Synthesis Of Water-dispersed Anionic Closed Polyurethane And Its Application In Special Paper

In recent years,water-dispersible polyurethane emulsions have received more and more attention due to their excellent environmental performance and the improvement of paper surface strength,especially the increasing application of water-based polyurethane surface sizing agents in industry.But water-based polyurethane as a special paper surface sizing agent has a great problem in application,that is,a cross-linking agent must be added to form a three-dimensional network to achieve the purpose of significantly improving strength and water resistance.In this way,it must be applied at low temperature.Glue,because under high temperature conditions,the cross-linking agent quickly reacts with the polyurethane to form a gel,and cannot achieve the surface sizing effect.Therefore,how to realize the sizing of polyurethane at high temperature has always been a problem faced by the special paper industry.The design idea of this subject is to first synthesize water-dispersible polyurethane,and then add a blocking agent to the water-dispersible polyurethane to perform a capping reaction to prepare a closed-type water-dispersible polyurethane,which can be combined with fibers in the surface sizing process at the designed temperature.Then,it is deblocked under drying conditions,re-forms the highly active isocyanate groups,and quickly forms chemical crosslinks to achieve crosslinking between synthetic polymers and between polymers and fibers,thus solving the problem of water at room temperature(room temperature)The problem of the reactive isocyanate group in dispersing polyurethane reacts with other substances,and it will not cause side reaction with water when dispersed in water.The emulsion polymer has good stability and can be stored for a long time.In use,after being unsealed at a certain temperature,the isocyanate groups are released again and interact with the fibers in the paper,thereby enhancing the performance of the paper and resisting water.In order to enhance the affinity of the surface sizing agent and paper fibers,this paper uses polyethylene glycol-1000(PEG-1000)and isophorone diisocyanate(IPDI)as the basic monomers for the polymerization reaction,using different molar Compared with hard and soft monomers and chain extenders,water-dispersed anionic closed polyurethane(WPUD)is obtained,and it is formulated into a special paper surface sizing liquid for comparison of different sizing processes,and the sizing agent is used for special paper.Various performance tests.(1)Use PEG-1000 and IPDI as polymerized monomers and 2-2-dimethylolpropionic acid(DMPA)as anionic hydrophilic chain extender to prepare polyurethane prepolymers;perform prepolymers with butanone oxime Block reaction;neutralize salt with triethylamine(TEA);add deionized water as the dispersed phase for emulsification,and finally prepare WPUD emulsion.The study found that when the prepolymer R(the ratio of the amount of-NCO and-OH in the prepolymer)value is 1.2,the DMPA content(mass percentage)is 7%,and the degree of neutralization is 90%to 100%,During the prepolymerization reaction,the solvent is N-methylpyrrolidone(NMP),the time is controlled from 3.5 h to 4 h,and the reaction temperature is controlled between 80℃ and 85℃;through the particle size,viscosity and stability,rheological properties According to the test,the prepared WPUD emulsion has better comprehensive performance;through infrared analysis,molecular weight and isocyanate content determination,the reaction temperature of the blocking reaction process is controlled at 60℃-65℃,the time is controlled at 3 h-3.5 h,the blocking rate can reach the maximum The value is 100%;the unsealing temperature of the polymer is 105-120℃,and the mechanical properties and thermal properties of the film formed by WPUD are up to the standard.(2)Physically mix the solution of polyvinyl alcohol(PVA-1799)with a mass fraction of 10%and WPUD emulsion(solid content of 30%),and then add glycerin with a mass concentration of 25%to prepare a composite special paper sizing solution.The study found that when the sizing temperature is 70℃ and the drying time after paper sizing is about 10 minutes,the paper sizing degree reaches the maximum value,and when the amount of WPUD dispersion(solid content is 30%)is 3%,PVA(Mass fraction is 10%)When the dosage is 3.5%,the maximum sizing degree is 27.3%,tear index 8.82 mN·m2/g,tensile index 54.34 N·m/g,dry tensile 83.01 N,wet tensile 31.51 N,folding resistance 3189 times,stiffness 85.65 mN,the mechanical properties of specialty papers have reached the maximum,the contact angle can reach 89.54° through the contact angle test,and the paper has good water resistance.Finally,by testing the micro-topography before and after the sizing of the paper surface,it can be seen that the fibers are tightly bound to each other,the sizing solution is evenly attached to the fiber surface,and the paper fiber surface morphology is smooth and neat.