Rheology and fiber degradation during shear flow of carbon-fiber-reinforced polypropylenes

The processing of fiber-reinforced thermoplastics is often accompanied by a significant fiber fracture. Therefore, it is important to assess the effect of processing variables on the extent of fiber damage occurring during product fabrication, such as extrusion or injection molding. The present paper discusses fiber damage caused by shear forces exerted on the composite by a molten matrix in both experimental and theoretical terms. The degradation process in carbon fiber-polypropylene composites is studied in a broad range of shear rates, although it occurs significantly only under high shearing in a capillary. Changes in fiber length and its distribution during the multi-flow through a capillary, as well as the materials’ rheological properties found in research after shearing, are discussed and the results are compared with a model of fiber-length analysis for the mixing-regrinding process. Published in Russian in Vysokomolekulyamye Soedineniya, Ser. A, 2006, Vol. 48, No. 9, pp. 1628–1639. The text was submitted by the authors in English.