Study On Rheology Properties Of Polyurethane Adhesive

Polyurethane adhesives contained many polar groups show a high chemical activity and could have excellent chemical adhesion with the substrates contained active hydrogens, such as wood, plastic, fabric, ceramics, paper and so on. Thus, polyurethane adhesives are widely used in many fields, such as construction, automotive, spinning, packaging and shoes.In this paper, we have prepared seven kinds of different structures of the isocyanate components and two different polyol components through different formulations designs. The molecular weight and structure were characterized by GPC and IR respectively.The analysis which studied the dynamic rheological properties of polyurethane adhesive components had a research of the relationship between the rheological properties and the adhesive’s properties, during and after the curing reaction.In the first part, through the steady state frequency scan mode of HAAKE rheometer, the isocyanate component of polyurethane adhesive was confirmed as pseudoplastic fluid according to the formula of power-law non-Newtonian fluid. The activation energy of viscous flowwas calculated by the Arrhenius equation and the relationships betweenstructure and temperature sensitivity of the samples were discussed in themeantime. By means of deducing the multi-mode Maxwell modelconstitutive equation, each sample’s discrete relaxation time spectrum wascalculated by nonlinear least squares method and we also discussed therelevant factors which affected the relaxation time spectrum. Finally thematching of samples’ viscosity and elasticity was discussed. The resultsshowed that the best mobility and the minimum elasticity should bechosen as the formula.In the second part, through the dynamic state frequency scan mode ofHAAKE rheometer, we have proved that the adhesive prepared was stableby comparing the modulus-frequency curves before and after blending.Polymer chains’ entanglement degree were evaluated by the crossingpoints of the storage modulus G’ and loss modulus G’’ ofmodulus-frequency curves. Then, adhesive cured at different temperatureswere characterized by HAAKE rheometer’s steady state frequency scanmode. The result showed that the higher the curing temperature used theshorter the gel time obtained. The activation energy of crosslinking wascalculated by Arrhenins equation. The adhesives’ modulus-temperaturecurves and glass transition temperatures were obtained by DMTA testwhich showed that the samples’ glassy state platform modulus was about 10⁷Pa and rubbery state platform modulus was about10⁵Pa. The test alsoshowed that the adhesive’s glass transition temperature could be improvedby raising the curing temperature. Finally adhesive’s tensile shearstrengths were characterized by universal testing machine. Observe resultsof the adhesive’s properties under different curing temperatures （the geltime the glass transition temperature and tensile shear strength）, it wasfound that the higher the curing temperature was the shorter gel time andthe higher tensile shear strength would obtain after curing.