Characterization of carbon fiber surfaces and their impact on the mechanical properties of short carbon fiber reinforced polypropylene composites

The aim of this paper is to evaluate the influence of carbon fibers (CF) surface properties and the amount of a coupling agent on the mechanical properties of injection molded CF reinforced polypropylene (PP) composites. Five types of CF, three sized, a de-sized and a de-sized and afterwards plasma-treated type, were characterized by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. All fiber types were mixed with PP and various amounts of maleic anhydride grafted PP as coupling agent. Subsequently, all compounds were injection molded and characterized by measurement of flexural/tensile strength and modulus, notched/unnotched impact resistance, heat deflection temperature and fiber length. In addition fracture surfaces were analyzed by means of scanning electron microscopy (SEM). Both, contact angle measurements and XPS, showed, in good agreement, key differences in surface properties between the five CF samples. Mechanical testing and SEM images of fracture surfaces proved that fiber surface properties and the amount of coupling agent have major impacts on fiber/matrix interaction, hence on mechanical composite performance. (C) 2015 Elsevier Ltd. All rights reserved.