Effect of Heat Treatment on Mechanical Properties of Polycarbonate Exposed by Positron Annihilation Spectroscopy
The influence of different heat treatment temperatures and time used for annealing and quenching on the mechanical properties of polycarbonate(PC)was investigated.Positron annihilation spectroscopy(PALS)was used to analyze the free volume content of PC after different heat treatment processes.The results show that the toughness of PC,especially the notch impact strength and fracture strength can be improved significantly by quenching near or above glass transition temperature for a period of time,while the yield strength and bending strength can be reduced.The toughness of PC is affected by the internal free volume content and size which will be changed through quenching near or above glass transition temperature.By this way,the internal free volume content and size of PC which is quenched near or above glass transition temperature are similar with unheated PC.However,the toughness cannot be improved by extending quenching time below glass transition temperature because the free volume content and size have been reduced.The internal free volume content and size of PC can be only reduced by annealing,which is not affected by annealing temperature or time,resulting in a significant decrease in the tensile fracture strength,elongation at break,and notch impact strength of PC.
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