Real-time SAXS measurements and rheological behavior of poly(lactic acid) crystallization under continuous shear flow

This work incorporates comprehensive real-time SAXS measurements, optical microscopy and rheometry to investigate the polymer crystallization process under continuous shear flow. The use of rheometry and optical microscopy offered a clear division of stages in the crystallization under continuous shear. The combination of three investigative tools revealed that cylindrical ordered structures, including shish-kebab and cylindrically stacked lamellae could form, survive and grow under flow as long as a critical rate was exceeded. Time at the emergence of cylindrical structure was shortened as the shear rate increased and the relation between the time and the flow strength could be described by Arrhenius equation. Lamellae in crystallites which formed under shear enjoyed a longer period and higher thickness than those stemming from quiescent crystallization. The period and thickness were found to be independent of shear life and shear strength, implying that the nucleus determined the size of epitaxially grown lamellae. Weak continuous shear flow was favorable to the degree of crystallinity, while strong shear flow could reduce the crystallinity.