conclusive evidence to justify a ban on PVC waste landfilling; for example, there was hardly any indication of stabilizers’ organotin and phthalic compounds release from the PVC items in the landfill simulation assays (leachate) studied by Mersiowsky. ²³² Also, nothing indicated a state of deterioration, PVC was not the source of vinyl chloride, and no solute or volatile chlorinated gases or compounds were released when these PVC landfill experimental assays were carried out. These compounds were rather believed to originate from various landfill conditions and other sources (than PVC items) via intricate processes occurring within the landfill body.^232,237 Therefore, unless they are subject to extra recovery targets, PVC wastes are expected to continue being disposed of in landfills, especially in countries where no significant limits on landfilling beyond those mandated by the Landfill Directive are proposed.^14,199,232

There is a great deal of variety throughout countries in terms of the level of PVC waste recycling advancement, the impact of other planned solutions for this type of waste, and its landfilling. ¹⁹⁹ That being said, it remains unclear how particular national landfilling regulations are influencing PVC waste streams’ method of disposal as landfilling continues to be a cost-effective alternative to managing PVC waste, despite public debate regarding the fate and prospective environmental effects of PVC items as well as their additives and long-term behaviours.^14,157,232 PVC waste landfilling is seen primarily in least-developed and developing countries, where recycling accounts for <1% of total plastic waste is generated, as it is comparatively more costly than landfilling.^11,197,238 Because these countries lack both the infrastructure necessary for energy recovery and the domestic recycling capabilities, they are exempt from landfilling regulations. ¹⁵⁷ These countries also rely on landfilling because it is affordable and suitable for all waste streams, without requiring any special equipment. ¹⁵⁷

Conclusion

Polyvinyl chloride (PVC) is typically acknowledged for its various applications in different industries due to its versatility, durability, and cost-effectiveness. Given how important it is in the modern world—from building to healthcare materials—its significance cannot be underestimated. Its prominence has not just dominated the plastic sector recently; rather, for many years, its manufacturing and consumption-based market has been expanding rapidly worldwide. It is anticipated that this trend will continue, especially due to the competition that exists between multiple regions and entities concerning PVC product quality, demand, cost, trade, innovation, and market presence. Consequently, one may anticipate an upsurge in the challenges involved in managing the overall plastic solid waste. Although PVC solid waste repurposing has become a crucial ecological and economic priority due to the need to lessen the negative effects plastic wastes have on the environment, this waste management approach is not developing as rapidly as it should be due to the high expenses associated with it compared to landfilling. However, because PVC does not decompose easily in anaerobic environments and contains chlorine, which could be hazardous to the environment, stricter regulations have been established to prevent landfilling of PVC solid waste. This has incentivized scholars to explore repurposing methods that are not only effective but also compliant with these regulations, which are primarily grounded on economic viability and environmental preservation. These include mechanical (primary and secondary) recycling, chemical recycling, energy recovery, and blending methods, though chemical recycling and energy recovery processes have environmental consequences similar to landfilling. In addition to resulting secondary pollution that is harmful to lifeforms, these processes are expensive because of their high energy consumption, especially if a specialized rector is used over a cement kiln. On the other hand, the mechanical (secondary) recycling approach generates PVC recyclate with inferior properties and thus is considered an energy waster because of the lack of this recyclate’s applicability. Nevertheless, blended with other materials, PVC recyclates have found widespread applications in various areas, such as lightweight building blocks, cementitious and bituminous products, electrical fittings, ultrafiltration membranes, pyrolytic products, etc. Moreover, the blending approach improves the usability of PVC recyclate as its mechanical, thermal, and electrical properties can be rehabilitated by blending it with a particular virgin or recycled polymer or elastomer, usually in the presence of a compatibilizer. In addition to being inexpensive, this approach can also manage both homogeneous and heterogeneous PVC solid waste streams and thus is perceived as a promising option for recycling PVC solid waste, as sorting—which is typically required by primary recycling approaches—adds expenses to the overall recycling operations.