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 (Tcs), especially in the range of 100-120°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°C is a critical temperature for PLLA crystallization. At Tc < 110°C and Tc >= 110°C, the α' and α crystals were mainly produced, respectively. Besides, the structural feature of the α'-form was illustrated, and it was found that the α'-form has the larger unit cell dimension than that of the α-form. Moreover, the crystallization kinetics of the α' and α crystals are different, resulting in the discontinuousness of the curves of spherulite radius growth rate (G) versus Tc and the half time in the melt-crystallization (t₁/₂) versus Tc investigated by Polarized optical microscope and Differential scanning calorimetry, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008