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Interfacial studies in fiber-reinforced thermoplastic-matrix composites
Abstract
The major theme of this dissertation is structure/property relationships in fiber-reinforced thermoplastic-matrix composites. Effort has been focused on the interface: interfacial crystallization and fiber/matrix adhesion. Included are investigations on interfacial nucleation and morphology, measurement of fiber/matrix adhesion, effects of interfacial adsorption and crystallization on fiber/matrix adhesion, and composites reinforced with thermotropic liquid crystal copolyester fibers. Crystallization of a copolyester and poly(butylene terephthalate) with glass, carbon, or aramid fibers has been studied with regard to interfacial mophology. Techniques employed included hot-stage optical microscopy and differential scanning calorimetry. Nucleation by the fibers was found to be a general phenomenon. Morphology could be varied by changing the cooling rate. In order to better monitor fiber/matrix adhesion, a buckled plate test has been developed. The test measures transverse toughness as the parameter characterizing interfacial adhesion in unidirectional, continuous-fiber composites. The test is simple to perform yet has advantages over other interfacial evaluation techniques. The buckled plate test was found to be a sensitive measure of fiber/matrix adhesion. The buckled plate test has been used along with the transverse tensile test to examine how interfacial adsorption and crystallization affect fiber/matrix adhesion in polycarbonate/carbon fiber composites. Adsorption was found to be of primary importance in developing adhesion, while crystallization is a secondary effect. The toughness data have been fit successfully for annealing time and temperature dependence. The dependence of adsorption and transverse toughness on matrix molecular weight was found to be large, with higher molecular weights adsorbing more effectively. Studies of the fiber/matrix interface have been extended to composites reinforced with thermotropic liquid crystal copolyester fibers. Composites made with these fibers had poor transverse properties, regardless of matrix. Surface treatment such as ozonation increased transverse properties, but values were still low. Scanning electron micrographs of fracture surfaces indicated that fiber splitting occurs, especially for surface treated fibers. Poor fiber transverse properties rather than fiber/matrix adhesion thus appear to limit composite transverse properties.
Subject Area
Materials science
Recommended Citation
Brady, Richard L, "Interfacial studies in fiber-reinforced thermoplastic-matrix composites" (1989). Doctoral Dissertations Available from Proquest. AAI9001485.
https://scholarworks.umass.edu/dissertations/AAI9001485