Effect of crystallization temperature on crystal modifications and crystallization kinetics of poly(L-lactide)

The crystalline structure of poly(L-lactide) (PLLA) have been found to quite depend on the crystallization temperatures (T(c)s), especially in the range of 100-120 degrees C, which is usually used as the crystallization temperature for the industrial process of PLLA. The analysis of wide-angle X-ray diffraction and Fourier transformed infrared spectroscopy revealed that 110 degrees C is a critical temperature for PLLA crystallization. At T-c < 110 degrees C and T-c >= 110 degrees C, the alpha' and alpha crystals were mainly produced, respectively. Besides, the structural feature of the alpha'-form was illustrated, and it was found that the alpha'-form has the larger unit cell dimension than that of the a-form. Moreover, the crystallization kinetics of the alpha' and alpha crystals are different, resulting in the discontinuousness of the curves of spherulite radius growth rate (G) versus T-c and the half time in the melt-crystallization (t(1/2)) versus T-c investigated by Polarized optical microscope and Differential scanning calorimetry, respectively. (C) 2007 Wiley Periodicals, Inc.