Enhanced crystallization rate and morphological behavior of PLA containing composites

Polylactide (PLA) is a biodegradable, biocompatible polyester derived from annually renewable resources (e.g., corn). These desirable attributes make it an attractive material for use in both the biomedical field and commodity applications. This thesis addresses two deficiencies inherent to PLA, a relatively slow crystallization rate and the brittle nature of the parent material under impact and tensile testing.; We set out to toughen PLA through the controlled incorporation of a rubbery hydrocarbon component (i.e., polyisoprene (PI) or poly(ethylene-alt-propylene) (PEP)). PLA-rubber (A-B) diblocks were considered, as were the simple two component (A/A-B) blends of PLA and PLA-rubber diblocks. The synthetic protocols utilized to attain model PEP-PLA and PI-PLA diblock copolymers through a combination of living anionic (PI or PEP) and controlled ring-opening polymerization (PLA) techniques were described.; The fundamental morphological behavior of well-defined PEP-PLA diblock copolymers was presented through the construction of a detailed experimental morphology diagram based on a set of model diblocks containing a full range of PLA volume fractions (f_PLA = 0.08–0.91). This study was intended to serve as a benchmark for the morphological behavior of PLA containing diblock copolymers. This morphology behavior was extended to include binary A/A-B blends containing low concentrations (1–12 wt%) of slightly asymmetric PEP-PLA or PI-PLA diblock copolymer in excess PLA homopolymer. These blends formed spherical micelles of the minority phase (i.e., PI or PEP) suspended in the PLA matrix and were characterized by small-angle x-ray scattering (SAXS) and transmission electron microscopy (TEM). The effect of temperature on the corresponding morphological behavior was also examined.; Enhanced crystallization rates in isotactic poly(L-lactide) (PLLA) were attained through an increase in nucleation density using enantiomeric poly(D-lactide) (PDLA)/PLLA blends containing low concentrations of PDLA. Through controlled thermal processing, 1:1 (PLLA:PDLA) stereocomplex crystallites were formed and subsequently functioned as nucleation sites for the crystallization of the excess PLLA homopolymer. The stereocomplex crystallites were found to have a marked influence on the overall crystallization rate and subsequent morphology of the excess PLLA.