Synthesis And Characterization Of Room-temperature Self-crosslinking Polyurethane Emulsion

Aqueous polyurethane is a kind of dispersible polymer with water as dispersing medium,which not only has the advantages of traditional polyurethane coating,but also has the advantages of low cost,safety and a low and even zero VOC,so it will be the trend of future development.As we know,self-emulsifying method is a commonly used method for the synthesis of polyurethane emulsion.However,the hydrophilic groups remain in the film formed by the self-emulsifying resin,so the water resistance of the film is poor,which greatly limits the application of polyurethane emulsion.Crosslinking is a main method to improve the water resistance,but the crosslink agent usually has some defects such as leaving volatile toxic substances in printout,taking a long time to dry in high temperature or reducing stability of the emulsion,so safe and efficient crosslinking system is still a research hotspot at present.In this paper,Isophorone diisocyanate(IPDI),polycarbonate diols(PC)and dimethylol butyric acid(DMBA)are used in the synthesis of waterborne polyurethane.And what's more,ketone hydrazide crosslinking system and modified HDI trimer crosslinking system were used to modify polyurethane.The main work is as follows:1.A kind of multiple amine chain extender which consists of(EDA-di(diacetone propionamido)(EDDP)and EDA-diacetone propionamido(EDP))was synthesized firstly by Micheal addition method.The products are characterized by mass spectrometry,IR,TLC analysis,indicating that the product can be used in the preparation of polyurethane emulsion without purifying.Then the extender reacted with polyurethane prepolymer emulsion to form a polyurethane emulsion,containing carbonyl groups in the side chains of molecules,so that the main chains could crosslink with each other under the existence of adipic acid dihydrazide(ADH)when the film is forming in room temperature.Moreover,The emulsion preparation conditions were optimized:the proportion of soft monomer was PC-1000:PC-2000=1:8;the amount of polyamine chain extender was 6%(wt);the amount of hydrophilic chain extender was 3%(wt).The particle size,Z-potential,stability data were measured,and latex film properties including water absorption rate,mechanical properties,degree of crosslinking were investigated.The result shows:the emulsion has good adhesion and moisture resistance to PVC;the addition of room temperature self-crosslinking extender has no influence on particle size,Z-point and the emulsion stability;the water absorption rate of the film decreased from 84%to 9.8%,meanwhile the tensile strength and elongation,cross-linking density increased greatly.2.We optimized the ketone and hydrazide crosslinking system.Trifunctional chain extender synthesized by the reaction of acrylamide(DETA)and acrylamide(DAAM)was used in the preparation of polyurethane emulsion to replace the extender above.We also explored the effect of carbodiimide by texting water absorption rate of the modified latex film and adhesion to base material.The result shows that,with the same amount of trifunctional chain extender or the additon of carbodiimide,the water absorption rate of the latex film can be further reduced to 7.3%.In addition,adhesion and moisture resistance to PP and PVC are improved in some degree.3.Sulfhydryl siloxane modified HDI trimer was synthesized in two methods.One is that sulfhydryl siloxane react with HDI trimer directly.The other is modifying-trimerizing method in which parts of HDI was modified by sulfhydryl siloxane firstly,and then the trimerization was carried out subsequently,the reaction conditions were investigated for both methods,the optimum conditions were obtained:the modification reaction was for 6h under 80 ?,and the trimerizing reaction was for about 3h at the temperature of 55.The products were characterized,and the value of isocyanate was measured.With the modified HDI trimer to replace mass of the IPDI monomer,polyurethane emulsion was prepared,and the effects of the modified trimer on polyurethane emulsion were studied.The crosslinking density,tensile strength,water absorption rate and other properties were characterized.The results showed that with ratio nHS:nNCO=1:5,the proportion ntrimer:nIPDI=1:11,the prepared emulsion has the best performance.The storage stability of the prepared emulsion was over 6 months at room temperature;the tensile strength of the film was more than 30 MPa;elongation at break was over 1000%,and the water absorption rate was 9.8%.