Crystallization kinetics of poly (L-lactic acid)/montmorillonite nanocomposites under isothermal crystallization condition

Poly(L-lactic acid)/o-MMT nanocomposites, incorporating various amounts of organically modified montmorillonite (o-MMT; 010 wt %), were prepared by solution intercalation. The montmorillonite (MMT) was organically modified with dilauryl dimethyl ammonium bromide (DDAB) by ion exchange. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that the o-MMT was exfoliated in a poly(L-lactic acid), (PLLA) matrix. A series of the test specimens were prepared and subjected to isothermal crystallization at various temperatures (T1T5). The DSC plots revealed that the PLLA/o-MMT nanocomposites that were prepared under nonisothermal conditions exhibited an obvious crystallization peak and recrystallization, but neat PLLA exhibited neither. The PLLA/o-MMT nanocomposites (210 wt %) yielded two endothermic peaks only under isothermal conditions at low temperature (T1), and the intensity of Tm2 (the higher melting point) was proportional to the o-MMT content (at around 171 degrees C). The melting point of the test samples increased with the isothermal crystallization temperature. In the Avrami equation, the constant of the crystallization rate (k) was inversely proportional to the isothermal crystallization temperature and increased with the o-MMT content, especially at low temperature (T1). The Avrami exponent (n) of the PLLA/o-MMT nanocomposites (410 wt %) was 2.613.56 higher than that of neat PLLA, 2.102.56, revealing that crystallization occurred in three dimensions. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012