Radiation Stability of Elastomers

Abstract

Ordinary elasticity, high elasticity, and viscous flow are the mechanisms of deformation of solid polymers. Qualitatively, the effect of radiation on the mechanical properties of polymers can be described by considering the effect of crosslinking and cleavage on these mechanisms. Crosslinking tends to impede viscous flow. The equilibrium value of Young's modulus for high elasticity is directly proportional to the concentration of crosslinks, but for ordinary elasticity the sensitivity of Young's modulus is less for more rigid materials. Cleavage reduces the yield stress for viscous flow, and decreases the equilibrium value of Young's modulus for high elasticity. Young's modulus for ordinary elasticity is again insensitive for the more rigid materials. The changes in the mechanical properties of irradiated elastomers depend on the rates of crosslinking and cleavage. These rates are governed both by the polymer's chemical structure and by the strength of the van der Waals forces. For uncrosslinked polymers, the change of Young's modulus is a measure of the crosslinking rate in the case of less rigid materials. Sensitivity to chain cleavage has been correlated with chemical structure for the materials studied.