Abstract
Using recycled textile fibers in composites is currently one of the most effective approaches to reutilize textile waste. To explore the research progress and trends in recycled fiber composites, a visual analysis of the relevant literature is conducted using the software Citespace. Furthermore, the study systematically reviews the preparation methods, influencing factors, and recent applications of recycled fiber composites with various functional properties. The results indicate that fiber reinforcements, polymer matrix materials, and fabrication techniques are critical factors influencing the performance of fiber composites. Current research primarily focuses on five main areas: reinforcement composites, sound-absorbing and thermal-insulating composites, flame-retardant composites, pressure-sensing composites, and filtration and adsorption composites. Existing manufacturing techniques such as hand lay-up molding (HND), compression molding (COM), resin transfer molding (RTM), and vacuum-assisted resin transfer molding (VARTM) have been employed in the fabrication of these composites, among which VARTM and COM have been more prevalently adopted compared to HND and RTM. In addition, the recycled fibers used in these composites are predominantly cotton and wool, typically accounting for 1–81% of the total composition, with most composites containing less than 50% recycled fibers. It is recommended that future developments of regenerated fiber composites emphasize improvements in durability, uniformity, and sustainability.
Introduction
With the development of the global economy and the increase in consumption, the turnover rate of clothing and textiles has increased, leading to a higher demand for textile raw materials. Statistically, global textile consumption is expected to double, 1 and the amount of discarded waste clothing and textiles has reached 90 million tons. 2 Recycling and reusing waste textiles could expand the sources of textile fibers, and reduce resource wastage. At present, the treatment of waste textiles mainly includes energy recovery, physical recovery, and chemical recovery. However, due to various constraints, approximately 85% of waste textiles are still disposed by means of incineration or landfill. 3 This treatment approach not only causes secondary environmental pollution but also contributes to soil degradation from non-degradable synthetic fibers. Additionally, it releases a large number of microplastics to oceans and rivers. These microplastics will be absorbed by marine and freshwater organisms through the water cycle system, and ultimately enter the human bodies, which poses serious risks to ecological and human health. 4
Mixing waste textiles with thermosetting or thermoplastic polymers in different proportions to fabricate composites is one of the ways to recycle waste textiles today. Composite materials capitalize the synergistic effects of their mixed components, allowing them to outperform individual materials. 5 As a result, composites could replace many traditional materials. For example, in the automotive industry, recycled fiber composites were used in body structures, seats, and interiors to reduce vehicle weight. 6 In construction, some composites were used to manufacture lightweight yet strong building materials. 7 The aerospace industry also employed recycled fiber composites in aircraft structures and spacecraft components to improve performance and minimize weight. 8 This paper systematically researched and summarized the preparation processes and the latest research developments of recycled fiber composites, as well as analyzed the challenges faced by this recycling system, which provides valuable insights for advancing recycled composite technology derived from waste textiles.
Literature analysis
Literature collection
In the literature analysis of recycled fiber composites, CiteSpace software was adopted for data-based quantitative and qualitative analysis. The Web of Science was used as the source of English literature, and the search period was set from 1st January 2014 to 31st December 2024. The search terms included “subject=waste textiles OR=recycling OR=textile recycled fibers OR=textiles fiber composites OR=waste cotton OR=waste wool.” After obtaining the search results, the retrieved literature were filtered according to their relevance to the research topic, resulted in a collection of 135 publications. Among them, the literature published in every year were calculated and presented in Figure 1. Generally, the related research has obviously increased in the past over the past decade, except for the years of 2016 and 2020; and the number of publications reached up to over 35 in 2024.
Annual quantities of publications related to recycled fiber composites.
Analysis of research hotspot areas
In this paper, keyword co-occurrence and clustering map were abstracted and drawn by using CiteSpace software. In the map, as shown in Figure 2, the size of the node represents the degree of keyword prominence, while the color of the patterns indicates the year in which the keywords appeared. Correspondingly, it clearly depicted the changes and distribution of research hotspots in the field of recycled fiber composites over the past decade. After filtering and merging similar terms, a total of 130 keywords were identified in the literature. The top five keywords are “#0 mechanical properties” “#1 textile” “#2 nonwoven” “#3 waste viscose fiber” and “#4 circular economy,” indicating that researchers primarily focused on the processes and properties of recycled fiber composites within the context of a circular economy. Therefore, this research systematically reviewed the fabrication processes, the influencing factors of the properties of recycled fiber composites, and their different functions.
Keyword co-occurrence and clustering mapping of studies related to recycled fiber composites.
Fabrication of recycled fiber composites
Conventional processes
With the continuous development of technologies, the fabrication process for composites is becoming increasingly refined. Currently, the fabrication processes of regenerated fiber composites primarily include hand paste molding (HND), compression molding (COM), and resin transfer molding (RTM). 9
Hand lay-up molding (HND) and compression molding (COM)
Hand lay-up molding (HND) is suitable for small-batch production or manufacturing of parts with complex shapes. 10 It is commonly used to produce composites with inorganic materials (such as concrete or gypsum) as the bonding agent. However, the process involves manual laying of fibers and resin coating, will lead to inconsistencies of composites. Compression molding (COM), on the other hand, involves stacking pre-treated fibers together and placing them in a mold to cure under a specific temperature and pressure. This process typically uses thermosetting resins (such as polypropylene, PP) as the bonding agent. As a result, COM process could produce fiber composites with high performances in a short period, such as better surface quality and consistency, as well as fewer restrictions on the shapes and dimensions of the products. 11 Despite these benefits, both fabrication processes have certain limitations when applied to industrial-scale mass production. For example, the HND process, which is mainly hand-operated, results in low productivity, making it difficult to achieve uniformity and automation. This also limits its suitability for small-scale production and prototyping. Although the COM process has advantages in terms of high performance and flexibility in shape and size, its manufacturing efficiency and production speed are relatively low, making it challenging to meet the demands of large-scale industrial production.
Resin transfer molding (RTM)
Resin Transfer Molding (RTM) process has unique advantages in the fabrication of recycled fiber composites. It is typically applicable to resin materials such as epoxy resin, phenolic resin, polyester resin, etc. The RTM process is more attractive compared to HND and COM processes. Firstly, the RTM process allows for a precise control of resin flow, resulting in a better wetting of the resin with the reinforcing fibers. 12 Secondly, the process is well-suited for fabricating more complex shapes, 13 as the resin can effectively penetrate all corners of the fiber reinforcement, and facilitating the production of intricate geometries. With the advancements of automation technologies, the RTM process also has the potential for automated production, which will enhance the manufacturing efficiency and composites consistency, thus enabling industrial-scale manufacturing and providing high-quality, high-performance materials for a wide range of applications.
Additionally, vacuum-assisted resin transfer molding (VARTM), an evolution of the RTM process, utilizes the pressure differential created by the vacuum technology to drive the resin into the pre-positioned fiber reinforcement inside the mold. This helps reduce air bubbles and porosity, thereby improving the quality of the fiber composites. 14 VARTM also allows for the precise fabrication of complex geometries, as the vacuum assistance enables the uniform resin penetration in tiny areas. Therefore, complex shapes could be precisely molded to meet a wider range of morphological requirements. Compared to the RTM process, VARTM facilitates faster resin infiltration and shorter cycle times, making it well-suited for large-scale and industrial production.
Although RTM and VARTM have significant advantages over HND and COM, they still have limitations in terms of manufacturing quality and production efficiency. One of the main difficulties of the RTM process is the presence of voids in the parts, which will have an adverse effect on the mechanical properties of the composites. 15 Moreover, the use of RTM process requires the cooperation of molds and resin injection systems, which further increases the usage cost. In VARTM process, the resin flows under the action of negative vacuum pressure, resulting in a restricted resin flow rate and prolonged curing cycle of the composites. 16 The vacuum demand of VARTM, on the other hand, further increases the cost.
Influencing factors of the composite properties
The mechanical properties of fiber composites determine their applications such as aerospace, automotive, construction, etc. The influencing factors of their mechanical properties include the reinforcement materials and polymer matrix, as well as the fabrication processes used for the composites. 17
Fiber reinforcers
When the fibers are used as reinforcement in composites, fiber orientation, length, and hygroscopicity could significantly affect the mechanical properties of the composite. When the fiber alignment direction is consistent with the load direction, the mechanical performance will be enhanced. 17 However, the arrangement of natural fibers tends to be random, thus, when fabricating composites using natural fibers, it was common to align the fibers before adding the curing agent to achieve better fiber orientation. 18 Additionally, studies have shown that the moisture content in fibers also impacted the mechanical properties of composites. 19 Research indicates that natural fibers possess a high hygroscopicity, and the moisture can reduce the adhesion between the fibers and the polymer, 20 thereby diminishing their mechanical performance. 21 For instance, the hemicellulose in cotton fibers is highly hydrophilic, which weakened the adhesion between the fibers and hydrophobic polymers.22,23 Besides, the high hydrophilicity leads to a greater water absorption, which increased the risk of crack formation in the bonding areas between the fibers and the polymer. 24 If the composite is exposed to external environments, this problem became even worse. To address these challenges, surface modification has become a crucial strategy to enhance the compatibility between natural fibers and the matrix material. 25 Enhancing the hydrophobic properties of the fibers through surface treatment or modification can improve the mechanical strength of the composites. 26
Polymer bonding materials
The selection of polymer bonding materials significantly influences the mechanical properties of fiber composites. They form a protective layer, protecting the fibers from mechanical damage, and transmitting the loads to the fibers. 17 The bonding materials are primarily thermosetting or thermoplastic polymers. 27 Thermoplastic resins will be softened when heated, allowing for the reshaping of thermoplastic composites. In contrast, thermosetting resins cannot be softened once cured, but thermoset composites are generally more stable than thermoplastic composites. A strong connection between the fibers and the bonding material is required for an effective load transfer, ensuring optimal fiber reinforcement. 28
The selection of fiber materials and resins requires comprehensive consideration of various factors, including the application area, the performance of the composite, the fabrication process, and the production cost. Different resin should be chosen according to different fibers. For example, the composites containing cotton fibers are often used in furniture and fiber-reinforced concrete,29,30 necessitating the use of high-strength resins such as epoxy or phenolic resins. Protein fibers, due to their low compatibility with inorganic resins, typically require bio-compatible protein-based resins or chemical modifications to enhance compatibility. 31 Hemp fibers are usually combined with thermoplastic resins like polyethylene and polypropylene to form composites. 32
Fabrication process of fiber composites
During the fabrication of fiber-reinforced composites, temperature and pressure are key factors that significantly affect the properties of the materials. High temperatures can alter the physical and mechanical properties of natural fibers, which in turn impact the overall quality and performance of the composites. For example, the keratin from waste wool textiles may undergo hydrolysis at high temperatures, 33 which limits the use of some bonding polymers that require high-temperature processing. 17
Additionally, applying appropriate pressure during the fabrication process facilitates better infiltration of the resin into the fibers, reduces the formation of bubbles and voids, and thereby enhances the quality and mechanical properties of the resulting composites. However, an excessive pressure could damage the fiber structure. The pressure adopted in the fabrication process should be varied based on the specific process and materials used.
With the improvements in fabrication techniques, the mechanical properties of natural fiber composites have been significantly enhanced. Kacimi and Tafraoui 34 combined damaged wool fibers with resin to prepare composite sheets, and the mechanical properties of the composites were comparable to those of glass fiber composites. Aramwit et al 35 combined wool and coir fibers with gypsum in different proportions to develop wool-coir-gypsum composites. Wool and coir fibers compensated for the poor moisture resistance and limited acoustic performance of gypsum. Accordingly, the composite showed an 125% increase in strength, an 8% increase in elastic modulus, and improved moisture resistance. In this composite, the wool fibers provided enhanced moisture resistance, and the coir fibers served as reinforcement, improving the composite mechanical strength. 35
Recycled fiber composites with different functions
The composites made from recycled fibers effectively extend the lifecycle of the fibers. These fibers were usually obtained from waste textiles through physical or chemical processing methods. Among these, the regenerated fibers produced by the physical and mechanical method retained the inherent characteristics of the original fibers. Therefore, these fibers could partially replace virgin fibers in fiber composites, interacting with the polymer to provide a variety of functionalities. According to the different functionalities, regenerated fiber composites could be classified into five categories including enhancement composites, sound-adsorption and heat insulation composites, flame retardant composites, pressure sensing composites, as well as filtration and adsorption composites, which are depicted in Figure 3(a) to (e) and Table 1.
Recycled fiber composites with different functions: (a) Enhancement composites. Source: Ailenei et al 36 (b) Sound absorption and heat insulation composites. Source: Ghermezgoli et al 37 (c) Flame retardant composites. Source: Guna et al 49 (d) Pressure sensing composites. Source: Tang et al 39 (e) Filtration and adsorption composites. Source: Gore et al 40
Recycled fiber composites with various functions.
As shown in Table 1, it is evident that the regenerated fibers used in composites were predominantly natural fibers, such as recycled cotton and wool. Overall, the volume ratio of regenerated fibers in composites presented a large range, varying from 1% to 81%, most of which fell below 50%. VARTM and COM processes were adopted more in recycled fiber composites than the other fabrication processes. These composites were mainly utilized in industries such as construction, furniture, and automotive interior.
Enhancement composites with recycled fibers
Cotton fibers exhibit excellent moisture absorption, moisture retention, heat resistance, and alkali resistance. Recycled cotton fibers were commonly used in enhancement composites, to replace virgin fibers as the reinforcing structure. Mishra et al 58 mechanically opened waste cotton textiles to obtain recycled cotton fibers, which were then woven into a mesh with polypropylene (PP) materials at various mass ratios. PP resin can compensate for the strong hygroscopic nature of cotton fibers. In addition, it was found that humidity had little impact on the mechanical properties of the composites. Therefore, using cotton fibers as reinforcement material will not significantly reduce the quality of the composites. Some researchers also used textile waste as a reinforcement for polypropylene (PP) matrix and prepared recycled cotton/polyester fiber composites by means of hot pressing. Mechanical tests, including tensile, impact, and thermal loading tests, showed that the addition of recycled cotton fibers significantly improved the tensile strength and stiffness of the composites, with the synergistic mechanical enhancement of the mixed fiber structure. 43 This fiber mesh was subsequently transformed into recycled cotton fiber/PP composite sheets using a hot-pressing method. Performance analysis containing tensile, impact, and thermal load tests, revealed that the mechanical properties of the regenerated fiber composites improved with the increasing mass ratio per unit area of the cotton/PP blended fiber mesh.
However, the composites produced using this method have a laminated structure. The lamination resulted in a lack of fibers in the thickness direction, that is, Z-direction leading to weakened interlaminar properties. To address this limitation, Meng et al 42 obtained regenerated cotton fibers from waste jeans and applied three-dimensional needle-punching technology to create a felt structure with interwoven fibers across different layers of the fiber network. This needle-punched structure overcome the weakness of the laminated composites, which lacked fiber connection between layers, significantly enhancing interlayer performance. The mechanical properties of the composites produced in this manner even surpassed those of particle boards of the same specifications, making them suitable for manufacturing household products such as tables and chairs. 59
Although recycled fiber played a positive role in improving the reinforcement properties of composites, there were still some limitations. Some studies described that waste textile fiber composites could be recycled maximally 4–6 times. 60 Bakkal et al 41 reprocessed composite sheets containing waste cotton fibers six times, and their experimental results indicated that the tensile strength and modulus of the composites first increased and then decreased as the number of reprocessing cycles times. These changes in properties were attributed to fiber damage incurred from the recycling process. Additionally, some researchers explored the use of recycled cotton fiber as reinforcement material for concrete. 61 Experiments demonstrated that concrete composites utilizing recycled cotton fibers as reinforcement showed improved mechanical properties. However, these composites exhibited brittleness upon reaching their limited values, which restricts their applicability in certain environments.
Sound-absorption and heat-insulation composites with recycled fibers
Recycled fiber composites with sound absorption and heat insulation functions have been widely studied and applied in the automotive and construction industries. Wool fibers are an environmentally friendly and renewable resource that can be completely recycled and reused. They possess excellent sound-absorbing and heat-insulation properties, making recycled wool fibers become the most commonly used material in sound-absorbing and heat-insulating composites.37,62 Waste wool textiles were mechanically opened to regenerated wool fibers, which were fabricated to non-woven fabrics by using a needle-punching technique. 45 These non-woven fabrics were subsequently used to produce sound- and heat-absorbing composites. 46 Researcher Alyousef 44 explored the potential of recycled wool fibers to enhance the mechanical and acoustic properties of concrete. The findings indicated that while the mechanical strength and the elastic modulus of the concrete containing recycled wool fibers were slightly lower than those of pure concrete, but the sound insulation and noise reduction of the fiber-concrete composite blocks were significantly improved. Specifically, the sound absorption coefficient of the concrete with 2.5% recycled wool fibers reached 0.66 at 2000 Hz. It outperformed the control sample without recycled fibers, which had a coefficient of 0.25. Cai et al 63 investigated the feasibility of using recycled wool fibers as a low-cost and sustainable acoustic and heat insulation material for automobiles. They prepared non-woven fabrics from regenerated wool fibers through the needle-punching process and applied them in automotive interiors. They also examined the effects of fiber diameter, non-woven fabric surface, layer structure, thickness, and area density of the composites on the acoustic and heat insulation properties. The results showed that the heat and acoustic insulation properties of the recycled wool non-woven were comparable with those of commonly used synthetic fibers in this field. Furthermore, wool’s hygroscopic nature allows it to absorb moisture effectively, with an ultimate moisture absorption rate of up to 35%. 62 Whereas, it will not make users feel damp, 64 which helps regulate the humidity inside vehicles, creating a pleasant interior environment. Additionally, wool composites possess inherent antibacterial and antifungal properties, the biodegradation rates of which could reach 50% or more. Islam et al 47 also explored the possibility of producing sustainable thermal insulation materials from waste cotton textiles. They found that the thermal insulation materials made from waste textiles exhibited excellent thermal insulation properties, and the global warming potential of these insulation materials was four times lower than that of hemp-based insulation boards. Thus, it is evident that recycled fiber composites represent a sustainable solution for noise reduction, with numerous potential applications yet to be explored.
Flame retardant composites with recycled fibers
Wool is primarily composed of natural keratin, which causes wool fibers to be gradually carbonized during combustion rather than burn rapidly, thereby reducing heat release and flame spread. 62 Recycled wool fibers obtained from waste textiles retain the inherent flame-retardant properties of the wool. Therefore, incorporating recycled wool fibers into the composites could impart a degree of flame retardant to them. 48 Guna et al 49 explored using wool’s excellent heat insulation and flame-retardant properties, and coir’s durability, to enhance the performance and application of gypsum ceiling tiles. This composite ceiling tile not only alleviated the insufficient strength and the poor sound and heat insulation performance of gypsum ceiling tiles, but also reduced the production costs. Experimental results showed that the fiber composite achieved a flame-retardant rating of V1, better than the V0 rating of pure gypsum. Guna et al 38 examined the feasibility of using recycled wool fibers as a cost-effective and sustainable solution for sound and heat insulation, as well as flame retardant, in automotive and green building applications. They studied the effects of fiber morphology as well as the interactions between fibers and adhesive materials on acoustic insulation, heat insulation, water absorption, and flame-retardant properties. The results demonstrated that the composites containing up to 90% recycled wool fibers, without any added flame retardants, were not only more cost-effective but also more sustainable compared to commercially available composites with added flame retardants. Angelotti et al 50 revealed that cotton fibers exhibited equivalent thermal performance to conventional insulation materials, cause their inherent low thermal conductivity qualified them to be viable flame retardant fillers in building envelope assemblies.
Pressure sensing composites with recycled fibers
Cotton fibers, as a type of porous natural fibers, 51 possess a special structure that endows them with a low density and high porosity. Correspondingly, the cotton fiber-based composites were widely recognized in various applications. In addition to the enhancement and heat insulation properties, pressure-sensing composites derived from cotton fibers have also attracted considerable interests. Zhang et al 52 combined cotton cellulose with multi-walled carbon nanotube to create a pressure sensor with a porous structure, which shows promise for applications in smart clothing, electronic skin, medical diagnosis, and treatment. Similarly, Chen et al 65 prepared pressure-sensing composites by impregnating carbonized waste cotton fabrics with natural rubber. They adopted three methods: vacuum bagging, pressure adsorption, and drop coating. The resultant composite demonstrated good electrical conductivity, and its resistance varied with applied pressures, making it suitable for monitoring human motion. Bartoli et al 53 developed a low-cost, easily accessible, and environmentally friendly conductive polyvinyl alcohol composites incorporating waste cotton fibers, which not only met pressure-sensing requirements but also, for the first time, exhibited charge transport within bio-char fibers.
Although natural fibers exhibit inherent piezoelectric activity, their constrained performance (d₃₃ = 0.4 pC·N⁻¹) restricts practical implementations. 66 To overcome this limitation, Pan et al 54 fabricated composite porous materials by integrating reduced graphene oxide (rGO) and barium titanate (BaTiO₃) into regenerated cellulose substrates. The rGO addition established continuous conductive networks while BaTiO₃ contributed ferroelectric polarization, collectively enhancing piezoelectric performance. The optimized composite exhibited a piezoelectric coefficient of 41.5 pC·N⁻¹, demonstrating the technical feasibility of repurposing waste cotton fibers for flexible piezoelectric components in integrating flexible piezoelectric nanogenerators.
Filtration and adsorption composites with recycled fibers
Dye wastewater contains numerous harmful chemicals such as acids, alkalis, salts, halogens, and hydrocarbons, as well as dyes, oils inorganic salts, and other organic substances. If these chemicals are discharged directly without treatment, it will cause significant environmental harm. 67 Adsorption is considered one of the most effective ways of wastewater treatment. 68 Waste cotton fibers can be transformed into porous adsorbent materials through pyrolysis or chemical treatment, allowing them to adsorb textile residues, heavy metals, and other pollutants from wastewater. 69 Silva et al 55 used H3PO4 to impregnate and pyrolyze waste denim fabrics to obtain activated carbon fibers, which were then employed to remove textile dyes from aqueous solutions, achieving a maximum adsorption capacity of 292 mg/g. Additionally, silk fibers are both hydrophobic and lipophilic, exhibiting excellent oil absorption properties, making them suitable for applications in oil-water separation and oil recovery. 40 Viju et al 56 processed waste silk fiber through degumming, carding, laying, and needle punching to produce a needle-punched felt. This waste silk fiber felt achieved a separation rate of over 70% for oil-water mixtures. Furthermore, the silk felt naturally degraded within 100 days in soil, and the degradation products that is, peptide mixtures, posed no risk of secondary environmental pollution. 70 Yao et al 57 fabricated composites through carbonization of waste wool into porous structures, and it was followed by TiO₂ integration. The resultant composites had a 13.8-fold enhancement in methylene blue adsorption capacity compared to pure TiO₂ materials, and they could maintain 99% adsorption capacity retention after two calcination cycles.
Discussion
Recycled fibers demonstrate excellent performance in composites fabrication and properties, enhancing various functional characteristics, such as enhancement composites, sound-adsorption and heat insulation composites, flame retardant composites, pressure sensing composites, filtration and adsorption composites, etc. These attributes make recycled fiber composites highly promising in areas like sustainable materials, green building, and automotive applications. However, the practical application of these composites is still limited due to their durability, uniformity, and sustainability. Therefore, the future research and development in recycled fiber composites could focus on the following aspects:
(1) Technologies for improving the durability of the recycled natural fiber composites should be developed through surface modification. Natural fibers, such as cotton fibers and wool fibers, have lower physical and mechanical properties than most synthetic fibers due to the differences of their chemical molecular structures. Surface modification techniques can significantly enhance the inter-facial bonding between natural fibers and matrix materials, thereby improving the durability and overall performance of the composites. Current fiber surface modification techniques include nanotechnology and plasma treatment, which could be utilized to improve the durability and unity of the regenerated fiber composites. In nanotechnology applications, cellulose nanocrystals or graphene oxide coatings are introduced to optimize fiber-matrix interfacial bonding. Plasma treatment utilizes low-temperature plasma to modify fiber surface properties through gas-phase interactions, achieving surface functionalization without chemical solvents, for example, plasma treatment for enhancing fiber hydrophobicity. However, modification of natural fibers still faces technical challenges. For instance, modification treatments may affect the biodegradability and environmental friendliness of fibers, so a clear balance needs to be struck between enhancing performance and maintaining environmental sustainability. Additionally, during the preparation of composite materials, the bonding strength between the fiber reinforcements and the adhesive materials is one of the key factors influencing the composite performance. Therefore, the future research should focus on innovative modification methods, and the optimization of the fabrication processes to improve the overall performance of the recycled fiber composites.
(2) The fiber separation technology of waste textiles urgently needs improvement. Waste textiles contain various types of fibers with significant differences in performance, and many textiles are made from blends or interwoven fibers. Due to the differences in the composition and structure of different fibers, effectively separating these fibers has become a significant challenge. Emerging fiber separation technologies include AI-driven sorting systems employing hyperspectral imaging coupled with machine learning algorithms for precise fiber identification and segregation, as well as ionic solvent systems that selectively dissolve synthetic polymer matrices while preserving natural fiber integrity. However, these technologies are mainly carried out in the laboratory or in a preliminary stage, and their large-scale application in industries has not been realized. This technological bottleneck prevents the efficient acquisition of single, pure fiber materials during the production process, thus limiting the uniformity and standardized production of recycled fiber composites. Therefore, improving the efficiency and accuracy of blended fiber separation technology will be key to enhancing the recycling of waste textiles.
(3) The repeated recycling of recycled fiber composites should also be included in sustainable research considerations. The sustainability of these composites must account for energy consumption and durability during raw material production and manufacturing, as well as the recycling and disposal processes at the end of their life cycle. Although fiber recycling is generally seen as green and sustainable, recycled fiber composites would become a waste of resources if they are not properly recycled and are instead disposed of in landfills or incinerated. Therefore, both recycled fibers and the polymers in the composites should be properly recycled. However, during multiple cycles of reuse, the quality and mechanical properties of waste fibers will gradually degrade, limiting their reprocessing and reuse. As a result, maintaining the mechanical properties of the fibers and enhancing their recyclability remain a significant challenge in the field of recycled fiber composites.
In conclusion, to achieve the sustainable utilization of waste textiles, the fabrication of recycled fiber composites should not only consider resource efficiency, but also focus on every stage of the recycling process, that is, from raw material selection to final recycling treatment, ensuring a comprehensive improvement in their environmental friendliness and economic benefits throughout their life cycle.
Conclusion
This paper systematically reviews the fabrication processes, influencing factors, and applications of recycled fiber composites. Four fabrication methods—hand lay-up molding (HND), compression molding (COM), resin transfer molding (RTM), and vacuum-assisted resin transfer molding (VARTM)—have been compared and employed in the production of textile composites. Among them, VARTM and COM are more commonly utilized in the fabrication of recycled fiber composites. Additionally, fiber reinforcements, polymer matrix materials, and processing techniques play critical roles in determining the properties of fiber composites. By incorporating various types of recycled fibers, the composites exhibit diverse functionalities, including reinforcement, sound absorption and thermal insulation, flame retardant, pressure sensing, and filtration or adsorption. The regenerated fibers used in these composites are primarily cotton and wool, comprising between 1% and 81% of the total content, with the majority containing less than 50% recycled fibers. However, the large-scale industrial application of these composites remains constrained by challenges related to durability, uniformity, and sustainability. Accordingly, three directions are recommended for future research on recycled fiber composites: surface modification technologies to enhance composite durability, fiber separation techniques, and strategies for repeated recycling of recycled fiber composites.
Footnotes
Authors’ Note
Lin Zhao is now affiliated to Hangzhou Silk Maganize Co., Ltd., Hangzhou, Zhejiang Province, China.
Author contributions
Xinxin Huang: Conceptualization, Data analysis, Funding acquisition, Project administration, Writing and editing.
Runling Ye: Investigation, Methodology, Data analysis, Figure drawing, Writing – original draft & editing.
Lin Zhao: Data analysis, Figure drawing, and Writing-editing.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work is partly supported by Regional joint Fund – Youth Fund project of Guangdong Province (2021A1515110445), Guangdong Philosophy and Social Sciences Plan 2021General Project (GD21CYS02), Humanities and Social Science Youth Foundation, Ministry of Education of China (22YJCZH063).
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Data availability statement
Data will be made available on request.