Preparation Of Ammonium Stearate Emulsion And Its Application In Waterborne Polyurethane Foam Coating

Ammonium stearate emulsion can be used as a foam stabilizer to be added to the waterborne polyurethane foam coating,and has a good foam stabilization effect.However,the ammonium stearate emulsion prepared under the existing technology has some shortcomings,such as high viscosity during application,low saponification rate,poor product stability,easy to thicken after long-term storage and easy to solidify at low temperature,etc.In this paper,by preparing stearic acid into stearic acid emulsion,the particle size of stearic acid is reduced,thereby greatly increasing the contact area with lye and improving the reaction efficiency.Since the stearic acid becomes an emulsion,the soap base generated during the reaction will not be agglomerated and has a better dispersion effect.After the reaction is completed,viscosity reducer and stabilizer are added to the product to make the product easy to store and use.The ammonium stearate emulsion prepared by the improved process and the traditional process was added to the waterbone polyurethane(WPU)and subjected to physical foaming,and the difference in foam stability between the two was compared.The main research contents and conclusions are as follows:The anionic emulsifiers K12(sodium lauryl sulfate),LS(sodium lauroyl sarcosinate),PO(potassium oleate),LAS(sodium dodecyl benzene sulfonate),MOA-3PK(fatty alcohol ether phosphate potassium salt)and nonionic emulsifiers Span-60(sorbitic monostearate),Span-80(sorbitic monooleate),GMS(glyceryl monostearate),Tween-60(polyoxyethylene(20)ether sorbitan monostearate),Tween-80(polyoxyethylene(20)ether sorbitan monooleate),OP-10(octylphenol polyoxyethylene ether-10),AEO-9(fatty alcohol polyoxyethylene ether)are used to emulsify stearic acid.Taking the size of emulsion droplets and particle size distribution and emulsion viscosity as evaluation indicators,the appropriate emulsifiers were selected by means of laser particle size analyzer,viscometer and transmission electron microscope.The results show that when a single emulsifier is used,the emulsification effect of MOA-3PK is the best.After optimizing the process conditions,the optimal emulsification conditions are obtained as follows:the dosage of MOA-3PK is 6%of the mass of stearic acid,the emulsification temperature is 70?,the emulsification time is 30min,the stirring rate is 600rpm,and the mass fraction of stearic acid is 22%-28%.The particle size of the final emulsion is 570nm-630nm,and the emulsion viscosity is about 100mPa·s.The following 6 composite systems are obtained by compounding nonionic emulsifiers:Span-80+Tween-80?Span-80+Tween-60?Span-80+GMS?Span-60+Tween-80?Span-60+Tween-60 and Span60+GMS,among which Tween-80+GMS has the best emulsification effect.After the optimization of the process conditions,the optimal emulsification conditions are obtained as follows:the mass ratio between Tween-80 and GMS is 8:2,the dosage of Tween-80+GMS is 10%of the mass of stearic acid,the emulsification temperature is 75?,the emulsification time is 20min,the stirring rate is 500rpm,and the mass fraction of stearic acid is 22%-28%.The particle size of the final emulsion is 530nm-630nm,and the emulsion viscosity is about 166mPa·s.Anionic emulsifiers K12 and MOA-3PK were added to Tween-80+GMS composite emulsifier,and it was found that K12 could reduce the viscosity of the emulsion and improve the stability of the emulsion,and also reduced the dosage of the composite emulsifier.The particle size of the emulsion droplets is similar,and the viscosity is reduced to about 92mPa·s.The prepared stearic acid emulsion is subjected to saponification reaction with ammonia water,and compared with the traditional process.The saponification rate was determined by acid-base titration and characterized by infrared spectroscopy and X-ray diffraction.The results show that the saponification rate of ammonium stearate emulsion increases with the decrease of particle size of stearic acid emulsion,and the lower the solid content of stearic acid,the higher the saponification rate,and the process conditions are optimized.The effects of reaction temperature,reaction time,ammonia water consumption and other factors on the saponification rate were explored,and the optimal reaction conditions were obtained as follows:the saponification temperature was 50?,the saponification time was 1.5h,and the molar ratio of ammonia water to stearic acid was 1.3:1.Finally,the saponification rate under the improved process is 78%,while the saponification rate under the traditional process is about 46%.The Krafft point of ammonium stearate was determined to be 58? by visual inspection and electrical conductivity.Sodium tripolyphosphate was added to reduce the viscosity of ammonium stearate emulsion,which was characterized by viscometer,optical microscope and Zeta potential analysis.The results showed that the viscosity of ammonium stearate emulsion decreased first and then increased with the addition of sodium tripolyphosphate,and the optimum addition amount was 0.08%.The viscosity of ammonium stearate emulsion with a solid content of 30%can be reduced from 1013 mPa·s to 390 mPa·s.The change trend of Zeta potential is similar to the change trend of viscosity of emulsion system.When the addition amount of viscosity reducer is 0.08%,the absolute value of Zeta potential can be increased from 78.9 mV to 87.6 mV,and the fluidity of the emulsion is better.Four surfactants,K12,CTAB(hexadecyltrimethylammonium bromide),6501(coconut oil fatty acid diethanolamide),and OB-2(dodecyldimethylamine oxide)were added as stabilizer to improve the stability of ammonium stearate emulsion,characterized by centrifugation and viscosity measurement.The results show that OB-2 has the best effect,improving the stability of the emulsion without increasing the viscosity of the emulsion.Ammonium stearate emulsion was added as foam stabilizer to WPU foam coating,and the foam stabilization effect of ammonium stearate emulsion prepared by traditional process and improved process was compared.Taking the half-life and pore diameter as the evaluation indicators,the results show that when the addition amount is the same,the half-life of the ammonium stearate emulsion prepared under the improved process is longer,the foam stabilization effect is better,and the pore diameter is smaller than that of the WPU foamed coating prepared by the ammonium stearate emulsion under the traditional process.The relationship between the pore diameter of WPU foamed coating and the drying temperature was investigated,and the results showed that with the increase of the drying temperature,the pore diameter first decreased and then increased.The relationship between the moisture permeability of WPU foam coating and the addition amount of ammonium stearate emulsion was investigated.The results showed that the moisture permeability of WPU foam coating first decreased and then increased with the increase of the addition amount of ammonium stearate.And under the same amount of addition,the moisture permeability of the WPU foam coating prepared by the ammonium stearate emulsion under the improved process is better.The water resistance of the WPU foam coating was investigated,and it was found that under the same amount of addition,the swelling rate and water absorption rate of the WPU foam coating prepared by the ammonium stearate emulsion under the improved process were lower,indicating that the water resistance has a certain improve.The influence of the ammonium stearate emulsion prepared by the two processes on the drying time under different addition amounts was investigated,and it was found that the time under the improved process could be shortened by 22.7%.