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Abstract

Wood polymer composite (WPC) was prepared using solution-blended high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), poly(vinyl chloride) (PVC), wood flour (WF) and polyethylene-co-glycidyl methacrylate (PE-co-GMA). The effect of nanoclay, SiO₂ and ZnO addition on the properties of the composite was examined. The distribution of silicate layers, SiO₂ and ZnO nanopowder was studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The improvement in miscibility among polymers was studied by scanning electron microscopy (SEM). Fourier transform infrared spectroscopic (FTIR) studies reveal the interaction between polymer, wood, clay, SiO₂ and ZnO. WPC treated with 3 phr each of clay, SiO₂ and ZnO showed an improvement in mechanical properties, thermal stability and a decrease in water uptake capacity.

Keywords

Nanocomposites wood polymer organoclays mechanical properties thermal properties

Introduction

Now a days, wood polymer composite (WPC) occupies a significant part in the field of composite.¹ It is used in all classes of materials ranging from household items to different exterior products viz. automobiles industries, different outdoor and indoor applications like decking, railing, fencing, docks, landscaping timbers, and many more.² They have relatively high strength and stiffness, low cost, low density, low CO₂ emission, and are biodegradable and renewable. Moreover, they can also be used widely with other materials to improve various properties.

Nal (Phragmites karka), a conventional plant, is widely available as biowaste in the forest of Assam, India. They can be made into value-added material for the preparation of structural components by making composites with plastic materials. Sui et al.³ has prepared WPC using nonconventional plant like sunflower hull sanding dust (SHSD) as the reinforcing agent and polypropylene (PP) as the matrix.

The disposal of plastic materials in the form of carry bags, boxes and packaging film causes a serious threat to the environment. Recycling and reusing is one of the processes to reduce this environmental pollution. But the poor mechanical properties of recycled plastic materials restrict their use for different applications.⁴ These properties can be improved substantially if composites are made by combining these waste materials with cellulosic materials.

In order to improve the miscibility between organic polymer and inorganic wood fiber, certain compatibilizers are used. The compatibilizer enhances interaction between hydrophilic wood fibers and hydrophobic polymers and at the same time improves the interfacial adhesion among different thermoplastic materials. The uses of glycidyl methacrylate⁵ and PE-co-GMA⁶ as compatibilizer for making WPC have been reported.

Solution blending is one of the process used for blending of different kinds of plastics. The effectiveness of the blending process can be improved using a mixture of solvents. Although solution blending involves the use of some hazardous solvents, it is still useful in many cases. A high level of intercalation with partial exfoliation of nanofillers has been obtained only for solution blending process.⁷ Chiu et al.⁸ observed good dispersion of silicate layers when they studied PP/clay composite by solution blending method. Melt blending suffers from some disadvantages like stress development, temperature, and so on.⁹ So, in order to obtain a good property development, it is assigned to develop the composite by solution blending method.

Nanocomposite technology with layered silicate as reinforcing phase has been the subject matter of many discussions in recent years. Due to the high aspect ratio of silicate nanolayers, it is ideal for reinforcement and enhancing the properties.¹⁰ The performance of wood/polypropylene composite has been found to improve by the addition of nanoclay.¹¹

In the polymer composites, different types of metal oxide nanoparticles such as SiO₂, TiO₂, ZnO, and so on are widely used for improving the thermal, mechanical as well as other properties. These are nontoxic, stable and highly thermostable inorganic filler. Polymer-SiO₂ and ZnO composites have been explored as technologically important due to their potential applications in electrochromic windows, fuel cells, chemical separation, electrochemical sensing, solar cells and in paint industries.^12
–14 Most of the cited reports have addressed the use of single nanoparticle in the preparation of composite. To the best of our knowledge, there are no reports regarding the use of multiple nanoparticles for making composites.

The present study is aimed to discuss the effect of SiO₂ and ZnO nanopowder along with nanoclay on the thermal and mechanical properties of high-density polyethylene (HDPE)/low-density polyethylene (LDPE)/polypropylene (PP)/poly(vinyl chloride) (PVC) blend and wood flour (WF). The aim is also to study the effect of these nanoparticles on other properties like hardness and water uptake capacity of the composites.

Experimental

Materials

Both HDPE and LDPE (grade: PE/20/TK/CN) were obtained from Plast Alloys India Ltd. (Harayana, India). PP homopolymer (grade: H110MA, MFI 11 g/10 min) and PVC (grade: SPVC FS: 6701) were purchased from Reliance Industries Ltd. (Mumbai, India) and Finolex Industries Ltd. (Pune, India), respectively. The compatibilizer poly(ethylene-co-glycidyl methacrylate) (PE-co-GMA) and N-cetyl-N, N, N-trimethyl ammonium bromide (CTAB) were supplied by Otto chemicals, Mumbai, India, and Central Drug house (P) Ltd, Delhi, India, respectively. Nanomer (clay modified by 15–35 wt.% octadecylamine and 0.5–5 wt.% aminopropyltriethoxy silane; Sigma-Aldrich, USA), SiO₂ nanopowder (5–15 nm, 99.5% trace metals basis; Aldrich, China) and ZnO nanopowder (<100 nm; Aldrich, Germany) were used as received. Nals (Phragmites karka) a type of nonconventional wood was collected from the local forest of Assam. Other reagents used were of analytical grade.

Preparation of wood samples

Nals (Phragmites karka) is available in the forest of Assam. It was collected and chopped into small strips. These were initially washed with 1% soap solution followed by washing with 1% NaOH solution and finally with cold water. The washed wood strips were oven-dried at 100 ± 5°C till the attainment of constant weight. These dried wood strips were grinded in a mixer, sieved and kept for subsequent uses.

Modification of SiO₂ and ZnO

Ten grams each of SiO₂ and ZnO was taken separately in two round-bottom flasks containing 1:1 ethanol–water mixture. It was stirred at 80°C for approximately 12 h; 12 g each of CTAB was taken in two separate beakers containing ethanol–water mixture and stirred at 80°C for 3 h. These mixtures were added slowly to the two flasks containing SiO₂ and ZnO mixture under stirring condition. The stirring was continued for 6 h. The mixtures from both the flasks were then filtered separately and washed with deionized water for several times. It was collected, dried in vacuum oven at 45°C, grinded, stored in separate ampule and kept in desiccator to avoid moisture absorption.

Preparation of wood polymer nanocomposite

The minimum ratio of xylene and THF, at which a homogenous solution of HDPE, LDPE, PP and PVC was obtained, was optimized as 70:30. Six grams each of HDPE, LDPE and PP (1:1:1) were added slowly to 105 ml of xylene taken in a flask fitted with a spiral condenser at room temperature. This was followed by the addition of the PE-co-GMA (5 phr). The temperature of the flask was increased from room temperature to 130°C in order to make a homogenous solution. Now, another solution containing 3 g of PVC in 35 ml of tetrahydrofuran (THF) was prepared. The temperature of the polymer solution containing HDPE, LDPE and PP was brought down to 120°C. To this, PVC solution was added gradually and stirred continuously at 120°C (approximately) for 1 h. A known quantity of CTAB-modified SiO₂ nanopowder (1–5 phr) and ZnO (1–5 phr) was dispersed in 15 ml of THF solution by sonication. This dispersed mixture was added gradually to the polymer solution under stirring condition. Oven-dried WF (40 phr) was added slowly to this solution. The whole mixture was stirred for another 1 h. The mixture was transferred in a tray, dried and grinded. The composite sheets were obtained by the compression molding press (Santec, New Delhi) at 150°C under a pressure of 80 MPa.

Polymer blend (HDPE + LDPE + PP + PVC), polymer blend/5 phr PE-co-GMA and polymer blend/5 phr PE-co-GMA/40 phr wood were designated as PB, PB/G5 and PB/G5/W40. WPC filled with 3 phr nanoclay and 1, 3 and 5 phr each of SiO₂ and ZnO were designated as PB/G5/W40/N3/S1/Z1, PB/G5/W40/N3/S3/Z3 and PB/G5/W40/N3/S5/Z5.

Measurements

X-ray diffraction

The degree of nanoclay, SiO₂ and ZnO distribution in the WPC was evaluated by X-ray diffraction (XRD) analysis. It was carried out in a Rigaku X-ray diffractometer (Miniflax, UK) using CuKα (λ = 0.154 nm) radiation at a scanning rate of 1° per min with an angle ranging from 2° to 70°.

Transmission electron microscopy

The dispersion of the silicate layers of nanoclay and SiO₂/ZnO nanoparticles in WPCs was examined using transmission electron microscope ([TEM] JEM-100 CX II) at an accelerated voltage of 20–100 kV.

Scanning electron microscopy

The compatibility among different polymers as well as the morphological features of the WPC was studied using scanning electron microscope ([SEM] JEOL JSM–6390LV) at an accelerated voltage of 5–10 kV. Fractured surface of the samples, deposited on a brass holder and sputtered with platinum, were used for this study.

Fourier transform infrared spectroscopic studies

Fourier transform infrared spectroscopic (FTIR) spectra of WF, nanoclay, SiO₂, ZnO nanopowder and WPC loaded with nanoclay/SiO₂/ZnO nanopowder were recorded in FTIR spectrophotometer (Impact-410, Nicolet, USA) using KBr pellet.

Mechanical property

The tensile and flexural tests for polymer blend, PE-co-GMA treated polymer blend, and WPC loaded with different percentage of SiO₂ and ZnO were carried out in a Universal Testing Machine (Zwick, model Z010) at a crosshead speed of 10 mm min⁻¹ at room temperature, according to ASTM D-638 and D-790, respectively. Eight samples of each category were tested and their average values were reported.

Statistical analysis

All the data are expressed as means ± SD. All mechanical property results were statistically analyzed using one-way analysis of variance (ANOVA) followed by Tukey’s honestly significant difference (HSD) test. (All data have been given as supplementary file.)

Hardness

The hardness of the samples were measured according to ASTM D-2240 using a durometer (model RR12) and expressed as shore D hardness.

Thermal property

Thermal properties of polymer blend and the WPCs were measured in a thermogravimetric analyzer (TGA; TGA-50, Shimadzu, USA) at a heating rate of 10°C min⁻¹ up to 600°C under nitrogen atmosphere at a flow rate of 30 ml m⁻¹.

Water uptake test

WPC samples were cut into 2.5 × 0.5 × 2.5 cm³ for the test. Percentage water uptake was measured by submerging the samples in distilled water at room temperature (30°C) for different time periods after conditioning at room temperature (30°C) and 65% relative humidity. It is expressed according to the formula,

W a t e r u p t a k e (%) = (W_{s} - W_{1}) / W_{1} \times 100

where W_s is the weight of the water saturated specimen and W ₁ is the weight of the oven-dried specimen.

Results and discussion

XRD study

Figure 1 shows the XRD results of nanoclay, polymer blend, SiO₂, ZnO and WPC loaded with clay (3 phr) and 1–5 phr each of SiO₂ and ZnO. The diffraction peak appeared at 2θ = 4.11° with basal spacing of 2.15 nm for the organically modified nanoclay (curve a). Curve b represents the diffractrogram of polymer blend. The most prominent wide-angle XRD peaks that appeared at 2θ = 14.12 (200), 17.06 (040), 18.64 (211), 21.62 (110) and 24.02 (200) were for crystalline portion of different polymers present in the blend.^15
–17 Curve c shows a broad diffraction peak at 2θ = 23.5 for the amorphous SiO₂ nanoparticles. The crystalline peaks appeared above 2θ = 30° (shown in curve d) were the characteristic peaks of ZnO nanopowder.¹⁸ Curves e–g were for WPC loaded with nanoclay (3 phr) and 1–5 phr each of SiO₂ and ZnO (1:1 mixture). The diffractograms of composites did not exhibit any characteristic peak of nanoclay, reflecting the delamination or exfoliation of silicate layers. With the increase in the level of incorporation of SiO₂ and ZnO (1–5 phr), the crystalline peak intensity of the polymer blend that appeared in the range 2θ = 14–25° was found to decrease. Although the presence of amorphous portion of SiO₂ reduced the peak intensities of ZnO nanopowder but still the intensities of peak corresponding to ZnO nanopowder increased with the increase in the concentration of ZnO in the composite. Similar effect of SiO₂ on peak intensity was observed by Bao and Ma¹⁹ while studying the XRD profile of exfoliated Na-MMT and SiO₂ on polymethacrylic acid composite. From the study, it could be concluded that nanoclay layers were delaminated and SiO₂ and ZnO particles were dispersed in the wood polymer matrix.

Figure 1.

X-ray diffraction of (a) nanoclay, (b) polymer blend (PB), (c) nano-SiO₂, (d) nano-ZnO, (e) PB/G5/W40/N3/S1/Z1, (f) PB/G5/W40/N3/S3/Z3, (g) PB/G5/W40/N3/S5/Z5.

TEM study

Figure 2 shows the TEM micrographs of WPC loaded with nanoclay (3 phr) and 1–5 phr each of SiO₂ and ZnO. The dark lines correspond to the layers of nanoclay while the dark spots were for SiO₂ and ZnO nanoparticles. The nanoparticles were found to be well distributed in the WPC till the addition of 3 phr each of SiO₂ and ZnO beyond which a tendency to agglomeration (5 phr) was observed as shown in Figure 2(c). Park et al.²⁰ prepared nanosilica incorporated polypropylene/polypropylene elastomer blend and found that the silica nanoparticles were well dispersed within the blend. At higher concentrations of SiO₂ and ZnO, the distances between the particles became less and this might have enhanced the tendency for agglomeration.

Figure 2.

Transmission electron microscope (TEM) micrographs of (a) polymer blend (PB)/G5/W40/N3/S1/Z1, (b) PB/G5/W40/N3/S3/Z3, and (c) PB/G5/W40/N3/S5/Z5.

SEM study

SEM micrographs of polymer blend with and without compatibilizer, WPC and WPC loaded with nanoclay and mixture of different percentage of SiO₂ and ZnO nanopowder are shown in Figure 3. Figure 3(a) and (b) shows the miscibility among different polymers before and after the addition of compatibilizer. The improved miscibility among polymers as shown by decreased segregation or roughness was due to the improvement in interfacial adhesion among polymers by the compatibilizer.²¹ The addition of WF improved the smoothness of composites (Figure 3(c)). It increased further after the incorporation of WF, clay, SiO₂ and ZnO to the polymer blend (Figure 3(d) to (e)). The surface smoothness of composites having 3 phr each of SiO₂ and ZnO and nanoclay appeared to be more compared to those of the composites prepared with either 1 or 5 phr each of SiO₂ and ZnO mixture and nanoclay. This might be due to the improvement in interaction among PE-co-GMA, nanoclay, SiO₂, ZnO, wood and polymer. The decrease in smoothness at higher concentrations of SiO₂ and ZnO mixture was due to the aggregation of SiO₂ and ZnO. Wang et al.²² observed the agglomeration of SiO₂ nanoparticles at higher loading while developing poly (methyl methacrylate)-SiO₂ nanocomposite film.

Figure 3.

Scanning electron microscope (SEM) micrographs of (a) polymer blend (PB), (b) PB/G5, (c) PB/G5/W40, (d) PB/G5/W40/N3/S1/Z1, (e) PB/G5/W40/N3/S3/Z3 and (f) PB/G5/W40/N3/S5/Z5.

FTIR study

The FTIR spectra of CTAB, SiO₂, CTAB-modified SiO₂, ZnO and CTAB-modified ZnO are shown in Figure 4. In the spectrum of CTAB (Figure 4(a)), the absorption peaks at 2917 and 2847 cm⁻¹ were assigned to asymmetric and symmetric stretching modes of –CH₂ in the methylene chains. Presence of peaks at 1491, 1475 and 1396 cm⁻¹ were for the asymmetric and symmetric CH₃–N⁺ deformation modes of the CTAB head group, respectively.²³ The spectrum of unmodified SiO₂ (Figure 4(b)) shows absorption peaks at 3472 and 1633 cm⁻¹ for –OH stretching and –OH bending of hydroxyl group adsorbed on the particle surface. The other peaks that appeared in the range 1088–464 cm⁻¹ were due to Si–O–Si group in the SiO₂.²⁴ The peaks around 3424, 2931, 2852, 1633 and 1481 cm⁻¹ and 1088–464 cm⁻¹ were found on the spectrum of CTAB-modified SiO₂ (Figure 4(c)). The intensity of –OH stretching in the modified SiO₂ was found to decrease and shift toward lower wave number, indicating an interaction of the hydroxyl group absorbed on SiO₂ surface with CTAB. The other characteristic peaks for CTAB were also present in the curve. FTIR spectrum of unmodified ZnO nanoparticles is presented in Figure 4(d). Absorption peaks at 3497 and 1635 cm⁻¹ in the spectra was due to –OH (-stretching) and –OH (-bending) vibrations, while the peaks around 422 cm⁻¹ was due to the vibration of metal–oxygen (M-O) bond as reported in the literature.²⁵ The FTIR spectrum of CTAB-modified ZnO is represented by the curve 4e. It was observed that the intensity of the peak for –OH group decreased to a desired extent. Besides this, two new peaks at 2918 and 2848 cm⁻¹, which were due to the presence of –CH₂ group of CTAB that appeared in the spectrum. The peaks at 1496 and 1476 cm⁻¹ were due to the asymmetric CH₃–N⁺ deformation mode of the CTAB head group. Another peak present at 1397 cm⁻¹ was due to the symmetric CH₃–N⁺ deformation mode of CTAB head group. These results indicated that long chain of CTAB group had been incorporated on the surface of the both SiO₂ and ZnO nanoparticles. Further, both CTAB-modified SiO₂ and ZnO were dispersed in a flask containing xylene and kept for checking of any particle settling. The dispersion of SiO₂ and ZnO were found to be stable. This indicated that proper modification occurred.

Figure 4.

Fourier transform infrared spectroscopic (FTIR) spectra of (a) N-Cetyl-N, N, N-trimethyl ammonium bromide (CTAB), (b) unmodified SiO₂, (c) CTAB-modified SiO₂, (d) unmodified ZnO and (e) CTAB-modified ZnO.

Figure 5 shows the FTIR spectra of wood, nanoclay, WPC and WPC loaded with nanoclay and different percentage of SiO₂ and ZnO mixture. Curve a representing the wood sample shows the presence of bands at 3433 cm⁻¹ for –OH stretching, 2930 and 2849 cm⁻¹ for –CH stretching, 1730 cm⁻¹ for C=O stretching, 1637 cm⁻¹ for –OH bending, 1161 and 1045 cm⁻¹ for C–O stretching and 1000–650 cm⁻¹ for C–H bending vibration (out of plane). Organically modified nanoclay (curve b) exhibits the peaks at 3472 cm⁻¹ (–OH stretching), 2934 and 2850 cm⁻¹ (–CH stretching of modified hydrocarbon), 1621 cm⁻¹ (–OH bending) and 1030–460 cm⁻¹ (oxide bands of metals like Si, Al, Mg, etc.). PB/G5/W40 (curve c) shows peaks at 3430 cm⁻¹ (–OH stretching), 2931 and 2847 cm⁻¹ (–CH stretching), 1729 cm⁻¹ (C=O stretching), 1631 cm⁻¹ (–OH bending) and 715 cm⁻¹ (–CH₂ stretching).

Figure 5.

Fourier transform infrared spectroscopic (FTIR) spectra of (a) Wood, (b) nanoclay, (c) PB/G5/W40, (d) PB/G5/W40/N3/S1/Z1, (e) PB/G5/W40/N3/S3/Z3 and (f) PB/G5/W40/N3/S5/Z5.

Figure 5(d) to (f) represent the FTIR spectra of WPC loaded with 3 phr nanoclay and 1, 3 and 5 phr each of CTAB-modified SiO₂ and ZnO. From the figure, it was observed that the intensity of –OH stretching was decreased and shifted to 3384 cm⁻¹ (curve d), 3323 cm⁻¹ (curve e) and 3352 cm⁻¹ (curve f) from 3434 cm⁻¹ (wood). The decrease in intensity and shifting to lower wave number confirmed the bond formation between polymer and the hydroxyl groups of wood, nanoclay, SiO₂ and ZnO. A similar decrease in the intensity of –OH absorption peak and shifting to lower wavelength was reported by Deka and Maji.²⁶ Moreover, the intensity of –CH stretching peaks at 2930 cm⁻¹ and 2849 cm⁻¹ (curves d–f) was found to increase. Similar increase in –CH peak intensities was observed by Awal et al.²⁷ The peak intensities (1088–464 cm⁻¹) of metal oxide bonds of SiO₂, ZnO and nanoclay (curves d–f) decreased to a considerable extent. All these suggested a strong interaction between wood, nanoclay, SiO₂, ZnO and polymer.

Mechanical property

Table 1 shows the flexural and tensile properties of polymer blends and WPC loaded with nanoclay and different percentages (1:1) of SiO₂ and ZnO nanopowder. After the incorporation of compatibilizer, both flexural and tensile properties of the polymer blend increased. This was because of the increase in interfacial adhesion between the polymers due to which both flexural and tensile properties increased. The flexural and tensile properties of the composite were further improved after the addition of WF. The WF acted as a load carrier, reinforced the composites and increased the flexural and tensile properties. Nourbakhsh et al.²⁸ developed WF/polypropylene composite and found an improvement in mechanical properties due to reinforcement by WF. Moreover, the compatibilizer, PE-co-GMA, provided strong interfacial adhesion between wood and polymers through its glycidyl linkage and long olefinic chain. Sailaja²⁹ used PE-co-GMA as compatibilizer to improve the compatibility of wood pulp-LDPE composite. The properties of the WPCs were further improved after the incorporation of clay, SiO₂ and ZnO nanopowder. At a fixed clay loading (3 phr), both flexural and tensile properties improved till the addition of 3 phr each of SiO₂ and ZnO. At higher amount of SiO₂ and ZnO (5 phr each) loading, the properties were found to decrease. The observed higher values might be due to the combined effect of nanoclay, SiO₂ and ZnO. The silicate layers of nanoclay acted as a reinforcing agent and the long polymer chains inserted inside the gallery space restrict the mobility of the polymer chain. Lei et al.³⁰ found an increase in mechanical properties of wood/HDPE composite after the incorporation of nanoclay. CTAB-modified SiO₂ and ZnO improved the interaction between clay, wood and polymer through its surface hydroxyl group and cetyl group, respectively. Higher the dispersion of nanoparticles, higher would be the interaction. At higher level of SiO₂ and ZnO loading (5 phr each), the agglomeration occurred and hence the interaction of SiO₂ and ZnO with the clay, polymer and wood decreased. Liu and Kontopoulou³¹ observed an increase in the mechanical properties of thermoplastic olefin/nanosilica composite at lower loading of nanosilica. The increase in tensile modulus of polyacrylonitrile due to the interaction of ZnO nanoparticles was reported in the literature.³²

Table 1.

Flexural, tensile and hardness properties of polymer blend and WPC loaded with nanoclay and different percentages of SiO₂ and ZnO.^a

	Flexural properties		Tensile properties		Hardness
	Strength, MPa (±SD)	Modulus, MPa (±SD)	Strength, MPa (±SD)	Modulus, MPa (±SD)	Shore D, (±SD)
PB	13.39 (±0.42)^b	754.89 (±0.69)^b	6.44 (±0.48) ^b	89.78 (±17.15)^b	66.5 (±0.4)
PB/G5	16.96 (±0.53)^c	1107.19 (±0.42)^c	9.69 (±0.39)^c	127.67 (±19.29)^c	68.3 (±0.6)
PB/G5/W40	19.56 (±0.54)^d	3791.42 (±0.40)^d	19.74 (±0.58)^d	271.88 (±19.65)^d	67.2 (±0.5)
PB/G5/W40/N3/S1/Z1	28.64 (±0.51)^e	4826.69 (±0.48)^e	34.34 (±0.43)^d	591.54 (±21.36)^e	77.2 (±0.5)
PB/G5/W40/N3/S3/Z3	33.99 (±0.72)^f	5186.68 (±0.56)^f	37.25 (±0.56)^f	697.52 (±19.59)^f	80.3 (±0.6)
PB/G5/W40/N3/S5/Z5	31.32 (±0.58)^g	5021.65 (±0.34)^g	33.76 ±(0.42)^g	637.51 (±20.80)^g	78.5 (±0.3)

WPC: wood polymer composite.

^aEach value represents the average value of eight samples. The same letters are not significantly different at p = 5%. Comparisons were done within each formulation.

Hardness results

Table 1 shows the hardness results of polymer blend and WPC loaded with clay and different percentage of SiO₂ and ZnO. Addition of compatibilizer increased the hardness value of the polymer blend. The hardness value was found to decrease on the addition of WF to the polymer blend. But after the incorporation of nanoclay, SiO₂ and ZnO, the hardness value of the WPC was found to increase again. The improvement was due to the combined effect of decrease in mobility of intercalated polymer chain and increase in reinforcing action of SiO₂ and ZnO. At a fixed clay concentration (3 phr), the hardness value was found to be maximum at 3 phr each of SiO₂ and ZnO loading but decreased after that. The reason for this was stated as earlier.

TGA

Initial decomposition temperature (T_i ), maximum pyrolysis temperature (T_m ), decomposition temperature at different weight loss (%; T_D ) and residual weight (RW, %) for polymer blend and WPCs are shown in Table 2. T_i value of the polymer blend increased after the incorporation of compatibilizer and WF. The addition of nanoclay, SiO₂ and ZnO nanoparticles further increased the T_i value. It was found to be maximum at 3 phr loading of nanoclay and at 3 phr each of SiO₂ and ZnO loading. At higher concentrations of SiO₂ and ZnO, the T_i value decreased again.

Table 2.

Thermal analysis of polymer blend and WPC loaded with nanoclay, SiO₂ and ZnO.

Sample	T _i	T _m	T _m	Temperature of decomposition (TD) in °C at different weight loss (%)				RW% at 600°C
Sample	T _i	T _m	T _m	20%	40%	60%	80%	RW% at 600°C
PB	248	266	403	288	389	439	468	6.2
PB/G5	251	271	409	292	393	443	471	6.7
PB/G5/W40	256	279	453	297	399	448	475	9.7
PB/G5/W40/N3/S1/Z1	281	330	508	336	464	488	507	10.6
PB/G5/W40/N3/S3/Z3	294	339	521	356	482	504	519	14.7
PB/G5/W40/N3/S5/Z5	287	335	516	341	471	495	513	12.6

T _i: value for initial degradation; T _m: value for first step; T _m: value for second step; PB: polymer blend; WPC: wood polymer composite.

Both the polymer blend and the composites showed two decomposition peaks. The T_m value for the first step in both WPC and WPC loaded with clay, SiO₂ and ZnO was due to the depolymerization of hemicellulose, glycosidic linkage of cellulose, thermal decomposition of cellulose³³ and dehydrochlorination of PVC, while the peak for second step was due to decomposition of HDPE and PP.^34
–36 The T_m values of the composites for both the steps were found to follow the similar trend as those of T_i values.

The percentage weight loss in samples at different temperatures is listed in Table 2. T_D values of composite containing nanoclay, SiO₂, ZnO were more compared to either polymer blend or polymer/wood composites. The higher the percentage of ZnO and SiO₂, the higher was the decomposition temperature.

The compatibilizer enhanced the interaction between the polymer blend and WF and as a result the thermal stability improved. Araujo et al.³⁷ reported the improvement in thermal stability after inclusion of compatibilizer to HDPE and natural fiber composites. The silicate layers present in nanoclay of the composites provided a long tortuous path which delayed the diffusion of the decomposed volatile products through the composite. The improvement in thermal stability of WF and polypropylene composite after addition of nanoclay was reported by Ashori et al.³⁸ Moreover, the incorporation of CTAB-modified SiO₂ and ZnO nanopowder might play a role in enhancing the thermal stability by interacting with clay, wood and polymer through its surface hydroxyl group and cetyl groups, respectively. At higher loading of SiO₂ and ZnO, the interaction of SiO₂, ZnO and clay with wood and polymer might decrease due to agglomeration and hence a reduction in thermal stability was observed. Bailly and Kontopoulou³⁹ developed thermoplastic olefin/nanosilica composite and found an increase in thermal properties due to the incorporation of nanosilica. The increase in thermal stability was also reported by He et al.⁴⁰ while studying the thermal behavior of PET-ZnO nanocomposite.

Water uptake results

The water uptake of polymer blend, PE-co-GMA-treated polymer blend and WPC loaded with clay and different percentages of SiO₂ and ZnO are shown in Figure 6. On addition of PE-co-GMA compatibilizer, the water uptake capacity of the polymer blend decreased. The decrease in the water uptake capacity of PE-co-GMA-treated polymer blend was due to the increase in interfacial adhesion between the polymers by the compatibilizer. After the addition of WF to the blend, the water uptake capacity increased suddenly. The hydrophilic nature of WF caused an increase in the water uptake capacity. The water uptake was again decreased after the addition of clay, SiO₂ and ZnO nanoparticle. WPC loaded with 3 phr each of clay, SiO₂ and ZnO showed lowest water uptake followed by WPC with 3 phr clay and 5 phr each of SiO₂ and ZnO, and WPC with 3 phr clay and 1 phr each of SiO₂ and ZnO. The silicate layers of the clay provided tortuous path and increased the barrier property for water transport. Deka and Maji⁵ obtained similar increase in barrier properties of WPC after the incorporation of clay. The presence of SiO₂ and ZnO nanopowder also provided a barrier to the passage of water. The strong affinity of water molecules toward nano-SiO₂ and ZnO particles restricted its free motion and reduced the diffusion coefficient of water. The distribution nature of modified nanoparticles further improved the resistance and retarded the motion of water molecules through the composites. Moreover, the water absorption of inorganic particles reduced after the modification of particles by organic surfactant. Better the distribution of nanoparticles, the higher was the barrier property. The incorporation of SiO₂ nanoparticles increased the water barrier properties of polyvinyl alcohol–based hybrid coatings.⁴¹ The agglomeration of nanoparticles took place at higher concentration SiO₂ and ZnO nanoparticles and as a result increased water uptake capacity was observed.

Figure 6.

Water absorption of (a) polymer blend (PB), (b) PB/G5, (c) PB/G5/W40, (d) PB/G5/W40/N3/S1/Z1, (e) PB/G5/W40/N3/S5/Z5 and (f) PB/G5/W40/N3/S3/Z3.

Conclusions

The optimized ratio of xylene and THF for solution blending of HDPE, LDPE, PP and PVC (1:1:1:0.5) was 70:30. The compatibility among the polymers and WF was improved using PE-co-GMA compatibilizer as revealed by SEM study. The distribution of silicate layers of nanoclay and SiO₂/ZnO in WPCs was examined by XRD and TEM study. The shifting of peak corresponding to –OH stretching to lower wave number and decreased intensity confirmed the reaction between polymer, wood, SiO₂, ZnO and nanoclay. Surface modification of SiO₂ and ZnO nanoparticles by cationic surfactant CTAB was examined by FTIR studies. The interactions among wood, PE-co-GMA, SiO₂, ZnO and nanoclay were also studied by FTIR. At higher concentration of SiO₂ and ZnO loading, the particles became agglomerated. WPC loaded with nanoclay, SiO₂ and ZnO enhanced the mechanical, hardness, thermal properties and reduced the water absorption capacity. WPC loaded with 3 phr each of clay, SiO₂ and ZnO exhibited maximum improvement in properties.

Footnotes

Funding

This work was supported by Council of Scientific and Industrial Research (CSIR), New Delhi (grant number: 01(2287)/08/EMR-II).

References

Saheb

Jog

. Natural fiber polymer composites: a review. Adv Polymer Tech 1999; 18(4): 351–363.

Ashori

. Wood plastic composites as promising green composites for automotive industries. Bioresour Technol 2008; 99(11): 4661–4667.

Sui

Fuqua

Ulven

Zhong

. A plant fiber reinforced polymer composite prepared by a twin-screw extruder. Bioresour Technol 2009; 100(3): 1246–1251.

Cavalieri

Padella

. Development of composite materials by mechanochemical treatment of post-consumer plastic waste. Waste Manag 2002; 22(8): 913–916.

Deka

Maji

. Study on the properties of nanocomposite based on high density polyethylene, polypropylene, polyvinyl chloride and wood. Composites: Part A 2011; 42(6): 686–693.

Dikobe

Luyt

. Effect of poly(ethylene-co-glycidyl methacrylate) compatibilizer content on the morphology and physical properties of ethylene vinyl acetate wood fiber composites. J Appl Polymer Sci 2007; 104(5): 3206–3213.

Qiu

Chen

. Morphology and thermal stabilization mechanism of LLDPE/MMT and LLDPE/LDH nanocomposites. Polymer 2006; 47(3): 922–930.

Chiu

Chu

. Characterization of solution-mixed polypropylene/clay nanocomposites without compatibilizers. J Polymer Res 2006; 13(1): 73–78.

Filippi

Marazzato

Magagnini

Famulari

Arosio

Meille

. Structure and morphology of HDPE-g-MA/organoclays nanocomposites: effects of the preparation procedures. Eur Polymer J 2008; 44(4): 987–1002.

10.

Karak

. Polymer (epoxy) clay nanocomposites. J Polymer Mater 2006; 23: 1–20.

11.

Lee

Kim

. Preparation and physical properties of wood/polypropylene/clay nanocomposites. J Appl Polymer Sci 2009; 111(6): 2769–2776.

12.

Yang

. Synthesis and characterizations of novel, positively charged poly(methyl acrylate)–SiO₂ nanocomposites. Eur Polymer J 2005; 41(8): 1901–1908.

13.

Shih

Fang

Peng

Meen

. Preparation and characteristics of hybrid ZnO-polymer solar cells. J Mater Sci 2010; 45(12): 3266–3269.

14.

Yang

Xiao

Liu

Feng

. Chemical precipitation synthesis and optical properties of ZnO/SiO₂ nanocomposites. J Am Ceram Soc 2008; 91(5): 1591–1596.

15.

Mina

Seema

Matin

Rahaman

Sarker

Gafur

Improved performance of isotactic polypropylene/titanium dioxide composites: effect of processing conditions and filler content. Polymer Degrad Stabil 2009; 94(2): 183–188.

16.

Han

Lei

Kojima

. Bamboo fiber filled high density polyethylene composites: effect of coupling treatment and nanoclay. J Polymer Environ 2008; 16(2): 123–130.

17.

Liu

Chen

Yang

. Preparation and characterization of poly(vinyl chloride)/layered double hydroxide nanocomposites with enhanced thermal stability. Polymer 2008; 49(18): 3923–3927.

18.

Leung

Djuriic

Gao

Xie

Wei

Zinc oxide ribbon and comb structures: synthesis and optical properties. Chem Phys Lett 2004; 394 (4–6): 452–457.

19.

Bao

. Polymethacrylic acid/Na-montmorillonite/SiO₂ nanoparticle composites structures and thermal properties. Polymer Bull 2011; 66(4): 541–549.

20.

Lee

Kontopoulou

Park

. Effect of nanosilica on the co-continuous morphology of polypropylene/polyolefin elastomer blends. Polymer 2010; 51(5); 1147–1155.

21.

Pracella

Chionna

Ishak

Galeski

. Recycling of PET and polyolefin based packaging materials by reactive blending. Polymer Plast Tech Eng 2004; 43(6): 1711–1722.

22.

Wang

Chen

Kang

Yang

Zhang

. Preparation of superhydrophobic poly(methyl methacrylate)-silicon dioxide nanocomposite films. Appl Surf Sci 2010; 257(5): 1473–1477.

23.

Tripp

. Spectroscopic identification and dynamics of adsorbed cetyltrimethylammonium bromide structures on TiO₂ surfaces. Langmuir 2002; 18(24): 9441–9446.

24.

Kang

Zhang

. Effect of silane modified SiO₂ particles on poly(MMA-HEMA) soap-free emulsion polymerization. Iranian Polym J 2009; 18(12): 927–935.

25.

Dhoke

Khanna

Sinha

TJM

. Effect of nano-ZnO particles on the corrosion behavior of alkyd-based waterborne coatings. Progr Org Coating 2009; 64(4): 371–382.

26.

Deka

Maji

. Effect of coupling agent and nanoclay on properties of HDPE, LDPE, PP, PVC blend and phargamites karka nanocomposite. Compos Sci Tech 2010; 70(12): 1755–1761.

27.

Awal

Ghosh

Sain

. Thermal properties and spectral characterization of wood pulp reinforced bio-composite fibers. J Therm Anal Calorim 2010; 99(2): 695–701.

28.

Nourbakhsh

Ashori

Ziaei

Rezaei

. Mechanical and thermo-chemical properties of wood-flour/polypropylene blends. Polymer Bull 2010; 65(7): 691–700.

29.

Sailaja

RRN

. Mechanical and thermal properties of bleached kraft pulp LDPE composites: effect of epoxy functionalized compatibilizer. Compos Sci Tech 2006; 66(13): 2039–2048.

30.

Lei

Clemons

Yao

. Influence of nanoclay on properties of HDPE/wood composites. J Appl Polymer Sci 2007; 106(6): 3958–3966.

31.

Liu

Kontopoulou

. The structure and physical properties of polypropylene and thermoplastic olefin nanocomposites containing nanosilica. Polymer 2006; 47(22): 7731–7739.

32.

Chae

Kim

BC.

Effects of zinc oxide nanoparticles on the physical properties of polyacrylonitrile. J Appl Polymer Sci 2006; 99(4): 1854–1858.

33.

Fung

RKY

Tjong

. Interface modification on the properties of sisal fiber reinforced polypropylene composites. J Appl Polymer Sci 2002; 85(1): 169–176.

34.

Meng

Tjong

. Preparation and properties of injection-moulded blends of poly(vinyl chloride) and liquid crystal copolyester. Polymer 1999; 40(10): 2711–2718.

35.

Yemele

MCN

Koubaa

Cloutier A Soulounganga

Wolcott

. Preparation and properties of injection-moulded blends of poly(vinyl chloride) and liquid crystal copolyester. Composites: Part A 2010; 41(1): 131–137.

36.

Bouza

Pardo

Barral

Abad

. Design of new polypropylene woodflour composites: processing and physical characterization. Polymer Compos 2009; 30(7): 880–886.

37.

Araujo

Waldman

De Paoli

. Thermal properties of high density polyethylene composites with natural fibres: coupling agent effect. Polymer Degrad Stabil 2008; 93(10): 1770–1775.

38.

Tabari

Nourbakhsh

Ashori

. Effects of nanoclay and coupling agent on the physico-mechanical, morphological, and thermal properties of wood flour/polypropylene composites. Polymer Eng Sci 2011; 51(2): 272–277.

39.

Bailly

Kontopoulou

. Preparation and characterization of thermoplastic olefin/nanosilica composites using a silane-grafted polypropylene matrix. Polymer 2009; 50(11): 2472–2480.

40.

Shao

Zhang

Deng

. Crystallization behavior and uv-protection property of PET-ZnO nanocomposites prepared by in situ polymerization. J Appl Polymer Sci 2009; 114(2): 1303–1311.

41.

Minelli

Angelis

MGD

Doghieri

Rocchetti

Montenero

. Barrier properties of organic inorganic hybrid coatings based on polyvinyl alcohol with improved water resistance. Polymer Eng Sci 2010; 50(1): 144–153.

Supplementary Material

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Synergistic effect of SiO 2,ZnO and nanoclay on mechanical and thermal properties of wood polymer nanocomposite

Abstract

Keywords

Introduction

Experimental

Materials

Preparation of wood samples

Modification of SiO2 and ZnO

Preparation of wood polymer nanocomposite

Measurements

X-ray diffraction

Transmission electron microscopy

Scanning electron microscopy

Fourier transform infrared spectroscopic studies

Mechanical property

Statistical analysis

Hardness

Thermal property

Water uptake test

Results and discussion

XRD study

TEM study

SEM study

FTIR study

Mechanical property

Hardness results

TGA

Water uptake results

Conclusions

Footnotes

Funding

References

Supplementary Material

Modification of SiO₂ and ZnO