Viscoelastic Behavior of Composite Systems Composed of Polybutadiene Particles and Polystyrene at Elevated Temperatures
Dynamic viscoelastic and extensional properties have been measured for composite systems composed of crosslinked polybutadiene particles and polystyrene at elevated temperatures. The experimental results have been discussed in terms of particle content, molecular weight of medium polystyrene and so on. Effect of temperature on viscoelastic functions can be expressed by the WLF equation by use of different reference temperatures according to particle content. The rubbery plateau modulus of the system can well be espressed by the Okano equation, in which the relative stiffness of particle to that of medium is taken into account. The characteristic time constant for slipage of entanglement couplings in medium polymer is proportional to the 3.5 power of molecular weight, and slightly increases with increasing particle content. The frequency dependence curve of dynamic modulus exhibits the second plateau at lower frequencies in spite of the isolation of particles in the material, suggesting a relaxation mechanism associated with motion of each particle. The second plateau modulus have been expressed by particle content, molecular weight of medium polystyrene and the mean distance between two particles in the system. From these results, a relaxation mechanism related to the second plateau in particle-filled system has been discussed.