| Metal corrosion brings lots of problems,such as huge economic loss,environmental pollution and serious loss of social resources to human society,and even poses a serious threat to the safety of human life.At present,the most common and effective method of corrosion prevention is anticorrosive coatings.However,traditional solvent-based anticorrosive coatings cause two environmental problems.Firstly,they contain a large number of toxic volatile organic compounds,a considerable part of which have been listed as carcinogenic substances,seriously endangering people's health;Secondly,the organic resin in the coating can not be degraded after being discarded,which causes secondary pollution to the environment.Water-based coatings with water as solvent or dispersant,do not contain toxic volatile organic compounds,but the current water-based coatings are difficult to achieve the effect of solvent-based coatings in the anti-corrosion performance,and because of this,the application of water-based coatings are limited.Therefore the research and development of the green anticorrosive coatings which are environmentally friendly are extremely urgent.In this paper,based on the fact that polyvinyl alcohol has both good film-forming and biodegradable properties,and the potential to make biodegradable anti-corrosion coating,we modified the polyvinyl alcohol and the anti-corrosion properties of polyvinyl alcohol are explored.The corrosion resistance of the polyvinyl alcohol varnish was explored firstly.And then the different content of nanometer silicon dioxide and glutaraldehyde were added to the polyvinyl alcohol respectively.The influence of the nanoparticles and chemical modification mechanicals on the structure,properties and corrosion resistance of polyvinyl alcohol coating was explored,and the corrosion protection mechanism of the modified coatings was analyzed.The conclusions are as follows:(1)Polyvinyl alcohol coating is a semi-crystalline polymer containing crystalline regions and amorphous regions.The coating contains a large number of hydroxyl groups,and the contact angle is 24.9°.The coating showes strong hydrophilicity.The polyvinyl alcohol coating has a high water absorption rate,which is up to 256%after soaking for 10 minutes.The corrosion resistance of polyvinyl alcohol coating is poor,and it is difficult to carry out effective corrosion protection on the matrix of Q235.(2)Nano-silica added in polyvinyl alcohol can cross-link with the hydroxyl group of polyvinyl alcohol through the silica alcohol group on the surface.Nano-silica can decrease the crystallinity and improve the glass transition temperature.Properties have also been improved to a certain extent.The modification effect of nano silica with a mass fraction of 3%is obvious,and the tensile strength,adhesion and contact angle of polyvinyl alcohol coating are improved by 31.53%,40.56%and 66.5%,respectively.Nano-silica has a certain hindering effect on the penetration of electrolyte solution.It is speculated that nano-silica improves the compactness of the coating,and the electrolyte solution is not easy to penetrate into the interface between the coating and the base metal,so that the corrosion resistance of the polyvinyl alcohol coating can be improved to a certain extent.The results show that the modification effect of nano-silica with a mass fraction of 3%is best.(3)When the crosslinking ratio is 0.3,the main reaction glutaraldehyde reacting with polyvinyl alcohol is crosslinking;When the crosslinking ratio is 1.2,mainly branching.The condensation of glutaraldehyde with polyvinyl alcohol hinders the orderly arrangement of the molecular chain of polyvinyl alcohol,and thus hinders the movement of the molecular chain,resulting in lower crystallinity,lower melting temperature,higher glass transition temperature and higher crosslinking density of the polyvinyl alcohol coating.With the addition of glutaraldehyde,the tensile strength of polyvinyl alcohol coating decreases,and the contact angle of the coating increases.The glutaraldehyde modified polyvinyl alcohol coating with a crosslinking ratio of 0.3 has the best performance,which can form a relatively dense three-dimensional space network structure and effectively hinder the penetration of electrolyte solution.The modified coating has a good protective performance on the metal matrix. |
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