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°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 T c < 110°C and T c ≥ 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 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.