Growth and dissolution of crystal nuclei in poly(l-lactic acid) (PLLA) in Tammann's development method

By fast scanning calorimetry (FSC), the influence of the transfer of nuclei from the nucleation stage at low temperature to the growth stage at higher temperature was systematically studied. Heating rates above 1000 K s(-1) are sufficient to prevent growth of crystal nuclei at the transfer from 60 degrees C to 125 degrees C in Poly(L-lactic acid) (PLLA). The critical heating rate for preventing nuclei growth is about 1000 times higher than the critical heating rate to prevent crystal growth in a nucleated sample on heating. In a second experiment, the cluster size distribution after isothermal nucleation of PLLA at 60 degrees C for 1000 s was estimated. In the temperature interval from 125 degrees C to 145 degrees C, the density of critical nuclei decreases from the initial value similar to 4 x 10(24) M-3 to zero, as nuclei with R > 2 nm, the critical radius for 145 degrees C, were not formed at the nucleation temperature.