Research On The Relationship Between Waterborne Polyurethane Molecular Structure And The Adhesive Strength

As a kind new polymer material，polyurethane（PU）is widely used．Organic solventsused in solvent-based polyurethane is harmful to environment． In order to reduceenvironmental pollution of solvent evaporation, more and more attention is focused onresearch and development of water-based polyurethane worldwide. The relationship betweenwaterborne polyurethane molecular structure and the adhesive strength is investigated in thispaper, and the main contents are as follows:1.Effect between adhesive strength with HMDI-based waterborne polyurethaneA series of waterborne polyurethane adhesives are prepared in the pre-polymer processwith poly(tetramethy-lene oxide glycol)(PTMEG)，4,4-dicyclohex-ylmethane diisocyanate(HMDI)，2,2-Dimethylol pro-pionic acid (DMPA)，1,4-butanediol (BDO)．The properties ofWPU are characterized by water absorption，ethanol swelling，tensile strength testing andadhesive strength．Effect of waterborne polyurethane adhesive on HMDI content，DMPAcontent，PTMEG molecular weight，the size of R values are also investigated．The resultsshow that the maximum value of tensile strength and adhesive strength are11.48Mpa and0.56Mpa, when the content of HMDI is33wt%， chain extender is5wt.%，value of R is1.2，and the soft segents molecular weight of polyether polyols is2000．2. Effect between adhesive strength of waterborne polyurethane modified with silanecoupling agent KH-602In order to improve the adhesive strength of waterborne polyurethane，HMDI-basedwaterborne polyurethane is modified with silane coupling agent (KH-602)．Silane couplingagent can decline surface tension and the WPU easily wetting substrate better，the adhesivestrength had been improved a lot．Silane coupling agent can increase adhesive by the way ofthe formation of mesh structure，all of these made the material with good solvent resistance(ethanol)， and mechanical properties and adhesive strength had been improved considerably．The result showed: silane coupling agent is2wt.%，the adhesive strength ofmodified WPU can reach up to0.71Mpa，much higher than the unmodified WPU (adhesivestrength is only of0.56Mpa). Unmodified WPU dissolved in ethanol completely, whileethanol resistance of modified WPU is up to1.46%,which is greatly improved in the ethanolresistance．3.Effect between adhesive strength of waterborne polyurethane with differentstructures of diisocyanatesWaterborne polyurethanes with different hard segments are synthesized by use ofHMDI, isophorone diisocyanate (IPDI), diphenyly methane diisocyanate (MDI),all of theseare used as hard segments respectively，polyether diol (PTMEG-2000) is as soft chainsegment，2,2-Dimethylol pro-pionic acid (DMPA) is as hydrophilic monomer，1,4-butanediol(BDO) is as chain extender．The WPU are characterized by IR、DSC、TG etc．And theirperformances are investigated by measuring tensile strength，adhesive strength，waterabsorption．It is found that the decomposition temperature of HMDI-based WPU is about270℃，which is higher than IPDI-based WPU and MDI-based WPU．The mechanicalproperty and adhesive strength of the materials are tested by the electronic stripping tester andthe results show that MDI-based WPU containing aromatic isocyanate structure has bettermechanical property．...