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Crazing and the stress dependence of creep in two glassy polymers: Polystyrene and a poly(styrene–acrylonitrile) copolymer
Author(s) -
Moore R. S.,
Gieniewski C.
Publication year - 1970
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1970.070141119
Subject(s) - crazing , polystyrene , copolymer , materials science , stress (linguistics) , styrene , composite material , acrylonitrile , creep , polymer chemistry , polymer , philosophy , linguistics
The stress dependences of crazing and of tensile creep were studied at 30.5° and 80°C in polystyrene ( M v = 2.7×10 5 ) and in a poly(styrene–acrylonitrile) copolymer (73.5% styrene, M v = 2.35×10 5 ) at four stresses in the interval from 0.6 to 1.5×10 8 dynes/cm 2 . Material failure was observed in all cases for the polystyrene and in no cases for the copolymer. Crazing was found to occur at all stresses for polystyrene, the spacing between craze lines decreasing with increasing stress and temperature. A much higher stress level for the onset of crazing was found for the copolymer. An inverse stress dependence of the compliance was observed for polystyrene at 30.5°C, i.e., the compliance decreased with increasing stress. This behavior was partially reversed at 80°C below 10 2 sec and became a positive stress dependence at long times. The stress dependence of the compliance for the SAN copolymer was partially reversed at 30.5°C. At 80°C, the stress dependence was positive for stresses ≥0.9×10 8 dynes/cm 2 . The present results suggest that in the copolymer there may exist an enhanced local mobility which alters the stress dependence observed in pure polystyrene and which enhances the ability of the material to deform without failure. This concept is discussed further in light of the stress dependence of the compliance and of crazing in these materials and appears to be consistent with our previous studies of the stress dependence of creep and of the stress dependence of whitening in ABS systems.