Injection Molding Process

The reduction in fiber length during injection molding of two commercial glass-fiber reinforced polypropylene (PP) granules was studied. The first containing 20 percent by weight (wt%) of short-glass-fibers with the average fiber length around 350 
μm and the other filled with 40 wt% of relatively much longer fibers mostly around 7,000 μm. The fiber length distribution (FLD) was measured along the screw channels and after the molten composite was injected through a nozzle of an injection unit. The results indicated that the FLD moved to shorter fiber lengths along the screw channels further from the hopper. In both cases, fiber attrition occurred
predominately in the feed and the compression zones, particularly in long-glass-fiber reinforced polypropylene. More severe fiber attrition in this finding can be assumed due to higher fiber concentration and longer fiber length which result in a higher degree of fiber-fiber interaction and increased fiber-wall contacts.