The data show this is the most severe test method and should conservatively predict results in the most difficult field exposure. The 15-minute soak is also the most efficient and reproducible method. The solubility parameters cited were obtained from solvent literature. If the objective is to replace Trichloroethane with something that produces less stress cracking, then a great variety of options are available. Solvent blends can be compounded that meet existing telephone standards for stress cracking of polycarbonate.
Solubility parameters quantify and predict the molecular solvent properties of organic materials.
The extension of this theory to various solvents and solvent blends seems valid. The data shows that solubility parameters are good predictors of maximum percent strain limit for polycarbonate stress cracking. 1,1,1-Trichloroethane, with a solubility parameter of 8.5, has been found to actually dissolve polycarbonate. It could be possible that trichlor has been used without noticeable effect only because the evaporation rate is so quick and contact is incidental and of very short duration. It can be expected that any extended contact with Trichloroethane, such as a solvent-soaked rag, would have an effect on polycarbonate.