Preparation Of Waterborne Photocurable Polyurethane And Design Of Its Flame-retardant System

As an excellent surface treatment material,waterborne photocurable polyurethane（WPUA）is widely used in wood,construction industry,automobile coating and other fields.However,the photocurable polyurethane material has high flammability,accompanied by the phenomenon of melting drops,easy to cause fire spread.Therefore,flame retardant modification is needed in some specific applications.WPUA takes water as the dispersing agent and mainly exists in stable emulsion state.After curing,it is a transparent coating attached to the surface of the substrate.Its flame-retardant modification has its particularity.The flame retardant has good compatibility with WPUA after volatilization of water,which reduces the influence on the appearance,refraction,mechanical properties,adhesion and other properties of the coating film.The traditional flame retardant modification method is difficult to achieve the balance between flame retardant,emulsion stability and film performance.In this paper,a series of WPUA systems with emulsion stability and excellent film properties were prepared,and the flame retardant modification was studied.The advantages and defects of traditional physical addition flame retardant and bulk flame retardant were systematically compared,hoping to prepare a WPUA flame retardant system with good flame retardant and physical properties.Specific work is as follows:（1）A series of water-based photocurable polyurethanes（WPUA）were prepared using poly1,4 butanediol adipate（PBAG）as soft segment,isophorone diisocyanate（IPDI）as hard segment,2,2-dihydroxymethylpropionic acid（DMPA）as hydrophilic chain extender,and hydroxyethyl acrylate（HEA）as ending agent.The effects of R value（-NCO/-OH ratio）,DMPA content and polyol molecular weight on emulsion stability,particle size,hardness and water absorption of WPUA solidified film were investigated.The experimental results show that when R value（-NCO/OH ratio）is 1.8and DMPA is 3wt%of the prepolymer content,the prepared WPUA emulsion has small particle size,narrow distribution,good stability and excellent physical properties.（2）Two representative additive flame retardants,dimethyl phosphate（DMMP）and ammonium polyphosphate（APP）,were used for the flame retardant modification of WPUA,and the flame retardant characteristics of phosphorus series and phosphorus nitrogen series flame retardants on WPUA were studied.At the dosage of 10wt%,the flame retardancy of WPUA/DMMP system and WPUA/APP system can reach the V-0level of UL-94 test,but DMMP and APP reduce the appearance and refraction of the coating significantly.（3）Through molecular design,the reaction of phosphorus pentoxide（P₂O₅）with hydroxyethyl acrylate（HEA）as raw material to prepare water-based flame retardant monomer（WFRT）,in order to achieve bulk flame retardant of WPUA system.The results showed that when the WFRT dosage was 20wt%,the limit oxygen index（LOI）value of WPUA flame retardant material reached 30.5%,and passed the V-0 level of UL-94 test.Cone calorimetry test results show that the addition of WFRT can significantly reduce the peak heat release and total heat release of WPUA during combustion,and reduce the combustion hazard.Due to the special structure of WFRT,it can participate in curing film formation.The emulsion quality of WPUA/WFRT system is stable,and the film performance is comparable to that of WPUA.Meanwhile,the flame retardancy mechanism of WPUA/WFRT was discussed by analyzing the decomposition products of gas phase and liquid phase.