Volume relaxation in filled polystyrene

The restoration of the volume after sudden removal of pressure from bulk polystyrene (PS) samples containing 0, 5, 20, or 50 wt.% glass powder as filler was studied. The volume relaxation could not be quantitatively described within the limitations of the existing phenomenological theories. Addition of filler has been found to lead to a noticeable inhibition of the relaxation processes in the polymer at fairly high temperatures, but reduction of temperature to Tg greatly reduced the difference owing to the smaller temperature dependence of the activation energy of relaxation in filled samples when compared with that of the unfilled; the latter is assumed to be explainable by the decrease of the characteristic parameter T0 in the Vogel-Tamman equation, which is defined as the temperature at which the residual free volume disappears on adding the filler. The result is that the bulk viscosity of the unfilled PS is similar to that of the filled at the Tg, i.e. about (2–5) × 1014 poise.