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Wood fiber/poly(lactic acid) composites with 70 wt% wood fiber were prepared using a super mixing-hot press method. The biodegradability of composite panels made with one unmodified and three types of modified poly(lactic acid) was evaluated by comparing the mechanical strength, molecular weight, thermal properties and microstructures of composite wood fiber/poly(lactic acid) and 100% poly(lactic acid) panels before and after burial in soil. We found that wood fiber/poly(lactic acid) composites degraded more readily than 100% poly(lactic acid) panels during burial. The type of poly(lactic acid) used in wood fiber/poly(lactic acid) composites affected biodegradability. The flexural strength and modulus of wood fiber/poly(lactic acid) panels decreased sharply after burial in soil for 6 months. The molecular weight of poly(lactic acid) in wood fiber/poly(lactic acid) composites decreased more rapidly than 100% poly(lactic acid) panels that had been buried in soil for 6 months. Changes were observed in both the amorphous and crystalline structure of specimens buried in soil. The wood fiber/poly(lactic acid) composites prepared with unmodified poly(lactic acid) have better mechanical properties and degraded more easily during burial than did composites made with modified poly(lactic acid). [ABSTRACT FROM AUTHOR]

The efficiency of two coupling agents in wood-polymer composites was investigated in this study. Thermal behavior of neat polypropylene, wood flour/polypropylene composite, maleated anhydride polypropylene-reinforced wood-polymer composite, and oxidized polypropylene-reinforced wood-polymer composite was investigated by means of differential scanning calorimetry and scanning electron microscopy in order to obtain information on the dispersion of the wood flour in the polymeric matrix, on the crystallization kinetics of polypropylene, and the macrostructure of its composites. The results confirm the expected nucleant effect of wood with and without the coupling agents used. The wide angle X-ray diffraction patterns indicated enhanced compatibility between polypropylene and wood with the addition of coupling agent. As a coupling agent, maleated anhydride polypropylene had a better performance in wood-polymer composites than polypropylene oxide and neat polypropylene because of its stronger interfacial bonding. Coupling agents help overcome the polarity disparity increase. All the results showed that with maleated anhydride polypropylene, oxidized polypropylene or without any coupling agent, wood flour acted as nucleating agent and increased the crystallization rate of polypropylene. For the composites, wood with maleated anhydride polypropylene was a more effective nucleating agent for polypropylene than wood with oxidized polypropylene. The mechanical properties were evaluated and the samples with coupling agent showed superior results like tensile and flexural properties. [ABSTRACT FROM AUTHOR]

Nanomer and Cloisite are the popular commercial nanoclays (NC) available in the market. The mechanical properties of wood—plastic composite (WPC) based on linear low density polyethylene with or without wood fiber are compared for different added nanoclays. In addition, the moisture uptakes at 23°C and 45% RH and water uptake/loss after immersion in water are evaluated. I.34TCN type nanoclay as well as Cloisite Na+ lead to composites with superior mechanical properties and better water resistance behaviors compared to the other kinds of nanoclays. It should be noted that the discoloration occurs in WPC reinforced with unmodified NC. [ABSTRACT FROM AUTHOR]

Wood fiber-reinforced recycled plastic composites (WRPCs) manufactured from sawdust and post-consumer high density polyethylene (HDPE) were studied in this article. The thermal, flexural properties and impact strength of the manufactured WRPCs were determined according to the relevant standard specifications. Effects of mix ratio, wood fiber length, type, and content of coupling agent on the mechanical properties of WRPCs were investigated. The fracture surfaces of WRPCs after impact test were examined and the fracture mechanism of WRPCs due to impact was also analyzed in this article. The results indicated that incorporation of wood fibers resulted in higher melting and slower crystallization rate of WRPCs. A linear relationship between cooling rate and crystallization rate was observed. With the increasing of the wood fiber weight fraction, the flexural strength of WRPCs increases. The longer the wood fiber length, the less the flexural strength of WRPCs under the conditions of this study. The Charpy impact strength decreases with the increasing of wood fibers content in WRPCs. It appears that the optimum compatibilizer content for wood and recycled HDPE mixing is 5% in weight fraction. [ABSTRACT FROM AUTHOR]

Wood fiber reinforced polylactide is a biodegradable composite where both fibers and matrix are from renewable resources. In the development of such new materials, information on mechanical behavior on the macroscopic and the molecular level is useful. In this study, dynamic Fourier transform infrared (FT-IR) spectroscopy is used to measure losses at the molecular level during cyclic tensile loading for bonds that are characteristic of the cellulosic fibers and the polylactid matrix. This molecular behavior is compared with measured macroscopic hysteresis losses for different moisture levels. The results show that moisture ingress will transfer the load from the fibers to the matrix, and that a more efficient fiber-matrix interface would diminish mechanical losses. Although the dynamic FT-IR spectroscopy method is still qualitative, this investigation shows that it can provide information on the stress transfer of the constituents in wood fiber reinforced plastics. [ABSTRACT FROM AUTHOR]

The effect of wood fiber anisotropy and their geometrical features on wood fiber composite stiffness is analyzed. An analytical model for an N-phase composite with orthotropic properties of constituents is developed and used. This model is a straightforward generalization of Hashin's concentric cylinder assembly model and Christensen's generalized self-consistent approach. It was found that most macro-properties are governed by only one property of the cell wall which is very important in attempts to back-calculate the fiber properties. The role of lumen (whether it filled by resin or not) has a very large effect on the composite shear properties. It is shown that several of the unknown anisotropic constants characterizing wood fiber are not affecting the stiffness significantly and rough assumptions regarding their value would suffice. The errors introduced by application of the Hashin's model and neglecting the orthotropic nature of the material behavior in cylindrical axes are evaluated. The effect of geometrical deviations from circular cross-section, representing, for example, collapsed fibers, is analyzed using the finite element method (FEM) and the observed trends are discussed. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) and wood fiber (WF) composites (PP/WF) were compatibilized by maleic anhydride grafted Styrene-Ethylene-Butylene-Styrene (MAH-g-SEBS). The blending was performed on a twin-screw extrusion, followed by an injection molding. The torque rheology, dynamic mechanical analysis (DMA), thermal analysis (DSC), mechanical properties, as well as the morphology of the composites, were investigated and discussed. Rheology and DMA results showed that MAH-g-SEBS is an effective compatibilizer for PP/WF composites. Increased torque implied that the composites probably have a great frictional shear force, resulting from strong adhesion at the interface between the matrix and the dispersion phase. The mechanical test indicated that the tensile strength, tensile elongation and the flexural strength of the composites were improved with the increase of the content of MAH-g-SEBS; property enhancement is attributed to improved wetting and interactions between the PP matrix and WF, which is supported by scanning electron microscopy (SEM) analysis. [ABSTRACT FROM AUTHOR]