Fracture of uncured linear flexible-chain polymers of narrow molecular mass distribution in triaxial stress (behaviour of elastomers as adhesives)

Abstract

Possibly the simplest method of studying polymers under conditions of triaxial stress is the investigation of the behaviour of thin films of adhesive between two rigid surfaces. The adhesives used were uncured linear flexible chain polymers-polybutadienes. These polymers were of narrow molecular mass distribution ( MMD). The use of high molecular polymers of narrow MMD allows the evaluation of the behaviour of elastomers as adhesive joints to be simplified. It has been shown recently that, depending on the rate of deformation, the behaviour of polymers of this kind may be similar to that of viscoelastic liquids or systems in the high-elastic state, which behave as quasi-cured systems, The transition from the fluid to the high-elastic state is a pure relaxation process. It would be expected that the behaviour of the adhesive would vary substantially, depending on its physical state. The fracture behaviour of the adhesive and the rupture of its contact with the solid surface must be dependent on this factor. Cohesive, cohesive-adhesive and adhesive fractures may be observed in such cases. Cohesive fracture is typical for regimes of polymer deformation upon transition from the fluid to the high-elastic state. The further the transition of the polymer to the high-elastic state, the more sharply pronounced is the adhesive fracture of the polymer in triaxial stress. The present work is concerned with the investigation of the temperature-time dependence of the parameters characterizing the fracture of the adhesive and its contact with the solid surface. The results of experiments carried out under conditions of triaxial stress are compared with the data obtained for the same polybutadienes by experiments involving simple shear and uniaxial extension.