Synthesis Of High Solids Waterborne Polyurethane And Development Of Its New Emulsifier

Polyurethane(PU)possesses exceptional molecular tailoring and flexible performance regulation,making it a versatile material that is widely employed in coatings,adhesives,elastomers,and numerous other fields.Waterborne polyurethane(WPU),utilizing water as the dispersion medium,represents a green and environmentally friendly alternative,thereby expanding its potential for various applications.Owing to the high latent heat of evaporation of water,the application process of low solids waterborne polyurethane(WPU)is fraught with issues such as extended drying times.Additionally,low solids WPU poses concerns related to low equipment space utilization during production and arduous construction processes during application.Consequently,considerable attention is devoted to high solid content WPU(HSC WPU)as a promising research direction.Currently,the preparation of HSC WPU is primarily achieved through multi-step methods such as the emulsion mixing method based on the emulsified particle accumulation model and reduced hydration layer theory.However,such approaches are unsuitable for industrial-scale WPU production,and the development of a one-step method for HSC WPU synthesis is a pressing market need.Moreover,to confer exceptional long-term stability upon the prepared WPU,emulsifiers are utilized in the preparation process.However,the use of small-molecule emulsifiers leads to compromised water resistance and performance of WPU products,and small- molecule emulsifiers pose risks to human health and the environment,thereby limiting the application of WPU in the field of high-performance materials.Therefore,there is a dire need to explore novel and eco-friendly WPU emulsifiers.This study successfully synthesized high solid content waterborne polyurethane(HSC WPU)by strategically incorporating large diols containing ionic groups into the polyurethane(PU)main chain through molecular structure design.Notably,the hydrophilic groups in the soft segment did not disrupt the regularity of the PU hard segment chain structure,and were less prone to forming bound water on the surface of WPU pellets,which facilitated the production of HSC WPU.Moreover,to enhance the water resistance and overall performance of WPU products,this research explored the use of cellulose nanocrystals(CNC),an amphiphilic solid emulsifier derived from biomass raw materials,as an alternative to conventional small molecule surfactants.This novel approach yielded improved WPU product performance while addressing the issue of poor water resistance.The main findings are summarized below:1.In this study,high solid content waterborne polyurethane(HSC WPU)was synthesized using a polytetrahydrofuran ether diol(PTHF)and polyether diol containing sulfonate(PDS)as mixed soft segments,and isophorone diisocyanate(IPDI),2,2-dimethylbutyrate(DMBA),and sodium 2-[(2-aminoethyl)amino]ethanesulfonate(CA-95)as hard segments.By carefully regulating the percentage of ionic groups in the soft and hard segments(0.5 mol.% and 5 mol.%,respectively),a WPU with high solid content(57% solid content and 605.3 m Pa·s viscosity)was successfully prepared using the prepolymer.Gradually increasing the solid content of WPU emulsions eventually led to the production of WPU with 70% solid content,approaching the ultimate solid content.The resulting 70% solid content WPU emulsions were then diluted with water to different solid contents ranging from 30%-60%.Comparison of the particle size,stability,and mechanical properties of the diluted 70% solid content WPU emulsions and WPUP0.5D1C4 directly emulsified with different solid contents showed no significant differences in performance or stability,indicating that the WPU-P0.5D1C4 formulation was optimal and not affected by the amount of water added or degree of dilution.The drying time decreased with increasing solid content,with the best formulation(WPU with 57% solid content)having a drying time of 750 s.The results for water absorption and contact angle showed that the optimal formulation had a water absorption of 33.6% and a contact angle of 42.7°.2.A non-ionic waterborne polyurethane(NWPU)prepolymer was synthesized using PTHF,IPDI,and 1,4-butanediol(BDO)as the principal reaction monomers,and carboxylated cellulose nanocrystals(c CNC)as the solid emulsifier.The emulsification efficacy of c CNC was evaluated by regulating the p H of the aqueous phase and the c CNC concentration.The results demonstrated that NWPU Pickering emulsions(NWPU PE)were stable for more than six months when the p H of the aqueous phase was set at 4 and c CNC-6 was added at a concentration of 12.5 mg/m L or higher.Furthermore,mechanical properties and water resistance were improved compared with conventional emulsifiers.3.Anionic waterborne polyurethane(AWPU)prepolymers were fabricated using PTHF,IPDI,and DMBA as the principal reaction monomers,and c CNC as the solid emulsifier.The influence of the degree of carboxylation of CNC,p H of the aqueous phase,and c CNC concentration on the preparation of WPU stabilized emulsions was evaluated by characterizing centrifugal emulsions and other methods.The results showed that anionic WPU Pickering emulsions(AWPU PE)were stable for more than six months when the p H of the aqueous phase was set at 8 and the concentration of c CNC-6h was 7.5 mg/m L or higher.Additionally,the mechanical properties and water resistance of the AWPU PE were improved compared with conventional emulsifiers.