SynopsisThe applicability of time-temperature superposition to tensile stress relaxation of ABS plastics has been verified a t strains from 0.5 to 5% for temperatures in the range of l&50°C. Master curves have been compiled to predict the long-term stress relaxation at 23°C. and a stress-strain-reduced time surface has been constructed. A comparison of relaxation times and activation energies has confirmed that a strain increase facilitates stress relaxation up to yield. Thedecay of relaxation modulus at linear viscoelastic strains was shown to be equivalent to that of tensile creep modulus. By normalizing the master curves to originate at yield stress and then converting them into multiaxial form the strain which gives the best data fit with long-term hydrostatic pipe-burst strength was shown to be at yield or beyond. The ABS yield-strain master curves at 23°C. were shown to match satisfactorily the long-term pipe-rupture data. Activation energies for ABS relaxation have been compared below and above the rigidmatrix T,, to assess the degree of stiffening of the polymer in the solid state.

To meet the stringent requirements of PVC compounds intended for use in injection molded cabinets, housings and other electrical applications, impact modifiers are required which permit good melt flow while processing and allow passage of falling ball impact at −20°C. Extensive testing is described as differentiating the low temperature toughness imported by two similar impact modifiers which give the same mold flow in modified PVC.