Thermal Characterization of Polylactic Acid

摘要

High molecular mass polylactic acid belongs to an important class of polymers due to itsrnnatural biodegradability and versatility. This present study focuses on the thermalrncharacterization of the stressed and unstressed polylactic acid using Differential ScanningrnCalorimetry. The DSC studies were carried out at varying heating rates of 5, 10 and 20℃/min.rnThe results were compared in atmospheres of air (closed pan) and nitrogen (50 ml /min, withrnand without pinhole, closed sample pan). This polymer has a unique composition of amorphousrnand crystalline phases which were manifested by its glass transition temperature (T_g=58℃), postrncrystallization temperature (T_c=96℃) and melting temperature (T_m=172℃). Variations of thernDSC experimental protocol caused changes in the polymers' microstructure; for example,rnquench cooling from the melt enhanced the amorphous content and therefore decreased therncrystallinity. The as-received extruded and compressed polymer has specific tailoredrnmorphologies and microstructures of a reproducible polymeric substrate. Poly lactic acid wasrnfurther stress modified by mechanical means with a stretch ratio of 4:1 and monitored byrnDifferential Scanning Calorimetry. The stressed sample, when subjected to the same kind ofrnexperimental conditions as that of the unstressed one, showed significant changes in the thermalrncharacter owing to its high energy state.