Mechanical properties of composites from sawdust and recycled plastics

Mechanical properties of wood plastic composites (WPCs) manufactured from sawdust and virgin and/or recycled plastics, namely high density polyethylene (HDPE) and polypropylene (PP), were studied. Sawdust was prepared from beech industrial sawdust by screening to the desired particle size and was mixed with different virgin or recycled plastics at 50% by weight fiber loading. The mixed materials were then compression molded into panels. Flexural and tensile properties and impact strength of the manufactured WPCs were determined according to the relevant standard specifications. Although composites containing PP (virgin and recycled) exhibited higher stiffness and strength than those made from HDPE (virgin and recycled), they had lower unnotched impact strengths. Mechanical properties of specimens containing recycled plastics (HDPE and PP) were statistically similar and comparable to those of composites made from virgin plastics. This was considered as a possibility to expand the use of recycled plastics in the manufacture of WPCs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3641–3645, 2006     

Waste pine cones as a source of reinforcing fillers for thermoplastic composites

In this study, we evaluated some physical and mechanical properties of polypropylene (PP) composites reinforced with pine‐cone flour and wood flour. Five types of wood–plastic composites (WPCs) were prepared from mixtures of cone flour, wood flour, PP, and a coupling agent. The water resistance and flexural properties of the composites were negatively affected by an increase in cone‐flour content. Extractives in the cone flour had a significant effect on the flexural properties of the WPCs. However, the flexural properties and water resistance of the WPC samples were not significantly affected by the addition of 10 wt % of the cone flour when compared to the WPC samples made from wood flour. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The physical perspective on the solid and molten states associated with the mechanical properties of eco‐friendly HDPE/Pinus taeda wood‐plastic composites

The manufacture of wood plastic composites (WPCs) by reutilizing post‐consumed polymeric materials and post‐industry wood wastes contributes to reduce the environmental impact and the consumption of virgin plastics. In this work, the influence of interfacial adhesion on the solid and molten states of high density polyethylene (HDPE) containing WPCs wood dust of recycled Pinus taeda (PT) was evaluated. The composites were prepared by extrusion in a twin screw extruder using maleic anhydride as compatibilizer. The samples were analyzed by dynamic‐mechanical analysis (DMA), tensile and impact strength measurements, oscillatory rheometry, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). DMA analysis showed increase in module and an improved interface with physical interaction between the WPCs phases. The higher molecular interactivity interface improved the mechanical properties relative to pure HDPE. Melting state analysis showed increased WPCs flow restriction, this feature being correlated with reduction in the molecular degree of freedom during flow, which consequently reduces the crystalline degree changes in microstructure as well as in processing parameters of the material. These results lead to consider the development of an eco‐friendly and economic effective technology to reuse abundant recycled solid wastes in a new market. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42887.     

Effect of temperature on hygroscopic thickness swelling rate of composites from lignocellolusic fillers and HDPE

Effect of temperature on hygroscopic thickness swelling rate of lignocellolusic fillers/HDPE (high density polyethylene) composites was investigated. The composites were manufactured using a dry blend/hot press method. In this method, powder of plastic and dried powder of lignocellolusic material were mixed in high‐speed mixer and then the mixed powder were pressed at 190°C. Lignocellolusic fillers/HDPE composites panels were made from virgin and recycled HDPE (as plastic) and wood sawdust and flour of rice hull (as filler) at 60% by weight filler loadings. Nominal density and dimensions of the panels were 1 g/cm³ and 35 × 35 × 1 cm³, respectively. Thickness swelling rate of manufactured wood plastic composites (WPCs) were evaluated by immersing them in water at 20, 40, and 60°C for reaching a certain value where no more thickness was swelled. A swelling model developed by Shi and Gardner [Compos. A, 37 , 1276 (2006)] was used to study the thickness swelling process of WPCs, from which the parameter, swelling rate parameter, can be used to quantify the swelling rate. The results indicated that temperature has a significant effect on the swelling rate. The swelling rate increased as the temperature increased. The swelling model provided a good predictor of the hygroscopic swelling process of WPCs immersed in water at various temperatures. From the activation energy values calculated from the Arrhenius plots, the temperature had less effect on the thickness swelling rate for the composites including wood sawdust compared with the rice hull as filler and the composites including recycled compared with the virgin HDPE as plastic. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Comparative study of maleated polypropylene as a coupling agent for recycled low‐density polyethylene/wood flour composites

The effects of the type of coupling agent and virgin polypropylene (PP) content on the mechanical properties and water absorption behavior of recycled low‐density polyethylene/wood flour (WF) composites were investigated. The fractured surfaces of these recycled wood/plastic composites (rWPCs) were examined to gain insight into the distribution and dispersion of WF within the polymer matrix. The results indicate that the use of 100% recycled polymer led to inferior mechanical properties and to a greater degree of moisture absorption and swelling when compared to recycled polymer–virgin PP wood/plastic composites. This could have been related to the poor melt strength and inferior processability of the recycled polymer. The extent of improvement of the mechanical properties depended not only on the virgin PP content in the matrix but also on the presence of maleic anhydride (MA) modified PP as the coupling agent. Higher concentrations of MA group were beneficial; this improvement was attributed to increased chemical bonding (ester linkages) between hydroxyl moieties in WF and anhydride moieties in the coupling agent. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Wood/plastic composites co‐extruded with multi‐walled carbon nanotube‐filled rigid poly(vinyl chloride) cap layer

Wood/plastic composites (WPCs) can absorb moisture in a humid environment due to the hydrophilic nature of the wood in the composites, making products susceptible to microbial growth and loss of mechanical properties. Co‐extruding a poly(vinyl chloride) (PVC)‐rich cap layer on a WPC significantly reduces the moisture uptake rate, increases the flexural strength but, most importantly, decreases the flexural modulus compared to uncapped WPCs. A two‐level factorial design was used to develop regression models evaluating the statistical effects of material compositions and a processing condition on the flexural properties of co‐extruded rigid PVC/wood flour composites with the ultimate goal of producing co‐extruded composites with better flexural properties than uncapped WPCs. Material composition variables included wood flour content in the core layer and carbon nanotube (CNT) content in the cap layer of the co‐extruded composites, with the processing temperature profile for the core layer as the only processing condition variable. Fusion tests were carried out to understand the effects of the material compositions and processing condition on the flexural properties. Regression models indicated all main effects and two powerful interaction effects (processing temperature/wood flour content and wood flour content/CNT content interactions) as statistically significant. Factors leading to a fast fusion of the PVC/wood flour composites in the core layer, i.e. low wood flour content and high processing temperature, were effective material composition and processing condition parameters for improving the flexural properties of co‐extruded composites. Reinforcing the cap layer with CNTs also produced a significant improvement in the flexural properties of the co‐extruded composites, insensitive to the core layer composition and the processing temperature condition. Copyright © 2009 Society of Chemical Industry     

Experimental investigation on reprocessing of extruded wood flour/HDPE composites

This article presents an experimental study on the change in the properties of wood–plastic composites (WPCs) when reprocessed. The degree of properties degradation upon reprocessing, for recycling purpose, can be considered as a key factor to choose an alternative against discarding into the environment. A material which retains its properties when recycled, or at least exhibits insignificant reduction in its properties, is favorable in environmental point of view. To investigate the reprocessing effect on the WPC properties, in this study, cylindrical profiles of WPC, with 60 wt% of wood content, were produced using a twin screw extruder, at first stage (virgin WPC). These profiles were then chopped into granules and used in the reproduction of the same shaped product (recycled WPC). For the measurement of mechanical properties, tensile and three‐point bending tests were conducted. Differential scanning calorimetry (DSC) test was performed to compare thermal behavior of the neat HDPE, virgin and recycled composites. Scanning electron microscopy (SEM) images were also produced to observe the adhesion quality of the components and changes in wood particles size. Physical properties such as density and water uptake were also measured. A reduction in strength was observed upon recycling which was accompanied with the decrease in density, while an increase in the flexural modulus was noticed. The results also indicate that the recycled samples exhibit a higher water uptake. Analysis of thermal behavior showed a slight increase in the melting temperature of the reprocessed composite and decrease in the degree of crystallinity especially at the first stage of the HDPE process. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effect of highly degraded high‐density polyethylene (HDPE) on processing and mechanical properties of wood flour‐HDPE composites

The influence of highly degraded high‐density polyethylene (HDPE) on physical, rheological, and mechanical properties of HDPE‐wood flour composites was studied. For this purpose, the virgin HDPE was subjected to accelerated weathering under controlled conditions for 200 and 400 h. The virgin and exposed HDPE and pine wood flour were compounded to produce wood flour‐HFPE composites. The results showed that the accelerated weathering highly degraded HDPE. Degradation created polar functional carbonyl groups and also produced extensive cross‐linking in HDPE and consequently poor processibility. The interruptions in the flow characteristics of the degraded HDPE potentially caused processing hurdles when using them for extrusion or injection molding manufacturing as only small part (10%) of virgin HDPE could be replaced by highly degraded HDPE for wood flour‐HDPE composite manufacturing. The mechanical properties of composites containing highly degraded HDPEs were similar to the composites with virgin HDPE and in some cases they exhibited superior properties, with the exception being with the impact strength. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical and thermal properties of wood‐plastic composites reinforced with hexagonal boron nitride

Mechanical, thermal, and morphological properties of injection molded wood‐plastic composites (WPCs) prepared from poplar wood flour (50 wt%), thermoplastics (high density polyethlyne or polypropylene) with coupling agent (3 wt%), and hexagonal boron nitride (h‐BN) (2, 4, or 6 wt%) nanopowder were investigated. The flexural and tensile properties of WPCs significantly improved with increasing content of the h‐BN. Unlike the tensile and flexural properties, the notched izod impact strength of WPCs decreased with increasing content of h‐BN but it was higher than that of WPCs without the h‐BN. The WPCs containing h‐BN were stiffer than those without h‐BN. The tensile elongation at break values of WPCs increased with the addition of h‐BN. The differential scanning calorimetry (DSC) analysis showed that the crystallinity, melting enthalpy, and crystallization enthalpy of the WPCs increased with increasing content of the h‐BN. The increase in the crystallization peak temperature of WPCs indicated that h‐BN was the efficient nucleating agent for the thermoplastic composites to increase the crystallization rate. POLYM. COMPOS., 35:194–200, 2014. © 2013 Society of Plastics Engineers     

Coextruded PVC/wood‐flour composites with WPC cap layers

Wood‐plastic composites (WPCs) can absorb moisture in a humid environment owing to the hydrophilic nature of the wood, thereby making the products susceptible to microbial growth and loss of mechanical properties. In this study, rigid poly(vinyl chloride) (PVC)/wood‐flour composites (core layer) were coextruded with either unfilled rigid PVC (cap layer) or rigid PVC filled with a small amount (5–27.5%) of wood flour (composite cap layers) in order to decrease or delay the moisture uptake. The thickness of the cap layer and its composition in terms of wood flour content were the variables examined during coextrusion. Surface color, moisture absorption, and flexural properties of both coextruded and noncoextruded (control) composite samples were characterized. The experimental results indicated that both unfilled PVC and composite cap layers can be encapsulated over rigid PVC/wood‐flour composites in a coextrusion process. The moisture uptake rate was lower when a cap layer was applied in the composites, and the extent of the decrease was a strong function of the amount of wood flour in the cap layer but insensitive to cap layer thickness. Overall, coextruding PVC surface‐rich cap layers on WPCs significantly increased the flexural strength but decreased the flexural modulus as compared with those of control samples. The changes in bending properties were sensitive to both cap layer thickness and wood flour content. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers     

Effects of different filler types on decay resistance and thermal,physical, and mechanical properties of recycled high-density polyethylene composites

In this study, flexural properties, impact strength, thermal performance, water absorption, biological durability, and morphology of wood-plastic composites (WPCs) filled with different filler types were investigated. Six different formulations of WPCs were fabricated from mixtures of carpenter waste and recycled high-density polyethylene (R-HDPE). The carpenter waste was derived from wood and particle board wastes, and R-HDPE was used as the polymer matrix, with and without addition of maleic anhydrite grafted polyethylene (MAPE). All formulations were compression moulded in a hot press for 3 min at 170 °C. Investigations on the compression moulded specimens revealed that water absorption values in the particleboard waste flour specimens were lower than in the wood-waste flour WPCs. However, the wood-waste flour-filled composites exhibited higher mechanical property values than the particleboard waste flour WPCs. Statistically, only the wood-waste flour-filled composites with MAPE were significantly different. The use of MAPE (3 wt%) had a positive effect on the water absorption, crystallinity degree, and flexural properties of the WPCs. In addition, the peak temperatures of the composites did not show any variation, while thermal decomposition of the composites showed minor variations under the thermogravimetric analysis. Furthermore, the decay resistance of the composites improved with the use of particleboard waste flour. The obtained results demonstrate that particleboard waste flour, such as wood-waste flour, is potentially suitable as a raw material in WPCs.     

Rheological and mechanical properties of composites made from wood flour and recycled LDPE/HDPE blend

The effect of compounding method is studied with respect to the rheological behavior and mechanical properties of composites made of wood flour and a blend of two main components of plastics waste in municipal solid waste, low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The effects of recycling process on the rheological behavior of LDPE and HDPE blends were investigated. Initially, samples of virgin LDPE and HDPE were thermo-mechanically degraded twice under controlled conditions in an extruder. The recycled materials and wood flour were then compounded by two different mixing methods: simultaneous mixing of all components and pre-mixing, including the blending of polymers in molten state, grinding and subsequent compounding with wood flour. The rheological and mechanical properties of the LDPE/HDPE blend and resultant composites were determined. The results showed that recycling increased the complex viscosity of the LDPE/HDPE blend and it exhibited miscible behavior in a molten state. Rheological testing indicated that the complex viscosity and storage modulus of the composites made by pre-mixing method were higher than that made by the simultaneous method. The results also showed that melt pre-mixing of the polymeric matrix (recycled LDPE and HDPE) improved the mechanical properties of the wood–plastic composites.     

Nanoclay‐reinforced,polypropylene‐based wood–plastic composites

Wood plastic composites (WPCs) are a new class of materials which combine the characteristics of plastic and wood. In appearance, they are similar to wood, but the low stiffness of plastics makes the composite modulus significantly lower than that of solid wood. Increasing the wood content in the WPCs can improve stiffness, but the rate of water absorption also goes up. Here, nanoclay was compounded with wood and plastic using a twin screw extruder to form a three‐component composite to improve the stiffness of WPCs. To overcome the previously observed reduction in strength and increase in the rate of water absorption, different compounding procedures were used. It was found that pre‐compounding wood flour with polymer followed by incorporation of clay in a second step resulted in an increase in stiffness, retention in strength, and a reduction in the rate of water absorption. Thus, adding nanoclays is an alternative for increasing properties instead of adding extra wood flour to a concentration in excess of 55 wt% as this involves processing difficulties. POLYM. ENG. SCI., 50:2013–2020, 2010. © 2010 Society of Plastics Engineers     

Impact strength improvement of wood flour–recycled polypropylene composites

In this research, the improvement of the impact strength of wood flour–recycled polypropylene (PP) composites through impact modification was studied. For this purpose, a virgin polypropylene (VPP) was thermomechanically degraded by five extrusions under controlled conditions in a twin‐screw extruder at a rotor speed of 100 rpm and a temperature of 190°C. PP (VPP and recycled PP at the second and fifth stages) and wood flour were compounded at 50 wt % wood flour loading in a counterrotating twin‐screw extruder in the presence different contents of ethylene vinyl acetate (EVA) to produce the wood flour–PP composites. From the results, the composites containing recycled PP exhibited significantly lower impact strengths. The addition of EVA up to 9 wt % increased the impact strengths of the composites made with PP recycled two and five times by about 63 and 41%, respectively. The composites containing VPP exhibited higher impact strengths than those containing recycled PP and EVA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Durability of wood flour‐plastic composites exposed to accelerated freeze–thaw cycling. II. High density polyethylene matrix

This study examined the durability of extruded HDPE/wood‐flour composites exposed to 15 accelerated cycles of water submersion, freezing, and thawing, according to ASTM standard D6662. The durability of both maple and pine composites was assessed by testing the flexural properties and density. Mercury intrusion porosimetry and scanning electron microscopy were also used to evaluate the interfacial adhesion between the matrix and wood flour before and after exposure to accelerated freeze–thaw cycling. Freeze–thaw actions had no apparent effect on the density of the composites after exposure, regardless of the wood species. However, these actions led to moisture uptake, which decreased the interfacial adhesion and increased the pore size and quantity in the composites, which resulted in a significant loss in flexural properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 100: 35–39, 2006     

Effects of alkaline and silane treatments on the water‐resistance properties of wood‐fiber‐reinforced recycled plastic composites

The water‐resistance properties of wood‐fiber‐reinforced recycled plastic composites (WRPCs) prepared from postconsumer high‐density polyethylene (HDPE) and wood fibers from saw mills were studied. Three methods consisting of an alkaline method (AM), a silane method (SM), and a combination of the alkaline and silane methods (ASM) were used to modify the wood fibers. The effects of fiber/matrix mix ratio and surface treatment on the moisture content, thickness swelling, and flexural strength change of the WRPCs, before and after immersion in 60°C water for 8 weeks, were studied and analyzed. The flexural fractured surfaces of the WRPCs before and after immersion in hot water were examined, and the fracture mechanism of the WRPCs was discussed. The results showed that the different surface treatments of the wood fibers had significant effects on the moisture content, thickness swelling, and flexural strength of the WRPCs after a long immersion time in hot water. For WRPCs treated by ASM, the moisture content was the lowest, the thickness swelling was at a minimum, and the flexural strength was the highest. Higher water absorption of composites with fiber treated by the AM or SM methods, as compared to those treated by ASM, could be attributed to the incomplete adhesion and wettability between the wood fibers and the polymer matrix, which may have caused more gaps and flaws at the interface. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.     

The effect of epoxy‐polyester hybrid resin on mechanical properties,rheological behavior,and water absorption of polypropylene wood flour composites

The effect of epoxy resin on mechanical and Rheological properties, and moisture absorption of wood flour polypropylene composites (WPCs) were investigated. The reactive mixing of epoxy resin with 30, and 40 wt% wood flour and polypropylene (PP) was carried out in twin screw extruder with a special screw elements arrangement. PP grafted maleic anhydrides (MPP) were used as coupling agent to improve the interfacial interactions of wood flour, epoxy resin, and PP. The tensile strength of composites decreased, and elastic modulus and moisture absorption increased with increasing epoxy resin content. The complex viscosity η* increased with increasing epoxy resin content of composites, and a synergistic effect in increasing the η* was observed at 3 wt% resin. The epoxy resin modified wood‐PP composites that chemically coupled by MPP showed minimum water absorption with highest elastic modulus. The experimental oscillation rheologyical data were used to drive a model to predict the flow behavior of WPCs, in a wide range of frequencies. POLYM. ENG. SCI., 47:2041–2048, 2007. © 2007 Society of Plastics Engineers     

Effect of extractives on the performance properties of wood flour‐polypropylene composites

In this study, the effects of extractives in wood flour on the physicomechanical properties of wood flour‐polypropylene (PP) composites have been investigated. Three different solvents, hot‐water (HW), 1% NaOH (AL), and dichloromethane (DM), were used to remove extractives in both poplar and eucalypt wood flour. The obtained results showed that mechanical properties of the composites were moderately enhanced on using extractive‐free lignocellulosic materials in both the wood types. A large increase in the strength of eucalyptus flour‐PP composites was observed upon the removal of extractives from eucalyptus flour. Unlike the mechanical properties, no improvement in the water absorption and thickness swelling was observed for any type of extracted‐free samples. The thermal degradation behavior of the composites showed that in both cases, the degradation temperatures shifted to higher values after removing the extractives. In general, the removal of AL solubles was more effective in its improvement of the physicomechanical properties than the removal of HW and DM extractives. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of silane on the properties of wood‐plastic composites with polyethylene‐polypropylene blends as matrices

The influence of 3‐(trimethoxysilyl)propyl methacrylate and benzoyl peroxide on gel content, crystallinity, and mechanical performance of unfilled PP‐PE blends, and their composites with wood was investigated. All materials were compounded in a twin screw extruder and then injection molded. Specimens were then exposed to high‐humidity and elevated temperature in a humidity chamber to cross‐link any unhydrolyzed silane. Adding wood to the PE‐PP blends, increased premature cross‐linking but also increased gel contents. However, the gel contents of the composites were still low. The PP component did not appear to cross‐link well and our gels were almost entirely HDPE. Fourier Transfer Infrared (FTIR) spectra provided additional evidence that TMSPM is grafted and cross‐linked in unfilled PE‐PP blends. Unfortunately, the spectra of wood composites proved difficult to interpret because of the complexity and overlap of the FTIR spectra of the wood. The HDPE component annealed when exposed to high‐humidity and elevated temperature, although less so in samples with high‐gel contents, presumably because of the decreased mobility. Annealing influenced mechanical performance, especially increasing moduli. Adding peroxide and silane appeared to improve adhesion between the wood flour and matrix in the composites but had little effect on energy absorbed during high‐speed puncture tests. Published 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The comparison of properties of (rubber tree seed shell flour)‐filled polypropylene and high‐density polyethylene composites

The effect of varied rubber tree seed shell flour (RSSF) filler loadings on processing torque, mechanical, thermal, water absorption, and morphological properties of polypropylene (PP) and high‐density polyethylene (HDPE) composites has been studied. The addition of RSSF in the composites increased the stabilization torque in both PP‐ and HDPE‐based composites. Tensile strength, elongation at break, flexural strength, and impact strength show significant reduction when higher loading of RSSF was incorporated, while tensile modulus and flexural modulus were improved. The phenomenon was noted for both matrices, PP and HDPE, but HDPE‐based composites showed clear effects on the reduction of the mechanical properties compared with RSSF‐filled PP. Scanning electron microscopy of tensile fracture specimens revealed the degree of dispersion of RSSF filler in the matrices. At higher filler loadings, agglomerations and poor dispersion of RSSF particles were spotted, which induce the debonding mechanism of the system. Thermogravimetric analysis thermograms showed that both PP‐ and HDPE‐based composite systems with higher RSSF content have higher thermal stability, initial degradation temperature, degradation temperature, and total weight loss. Water absorption ability of the composites increases as the filler loading increases for both matrices. J. VINYL ADDIT. TECHNOL., 22:91–99, 2016. © 2014 Society of Plastics Engineers