Processing-property characteristics of a polymer-cement composite

A unique methodology was developed to allow quantification of the relationships between processing conditions, rheological properties of the formed paste, and the morphology and mechanical attributes of hardened calcium aluminate cement-poly(vinyl) alcohol (CAC-PVA) composites. Effects of cement particle size and polymer molecular weight were also investigated.A torque rheometer with a Banbury-type internal mixer attachment was used to monitor paste development during mixing. Pastes removed from the mixer at various points were rheologically characterized using a capillary device and an equibiaxial extensional rheometer. Flexural strength and toughness of the corresponding hardened materials were measured using the biaxial flexural test method. Scanning and transmission electron microscopy (SEM and TEM, respectively) were employed for microstructural and microchemical analysis.Torque and temperature were monitored in the Banbury system as a function of initial mix temperature and mixing rate. TEM micrographs of the quiescently formed composite, the behavior of the mixing torque plots, as well as the activation energy derived from the temperature dependence of the mixing curve suggest that a mechanically induced crosslinking reaction takes place between the polymer and cement phases during mixing. This interaction between the two phases results in a "window of processibility" within which the composite formulation exists as a paste having optimal processing characteristics. The processing window shrinks with increasing temperature, mixing rate and PVA molecular weight, and increases with increasing cement particle size.Flexural strengths of the hardened material display a behavior consistent with the notion of a "window of processibility". Structure development in the paste during mixing is reflected in the mechanical strength of the composite. This conclusion is supported by scanning and transmission electron micrographs of the same samples that were tested for their mechanical properties.Extensional viscosity and relaxation characteristics of the CAC-PVA composite pastes were determined using the lubricated squeeze flow technique, while shear viscosity was measured with a capillary device. The rheological characteristics and their trends with mixing suggest the formation of an increasingly dense crosslinked, network structure in the paste. PVA solution rheology was also performed to determine the mechanism for paste formation. Results show a critical concentration above which the PVA phase forms a binder for this organo-ceramic system.U of I OnlyETDs are only available to UIUC Users without author permissio