Preparation And Performance Of Microencapsulated Epoxy Self-healing Materials

Thermosetting resin matrix composites,such as epoxy resins,are prone to internal cracks under overload condition,which will reduce the mechanical properties and service life of materials.If the self-repairing functional microcapsules are added to the resin matrix,when the cracks extend to the microcapsules,the repairing agent will flow out to fill the cracks,thus realizing the self-repairing of materials,which is of great significance to improve the safety of materials.In this paper,the microencapsulation of epoxy resin E51 was prepared by in-situ emulsion polymerization which reported by numerous literatures.It was found that spherical microcapsules with regular morphology could be prepared by using Tween 80 and Span 80 as emulsifiers(mass ratio 4:1).In order to investigate the optimum preparation conditions of microcapsules under the influence of multiple factors,the coating temperature,surfactant concentration,core-wall ratio and coating speed were selected as research variables,and the central composite(CCD)response surface methodology was used to optimize the preparation process of microcapsules.Response surface analysis showed that the optimum process conditions were as follows: surfactant concentration was 1.10 wt%,stirring speed was 641.64 rpm,core-wall ratio was 0.88:1,and reaction temperature was 61.7 C.Under this condition,the morphology of microcapsules is regular and compact sphere,the particle size is about 87 ?m,the wall thickness is 3-5 ?m,and the coating rate is 85.43%.The inner core material has reactivity.In addition to the preparation of liquid core microcapsules directly by in situ polymerization,hollow microcapsules can be prepared first and then subjected to negative pressure osmosis to obtain self-repairing microcapsules.In this paper,the hollow microcapsules with urea-formaldehyde as wall material were prepared by foaming technology and in-situ polymerization.The effects of surfactant,prepolymer concentration,stirring speed,salting-out agent and curing agent on the preparation of hollow microcapsules were discussed.Under the optimum conditions,hollow microcapsules with a particle size distribution of about 100 ?m,compact and rough surface and regular spherical morphology can be prepared.Epoxy resin with dynamic DA bond has been reported to be self-healing for many times.Epoxy resin containing dynamic DA bond was prepared by literature method.Epoxy resin containing dynamic DA bond microcapsules and triethylenetetramine microcapsules were prepared by negative pressure osmosis.The encapsulation rates of epoxy resin with DA bond and triethylenetetramine were 61.10% and 76.32% respectively.On this basis,the self-repairing properties of microcapsules were tested by scratch method.The experimental results show that the self-healing effect of microencapsulated epoxy resin with 15 wt% content and 150-200 ?m particle size is better.The self-healing effect of epoxy resin microencapsulated with DA bond can be achieved many times.The addition of microencapsulation less than 10 wt% has little effect on the thermal and mechanical properties of resin matrix.The effect of microcapsules on the curing kinetics of resin matrix was also studied.The results showed that microcapsules had little effect on the curing kinetics of resin matrix,but the parameters of the curing kinetics model changed little.The curing mechanism is still dominated by anionic polymerization.Generally speaking,the addition of microcapsules has little influence on the matrix,and can also achieve self-healing performance,which has great application value.