Polymer-oxygen compatibility testing: Effect of oxygen aging on ignition and combustion properties

The oxygen (O-2) compatibility of six polymers used in O-2 service was evaluated after 48 h exposures at 121 degreesC (250 degreesF) to O-2 pressures of 620 and 6200 kPa (90 and 900 psia). Three elastomers were tested: chloroprene rubber (C873-70), fluorocarbon rubber (Viton(R)(3) A), and silicone rubber (MVQ type); and three thermoplastics were tested: polyhexamethylene adipamide (Zytel(R)(3) 42), polytetrafluoroethylene (PTFE Teflon(R)(3) 500A), and polychlorotrifluoroethylene (Neoflon(R)(3) CTFE M400H). Post-aged changes in mass, dimensions, tensile strength, elongation at break, durometer hardness, and thermomechanical properties were evaluated. For selected materials, gaseous nitrogen- (GN(2)-) aged controls were used to ascertain the effect of thermal versus oxidative degradation. Finally,. the effect of O-2 aging on selected ignition (AIT) and combustion (DeltaH(c)) properties was determined. As expected, aged polymers were less ignitable and combustible. Special attention was given to Neoflon CTFE; namely, the possible effect of percent crystallinity (quick- versus slow-quenched) on the aging, ignition, and combustion behavior was evaluated.