Preparation and characterization of wood–plastic composite reinforced by graphitic carbon nitride

Accepted Manuscript Preparation and characterization of wood-plastic composite reinforced by graphitic carbon nitride Bingrong Lei, Yaru Zhang, Yanjin He, Yongfeng Xie, Baiping Xu, Zhidan Lin, Langhuan Huang, Shaozao Tan, Meigui Wang, Xiang Cai PII: DOI: Reference:

S0261-3069(14)00829-2 http://dx.doi.org/10.1016/j.matdes.2014.10.041 JMAD 6900

To appear in:

Materials and Design

Received Date: Accepted Date:

9 June 2014 16 October 2014

Please cite this article as: Lei, B., Zhang, Y., He, Y., Xie, Y., Xu, B., Lin, Z., Huang, L., Tan, S., Wang, M., Cai, X., Preparation and characterization of wood-plastic composite reinforced by graphitic carbon nitride, Materials and Design (2014), doi: http://dx.doi.org/10.1016/j.matdes.2014.10.041

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Preparation and characterization of wood-plastic composite reinforced by graphitic carbon nitride

Bingrong Lei1 , Yaru Zhang1 , Yanjin He 1, Yongfeng Xie 1, Baiping Xu2 , Zhidan Lin4 , Langhuan Huang1 , Shaozao Tan1, *, Meigui Wang2, *, Xiang Cai3, *

1

Department of Chemistry, Jinan University, Guangzhou 510632, China

2

Department of Light chemical engineering, Guangdong Industry Technical College,

Guangzhou 510300, China 3

Department of Light chemical engineering, Guangdong Polytechnic, Foshan 528041.

China 4

Department of Materials Science and Engineering, Jinan University, Guangzhou

510632, China

Correspondence should be addressed to S. Tan ([email protected]) or X. Cai ([email protected]) or M. Wang ([email protected] n)

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Abstrac t The aim of this study was to evaluate and characterize various properties of experimental compos ition prepared from graphitic carbon nitride (g-C 3 N4 ), wood flour (WF) and polypropylene (PP). G-C 3 N4 with different concentrations (1 wt.%, 3 wt.%, 5 wt.% and 10 wt.%) were used as reinforcing filler for wood plastic compos itions (WPC). Maleic anhydride grafted polypropylene (PP-g-MA) was added as a coupling agent to increase the interaction between the components. Water absorption, morphology, physical, mechanical and thermal properties of the as-prepared compos ites were evaluated. The results showed that the tensile modulus of the compos ite was increased by 142.9 % with increasing of g-C 3 N4 contents to 5 wt.%, reaching approximately 498 MPa compared to WPC. Moreover, the flexural and tensile strengths reached their maximum values when the concentrations of g-C 3 N4 were 1 wt.% and 3 wt.%, respectively. When maintaining the g-C 3 N 4 at a low concentration, it was well dispersed in the WPC with thin plate shape. How ever, when more g-C 3 N4 (3~10 wt.%) was introduced, the enhancing effect began to diminish because of the agglomeration of g-C 3 N4 which caused poor interfacial adhesion. The water absorption results showed a lower va lue with the addition of 1 wt.% g-C 3 N 4 , and the thermal tests showed that the degradation temperature shifted to higher value clearly after the addition of g-C 3 N4 . Besides, with the addition of g-C 3 N4 improved the outward color compared to the control sample. Key words: wood plastic compos ite; graphitic carbon nitride; mechanical properties; thermal properties; outward color

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1. Introduction Wood flour (WF) is gaining more and more acceptance as a kind of filler for polymers due to its low density, easy availability, biodegradation, high stiffness, renewability and relatively low cost. In addition, the renewable and biodegradable characteristics of wood fibers facilitate their ultimate disposal by composting or inc ineration. According to the advantages of wood fiber, the production of wood plastic compos ites (WPC ) and its application in many areas has attracted much attention in the past ten years [1]. They were used in interior decoration and construction ind ustries such as decking, railing, fencing, docks, landscaping timbers, and in a number of automobile industries [2]. However, when combining thermoplastics with wood fibers by conve ntional methods, the highly hydrophilic characters of the lignocelluloses materials make them incompatible with the thermoplastics which are highly hydrophobic. The incompatibility leads to poorer interfacial adhesion between thermoplastics and wood filler, and wor se of the composite properties. In add ition, the hydroxyl groups between wood fibers can for m hydrogen bonds which can lead to agglomeration the fibers into bundles and unevenly distribution throughout the non-polar polymer matrix during the compounding processing [3, 4]. However, the WF is mainly made of cellulose, hemicelluloses, lignin and pectins, which leads to water absorption of the WPC resulting in debonding fibers and degradation of the fiber- matrix interface. In add ition, the high moisture absorption of natural fibers may cause dimensional change of the resulting composite and weakened the interfacial adhesion [5, 6]. WPC in the extrus ion process are mainly

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affected by the barrel temperature and the die temperature. Due to the high temperate leads to the carbonization of WF, the appearance color of the products is affected. Many studies were devoted to enhancing the physical and mechanical properties of these compos ite materials, such as the tensile and flexural strengths [7]. Usually there are two approaches to accomplish this through the use of different fillers. On one hand, the filler can be treated with coupling agent or can be changed in terms of the particle size, such as processing WF with acetylation [8], silane treatment [9], heat treatment [10], or treatment with sodium hydroxide [11]. On the other hand, using nano- materials such as nanoc lay or carbo n nanotubes is one of effective methods to reinforce the mechanical properties of the composites. These nano-materials have positive results including high modulus, increased tensile and flexural strength, high thermal stability and low water absorption [12, 13]. Many researchers have foc used on the nanoc lay as nano ¿OOHU to improve physical and mechanical properties of WPC [12, 14]. In the recent years, graphitic carbon nitride (g-C 3 N4 ) has been wide ly used in many catalytic areas, especially for oxygen reduction reaction since Wang et al. have founded its photocatalytic ability to prod uce hydrogen from a methanol aqueous solution under visible- light irradiation [15]. However, to the best of our knowledge, g-C 3 N 4 has not been used as reinforcement for WPC. In this study, pure melamine was used to prepared the g-C 3 N4 by directly heating [16]. The main objective of this work was to study the effect of g-C 3 N4 as a reinforcing agent on the physico- mechanical properties of WPC.

2. Experime ntal details 4/38

2.1. Materials Melamine was purchased from Tianjin Municipality kemi'ou Chemical Reagent Co., Ltd. ; PP (T30S) was purchased from China Petroleum Chemical Co., Ltd. (Maoming, China); the satiric acid (lubricant) and coupling age nt (PP-g-MA, grafting degree was 0.8 %) were supplied by Ma Ji Sen compos ite materials Co., Ltd.; wood flour (WF, <150 µm) was supp lied b y Wei Hua spice Co., Ltd. (Guangdong, China). 2.2. Preparat ion of g-C3 N4 The g-C 3 N4 was prepared by simple calcination of melamine powder under air atmosphere. First, an certain amount of the melamine power were put into a semi-closed alumina crucible with a cover. Second, the crucible was heated to 550 ºC for 2 h, at a heating rate of 2 ºCminí1 . After cooling to room temperature, the obtained yellow sample was grinded into powder and dried at 85 ºC. 2.3. Preparat ions of samples The g-C 3 N 4 , WF, PP, stearic acid and PP-g-MA were weighed according to formulations given in Table 1. All of the pure fillers were dried at 85°C in the convection oven for 48 h prior to use. Process for preparing WPC based on PP was schematically shown in Fig. 1. The mixtures were prepared by using a twin screw extruder (SHJ-20 with average screw diameter of 20 mm and average L/D ratio of 40), with a temperature profile of 175/180/185/190/195/195/190 °C and a rotating speed of 150 rpm, and then the extruded strands were passed through a trough before palletized. Totally 6 sets of blends and composite samples were fabricated. The pellets were injected into ISO standard specimens by using an injection molding machine (HMT

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OENKEY) at 190 °C. The actual samples were shown in the Fig. 2.

Tab le 1

Fig. 1.

Fig. 2.

2.4. Characterization X-ray diffraction (XRD) patterns were recorded on a diffractometer (D/max-1200) using graphite monoc hromatic CuKĮ radiation (Ȝ= 0.1541 nm) at a generator voltage of 40 kV and a current of 40 mA. Measurements were conducted within a 2ș range of 2.0-70.0º at a scanning rate of 2º/min. Fourier transform infrared spectrometer (FTIR) spectra between 500 and 4000 cmí1 were obtained on a Nicolet 6700 spectrometer (USA). Scanning electronic microscope (SEM) was performed on JSM-6330F scanning electron microscope with an accelerating voltage of 20.0 Kv. The fracture surfaces of samples were coated with a thin layer of gold before SEM observation. 2.5. Water absorption properties The water absorption test was conducted as per ASTM: D570-98. Before testing, five specimens were dried in an oven for 48 h at 100 ± 3 °C. The weight of dried specimens was measured at an accuracy of 0.001 g. The dimensions of samples for water absorption test were 80 mm × 10 mm × 4 mm. The conditioned specimens were placed in a container filled with deionized water, supported on their edges, and

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ent irely immersed and kept at 23 ± 1 °C for 16 days. At the end of 24 ± 1 h, 48± 1 h, 96 ± 1 h, 192 ± 1 h, 384 ± 1 h, the specimens were removed from the water one at a time, all surface water wiped off with a dry cloth and weighed immediately. Five

replications were tested and their average values were reported. The value of the water absorption in percentage was calculated by using the following equation (1): WAt (%)  (

W t W0 ) r 100 W0

(1)

Where WAt is the water absorption (%) at time t, W 0 is the oven dr ied weight and W t is the weight of specimen at a given immersion time. 2.6. Mechanical properties The tensile and flexural tests were carried out by using a Universal Testing Machine (LLOYD LR100K) according to the ISO standards 527-1 [17] and 178 [18], respectively. The notched Izod impact strengths were conducted following ISO standards 179-1 [19] with impact type test machine (ZBC-50). Five replications were tested and their average values were reported. 2.7. The rmal properties Thermal be haviors of WPC and WPC/CN were examined by using a thermo gravimetric analyzer (TGA) to determine the weight loss as a function of temperature. Each composite was heated from 30 to 800 °C at a rate of 10 °C/min under nitrogen atmosphere.

3. R esults and discussion 3.1. XRD analysis 7/38

Fig. 3 illustrates the X-ray diffraction pattern of the prepared g-C 3 N4 , which showed two distinct diffraction peaks at 2ș = 13.2º and 27.3º. The g-C 3 N4 was based on the tri-s-triazine building blocks [20]. The strong peak at 27.3º is a characteristic interplanar stacking peak of aromatic units corresponding to a stacking distance (d 002 ), which was closed to the one of the graphite (d 002 ). The weak peak at 13.2º can be associated with the interlayer stacking distance (d 100 ) of 0.675 nm. This distance was smaller than the size of one tris-s-triazine unit (0.713 nm), which could be attributed to the presence of a tilt angularity in the structure [15, 16]. The above result indicated that the as-prepared g-C 3 N4 possessed a tri-s-triazine-based structure and the g-C 3 N4 phase was formed.

Fig.3.

3.2. FTIR spectra

Fig. 4.

FTIR spectra of g-C 3 N4 were shown in Fig. 4, which exhibited three characteristic absorption regions located around 3412 cmí1 , 1200~1650 cmí1 and 799 cmí1 . The adsorption band centered at 3412 cmí1 could be ascribed to the stretching mode of OH bond. The broad absorption band at 3231 cmí1 could be attributed to the stretching vibration of NH2 or N-H groups, suggesting the small amount of contamination of hydrogen [21, 22]. It was suggested that a small amount of amino

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groups remained in the samples prepared by direct heating of the melamine. Zhao e t al [23] reported that residual hydrogen atoms bound to the edges of the graphic- like C-N sheet in the form of C-NH2 and 2C-NH bonds. Peaks appeared at the range from 1241 to 1638 cmí1 were attributed to the stretching vibration of graphitic C-N single and double

bond

characters

[24],

which

again

confirmed

the

existence

of

poly(tri-s-triazine)-EDVHGʌ-conjugated systems in g-C 3 N4 heterojunctions. The sharp peak at 799 cmí1 was ascribed to the typical breathing vibration of the triazine units [16, 25]. The FTIR spectra which obtained con ¿UPLQJ WKDWWKH products were the same to the literature treated at 550°C under the air atmosphere. 3.3. Water absorption properties

Fig. 5.

The water absorption behavior was important to investigation of the durability of the WPC exposing to the environmental conditions. The water uptake results of PP, WPC and WPC/CN after immersion in distilled water for sixteen days were shown in fig .5. As seen, pure PP barely absorbed moisture due to its hydrophobic nature. However, the amount of water uptake was suddenly increased with the incorporation of WF into PP. So the absorption value would be mainly ascribed to the hydrophilic WF component in the composite and the gap between matrix and filler. With the high content of WF into WPC would result in creating gap between WF and PP, since PP was impossible to cover all of the WF, which weaken the interfacial bonding between wood fiber and PP. This hypothesis was confirmed by SEM obs ervations (Fig. 7b). In 9/38

constant level of wood fiber content (40 wt.%), the compos ite with 1 wt.% content of g-C 3 N 4 exhibited the least water absorption, which was even lower than the WPC sample. The reason might be that well dispersity was achived for 1 wt.% of g-C 3 N4 which gave better interfacial adhesion of the g-C 3 N4 to the matrix and better water barrier performance [26]. According to Das et al [27], water saturated the cell wall of fiber, and then water occupied void spaces. However, when the g-C 3 N4 filler was added from 1 wt.% to 10 wt.%, the water uptake of compos ite was increased, and it was attributed to the agglomerate of g-C 3 N4 that increased voids and crack fractions during the compounding process. This hypothesis was also confirmed by SEM images (Fig. 7d, Fig. 7e and Fig. 7f). From which it can be seen that more crack were created when the composite contained 10 wt.% g-C 3 N4 . So the compos ite would absorb more water in our experimental ranges of ¿OOHUV

more than 1 wt.%).

3.4. SEM analysis

Fig. 6.

Fig. 7.

Fractured surfaces of the compos ites were obtained by impact fracture at room temperature. Fig. 7 showed the SEM photographs of the fracture surfaces of the composites. Usually some of the stacked plate-shaped g-C 3 N4 would delaminate under plastic shearing process (Fig. 6). Thus, the delaminated g-C 3 N4 had higher surface area to be in contact with polymer matrix which it would partly increase the

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mechanical strength of the compos ites [28]. Through SEM study, the distribution and compatibility between the fillers and the matrix can be found. Fig. 7a showed that the surface of the as-prepared g-C 3 N4 was quite smooth and it was in stacked plate shapes. In Fig. 7b, the crack could be clearly found between the matrix and the wood fibers. This was attributed to the hydrophilic nature of the fibers and their poor homogeneity in the plastic matrix. Thus, it could be implied that the interfacial interaction between the WF and the PP matrix in the compos ites was weak, which means the fibers can leave the matrix easily and cavities can also be easily created when stress was applied. Finally, the generated cavities and cracks in WPC would accelerate to water absorpt ion and reduce the mechanical properties. The surface of WPC containing 1 wt.% g-C 3 N4 analyzed by SEM was depicted in Fig. 7c. The stacked plate-shaped g-C 3 N4 was delaminated under plastic shearing process, and the g-C 3 N4 was well dispersed in the PP matrix. Thus the 1 wt.% content of g-C 3 N4 ¿ller showed the maximum flexural strength value which was larger than the other samples, and the decrease in water absorption. This could be further supported by Fig. 5. However, Fig. 7d showed that the interfacial interaction between g-C 3 N4 and PP matrix was weak, this might due to the hydrophilic nature of the nanofiller, it would easily cause agglomerate when high content of g-C 3 N4 was added. Large agglomeration of g-C 3 N4 can be found in Fig. 7e and Fig. 7f. Due to the agglomeration, the g-C 3 N 4 existed in the form of stack plate but not the delaminated plates. In addition, the agglomeration caused bad interfacial adhesion and more cracks and cavities in the interfacial area. The weak interfacial adhesion hindered stress transfering from the matrix to the ¿bres which was harmful

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to the mechanical properties and water absorption of the composite compared with the compos ite filled with lower content of g-C 3 N4 . This were further suppor ted by the mechanical tests and water absorption tests. 3.5. Mechanical properties

Tab le 2

When the wood fiber was added into PP, the Àexural and tensile modulus of the compos ites were increased compared to PP as shown in Table 2. This might be attributed to the better stiffness of wood ¿bers compared with PP. The Àexural and tensile strengths of WPC/CN had the maximum values when the contents of g-C 3 N4 are 1 wt.% and 3 wt.% respectively. However, they were decreased when more g-C 3 N 4 was added compared with the control sample. As observed from Table 2, the composites exhibited a negative elongation at break effect with the addition of g-C 3 N 4 . When PP filled with wood flour show brittle behavior, thus the elongation at break of WPC and WPC/CN decreased markedly compared to PP. Fig. 8. Fig. 8 illustrated the effect of g-C 3 N4 content on the Àexural properties of WPC/CN. The Àexural strength of the compos ites was increased slightly at the 1 wt.% content of g-C 3 N4 compared to the WPC sample and it began to decrease as more g-C 3 N 4 was added. The Àexural strength of the compos ite mainly depe nded on the interfacial interaction and the properties of constitue nts [29, 30]. The result suggested 12/38

that the low content of g-C 3 N4 (1 wt.%) had better homogeneous dispersion and be tter interfacial interactions in the WPC, which enabled effective stress transferring from matrix to ¿EUHV and then leading to highÀ exural strength. But with higher content, the g-C 3 N 4 began to agglomerate which resulted in poor dispersion in WPC and then the Àexural strength began to decrease, so the composite with 10 wt.% g-C 3 N4 showed the minimum Àexural strength, decreased by 7.6% compared to the WPC sample. Fig. 8 showed that the flexural modulus increased with increasing g-C 3 N4 content in the compos ite, the reason might be that the flexural modulus of g-C 3 N4 was higher than WF. Since the flexural modulus in composite mainly depended on the modulus of individual component [33]. In addition, plate-shaped fillers had high aspect ratios, and this property increased the wettability of the fillers by the matrix, therefore it was helpful to transfer stress from polymer to the plate-shaped fillers. Fig. 9. Fig. 9 illustrated the effect of g-C 3 N4 content on the tensile properties of WPC/CN. When wood fiber was added, the tensile strength of WPC was decreased compared to pure PP (Table 2). When WF was added in thermoplastics, the tensile strength would be decreased [31]. Similar to the ÀH[XUDO VWUHQJWK WKH WHQVLOH VWUHQJWK RI :3&&1 was increased at first, showing the highest tensile strength (3 wt.% g-C 3 N4 ) among the tested compos ites. Then, it was decreased as the g-C 3 N4 was agglomerated, indicating that 3 wt.% g-C 3 N4 had positive effect on tensile strength of the g-C 3 N4 reinforced polymer compos ite. This might be due to bridge’s function of g-C 3 N 4 , which led to better stress transfer efficiency from the matrix to the¿OOHU DQG 13/38

improvement of tensile strengths. Similar observations of other lignoc ellulosic fibers based PP composites were reported [32]. Fig. 9 also clearly illustrated that more add ition (more than 3 wt.%) of g-C 3 N 4 was not he lpful to improve tensile strength. This could be explained again by the agglo meration of the g-C 3 N 4 . The aggregation of g-C 3 N4 was harmful to mechanical properties of the resultant nanocompos ites. The tensile modulus of WPC/CN was increased with increasing g-C 3 N4 content in the compos ite. But when 10 wt.% g-C 3 N4 was added into WPC, the tensile modulus was decreased slightly. As it could be seen from Fig. 9, with increasing of g-C 3 N4 contents to 5 wt.%, the tensile modulus value was increased by 142.9 %, reaching approximately 498 MPa compared to WPC. This enhancement in tensile modulus might be attributed to the decrease in mobility of the polymer chains which might that because the stack state g-C 3 N4 had restrained the mobility of polymer chains.

Tab le 3

Fig.10.

Fig. 10 illustrated the Izod impact strengths of the compos ites made with different content of g-C 3 N4 . The test results showed that the impact strengths of compos ite were reduced with increasing content of g-C 3 N4 in WPC. But the impact strengths of the compos ites with 1 wt.% and 3 wt.% g-C 3 N4 content were almost the same. The most important reason for the decrease might be that g-C 3 N4 platelet restricted the motion of polymer chains and made the compos ites brittler. Usually, increasing 14/38

g-C 3 N 4 content would constrain ductile deformation of the PP matrix and an increasing proportion of the fracture energy, thus the Izod impact strengths decreased with increasing content of g-C 3 N4 in WPC. 3.6. The rmal properties

Fig. 11.

The TGA cur ves were very impor tant to study the thermal properties and degradation behaviors of the composite applied in high temperature. Manufacture of the WPC containing high content of wood fiber at high temperature would de grade the cellulosic materials that led to undesirable effects on the properties of the compos ite. Fig. 11 showed the mass loss curves of PP, WPC and WPC/CN. The TGA curve of pure PP showed single-mass loss step from 333 ºC to 466 ºC. How ever, the maximum degradation rate shitted to a higher temperature whe n PP was mixed with wood fiber, indicating that the WF improved the thermal stability of the polymer compared with the pure PP. This could be attributed to the high thermal stability of lignin in WF [33]. The cure for WPC mainly had two decompos ition stages. The first decomposition peak (248 to 375 ºC) was mainly due to the thermal decomposition of WF [34], and the second one (406 to 490 ºC) was mainly due to thermal decomposition of PP. Another important feature was that the addition of g-C 3 N4 to the polymer blend clearly increased the degradation temperature of the composite. Obviously, the WPC/CN mainly showed two decompositions stages .The temperature of degradation of the polymer blend with varying amounts of g-C 3 N4 increased from 422 to 440 ºC 15/38

in comparison to WPC sample. Table 4 shows the decomposition temperature at different weight loss (TD %) and residual weight (RW %) for WPC and WPC/CN. It was observed that the decomposition temperature values were increased due to the addition of g-C 3 N 4 into the polymer blend.

Tab le 4

The 20 % weight loss temperature of compos ite was increased by about 30.5 ºC when the addition of g-C 3 N4 was up to 10 wt.%. It was obvious that the decomposition temperatures of 40 %, 60 % and 80 % weight loss were all increased when the g-C 3 N4 content was increased. But the 40 % and 60 % weight loss temperatures of compos ites made scarcely influence between 3 wt.% and 5 wt.% addition of g-C 3 N4 . This might be due to the poor dispersion and agglomeration of g-C 3 N 4 . The maximum improvement in thermal stability was observed by the inclusion of 10 wt.% g-C 3 N4 . The RW% value at 600 ºC for composites was increased with increasing content of g-C 3 N4 . This might be attributed to the presence of g-C 3 N4 plate which acted as a barrier and delayed the decomposition of volatile products [35].

4. Conclusions The effects of g-C 3 N 4 on the physical, mechanical and morphological properties of the WF/PP composites were investigated. The physical and mechanical test results indicated that the properties of the WPC were significantly infuluenced by the

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content of g-C 3 N4 . The large surface area of g-C 3 N4 enhances flexural and tensile modulus of the composites. A suitable content of g-C 3 N 4 could also improve flexural and tensile strength of the composites. The sample with 1 wt.% g-C 3 N4 showed lower water absorption. However, the overloaded g-C 3 N4 caused the aggregation and then affected the physical and mechanical properties. The addition of g-C 3 N4 obviously improved the de gradation temperature and the outward color of the WPC. In this study, the addition of g-C 3 N4 from 1 wt.% to 3 wt.% was found to be the optimal condition to prepare WF/PP compos ite.

Acknowledge ments This work was financially supported by the National Natural Science Foundation of China (21271087, 51172099 and 21006038), the Foundation of Science and Technology Projects of Guangdong Province (2011B010700080), and the 2013 Jinan University Challenge Cup for Stude nt Extracurricular Acade mic Science and Technology Work Competition (201312B07 and 201312B49).

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Ashor i

A,

Nourbakhsh

A.

Preparation

and

characterization

of

polypropylene/wood flour/nanoclay composites. Europ J wood wood produc 20 11; 69: 663–6. [33] Yildiz S, Gümüs Kaya E. The effects of thermal modi ¿FDWLRQ RQ FU\VWDOOLQH structure of cellulose in soft and hardwood. Build Environ 2007; 42: 62–7. [34] Fisher T, Hajaligol M, Waymack B, Kellogg D. Pyrolys is be havior and kinetics of biomass derived materials. J Anal Appl Pyrol 2002; 2: 331–49. [35] Sheshmani S, Amini R. Preparation and characterization of some graphene based nanocompos ite materials. Carbohyd Polym 2013; 95: 348–59.

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Tab le 1. The blend design of compounding materials for respective composite. Sample PP WPC WPC/CN 1 WPC/CN 3 WPC/CN 5 WPC/CN 10

PP (wt.%)

WF (wt.%)

PP-g-MA (wt.%)

g-C 3 N 4 (wt.%)

95 55 54 52 50 45

0 40 40 40 40 40

3 3 3 3 3 3

0 0 1 3 5 10

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Stearic acid (wt.%) 2 2 2 2 2 2

Table 2. The mechanical properties of PP, WPC and WPC/CN.

Sample

PP WPC WPC/CN 1 WPC/CN 3 WPC/CN 5 WPC/CN 10

Flexur al properties Flexur al Flexur al strengths modules (MPa) (MPa) 1300±30 42.6±0.3 2236±14 47.4±0.2 2250±30 47.8±0.2 2310±10 46.6±0.4 2356±16 45.9±0.3 2442±28 43.8±0.4

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Tensile prope rties Tensile Elongation Tensile strengths at break modules (MPa) (MPa) (%) 187±9 36.5±0.4 615.0±5.0 205±8 34.6±0.1 7.9±0.3 210±14 34.6±0.3 7.9±0.5 416±17 35.9±0.3 6.3±1.2 498±24 33.8±0.3 6.2±0.5 428±6 32.3±0.5 5.6±0.7

Table 3. The notched Izod impact strengths of PP, WPC and WPC/CN. Samples

Impact strengths (KJ/m2 )

PP

3.556±0.055 3.481±0.227 3.295±0.206 3.287±0.197 3.091±0.163 2.394±0.048

WPC WPC/CN 1 WPC/CN 3 WPC/CN 5 WPC/CN 10

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Table 4. Thermal analysis of WPC and WPC/CN compos ites.

Samples

Temperature of decomposition (TD ) in ºC at different weight loss (%)

RW% at

600ºC

20%

40%

60%

80%

WPC

382.36

454.36

467.46

482.18

15.01

WPC/CN 1

383.45

457.10

470.73

488.73

16.96

WPC/CN 3

386.18

460.10

475.09

599.45

20.20

WPC/CN 5

402.55

460.9

475.63

645.82

21.50

WPC/CN 10

412.91

465.23

480.00

670.36

25.21

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Figure capture: Fig. 1. Scheme of the process for preparing WPC based on PP. Fig. 2. Images of samples made with different content of g-C 3 N 4 . Fig. 3. XRD patterns for the synthesized g-C 3 N4 . Fig. 4. FTIR spectrum for the synthesized g-C 3 N4 . Fig. 5. Water absorption curves of PP, WPC and WPC/CN. Fig. 6. The schematic illustrations of changes of g-C 3 N4 during compounding process. Fig. 7. S EM images: (a) g-C 3 N4 , (b) WPC, (c) the fracture surface of WPC/CN 1 , (d) the fracture surface of WPC/CN 3 , (e) the fracture surface of WPC/CN 5 and ( f) the fracture surface of WPC/CN 10 . Fig. 8. Effect of g-C 3 N4 content on the flexural properties of WPC/CN. Fig. 9. Effect of g-C 3 N4 content on the tensile properties of WPC/CN. Fig. 10. Effect of g-C 3 N4 content on the Notched Izod impact strength of WPC/CN. Fig. 11. TGA curves for PP, WPC and WPC/CN.

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Fig. 1.

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Fig. 2.

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Fig. 3.

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Fig. 4.

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Fig. 5.

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Fig. 6.

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Fig. 7.

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Fig. 8.

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Fig. 9.

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Fig. 10.

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Fig. 11.

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Highlights graphitic carbon nitride (g-C 3 N4 ) was prepared by heated in a mufÀH furnace g-C 3 N 4 was used as reinforcing¿OOHU of wood-plastic composites (WPC) The WPC/ g-C 3 N4 composites displayed higher Àexural and tensile properties g-C 3 N 4 evidently improved the de gradation temperature of the WPCs g-C 3 N 4 evidently enhanced the outward color of WPCs

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