Abstract
A thermomechanieal study has been made of the softening of crystalline polymers during uniform, uniaxial stretch and also of the effect of the rate of heating upon the softening of amorphous polymers. The effect of the tensile force on the thermomechanical behavior of various polymers has been followed over the range 20 to 100 kg/cm2 and within wide temperature limits ( −150° to 250°). Ribbons 50 mm long, 2 to 4 mm wide and 0.05 to 0.5 mm thick served as specimens. Of the crystalline polymers the study included: isotactic polypropylene, polyethylene, polytetrafluoroethylene and polyethyleneterephthalate; of the amorphous: polyethyleneterephthalate and styrene-butadiene SKS-80 copolymer. The simplest thermomechanical curves were those of the amorphous linear isotropic polymers. The curves are characterized by a point of inflexion—abrupt increase in deformation on reaching the softening point. The thermomechanical curves of crystalline polymers are more complicated and are characterized by three differing regions of creep: below the glass, temperature, cold flow and the beginning of melting.