The Effect of WS Nanosheets on the Non-Isothermal Cold- and Melt-Crystallization Kinetics of Poly(l-lactic acid) Nanocomposites.

In the present work, hybrid nanocomposite materials were obtained by a solution blending of poly(l-lactic acid) (PLLA) and layered transition-metal dichalcogenides (TMDCs) based on tungsten disulfide nanosheets (2D-WS) as a filler, varying its content between 0 and 1 wt%. The non-isothermal cold- and melt-crystallization and melting behavior of PLLA/2D-WS were investigated. The overall crystallization rate, final crystallinity, and subsequent melting behavior of PLLA were controlled by both the incorporation of 2D-WS and variation of the cooling/heating rates. In particular, the analysis of the cold-crystallization behavior of the PLLA matrix showed that the crystallization rate of PLLA was reduced after nanosheet incorporation. Unexpectedly for polymer nanocomposites, a drastic change from retardation to promotion of crystallization was observed with increasing the nanosheet content, while the melt-crystallization mechanism of PLLA remained unchanged. On the other hand, the double-melting peaks, mainly derived from melting-recrystallization-melting processes upon heating, and their dynamic behavior were coherent with the effect of 2D-WS involved in the crystallization of PLLA. Therefore, the results of the present study offer a new perspective for the potential of PLLA/hybrid nanocomposites in targeted applications.