Studies on Polypropylene/Carbon Fiber Composite Foams by Nozzle-Based Microcellular Injection Molding System

Abstract

A continuous production of microcellular polypropylene (PP)/30% carbon fiber composite was achieved in a newly developed nozzle-based microcellular injection molding system. In this work, a conventional injection molding machine was retrofitted with a nitrogen (N2) gas injection system. A specially designed “injection cum mixing nozzle” was added between the machine barrel and a shut-off nozzle to form a polymer/gas mixture as against barrel injection where the screw and barrel are usually modified for gas insertion. The foamed plastic was formed due to the thermodynamic instability caused by sudden pressure drop in the mold. The effectiveness of foam molding system developed in this study was verified by change of process parameters resulting into variety of cell morphology and cell size. Further, PP/30% carbon fiber composite was injection molded into ASTM tensile test sample with both conventional and foam molding system. These samples were then subjected to scanning electron microscope (SEM) as well as tensile testing to study the effect of injection speed on the cell morphology and tensile properties of foam molded composites. It was observed that cell size decreased and cell density increased with increase in injection speed. The mechanical properties of the foamed composites depend largely on the processing conditions.