Research On Reinforced Polypropylene (PP) Structural Foam Extrusion

Foamed plastic is a kind of polymer/gas composites material which has outstanding performances. It is widely used in every walk of life for its excellent performance. Structural foam plastic belongs to foamed plastic and it has cortex without foam or less foam, which makes it not only has smooth surface but also has better mechanical properties than free foamed plastic. All that makes foamed plastic is used much widely.Structural foam extrusion appeared as early as 1960's and it was firstly used for polyvinyl chloride (PVC) novel imitation wood. At present, PVC structural foam extrusion technology is more mature. Other plastics structural foam extrusion is also got attention. Polypropylene (PP) structural foam extrusion is got more attention for its low density, excellent mechanical properties, nice degradation and recycling. However, PP foam process is difficult to control for its narrow temperature range and low melt strength.Reinforced PP structural foam extrusion was researched in this paper. An extruder die was designed especially for PP structural foam extrusion according to Celuka principle. The die had achieved structural foam and PP structural foam products were got. Reinforced PP structural foam products which had improved mechanical properties were got with modified PP by glass fiber. A lot of experiments were made using the die. Effects of formula and process parameters on reinforced PP structural foam extrusion were mainly researched through both macroscopic properties and microstructure.In this paper, better formula proportion was gained based on experiments using foaming agent and auxiliary foaming agent. Melt strength was improved, foam size was decreased and foam density was increased through blending modification with high melt strength polypropylene (HMSPP), low density polyethylene (LDPE) and ethylene propylene diene monomer (EPDM). Reinforced PP structural foam products were got adding modified PP by glass fiber to reinforce PP. Comparing with products without modified PP by glass fiber, as the increasing of modified PP by glass fiber content, the foam size increased and the foam density decreased, but the apparent density got lower and the mechanical properties improved significantly. Better products could be got with suitable die temperature and screw rotation speed.Based on the experiments, the optimal formulation was got with the contents of LDPE, EPDM, modified PP by glass fiber, foaming agent, auxiliary foaming agent, nucleating agent corresponding to 15 portions, 5 portions, 15 portions, 2.0 portions, 0.025 portions and 0.1 portions, respectively. The products with better macroscopic properties and microstructure could be got under the conditions of die temperature, screw rotation speed, die pressure corresponding to 160℃, 20rmin^-1 and 12.5MPa, respectively. Comparing with products without modified PP by glass fiber, tensile strength, impact strength and flexural modulus of the products were increased by 44.1%, 56.8% and 16.3%, respectively.The research results of the paper provide theory and experience for the industrial development of reinforced PP structural foam extrusion.