Thermal behavior of carbon black filled polymers

DSC measurements suggest that polybutyl methacrylate interacts more strongly with carbon black than polystyrenes and corresponding random copolymers do, showing an increase in Tg of 8.6°C, compared to 2–3°C, by the inclusion of 20% carbon black of surface area 625 m2/g, in agreement with rheological studies. Enthalpy relaxation in the vicinity of Tg is increased by annealing at Tg – 10°C, attaining a maximum of 1.65 kJ/kg for polybutyl methacrylate and 2.6 kJ/kg for polystyrene. At constant annealing temperature, the rate of enthalpy relaxation in polybutyl methacrylate was reduced by a factor of about two by the addition of carbon black. However, both pure polystyrene and polybutyl methacrylate show the same rate of enthalpy relaxation as the corresponding filled polymers, following annealing at the appropriate Tg – 10°C.