THE OCCURRENCE OF TRANSCRYSTALLIZATION OR ROW-NUCLEATED CYLINDRITIC CRYSTALLIZATION AS A RESULT OF SHEARING IN A GLASS-FIBER-REINFORCED POLYPROPYLENE

The formation and build-up of transcrystalline-like superstructures produced by pulling a glass fiber (GF) from an isothermal crystallizing (T(c) = 130-140-degrees-C) isotactic polypropylene (iPP) melt has been studied by thermo-optical methods. It was found that these morphological structures are caused by row-nucleation (self-nucleation), and that they should therefore be termed cylindrites instead of transcrystalline layers. The build-up of the cylindrites depends on whether the pulling and crystallization temperatures (T(pull) and T(c), respectively) are above or below the upper threshold temperature of the possible beta crystallization (T(betaalpha)). The thermal stability and beta nucleation ability of the primary alpha row-nuclei at T(pull) = T(c) < T(betaalpha) depend on their molecular orientation, caused by the shear stress field accommodated during pulling. In addition, the thermal stability of the row-nuclei is also affected by T(pull). It is suggested that the observed alpha-beta bifurcation at T(pull) = T(c) < T(betaalpha), which is the main argument for cylindritic crystallization, may be related to epitaxial growth.