Study On Polyurethane/polyacrylate Composite Emulsion Based On Carbonyl-hydrazide Reaction

Polyurethane/polyacrylate?PUA?composite emulsions have been widely used in coatings,adhesives and printing inks,which combines their potential cost reduction and tunable properties.However,simple physical blending of polyurethane dispersion?PUD?and polyacrylate latex?PA?cannot achieve excellent properties as expected due to the poor compatibility between two polymer systems.In view of this,vinyl terminated polyurethane ionomer was synthesized by using polyether diol containing sulfonate?SPPG?as hydrophilic monomer,hydroxyethyl methacrylate?HEMA?or pentaerythritol triacrylate?PETA?as end-capping agent,poly-neopentylene adipate glycol?PNA-100?,isophorone diisocyanate?IPDI?,1,4-butanediol?BDO?as main materials,and then polyurethane dispersion incorporating multiple hydrazide groups was synthesized by introducing the poly-hydrazide groups into the end of the vinyl-terminated polyurethane chains.Then,core shell polyacrylate latexes containing keto groups in shell layer were prepared by semi-continuous seed emulsion polymerization,using methyl methacrylate?MMA?as the core monomer,acrylic acid?AA?and diacetone acrylamide?DAAM?as shell monomers.Polyurethane/polyacrylate composite emulsions based on carbonyl-hydrazide reaction were prepared by blending of polyurethane dispersion and polyacrylate latex.The structure of polyurethane dispersions incorporating multiple hydrazide groups were characterized by Fourier transform infrared spectroscopy?FTIR?and gel permeation chromatography?GPC?.FTIR result indicated that poly-hydrazide groups had been incorporated in the polyurethane.GPC result showed that the values of molar mass for all PUD samples are similar and consistent with designed values,indicating that one molecule of poly-hydrazide reacted with one carbon-carbon double bond,no crosslinking reaction occurred during the synthesis process.The morphology of PA latex was analyzed by transmission electron microscopy?TEM?.The results showed that the PA latex showed clear core shell morphology,hydrophilic monomers AA and DAAM were polymerized in the shell,and ketone carbonyl groups were also successfully introduced onto the shell part.The effect of PA/PU mass ratio,n?-CO-?/n?-NHNH₂?ratio and the content of reactive group on the performance of the composite emulsion and the composite film were studied.The appearance of the characteristic peak of-C=N at 1645cm-1 in spectrum of composite film,indicating that crosslinking reaction between the-CO-of PA and the-NHNH₂ of PU has happened.scanning electron microscopy?SEM?,differential scanning calorimetry?DSC?,Thermogravimetric analysis?TGA?and tensile test results showed that there was obvious interface between the two phases,the phase interface between PA and PU is ambiguous after the introduction of crosslinking reaction,thermal stability,mechanical properties like tensile strength and Young's modulus,and chemical resistance including alcohol resistance of films were enhanced with the increment of crosslinking density.With the increase of the mass ratio of PA/PU,the film forming properties of the emulsions became worse,and the hardness of the films were increased,but the water absorption ratio and the absorption ratio of the films decreased firstly,and then increased.When the content of PA was lower than 50%,the composite emulsions exhibited excellent stability and film forming properties.When the content of PA is 30%,the comprehensive performance of the film was the best.With the increase of the molar ratio of?-CO-?/?-NHNH₂?,the gel fraction increased firstly and then decreased,and the water absorption ratio and the alcohol absorption ratio decreased firstly and then increased.When the n?-CO-?/n?-NHNH₂?ratio was 1.5:1,the film performance was the best.