EVOLUTION OF MECHANO-CHEMISTRY AND MICROSTRUCTURE OF A CALCIUM ALUMINATE-POLYMER COMPOSITE .2. MIXING RATE EFFECTS

Microstructure, microchemistry and mechanical properties of hardened m acrodefect-free (MDF) composites processed at various rotor rates in a Banbury mixer were investigated, A quiescently formed calcium alumina te-polyvinyl alcohol composite served as a substitute for an unmixed s ystem. Results from the Banbury studies in conjunction with microchemi cal 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. Scann ing electron micrographs (SEM) and transmission electron micrographs ( TEM) of hardened composites mixed for 15 min at 30, 50, 100, and 200 r pm 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 t o a weaker hardened composite. Microchemical analysis revealed that th e mechano-chemistry of the system did not vary with changes in the mix ing conditions studied.