Abstract:
This work demonstrates that, despite the existence of a significant number of works on PLA
crystallization, there is still a relatively simple way, different from those already described, in which
its complex kinetics can be observed. The X-ray diffraction (XRD) results presented here confirm
that the PLLA under study crystallizes mostly in the and 0 forms. An interesting observation
is that at any temperature in the studied range of the patterns, the X-ray reflections stabilize with
a given shape and at a given angle, different for each temperature. That means that both and
0 forms coexist and are stable at the same temperatures so that the shape of each pattern results
from both structures. However, the patterns obtained at each temperature are different because the
predominance of one crystal form over the other depends on temperature. Thus, a two-component
kinetic model is proposed to account for both crystal forms. The method involves the deconvolution
of the exothermic DSC peaks using two logistic derivative functions. The existence of the rigid
amorphous fraction (RAF) in addition to the two crystal forms increases the complexity of the whole
crystallization process. However, the results presented here show that a two-component kinetic
model can reproduce the overall crystallization process fairly well over a broad range of temperatures.
The method used here for PLLA may be useful for describing the isothermal crystallization processes
of other polymers.
