Crystallization and thermal properties of melt-drawn PCL/PLA microfibrillar composites

Microfibrillar composites (MFC) are advanced systems with reinforcement formed in situ by melt or cold drawing of suitable polymer blends. In the case of biodegradable poly (ɛ-caprolactone)/poly (lactic acid) (PCL/PLA) system, formation of microfibrillar structure by melt drawing is only possible by modification of the polymer components by clay. The effect of clay is quite complex; this study is focused on the effect of in situ formed fibrillar structure of PLA and clay in MFC with the PCL matrix on crystallinity and glass transition of both polymer components. The DSC analysis shows that clay addition to neat PCL, its blending with PLA, and addition of clay to the PCL/PLA blend increase PCL crystallinity. Clay addition and blending with PCL dramatically increase crystallinity of originally almost amorphous PLA. The non-isothermal PCL crystallization kinetics evaluated by the new recently proposed method reveals pronounced nucleation effect of clay addition and blending on PCL crystallization. An indication has been found of a negative correlation between maximum crystallization rate of PCL and its crystallinity. The glass transition temperature Tg of both components evaluated by DMA in the undrawn system mostly decreases with clay addition and increases with drawing. These effects are more significant for PLA due to its fibrillar structure. Tg is affected by the mixing protocol, as a result of different course of clay migration between components and localization, especially in the interfacial area.