Evolution of mechano-chemistry and microstructure of a calcium aluminate-polymer composite: Part I. Mixing time effects

Paste development and evolution of microstructure, microchemistry, and mechanical properties of macro-defect-free composites were investigated. Mixing torque plots from a Banbury mixer showed a “window of processibility” within which an optimum polymer-particle network structure formed. This processing window can be controlled by mixing rate and temperature. Network development during paste formation governed the flexural strength and microstructure of the cured material. Electron microscopy studies of the composites corresponding to various points along the mixing torque curve revealed a matrix formation-destruction process that was linked to the mixing activity and the mechano-chemistry of the system. Microchemical evolution in the composite was studied by EDS. These studies suggested that a combined convection and diffusion mechanism was responsible for the migration of Al³⁺ and Ca²⁺ ions into the different regions of the microstructure. Increasing concentrations of these elements in the polymer regions stiffened the matrix, leading to complete degradation on further mixing.