Effect of wood dust type on mechanical properties, wear behavior, biodegradability, and resistance to natural weathering of wood-plastic composites

Abstract

The present work reports the inclusion of different proportions of Mango/Sheesham/Mahogany/Babool dust to polypropylene for improving mechanical, wear behavior and biodegradability of wood-plastic composite (WPC). The wood dust (10%, 15%, 20% by weight) was mixed with polypropylene granules and WPCs were prepared using an injection molding technique. The mechanical, wear, and morphological characterizations of fabricated WPCs were carried out using standard ASTM methods, pin on disk apparatus, and scanning electron microscopy (SEM), respectively. Further, the biodegradability and resistance to natural weathering of WPCs were evaluated following ASTM D5338-11 and ASTM D1435-99, respectively. The WPCs consisting of Babool and Sheesham dust were having superior mechanical properties whereas the WPCs consisting of Mango and Mahogany were more wear resistant. It was found that increasing wood powder proportion results in higher Young’s modulus, lesser wear rate, and decreased stress at break. The WPCs made of Sheesham dust were least biodegradable. It was noticed that the biodegradability corresponds with resistance to natural weathering; more biodegradable WPCs were having the lesser resistance to natural weathering.

Keywords

wood-plastic composites / mechanical testing / wear / biodegradability / injection molding / weathering

Introduction

The wood-plastic composites (WPCs) are gaining popularity in construction, automotive and infrastructure applications due to recyclability, high stiffness, low cost, low density, environment friendliness, and good mechanical properties [¹–³]. WPCs decrease the green house effects and considered eco-friendly [⁴–⁶]. Wood flour (WF) is the suitable filler for polymers due to easy availability, low density, biodegradation, renewability, stiffness, and relatively low cost. The research community is continuously looking forward to improving the properties of WPCs [⁷–¹¹]. The properties of WPCs depend on the wood flour content, coupling agent, wood species, and plastic matrix [⁷,⁸]. However, when combining thermoplastics with the wood fibers by the conventional methods, the highly hydrophilic natures of the lignocelluloses materials make them incompatible with the thermoplastics which are highly hydrophobic in nature. The incompatibility leads to a weak interfacial adhesion between thermoplastics and the wood fillers which results in the poorer composite properties [¹²]. Besides, the hydroxyl groups between the wood fibers can form the hydrogen bonds which can lead to agglomeration of the fibers into bundles and uneven distribution throughout the non-polar polymer matrix during the compounding processing. The flex, jute, hemp, banana, and bamboo fibers are commonly used in WPCs [¹³,¹⁴]. The use of the surface treated fibers is common in WPCs [¹⁵,¹⁶]. From the environmental point of view, the natural fibers are preferred to the synthetic fiber reinforcement in Polymer Matrix Composites [¹⁷,¹⁸].

The physical and mechanical properties of WPCs degrade due to the natural weathering and ultraviolet sunlight [¹⁹–²²]. The reason for the degradation includes the changes in crystallinity of the matrix phase, oxidization of WPC surfaces and the interfacial strength degradation in WPCs [²⁰,²³–²⁷]. The effect of natural weathering on WPCs is reported in many studies [²⁸–³⁰] as fencing, decking, outdoor furniture, window parts, roofline products, door panels, etc., are frequently made by WPCs, are subjected to natural weathering [³¹–³³]. The elastic modulus and the strength of wood fibers are roughly 40 times and 20 times higher than that of the polyethylene [³⁴]. The mechanical behavior of wood dust-polymer composites is discussed considerably in the literature [³⁵–³⁹]. The wood fiber surface chemistry [⁴⁰], bio-deterioration and biodegradation of WPCs [⁴¹], the influence of weathering on visual and the surface aspect of WPCs [⁴²–⁴⁴], and fire retardant behavior of WPCs [⁴⁵] are reported in the literature. The water absorption effects on mechanical (tensile, bending, hardness test) properties [⁴⁶,⁴⁷], rheological properties [⁴⁸], tribological properties [⁴⁹], wear behavior [⁵⁰–⁵⁶], and morphology of WPCs [⁵⁷] are reported in the literature.

Despite the numerous studies related to WPCs, the influences of abundantly available (In India) Babool Wood (Acacia Wood), Mango Wood, Sheesham Wood (Dalbergia Sissoo), and Mahogany powders on the mechanical properties (tensile, bending, hardness, and impact), wear behavior, biodegradability, effect of natural weathering on WPCs are not reported in the cited literature. Therefore, the aim of the present work is to evaluate the influences of the different wood powders on the mechanical behavior and the biodegradability of the WPCs. The effect of the weathering on the WPC properties is also reported. An additional objective is to utilize the waste, cheap, and abundantly available wood in India to strengthen the plastic product in an environment friendly manner.

Materials and methods

Fabrication of WPCs

The WPCs were prepared using an injection molding machine (Fig. 1). Babool Wood (Acacia Wood), Mango Wood, Sheesham Wood (Dalbergia Sissoo), Mahogany Wood floor of 600 microns (obtained by sieve analysis) and Polypropylene (PP) were the reinforcements and the matrix material, respectively. As the PP is having high melting point whereas the wood particles have a low burning point and burns quickly, injection molding was found most suitable fabrication method after attempting a number of conventional fabrication techniques. For the preparation of the WPC samples, the wood floor mixed with the plastic granules was poured into the nozzle, the mixture was then passed through the plunger having the heating coils for maintaining a temperature of 200°C to 240°C. Further, the pressurized mixture was poured into the mold cavity. This pressure allows the material to fully occupy the mold structure. After the solidification, the additional waste material present due to the spur, runner and gate arrangements was removed to obtain the WPC samples.

Testing of WPCs

The tensile tests (ASTM D638-99), three-point bending test (ASTM D143-14), shore hardness test, impact test (Charpy (ASTM D6110-10) and Izod test), wear test (pin on disc) were performed following the standard procedures.

Figures 1(a) and 1(b) show the photographs of WPC samples and the different experimental setups used, respectively. A minimum of five samples (of each type) were tested for every reading. The natural weathering test was performed according to ASTM D 1435-99 for 13 weeks (2160 h), by exposing WPCs to the natural weathering. The test was performed during July to September in the open ground of Invertis University, Bareilly, Uttar Pradesh, India. The WPC samples were placed at 45° to the horizontal in an in-house made arrangement. The temperature varied from 24°C to 34°C (29°C average), precipitation varied from 124 to 188.3 mm (160 mm average), humidity varied from 78% to 81%, and the dew point varied from 25°C to 26°C during the natural weathering tests.

Biodegradation test was carried out according to ASTM D5338-11. The WPCs were subjected to the degradation experiment in the earth and the water. The percentage of decrease in weight (WD) after the degradation experiment in the earth and the water was calculated. This experiment was carried out for three weeks and the mechanical characterization was performed after every week. The WD % was evaluated using Eq. (1).

(1)WD=({{\displaystyle W}}_{\mathrm{a}\mathrm{d}}-{{\displaystyle W}}_{\mathrm{b}\mathrm{d}}/{{\displaystyle W}}_{\mathrm{b}\mathrm{d}})\times \mathrm{100},

where W_ad and W_bd are oven-dried weight of WPC after degradation experiment and oven-dried weight of WPC before degradation experiment, respectively. The surface morphology of the WPCs was examined using the SEM micrographs.

Result and discussion

Mechanical and wear behavior

Figure 2(a) shows the load-deflection diagram obtained from the tensile test of WPCs. Figure 2(a) shows the tensile test results of WPC having 10% (by weight) Babool wood dust as reinforcement in the PP matrix. The maximum load before the fracture varied from 849 to 828 N and the maximum deflection varied from 12.8 to 14.2 mm. For 15% Babool wood floor proportion (Fig. 2(b)) the ranges of the load and the deflection were not having a significant variation; however, the average maximum load before fracture and the average deflection were 5.6% and 8.2% lesser than 10% Babool WPCs. The load before fracture and deflection were least (Fig. 2(c)) for 20% Babool wood WPCs. Figure 2(d) shows the tensile test results of WPC having 10% Mango wood as the reinforcement in the PP matrix. The maximum load before the fracture is less than 700 N and the maximum deflection varied from 11 to 13.1 mm. For 15% Mango wood floor proportion (Fig. 2(e)) all the WPC samples were fractured below 700 N; however, the maximum deflection was higher for the 15% Mango wood WPCs. All the 20% Mango wood WPCs were fractured over 700 N (Fig. 2(f)), the highest load among all other compositions of Mango WPCs. The average load before fracture and the maximum deflection were lesser for Mango wood WPCs in comparison to Babool wood WPCs. Figure 2(g) shows the tensile test results of WPC having 10% Sheesham wood as the reinforcement in PP matrix. The maximum load before the fracture varied from 721 to 749 N and the maximum deflection varied from 5.2 to 14.2 mm. For 15% Sheesham wood floor proportion (Fig. 2(h)) all the WPC samples were fractured below 754 N and 14 mm deformation. For the 20% Sheesham wood (Fig. 2(i)), four WPCs were fractured below 700 N, one unusual observation reported multiple fractures, and the final fracture above 700 N. The average load before fracture and the maximum deflection were lesser for Sheesham wood WPCs in comparison to Babool wood WPCs and competitive to Mango wood WPCs. Figure 2(j) shows the tensile test results of the WPC having 10% Mahogany wood dust as the reinforcement in the PP matrix. The maximum load before the fracture varied from 668 to 731 N and the maximum deflection varied from 9.5 to 12.8 mm. For 15% and 20% Mahogany wood floor proportions (Figs. 2(k) and 2(l)), all the WPC samples were fractured below 700 and 650 N, respectively. The average load before fracture and the maximum deflection were lesser for Mahogany wood WPCs in comparison to Babool wood WPCs and competitive to Mango & Sheesham wood WPCs. TPB, TPM, TPS, and TPT symbols were used for WPCs of Babool, Mango, Sheesham, and Mahogany, respectively.

Figure 3 shows a comparison of tensile strength (TS) of different WPCs. The TS of Babool WPCs for 10%, 15%, and 20% ranges from 18 to 22 MPa. Similarly, the TS for Mango wood ranges from 16 to 17 MPa for the three proportions, for Sheesham wood the range is between 16 to 19 MPa and for Mahogany TS varies from 15 to 18 MPa. In general, the TS decreases as the wood proportion increases in WPCs. Babool and Mahogany WPCs have observed noticeable decrement. An increment in Young’s modulus at an average was reported with an increase in wood dust proportion in all WPCs.

The WPCs were tested under 3-Point bending, and the results of the different woods used in composite along with the different wood particle ratios were compared. Figure 4 shows the comparison of bending strength (BS) of WPCs of the different woods.

The BS of WPCs having Babool wood was the highest, WPCs having Mango wood showed the different behavior from other three kinds of woods as the BS of WPC was increased considerably when the wood dust proportion reaches 20%. Babool wood dust at 10% proportion showed an excellent BS. The BS of WPCs having 10% Babool dust proportion was 43 MPa at an average, which was considerably higher than the other WPCs and the pure PP sample.

The breaking energy associated with the WPCs was evaluated by Izod and Charpy Impact tests. Figure 5 shows the results of Charpy tests. Figure 5 shows that the WPCs having 10% Babool wood by weight; the breaking energy was increased promisingly whereas at 15% the breaking energy decreases and for 20% proportion the breaking energy was the highest. WPCs having Mango wood were having the highest breaking energy among all the tested WPCs. The breaking energy of WPCs having 10% Sheesham wood floor and 15% Mahogany wood was significantly low. In general, WPCs having Mango and Babool wood floor have shown an excellent impact behavior. The Mahogany and Sheesham WPCs showed the nonlinear impact behavior.

Figure 6 shows the results of Izod test on WPCs. The Mango wood floor WPCs were having the highest breaking energy, however, unexpectedly WPCs having 15% Sheesham have shown the highest fracture energy (even in the verification experiment) among all tested samples. The reason behind same requires an intensive investigation of the morphology, structure-property relation of the WPCs and considered as the future work. However, the possible reason would be an optimum combination of the wood dust and matrix proportions resulted in the interface strengthening and the higher fracture energy. This theory is partially supported by other mechanical properties as well for the WPCs having 15% Sheesham wood floor.

The comparison of hardness (Shore Hardness scale) for different woods having different proportions is given in Fig. 7. The Fig. 7 highlights that the Mahogany wood WPCs have a linear increment in the hardness with an increment in the proportion of the wood floor, which is quite different from other woods. WPCs having Babool and Mango wood floor showed similar behavior as for 10% proportion of floor the hardness increases, further at 15% hardness decreases than again increases for 20% floor proportion. WPCs having Sheesham floor showed a small decrement in the hardness at 20% floor proportion. The reason of this unusual observation requires further investigation as in general, the hardness was increased by the inclusion of wood floor in most of the cases.

Figure 8 shows the results of the pin on disc wear test based on the average values of wear for all the samples. It is evident from the Fig. 8 that the inclusion of the wood floor has significantly improved the wear behavior of WPCs. An increment in the wood floor percentage increases the brittleness and the resistance to wear of the WPCs. The maximum and minimum wear were observed at 10% and 20% proportion of the Mango wood floor, respectively, thus, household products having 20% Mango wood floor WPCs will be comparatively durable. The WPCs of Sheesham wood floor (20%) are competitively wear resistant.

Effect of natural weathering on behavior of WPCs

Table 1 shows the effect of weathering on the mechanical behavior (flexural, tensile, impact and wear) of the WPCs. The average values of five replications for each result are summarized in Tables 1. It is clear that the TS, BS, impact strength (IS) of WPCs were significantly decreased and wear was considerably increased due to the weathering because of the ultraviolet radiation and the moisture. For the WPCs having Babool dust, increasing the wood proportion have increased the degradation in TS, WPCs with 20%, 15%, and 10% Babool dust have experienced 7.55%, 26.55%, and 30.74% decrease in TS, respectively. For WPCs with Mango dust, the rage of decrease was wider than WPCs with Babool dust, a minimum decrease in TS for 10% (4.72%) and maximum for 20% wood dust proportion (34.94%). The Sheesham dust WPCs have experienced 9.54%, 20.17% and 30.79% decrease in TS for 10%, 15%, and 20% proportions, respectively. For Mahogany dust WPCs, the rage of decrement in TS was least, 14.18% (for 10% dust proportion) to 25.78% (for 20% dust proportion), among all tested WPCs. The BS of the WPCs was also degraded due to the natural weathering. For Babool, BS was decreased 10.28% (for 10%), 19.94% (for 15%), 32.95%(for 20%), for Mango, BS was decreased 7.91% (for 10%), 20.69% (for 15%), 35.43%(for 20%), for Sheesham BS was decreased 8.31% (for 10%), 26.97% (for 15%), 31.73%(for 20%), and for Mahogany WPCs BS was decreased 8.52% (for 10%), 23.36% (for 15%), 32.04%(for 20%). The IS of WPCs has followed the similar trend as TS and BS have followed. For Babool, IS was decreased 8.83% (for 10%), 22.2% (for 15%), 36.1% (for 20%), for Mango, IS was decreased 10.7% (for 10%), 26.1% (for 15%), 32.65% (for 20%), for Sheesham IS was decreased 10.8% (for 10%), 19.5% (for 15%), 34.7% (for 20%), and for Mahogany WPCs IS was decreased 12.2% (for 10%), 29.19% (for 15%), 35.12% (for 20%). The wear was increased for WPCs after subjecting to the natural weathering, however, there was no clear pattern in the wear variation based on the wood proportion in different WPCs was identified. In general, the WPCs having 15% proportion of wood have experience a lesser change in wear (g) for all WPCs. This is possibly because of the changing crystallinity of PP matrix, the oxidation on surface of WPCs, and the mechanism of wood flour encapsulation in the matrix [¹⁹,²¹]. The WPCs with 10 wt% wood floor had the least losses of TS, BS, and IS regardless of the type of wood floor as possibly the PP matrix had encapsulated wood dust completely to protect the fibers from ultraviolet radiation and humidity [¹⁹,²¹,²²]. These results are in line with the earlier reported results [¹⁹–²²]. Moreover, the ultraviolet radiation results in decreased crystalline PP as the lacerated polymer chains have caused the fractures [⁵⁸,⁵⁹] and moisture might have penetrated the WPC surface which resulted in the larger gaps in the phases [⁶⁰]. The decrement in TS and BS was reported in [⁶¹,⁶²] due to humidity absorption, and it was reported that the humidity demolishes the phase compatibility by esterification reactions. Additionally, the lesser losses in the mechanical properties of WPCs having a lesser wood floor proportion may be resulted due higher PP proportion increases the ductility of WPCs [⁶²,⁶³]. It is reported that the enhanced interfacial adhesion results decreased flexibility and increased BS of WPCs [⁶⁴]; however, the natural weathering may degrade the interfacial adhesion and thus the FS [¹⁹,²¹,⁶²]. This is supported by the SEM images (Fig. 9) of WPC sample 20% having Sheesum wood floor after wear test.

The decrease in TS once wood dust proportion increases above 15% wt. proportion is in line with [⁶⁵] in which it is reported that as to PP has high stiffness but poor interfacial strength with wood dust, the aggregates of the dust decrease the TS. To further verify this two samples having 5% and 30% Babool wood dust proportion were prepared and TS was evaluated, The WPC with lower wood proportion was having 24.6% higher TS due to the formation of aggregates of wood dust, as clearly reflected in the SEM image (Fig. 10 a), in WPC having 30% wood dust.

Another reason could be the increment of PP proportion improves the esterification between PP and hydroxyl groups of wood [¹²,⁶²]. The totally encapsulated wood dust by the plastic matrix results in the superior interfacial stress transfer [⁶²]. However, the TS of WPCs with 15 wt% wood dust proportion is higher to 10% wood proportion because of excessive pp proportion [⁶⁶]. The higher PP proportion increases the softer phase, which results in decreased stress resistance, increased elongation at break [⁶⁷], and decreased tensile modulus.

Figure 11 shows the probability plots for Cox-Snell residuals and standardized residuals of TS, BS, IS, and wear. The plots were drawn for a range of values that represents the true mean of the population with 95% certainty. A prediction interval for estimating the future observation may also be evaluated [⁶⁸]. The Cox-Snell and standardized plots indicate that wear requires additional investigation whereas TS, BS, and IS represents the population. One extreme observation is reported in the probability plots for wear.

The empirical cumulative distribution functions (CDF) and probability plots along with the means and standard deviations of mechanical properties and wear without weathering and with natural weathering (NW) are given in Fig. 12. The plots estimated a good fit, normal distribution, and qualification of sufficient percentile of data points to represent the population for both the without and with NWWPC samples.

Figure 13 shows the surface plots representing a relative variation between the different mechanical properties of WPCs without and with natural weathering. The surface plots clearly indicate that the pattern of the variation of the mechanical properties is similar; however, the maximum and minimum values are lesser for the natural weathered WPCs. Table 1 and probability plots reflect that the values of TS, BS, IS, TS-NW, BS-NW, IS-NW represents the population and data are normally distributed with an error within the considerable limit. Figure 14 reflect the summary statistical reports for the wear and wear-NW, the summary includes results of Anderson-Darling normality test, mean, median, standard deviation, kurtosis, Skewness, box plots, and other important statistical details.

The wear and wear-NW require further intensive observation for the conclusive suggestions as p-value reports a partial deviation from normality. Further, in order to find whether the wear-NW depends on wear and type of wood, an analysis of variance (ANOVA) is conducted (see Table 2).

The ANOVA confirms the dependency of wear-NW on wear. Further, the effect of wood type and wear on wear-NW is represented in the interaction plot and main effect plot shown in Fig. 15. The dependency of wear-NW on the wood type and wear is confirmed by the interaction plot as the data points are not representing the parallel lines. The presence of main effect is highlighted by the main effect plot. The greater effect of wood type on wear-NW is clearly reflected by the steeper lines in the main effect plots. However, the general linear model of ANOVA indicates the main effect is not statistically significant and the difference in the wear-NW reading is caused by the random chance.

Figure 16 represents the orthogonal and least square fitted relation of wear and wear-NW. The bubble plot for the wear-NW Vs wear (Fig. 16) reflects consistent bubble size (and thus the within limits variability in data) and consistent effect of the proportion of wear on wear-NW. Additionally, other regression models such as Moving Least Squares, Kridging, Penalized Spline regression model may be plotted for a possibly better approximation [⁶⁹–⁷²].

Biodegradability of WPCs

Table 3 shows the results of biodegradability testing of WPCs. Table 3 indicates the weight loss/gain by the WPCs. The weight loss was observed for all WPCs as the time duration of exposure to the earth and water increases. In general, it was observed that WD% was increased with the wood dust proportion for all WPCs. This trend was observed possibly due to wood dust metabolization by fungus and microorganism [⁷³]. It can be noticed from Table 3 that type of wood dust affects the WD% along with the time duration. The WD% in water degradation is higher than the earth degradation as possibility clay and dust have filled the wood pores. However, in the case of water degradation, WPCs might have absorbed calcium carbonate and sodium carbonate with water.

Figure 17 represents summary statistical report which indicates higher mean degradation, standard deviation, variance, negative skewness, and lesser negative kurtosis in WD than ED. The probability plot (shown in Fig. 18) reflects that the data are normally distributed, and error will be within considerable limits for 95% confidence interval.

Figure 19 shows the time series and dot plots that represent the trend followed by WPCs underwent water/earth degradation and the effect of different wood type on biodegradability. Further, to ensure that the data obtained from biodegradability test hold good for population residue were calculated. Figure 20 shows the residue plots for results of biodegradability after 21 days earth and water degradation. It is clearly represented from the residue plots that the data qualifies the thick pencil test and normally distributed. Thus, the results will hold good for the population and error is within the considerable limits.

In addition to experimental and statistical study, the present work could be extended as the numerical modeling of the polymer matrix composite [⁷⁴–⁷⁷] would be a useful tool for prediction of performance of WPCs. There can be a possibility of having useful results for the compositions yet to be tested and numerical modeling is a cost effective way of analyzing the same without wasting the material.

Conclusions

The presented experimental investigation reflected the suitability of the injection molding process for the fabrication of WPCs. The mechanical properties (Tensile Strength, Flexural Rigidity, Hardness, Wear, Impact Strength, etc.) of WPCs depend on the wood dust type. Babool followed by Sheesham wood dust composites were having a higher average TS, Babool wood dust WPCs were having the highest average BS (Mango WPCs were having least BS), Mango wood WPCs were having the highest average IS, Babool wood WPCs were the hardest and Mango wood WPCs were most wear resistant at the lower wood proportion. It can be concluded that weight percentage of filler material plays a vital role in the determination of the properties of the WPCs. The higher wood proportion resulted in lower TS for all types of WPCs for the tested proportions. The effect of increasing wood dust proportion on BS of WPCs depends on the type of wood dust i.e. for Babool dust increasing wood dust proportion decreases TS whereas for Mango dust WPCs 20% of wood dust resulted in the highest BS. The variation in the IS and hardness of WPCs due to change in the proportion of wood dust depends on wood dust type. Increasing wood dust proportion decreases the resistance to wear for all types of WPCs for the tested proportions. The TS, BS, and IS of WPCs decreases and wear increases due to weathering.

Weathering of WPC caused significant variations in the properties. The TS, BS and the IS decreases whereas the wear increases for all WPCs. The WPC containing Babool, Mango have considerable decrement in TS with an increment in the wood proportion (4% to 35%) followed by Babool, Sheesum and Mahogany. The BS of Mango is most affected by the weathering (7% to 35%) followed by Babool, Mahogany and Sheesum. The IS of Babool was affected mostly (8% to 36%) with increment in the wood proportion. The wear result showed no specified pattern but it was observed that the WPC containing 15% of wood was affected mostly. Biodegradation on the other hand showed the degradation in water is way more than that of in earth. The wood dust proportion affects the biodegradability of WPCs; a higher wood proportion increases the biodegradability in both water and earth. The WPCs made of Sheesum dust were least biodegradable. The more biodegradable WPCs have a lesser resistance to the natural weathering.

References

[1] 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 & Design, 2015, 66: 103–109

[2] Homkhiew C, Ratanawilai T, Thongruang W. Composites from recycled polypropylene and rubberwood flour: Effects of composition on mechanical properties. Journal of Thermoplastic Composite Materials, 2015, 28(2): 179–194

[3] Shahinur S, Ullah A S. Quantifying the uncertainty associated with the material properties of a natural fiber. Procedia CIRP, 2017, 61: 541–546

[4] Väisänen T, Das O, Tomppo L. A review on new bio-based constituents for natural fiber-polymer composites. Journal of Cleaner Production, 2017, 149: 582–596

[5] Sanjay M R, Madhu P, Jawaid M, Senthamaraikannan P, Senthil S, Pradeep S. Characterization and properties of natural fiber polymer composites: A comprehensive review. Journal of Cleaner Production, 2018, 172: 566–581

[6] Mittal V, Saini R, Sinha S. Natural fiber-mediated epoxy composites—A review. Composites. Part B, Engineering, 2016, 99: 425–435

[7] Sombatsompop N, Prapruit W, Chaochanchaikul K, Pulngern P, Rosarpitak V. Effects of cross section design and testing conditions on the flexural properties of wood/PVC composite beams. Journal of Vinyl & Additive Technology, 2010, 16(1): 33–41

[8] Najafi S K, Hamidinia E, Tajvidi M. Mechanical properties of composites from sawdust and recycled plastics. Journal of Applied Polymer Science, 2006, 100(5): 3641–3645

[9] Mijiyawa F, Koffi D, Kokta B V, Erchiqui F. Formulation and tensile characterization of wood-plastic composites: Polypropylene reinforced by birch and aspen fibers for gear applications. Journal of Thermoplastic Composite Materials, 2015, 28(12): 1675–1692

[10] Lisperguer J, Bustos X, Saravia Y. Thermal and mechanical properties of wood flour-polystyrene blends from postconsumer plastic waste. Journal of Applied Polymer Science, 2011, 119(1): 443–451

[11] Li X, Lei B, Lin Z, Huang L, Tan S, Cai X. The utilization of bamboo charcoal enhances wood plastic composites with excellent mechanical and thermal properties. Materials & Design, 2014, 53: 419–424

[12] Ratanawilai T, Taneerat K. Alternative polymeric matrices for wood-plastic composites: Effects on mechanical properties and resistance to natural weathering. Construction & Building Materials, 2018, 172: 349–357

[13] Bambach M R. Compression strength of natural fibre composite plates and sections of flax, jute and hemp. Thin-walled Structures, 2017, 119: 103–113

[14] Ramachandran M, Bansal S, Raichurkar P. Experimental study of bamboo using banana and linen fibre reinforced polymeric composites. Perspectives on Science, 2016, 8: 313–316

[15] Sanjay M R, Yogesha B. Studies on natural/glass fiber reinforced polymer hybrid composites: An evolution. Materials Today: Proceedings, 2017, 4(2): 2739–2747

[16] Singh J I P, Dhawan V, Singh S, Jangid K. Study of effect of surface treatment on mechanical properties of natural fiber reinforced composites. Materials Today: Proceedings, 2017, 4(2): 2793–2799

[17] Wambua P, Ivens J, Verpoest I. Natural fibers: Can they replace glass in fibre reinforced plastics? Composites Science and Technology, 2003, 63(9): 1259–1264

[18] Tserki V, Zafeiropoulos N E, Simon F, Panayiotou C. A study of the effect of acetylation and propionylation surface treatment on natural fibres. Composites. Part A, Applied Science and Manufacturing, 2005, 36(8): 1110–1118

[19] Eshraghi A, Khademieslam H, Ghasemi I, Talaiepoor M. Effect of weathering on the properties of hybrid composite based on polyethylene, woodflour, and nanoclay. BioResources, 2013, 8: 201–210

[20] Stark N M, Matuana L M. Influence of photostabilizers on wood floure–HDPE composites exposed to xenon-arc radiationwith and without water spray. Polymer Degradation & Stability, 2006, 91(12): 3048–3056

[21] Li Y, Mai Y W, Ye L. Sisal fibre and its composites: A review of recent developments. Composites Science and Technology, 2000, 60(11): 2037–2055

[22] Wong S, Shanks R, Hodzic A. Interfacial improvements in poly (3- hydroxybutyrate)-flax fibre composites with hydrogen bonding additives. Composites Science and Technology, 2004, 64(9): 1321–1330

[23] Van de Weyenberg I, Ivens J, De Coster A, Kino B, Baetens E, Verpoest I. Influence of processing and chemical treatment of flax fibres on their composites. Composites Science and Technology, 2003, 63(9): 1241–1246

[24] Gassan J. A study of fibre and interface parameters affecting the fatigue behaviour of natural fibre composites. Composites. Part A, Applied Science and Manufacturing, 2002, 33(3): 369–374

[25] Baiardo M, Zini E, Scandola M. Flax fibre-polyester composites. Composites. Part A, Applied Science and Manufacturing, 2004, 35(6): 703–710

[26] Markarian J. Additive developments aid growth in wood-plastic composites. Plastics Additives & Compounding, 2002, 4(11): 18–21

[27] Amir N, Abidin K A Z, Shiri F B M. Effects of fibre configuration on mechanical properties of banana fibre/PP/MAPP natural fibre reinforced polymer composite. Procedia Engineering, 2017, 184: 573–580

[28] Yang T H, Yang T H, Chao W C, Leu S Y. Characterization of the property changes of extruded wood—plastic composites during year-round subtropical weathering. Construction & Building Materials, 2015, 88: 159–168

[29] Taib R M, Zauzi S N A, Ishak Z A M, Rozman H D. Effects of photo-stabilizers on the properties of recycled high-density polyethylene (HDPE)/wood flour (WF) composites exposed to natural weathering. Malaysian Polymer Journal, 2010, 5: 193–203

[30] Lopez J L, Sain M, Cooper P. Performance of natural-fiber-plastic composites under stress for outdoor applications: Effect of moisture, temperature, and ultraviolet light exposure. Journal of Applied Polymer Science, 2006, 99(5): 2570–2577

[31] Lau K T, Hung P Y, Zhu M H, Hui D. Properties of natural fibre composites for structural engineering applications. Composites. Part B, Engineering, 2018, 136: 222–233

[32] Pritchard G. Two technologies merge: Wood-plastic composites. Plastics Additives & Compounding, 2004, 6(4): 18–21

[33] Oksman K, Selin J F. Plastics and composites from polylactic acid. In: Wallenberger F T, Weston N E, eds. Natural Fibers, Plastics and Composites, Vol 1. Norwell: Kluwer Academic Press, 2004

[34] Bledzki A K, Reihmane S, Gassan J. Thermoplastics reinforced with wood fillers: A literature review. Polymer-Plastic Technology and Engineering, 1998, 37(4): 451–468

[35] Turku I, Keskisaari A, Kärki T, Puurtinen A, Marttila P. Characterization of wood plastic composites manufactured from recycled plastic blends. Composite Structures, 2017, 161: 469–476

[36] Zhang Y, Xue P, Ding Y, Jia M, Cai J, Jin X. Improvement of mechanical properties of wood-plastic composite floors based on the optimum structural design. Acta Mechanica Solida Sinica, 2016, 29(4): 444–454

[37] Sommerhuber P F, Wenker J L, Rüter S, Krause A. Life cycle assessment of wood-plastic composites: Analysing alternative materials and identifying an environmental sound end-of-life option. Resources, Conservation and Recycling, 2017, 117: 235–248

[38] Schirp A, Su S. Effectiveness of pre-treated wood particles and halogen-free flame retardants used in wood-plastic composites. Polymer Degradation & Stability, 2016, 126: 81–92

[39] Friedrich D, Luible A. Investigations on ageing of wood-plastic composites for outdoor applications: A meta-analysis using empiric data derived from diverse weathering trials. Construction & Building Materials, 2016, 124: 1142–1152

[40] Migneault S, Koubaa A, Perré P, Riedl B. Effects of wood fiber surface chemistry on strength of wood-plastic composites. Applied Surface Science, 2015, 343: 11–18

[41] Catto A L, Montagna L S, Almeida S H, Silveira R, Santana R M C. Wood plastic composites weathering: Effects of compatibilization on biodegradation in soil and fungal decay. International Biodeterioration & Biodegradation, 2016, 109: 11–22

[42] Badji C, Soccalingame L, Garay H, Bergeret A, Bénézet J C. Influence of weathering on visual and surface aspect of wood plastic composites: Correlation approach with mechanical properties and microstructure. Polymer Degradation & Stability, 2017, 137: 162–172

[43] Peng Y, Liu R, Cao J. Characterization of surface chemistry and crystallization behavior of polypropylene composites reinforced with wood flour, cellulose, and lignin during accelerated weathering. Applied Surface Science, 2015, 332: 253–259

[44] Butylina S, Hyvärinen M, Kärki T. A study of surface changes of wood-polypropylene composites as the result of exterior weathering. Polymer Degradation & Stability, 2012, 97(3): 337–345

[45] Ren Y, Wang Y, Wang L, Liu T. Evaluation of intumescent fire retardants and synergistic agents for use in wood flour/recycled polypropylene composites. Construction & Building Materials, 2015, 76: 273–278

[46] Tamrakar S, Lopez-Anido R A. Water absorption of wood polypropylene composite sheet piles and its influence on mechanical properties. Construction & Building Materials, 2011, 25(10): 3977–3988

[47] Brandt C W, Fridley K J. Load-duration behavior of wood-plastic composites. Journal of Materials in Civil Engineering, 2003, 15(6): 524–536

[48] Lewandowski K, Piszczek K, Zajchowski S, Mirowski J. Rheological properties of wood polymer composites at high shear rates. Polymer Testing, 2016, 51: 58–62

[49] Mysiukiewicz O, Sterzyński T. Influence of water on tribological properties of wood-polymer composites. Archives of Mechanical Technology and Materials, 2017, 37(1): 79–84

[50] Chin C W, Yousif B F. Potential of kenaf fibers as reinforcement for tribological applications. Wear, 2009, 267(9–10): 1550–1557

[51] Yousif B F, Lau S T W, McWilliam S. Polyester composite based on betelnut fiber for tribological application. Tribology International, 2010, 43(1–2): 503–511

[52] El-Sayed A A, El-Sherbiny M G, Abo-El-Ezz A S, Aggag G A. Friction and wear properties of polymeric composite materials for bearing applications. Wear, 1995, 184(1): 45–53

[53] Yousif B F, El-Tayeb N S M. Wet adhesive wear characteristics of untreated oil palm fiber reinforced polyester and treated oil palm fiber reinforced polyester composites using the pin on disc and block on ring techniques. Journal of Engineering Tribology, 2009, 224: 123–131

[54] Umar N, Jamil H, Low K O. Adhesive wear and frictional performance of bamboo fibers reinforced epoxy. International Journal of Trichology, 2012, 47: 122–133

[55] Bijwe J, Indumathi J, John Rajesh J, Fahim M. Friction and wear behavior of polyetherimide composites in various wear modes. Wear, 2001, 249(8): 715–726

[56] Singh N, Yousif B F, Rilling D. Tribological characteristics of sustainable fiber-reinforced thermoplastic composites under wet adhesive wear. Tribology Transactions, 2011, 54(5): 736–748

[57] Petchwattana N, Covavisaruch S. Mechanical and morphological properties of wood plastic biocomposites prepared from toughened poly (lactic acid) and rubber wood sawdust (hevea brasiliensis). Journal of Bionics Engineering, 2014, 11(4): 630–637

[58] Muasher M, Sain M. The efficacy of photostabilizers on the color change of wood filled plastic composites. Polymer Degradation & Stability, 2006, 91(5): 1156–1165

[59] Du H, Wang W, Wang Q, Zhang Z, Sui S, Zhang Y. Effects of pigments on the UV degradation of wood-flour/HDPE composites. Journal of Applied Polymer Science, 2010, 118: 1068–1076

[60] Yang T H, Yang T H, Chao W C, Leu S Y. Characterization of the property changes of extruded wood-plastic composites during year-round subtropical weathering. Construction & Building Materials, 2015, 88: 159–168

[61] Stark N M, Matuana L M. Influence of photostabilizers on wood floure HDPE composites exposed to xenon-arc radiation with and without water spray. Polymer Degradation & Stability, 2006, 91(12): 3048–3056

[62] Adhikary K B, Pang S, Staiger M P. Dimensional stability and mechanical behaviour of wood-plastic composites based on recycled and virgin highdensity polyethylene (HDPE). Composites. Part B, Engineering, 2008, 39(5): 807–815

[63] Ratanawilai T, Lekanukit P, Urapantamas S. Effect of rubberwood and palm oil content on the properties of wood-polyvinyl chloride composites. Journal of Thermoplastic Composite Materials, 2014, 27(6): 719–730

[64] Deka B K, Maji T K. Effect of silica nanopowder on the properties of wood flour/polymer composite. Polymer Engineering and Science, 2012, 52(7): 1516–1523

[65] Sultan M T, Haque M M, Maniruzzaman M, Alam M A. Composites of polypropylene with pulque fibres: Morphology, thermal and mechanical properties. Journal of Thermoplastic Composite Materials, 2015, 28(12): 1615–1626

[66] Gilbert M. Brydson’s Plastics Materials. 8th ed. Oxford: Elsevier Inc., 2017

[67] Prachayawarakorn J, Khamsri J, Chaochanchaikul K, Sombatsompop N. Effects of compatibilizer type and rubber-wood sawdust content on the mechanical, morphological, and thermal properties of PVC/LDPE blend. Journal of Applied Polymer Science, 2006, 102(1): 598–606

[68] Vu-Bac N, Silani M, Lahmer T, Zhuang X, Rabczuk T. A unified framework for stochastic predictions of mechanical properties of polymeric nanocomposites. Computational Materials Science, 2015, 96: 520–535

[69] Vu-Bac N, Lahmer T, Keitel H, Zhao J, Zhuang X, Rabczuk T. Stochastic predictions of bulk properties of amorphous polyethylene based on molecular dynamics simulations. Mechanics of Materials, 2014, 68: 70–84

[70] Vu-Bac N, Lahmer T, Zhang Y, Zhuang X, Rabczuk T. Stochastic predictions of interfacial characteristic of polymeric nanocomposites (PNCs). Composites. Part B, Engineering, 2014, 59: 80–95

[71] Vu-Bac N, Rafiee R, Zhuang X, Lahmer T, Rabczuk T. Uncertainty quantification for multiscale modeling of polymer nanocomposites with correlated parameters. Composites. Part B, Engineering, 2015, 68: 446–464

[72] Vu-Bac N, Lahmer T, Zhuang X, Nguyen-Thoi T, Rabczuk T. A software framework for probabilistic sensitivity analysis for computationally expensive models. Advances in Engineering Software, 2016, 100: 19–31

[73] Enamul Hoque M, Aminudin M A M, Jawaid M, Islam M S, Saba N, Paridah M T. Physical, mechanical, and biodegradable properties of meranti wood polymer composites. Materials & Design, 2014, 64: 743–749

[74] Khudari Bek Y, Hamdia K M, Rabczuk T, Könke C. Micromechanical model for polymeric nano-composites material based on SBFEM. Composite Structures, 2018, 194: 516–526

[75] Badawy M F, Msekh M A, Hamdia K M, Steiner M K, Lahmer T, Rabczuk T. Hybrid nonlinear surrogate models for fracture behavior of polymeric nanocomposites. Probabilistic Engineering Mechanics, 2017, 50: 64–75

[76] Hamdia K M, Ghasemi H, Zhuang X, Alajlan N, Rabczuk T. Sensitivity and uncertainty analysis for flexoelectric nanostructures. Computer Methods in Applied Mechanics and Engineering, 2018, 337: 95–109

[77] Hamdia K M, Silani M, Zhuang X, He P, Rabczuk T. Stochastic analysis of the fracture toughness of polymeric nanoparticle composites using polynomial chaos expansions. International Journal of Fracture, 2017, 206(2): 215–227

RIGHTS & PERMISSIONS

Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature