Microencapsulated Epoxy Resin And Design Of Self-healing Polymer Composites

According to the difference of chemical structure and healing mechanism,self-healing materials can be classified as intrinsic type and extrinsic type.The intrinsic self-healing composite materials do not need to consider the compatibility between the additive and the matrix,but the preparation process is complex and costly,which makes it difficult to produce on a large scale.Among the kinds of self-healing composite materials,microcapsule self-healing composite materials have good intelligent healing function and low cost,which make the research rapidly become the frontier field of material science and engineering application.But at present,most self-healing microcapsules have poor adhesion to epoxy resin matrix.In theory,the introduction of these microcapsules into epoxy resin matrix will form the breaking point of polymer composites considering the drawbacks of intrinsic and extrinsic self-healing composite materials,we designed a self-healing microcapsule without interface difference with epoxy resin matrix.The main research contents are as follows:The effects of emulsifier type and dosage,curing agent dosage,curing agent dropping speed,reaction temperature and rotational speed on microcapsules were analyzed by single factor variable experiment.The activation energies of the reaction of triethylenetetramine monomer with epoxy resin during the formation of capsule wall were calculated by titration method: The average activation energies of the reaction of primary amine/secondary amine with epoxy resin were E1=75.831 kJ/mol and E2=80.231 kJ/mol,respectively.The chemical reaction mechanism of epoxy resin-triethylenetetramine was studied by Fourier infrared spectrum dynamic analysis.It was found that the ring opening reaction of primary amine with epoxy group took place preferentially in the reaction process,and the content of secondary amine increased from the beginning of curing to almost complete reaction of primary amine,indicating that the reaction rate of secondary amine was lower than that of primary amine,which was consistent with the conclusion obtained by titration method.Orthogonal test was designed to extend the storage period of microcapsules.To optimize synthetic conditions as: 1.2% emulsifier dosage,1.2% curing agent dosage,1.2 g/h dropping speed of curing agent and 50? curing temperature.The epoxy resin microcapsules synthesized under these conditions have uniform particle size,smooth and compact surface,and the capsule core content is about 82.30%.After storage at room temperature for 12 days,the core content of the microcapsules decreases by only 3.30%.The average diameter of the microcapsules is 275.257?m,and the average wall thickness is 11.83?m.Through ATR-FITR analysis,it was found that there were unreacted amino groups and epoxy groups on the surface of microcapsules.The microcapsules were embedded in epoxy resin matrix.The unreacted amino/epoxy groups on the surface of microcapsules could form chemical bonds with the chemical groups of the matrix to increase the interfacial bonding energy.Thermal analysis curves showed that the initial weight loss temperature of epoxy resin microcapsules was 270?,thermal stability of microcapsules was better than liquid epoxy resin E-51.The effects of epoxy resin capsule content and particle size on the properties of epoxy resin matrix were studied by electronic tensile machine,dynamic mechanical analyzer and thermomechanical analyzer.When the dosage was less than 6%,the elongation at break and the bending strain at break of epoxy resin material were obviously increased,which indicated that microcapsules have toughening effect on brittle epoxy resin material.The larger the particle size and content of microcapsules,the lower the storage modulus of composites,the larger the loss modulus,loss factor and initial thermal expansion coefficient.However,when the particle size of microcapsules is larger than 300?m or the content of microcapsules is larger than 6%,the softening and collapse of microcapsules during heating will result in the decrease of CTE of composites.The results of cross section analysis showed that the interface between epoxy resin microcapsules and matrix tended to be homogeneous.The toughening effect of microcapsules on epoxy resin is the result of shear yield,craze effect and peeling and fracture of microcapsules.SEM,FTIR and EDS data showed that after micro-cracks occured in the material,microencapsule responded to the front stress of microcracks,the wall of the capsule was ruptured,the core of the epoxy resin flowed out,and the crack surface was wetted.During the heating process,DDM melted into the crack in the matrix and mixed with the core healing agent.The curing reaction took place at 100?,and the bonded crack surface of the cured product was formed.