Non-Isothermal Cold-Crystallization Behavior and Kinetics of Poly(L-Lactic Acid)/WS2 Inorganic Nanotube Nanocomposites

In order to accelerate the crystallization of poly(l-lactic acid) (PLLA) biopolymer and enhance its crystallizability, biocompatible and environmentally friendly tungsten disulphide inorganic nanotubes (INT-WS2) were introduced into the polymer matrix. The non-isothermal cold-crystallization and subsequent melting behaviour of pure PLLA and PLLA/INT-WS2 nanocomposites were investigated in detail by varying both the heating rate and INT-WS2 loading. The kinetic parameters of the cold-crystallization process of PLLA chains under confined conditions, successfully described using Liu model, shows that the addition of INT-WS2 significantly increased the crystallization rate and reduced the total cold-crystallinity of PLLA, while the crystallization mechanism and crystal structure of PLLA remained unchanged in spite of the INT-WS2 loading. Similarly, the final crystallinity and melting behaviour of PLLA were controlled by both the incorporation INT-WS2 and variation of the heating rate. The differential isoconversional method of Friedman was applied to estimate the dependence of the effective activation energy on the relative crystallinity and temperature for PLLA and PLLA/INT-WS2. On the other hand, the double-melting peaks, mainly derived from melting-recrystallization-melting processes upon heating, and their dynamic behaviour is coherent with a remarkable nucleation-promoting effect of INT-WS2 involved in accelerating the cold-crystallization of PLLA. These observations have considerable practical significance for the future sustainable, economic and effective technological utilisation of PLLA, as it will enable the development of novel melt-processable biopolymer nanocomposite materials.