Study On Preparation And Properties Of Polyvinyl Chloride Anticorrosive Coatings

Traditional coatings are mostly at the expense of the environment.With the promulgation of relevant laws and regulations on environmental protection around the world.New environment-friendly powder coatings in line with the regulations have become an important research direction in the current anticorrosive coatings industry.In this experiment,PVC with good weather resistance,good impact resistance and anti-chloride penetration was used as the main film-forming material,electrostatic spraying was carried out in the form of powder coating,and the film was formed by drying.Combined with the three elements of adhesion,barrier and self-repair necessary for the coating to play an effective protective role,the adhesion was enhanced by the preparation of epoxy modified double-layer coating,and the functional graphene oxide nano-filler of polyaniline was prepared.Combined with the small molecule effect of GO and the redox ability of polyaniline,the barrier property of the coating was improved,at the same time,a catalytic passive film was formed at the damaged part of the coating to improve the self-repair of the coating.In order to achieve the long-term protection of the substrate.First of all,through the optimization of plasticizers,antioxidants,pigments and fillers and other auxiliaries to improve the film-forming properties,adhesion and mechanical properties of PVC coatings.By testing the coating performance under different plasticizer dosage,it was concluded that when the amount of dioctyl phthalate（DOP）was 50wt%,the leveling performance of the film was the best,which played a positive role in the compactness of the coating structure.With the increase of DOP content,free DOP hindered the formation of covalent bond between the coating and the substrate,resulting in further corrosion of the coating.Through the observation of the mechanical properties and scanning electron microscope of the coatings with different amounts of pigments and fillers,when the content of pigments and fillers was 3wt%,the dispersion performance of fillers was the best.However,with the increase of filler content,the resin matrix could not wrap all the fillers,resulting in the agglomeration of some non wrapped fillers in the coating.Through the analysis of the aging resistance and thermal weight loss of the coating under different amounts of Ca/Zn,it was found that the Ca/Zn composite heat stabilizer could effectively neutralize the HCl released by polyvinyl chloride due to thermal degradation,so as to eliminate or inhibit its autocatalytic effect on the thermal degradation of PVC.When the amount of Ca/Zn composite heat stabilizer was 3wt%,the coating has a higher tolerable temperature and less mass loss.Through the analysis of gloss,contact angle and Atomic force microscope test（AFM）,it was concluded that the leveling agent migrated to the surface of the film through limited compatibility,which could promote the uniform spread of upper and lower layers,thereby reducing the surface tension and improving the leveling property.Therefore,when the amount of leveling agent was 2wt%,the leveling performance of the coating was the best,the gloss and dispersion were the highest,and the hydrophobicity was the strongest,which further improved the corrosion resistance of the coating.On this basis,the PVC powder coating was modified and a new type of environment-friendly and corrosion-resistant double-layer composite powder coating was developed.The polyvinyl chloride powder coating modified by epoxy resin was used as the primer and the pure polyvinyl chloride powder coating as the topcoat.At the same time,the properties of the coatings under co-curing and layer by layer curing were compared.The mechanical properties,salt spray resistance test and electrochemical test showed that the mechanical properties of the coatings under layer by layer curing were the best and the salt spray corrosion degree was the least.This was because the powder was affected by electric field force in the process of electrostatic spraying.When the iron sheet per unit area reached a certain coverage rate,then some topcoat powder particles were difficult to adsorb on the workpiece,resulting in a decline in the performance of the cured paint film.Scanning electron microscope（SEM）/Raman and transmission electron microscopy（TEM）tests were carried out to further investigate the structure of the coating.The results of FT-IR showed that the epoxy resin formed an insoluble and unfused macromolecular network structure through cross-linking reaction under the action of curing agent.And because the epoxy resin contained a large number of hydroxyl,ether and active epoxy groups,they could form a stable chemical bond with the metal surface containing hydrogen bond,so the adhesion of the coating was significantly improved.However,bisphenol A epoxy resin had high viscosity and tended to produce large internal stress after curing.Therefore,through mechanical property test,salt spray experiment,AFM analysis and SEM test of the coating,it was concluded that the adhesion and salt spray resistance of the coating was the best when the epoxy content in the primer was 50wt%.Finally,electrochemical tests showed that the corrosion rate of polyvinyl chloride/epoxy double-layer coating was much lower than that of pure epoxy double-layer coating and pure polyvinyl chloride double-layer coating after immersion for 15 days.This was because for polyvinyl chloride double-layer coating（PVC/EP）,the compound primer could ensure better adhesion,and the topcoat provides better barrier and corrosion resistance,effectively enhancing the corrosion resistance of the coating.A novel functionalized graphene oxide（GO）sheet of polyaniline（PANI）was prepared by in-situ polymerization of aniline.The results analyzed by FTIR,X ray diffraction（XRD）and SEM indicated the successful polymerization of aniline on GO tablets.And PANI was uniformly inserted into the GO lamellas that benefited the dispersion of PAGO.The anticorrosion properties of PAGO-PVC/EP coatings with different contents were analyzed and compared with GO-PVC/EP coatings.Electrochemical analysis showed that an appropriate amount of PAGO（0.5wt%）could significantly improve the long-term corrosion resistance of the coating.By exploring its anticorrosive mechanism,it was concluded that its excellent corrosion resistance was attributed to two parts:（1）PAGO had good dispersion and could improve the barrier property of the coating to delay the invasion of corrosive media;（2）PANI with complete electrical activity could timely transfer the electrons lost from the base to the coating surface,and form a passivation film composed of Fe₃O₄ and Fe₂O₃ by induction.The barrier property of GO and the self-healing ability of PANI made PAGO-based PVC/EP coatings excellent in corrosion resistance.