Preparation And Properties Of Environment-friendly Self-healing Coatings

To meet the sustainable development direction,environment-friendly coatings without organic compound(VOC)emission is bound to replace traditional oil coatings.Water-based coatings and solvent-free coatings are the two most common types of environmentally friendly coatings.The coatings of waterborne coatings show some defects such as low hardness and poor wear resistance,which shorten the service life and seriously affect the application of waterborne coatings.Light-cured coatings are a kind of solvent-free coatings with efficient,effective,economic,energy saving,environmental protection "5E" characteristics But its fast curing speed will produce structural defects in the internal,the material shows brittleness,easy to crack problems,which hinder the development of light curing coatings.Based on above problem,by introducing intrinsic self-healing system to waterborne coatings and UV-cured coatings and using dynamic reversible bonds to solve the defects of current coatings,this paper prepared a waterborne self-healing polyurethane coating with surface hardening and a Transparent high strength UV-cured self-healing polyurethane acrylate coating.For waterborne self-healing polyurethane coatings: based on IPDI,polyester polyol,2,2-bis(hydroxymethyl)propionic acid,2,6-diaminopyridine as raw materials,a "sparse inner and dense external" gradient double coordination structure with Zn(II)-carboxyl and Zn(II)-diaminopyridine was formed on the coating by means of ion permeation,and we prepared a "soft inner hard external" surface hardening self-healing waterborne polyurethane coating finally.The emulsion properties,hardness,wear resistance and adhesion of the coating were characterized by wear-resistant test,nanoindentation tester and pull-out tester,and the self-repair ability of the coating was characterized by 3D surface profilometer and optical microscope.The results show that the coating have 4H pencil hardness,excellent scratch-resistance,an elastic modulus of 15.3±1.2 GPa and a hardness of 73.4±3.1MPa,a adhesion strength more than 1.5MPa,the scratch repair efficiency(60? for 6 h)of 93% and the coating shows better self-healing efficiency in hot and humid environment.Metal coordination bonds lead to the formation of microphase separation structure,which is the main reason to promote the self-healing ability of coatings.In addition,through AFM(atomic force microscopy),DMA(Dynamic mechanical analysis),crystallization and thermodynamic analysis,we know that the micro-phase separation structure formed on the surface,the reversible action of coordination bonds and the low Tg characteristics of polyurethane are the reasons for the high hardness,good scratch-resistance and excellent self-healing ability of WPUU-x Zn-y coatings.For light-cured coatings: through molecular design and synthesis of a polyurethane acrylate oligomer as components,mixed suitable thinner,UV-light initiator and modified nano silica,finally,a transparent high strength UV-cured self-healing coatings based on reversible disulfide crosslinked network was prepared.Through a variety of test,the characterization of the materials,the synthesis of oligomer and the effects of the ratio of oligomer/thinner and the addition of modified nano silica on the material were studied.The results show that the pencil hardness of the coating is 4H,the elastic modulus is as high as 23.46± 0.4GPa,the adhesion of multiple substrates is good(the bonding strength is greater than 1 MPa,ISO level 1 or 0),the light transmittance in visible region is above 85% and the scratch self-healing efficiency is93%.The introduction of disulfide bonds and the fluidity of molecules together determine the self-healing ability of materials.Then,the effects of UV light on the reversible fracture of aliphatic disulfide bonds were investigated by means of mass spectrometry,DMA and dissolution experiments.In addition,by comparing the tensile strength changes of the UV-cured self-healing material before and after the repair treatment,it is proved that this method can solve the problem of internal structural defects of the light-cured material.