Processing of short-fiber reinforced polypropylene. I. Influence of processing conditions on the morphology of extruded filaments

An experimental investigation of the processing of glass fiber reinforced polypropylene is presented. Final fiber orientation distribution, fiber distribution in filament sections, rheological properties, final fiber length distribution and surface morphology were analyzed. This analysis was done taking into account the quantity of fibers and their interactions and now conditions. The final fiber orientation increased when shear rate increased and fiber concentration decreased. Moreover, inhomogeneities in fiber distribution increased as the concentration of fibers decreased. The density profile showed a significant variation with fiber concentration, but it was not dependent on the shear rate applied. The viscosity showed a linear dependence with shear rate. The average fiber length and the breadth of this distribution decreased with the increasing fiber concentration and extrusion rate. The extruded filament surface showed minor roughness when the shear rate increased or when the fiber concentration decreased. The results of this experimental characterization give useful information to determine the influence of the processing variables on the final properties of short-fiber reinforced polypropylene and constitutes the first part of a more ambitious project that also includes the development of a modeling strategy of the processing behavior for short-fiber composites.