Accelerated aging of Nylon 66 and Kevlar 29 yarns was carried out in humid air, smog, and ozone to establish aging trends in these environments. Tensile strengths of nylon yarn aged in a humid environment (50% RH at ambient temperature) for six months degraded from 40% at 1 10 O C to 85% at 150 OC. Kevlar yarns in the same test lost from 10% (130 "C) to 32% (170 "C) of their strength. Based on these data, the estimated energy of activation for the nylon degradation is 18 kcal/mol and for the Kevlar degradation is 13 kcal/mol. Nylon exposed to smog for six months lost -63% of its tensUe strength compared to -7% loss in ozone. Kevlar strength loss was -27% for smog exposure and insignificant for ozone exposure. No trend between oxygen depletion or carbon dioxide generation and strength loss was apparent in the gas analyses. Infrared spectrophotometry did not show changes in materials degraded at significant levels (40 % ). Preliminary nondestructive chemiluminescence studies indicate a linear relationship between thermally induced chemiluminescence and tensile strength.

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Two soluble polyurethanes have been develped for use as castable, removable encapsulants for electronic com ponents. These polyurethanes were formulated using bitolylene diisocyanate (TODI) terminated polytetramethylene glycol, chain extended with 1,4 butanediol. TODI was chosen to furnish the isocyanate moiety in this system for its tendency to form semi crystalline polymers and provide physical crosslinking to retard creep. The required physical properties for our applications (low creep, 400% elongation, yield strength ~ 2000 psi, and T g <-55°C) were achieved after carefully removing urea from the starting isocyanate and water from the ether and glycol com ponents. The encapsulants were cured 16 hours at 80°C to achieve the desired properties. Although infrared examination showed residual isocyanate after cure, postcuri ng did not improve the physical properties.