Crystallization Behavior of Poly(L-lactic acid)/Montmorillonite Nanocomposites

In this study, we modified montmorillonite (MMT) with dilauryl dimethyl ammonium bromide (DDAB) and then exfoliated the structures in a poly(L-lactic acid) (PLLA) matrix. We used polar optical microscopy and X-ray diffraction (XRD) to examine the morphologies of the resulting composites, differential scanning calorimetry to study the melting and crystallization behavior, and Fourier transform infrared (FTIR) and Raman spectroscopy to measure the influence of the intermolecular interactions between PLLA and MMT on the isothermal crystallization temperature. We found that the DDAB-modified MMT was distributed uniformly in the PLLA matrix. At temperatures ranging from 130 to 140 degrees C, the crystalline morphology resembled smaller Maltese cross-patterned crystallites; at temperatures from 150 to 170 degrees C, however, the number of crystallites decreased, their sizes increased, and they possessed ringed spherulite structures. In the XRD spectra, the intensity of the diffraction peaks of the 200/110 and 203 facets of the PLLA/MMT nanocomposites decreased as the crystallization temperature increased. In the FTIR spectra, the absorption peak of the C = O groups split into two signals at 1748 and 1755 cm(-1) when the isothermal crystallization temperature was higher than 140 degrees C. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 434-442, 2010