Modification of Polylactide/Poly(Methyl Methacrylate) Blend Properties by Reduction in Macromolecular Entanglements

Polylactide (PLA) having partially disentangled macromolecules was blended by extrusion with an equilibrium-entangled poly(methyl methacrylate) (PMMA). Partial disentanglement of PLA macromolecules was obtained by dissolving the polymer in methylene chloride, freezing the diluted solution, and removing the solvent. Blends with PLA macromolecules with three levels of entanglements, containing 10, 20 or 80% of PMMA, were characterized using rheological studies and by conducting non-isothermal and isothermal crystallization. Scanning electron microscopy showed that only a small fraction of PMMA did not disperse at the molecular level. The blends prepared using less entangled PLA had lower values of rheological moduli and viscosity, which confirmed the limited density of macromolecular entanglements in them. It was found that the crystallization of PLA in blends was controlled by two main factors: the disentanglement of PLA macromolecules, which promoted faster crystal formation, and the presence of PMMA macromolecules, which hindered the movement of PLA macromolecules to crystal growth sites, making crystallization more difficult. Spherulites grew in blends containing 0–20% PMMA. PMMA macromolecules were incorporated into their structure.