Preparation And Performance Of Binary Self-healing Polymeric Materials With Epoxy-containing Microcapsules

Microcracks are inevitably generated during the use of structural polymericcomposite when affected by the environmental factors such as outside load andtemperature. We designed two different kinds of binary self-healing polymericmaterials, which are based on anionic chain polymerization and additionpolymerization of epoxy and its curing agent, in order to prevent microcrackspropagating and prolong using life. Microencapsulation of epoxy resin and itshardeners were investigated respectively. Also, effect of stabilization of liquid-liquidinterface of oil-water emulsion on microcapsule’s yield and properties wereinterpreted through the theory of interface thermodynamics.A metastable emulsion system of liquid-liquid interface is essential formationfor all microencapsulation. Then shell material former polymerized at the interfacebetween dispersed phase and continuous phase, forming microcapsules. Therefore,the stabilization of emulsion would greatly influence on microcapsule’s yield andproperties. First of all, in this paper, the theory of interface thermodynamics wasapplied in microencapsulation process to explain the effect of stabilization ofemulsion on yield and properties of microcapsules. For the application example, wesuccessfully prepared chitosan-(urea formaldehyde) shell microcapsule usingparticle-stabilized emulsion by an interfacial gel layer which is self-assembled byelectrostatic adsorption between negatively charged surfactant SDS and positivelycharged polysaccharide chitosan in an oil-in-water emulsion. Finally, the optimumconditions for preparing microcapsules were concluded. Additionally, the theory ofinterface thermodynamics were also applied in other microencapsulation process inthis paper.Secondly, we investigated synthetic principle, synthesis condition and propertiesof epoxy-containing microcapsules. Microcapsules were synthesized by in situpolymerization of urea and formaldehyde in an emulsion. The optimum conditionsfor preparing microcapsules were concluded. Under the optimum conditions,resultant microcapsules possess adequate physical properties for application in self-healing materials. The core-shell structure of microcapsule was proved by FT-IR,OM and SEM. The reactivity of core material was proved by DSC. Besides,microcapsules possess good thermal stabilization, which can keep chemicalstabilization under253℃.On this basis, binary self-healing material based on anionic chainpolymerization of epoxy resin and DMP-30was developed. DMP-30-containingmicrocapsules were prepared by solvent evaporation method. The synthetic principle,synthesis process, surface morphology, size distribution and average diameter, chemical structure, core anti-permeability, reactivity of core material and thermalstabilization were investigated. The core-shell structure and core reactivity ofmicrocapsules were proved, but the anti-permeability of microcapsules in ethanolsolvent was poor. Otherwise, microcapsules can keep chemical stabilization under153℃. Finally, self-healing samples with epoxy-containing microcapsules and DMP-30-containing microcapsules were fabricated, and self-healing efficiency was testedby fracture toughness before and after healing process. The results shows that self-healing efficiency increases with the enhancement of content of microcapsules.Unfortunately, healing efficiency of this system is lower because of the poor anti-permeability of microcapsules. This system needs further investigation, especially onthe suitable carrier of core material.Besides, we also investigated binary self-healing system with epoxy-containingmicrocapsule and latent hardener2MZ-AZINE based on anionic chainpolymerization. Self-healing samples were prepared for measuring healing efficiency.It is worth noting that although healing efficiency increases with a rise inmicrocapsules content in the regime of low microcapsules content, the former isnearly independent of microcapsules content above a certain value. Once dosage of2MZ-AZINE reaches the prescribed minimum, anionic chain polymerization of thereleased epoxy begins at certain temperature. The requirement of stoichiometriccomposition at every inch of repair region is unnecessary. Therefore, the distributionof microcapsules and latent curing agent greatly influences the healing efficiency. Asa result, the optimal weight ratio of microcapsules and curing agent2MZ-AZINEembeded in the epoxy matrix are15wt%and2wt%, and the healing efficiency is~83%. The SEM photos of fracture surface before and after healing process provedthat healing process was successfully realized.At last, we investigated binary self-healing system with epoxy-containingmicrocapsule and ethylenediamine(EDA)-containing microcapsule based on additionpolymerization. EDA-containing microcapsules were successfully prepared bycombining solvent extraction method with interfacial polymerization method. Thesynthetic principle, synthesis process, chemical structure, surface morphology, sizedistribution and average diameter, thermal stabilization and reactivity of corematerial were investigated. The optimum conditions for preparing microcapsuleswere concluded. The core-shell structure and core reactivity of microcapsules wereproved. The appearance of resultant microcapsule was transparent, spherical and lessadhesion. The interface performance between microcapsules and matrix wasunnecessary to be considered because of the epoxy-EDA shell material when used inan epxoy-based composite. Additionally, microcapsules can keep chemicalstabilization under90℃, but unlimited exposure under thermal environment will leadto the increase of weight loss of core material. Finally, self-healing samples wereprepared for measuring healing efficiency. At lower content of epoxy-containing microcapsules and EDA-containing microcapsules, healing efficiency was mainlyinfluenced by distribution of both microcapusles in the matrix. At higher content ofboth microcapsules, content of both microcapsules was to be the main factor thatinfluenced the healing efficiency. As a result, the optimal weight ratio of epoxy-containing microcapsules and EDA-containing microcapsules embeded in the epoxymatrix are12wt%and8wt%, offering~80.4%healing efficiency. The SEM photosof fracture surface before and after healing process proved that healing process wassuccessfully realized.Additionally, epoxy/DMP-30self-healing system, epoxy/2MZ-AZINE self-healing system and epoxy/EDA self-healing system were comparatively investigatedat the aspect of preparation process, healing mechanism, healing efficiency andeconomic cost. In preparation process, we adopted double-microcapsule system onepoxy/DMP-30and epoxy/EDA self-healing system, which largely damaged themechanical performance of material. But epoxy/2MZ-AZINE self-healing systemwas adopted by single-microcapsule system, which weakly effected on themechanical performance of material compared with double-microcapsule system. Inhealing mechanism and healing efficiency, epoxy/DMP-30and epoxy/2MZ-AZINEself-healing system is based on anionic chain polymerization, which inferred that lesshardner content could initiate the polymerization. The epoxy/EDA self-healingsystem is based on addition polymerization, which inferred that content of thehealing agent largely influenced the healing efficiency at a certain range. Ineconomic cost, the expenditure of epoxy/DMP-30self-healing system is the most one.