Prediction of long‐term ABS relaxation behavior

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Abstract
The applicability of time–temperature superposition to tensile stress relaxation of ABS plastics has been verified at strains from 0.5 to 5% for temperatures in the range of 10–50°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. The decay 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 from 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 rigid matrix Tg, to assess the degree of stiffening of the polymer in the solid state.