Enhancing melt strength and crystallization kinetics in polylactide: Influence of chain topology

The generation of long-chain branches (LCB) in biobased and biodegradable polylactide (PLA) by adding different amounts of a chain extender is studied. The rheological and calorimetric behavior have been used to determine the effect of LCB presence and their topology on PLA melt strength and crystallization behavior. Rheological modeling of linear and non-linear viscoelastic shear and extensional properties identified several possible branched structures. Moreover, remarkable differences were observed for the different topologies regarding the intrinsic non-linear parameters and the intra-cycle elastic and viscous non-linearities. Differential scanning calorimetry and polarized light optical microscopy measurements revealed a significant increase in the nucleation density and rate of PLA with increasing the amount of LCB, albeit they provoke a decrease in the growth rate due to a reduction in chain diffusion. Nevertheless, overall crystallization rate values revealed a predominant effect of nucleation over crystal growth. The introduction of LCB within the chains is highly beneficial as they increase nucleation, crystallinity, and elongational viscosity, thus improving the properties of biodegradable PLA.