Synthesis,Characterization And Properties Of Waterborne Polyurethane-Acrylic Hybrid Emulsions

Waterborne polyurethane-acrylic(WPUA)hybrid emulsion combines the advantages of both waterborne polyurethane(WPU)and polyacrylates(PA),such as environment friendly,low cost,good film-forming performance,excellent physical and mechanical properties,which has been widely applied in the coatings,adhesives,leather finishes and so on.However,the PA weight ratio in the composition of WPUA is often less than 40% due to limitation of the self-emulsifying ability of these WPU dispersions,and meanwhile,their water-resistance is always poor due to the presence of hydrophilic groups in the WPUA macromolecules.In this research,the NCO-terminated urethane prepolymer containing carboxylic acid group was first synthesized by polycondensation of Isophorone diisocyanate(IPDI),polypropylene glycol(PPG),dimethylolpropionic acid(DMPA),1,4-butanediol(BDO).Coupling agent was used to react with NCO-terminated PU to form allyl-terminated PU.After neutralized by TEA and dispersed in water,allyl-terminated PU were prepared.The WPUA hybrid emulsions with high AC/PU weight ratio,modified with siloxane modification,modified with siloxane and fluorine modification were synthesized via a seeded emulsion polymerization.The main contents are as following.1.Allyl polyoxyethylene ether(APEE)was used as coupling agent between PU and AC to synthesize stable WPUA hybrid emulsions with high AC/PU weight ratio ranged from 45/55 to 70/30.The WPUA hybrid emulsions with good cost/performance benefits can be obtained by this method,and the effect of PA dosage on its performance were investigated.The results showed that the colloidal particles in the emulsions behaved core/shell structure,and the chemical bonds were built up between PU and AC,the hybrid copolymers are linear polymers.All the emulsions exhibited shear thinning behaviors at the initial stage of the shear process.While increasing the PA/PU weight ratio,the viscosity of the emulsions decreased,but the average particle size increased and their size distribution became broad.Meanwhile,the tensile stress,shore A hardness,storage modulus,glass transfer temperature,water resistance and water contact angle of their films increased.2.The WPUA hybrid emulsions were synthesized by introducing different content of hydroxyethoxypropyl-terminated polydimethylsiloxane(PDMS)into the PU backbone and then in situ copolymerizing with methyl methacrylate and butyl acrylate via emulsion process.The results showed thatall the synthesized emulsions exhibited a shear thinning behaviors and the average particle size increased with increasing PDMS content,but the viscosity of the emulsion decreased.The result of Soxhlet extraction showed that the hybrid copolymers were highly cross-linked,but the cross-linking fraction deceased with increasing PDMS content.FT-IR peak deconvolution showed that the introduction of the PDMS reduced hydrogen bonding and caused serous phase separation in the WPUA system.Increase in the PDMS content led to a decrease in the tensile strength,hardness,storage modulus and glass transitions temperature of the film,but the elongation at break increased.The introduction of the PDMS greatly improved water resistance of the film,resulting in forming the films with increased water contact angle.3.The WPUA hybrid emulsions were prepared via the radical emulsion polymerization,with Si PU as the seed emulsion and with methyl methacrylate(MMA)and dodecafluoroheptyl methacrylate(DFMA)as the main monomers.A series of FDMA modified WPUA hybrid emulsions were prepared,and their film properties were investigated.The results showed that all the synthesized emulsions exhibited a shear thinning behaviors and the average particle size increased with increasing FDMA content,but the viscosity of the emulsion decreased.FT-IR peak deconvolution showed that the introduction of the PDMS reduced hydrogen bonding and caused serous phase separation in the WPUA system.Increase in the FDMA content led to a decrease in the tensile strength,hardness,storage modulus and glass transitions temperature of the film,but the elongation at break increased.The introduction of the FDMA greatly improved water resistance of the film,resulting in forming the films with increased water contact angle.