Mechanical And Thermal Expansion Properties Of The Core-shell Structure Wood Plastic Composites

Mechanical/thermal expansion coefficients of co-extruded wood plastic composite(core-shell) or WPC were investigated in this paper. The filler involved talc,glass fiber, PrecipitatedCaCO3, pine fiber, bamboo flour. The effect of individual and combined filler on mechanical and thermal performance of the filled HDPE composites was studied to develop a suitable shell system for co-extruded wood plastic composites (core-shell) and mechanical/thermal expansion behavior of WPC. The model provides a way to optimize raw material composition for minimize thermal expansion behavior of co-extruded WPC(core-shell).The following conclusions can be drawn from the study.(1) The use of silane-modified short GFs had a much larger effect in improving mechanical properties and in reducing LCTE values of filled composites compared with the use of un-modified talc particles due to enhanced bonding to the matrix, larger aspect ratio and fiber alignment for GFs. Mechanical properties and LCTE values of composites with combined talc and GF fillers varied with talc and GF ratio at a given total filler loading level. The use of a larger portion of GFs in the mix can lead to better composite performance, while the use of talc can help lower the composite costs and increase its recyclability. The use of30wt%combined filler seems necessary to control LCTE values of filled HDPE in the data value range generally reported for commercial wood plastic composites. Tensile modulus for talc-filled composite can be predicted with role of mixture, while a PPA-based model can be used to predict the modulus and strength of SGF-filled composites.(2)Coextruded wood plastic composite(core-shell) with glass-fiber (GF) filled shells were manufactured and their mechanical/thermal expansion coefficients were evaluated. The use of GF-filled shell enhanced overall composite modulus and strength, and at the same time, lowered composite linear coefficient of thermal expansion (LCTE). The imbalance of shell and core LCTE and moduli led to complex stress field within the composite system. Three-dimensional finite element model based on linear isotropic material for both shell and core was developed to predict LCTE of the material. The model predicted a trend which is in general agreement with the experimental data. The model provides a way to optimize raw material composition for minimize thermal expansion of WPC. For coextruded wood plastic composite(core-shell)with talc filled shell system, flexural properties of composite increased with the increase of talc content. LTEC of the co-extruded wood plastic composite decreased with decrease of the LTEC for the shell. (3) Thermal expansion of the composites decreased with increased PCC and bamboo filler loading levels. The composite system with RBFs had smaller LCTE values than those from systems with GBPs. The use of silane treatment on bamboo fiber/particle surface helped with their bonding to the plastic matrix, leading to further reduction of LCTE values for both GBP and RBF systems. The observed behavior of reduced LCTE is attributed to a small filler LCTE value, reduced over-plastic volume, and enhanced interfacial bonding with treated materials. Thus, hybrid bamboo and PCC fillers are suitable materials for controlling the thermal expansion of the composite materials caused by temperature changes.(4) The flexural and thermal expansion properties of composites was investigated. The flexural strength and modulus of composites was higher than that of pure PE, which were increased with increasing fiber content. As the filler loading increased, the thermal expansion of composites slightly decreased, The modifier content showed better influences on the longitudinal LTEC than that of tangential; Without addition of modifiers, tensile strength of composites was lower than virgin HDPE. Tensile modulus is not sensitive to content of coupling agent.LTEC change of various composites was primarily caused by the matrix and filler content; Low impact strength is the major drawback of WPC in many end-use applications. The impact strength'change of composites is caused by coupling agents. The different matrix and ratio of modifier content showed different influences on the various Linear thermal expansion coefficients of composites in three temperature zone, the reduction of the LTEC appear in HDPE/Pine composites was not dependent on coupling agent. Therefore, LTEC change of various composites was primarily caused by the matrix and filler. When the PA, SEBS of bamboo flour filled to the matrix, the LTEC was reduced.SEBS-G-MA as couple agent can reduced the LTEC of the BF/PA/HDPE composite, but LTEC of composites was primarily caused by the bamboo flour...