Melt rheology of lightly crosslinked carbon black filled thermoplastics

Abstract

Polymer composites typical of those employed a toners for hot roll fusing in electrophotography were studied with the Rheometrics Mechanical Spectrometer using the cone plate geometry at temperatures between 100°C and 180°C. A series of three tests was defined to measure the viscoelastic response at fusing time-scale and temperature: (1) frequency-temperature sweep for time-temperature superpositon, (2) step strain to measure the short time shear relaxation modulus (<0.5 sec), and (3) step shear to measure transient stress overshoot and relaxation (<1 sec). These tests were used to examine the effects of processing shear history, crosslink density, molecular weight distribution, and carbon black filler on the rheological properties of the composite. It is shown that all these parameters can have a significant effect on the melt rheology. Observed variation in the absolute dynamic viscosity, stress overshoot, and relaxation are discussed in terms of molecular theory.