Isothermal crystallization and melting behaviors of bionanocomposites from poly(lactic acid) and TiO2 nanowires

Two representative poly(lactic acid) (PLA) nanocomposites with 1% TiO2 nanowires were prepared through in situ melt polycondensation and easy solution-mixing approaches, respectively. The former was denoted as ISPLANC, and the latter as SMPLANC. The isothermal crystallization kinetics and melting behaviors of pure PLA, ISPLANC, and SMPLANC were comparatively investigated by differential scanning calorimetry in the temperature range of 80-115 degrees C. Maximum crystallization growth rate (Gexp) was observed at 100 degrees C for all three samples. The well dispersed TiO2 nanowires acted as effective nucleation agents in ISPLANC, which exhibited much higher Gexp in compared to pure PLA and SMPLANC below 110 degrees C. However, much smaller crystallization enthalpy of ISPLANC was obtained because of its restricted chain mobility in forming crystalline lamellar. The crystallization behavior of all three samples fit the Avrami equation quite well, with most of the R2 values larger than 0.9990. Double-melting behaviors were observed after heating the samples after isothermal crystallization at various temperatures, which was explained by the melt recrystallization of the smaller and imperfect crystals formed at lower isothermal crystallization temperatures. We also obtained the equilibrium melting temperatures of the three samples by carrying out HoffmanWeeks plots. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012