ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The room-temperature tensile mechanical properties and fracture topographies of polycarbonate are reported as a function of strain rate, sample preparation, and thermal history above and below Tg. The bulk physical structural changes produced by various thermal treatments were monitored by density, yield stress, and differential scanning calorimetry observations. Ordered regions do not form in bulk polycarbonate at or below 145°C. The changes produced in the mechanical properties of polycarbonate on annealing below Tg, relative to a quenched or 145°C equilibrium-state glass, are caused by liquidlike packing changes in free volume. In room-temperature tensile a 125°C-6 day annealed glass exhibits transitional behavior from shear free volume, such as quenched and 145°C equilibrium-state glasses, this transition occurs at higher strain rates. Polycarbonate embrittles as a result of the cessation of shear yielding and reversion to a crazing failure mode with a corresponding decrease in molecular flow and energy to failure.Density measurements indicate that ordered regions do start to grow immediately above 145°C in bulk polycarbonate. This phenomenon allows precrystalline and/or crystalline entities to grow below the bulk Tg in thin films and on the free surfaces of thick films where mobility restrictions are less severe than in the bulk. From bright-field transmission electron micrographs of thin films and carbon-platinum surface replicas of etched thick films it is suggested that the observed spherical precrystalline structures are aggregates of 50-60 Å ordered molecular do mains.
Additional Material:
17 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1976.180140609
