Development and characterization of polyvinyl alcohol filled with date palm midrib powder

Abstract

Date palm (Phoenix dactylifera L) is one of the most widely cultivated crops in different parts of Saudi Arabia. The midribs rich in cellulose, hemicellulose, and lignin are often burnt in the farms, causes severe environmental problems. In the present study, date palm midrib (DPM), these waste materials were powdered and incorporated into polyvinyl alcohol (PVA). Composites were prepared by varying the DPM loading (0–10 wt.%) using the solution casting method. Tensile and thermal properties were analyzed for the composites with respect to filler loading. Addition of DPM as filler enhanced the tensile modulus while an inverse effect was observed in the elongation values. Differential scanning calorimeter (DSC) analysis showed a gradual increase in melting temperature (T_m) and crystallinity values for PVA. Thermogravimetric analysis (TGA) indicated that the incorporation of DPM into PVA can increase the thermal stability of PVA. Morphology of the composites was performed using scanning electron microscopy (SEM).

Keywords

Date Palm Midrib Mechanical Properties Thermal Properties Composites

Introduction

During the last three decades, polymers are increasingly crucial as the material of choice to prepare varieties of products. Polymers’ versatility, durability, and diversity in properties continue to empower researchers to expand their applications and invent new plastic products to meet growing requirements for plastic materials with diverse properties and applications. However, tremendous use of plastics’ and discarding may cause a waste management challenge and environmental concern despite the clear advantages of plastics. They contribute significantly to the amount of reliable waste stream and represent the fastest-growing component of solid waste. Hence, researchers concentrated their focus on producing environmentally friendly products without sacrificing properties up to a limit. Natural and biodegradable fibers from natural sources like sisal, kenaf, jute, hemp, banana, starch, wood flour, and date seed can be used as filler to fabricate different bio-composites.^1–12

Poly(vinyl alcohol), PVA often synthesized by the hydrolysis of poly(vinyl acetate), is a water-soluble, non-toxic, bio-compatible, biodegradable, and semi-crystalline polymer. It is used to fabricate eco-friendly bio-composites for different applications.^13–15 PVA based composites have been successfully developed using renewable and biodegradable materials such as starch, gellan, wheat gluten, collagen, gelatin, and cellulose (micro and nanocrystalline) chitosan as reinforcing agent.^16–31

Date palm (Phoenix dactylifera L) is one of the extensively cultivated traditional crops in different places in Saudi Arabia. According to a statistics, over 31 million date palm trees with an annual production of about 1.5 million tons of date fruits are there in Saudi Arabia.³² Annual pruning of these date palm trees can cause a huge amount of agrowaste. The date palm seeds, leaves, and midrib are the primary agricultural waste components of date palm trees. Generally, date seeds are used in animal feeds, as an organic additive in soil, etc., while the roasted seed powder is used to prepare caffeine-free drinks.³² However, the midrib cut off from the palm tree to burst date fruit production is often burnt in the farms, causing severe environmental concern. These rich waste materials are cellulose, hemicellulose, and lignin, could be used as a component of added value-products. Several investigations on the utilization of dates seed for different applications^5,33–43 were conducted while the use of midribs waste has not been fully exploited. Few investigations have been reported to benefit date palm midribs for applications such as cement/concrete reinforcement, insulating panels, paper making, and particle boards.³⁴

According to the literature, the use of date palm midrib powders to prepare PVA composites has not been reported. Possibly, these types of biodegradable composites can find applications in the packaging industry and other consumer product manufacturing. Hence, this article aims to brief the fabrication and characterization of polymer film composite using PVA as the polymer matrix and date palm midrib (DPM) powder as a reinforcement agent by varying the filler content up to 10 wt.%. Also this article demonstrates the use of one of the significant waste components of date palm tree for the preparation of polymer bio-composite with the view of agricultural substantial waste reduction and utilization.

Experimental

Materials

Polyvinyl alcohol, PVA (98–99% hydrolyzed, low molecular weight), were procured from Alfa Aesar Company. Glycerol which is used as a plasticizer was purchased from Sigma Aldrich Company. Date palm midrib was obtained from local sources of Saudi Arabia.

Preparation of Date palm midrib powder

The date palm midribs were cut into small cubes and dried at room temperature for 24 h. The dried midrib was then grounded into a fine powder using High-Speed Multi-function Comminutor (RRH 200) and screened through a USA Standard Testing Sieve (ASTME-11 Specification). Only the particles that pass through the Tyler Equivalent 40 mesh (420 µm) were considered for the sample preparation.

Preparation of Composites

The solution casting process was used for the preparation of the date palm midrib reinforced PVA composites. At first, the suspension of PVA containing glycerol (3 mL) was prepared. Date palm midrib at various concentrations (1, 3, 5, and 10 wt.% concerning the total polymer content) was added by keeping the total solution volume constant. The solution was stirred at 80°C until gelation. The gel-like solution was then transferred to a mold and allowed to dry. The prepared composites were designated as M1, M3, M5, and M10, where the 1, 3, 5, and 10 represent the filler content.

Characterization

FTIR analysis

The Infrared spectra of pure PVA and composite samples were recorded in the range of 500–4500 cm⁻¹ with a spectral resolution of 4 cm⁻¹ and 32 scans per spectrum using the Thermo NICOLET 6700 FT-IR Spectrometer.

DSC analysis

Differential Scanning Calorimetry (DSC) was carried out to investigate the melting and crystallization behavior of PVA and its composites using TA Q-1000 DSC. Samples were heated in a nitrogen atmosphere from 30 to 240°C at the heating rate of 10°C/min. Then a cooling was done at a rate of 10°C/min from 240 to 30°C followed by a second heat from 30 to 240°C at the same rate of 10°C/min. The percentage degree of crystallinity was calculated using the equation (1)

% Crystallinity = (Δ H_{fus} /w × Δ H_{fus}^{0}) × 100

(1)

where w is the weight fraction of matrix, ΔH_fus is the heat of fusion of starch/PVA blends, and

Δ H_{fus}^{0}

is the heat of fusion for 100% crystalline PVA, which is reported to be 141.932 J/g.⁴⁴

XRD analysis

XRD analyses of the samples were done using LABX XRD-6000 (Shimadzu) X-ray diffractometer with Cu Kα radiation source (1.5410 A° wavelengths) and angle of diffraction (2θ) varied from 5° to 60°.

Thermal stability

TGA-Q500 (TA Instruments) was used to conduct thermal degradation studies. For each measurement, about 10 mg of the sample was heated in a nitrogen atmosphere (purge gas flow of 50 mL/min) at a heating rate of 10°C/min from 25° to 800°C.

Tensile Properties

Tensile tests of the samples were carried out according to ASTM D882-12 using Lloyd Universal testing machine (1 K LF PLUS-UTM) with a standard of 2 mm/min. Five samples were tested for each composition and average values were reported.

Scanning electron microscopy (SEM) Analysis

The microscopic images of the prepared samples were taken using the scanning electron microscope LYRA3 TESCAN Field Emission SEM. To avoid charging of the samples during imaging, the samples were cryo-fractured, and the cross-sections of the samples were coated with gold.

Results and Discussion

Fourier infrared transform spectroscopy (FTIR)

Pure PVA film and PVA containing varying amount of the date palm midrib powder (1.0%, 3%, 5%, and 10 wt.%) obtained by solution casting method were analyzed using FTIR. Figure 1 illustrates the FTIR spectra of pure PVA film (top) and PVA-DPM composites (M1, M2, M5, and M10). The IR of pure PVA is characterized and dominated by a broad and robust absorption peak at around 3300 cm⁻¹ attributed by the hydrogen bonded –OH functional group of PVA. The peak appears in all PVA-DPM composites without significant changes. The absence of carbonyl (C=O) stretching peak at 1700 cm⁻¹ in the PVA spectrum shows that the PVA used in this analysis is fully hydrolyzed. Other peaks of PVA at about 2900, 1650, 1430, 1330, 1096, and 920 cm⁻¹ are due to the –CH stretching, H₂O bending, –CH₂ bending, –OH rocking, –CO stretching, C–C stretching, respectively. Similarly, the FTIR spectra of PVA-DPM composites are dominated by a broad and strong peak at 3300 cm⁻¹ due to the overlap between the hydroxyl stretching vibrations of PVA and the cellulose component of midrib.

Figure 1.

FTIR spectra for the PVA composites having midrib filler content 0, 1, 3, 5, and 10 wt.%.

Tensile properties

Tensile properties of PVA and PVA-DPM composites were given in Table 1. Remarkable enhancement can be seen for the tensile modulus of PVA by adding date palm midrib powder in PVA. For composite having 10 wt.% of the midrib, the tensile modulus increased from 66 to 126 MPa, that is, an increment of 125%. Beyond the 10 wt.% filler content, the composite becomes less ductile in nature. A slight increment in tensile strength was seen for PVA by the addition of filler in the matrix. While adding date palm midrib in PVA, hydrogen bonds were formed between filler and matrix, contributing to high dispersion throughout the matrix. This helps for the excellent load transfer from matrix to fillers that causes an increment in tensile modulus. However, the incorporation of date palm midrib caused a drastic lowering in the elongation at break value for PVA. Addition of 10 wt.% of date palm midrib decreased the elongation at break value from 366 to 28%. According to Cheng et al.,⁴⁵ the low deformability of composite under tensile load is attributed by the excellent interfacial attachment among the matrix and fillers and this adhesion did not allow the PVA to elongate.

Table 1.

Tensile properties for date palm midrib reinforced PVA having filler content 0, 1, 3, 5, and 10 wt.%.

Amount of date palm midrib (wt.%)	Tensile strength (MPa)	Young’s modulus (MPa)	Elongation (%)
0	16.6	66.1	366
1	18.6	78.8	175
3	18.4	82.5	157
5	17.5	95.2	143
10	17.3	126	28

X-ray diffraction

XRD spectra for PVA and date palm midrib reinforced PVA composites is as shown in Figure 2. The details of the XRD parameters are given in Table 2. As shown in the figure, the neat PVA exhibits peaks around 2θ =19.9° and 41° ascribed by the diffraction planes (200) because of the strong inter and intramolecular hydrogen bonding.^46–48 The addition of date palm midrib powder resulted in a smaller shift in crystalline peak towards a higher angle. For PVA, which contains 5 wt.%, date palm midrib shows a crystalline peak at 2θ = 20.3° with an interplanar distance d = 4.3 A° and crystallite size = 3.29 nm. For composite having 10 wt.% date palm midrib, there is not much variation in the 2θ and d values. XRD diagram, shows that addition of date palm midrib decreased the intensity of peaks (2θ =19.9° and 41°) which can be seen in PVA. This variation may be resulted from the lowering of intramolecular hydrogen bonding and enhancement in inter-molecular hydrogen bonding with date palm midrib.¹⁷ Moreover, polymer’s crystallinity is affected by the presence of date palm midrib.⁴⁹

Figure 2.

XRD spectra for the PVA composites having midrib filler content 0, 1, 5, and 10 wt.%

Table 2.

XRD parameter for date palm midrib reinforced PVA having filler content 0, 1, 3, 5, and 10 wt.%.

Amount of date palm midrib (wt.%)	Angle	D value	FWHM	Intensity	Crystallite size (nm)
0	19.9	4.45	2.54	9081	3.32
0	41.4	2.17	2.75	55	3.32
1	20.3	4.36	2.47	5433	3.41
1	41.3	2.18	2.76	556	3.41
3	20.3	4.36	2.50	4965	3.37
3	40.7	2.21	3.5	1051	3.37
5	20.3	4.3	2.56	4758	3.29
5	41.2	2.19	4.4	801	3.29
10	20.2	4.37	2.36	4880	3.57
10	40.7	2.21	3.68	1017	3.57

DSC analysis

Thermal properties (melting and crystallization) for the PVA and PVA-DPM composites were performed using Differential Scanning Calorimeter. Figure 3 a and b represent the DSC heating and cooling curves for PVA and PVA composites having midrib filler content 0, 1, 3, 5, and 10 wt.%. The data collected from the DSC analysis is summarized in Table 3. It can be seen that the variation in the amount of the filler affects the T_m, T_cry, ΔH_fus, ΔH_cry values. A slight increase was seen for the composites having filler content of 5 and 10 wt.%. It has been reported that the T_g value of composite can vary due to the plasticizing effect of the water molecules. The T_g values obtained from the DSC thermogram showed that the newly formed interactions between the hydrophilic date palm midrib fillers and the water molecules were strong enough to reduce the PVA chains’ molecular mobility, thus shifting the T_g values to a slightly higher temperature. But roughly, the T_g values obtained for composites were close to that of neat PVA. This result indicates that the small size of the date palm midrib powder could not cause any significant breaks of hydrogen bonds in PVA. The increase in inter-molecular hydrogen bonding caused by glycerol addition seems to have further nullified the effect. Moreover, this behavior could also mean that the interactions between these DPM powder and PVA did not change the amorphous phase’s molecular conformations. Subsequently, the flexible nature and the mobility of the chain were witnessed at about the same temperature. The T_g of the PVA composites remained roughly constant while adding the DPM powder. A slight but negligible increase was observed, which can be due to the strong interactions between the DPM fillers and hydrolyzed PVA matrices. It can be understood that the PVA/DPM interactions tend to shift the T_g to a slightly higher temperature attributed by the decrease in the molecular movement of PVA chains at the interfacial zone. This re-localization effect could have caused a decrease in the plasticizing effect of water. Both T_m and degree of crystallinity of composite increased with the addition of DPM, also owing to the above explanations.

Figure 3.

(a). DSC heating curves for the PVA composites having midrib filler content 0, 1, 3, 5, and 10 wt.%. (b) DSC cooling curves for the PVA composites having midrib filler content 0, 1, 3, 5, and 10 wt.%.

Table 3.

T_g, T_m, ΔH_fus, T_cry, ΔH_cry, and degree of crystallinity of for date palm midrib reinforced PVA having filler content 0, 1, 3, 5, and 10 wt.%.

Amount of date palm midrib (wt.%)	T_g (°C)	T_m (°C)	ΔH_fus (J/g)	T_cry (°C)	ΔH_cry (J/g)	Crystallinity (%)
0	75	178	21.5	141.9	42.5	15.14
1	75	170	22.3	125.6	33.6	15.87
3	76	171	21.3	128.8	36.6	15.47
5	78	188	20.9	150	43.8	15.50
10	79	190	22.7	151	27.5	16.83

TGA analysis

The thermal stability of composite widely depends upon the molecular interaction between the various macromolecules present in the mixture. In our case, it is the DPM powder, glycerol, and PVA. Table 4 represents the TGA data for date palm midrib reinforced PVA composites with filler content 0, 1, 3, 5, and 10 wt.%. All samples underwent a slight weight loss of roughly 10–12%, below 100°C owing to the loss of physically absorbed moisture. After 100°C, the thermal degradation of DPM-PVA composites occurred in three stages, as confirmed from the values in the table. Weight loss in the first degradation stage commenced due to dehydration and evaporation of organic volatiles present in the composition. The second degradation stage, which is the most crucial stage, showed us that incorporating DPM powder up to 5 wt.% in the PVA matrix decreased the onset temperature up to 42°C in comparison with the PVA. This significant reduction can be attributed to the DPM filler and PVA matrix’s compatibility within 5 wt.% filler loading. The thermal stability remains optimum until 5 wt.% filler loading, after which it starts to decrease. Due to the hydrogen bonding imparted by glycerol which is added during the preparation, the residue of PVA is higher than composites. Also at 600°C, the composite having filler content showed less residue due to the increase in the amount of less thermally stable DPF.

Table 4.

Results of thermogravimetric studies for date palm midrib reinforced PVA having filler content 0, 1, 3, 5, and 10 wt.%.

Amount of date palm midrib (wt.%)	Moisture content (%)	First degradation temperature range		Second degradation temperature range		Third degradation temperature range		Residue at 600°C (%)
Amount of date palm midrib (wt.%)	Moisture content (%)	T (°C)	mass loss (%)	T (°C)	mass loss (%)	T (°C)	mass loss (%)	Residue at 600°C (%)
0	11.8	106.8–243.7	23.08	243.7–279.8	44.25	289.2–469.9	12.43	8.8
1	11.3	108.4–232.9	21.13	232.9–284.1	46.35	279.9–469.0	12.12	8.5
3	11.1	110.7–228.0	20.20	228.0–289.9	49.27	286.6–472.2	11.95	7.1
5	10.9	114.3–201.3	17.10	201.3–293.1	53.80	289.9–466.3	11.63	5.2
10	10.7	120.5–249.5	27.01	249.5–305.9	43.68	305.9–462.1	11.57	4.4

Morphology analysis

The degree of distribution and the attachment of fillers to the matrix are the most important factors that can determine the properties of any composites. Figure 4(a) to (c) represent the SEM of PVA and PVA composites which contains 1 and 5 wt.% date palm midrib, respectively. The SEM of neat PVA is very smooth and more homogenized. The addition of date palm midrib increased the heterogenic nature of PVA, and small cracks can be seen on the surface. Moreover, there is no agglomeration between the filler and matrix, which causes an increase in the tensile strength, Young’s modulus and thermal stability of the composites.

Figure 4.

(a) SEM image for the PVA. (b) SEM image for the PVA composites having midrib filler content 1 wt.%. (c) SEM images for PVA composites having midrib filler content 5 wt.%.

Conclusions

Date palm midrib powder reinforced PVA composites were prepared by varying the filler content using the solution casting method. The tensile modulus increased as a function of filler content while a decrease in its percentage of elongation. The intensity of peaks which are characteristics of PVA decreased with an increase in the amount of filler. DSC analysis showed that T_m, ΔH_fus, and percentage of crystallinity can be influenced by the filler content. Also, the good compatibility between the date palm midrib and PVA resulted in better thermal properties and which can be corroborated with the SEM analysis.

Footnotes

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.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Yunusa Umar

Sreekumar P A

References

Quazi

THS

Alam

AKMM

Quaiyyum

. Mechanical properties of polypropylene composites: a review. J Thermoplast Compos Mater 2011; 26: 1–30.

Tajvivi

Takemura

. Thermal degradation of natural fiber reinforced polypropylene composites. J Thermoplast Compos Mater 2009; 23: 281–298.

Wang

Jones

, et al. Development and characterization of high-performance kenaf fiber-HDPE composites. J Reinf Plast Composites 2017; 37: 191–200.

Gao

Wang

. Preparation of highly filled wood flour/recycled high density polyethylene composites by in situ reactive extrusion. J Appl Polym Sci 2012; 124: 5247–5253.

Homkhiew

Ratanawilai

Thongruang

. Composites from recycled polypropylene and rubberwood flour. J Thermoplas Compos Mater 2013; 28: 179–194.

Ameri

Laperrière

Lebrun

. Mechanical characterization and optimization of a new unidirectional flax/paper/epoxy composite. Compos B Eng 2016; 97: 282–291.

Sullins

Pillay

Komus

, et al. Hemp fiber reinforced polypropylene composites: the effects of material treatments. Compos B Eng 2017; 114: 15–22.

Kılınc

Atagur

Ozdemir

, et al. Manufacturing and characterization of vine stem reinforced high density polyethylene composites. Compos B Eng 2016; 91: 267–274.

Puglia

Santulli

Sarasini

, et al. Thermal and mechanical characterisation of Phormium tenax-reinforced polypropylene composites. J Thermoplast Compos Mater 2014; 27: 1493–1503.

10.

Joy

Jose

, et al. The influence of nanocellulosic fiber, extracted from Helicteres isora, on thermal, wetting and viscoelastic properties of poly(butylene succinate) composites. Cellulose 2017; 24: 4313–4323.

11.

Sreekumar

Manirul Haque

Afzal

, et al. Preparation and characterization of microcellulose reinforced polyvinyl alcohol/starch biocomposites. J Compos Mater 2019; 53(14): 1933–1939.

12.

Appu

Ashwaq

Al-Harthi

, et al. Fabrication and characterization of composites from recycled polyethylene and date palm seed powder. J Thermoplast Compos Mater 2019; 34: 316–327. DOI: 10.1177/0892705719843960.

13.

O’Donnell

Oporto-Velásquez

Comolli

. Evaluation of acetaminophen release from biodegradable poly (vinyl alcohol) (PVA) and nanocellulose films using a multiphase release mechanism. Nanomater 2020; 10: 301.

14.

Khalaji

Golshan Ebrahimi

Hosseinkhani

. Enhancement of biocompatibility of PVA/HTCC blend polymer with collagen for skin care application. Int J Polymeric Mater Polymeric Biomater 2020; 70: 459–468. DOI: 10.1080/00914037.2020.1725761.

15.

Abu-Thabit

Judeh

Hakeem

, et al. Isolation and characterization of microcrystalline cellulose from date seeds (Phoenix dactylifera L.). Int J Biol Macromol 2020; 155: 730–739.

16.

Chiellini

Cinelli

Imam

, et al. Composite films based on biorelated agro-industrial waste and poly(vinyl alcohol). preparation and mechanical properties characterization. Biomacromolecules 2001; 2: 1029–1037.

17.

Jayasekara

Harding

Bowater

, et al. Preparation, surface modification and characterisation of solution cast starch PVA blended films. Polym Test 2004; 23: 17–27.

18.

Guohua

Cuilan

, et al. Water resistance, mechanical properties and biodegradability of methylated-cornstarch/poly (vinyl alcohol) blend film. Polym Degrad Stab 2006; 91: 703–711.

19.

Sudhamani

Prasad

Udaya Sankar

. DSC and FTIR studies on Gellan and Polyvinyl alcohol (PVA) blend films. Food Hydrocoll 2003; 17: 245–250.

20.

Dicharry

Saha

, et al. Wheat gluten−thiolated poly(vinyl alcohol) blends with improved mechanical properties. Biomacromolecules 2006; 7: 2837–2844.

21.

Alexy

Bakoš

Hanzelová

, et al. Poly(vinyl alcohol)-collagen hydrolysate thermoplastic blends: I. Experimental design optimisation and biodegradation behaviour. Polym Test 2003; 22: 801–809.

22.

Chiellini

Cinelli

Fernandes

, et al. Gelatin-based blends and composites. Morphological and thermal mechanical characterization. Biomacromolecules 2001; 2: 806–811.

23.

Chiellini

Cinelli

Corti

, et al. Composite films based on waste gelatin: thermal-mechanical properties and biodegradation testing. Polym Degrad Stab 2001; 73: 549–555.

24.

Bergo

Sobral

PJA

. Effects of plasticizer on physical properties of pigskin gelatin films. Food Hydrocoll 2007; 21: 1285–1289.

25.

Jahan

Khan Niazi

Gregersen

. Mechanical, thermal and swelling properties of cellulose nanocrystals/PVA nanocomposites membranes. J Indus Eng Chem 2017; 57: 113–124.

26.

Johari

Kurmvanshi

Mohanty

, et al. Influence of surface modified cellulose microfibrils on the improved mechanical properties of poly (lactic acid). Int J Biol Macromol 2016; 84: 329–339.

27.

Cano

Cháfer

Chiralt

, et al. Physical and microstructural properties of biodegradable films based on pea starch and PVA. J Food Eng 2015; 167: 59–64.

28.

Bonilla

Fortunati

Atarés

, et al. Physical, structural and antimicrobial properties of poly vinyl alcohol-chitosan biodegradable films. Food Hydrocoll 2014; 35: 463–470.

29.

Silva

GGD

Sobral

PJA

Carvalho

, et al. Biodegradable films based on blends of gelatin and poly (vinyl lcohol): effect of PVA type or concentration on some physical properties of films. J Polym Environ 2008; 16(4): 276–285.

30.

Tang

Alavi

. Recent advances in starch, polyvinyl alcohol based polymer blends, nanocomposites and their biodegradability. Carbohydr Polym 2011; 85(1): 7–16.

31.

Schoeler

Scremin

Fernandes de Mendonça

, et al. Cellulose nanofibers from cassava agro-industrial waste as reinforcement in PVA films. Quim Nova 2020; 43(6): 711–717.

32.

https://www.zawya.com/mena/en/business/story/Saudi_Arabia_second_largest_producer_of_dates_with_17_of_global_share-SNG_179116841/ .

33.

Rahman

Kasapis

Al-Kharusi

NSZ

, et al. Composition characterisation and thermal transition of date pits powders. J Food Eng 2007; 80: 1–10.

34.

Elseify

Midani

Shihata

, et al. Review on cellulosic fibers extracted from date palms (Phoenix Dactylifera L.) and their applications. Cellulose 2019; 26: 2209–2232.

35.

Kolawole

Abdullahi

Dauda

, et al. Physico-mechanical properties of dates palm (Phoenix dactylifera) pits reinforced unsaturated polyester composites. Inter J Sci Res 2015; 4: 1412–1418.

36.

Amedh

Isa

Sansui

. Effect of particle size and concentration on the mechanical properties of polyester/date palm seed particulate composites. Leonardo El J Pract Technol 2015; 14: 65–78.

37.

Marzouk

Bettaieb

Khiari

, et al. Composite materials based on low-density polyethylene loaded with date pits. J Thermoplast Compos Mater 2015; 30: 1200–1216.

38.

Ibrahem

. Effect of date palm seeds on the tribological behaviour of polyester composites under different testing conditions. J Mater Sci Eng 2015; 4: 206.

39.

AlMaadeed

Nógellová

Mičušík

, et al. Mechanical, sorption and adhesive properties of composites based on low density polyethylene filled with date palm wood powder. Mater Des 2014; 53: 29–37.

40.

Mirmehdi

Zeinaly

Dabbagh

. Date palm wood flour as filler of linear low-density polyethylene. Composites B Eng 2014; 56: 137–141.

41.

Alsewailem

Binkhder

. Preparation and characterization of polymer/date pits composites. J Reinf Plast Compos 2010; 29: 1743–1749.

42.

Ghazanfari

Emami

Panigrahi

, et al. Thermal and mechanical properties of blends and composites from HDPE and date pits particles. J Compos Mater 2008; 42: 77–89.

43.

Abu-Sharkh

Hamid

. Degradation study of date palm fibre/polypropylene composites in natural and artificial weathering: mechanical and thermal analysis. Polym Degrad Stab 2004; 85: 967–973.

44.

Nishio

Haratani

Takahashi

, et al. Cellulose/poly(vinyl alcohol) blends: an estimation of thermodynamic polymer-polymer interaction by melting-point-depression analysis. Macromolecules 1989; 22: 2547–2549.

45.

Cheng

Panthapulakkal

Sain

, et al. Aloe vera rind cellulose nanofibers‐reinforced films. J Appl Polym Sci 2014; 131: 40592.

46.

Zhang

Huang

Duan

, et al. Preparation of electrospun chitosan/poly(vinyl alcohol) membranes. Colloid Polym Sci 2007; 285: 855–863.

47.

Wang

Drzal

. Preparation and properties of microfibrillated cellulose polyvinyl alcohol composite materials. Compos A Appl Sci Manufact 2008; 39: 738–746.

48.

Sun

Liu

, et al. Melt-processed poly(vinyl alcohol) composites filled with microcrystalline cellulose from waste cotton fabrics. Carbohydr Polym 2014; 101: 642–649.

49.

Ahad

Saion

Gharibshahi

. Structural, thermal and electrical properties of PVA-sodium salicylate solid composite polymer. J Nanomater 2012.