Effect of wood species on the mechanical and thermal properties of wood–plastic composites

The effect of wood species on the mechanical and thermal properties of wood–plastic composites (WPCs) was explored. Various wood species, including cherry, sweet gum, hickory, yellow poplar, Osage orange, walnut, eastern red cedar, pine, maple, and red oak, were compounded with virgin isotactic polypropylene in a 50 : 50 weight ratio and injection‐molded. The tensile strength of WPCs made with cedar and hickory was higher than that of WPCs made with maple, oak, and Osage orange. The tensile modulus of WPCs made with gum and walnut was higher than that of oak WPCs. The tan δ peak temperatures and peak values from dynamic mechanical analysis indicated that pine and hickory WPCs had higher amorphous or void contents than walnut and cherry WPCs. The induction time during isothermal crystallization suggested that red cedar, cherry, and gum WPCs had higher nucleation density than walnut, pine, and oak WPCs. Dynamic mechanical properties of the WPCs appeared to be related to the crystallization behavior of the wood flour, which depends on the surface roughness. Although there were statistically significant differences in mechanical properties among the species, the differences were small, implying that wood flours from many species can be used successfully as raw materials for WPCs. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of compatibilizers on the physico‐mechanical and foaming properties of polyproylene/wood‐fiber composites

Polypropylene (PP)/wood‐fiber (WF) composites were prepared by intermeshing co‐rotating twin screw extruder, and microcellular closed cell PP/WF composite foams were prepared by using pressure‐quenched batch process method. The effect of various compatibilizers on the mechanical properties, morphology, crystallinity, rheological properties, and foamability of PP/WF composites were investigated. The results showed that PP/WF composite with addition of PP‐g‐MA as compatibilizer had the highest tensile strength, stiffness, and crystallinity, after foaming, it showed highest relative density and cell density, as well as the smallest cell size. Higher crystallinity of PP/WF composites, showed higher stiffness and higher relative density. J. VINYL ADDIT. TECHNOL., 19:250–257, 2013. © 2013 Society of Plastics Engineers     

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     

Polypropylene–wood fiber composites: Effect of treatment and mixing conditions on mechanical properties

Polypropylene/wood fiber composites were prepared at three different temperatures: 170°C, 180°C, and 190°C. The surface of wood fibers was modified through the use of silane coupling agents and/or coating with polypropylene or maleated polypropylene. The fiber coating was performed by propylene polymerization in the presence of wood fibers or by immersion in an o-dichlorobenzene polypropylene (or maleated polypropylene) solution. Tensile and three-point bending tests were performed in order to evaluate the adhesion between matrix and wood fibers. Evidence shows that 180°C is the best mixing temperature, while the use of vinyl-tris (2-methoxy ethoxy) silane with or without maleated polypropylene coating is the best surface treatment. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1227–1235, 1997     

Profile extrusion and mechanical properties of crosslinked wood–thermoplastic composites

Challenges for wood‐thermoplastic composites to be utilized in structural applications are to lower product weight and to improve the long‐term load performance. Silane crosslinking of the composites is one way to reduce the creep during long‐term loading and to improve the mechanical properties. In this study, silane crosslinked wood‐polyethylene composites were produced by reactive extrusion and subsequently manufactured into rectangular profiles. The silane crosslinked composites were stored in a sauna at 90 °C to increase the degree of crosslinking. The toughness of the silane crosslinked composites was significantly higher than for the non‐crosslinked composites. Improved adhesion between the wood and polyethylene phases is most likely the reason for the improved toughness of the crosslinked composites. There was no significant difference in flexural modulus between the crosslinked and non‐crosslinked composites. In addition, impact testing showed that the impact strength of the crosslinked composites was considerable higher (at least double) than the non‐crosslinked. The effect of temperature on the impact strength of the composites indicated slightly higher impact strength at −30 °C than at 0° and at 25 °C, and then an incrase in impact strength at 60 °C. Crosslinking also reduced the creep response during short‐term loading. Moreover, scanning electron microscopy on the fracture surface of the crosslinked composites revealed good adhesion between the polyethylene and wood phases. POLYM. COMPOS. 27:184–194, 2006. © 2006 Society of Plastics Engineers     

Effects of impact modifiers on the properties of rigid PVC/wood‐fiber composites

This study examined the effects of impact modifier types and addition levels on the mechanical properties of rigid PVC/wood‐fiber composites. The impact resistance of rigid PVC/wood‐fiber composites depends strongly on the type and content of impact modifier. With the proper choice of modifier type and concentration, the impact strength of rigid PVC/wood‐fiber composites can be significantly improved without degrading the tensile properties. Methacrylate‐butadiene‐styrene and all‐acrylic modifiers performed in a similar manner and were more effective and efficient in improving the impact resistance of rigid PVC/wood‐fiber composites than the chlorinated polyethylene modifier.     

Critical processing temperature in the manufacture of fine‐celled plastic/wood‐fiber composite foams

The main benefits of incorporating wood fibers (WF) in plastics are the increased stiffness and lowered cost of the resulting composites. However, these improvements are usually accompanied by a reduction in the ductility and impact resistance. These shortcomings can be removed by effectively foaming and incorporating a fine‐celled structure in these composites. The volatiles released from WF during processing are known to deteriorate the cell structure. The maximum processing temperature, which affects the amount of volatiles released by the WF during extrusion of fine‐celled plastic/WF composite, affects the cell morphology. This study was undertaken to identify the critical temperature above which the cellular structure of WF composite foams is significantly deteriorated. To clearly identify the effects of the volatiles generated from WF on the cellular morphology, neither a chemical blowing agent nor a physical blowing agent was used in the foam processing. The experimental results show that regardless of the drying method, the highest processing temperature of plastic/WF composites should be minimized, preferably below 170°C, to avoid the adverse effects of the volatiles generated from the WF during processing. A method of estimating the emissions from WF during extrusion processing by using the TGA data is also proposed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 621–629, 2004     

Thermal and mechanical properties of polypropylene/wood‐flour composites

In this research, polypropylene/wood‐flour composites (WPCs) were blended with different contents of wood and/or maleated polypropylene (MAPP) and clay. We found that the addition of MAPP or clay in the formulation greatly improved the dispersion of the wood fibers in the composite; this suggested that MAPP or clay may have played the role of an adhesion promoter in the WPCs. The results obtained with clay indicate that it also acted as a flame retardant. The thermal tests carried out with the produced samples showed an increased crystallization temperature (T_c), crystallinity, and melting temperature (T_m) with wood loading. The increase of the two former parameters was explained by the incorporation of wood flour, which played the role of nucleating agent and induced the crystallization of the matrix polymer. On the other hand, the T_m increase was ascribed to the insulating properties of wood, which hindered the movement of heat conduction. The effects of UV irradiation on T_m and T_c were also examined. T_c increased with UV exposure time; this implied that UV degradation generated short chains with low molecular weight that could move easily in the bulk of the sample and, thus, catalyze early crystallization. The flexural strength and modulus increased with increasing wood‐flour content. In contrast, the impact strength and tensile strength and strain decreased with increasing wood‐flour content. All of these changes were related to the level of dispersion of the wood flour in the polymeric matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Effects of copper amine treatment on mechanical properties of PVC/wood‐flour composites

Copper amine–treated wood flour was added to PVC [poly(vinyl chloride)] matrix in order to manufacture PVC/wood‐flour composites. Effects of copper treatments on the mechanical properties of PVC‐wood composites were evaluated. Unnotched impact strength, flexural strength, and flexural toughness of the composites were significantly improved by the wood‐flour copper treatment. The optimum copper concentration range was 0.2 to 0.6 wt% of wood flour. Fractured surfaces were examined by using scanning electron microscopy (SEM) combined with energy‐dispersive spectroscopy (EDS). PVC/wood interfacial debonding was the main fracture mode of untreated wood‐flour composites, whereas wood‐particle pullout and breakage dominating the fractured surfaces of copper‐treated wood‐flour composites. On the fractured surfaces, more PVC could be found on the exposed copper‐treated wood particles than on untreated wood, a result suggesting improved PVC‐wood interfacial adhesion after copper treatments. J. Vinyl Addit. Technol. 10:70–78, 2004. © 2004 Society of Plastics Engineers.     

Impact of melt impregnation on the color of wood–plastic composites

The aesthetics of wood–plastic composites (WPCs) can affect the acceptance of the products by consumers. This study was aimed at providing a better understanding of how impregnation variables affect color changes, thereby allowing for the development of an optimal process for WPCs. The effects of impregnation parameters and impregnants on the WPC color were investigated in this study via a screening design. Sixteen runs of resolution IV design for seven factors at two levels were conducted. The seven factors were the ratio of maleated polyethylene in the formulations, the ratio of polyethylenes with different molecular weights, four process factors (vacuum, pressure, time, and temperature), and wood species (red maple and aspen). The studied color parameters included the lightness change, chroma change, hue angle change, saturation change, and total color change. All treatments darkened the wood and increased the chroma values and the saturation. Even though all treatments had an impact on the hue angle, the changes were very small. The wood species, impregnants, impregnation time, and temperature played significant roles in the color change and chroma coordinates. However, no parameter dominated the hue angle change and saturation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2149–2157, 2006     

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.     

Effect of fiber length on processing and properties of extruded wood‐fiber/HDPE composites

Fiber length and distribution play important roles in the processing and mechanical performance of fiber‐based products such as paper and fiberboard. In the case of wood–plastic composites (WPC), the production of WPC with long fibers has been neglected, because they are difficult to handle with current production equipment. This study provides a better understanding of the effect of fiber length on WPC processing and properties. The objectives of this study were therefore to determine the role of fiber length in the formation process and property development of WPC. Three chemithermomechanical pulps (CTMP) with different lengths, distributions, and length‐to‐diameter ratios (L/D) were obtained by mechanical refining. Length, shape, and distribution were characterized using a fiber quality analyzer (FQA). The rheometer torque properties of high‐density polyethylene (HDPE) filled with the pulps at different loads were studied. Variations in fiber load and length distribution resulted in significant variations in melting properties and torque characteristics. Composites from the three length distributions were successfully processed using extrusion. Physical and mechanical properties of the obtained composites varied with both length distribution and additive type. Mechanical properties increased with increasing fiber length, whereas performance in water immersion tests decreased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

PANI/PP复合纤维对沥青混凝土力学性能的影响

以聚苯胺/聚丙烯(PANI/PP)复合纤维为导电相材料,采用非连续密级配制备了PANI/PP复合导电纤维沥青混凝土,采用马歇尔试验法对沥青混凝土的力学性能进行了测试。结果表明:随着PANI/PP复合纤维掺量的增加,PANI/PP复合导电纤维沥青混凝土的稳定度、流值、空隙率均有增大趋势,复合纤维的质量掺量为0.8%时,沥青混凝土稳定度可增加近50%,流值增加100%。复合纤维的质量掺量为0.2%~0.8%时,纤维在沥青混凝土中分散均匀性好。     

Effect of fiber pretreatment condition on the interfacial strength and mechanical properties of wood fiber/PP composites

The effect of fiber surface pretreatment on the interfacial strength and mechanical properties of wood fiber/polypropylene (WF/PP) composites are investigated. The results demonstrate that fiber surface conditions significantly influence the fiber–matrix interfacial bond, which, in turn, determines the mechanical properties of the composites. The WF/PP composite containing fibers pretreated with an acid–silane aqueous solution exhibits the highest tensile properties among the materials studied. This observation is a direct result of the strong interfacial bond caused by the acid/water condition used in the fiber pretreatment. Evidence from coupling chemistry, rheological and electron microscopic studies support the above conclusion. When SEBS‐g‐MA copolymer is used, a synergistic toughening effect between the wood fiber and the copolymer is observed. The V‐notch Charpy impact strength of the WF/PP/SEBS‐g‐MA composite is substantially higher than that of the WF/PP composite. The synergistic toughening mechanisms are discussed with respect to the interfacial bond strength, fiber‐matrix debonding, and matrix plastic deformation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1000–1010, 2000     

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.     

Effects of a new compatibilizer system on the flexural properties of wood–polyethylene composites

A novel wood–plastic compatibilizer system containing a paper wet‐strength agent as a wood‐binding domain and stearic anhydride as a polyethylene (PE) binding domain was investigated. Treatment of wood flour with a commercial paper wet‐strength agent Kymene® 557H (simply called Kymene) before the mixing of PE and the wood flour increased the modulus of rupture (MOR) and the modulus of elasticity (MOE) of the resulting wood–PE composites. Addition of stearic acid in the mixing of PE and the wood–Kymene mixture further increased the MOR and MOE. Stearic anhydride was even more effective than stearic acid in the increase of the MOR and MOE. Compared to wood–PE composites without a compatibilizer, the stearic anhydride–Kymene compatibilizer system increased the MOR by about 33% and the MOE by about 40%. The stearic anhydride–Kymene compatibilizer system gave a slightly lower MOR, but higher MOE than those of the commercially used compatibilizer (maleic anhydride‐grafted polypropylene). The compatibilization mechanisms were proposed as follows: Kymene not only bound to wood fibers, but also strengthened and stiffened the wood fibers. Stearic anhydride formed covalent linkages such as ester and amide with the Kymene‐consolidated wood fibers and the long hydrocarbon chain of the stearic anhydride bonded to the PE matrix through entanglements and/or cocrystallization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3667–3672, 2004     

Processing/structure/property relationships for artificial wood made from stretched PP/wood‐fiber composites

This article presents the processing/structure/property relationships for artificial wood made from stretched PP/wood‐fiber (WF) composites that have required strength and density. The die drawing of PP/WF composites causes a unidirectional orientation of the polymer molecules and enhances the mechanical properties significantly along the stretched direction. The drawing of the composites also lowers the density of artificial wood by generating voids at the WF and polymer matrix interface. The critical processing and materials parameters are identified. The effects of these parameters on the structure and the properties are also investigated. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers