Synergistic effects of oxidative environments and mechanical stress on in vitro stability of polyetherurethanes and polycarbonateurethanes

The in vitro structural stability of polyetherurethanes (PEUs) and polycarb onateurethanes (PCUs and PCUUs) was examined under strong oxidative conditi ons (0.5N HNO3, pH 0.3; and NaClO, 4% Cl-2 available, pH congruent to 13) a nd in the presence of a constant strain state. Solvent-cast dog-bone shaped specimens were strained at 100% uniaxial elongation over extension devices and completely immersed in the oxidative solutions at 50 degrees C for 15 days. Unstrained polyurethane (PU) samples were treated in the same way for comparison. The modification of the PU molecular structure was determined by DSC, GPC, ATR-FTLR, static contact angle, and surface roughness analyses . The incubation in nitric acid and sodium hypochlorite brought about a gre ater degradation of samples tested under the applied strain with the except ion of PEU treated with nitric acid. PEU was the most affected material, sh owing bulk deterioration in Na-ClO and significant modifications in nitric acid, with the appearance of new IR bands, which were assigned to oxidation products. A higher phase separation between soft and hard domains occurred in PCUs upon incubation in nitric acid, the treatment with NaClO gave rise to new bands in the LR spectra, denoting the presence of oxidation product s at the surface. The surface roughness greatly increased in strained PCUs with SEM evidence of deep cracks and holes or ragged and stretched fracture s perpendicular to the direction of stress. PCUU underwent complex chemical modifications with a marked decrease of N-H and urea IR absorptions and sh owed a lower degradation than PEU and PCUs under mechanical constraint. Fro m these results, sodium hypochlorite appears to be able to create an ESC-li ke degradation for PUs that are resistant to other aggressive chemical envi ronments. (C) 1999 John Wiley & Sons, Inc.