ENVIRONMENTAL-STRESS CRACKING OF PVC AND PVC-CPE .2. FAILURE MECHANISMS

The failure of unnotched PVC and PVC-CPE was studied in a number of va pour and liquid environments. The failure mechanisms observed are rela ted to craze initiation and logarithmic craze growth. A model to expla in the origin of the logarithmic craze growth is presented. The failur e mechanism in air and in benzene and toluene vapours is ductile, wher eas it is brittle in n-hexane, n-decane and ethanol vapours, n-octane/ benzene mixtures and natural gas condensate. Equations to describe the time to failure for both failure mechanisms are derived. The ductile failure is ascribed to plasticization and/or plastic deformation aroun d the craze. Brittle failure is thought to arise from crazes which rea ch a critical size.