Optimization Of Extrusion Molding Process Of Wood Flour/Polyolefin Composites

The extrusion molding technology of wood plastic composite is the combination and innovation of the traditional extrusion technology, formed technological process suit the features of WPC best. In extrusion manufacturing technology, formula and extrusion process are two of the most important elements. In this paper, we optimized the related formula and extrusion process of WPC.In this paper, we researched the effects of die temperatures on the appearance and mechanical properties of wood flour/HDPE (WF/HDPE), wood flour/PP (WF/PP), wood flour/PP/HDPE (WF/PP/HDPE) composites. The results indicated that, the surface color of three WPCs enhanced with the increasing of die temperature, contrast with WF/HDPE presented optimal performance when the die temperature was165℃, only when the die temperature was higher than165℃can WF/PP and WF/PP/HDPE composite get smooth stable extrusion. Combining the mechanical strength and appearance of the composites, the optimum die temperature of WF/HDPE was160～170℃, and the optimum die temperature of WF/PP and WF/PP/HDPE was170～175℃. Through X-ray diffraction (XRD) analysis, the intensity of the characteristic diffraction peaks and degree of crystallinity of three WPCs decreased in different degree with the die temperature increasing.Through the early exploration experiments, we found that the extrusion of WF/PP composite is difficult. Therefore, we consider the formula first, and optimize the formulations of WF/PP composites. We analyzes the effects of wood flour, lubricant, talcum powder with different content on the extrusion condition and mechanical property of WPCs according to orthogonal table, and integral balance method is used to select the most appropriate component proportion. Results showed that, wood flour content is the most significant factor which influenced the properties of composites; too much lubricant will decrease the bending strength. Multi-index integral balance method was used to determine the optimal formula which was wood flour (60wt%), lubricants (3wt%), talcum powder (5wt). Through scanning electron microscopy (SEM) analysis, the best interface bonding was obtained with the sixth group, which was the same with the result of wood flour content and talcum powder content through integral balance method.In order to reduce costs to the maximum extent, we consider added talcum powder as much as possible in WF/PP composites, and analyzed the effect of different talcum powder content on the density, water absorption and mechanical properties of the composites, and determine the most appropriate amount of talcum powder. Research indicated that when talcum powder was more than20wt%its influence to WPC began to significantly, the surface quality of the products becomes poor and the surface cracks increase gradually with the talcum powder content increased. With the talcum powder content increased, the density of the composites increased, water adsorption decreased gradually, while thickness swelling rate increase first and then decrease on the whole, and when talcum powder content was40wt%thickness swelling rate researched the minimum. Add talcum powder will significantly increase the modulus of elasticity of the composites, but has a negative influence on the impact strength and tensile strength, while the bend strength reached the maximum when the talcum powder content was1Owt%.