The Synthesis And Characterization Of Sulfonate/Carboxylate Composite Waterborne Polyurethane

Waterborne polyurethane(WPU)adhesive has been one of the most popular environmentally friendly products in the field of adhesive owing to its extremely low emission of VOCs and excellent performance.At present,the application of commercially available carboxylate WPU has been limited owing to several shortcomings,such as relatively poor stability,and strong sensitivity to pH value,poor water resistance and initial adhesive properties and so on.In the view of improving the above shortcomings,this paper uesd sulfonate polyester diol to modify the WPU.The sulfonate/carboxylate composite anionic waterborne polyurethanes were synthesized by introducing sulfonate polyester diol BY3301 to partially replace hydrophilic chain extender dimethyl methyl butyric acid(DMBA)which widely used in conventional carboxylate WPU.In the meantime,the sulfonate groups were introduced into the soft segments of the WPU in the form of pendant groups.Then this paper used high-crystallinity polyester diol PBAD to improve the crystallinity of soft segment of WPU and enhance the water resistance and adhesive properties of WPU films.In addition,this paper used nano-silica sol to modify the WPU to intensify the water resistance and adhesive properties.The effects of the amount of sulfonate,the crystallinity of the molecular chain of WPU and the effect of nano-silica sol on the properties of the film were systematically studied.The main work of this article are described below:(1)A commercially available water-soluble polyester diol BY3301 replaced the carboxylate hydrophilic chain extender DMBA in different proportions.And a series of sulfonate/carboxylate complex anionic WPUs were prepared by introducng sulfonate into the soft segment of the PU molecular chain and optimizing the synthetic process.The structure,the morphology,particle size and distribution of the sulfonate/carboxylate composite anionic waterborne polyurethane were characterized by FT-IR,TEM,nano-particle size analyzer and stability analyzer,and effect of sodium sulfonate group on the WPU emulsion stability was studied in detail.The results showed that introducing sodium sulfonate groups endow the latex particles with more regular spherical structure and larger average sizes.When the content of total hydrophilic groups(HGC,i.e.sodium sulfonate group of BY3301 and quaternary ammonium carboxylate group of neutralized dimethylol butanoic acid,DMBA)remains unchanged,the obtained composite anionic WPU films with higher BY3301 content exhibited higher Zeta potential,wider range of acid and alkali resistance,superior high-temperature stability and freeze-thaw stability.(2)A crystalline WPU was prepared by using polyester diol PBAD with high crystallinity,polyester diols BY3301 grafted sodium sulfonate group as soft segment,and Isocyanate IPDI and HDI,chain extender DMBA and EDA as hard segment.The effects of WPU synthetic process,PBAD molecular weight,R value,HDI/IPDI mass ratio on the crystallinity of the emulsion were investigated.Also the effect of crystallinity on the water resistance,mechanical properties and adhesive properties of the films were investigated.The results showed that the crystallinity of the soft segment decreased gradually in the process of synthesizing WPU.Compared sulfonate/carboxylate composite WPU with carboxylate WPU,the composite WPU possessed higher crystallinity.The improvement of the crystallinity of the soft segment of WPU can significantly enhance the water resistance and adhesive properties of WPU films.When adopting PBAD3000 and BY3301 as soft segment,the R(n(-NCO)/n(-OH))=1.6 on prepolymerization and the m(HDI)/m(IPDI)=1/2,the comprehensive performance including water resistance,the tensile strength and peel strength and so on of WPU films were the best.(3)The nano-silica/WPU hybrid emulsion was synthesized by introducing nano-silica sol into WPU emulsion.The water resistance,tensile strength,film's transect morphology and peel strength were characterized.The results showed that the appropriate amount of nano-silica sol can improve the crosslinking degree of WPU films and increase the compactness of the WPU films,so as to enhance the water resistance and mechanical properties of WPU.When the amount of nano-silica sol was 5%,the comprehensive performance of the WPU film was the best.At this point,the water absorption of the film was reduced to 4.4%,the tensile strength of the film attained 32.0 Mpa,the elongation at break reduced to 658%,the elastic modulus reached up to 320 Mpa,and the initial and final peel strength tests of PVC substrates showed that the substrates were damaged.