Development of semitransparent wood‐polymer composites

A new material has been developed consisting of pieces of wood embedded within a matrix of acrylic polymer, resulting in a transparent or semitransparent wood‐based product. This material presents quite appealing aesthetic features, thereby opening new possibilities for decorative applications. Because acrylic and methacrylic monomers are in the liquid state at room temperature, it is possible to introduce wood (in the current case, walnut wood) into a mixture of acrylic (hydroxypropyl acrylate) and/or methacrylic monomers (methyl methacrylate and 2‐hydroxyethyl methacrylate) along with a plasticizer (dioctyl phthalate) in the presence of a chemical initiator (benzoyl peroxide). A transparent polymeric matrix with dispersed wood is then obtained through bulk free‐radical polymerization. Introducing this reaction mixture along with pieces of wood into a mold results in a wood‐polymer composite. A 2^4?1 experimental fractional factorial design was implemented to study the importance of the composition of these materials on several relevant properties. The sheets produced were characterized by tensile testing, dynamic mechanical thermal analysis, thermal gravimetric analysis, and heat deflection temperature. The models obtained for predicting each property pointed to valuable insights regarding the influential constituents. In particular, our results suggested that monomers to be used in future applications of this material should be selected in terms of their cost and the desired flexibility for the final product, not in terms of their polarity. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

Evaluation of dynamic elastic properties of wood‐filled polypropylene composites

Dynamic modulus of elasticity (MoE) and shear modulus of wood‐filled polypropylene composite at various filler contents ranging from 10% to 50% was determined from the vibration frequencies of disc‐shaped specimens. Wood filler was used in both fiber form (pulp) and powder form (wood flour). A novel compatibilizer, m‐isopropenyl‐α,α‐dimethylbenzyl‐isocyanate(m‐TMI) grafted polypropylene with isocyanate functional group was used to prepare the composites. A linear increase in dynamic MoE, shear modulus, and density of the composite was observed with the increasing filler content. Between the two fillers, wood fiber filled composites exhibited slightly better properties. At 50% filler loading, dynamic MoE of the wood fiber filled composite was 97% higher than that of unfilled polypropylene. Halpin‐Tsai model equation was used to describe the changes in the composite modulus with the increasing filler content. The continuous improvement in elastic properties of the composites with the increasing wood filler is attributed to the effective reinforcement of low‐modulus polypropylene matrix with the high‐modulus wood filler. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1706–1711, 2006     

Ultraviolet weathering of photostabilized wood‐flour‐filled high‐density polyethylene composites

Wood‐plastic composites are being increasingly examined for nonstructural or semistructural building applications. As outdoor applications become more widespread, durability becomes an issue. Ultraviolet exposure can lead to photodegradation, which results in a change in appearance and/or mechanical properties. Photodegradation can be slowed through the addition of photostabilizers. In this study, we examined the performance of wood flour/high‐density polyethylene composites after accelerated weathering. Two 2⁴ factorial experimental designs were used to determine the effects of two hindered amine light stabilizers, an ultraviolet absorber, a colorant, and their interactions on the photostabilization of high‐density polyethyl‐ ene blends and wood flour/high‐density polyethylene composites. Color change and flexural properties were determined after 250, 500, 1000, and 2000 h of accelerated weathering. The results indicate that both the colorant and ultraviolet absorber were more effective photostabilizers for wood flour/high‐density polyethylene composites than the hindered amine light stabilizers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2609–2617, 2003     

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     

Dimensional stability of wood–polymer composites

Wood–polymer composites (WPC) were prepared by impregnation of polymeric monomers in wood and in situ polymerization. Three polymeric chemicals were chosen for this study: methyl methacrylate (MMA), hydroxyethylene methacrylate (HEMA), and ethylene glycol dimethacrylate (EGDMA). The effects of polymeric monomers and their combinations on moisture adsorption (M), anti–moisture adsorption efficiency (AME), liquid water uptake (D), water repellency efficiency (WRE), longitudinal, radial, tangential, and volumetric swelling properties (S) after soaking, and antiswelling efficiency (ASE) were investigated. It was found that M was different for different methacrylate combinations and depended not only on the composition of the impregnants, but also on wood properties. Liquid water uptake was similar regardless of the formulation of the WPC. Wood–polymer composites with high MMA content displayed enhanced dimensional stabilities, but WPCs with high HEMA content did not. Tangential and volumetric ASEs were strongly dependent on the type of treatment. Mold growth tests showed that wood treated with HEMA alone had no surface mold growth, and wood treated with MMA alone also showed less mold growth than did the control samples. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 5085–5094, 2006     

Preparation of soft wood–plastic composites

To extend the applications of wood–plastic composites (WPCs), soft WPCs were prepared with ethylene vinyl acetate (EVA) and wood flour (WF) as major components via a two‐step process involving two‐roll mixing and compression molding. The effect of the various factors, such as WF, unsaturated fatty acid (UFA), and dicumyl peroxide contents, on the mechanical properties, processability, and morphology of the WPCs was investigated in detail. The addition of UFA could effectively improve the processability and flexibility of the composites. The in situ grafting reaction between UFA and EVA considerably improved the adhesion of the WF and resin matrix. Consequently, soft WPCs with good performances in flexibility and processability were successfully obtained. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal and mechanical properties of wood‐plastic composites filled with multiwalled carbon nanotubes

Wood plastic composites (WPCs) are a new generation of green composites which can come mostly from recycled materials. This study focuses on the thermal conductivity and mechanical properties of WPCs filled multiwalled carbon nanotubes (MWCNTs). The thermal conductivity increases with increasing amount of MWCNTs and decreases with increasing temperature. By comparing the temperature changes of specimens during heating and cooling processes, WPCs with higher MWCNTs contents presents higher average temperature when heated until equilibrium temperature. From differential scanning calorimeter test, the melting temperatures of MWNTs reinforced WPCs change slightly, but the crystallinity is reduced with the increasing amount of MWCNTs. Based on a series of laboratory experiments carried out to investigate the mechanical performance, it can be concluded that the addition of the MWCNTs decreases the mechanical properties of WPCs due to the decohesion between thermoplastic matrix and MWCNTs particles under stress. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46308.     

FTIR characterization of tropical wood–polymer composites

Wood–polymer composites (WPC) of Geronggang (Cratoxylon arborescens), a light tropical hardwood, impregnated with methyl methacrylate (MMA), methyl methacrylate-co-acrylonitrile (1 : 1; MAN), and styrene-co-acrylonitrile (3 : 2; STAN), were prepared by in situ polymerization using gamma radiation or the catalyst–heat treatment. The FTIR spectra of the three types of WPC, with polymer loadings ranging from 10 to 70%, were compared with that of the wood itself and the respective polymers. Characteristic peaks due to C?O vibration of MMA, C?N stretching of acrylonitrile, and ring stretching and bending of styrene monomers, were prominent in the samples that had higher polymer loadings. For the copolymeric systems, quantitation of the FTIR spectra of these characteristic peaks enabled calculations of incorporated acrylonitrile and styrene monomers in the composites to be made. The FTIR spectra of the residues remaining, after exhaustive extraction to remove homopolymer, showed that graft copolymerization of wood components with acrylonitrile and styrene monomers was possible, but not with MMA. Composites prepared by the two methods, gamma radiation and the catalyst–heat treatment, were shown to be chemically very similar.     

Graft copolymers of lignin as hydrophobic agents for plastic (wood‐filled) composites

Poly[lignin‐g‐(1‐phenylethylene)] graft copolymers synthesized by free‐radical, graft copolymerization on lignin and verified by fractionation, infrared spectroscopy, and solubility change possess macromolecular surface activity as indicated by their capacity to form stable emulsions between incompatible fluid phases, to adhesively bond to wood surfaces, and to change the contact angle of water on coated wood. The surface activity of the copolymer changes with its composition. As the weight percent lignin in the copolymerization reaction product increases beyond 20 wt %, the amount of the emulsion phase formed in a water–benzene mixture decreases. Maple wood flour could be solvent‐coated with a copolymer and both coated and uncoated maple flour could be extruded through a stranding plate into a wood‐filled composite with polystyrene. Physical property tests show that composite control samples are about 3% stiffer and less deformable than are the copolymer composites when dry and about 5 or more percent more deformable than are the copolymer composites when wet, showing that the copolymer coating increased the wet strength. The copolymer samples are always denser than are the controls. Copolymer coating on wood filler decreases the swelling in the composite, the partial molar volume of the imbibed water, and the dimensional change in the solid. These effects cause increase in the density of the copolymer composite upon imbibition of water. Coating the wood component of the composite with a copolymer creates a hydrophobic barrier that produces a decrease in water imbibition into the composite, which will not disappear in 20 or more years of water immersion. Expansion in water is highly dependent on the direction of extrusion. The length expands about 1%, the width expands about five times as much, and the thickness expands over 10 times as much as does the length. This differential expansion may be due to the 22% reduction in the width and a 71% reduction in the thickness of the melt as it passes through the die and the alignment of the long axis of the fiber with the direction of flow through the die. The reaction product is a thermoplastic solid stable below 200°C and thermoformable at between 150 and 180°C. Products which contain between 10 and 50 wt % lignin are heterogeneous solids. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1266–1276, 2003     

Thermal properties of tropical wood–polymer composites

Wood–polymer composites (WPC) of Geronggang (GE; Cratoxylon arborescens), a light tropical hardwood, impregnated with methyl methacrylate (MMA), styrene-co-acrylonitrile (3: 2; STAN), methyl methacrylate-co-bis (2-chloroethyl) vinyl phosphonate (3 : 1; MVP) and methyl methacrylate-co-bis (chloropropyl)-2-propene phosphonate (3:1;MPP), were prepared by in situ polymerization using γ-radiation or catalyst-heat treatment. Thermal characterization of these WPC by limiting oxygen index measurements (LOI), thermogravimetry (TG), and differential scanning calorimetry (DSC) showed that the impregnants greatly modified the wood properties. The LOI values of the GE–MVP and GE–MPP composites were much higher than that for GE and the other composites, indicating the effectiveness of the phosphonates as flame retardants. Concomitantly, the flaming characteristics also compared favorably against that for GE and the other composites. The decomposition temperature and maximum rate of weight loss determined by TG for GE–MVP and GE–MPP were substantially reduced, whereas the char yields were greatly higher. These observations again indicate that phosphonates imparted flame-retarding properties to their composites. The thermal properties of GE–MMA and GE–STAN composites were not vastly different from that of untreated GE. Flame retardancy in the phosphonate-containing composites was effected through both the condensed- and gaseous-phase mechanisms due to the presence of phosphorus and chlorine, respectively. Indication of grafting of polymer to wood was found for GE–STAN, GE–MVP, and GE–MPP composites, but not for GE–MMA. Composites prepared by γ-radiation or by the catalyst-heat treatment had similar thermal characteristics.     

Dynamic mechanical analysis of tropical wood–polymer composites

Wood–polymer composites (WPC) of Geronggang (GE; Cratoxylon arborescens), a light tropical hardwood, impregnated with methyl methacrylate (MMA) and styrene-co-acrylonitrile (3 : 2; STAN), were prepared by in situ polymerization using γ radiation or catalystheat treatment. The dynamic flexural storage modulus, E′, for oven-dried GE, moist GE, and GE–MMA and GE–STAN composites decreased with increasing temperature. The percentage decreases for GE with 10 and 16.5% moisture contents were 74.5 and 98.2%, respectively, which were higher than those for GE and GE composites, which ranged between 40 and 50%. The impregnated polymers were not as effective as water in acting as plasticizers, due to their nonpolar nature and much higher molecular weights. The α-transition peaks for moist GE and GE composites were more distinct and were shifted to lower temperatures than those for oven-dried GE. The values ranged between 75 and 150°C for moist GE and between 102 and 170°C for the GE composites. The α-transitions of the catalyst–heat-treated GE composites were lower than that of the radiation-induced counterparts. GE–STAN composites were also observed to have lower α-transition temperatures than those for GE–MMA for the respective treatment process, which seems to suggest that STAN interacted to a greater extent with cell wall components than did MMA.     

Conducting polymer composites of zinc‐filled urea–formaldehyde

This article is concerned with the preparation and characterization of composite materials prepared by the compression molding of mixtures of zinc powder and urea–formaldehyde embedded in cellulose powder. The morphologies of the constituent, filler, and matrix were investigated by optical microscopy. The elaborated composites were characterized by density, which was compared with calculated values, and the porosity rate was deduced. Further, the hardness of samples remained almost constant with increasing metal concentration. The electrical conductivity of the composites was less than 10^?11 S/cm unless the metal content reached the percolation threshold at a volume fraction of 18.9%, beyond which the conductivity increased markedly, by as much as eight orders of magnitude. The obtained results interpreted well with the statistical percolation theory. The deduced critical parameters, such as the threshold of percolation, the critical exponent t, and the packing density coefficient were in good accord with earlier studies. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2011–2015, 2005     

Water vapor adsorption and volumetric swelling of melt‐impregnated wood–polymer composites

Wood–plastic composites were prepared through impregnation of solid wood with polyethylene. A resolution IV screening design of 16 runs for seven factors at two levels was adopted. The seven factors tested were ratio of maleated polyethylene in formulations, ratio of polyethylene of different molecular weights, four process factors (vacuum, pressure, time, and temperature), and wood species (red maple and aspen). Moisture adsorption content and volumetric changes as a function of time were investigated. This study also examined the effects of impregnation parameters and impregnants on water vapor adsorption and dimensional stability. The process parameters (pressure and temperature), polymer impregnants (polyethylene of different molecular weights), and wood species contributed significantly to the equilibrium moisture content (EMC), whereas the moisture adsorption rate was mainly affected by the polymer impregnants (polyethylene of different molecular weights). The EMC was inversely proportional to polymer retention. However, none of the variables significantly contributed to volumetric swelling; the volumetric swelling rate was mainly affected by wood species, the molecular weight of the polyethylene, and impregnation vacuum. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2668–2676, 2006     

A novel wood‐binding domain of a wood–plastic coupling agent: Development and characterization

Poly(N‐acryloyl dopamine) (PAD) was successfully synthesized through free‐radical homopolymerization of N‐acryloyl‐O,O′‐diphenylmethyldopamine and subsequent deprotection. The adhesive ability of PAD to wood was studied in detail. PAD underwent substantial oxidation and crosslinking reactions at about 80°C. Therefore, maple veneer samples bonded with PAD powder at a press temperature of 120°C had high shear strength and high water resistance. In contrast to conventional wood adhesives such as phenol‐formaldehyde and urea‐formaldehyde resins, PAD resulted in an increase, rather than a decrease, in the shear strengths of two‐ply laminated maple veneer test specimens that had undergone a water soaking and drying treatment. A mixture of PAD and polyethylenimine (PEI) resulted in much higher shear strength than PAD alone. To achieve high shear strength and high water resistance, the maple specimens bonded with PAD–PEI mixtures had to be cured above 150°C because reactions between PAD and PEI occurred at about 150°C. The water resistance of the maple specimens bonded with the PAD–PEI mixtures was dependent on the PAD:PEI weight ratio and the curing temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1078–1084, 2003     

Flame retarding effects of nanoclay on wood–fiber composites

This research article focuses on investigating the effects of nanoclay particles on the flame retarding characteristics of wood–fiber/plastic composites (WPC) using ASTM D635. The processing aspects of nanocomposites with WPC are presented. The processing techniques for controlling the degree of exfoliation and the cost aspect are also described. It turns out that the coupling agent used for wood–fibers is also effective for the exfoliation of clay, and therefore, no additional cost is required. This research indicates that the structure of nanocomposites (i.e., the degree of exfoliation) and the clay content used have a large impact on the flame retardancy of WPC. The flame retardancy is investigated as a function of these parameters. Based on this, a cost‐effective way to improve flame retardancy of WPC is presented. POLYM. ENG. SCI., 47:308–313, 2007. © 2007 Society of Plastics Engineers.     

High performance wood composites from highly filled polybenzoxazine

Highly filled systems prepared by compression molding of Hevea brasiliensis woodflour filled polybenzoxazine composites with high mechanical properties and reduced water uptake has been developed. The effects of percent filler content and particle size of woodflour on the obtained composite's properties were examined. The low melt viscosity of BA‐a type polybenzoxazine allows substantial amount of woodflour to be easily incorporated into the composites. The results showed that mechanical properties from dynamic mechanical analysis and flexural test at filler content below the optimum filler packing show approximately linear relationship with filler loading. The outstanding compatibility between the woodflour and the polybenzoxazine matrix is evidently seen from the large improvement in the composite's T_g and char yield. Scanning electron micrographs of the composite also reveals substantially strong interface between the woodflour filler and the polybenzoxazine matrix. Water absorption of the composites is greatly reduced with increasing the amount of polybenzoxazine due to the inherent low water absorption of the matrix. The polybenzoxazine is; therefore, a highly attractive candidate as high performance lignocellulosic binder or adhesive and other related applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1240–1253, 2006     

Friction and wear behavior of basalt‐fabric‐reinforced/solid‐lubricant‐filled phenolic composites

To improve the tribological properties of basalt‐fabric‐reinforced phenolic composites, solid lubricants of MoS₂ and graphite were incorporated, and the tribological properties of the resulting basalt‐fabric composites were investigated on a model ring‐on‐block test rig under dry sliding conditions. The effects of the filler content, load, and sliding time on the tribological behavior of the basalt‐fabric composites were systematically examined. The morphologies of the worn surfaces and transfer films formed on the counterpart steel rings were analyzed by means of scanning electron microscopy. The experimental results reveal that the incorporation of MoS₂ significantly decreased the friction coefficient, whereas the inclusion of graphite improved the wear resistance remarkably. The results also indicate that the filled basalt‐fabric composites seemed to be more suitable for friction materials serving under higher loads. The transfer films formed on the counterpart surfaces during the friction process made contributions to the reduction of the friction coefficient and wear rate of the basalt‐fabric composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dynamic crystallization of polypropylene and wood‐based composites

Thermoplastic composites made of an isotactic polypropylene (iPP) matrix and woodflour (WF) were prepared by melt‐blending, using twin‐screw extrusion and injection molding. Up to 20 wt % of the composite was composed of WF. The incorporation of an interfacial agent made of an ethylene/methacrylic acid copolymer to iPP and WF, PP/WF, binary blends causes a compatibilization effect that becomes evident due to a reduction in the crystallization temperature of PP. In both the binary composites and the compatibilized or ternary composites, the PP adopts an α or monoclinic structure when crystallization occurs from the melt under dynamic conditions at cooling rates between 1 and 20°C min^?1. On the other hand, X‐ray diffraction analysis using synchrotron radiation of the injection‐molded samples demonstrates the existence of a β or trigonal form in the binary as well as the ternary PP/WF composites. They reach k_β levels between 0.18 and 0.25, which can be interpreted as the co‐operation between a reduction of the crystallization rate and the shear effect induced during the injection. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6028–6036, 2006     

Characterization of highly filled wood flour–PVC composites: Morphological and thermal studies

Composites with polyvinyl chloride (PVC) as major matrix constituent, ethylene vinyl acetate (EVA) as polymeric plasticizer and wood flour (WF) and fly ash (FA) as filler were extruded. Morphology of the samples was studied using scanning electron microscopy (SEM). Morphological study indicated good dispersion of the constituents. Infrared spectroscopy (IR) indicates interaction between EVA and PVC and also between the polymeric matrix and WF. The effect of various constituents on glass transition temperature (T_g) was evaluated using differential scanning calorimetry. Addition of EVA decreased the T_g, whereas T_g was increased due to addition of WF and FA. Study indicated that reduction in T_g on addition of EVA was compensated by increase in T_g due to addition of WF. The contribution of FA to change in T_g was not significant. Resulting composites have T_g close to that of PVC. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Creep resistance of wood‐filled polystyrene/high‐density polyethylene blends

Creep, the deformation over time of a material under stress, is one characteristic of wood‐filled polymer composites that has resulted in poor performance in certain applications. This project was undertaken to investigate the advantages of blending a plastic of lower‐creep polystyrene (PS) with high‐density polyethylene (HDPE) at ratios of 100:0, 75:25, 50:50, 25:75, and 0:100. These various PS–HDPE blends were then melt blended with a short fiber‐length wood flour (WF). Extruded bars of each blend were examined to measure modulus of elasticity and ultimate stress. Increasing the ratio of WF increased modulus of elasticity in all composites, except between 30 and 40% WF, whereas the effect of WF on ultimate stress was variable, depending on the composite. Scanning electron microscopic images and thermal analysis indicated that the wood particles interacted with the PS phase, although the interactions were weak. Finally, creep speed was calculated by using a three‐point bending geometry with a load of 50% of the ultimate stress. Creep decreased only slightly with increasing WF content but more significantly with increasing PS content, except at pure PS. The WF/75PS–25HDPE blend showed the least creep. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 418–425, 2001