PROCESSING PROPERTY/STRUCTURE INTERACTIONS IN A CALCIUM ALUMINATE-PHENOL RESIN COMPOSITE/

Relationships among mixing conditions, extensional viscosities of the formed paste, and the morphology and flexural strength of hardened com posites have been studied for a calcium aluminate cement-phenol resin composite. Mixing torque was monitored as a function of temperature an d resin pH. The behavior of the torque time curves as well as C-13 nuc lear magnetic resonance and differential scanning calorimetry measurem ents suggest that paste formation is characterized by an induction per iod of flat torque, corresponding to dissolution of cement ions,follow ed by a stiffening: period of rapid torque rise, corresponding to an i onic interaction between the resin and cement particles. The viscoelas tic nature of the paste was studied using a biaxial squeeze flow devic e. The steady biaxial extensional viscosity trends with extension rate are consistent with the formation of an increasingly cross-linked bul k organic phase in the paste. Flexural strengths of hardened material processed tinder varying degrees of resin pH suggest that an optimal s tructure forms when the resin is allowed to simultaneously polymerize and ionically interact with cement particles. This conclusion is suppo rted by evidence of scanning electron microscopy, which shows structur e formation for a given set of mixing conditions. (C) 1998 Elsevier Sc ience Ltd.