PROCESSING CHARACTERISTICS OF THERMOPLASTIC SHEET COMPOSITES

While there are several alternatives for producing thermoplastic sheet composites, only two have the characteristics needed for large scale manufacturing; continuous melt impregnation, and deposition of a polymer-impregnated, fiber-dispersed mat from an aqueous slurry. The most important factor affecting the melt impregnation process was found to be the rate of penetration of the molten polymer into the fiber structure. While Darcy's Law, using the Kozeny-Carmen permeation coefficient, provides an initial estimate of penetration rate, it does not adequately consider the slow flow around closely spaced fibers. The slurry deposition process incorporates the polymer directly within the fiber structure, and is not flow rate limited. The most important parameter affecting the consolidation of slurry formed mats was found to be the rate of heat transfer prior to consolidation. In both processes the time of contact between the molten polymer and glass fiber was shown to be important to the development of good adhesion.