MECHANICAL BEHAVIOR OF POLYTETRAFLUOROETHYLENE AROUND THE ROOM TEMPERATURE FIRST ORDER TRANSITION.

The effect of the room temperature first order transition on the plastic yield behavior of polytetrafluoroethylene PTFE has been investigated. Stress-strain curves were measured at different strain rates and temperatures. Tensile creep under constant dead load was also measured as a function of temperature and stress level. The effect of degree of crystallinity was investigated by using both a rapidly quenched and slow cooled polymer. The curve of yield stress vs temperature in the temperature range from -50 to 68C was found to be almost identical with the curve of elastic modulus vs temperature the yield stress shows a marked local decrease at the first order transition. The experimental observations suggest a model of the solid-state structure of PTFE which could be described as an elastic-plastic network, in which crystalline domains are connected by elastic amorphous regions, and in which the crystalline domains can flow plastically at sufficiently high stress or temperature. Author