Preparation, Curing Reaction And Properties Of Silica Encapsulating Rosin-based Epoxy Resin Microcapsules

Maleopimaric acid glycidyl ester type epoxy resin （MPTGE） with phenanthrene ringskeleton structure, which was synthesized from the raw material rosin. In this paper, nonionicwaterborne epoxy surfactant （MP） was synthesized by MPTGE reacted with polyoxyalkylene（PEG）. Then MP was used to emulsify MPTGE to obtain a stabilized emulsion. The silicaencapsulating MPTGE microcapsule was synthesized by sol-gel process with MPTGEemulsion acted as core material and tetraethyl silicate （TEOS） acted as silica shell material.Finally, these microcapsules were cured with anhydride curing agent, the curing reaction andthe properties of cured products were investigated.The main contents and conclusions of this paper were listed as follows:1. The waterborne epoxy resin emulsion was prepared by phase inversion technique usingpolymer reactive surfactant （MP） with different molecular structures synthesized by MPTGEand PEG. The effects of the dosage of catalyst, the molecular weight of PEG, the molar ratio ofepoxy group to hydroxyl group, the reaction temperature and reaction time, the content ofemulsifier, emulsification temperature on emulsion centrifugal stability, particle size andconsistency of particle size distribution of the emulsion were investigated. The results showedthat epoxy emulsifier which was prepared by PEG4000or PEG6000reacted with MPTGE, inthe molar ratio of epoxy group to hydroxyl group1.5:1, at about95℃for60min, catalyzedby2%boron trifluoride in ether solution with amount about4%⁶%of the total reactions,had a good emulsifying effect for MPTGE. When the content of emulsifier was13.7%¹6.7%,agitation rate was greater than or equal to600r/min and emulsification temperature was80℃,the waterborne epoxy showed a good particle size, consistency of particle size and centrifugalstability.2. Silica encapsulating MPTGE microcapsules were prepared by sol-gel process in asurfactant stabilized O/W emulsion. In these microcapsules system, MPTGE was used as the core material, and SiO2was acted as the shell material that was formed via hydrolysis andsubsequent polycondensation of tetraethyl silicate （TEOS） in the presence of hydrochloric acid（HCl） as catalyst. The effects of different surfactants and concentration, the ratio of shell tocore, the pH value of reaction emulsion, the reaction time on the properties of microcapsuleswere investigated. Experimental results indicated that the state of microcapsules wasdramatically dependent on the ratio of core to shell, the effects of different surfactants and itsdosage, the ratio of core to shell, the pH value and reaction time. The surfactant MP wasfavorable to form TEOS encapsulating MPTGE microcapsules and the microcapsules sizedecreased with the increasing of the surfactant. When the content of surfactant was16.7%, thepH value was2.50, the ratio of core material to shell material was1:1, the temperature was50⁶0℃，and the reaction time was3.5h, a smooth and compact microcapsule with awell-defined core-shell microstructure and mean diameter8.4μm could be prepared. Theseprepared microcapsules presented a good thermal stability, and the core material content wasabout67.5%by weight.3. The curing reaction process and nth order kinetic of microcapsules with anhydridecuring agent were investigated by FT-IR method and DSC. The results showed that the nthorder kinetic equations from Kissinger and Crane Equations were able to well describe thecuring reaction of these two systems. The microcapsule could react with the curing agent well,and as a result of the existence of silica shell material, the MC/MeTHPA system had a betterstorage stability at room temperature than MPTGE/MeTHPA system. The MC/MeTHPAsystem could be completely cured at180℃for5h. MPTGE/MeTHPA and MC/MeTHPAshowed relatively consistent activation energy, which were68.13kJ/mol and65.29kJ/mol,respectively. The kinetic equations of these two curing systems were listed as follows:The kinetic equation of MPTGE/MeTHPA system:da/dt=2.773×10³exp（68.13×10³/RT）（1-a）^0.9099kinetic equation of MC/MeTHPA system: da/dt=9.194×10²exp（65.29×10³/RT）（1-a）^0.92714. The thermal stability, glass transition temperature and mechanical properties ofMPTGE/MeTHPA and MC/MeTHPA were determined by TG, DSC and DMA, respectively.The results showed that the curing residual silica shell material had good compatibility with theepoxy resin system and it could be a modifier on toughness of epoxy resin.