Date of Award

Spring 2013

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering - (M.S.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

Costas G. Gogos

Second Advisor

N. M. Ravindra

Third Advisor

Ken Keunhyuk Ahn

Fourth Advisor

Nicolas Ioannidis

Abstract

Poly (lactic acid) (PLA) is a biodegradable polymer with good renewability and processability. However, it has some drawbacks. The Poly (lactic acid) (PLA) stereocomplex formed via the interaction between optical isomers Poly (L-lactic acid) (PLLA) and Poly (D-lactic acid) (PDLA), provides improvements on PLA thermomechanical properties. To investigate the nucleating effect brought by the PLA stereocomplex, samples of PLLA blended with different content of PDLA are prepared by the solution casting method. With different cooling rates (5, 15, 25 °C/min), DSC non-isothermal crystallization experiments are performed. The results suggest that in the presence of the stereocomplex, the PLLA crystallization temperatures are found to be higher than that of pure PLLA. By annealing PLLA at different temperatures with the existence of the stereocomplex, the crystallization process is significantly expedited. Using hot stage polarized microscope, the increasing number of spherulites observed at higher temperature, confirms the enhancement on PLLA nucleation brought by the stereocomplex. Yet, the irregular morphology of crystallites may indicate that the stereocomplex does not promote higher degree of crystallinity. Finally, the saturated nucleating effect is due to the unfavorably high molecular weights of PLLA and PDLA.

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