Cure shrinkage defects in epoxy resins

The formation of shrinkage defects in eight epoxy compositions was investigated during isothermal cure in a constraining vessel. For an epoxy resin there may be three ranges of isothermal cure temperatures distinguished by the type of cohesive defects formed. The boundaries of the ranges are individual for each polymer. The mechanisms of shrinkage damage and type of defects are defined initially by gelation and vitrification processes. Dependence of the processes upon temperature leads to a dramatic change in the influence of the type of defect formation and defines the boundaries of the temperature ranges. The quantity of cohesive defects depends on temperature range to a large extent and polymer chemical composition to a lesser extent. Vitrification may be the cause of shrinkage defect formation in both network and linear polymers.