Preparation Of Microencapsulated Curing Agent And Its Effect On Curing Behaviors Of Epoxy Resin

An epoxy resin-based system containing microencapsulated curing agents was employed to prolong its shelf life by separating the curing agents from epoxy resin during storage. When the temperature increased to a desired point, the capsules were broken and the curing agents would be liberated to cure epoxy resin.Obviously, from a practical standpoint, the polymers used to encapsulate the curing agents of an epoxy resin should possess a controllable softening-point or suitable decomposition temperature besides good compatibility with epoxy resin. Suitable wall materials and core curing agents were reported in patents. Examples of wall materials include, among others, gelatin, agar, methylcellulose, starch, starch degradation products, vinyl polymers and so on. The curing agents capsulated in protective polymers may be any material that reacts with epoxy groups. This includes the amines, amino-containing polyamides, acids, acid anhydrides et al.Microcapsules containing curing agent, 2-phenyl imidazole (2PZ), for diglycidyl ether of bisphenol A (DGEBA) epoxy resin, are prepared by solid-in-oil-in-water (S/O/W) emulsion solvent evaporation technique, using poly (methyl methacrylate) (PMMA) as polymeric wall. The mean particle size of the microcapsules and the concentration of 2PZ are about 10 μm and nearly 10 wt%, respectively.Onset cure temperature (T_o) and peak temperature (T_p) of EP/Micro20 system appear to increase nearly 30(?) and 10(?) respectively than EP/2PZ system due to the increased reaction energy of cure (E_a). The former can reserve even more than six months under room temperature while the latter is cured after only a week. Curing kinetic parameter reaction order n of EP/2PZ system, EP/Micro20 system are quite closed, which illuminates that cure reactions of two samples are preceding conformably.A two-step initiation mechanism during curing process is considered, the first is assigned to adduct formation while the second one is due to alkoxide initiated polymerization. T_g of EP/2PZ system is 165.2℃, nearly 20℃ higher than those ofEP/Micro20 system determined by DSC measurements. The mechanical properties and thermal stabilities of EP/2PZ system, EP/Micro20 system and EP/2PZ+PMMA system are determined by DMA and TGA, respectively.