Research Of Preparation And Properties Of Composites Of Wheat Straw And Thermoplastics

The study mainly use the wheat straw powder and thermoplastic plastics as the raw material, to manufacture the bio-composite of straw powder and HDPE/PP by the two-step extrusion process. With the helping of one-way analysis of variance and quadratic orthogonal rotation analysis, this paper studied the effect of different processes on composite and tested the physical and mechanical properties of composite materials; observed the state of interface between wheat powder and plastic in the composite and evaluated the integral performance on composite. The main research content is as follows:The bio-composites were produced through extruding the hybrids that made by blending wheat straw powder with two thermoplastics:high density polyethylene and polypropylene, respectively. By using the method of single-factor experiment, mechanical properties (bending strength tensile strength and impact strength) of composites were tested and analyzed based on the GB standard of China. The mechanical properties of the two kinds of composite were significantly influenced by content of straw powder. With the increasing of content of wheat straw powder in a certain range, bending strength and tensile strength increased and impact strength decreased; compared the wheat straw powder/HDPE composite to wheat straw powder/PP composite, the performance has very minor differences.The wheat straw powder/HDPE composite was made by wheat straw powder and high density polyethylene (HDPE). By using of quadratic orthogonal rotation analysis, we studied the effect of three factors which have significant effect on composite material performance, such as content of coupling agent, speed of rotation, percentage of wheat straw powder on mechanical properties of composite and built a quantified mathematical model through optimizing the mechanical strength of the composite.Composites experienced in water to measure the hygroscopic expansion of composites for3months. Effects of content of coupling agent, speed of rotation and wheat straw powder on the hygroscopic expansion of composites were studied. Influence rules were as follows: content of wheat straw powder>content of coupling agent>speed of rotation. In the different directions, composites have significant differences on water absorption rate:thickness> width> length (extrusion direction). Through scanning electron microscope, the change of interfacial morphology of the composite was observed and concluded that:the phenomenon of crack and fiber (pulled out of matrix) were found on the interface of composite which indicated their (powder and plastic) compatibility became weak after water absorption.