The effect of MAPE as compatibilizer on mechanical and morphological properties of a wheat straw/high density polyethylene composite was investigated. Tensile strength, tensile modulus, tensile energy absorption, failure strain, and notched Izod toughness were much higher for composites with compatibilizer as compared with the composites with no compatibilizer. The use of 2% compatibilizer improved the tensile strength as high as 43%, tensile modulus to 116% and impact strength (notched) by 12%. Remarkably improvements were attained even with 1% compatibilizer. There was little difference in the properties obtained between the 1% and 2% compatibilizer. SEM micrographs of tensile fracture surfaces with 2% compatibilizer indicated a continuous failure and the particles are not released from the matrix which is the case in samples without compatibilizer.

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As the major component of WPCs, wood flour species plays an important role on the properties of the resulting composites. The effect of wood species as filler and reinforcement and MAPE as compatibilizer on mechanical properties of wood flour/high-density polyethylene composite was investigated. The wood species used in this study were loblolly pine and hybrid Euro-American poplar. The mechanical properties such as tensile properties and notched impact toughness were tested. Poplar flour provides an improvement in tensile strength, tensile modulus, tensile energy absorption, and failure strain over pine. Tensile strength of both the composites was much higher for compatibilized composites as compared with uncompatibilized ones. For the pine composites, tensile modulus improvements were attained even with 1% compatibilizer. There was little difference in the properties obtained between the 1% and 2% compatibilizer. For the poplar composites, adding 1% compatibilizer did not have significant effect on tensile modulus and there was a significant drop in tensile modulus with further 2% increase in the compatibilizer. Wood species and compatibilizer percent did not have significant effect on the notched Izod toughness.

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The effect of strain rate on flexural modulus (MOE), and flexural strength (MOR) was studied in a wood flour/high density polyethylene composite. Testing was performed in a three-point bending mode. Four different strain rates were used: 0.01, 0.02, 0.05, and 0.08 (min-1). The variations of flexural strength and flexural modulus were explained equally well by a linear relationship to strain rate. It was found that the mechanical properties of this material are significantly sensitive to strain rate. Based on statistical analysis, it was inferred that the flexural modulus was strain rate dependent and the sensitivity of MOE was more than that of MOR to strain rate. Relationships between flexural modulus, flexural strength, and strain rate allowing for the adjustment of these properties at different strain rates were also developed.

Flat-pressed composites using linear low-density polyethylene (LLDPE) and rapeseed waste were made by hot pressing. This study investigated the effects of filler loading on the flexural and physical properties of rapeseed-filled thermoplastic polymer composite panels. The modulus of elasticity and flexural strength were mainly influenced by the filler content. The flexural strength was shown to decrease significantly with an increase in the filler content, while the flexural modulus increased insignificantly. With the increase of the filler content, the water absorption and the thickness swelling were increased significantly due to the strong hydrophilicity of lignocellulosic filler. Water absorption was proved to follow the kinetics of a Fickian diffusion process. The swelling model presented by Shi and Gardner [(2006). Hygroscopic Thickness Swelling Rate of Compression Molded Wood Fiberboard and Wood Fiber/polymer Composites, Composite Part A Applied Science and Manufacturing, 37(9): 1276-1285] provided a very good prediction of the hygroscopic swelling process of rapeseed/LLDPE composite panels.

The tensile and thermal properties of chemimechanical pulp/high-density polyethylene composites made using virgin high-density polyethylene as the matrix polymer, chemimechanical pulp as reinforcing fiber, and maleic anhydride grafted polyethylene as compatibilizing agent were examined by assessing the tensile properties and thermogravimetric analysis. The results indicated that 2% compatibilized composites and uncompatibilized composites exhibited the highest and the lowest tensile strength values, respectively, while the tensile modulus is partially independent of compatibilizing agent. Using maleic anhydride grafted polyethylene increases composites’ failure strain and tensile energy absorption as well. Based on the TGA analysis during the manufacturing of the composites, blending and injection temperatures should be less than 230°C to prevent the chemimechanical pulp from decomposition.

Short-term flexural creep and stress relaxation tests were conducted on a wood plastic composite containing 30% high density polyethylene (HDPE), 67% fir wood flour, 2% compatibilizer (MAPE), and 1% lubricant. In creep tests, applied stress levels ranged from 30 to 60% of measured flexural strength. The principle of time-stress superposition was applied to form a master curve extending for a maximum of 4 years. The horizontal shift factors conformed to an Arrhenius type equation. Stress relaxation tests were also carried out at strain levels ranging from 30 to 60% of the ultimate strain. The principle of time-strain superposition was applied to form a stress relaxation master curve that extended for 67 days. The horizontal shift factors also conformed to an Arrhenius type equation. The resulting master curves were compared with extrapolated creep and stress relaxation models. To determine whether time-stress superposition is valid for the studied composite material, creep shift factors were applied to stress relaxation data and vice versa. In both creep and stress relaxation tests, it was found that the application of superposition was verified. The results indicated that the studied composite material was rheologically simple, and a single horizontal shifting on time axis was adequate to predict the long term performance of the material.