DIRECT EVIDENCE OF ROW-NUCLEATED CYLINDRITIC CRYSTALLIZATION IN GLASS FIBER-REINFORCED POLYPROPYLENE COMPOSITES

The development and nature of the transcystalline-like superstructure produced by pulling the glass fiber (GF) from the isothermal crystallizing (T(c)almost-equal-to 135-degrees-C) isotactic polypropylene (PP) melt was studied thermooptically. In the vicinity of the pulled GF alpha row-nuclei form which induce selective beta-nucleation resulting in beta-cylindrites.The presence of alpha row-nuclei was evidenced by selective melting of the beta-phase having lower melting temperature than the alpha. Because of the above change in the crystal modification this phenomenon can not be termed by transcrystallinity. The thermal stability and beta-nucleation ability of the primary alpha row-nuclei depend both on the applied shear stress (i.e. molecular orientation) and pulling temperature (T(pull)) under the testing conditions: T(alphabeta) < T(c) < T(betaalpha) and T(alphabeta) < T(pull) < > T(betaalpha), where T(alphabeta) and T(betaalpha) are the lower and upper threshold temperature of the beta-formation, respectively. It was suggested that the observed alphabeta-bifurcation may be related with epitaxial growth.