Research On Injection Foaming Molding Of Polypropylene (PP)/Wood-Flour Composite

Foaming wood-plastic composite (WPC) is not only possessing of lower density and cost than general WPC, but also better properties of soundproofing and heat insulation. At present, main products of domestic WPC are extrusion foaming wood-plastic composite, which is special-shaped with low added value and surface quality, and functional products with complex shape are few. Injection foaming wood-plastic composite has figured out the problem that the shape of existing WPC can not meet the actual demand and extended its application field. Moreover, the appearance and texture of new products is not only exactly like wood but also with high lustrousness and accurate apparent size. Injection foaming wood-plastic composite has both economical benefit and social effect, because of its further saving energy, and reducing production costs and raising productivity.In this study, the samples of composites were prepared with polypropylene (PP) and wood-flour operating on ordinary injection molding machine by chemical foaming method. On the basis of modified AC and determined the mark of PP, effects of formula and processing parameter on appearance, performance density, microstructure and mechanical properties of the samples had been studied.The main conclusions are below:(1) PP/wood-flour complex system melt is pseudoplastic fluid. The MFR of PP/wood-flour complex system is closely tied to the matrix resin, and decrease with the increase of wood-flour content.Temperature, wood content and matrix resin have great effect on apparent viscosity of complex system, and higher or lower viscosity has an unfavorable impact on cellular structure.(2) Formula plays an important role on properties of sample. The results show that when the content of AC are 1.2 shares, the foaming effect of sample is the best; The results also show that PP-g-MAH can significantly improve the interfacial compatibility between wood-flour and PP, and improve flowability,mechanical properties and foaming effect, the better content of PP-g-MAH are 9～12 shares. Plasticizer EPDM make a big contribution to impact strength of improving. Excessive adding of wood-flour lead to decreasing of mechanical properties, cell number and melt flow rate of sample, increasing of performance density, the optimum content of wood-flour are 30-40 shares.(3) Effects of injection technological parameter on apparent quality and cellular structure of sample are obvious. Sample with better cellular structure can be obtained in injection pressure 100MPa; Lower injection speed leads to filling few melt into molding chamber; Excessive barrel temperature leads to decreasing of melt viscosity and cell number, and increasing observably of average diameter of cell. The best barrel temperature is 170～180℃. Mold temperature had great influence on surface quality, lower mold temperature leads to flowing mark on the surface of sample in filling process. Smooth surface and single color can be obtained when mold temperature was 70～80℃.