Study On Preparation And Properties Of High Solid Content Sulfonated Waterborne Polyurethane

In this paper, sulphonated waterborne polyurethane (PU) emulsions with50%solidscontent were successfully synthesized, on the basis of actone process and prepolymer mixingprocess, by using polyethylene glycol adipate diol (PBA), isophorone diisocyanate (IPDI) andhexamethylene diisocyanate (HDI) as main raw materials, and N-(2-aminoethyl)-aminoethane sulphonated sodium (AAS) or AAS and dimethylol propionic acid (DMPA) as thehydrophilic chain extenders. Some factors influencing the performances of waterborne PUemulsions and the cast films were in detail investigated by Fourier Transform Infrared (FTIR),1H-NMR spectra, Thermal Gravimetry Analysis (TG), Differential Scanning Calorimetry(DSC), X-ray Diffraction spectrum (XRD), Dynanmic Mechanical Ananlysis (DMA),Transmission Electron Microscope (TEM), Scanning Electron Microscopy (SEM) and AtomicForce Microscope (AFM).The results showed that the method of dibutylamine-acetone titration or Fourier transformsinfrared spectroscopy could be used to determine the reaction time of polyurethane pre-polymerization,and when pre-polymerization time was above60min, the measured content of－NCO group almostkept the same and closed to the theoretical value of－NCO group, so60min was assigned asthe PU prepolymer reaction time. When the dosage of AAS was9.2mmol (100g resin)-1, the chainextending time was25~40min, and a one-time feeding mode of AAS was applied, the sulfonatedwaterborne PU with high quality and high-solid content was obtained. When the molecular weight ofPBA increased from2000to3000, the thermal decomposition temperature T5%and T10%(shownin TG curve) of PU cast films increased34.7℃and29.4℃, respectively, while thecrystallinity of soft segments in PU chain had also been improved. With the increase of DMPA/AASratio, the thermal stability of PU cast films became worse, the crystallization enthalpy ΔHc had asignificant reduction and the crystallization temperature Tp was significantly improved, which meaned thatthere was no need of the carboxylic acid-type hydrophilic chain extender for preparing thesulfonated waterborne PU with high solid content and high crystallinity. The PU films showedbetter crystallization performances when the NCO/OH value was about1.8. On the basis ofthe above studies, the Optimized formulation and processes for synthesizing waterborne PUwith50%solid content and high quality were determined, and the properties of the synthesized waterborne PU was very close to that of Dispercoll U54from Bayer AG. So thesynthesized waterborne PU could be used to prepare high-performance waterborne PUadhesive or other related products.In order to improve the mechanical properties and water resistance properties of the castfilms of waterborne PU, epoxy resin was used to modify the waterborne PU. The resultsshowed that with the increase of epoxy resin from0to4%, the appearance of PU emulsiongradually changed from a milky opaque to translucent, the corresponding latex particlediameter increased from95.8nm to169nm, and the water absorption of waterborne PU filmsreduced from5.8%to2.5%, which meaned the water resistance of PU films were improved.The decomposition temperature of epoxy resin modified PU film moved towards the hightemperature direction, indicating that the epoxy resin could significantly improve the thermalstability of PU films.The tensile strength of epoxy-modified PU film also increasedsignificantly from16.21MPa to49.3MPa. However, with the increase of epoxy content (from0to4%), the zeta potential of epoxy modified PU latex particles gradually decreased, but itwas still greater than-30mv, which was enough for forming a stable epoxy resin modified PUemulsion. The relative crystallinity of films decreased from64.61%to51.41%when epoxycontent increased from0to4%. Therefore, considering the above results, the optimal epoxycontent of3%was determined, and on this basis, the epoxy resin modified waterborne PUemulsion with50%solid content, excellent water resistance and mechanical properties wasprepared.