Temperature dependent variations in the lamellar structure of poly( l-lactide)

Time- and temperature-dependent SAXS and WAXS experiments on poly( l-lactide) were used (i) to establish the relationships between the crystallization temperature, the crystal thickness and the melting point, (ii) to follow recrystallization processes during heating, and (iii) to detect perturbations of the crystalline order. The studies showed several peculiarities: (i) although no solid state thickening occurs during a crystallization, crystal thicknesses are with values between 11 and 20 nm very large (ii) crystal thicknesses and long spacings have a minimum at 120 °C and increase for both higher and lower crystallization temperatures. The anomalous behavior at low crystallization temperatures is to be related with a disordering of the crystal lattice (iii) there exists an extended temperature range where crystal thicknesses change in controlled manner by recrystallization processes (iv) as it appears, a triple point where the fluid, the crystalline and a mesomorphic phase coexist is located near to normal pressure and a temperature of 190 °C.