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Degradation of polystyrene by gamma irradiation: Effect of air on the radiation‐induced changes in mechanical and molecular properties
Author(s) -
Bowmer T. N.,
Cowen L. K.,
O'Donnell J. H.,
Winzor D. J.
Publication year - 1979
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.1979.070240211
Subject(s) - irradiation , materials science , polystyrene , ultimate tensile strength , chain scission , gel permeation chromatography , composite material , analytical chemistry (journal) , polymer , chemistry , chromatography , physics , nuclear physics
Irradiation of 3 mm polystyrene sheet in air at 30°C with γ rays caused a rapid decrease in the tensile and flexural strengths and strains to fracture. These properties were decreased to 50% of their initial values after ca. 80 Mrads and to 25% after ca. 200 Mrads, beyond which dose the rate of change was relatively small. These results contrast with the negligible changes that are observed after 600 Mrads in vacuum. The effect of irradiation in air has been correlated with decreasing molecular weight at the surface, even though crosslinking predominated over the complete sample so that a gel point was reached at a dose slightly in excess of 100 Mrads. Scission and crosslinking yields, G ( S ) and G ( X ), were determined as a function of depth by gel permeation chromatography of layers removed progressively from the surface. G ( S ) decreased and G ( X ) increased with depth, in accord with the concepts of increased scission by reaction with oxygen and a diffusion effect. Unusual transverse cracking to a limited depth occurred during tensile measurements, a phenomenon that is attributed to the nonuniform molecular weight profile.