Crystallization Behavior of Poly(l-lactic acid) Nanocomposites:  Nucleation and Growth Probed by Infrared Spectroscopy

Time-lapsed Fourier transform infrared (FTIR) spectroscopy was employed to probe chain conformational changes during the isothermal crystallization of poly(l-lactic acid), PLLA, and its nanocomposites from the melt. To study the effect of clay exfoliation extent on the crystallization behavior of PLLA, intercalated and exfoliated nanocomposites were fabricated by solution casting two commercially available organoclays with different degrees of matrix miscibility. By solely varying the degree of miscibility between the organic modifier and the polymer matrix, fully intercalated and exfoliated nanocomposites were obtained. This system allowed us to systematically investigate the effect of degree of clay exfoliation on the chain conformational changes during the crystallization process. In the case of neat PLLA, interchain interactions preceded intrachain interactions during the crystallization. Conversely, the exfoliated nanocomposites exhibited an opposite behavior in that 103 helix formation and backbone reorientation were followed by the interchain interactions. These results explain the nonnucleating behavior of highly miscible and exfoliated nanocomposites reported in our previous contribution.