Influence of Extrusion Temperature on Molecular Architecture and Crystallization Behavior of Peroxide-Induced Slightly Crosslinked Poly(L-lactide) by Reactive Extrusion

The influence of temperature during reactive extrusion of poly(L-lactide) (PLLA) on the molecular architecture and crystallization behavior was investigated for OO-(t-butyl) O-(2-ethylhexyl) peroxycarbonate-modified polymer. The long chain-branched PLLA (LCB-PLLA) content and its structure in the resulting slightly crosslinked PLLA (chi-PLLA) containing linear and LCB-PLLA were characterized by both analyses, size exclusion chromatography equipped with multiangle laser light scattering and rheological measurements. A reduction of LCB-PLLA content in chi-PLLA and an increase of number of branches in LCB-PLLA were found with increasing the extrusion temperature. An increase of extrusion temperature induces different process in the polymer: decrease of the lifetime of peroxide, increase of the radical concentration due to rapid peroxide decomposition rate, and increase of the chain diffusion to the amorphous phase. Among these indices, the lifetime of peroxide is a good index for crosslinking behavior of PLLA during extrusion. As for the isothermal crystallization behavior from the melt, the Avrami crystallization rate constant of chi-PLLA increases as an increase of LCB-PLLA content in chi-PLLA. This implies that LCB-PLLA acts as a nucleating agent for PLLA. Furthermore, regime analysis and the free energy of nucleus of chi-PLLA were investigated using Hoffman-Lauritzen theory. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1468-1478, 2012