An investigation of the rheology of reactive and nonreactive highly filled polymer systems.

摘要

Studies were undertaken in this dissertation to develop and demonstrate two new techniques for the measurement of the rheology of highly filled polymer systems that stiffen as they are processed. Lubricated squeezing flow was used to measure the relaxation modulus following a step strain and the steady viscosity in equibiaxial extensional flow, and oscillatory compressional flow was used to measure the linear viscoelastic storage and loss moduli. Three reactive model systems that stiffen due to polymerization, crosslinking, or flocculation and a nonreactive model system consisting of spherical glass bead particles and a polydimethylsiloxane polymer phases were studied in addition to two calcium aluminate cement-polymer systems of technological interest. The relaxation modulus of the three model reactive systems showed distinguishable signatures of modulus growth characteristic of the active stiffening mechanism in each case. The signatures were modeled using a multimode Maxwell model with fixed relaxation times. Insight into the active mechanism responsible for stiffening in the two calcium aluminate systems was gained by comparing their relaxation behavior with the signatures determined for the reactive model systems. Comparison of the viscosity behavior of the model systems with those of the calcium aluminate cement-polymer systems revealed that, similar to the finding in the relaxation modulus comparisons, stiffening in the cement systems is likely driven by changes occurring in the particulate phase structure. Measurements of the frequency dependent storage and loss moduli revealed that the oscillatory compressional rheometer accurately measures the dynamic linear viscoelastic material functions of highly filled materials. The relative behavior of the storage and loss moduli with increasing filler content was studied for four different molecular weight materials. The effect of an increase in filler amount on the elasticity of the material was shown to depend on both the polymer molecular weight and the frequency of oscillation, and was explained in terms of the influence of the filler on the Deborah number of the system.