Preparation And Properties Of Polysiloxane Modified Vinyl Acetate Copolymer For Concrete

With the rapid development of foundation construction engineering in China,concrete that is vulnerable to erosion in harsh environments has been unable to meet the needs of industrial applications.For the problem of concrete durability protection,the most effective method is to coat a protective coating on the surface to prevent harmful particles from invading its interior and achieve the purpose of protection durability.Vinyl acetate polymer（PVAc）is one of the most promising polymer coating materials due to its excellent flexibility,high bonding strength,low cost and abundant production.However,its hydrophilicity and low hardness greatly limit its application in the field of foundation construction engineering.Therefore,it is urgent to design scientific and effective modification methods to cope with the shortcomings of PVAc performance.Based on the surface structure mechanism of concrete,the construction of strong bonding adhesion between coating and concrete surface is the key to ensure its protective durability.In this paper,starting from the molecular structure design,the siloxane monomer was copolymerized with vinyl acetate,and two kinds of tertiary vinyl carbonate monomers with different soft and hard were introduced to synergistically regulate the properties of polymer molecules.On this basis,the superhydrophobic antifouling coating was obtained by filling inorganic nanoparticles,in order to improve the performance defects of PVAc,optimize the comprehensive performance of polymer coating and expand its application range.The main research contents are as follows:（1）Vinyltriethoxysilane（VTES）,vinyl neononate（Veo Va-9）and vinyl neodecanoate（Veo Va-10）were used as monomers to modify PVAc by free radical copolymerization to prepare siloxane-modified vinyl acetate copolymer（PVSND）for concrete protection research.The former VTES as a coupling agent in the polymer,on the one hand self-crosslinks to form a 3D network structure,on the other hand forms a chemical bond with the substrate hydroxyl group.The steric hindrance effect of the long carbon chain alkyl of the latter tertiary vinyl carbonate further enhances the protective effect of the polymer coating.The structure and coating morphology of the polymer were characterized,and the thermal stability,mechanical properties,waterproof and corrosion resistance of the modified polymer were investigated.Characterization tests showed that a Si-O-Si cross-linked network was formed on the polymer chain after wet curing.The Tg distribution of the polymer confirms that the two tertiary ethylene carbonates regulate the rigidity and flexibility of the polymer molecular chain.Due to the chemical bonding between siloxane and the substrate,the adhesion and wear resistance of the coating after siloxane modification were significantly enhanced compared with the unmodified PVAc.The modified polymer changed the hydrophilic PVAc into hydrophobic,the contact angle reached 98°,and the minimum water absorption was only1.25%.Electrochemical tests showed that the anti-corrosion efficiency increased to 98%,and the 480-h salt spray test of reinforced concrete model also verified its excellent anti-corrosion performance.（2）The fluorine-modified Si O₂nanoparticles（F-Si O₂）were sprayed on the semi-cured siloxane-modified vinyl acetate coating to construct a superhydrophobic composite coating with rough structure.The silicon hydroxyl group on the polymer molecular chain condenses with the hydroxyl group of the nanoparticles,giving the nanoparticles excellent bonding stability.Compared with the ordinary hydrophobic coating,the siloxane modified vinyl acetate superhydrophobic composite coating obtained by spraying not only has good mechanical stability and acid-base resistance,but also has excellent water resistance and corrosion resistance due to the chemical bonding effect.The water contact angle of the composite coating can reach 163°,and the water absorption rate in one week is reduced to below 0.91%.The electrochemical test shows that the anti-corrosion efficiency is 98.27%.The reinforced concrete coated with the composite coating can withstand 720 h salt spray,and the internal structure is not damaged by erosion.In summary,based on the molecular structure design,the siloxane modified vinyl acetate copolymer was prepared for concrete protection.Compared with the unmodified polymer coating,the mechanical properties and water corrosion resistance of the modified polymer coating were significantly improved.At the same time,the superhydrophobic anti-fouling surface was constructed for the modified polymer,which expanded its application range and provided new ideas and research directions for the application research and development of vinyl acetate modification.