Preparation Of Isocyanate Prepolymer Microcapsules And Its Application Research

In recent years,self-healing materials based on microcapsules have received increasing attention and extensive research,and are one of the hot spots for research in the field of polymeric materials.Self-repairing materials embedded in microcapsules can provide immediate feedback to external signals and heal automatically,significantly extending the service life of the material and effectively reducing the maintenance cost of the material.At present,research on microcapsules in the field of self-healing is mainly focused on the types of wall materials,core materials and wall raw materials,types of core materials and preparation methods,while less research has been conducted on the morphological particle size affecting the microcapsules and the self-healing efficiency.In this study,isocyanate prepolymer with high restoration efficiency was synthesised and used as core material to prepare high restoration efficiency microcapsules with high sphericity and suitable particle size by interfacial polymerisation,and its related properties were investigated,and the main research contents and results are as follows:(1)Synthesis of isocyanate prepolymer with isophorone diisocyanate(IPDI)blocked polyetheramine D2000.Prepolymer microcapsules encapsulated by polyurethane shells were prepared by interfacial polymerization using a synthetic isocyanate prepolymer as the core material and 1,4-butanediol(BDO)reacted with commercial curing agent Bayer L-75 to synthesize a high strength polyurethane as the wall material.Microcapsules,cores and shells were tested using a Fourier transform infrared spectrophotometer(FT-IR).The size of the microcapsules was observed by optical microscopy(OM)and further observed by scanning electron microscopy(SEM);the particle size distribution was measured by laser particle size measurement;and the thermal decomposition curves of the microcapsules,microcapsule shell and core were plotted by simultaneous thermal analysis(TGA).The effects of the reaction temperature,stirring rate,the amount of emulsifier Gum Arabic and the addition of BDO on the particle size,yield and encapsulation rate of the microcapsules were investigated,and the process parameters of microcapsule preparation were optimized.The experiments showed that the core prepolymer was successfully encapsulated by the synthesized polyurethane film,and the microcapsules were prepared with high sphericity,dense and smooth polyurethane shell,and moderate particle size in the range of 50.48-239.89 μm.After optimisation,when the mass fraction of emulsifier Gum Arabic(GA)was 7.5 wt%,the emulsification speed was600 rpm and the mass fraction of chain extender BDO was 15.38 wt%,the size distribution of the synthesised prepolymer microcapsules was narrower with an average size of 124.29 μm,the surface of the microcapsules was smooth and dense,and the yield and encapsulation efficiency of the microcapsules were high.(2)The microcapsules synthesised under optimum process conditions were uniformly mixed into the AB component of the epoxy resin to make a self-healing coating,which was subsequently brushed onto the surface of the tinplate as required,and the coating was frozen to produce cracks by brittle fracture,and the morphology of the coating and the self-healing effect were observed using an optical microscope(OM).The effect of the incorporation of microcapsules on the corrosion resistance of the coating was investigated.The experimental results showed that the microcapsules were evenly dispersed in the epoxy resin coating and a bright liquid flow could be seen at the crack after brittle fracture,indicating that the core isocyanate prepolymer was released;when the microcapsules were added at 10%,the selfhealing coating was corrosion-free and basically self-healing after immersion in Na Cl.(3)The self-repairing microcapsules were mixed with epoxy resin AB to produce selfrepairing strips and the tensile properties were tested using a tensile strength tester to verify the repair performance of the self-repairing strips.The results showed that the stress value of the self-repairing strip was about 89% of the first one after 24 h of immersion in water,which proved the repairing effect.