The Influence of Yarn Structure and Processing Conditions on the Laminate Quality of Stampformed Carbon and Thermoplastic Polymer Fiber Commingled Yarns

Abstract

Laminates with unidirectional (UD) fiber orientation of three different commingled yarns, comprising poly(amide-12) and poly(butylene-terephthalate) fibers blended with stretch broken carbon fibers (CF), were produced at different processing conditions. The achieved laminate quality was evaluated by means of void content measurement, mechanical testing along and transverse to the fiber direction, and optical microscopy. It was found that - under the investigated processing conditions - the cooling/consolidation time is not sufficiently long to obtain laminates with satisfactorily low void content, unless a commingled yarn with exceptionally intimate blending quality is employed. Incomplete fiber impregnation resulted in a drastic decrease of transverse tensile strength as compared with values obtained for compression-molded reference laminates. Stamp forming of carbon and poly(butylene-terephthalate) fiber commingled yarn with extraordinary degree of commingling delivered laminates with as low void contents as 1% at some processing conditions, but fiber-matrix adhesion was not satisfactory. Nevertheless, the presented carbon and poly(butylene-terephthalate) fiber commingled yarn offers great potential to be successively processed by stamp forming, as the interfacial adhesion problem is expected to be solved by using optimized fiber sizing.

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