Research On Polyester-polyether Based Crosslinked Waterborne Polyurethaneadhesive

Solvent based polyurethane contains volatile organic compounds (VOC) which restrainsits use. Waterborne polyurethane adhesive, using water as solvent, is a kind ofenvironment-friendly and low cost adhesive, and it is used more and more.However, it hassome disadvantages such as water resistance, slow drying rate,low solid content and so on,therefore, much research has been done on it.In this paper, a series of waterborne polyurethane(WPU) were prepared through aprepolymer process using isophorone diisocyanate(IPDI), hexamethylene diisocyanate(HDI),dimethylol propionic acid(DMPA), propylene glycol(PPG) and polybutylene adipate(PBA) asmaterials, and trimethylolpropane(TMP) as crosslinker.The effects of NCO/OH mole ratio, DMPA content, TMP content, mass ratio betweenpolyester and polyether, degree of neutralization and chain extensionon on the properties ofwaterborne polyurethane emulsion and its films were studied. The adhesion mechanism foradhesive to substrates and the factors affected the T-peel strength was analysed. Theproperties of emulsions and films were characterized by FT-IR, particle size analyzer, contactangle measuring instrument, thermo gravimetric analysis (TGA), X-ray diffraction (XRD),differential scanning calorimetry (DSC), scanning electron microscopy (SEM).The experimental results of showed that the particle size and tensile strength increased,however, the viscosity, zeta potential and elongation at break decreased with the increasing ofNCO/OH mole ratio. The WPU with higher DMPA content possessed higher dispersionviscosity, zeta potential and smaller particle size. And the WPU films with higher DMPAcontent exhibit higher tensile strength, but lower elongation at break and lower contact angle.When the content of TMP increased, the degree of crosslinking increased,and the films’swater resistance was improved. With the increasing of mass ratio between polyester andpolyether, the emulsions particle size became large, and the tensile strength increased.However, the elongation at break decreased first and then increased, and the wateraborsptionshowed the opposite trend. The XRD analysis shows that the crystallization in soft regionsdisappears when w(DMPA) is above5.1%, and the soft segment crystallinity decreased withthe increasing of DMPA content. Effectsof NCO/OH molar ratio, DMPA and TMP content on the adhesion strength was studied. And the adhesion strength between PU adhesive andsubstrates was analyzed by the absorption theory and mechanical bonding theory at the sametime.These two theories will explain better to adhesive mechanism and it will give guide tothe reserch on adhesive.