Effect of microencapsulated curing agents on the curing behavior for diglycidyl ether of bisphenot a epoxy resin systems

Microcapsules containing a curing agent, 2-phenyl imidazole (2PZ), for a diglycidyl ether of bisphenol A (DGEBA) epoxy resin were prepared by a solid-in-oil-in-water emulsion solvent evaporation technique with poly (methyl methacrylate) (PMMA) as a polymeric wall. The mean particle size of the microcapsules and the concentration of 2PZ were about 10 mu m and nearly 10 wt %, respectively. The onset cure temperature and peak temperature of the DGEBA/2PZ-PMMA microcapsule system appeared to increase by nearly 30 and 10 degrees C, respectively, versus those of the DGEBA/2PZ system because of the increased reaction energy of curing. The former could take more than 3 months at room temperature, whereas the latter was cured after only a week. The values of the reaction order (a curing kinetic parameter) for DGEBA/2PZ and DGEBA/2PZ-PMMA microcapsules were quite close, and this showed that the curing reactions of the two samples proceeded conformably. The curing mechanism was investigated, and a two-step initiation mechanism was considered: the first was assigned to adduct formation, whereas the second was due to alkoxide-initiated polymerization. The glass-transition temperature of DGEBA/2PZ was 165.2 degrees C, nearly 20 degrees C higher than the glass-transition temperatures of DGEBA/2PZ-PMMA microcapsules and DGEBA/2PZ/PMMA microspheres, as determined by differential scanning calorimetry measurements. (c) 2007 Wiley Periodicals, Inc.