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

Microstructure, microchemistry and mechanical properties of hardened macro-defect-free (MDF) composites processed at various rotor rates in a Banbury mixer were investigated. A quiescently formed calcium aluminate-polyvinyl alcohol composite served as a substitute for an unmixed system. Results from the Banbury studies in conjunction with microchemical analysis of the unmixed composite showed evidence that the polymer-particle interaction is a mechanically induced crosslinking reaction. The rate of the mechano-chemistry increases with mixing speeds. Scanning electron micrographs (SEM) and transmission electron micrographs (TEM) of hardened composites mixed for 15 min at 30, 50, 100, and 200 rpm indicate that much of the mechanical strength of MDF is due to the crosslinked interphase zones that blanket the cement grains. Stresses in the paste due to mixing can destroy the interphase layer, leading to a weaker hardened composite. Microchemical analysis revealed that the mechano-chemistry of the system did not vary with changes in the mixing conditions studied.