Shrinkage and internal stress during curing of epoxide resins

The shrinkage and internal stress of bisphenol‐type epoxide resins cured with aliphatic α,ω‐diamines, H 2 N(CH 2 ) m′ NH 2 ( m′ = 2, 4, 6, and 12), were investigated by measuring the change of density and the strain of the steel ring embedded in the cured resins. Internal stress was found to be induced by the shrinkage occurring in the cooling process from the glass transition temperature ( T g ) to room temperature. Shrinkage and internal stress increased with increase in the concentration of network chains and T g of the cured systems, and then with a decrease in m′ of the curing agents. It appears that the reductions in the concentration of network chains and T g were necessary to reduce the shrinkage and internal stress caused by the curing.