| Based on in-situ polymerization,two kinds of microcapsule self-healing systems were successfully prepared: styrene / benzoyl peroxide（BPO）and epoxy resin /mercaptan microcapsule self-healing system.The preparation process,properties and morphology of the four microcapsules were characterized.Two groups of microcapsules were used as two component healing agents and dispersed in epoxy resin matrix respectively.The mechanical properties and self healing efficiency of two kinds of self healing systems of double microcapsules were explored.The main results are as follows:1.By the in situ polymerization method,Styrene and BPO microcapsules with melamine urea formaldehyde resin as wall were synthesized respectively.The microcapsules were prepared at p H3,emulsifier are 0.2% DBS + 0.1%GA,stirring rate 700 r/ min.And the particle size concentrated at 4.5 μm,The encapsulation efficiency of styrene and BPO microcapsules were 87.79% and 82.24% respectively,and the content of core was more than 80%.2.With UMF resin as wall,epoxy resin microcapsules and mercaptan microcapsules are successfully synthesized.The microcapsules are obtained when the p H value is 3.5,the surfactant concentration was 0.6g/l,and the stirring rate is700r/min.The successful encapsulation and thermal stability of the core were confirmed by IR and TGA.The core content was 74% and 78.5% respectively,and the encapsulation efficiency of microcapsules was 95.2% and 86.4% respectively.SEM observation shows that the appearance of the microcapsule was rough and the morphology was dense,which could form a tight connection with the epoxy matrix.3.SEM to observe the existence of styrene /BPO and epoxy resin / mercaptan microcapsules self healing system in epoxy resin matrix.The microcapsule is stable in the matrix and is spherical in shape.It is closely connected with the matrix.When the crack is present,the microencapsulated microcapsules can better respond to the crack propagation and release the reagents to repair the cracks effectively.4.The self healing efficiency of microcapsule was calculated by TDCB experiment,according to the difference of fracture load before and after healing.The samples of styrene/BPO and epoxy/mercaptan dual microcapsules self-healing system were prepared respectively.The samples were doped into the matrix materials according to the mass ratio of 0,2.5,5,7.5,10 and 12.5wt%.Use tensile testing machine to measure fracture load values of the matrix materials before and after self-healing.It confirmed that with the increase of microcapsule content,the fracture load of matrix materials first increased and then decreased.For the BPO/ styrene microcapsule self healing system,the fracture load of the matrix material reaches the maximum when the mass ratio of microcapsule is 5wt%,and the maximum is reached at 7.5wt% when the epoxy resin / mercaptan self healing system is applied.When the content of microcapsules in the matrix is 12.5wt%,the self-healing efficiency is37.3% and 51.3%,respectively.We choose the amount of 10wt% as the criterion,and the comprehensive performance is relatively good at this time.The healing rates are34.66% and 49.87% respectively.The conclusion is that epoxy/mercaptan self healing system is superior to BPO/ styrene self healing system.5.Use DTA to analysis the healing behavior of two microcapsule self repairing systems.For styrene/BPO microcapsule healing samples,the exothermic reaction peak was detected at 65℃ centigrade,and the initial temperature was about 62 ℃.The exothermic reaction peak was detected around 58 ℃ at the epoxy resin/mercaptan microcapsule healing sample,and the initial temperature was about 53℃.In the epoxy matrix without microcapsules,the smooth curve shows that the healing behavior of the epoxy matrix without the healing agent almost remained unchanged,indicating that the matrix of the non doped microcapsule had no self healing property. |
