Water Resistance Of Polyvinyl Acetate Emulsion

The technology of emulsion polymerization and the development of polyvinyl acetate emulsion included the water resistance of the emulsion were summarized in this paper.The copolymer emulsions of vinyl acetate(VAc)/vinyl ester of versatic acid(Veova) with elevated water resistance were synthesized by the semi-continuous seeding emulsion polymerization in the presence of methacrylic acid(MAA).The stability,the viscosity and the latex particle diameter of the emulsion,and the water resistance of the emulsions were greatly dependent on the types of carboxylic acid,the content of MAA,the method of introduction of MAA and the degree of neutralization of MAA.Zeta potential,density of surface carboxyl groups,the interaction between carboxyl groups and component in copolymerization emulsion,mechanical properties of films,state of water,particle diameter and distribution of particle diameter and theological behavior of emulsion were investigated by Zeta meter,the conductometric titration, particle size apparatus,dynamic mechanics analysis(DMA),differential scanning calorimmetry(DSC),scanning electron microscope(SEM),rheological apparatus,respectively, to study the mechanism on the water resistance of modified PVAc emulsion.After modification of vinyl acetate and vinyl ester of versatic acid copolymerized with MAA,partial carboxylic groups exist on the surface of latex particles with negative electric charge,and the stability of modified emulsion was increased with the increase of the Zeta potential.The morphology of dispersive emulsion particle was observed by SEM.The results showed that the moderate amount of surface carboxyl groups and ionization carboxyl were available to the improvement of water resistance of latexes.The storage modulus of modified emulsion film with the addition of MAA was increased and the shear rate of the emulsion with maximum viscosity was lower than that of the emulsion with poor water resistance.The peak of freezing bound water was observed between -42.6℃and -50.1℃and the value of onset for the thawing peak of the emulsion was decreased than that of the PVAc and the VAc/Veova emulsion.The moderate particle size and its distribution can improve the water resistance of the emulsion film.The mechanism of improved water resistance of modified PVAc emulsion with MAA was summarized as follows:some carboxyl groups and ionization carboxyl were located on the surface of the latex particles.Freezing bound water was observed in modified emulsion with MAA by hydrogen bond between carboxyl and hydroxyl of polyvinyl alcohol(PVA) and H₂O,and the state of free water was different with pure water.The moderate amount of freezing bound water could protect the hydroxyl to improve water resistance.Carboxyl could influence the congregate structure of PVA and the emulsifiers,affecting rheology of emulsion, water resistance were intensified.The storage modulus of modified film were increased compared with the film of PVAc and VAc/Veova to make the film compact to enhance water resistance.Carboxyl had greatly effect on the formation of particles in the aqueous phase.The moderate particle size and narrow distribution particles could rise the amount of the emulsion in porous wood,so water resistance were improved.The nano-silica/polyvinyl acetate organic-inorganic composite latex was synthesized by in-situ emulsion polymerization of vinyl acetate in the presence of silica nano-particles.The mechanics properties,the state of water,the dispersibility of the silica nano-particles and latex particles and the rheological behavior of the emulsion were studied by the analysis of DMA, DSC,SEM and rheology apparatus.The results indicated that the process of the nano particles by ultrasonic can make a good dispersibility of the silica nano particles and the latex particles in emulsion,which induced better water resistance than the PVAc emulsion.The modified organic-inorganic composite latex had low shear rate of emulsion under the maximum viscosity and the storage modulus of the film increased.The value of the peak for thawing onset of the emulsion was decreased to that of PVAc emulsion,but the peak of freezing bound water was not observed in the composite latex.The observed results are different compare with modified emulsion with MAA.The polymeric emulsifier,reactive emulsifier DNS-86 and composite emulsifier DNS-628 were used in the synthesis of the PVAc emulsion.The poly(vinyl acetate-co-acrylic acid) P(VAc/AA)emulsion was synthesized with acrylic acid and vinyl acetate.The water absorption of film with the polymeric emulsifier was less than original OP-10/SDS emulsifiers.At the same time,the polyvinyl acetate emulsions were prepared by batch polymerization with HAPS, HPMAS,SVS,DNS-86 and DNS-628 as emulsifier.The results showed that the PVAc emulsion with DNS-86 and DNS-628 were better than that with HAPS,HPMAS and SVS in polymerization stability.The stable PVAc emulsion was synthesized with DNS-628 by semicontinuous emulsion polymerization.However,the pre-emulsified process were used to prepare stable PVAc emulsion with DNS-86.