Preparation, Characterization And Property Study Of Foamed Composites Of Polypropylene And Wood Flour

The foamed wood polymer composite is developed base on the wood polymer composite, with lower density, better surface quality and less cost of the products. In the general purpose plastics, polypropylene (PP) has some excellent properties such as the lowest density and excellent mechanical property. However, there are few researches on PP as a polymer in the foamed wood polymer composite, because of the crystallinity, low melt strength, narrow window of the foaming operation temperature, and difficulty of processing parameter control of the polymer.The preparation and property study of foamed composites of polypropylene and wood flour was explored in this paper. PP matrix resin was filled with wood flour (under 80 mesh), with titanate as coupling agent or maleic anhydride grafting polypropylene (MAH-g-PP) as compatibilizing agent in order to improve interface compatibility between PP and wood flour phases, azodicarbonamide (AC) as blowing agent, nano-ZnO as blowing promoter, and dicumyl peroxide (DCP) as crosslinking agent to enhance melt strength of PP resin. All the materials were mixed well on the twin-roll mill mixer at certain temperature for a certain period of time. Then the mixture was put on the compression molding machine to be foamed at temperature of 175℃and then at 190℃for 30 minutes under pressure of 10MPa. After 24 hours in room temperature, the samples were cut into standard shape for mechanical property tests and fractography.Effects of wood flour, modification agents, blowing agent and crosslinking promoter on mechanical properties, density and water absorption of the foamed wood flour/PP composite and the fractography were discussed. The main conclusions were listed as follows: (1) The specific tensile strength, specific impact resistance, and density of the composites were reduced with the addition of the wood flour, and the water absorption was raised. When the wood flour content increased from 10 parts to 50 parts, the tensile property, impact property, and density of the foamed composites were reduced slowly, and the water absorption was raised at the same time. Compared with unfoamed wood polymer composite, the specific tensile strength and density of foamed composite were depressed and the specific impact resistance and water absorption were enhanced a little. For composite with 30 parts of wood flour, the specific tensile strength was got down by 30%, the specific impact resistance was enhanced by 20%, and the density was lowered by 25%. (2) The titanate coupling agent and MAH-g-PP compatibilizing agent can improve interface compatibility between PP and wood flour phases. Their effects were not at the direct ratio to additive content, but there were optimal values for different agents. The tensile property and impact property were raised, and the density and the water absorption were reduced first and then raised with addition of more titanate coupling agent or MAH-g-PP compatibilizing agent. (3) The specific tensile strength and specific impact resistance of the foamed composites were increased all the while with addition of more blowing agent within this experimental sight, the density was decreased and the water absorption was raised all along with more blowing agent was added. The best blowing agent AC content was 1.5 parts. (4) There is a best ratio between crosslinking agent and crosslinking promoter, and the content also have the most suitable value.