Preparation Of Reactive Microcapsules And Their Application In The Construction Of Self-healing

Self-healing microcapsules have been used in concrete,textiles,biomimetic intelligent materials,metal materials and other fields.A large number of losses are caused by the corrosion of metal materials in the world every year.Traditional coating technology is used to protect metal materials.Once the coating is damaged,the metal matrix loses protection and then corrosion occurs.In recent years,intelligent repair coating,as a new star in the field of metal corrosion prevention,has gradually entered people's vision,among which the microcapsule self-healing coating can repair the micro-cracks of the coating,restore the mechanical properties of the coating and extend the service life of the coating,which is a research hotspot in the field of anticorrosion.At present,there are many researches on the self-healing microcapsules using catalysts.The catalysts used in this kind of microcapsules are expensive,not universal,and not of high practical application value.In addition,some coatings with self-healing ability using dynamic covalent bonds often require higher external temperature.Therefore,it is of great significance to develop a self-healing microcapsule without catalyst,with good repair effect at low temperature,cheap price and wide application sites.Isocyanate has active chemical properties.It can react with active hydrogen.For example,it can react with water in the air at room temperature.It is a self-healing agent without catalyst that can also achieve good repair performance at low temperature.However,compared with other studies on self-healing microcapsules,the isocyanate microcapsule selfhealing coating still faces many problems,such as the shallow research on the repair mechanism of the coating and the less research on the factors affecting the repair performance of the coating.To solve the above problems,in this study,isoverone diisocyanate(IPDI),tung oil(TO),polyaspartic acid ester(PAE)and TO mixture(PAE/TO)was selected as the content active substance to prepare microcapsules,and the microencapsulation-type epoxy resin coating was constructed.Three kinds of microencapsulated self-healing coatings were compared and the influence of different factors on the self-healing properties of microencapsulated self-healing coatings and their changing rules were revealed.The repair effect of isocyanate microencapsulated self-healing coating was affected by adjusting the external environmental factors,which provided a reference for the practical application of this kind of self-healing coating.The details are as follows.Firstly,IPDI microcapsules with polyurethane(PU)wall material were prepared by interfacial polymerization,trimer of toluene diisocyanate(TDIt)and 1,4-butanediol(BDO)as monomers in oil and water phases.The morphology,particle size and structure of the microcapsules were characterized by microscopy,scanning electron microscopy(SEM),laser particle size analyzer and fourier transform infrared spectroscopy(FTIR),etc.It was proved that the microcapsules had good morphology and uniform size distribution.The results of acetone extraction showed that the encapsulation efficiency of IPDI microcapsules coated with polyurethane was 59.6%,and the content of core material was high.Also,microcapsules have good storage stability at room temperature and high temperature.The influence of polymerization parameters on the preparation process of IPDI microcapsules was further investigated.It was found that the particle size of the microcapsules decreased with the increase of the shear rate.When the shear rate was 1000 rpm,the microcapsules had good morphology and moderate particle size.The dispersion time should not be too short or too long,and 10 min is the optimal dispersion time under this condition.The amount of dispersant also affects the morphology and size of microcapsules.When the amount of dispersant is 2wt%,microcapsules with good morphology and average particle size of 65.3 ?m can be obtained.The oil/water ratio and core/wall ratio should also be moderate.Under the condition of oil/water ratio of 1:2 and core/wall ratio of 3:1,the microcapsules obtained have good morphology and moderate shell wall thickness.Through a series of factors,the change of particle size and morphology of microcapsules under different polymerization parameters was revealed.TO and PAE/TO microcapsules with melamine/formaldehyde(MF)resin wall material were synthesized by in-situ polymerization.A series of characterization methods were used to characterize the structure and properties of the microcapsules.The surface of the microcapsules was smooth and had good morphology observed by microscope and SEM images.The TGA test showed that PAE/TO microcapsules had good thermal stability.The release behavior of the microcapsules was studied at room temperature and high temperature.After 40 days,the mass loss of PAE/TO microcapsules was 1.2wt% and 5.2wt%,respectively,indicating that the microcapsules had good storage stability.On this basis,the effects of different factors on the morphology and particle size of PAE/TO microcapsules were studied.The shear rate had little effect on the particle size and morphology of PAE/TO microcapsules.The dispersion time of microcapsule emulsion should not be too short,if the emulsification time is too short,the effect of stabilizing microcapsule droplets may not be achieved.When the amount of dispersant was 5wt%,TO and PAE/TO microcapsules with good morphology and average particle size of 3.9 ?m and 2.3 ?m could be obtained.The oilwater ratio and core-wall ratio also have a great influence on the preparation process of microcapsules.When the oil-water ratio and core-wall ratio are too large,the microcapsule system is prone to agglomeration.Under the condition that the core material content is sufficient,when the oil-water ratio is 1:3 and the core-wall ratio is3:1,microcapsules with good morphology can be obtained.Under the experimental conditions of this paper,the optimal synthesis conditions of microcapsules were determined,and the morphology of microcapsules was controlled by different factors.Finally,the corrosion resistance and self-healing properties of three different microencapsulated self-healing coatings were studied.The steel plate coated with the microcapsule self-healing coating was scratched and immersed in a 10wt% Na Cl aqueous solution for 48 hours,and no rust appeared,but the steel plate coated with pure epoxy resin showed obvious rust at the scratch,indicating that the microencapsulated self-healing coating has excellent corrosion resistance.The effect of the amount of microcapsule on the self-healing property of the coating was also studied.The coating repair effect of the amount of microcapsule of 10wt% was relatively good.Humidity and temperature have great influence on IPDI microencapsulated epoxy coating and double microencapsulated epoxy resin coating after mixing IPDI microcapsule and PAE/TO microcapsule.Under the conditions of low temperature and low humidity,IPDI microencapsulated epoxy coating has poor repair performance.The mixed double microencapsulated epoxy coating had good repair effect.Under the condition of T=30 ?and RH=55%,both microencapsulated epoxy coatings have good repair properties,and the repair rate of two-component microencapsulated epoxy resin coating is higher than that of one-component IPDI microencapsulated epoxy resin coating under the same conditions.In this paper,three self-healing microcapsules were prepared successfully,and the morphology,structure and properties of microcapsules were characterized.The influence of polymerization parameters on the preparation process of microcapsules was discussed.The microcapsules were dispersed in epoxy resin and the microcapsule type self-healing coating were constructed.The effects of different factors on the healing properties of TO,IPDI and two-component self-healing epoxy resin systems were studied,which provided some research ideas for the reasonable control of the selfhealing properties of coatings.