Preparation And Properties Of Emulsifier-free Poly(Vinyl Versatate-acrylate) Emulsion Based On Power Feeding Method

With the development of the coating industry and requirements for environmental protection,water-borne coatings gradually replace solvent-based coatings,and become the main part of water-borne industrial coatings and architectural coatings.The traditional water-borne acrylic coatings have excellent weather-resistance and light-resistance,but their water-resistance,anti-stickiness and corrosion resistance are difficult to meet the needs of production and life.In this paper,a kind of vinyl versatate-acrylate emulsion with a gradient structure was preparied by the power feeding method,and the anti-stickiness was improved.Meanwhile,reactive emulsifiers were intrudced to eliminate that the emulsifier small molecules residue on the surface of the coating film,and improve its water-resistance.The properties of vinyl versatate-acrylate emulsion and films were characterized by FT-IR,¹H NMR,DMA and electrochemical method.The main research contents are as follows.First,a kind of emulsifier-free vinyl versatate-acrylate emulsion with a gradient structure was prepared derived from methyl methacrylate（MMA）and methacrylic acid（MAA）as hard monomers,vinyl versatate and butyl acrylate（BA）as soft monomers,K₂S₂O₈ as an initiator,NaHCO₃ as a buffer and the diacetone acrylamide（DAAM）/adipate diamide（ADH）as a cross-linking system by the power feeding method.The effect of a amount of reactive emulsifier and monomers,feeding order of monomers and DAAM/ADH ratio on the properties of the vinyl versatate-acrylate emulsion and film was investigated systematically.the structure,particle morphologyary,particle size and distribution,and Zeta potential of the vinyl versatate-acrylate emulsion was analysized by FT-IR,¹H NMR,TEM,laser particle size distribution meter,respectively.Meanwhile,the thermal properties and glass transition temperature of vinyl versatate-acrylate latex film was characterized by TGA,DSC and DMA,respectively.The results show that vinyl versatate-acrylate emulsion is an excellent stability,the Zeta potential is 68.5 m V,the viscosity is 395 m Pa·s,the heat resistance is the best,the internal structure gradient is small,the flocculation rate less than 0.61%and the size of particle of 113.2 nm,and latex film is of good thermal-resistant,the glass transition temperature of 31.9℃,the water contact angle is 90.4°,the crosslinking degree of 140.79 mol/m³,the water absorption rate of 2.5 wt%and the better mechanical properties,when reactive emulsifier,vinyl versatate and the ratio of DAAM/ADH was 3.0 wt%,25 wt%and 2.0:0.8,respectively,soft monomers and hard monomers account for about 1/3 of the total monomers in feeding bottle 1 and feeding bottle 2,respectively.Secondly,the influence of the reactive emulsifier dosage,vinyl versatate dosage,monomer feeding sequence and DAAM/ADH ratio on the corrosion resistance of the vinyl versatate-acrylate emulsion was analysized by the polarization curve and electrochemical impedance spectroscopy（EIS）.The results show that the coatings is of smaller self-corrosion current density,relatively close to the positive potential self-corrosion voltage,the higher phase angleθin the EIS,and the strongest anti-flash rust performance when the amount of VV-10,emulsifier,the soft monomers VV-10 and BA in the feed bottle 1,and the ratio of DAAM to ADH is 25 wt%,3.0 wt%,15 wt%and 2.0:08,respectively.When an electrode prepared from a tertiary acrylate emulsion with a dosage of 25 wt%of VV-10 is immersed in a 3.5%NaCl solution,as the immersion time increases,θfirst decreases and then increases,and the impedance first decreases and then increases.Then,a series of waterborne anti-corrosive paints was prepared based on vinyl versatate-acrylate emulsion containing 15 wt%vinyl versatate and glass transition temperature of 26.9℃.The effect of the type and dosage for inhibitor on the corrosion resistance of waterborne coatings was investigated by polarization curve and EIS.It is concluded that when the dosage of FA179 was 3 wt%,the self-corrosion current density was the minimum,which was 7.73×10^-7 A/cm²,when the amount of NaNO₂ is 3 wt%,the self-etching voltage of nagetive 0.624 V is the closest to the positive potential and the strongest anti-flash rust performance.When an electrode prepared from a tertiary acrylate emulsion with a NaNO₂ solution dosage of 3 wt%is immersed in a 3.5%NaCl solution,as the immersion time increases,θand impedance arc gradually decrease,indicating that the corrosion phenomenon of the coating becomes more and more obvious.