Flexural properties of fiber-reinforced polypropylene composites with and without a transcrystalline layer

The flexural properties of isotactic polypropylene (PP) matrix composites r einforced with 5-30 vol% of unidirectional pitch-based carbon, polyacryloni trile (PAN)-based carbon, e-glass or aramid Fibers were measured using both static and dynamic test methods. Previous research has shown that these pi tch-based carbon and aramid fibers are capable of densely nucleating PP cry stals at the fiber surface, leading to the growth of an oriented interphase termed a "transcrystalline layer" (TCL), while the e-glass and PAN-based c arbon fibers show no nucleating ability. The PP matrices examined included unmodified homopolymers, nucleated homopolymers and PP grafted with maleic anhydride (MA). The composites based on the unmodified PP homopolymers all exhibited poor fiber/matrix adhesion, regardless of fiber type and presence or absence of a TCL. The addition of nucleating agent to the PP matrix had no measurable effect on either the amount of TCL material in pitch-based c arbon-fiber-reinforced composites, as measured by wide-angle X-ray scatteri ng WAXS, or the static flexural properties of the composites reinforced wit h either type of carbon fiber. However, MA grafting reduced the transcrysta lline fi action of the matrix in pitch-based carbon-fiber-reinforced compos ites; at the highest level of MA grafting, the TCL was completely suppresse d. In addition, high levels of MA grafting improved the transverse Flexural modulus of the composites containing both types of carbon fibers, and redu ced the extent of fiber pull-out, indicating an improvement in fiber/matrix adhesion. Copyright (C) 1999 John Wiley & Sons, Ltd.