| Epoxy resin is a kind of thermoplastic polymer prepolymer,and it has wide applications when it reacts with curing agent to form a three-dimensional structure.In the one componet epoxy resin,the curing agent is usually modified physically or chemically to make it a latent curing agent in order to have a longer storage period and make processing more convenient.Using microcapsules to encapsulate the curing agent is a common method of giving the curing agent latency.In this thesis,a series of curing agent microcapsules with polyurethane and polyurethane/polymethyl methacrylate as shells were prepared by the interfacial polymerization method,and their curing behavior and storage period in epoxy resin were investigated.The main conclusions of this thesis were as follows.(1)Synthesis and characterization of curing agent microcapsules with waterborne polyurethane as the shellA series of polyurethane curing agent microcapsules with different NCO:OH ratios were prepared by interfacial polymerization.With the increase of NCO:OH,the amount of imidazole derivative encapsulated in microcapsules increased and encapsulation efficiency improved.When the ratio of NCO/OH was 5/1,microcapsules with curing agent encapsulation of 22.4 % were obtained,and the encapsulation efficiency reached 90 %.The microcapsules can be added to epoxy resin to make one-component resin curing system with about 30 days storage period at room temperature and could rapidly cure epoxy resin between 140-150°C.(2)Synthesis and characterization of PU/PMMA double-shell curing agent microcapsulesThe PU/PMMA double-shell curing agent microcapsules with different PMMA content were prepared by the interfacial polymerization method.With the increase of PMMA,the particle size of the curing agent microcapsules increased significantly.Compared with polyurethane microcapsules,the surface of the double-shell microcapsules was smoother,the core-shell structure was more obvious,and the amount of imidazole derivative encapsulated in microcapsules increased.When the PMMA content is 20 %,the curing agent encapsulation reached 24.8 %.The onset curing temperature of the microcapsule/epoxy resin(20/100)system was 99°C,and the peak curing temperature was 110°C.Latency test at 60°C for 8 hours showed thatthe curing degree was only 20 %,which is better than that of polyurethane curing agent microcapsules.(3)Application of curing agent microcapsules as epoxy resin curing acceleratorThe curing agent microcapsules of two different shell materials are used as the accelerator of dicyandiamide to prepare a dicyandiamide/microcapsules curing system.When the amount of dicyandiamide was 10 % and the amount of microcapsules was 5 %,7 % and 10 % of the epoxy resin,the onset curing temperature of dicyandiamide/microcapsule/epoxy resin system was lowered from 170 ? to 142.5 ?,136.5 ? and 134.5 ?,respectively.At 120 ?,both polyurethane microcapsules and PU/PMMA microcapsules had the gel time of less than 8 minutes.The epoxy-curing system can be stored for more than 60 days at room temperature.(4)Curing kinetics of curing agent microcapsulesThe Kissinger,Ozawa and Crane methods were used to study the curing kinetics of the polyurethane curing agent microcapsule/epoxy resin system and the PU/PMMA curing agent microcapsule/epoxy resin system,respectively.The order of reaction of the epoxy resin cured by the microcapsules was the same as the reaction order of the epoxy resin cured by the imidazole derivative.They were first-order reaction,which means the encapsulation of the microcapsules did not change the order of reaction.The activation energy of the polyurethane curing agent microcapsule/epoxy resin system was between66.61 and 69.16 KJ/mol,and the activation energy of the PU/PMMA curing agent microcapsule/epoxy resin system was between 72.26 and 83.77 KJ/mol. |
PDF Full Text Request