Environmental stress cracking behaviour of urethane methacrylate based resins

Abstract

Two kinds of cross-linked urethane methacrylate resins have been investigated using three-point bend tests to determine their environmental stress cracking (ESC) behaviour in a range of liquids (water, sodium hydroxide, ethylene glycol, acetonitrile, acetic acid, acetone, tetrahydrofuran, toluene, 3,5,5-trimethylhexanol and petrol). The resins were found to undergo ESC in organic liquids only, and the critical strains, ɛ_c, and critical stresses, σ_c, have been related to the solubility parameters, δ, of the liquid environments. The most severe ESC was observed in solvents with δ−19–20 MPa^1/2, corresponding to minimum points in the plots of ɛ_c and σ_c against δ. Generally, the resin with the higher cross-link density had a greater resistance to ESC, but the effect of liquid diffusion complicated the situation and was found to play an important role in the ESC behaviour of these materials. The results confirmed that liquid diffusion into the resins lowered the critical strain (and stress), leading to earlier failure. In the case of the lower cross-link density resin, very fast diffusion was found to cause softening. However, it was noted that liquid diffusion can also blunt crazes and cracks.