Study On The Preparation Of Polyurethane Microcapsules And The Self Repairing Performance Of The Coating

Coating is widely used in the fields of architecture,furniture,large industrial equipment,automobile and so on.However,in service,the microstructure of the coating changes easily due to the external stress,and micro cracks of different sizes are produced.If there is no repair in the specified time,the cracks will expand and spread under stress.Finally,the cracking and peeling of the coating will seriously affect the corrosion resistance,insulation and decoration effect of the coating.Up to now,the existing technology to repair scuffing coatings is to spray new coatings after exterminating the old ones.Therefore,in order to overcome the above-mentioned predicament,research on the self-repairing technology of the coating has arisen domestically and internationally.Among them,microcapsule technology is simple,low cost,and suit better to coat repairing.In this context,a new type of microcapsules was prepared and the effects of its addition in the performance of self-healing coatings were studied.In this paper,the self repairing microcapsules of polyurethane coated isocyanates were prepared by interfacial polymerization with toluene diisocyanate(TDI)as core material and two phenyl methane diisocyanate(MDI)and polyethylene glycol(PEG)as wall materials.The influence of reaction temperature,emulsification time,stirring rate and other reaction parameters on the properties of microcapsules were investigated,and the optimum conditions to synthesis microcapsule were obtained.Fourier transform infrared spectrometer(FTIR),optical microscope(OM),scanning electron microscope(SEM),thermogravimetric analyzer(TGA),and Nano Measurer version 1.2 particle size distribution calculation software were used as analysis tools for microcapsules structure,morphology,thermal stability,and average particle size and particle size distribution.The experimental results showed that the microcapsules with polyurethane as the wall material and toluene diisocyanate(TDI)as the core material were successfully prepared by the interfacial polymerization method.The process parameters were as follows:the emulsifier was OP-10,and the stirring rate was 300 r/min,the reaction temperature is 35~oC,the mass ratio of the core wall is 1:0.8,the emulsification time is 20 min,the reaction time is 3.0 h,and the emulsifier dosage is 12%.Under these conditions,the prepared microcapsules have a regular spherical shape,a smooth and dense surface,good dispersibility,at the same time,the yield and encapsulation efficiency reach the maximum value,and the thermal stability is good,the distribution of microcapsules also narrowed obviously after the optimization,and the average particle size decreased from 31.81?m to 20.14?m.To prepare self-healing coatings,the microcapsules prepared under the best process parameters were added into polyurethane coatings,and then the coatings were sparyed on the metal surface according to the requirements,and the effects of microcapsule content on the mechanical properties,the corrosion resistance and self repairing properties of self repair coatings were studied,meanwhile,the self repair effects of the coating was preliminarily characterized by optical microscope(OM)and scanning electron microscope(SEM).The experimental results show that the microcapsules show good dispersion in the coating,and the bright liquid can be seen in the scratches when the scratches are scratched manually,which indicating that the repair agent in the microcapsules was released;in addition,when the content of microcapsules is 10%~15%,the coating can maintain good mechanical properties;and when the dosage is 15%,the corrosion resistance and the self repairing performance of the coating is the best.