Effect of the Cooling Rate on the Nucleation Kinetics of Poly(L-Lactic Acid) and Its Influence on Morphology

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• 作者：Manuel Salmer&oacute ; n Sá ; nchez ; Vincent B. F. Mathot ; Geert Vanden Poel ; José ; Luis G&oacute ; mez Ribelles
• 刊名：Macromolecules
• 出版年：2007
• 出版时间：October 30, 2007
• 年：2007
• 卷：40
• 期：22
• 页码：7989 - 7997
• 全文大小：354K
• 年卷期：v.40,no.22(October 30, 2007)
• ISSN：1520-5835

文摘

Although the crystallization kinetics of PLLA is slow enough to allow one to obtain amorphoussamples by cooling from the melt at moderate rates, surprisingly, at the same time, the formation of crystallizationnuclei is difficult to avoid. Their amount depends on the cooling rate from the melt: the higher the cooling rate,the lower the amount of available nuclei after reaching the glass state. Cooling at controlled rates of 5-300C/min was performed by making use of a relatively new high-speed calorimetry technology, high-performanceDSC (HPer DSC). Subsequent isothermal cold crystallization of amorphous PLLA, at different temperaturesdistributed across the bell-shaped crystal growth curve, was shown to depend on the rate at which the glass statewas attained, reflecting the number of nuclei formed. However, (only) after complete cold crystallization, theDSC heating curves and the resulting morphology measured by optical microscopy and AFM were shown to beindependent of the previous cooling rate into the glass, i.e., of the number of nuclei formed during the coolingprocess. In cases where the DSC heating curves subsequent to isothermal cold crystallization show two meltingpeaks, their origin, recrystallization, was clarified by heating at rates varying from 10 to 300 C/min. Themorphologies of the cold crystallized systems have been assessed by AFM and were correlated with the calorimetricresults. Using HPer DSC, isothermal cold and hot crystallization at the same temperature has been studiedsuccessfully.