Study On Epoxy Modified Waterborne Polyurethane

Waterborne polyurethane(WPU) is an environment-friendly material taking water as thedispersant. In order to achieve the self-emulsion, a hydrophilic chain extender is used to preparewaterborne polyurethane. But compared with solvent-borne polyurethane, the water and solventresistance， thermal resistance and mechanical properties of waterborne polyurethane isreduced since the presence of the hydrophilic chain extender. Crosslinking is an effective meansto improve the performance of waterborne polyurethane. In this article, bisphenol A diglycidylether(E44) and epoxidized castor oil(ECO) were chosen as crosslinking agent to modifiedwaterborne polyurethane.The epoxidized compounds modified waterborne polyurethane emulsion was synthesizedwith polytetramethylene ether glycol (PTMEG), toluene diisocyanate80(TDI80),dimethylolpropionic acid (DMPA), triethylamine (TEA), ethylenediamine (EDA), bisphenol Adiglycidyl ether(E44) and epoxidized castor oil(ECO) were selected as crosslinking agent tomodified hard segment and soft segment. The relationship between performance and structureof the epoxidized compounds modified waterborne polyurethane were studied by infraredspectroscopy (IR), dynamic light scattering (DLS), transmission electron microscopy (TEM),dynamic mechanical analysis (DMA), Thermogravimetric analyzer(TG), Contact angle tester,X-ray photoelectron spectroscopy(XPS),mechanical test etc.The molecule of bisphenol A diglycidyl ether (E44) contains a large number of hydroxyland epoxy groups. When E44was used to modified waterborne polyurethane, the hydroxylcrosslink with isocyanate. The epoxy group also crosslink with isocyanate after ring-openreaction. The results show that, during the prepolymer stage, N-H bond in carbamate promotesthe ring opening of epoxy group to crosslink with the polyurethane chain. With the increase ofthe E44content, both particle size and Zeta potential of modified waterborne polyurethaneemulsion showed the trend of decreased and then increased, the degree of micro-phaseseparation between soft and hard segments increased and then decreased, the content of elementC increased in the surface of waterborne polyurethane film, the hydrophobicity is improved,and contact angle increased, the water resistance and solvent resistance of the film increased,mechanical properties and thermal stability was enhanced.Castor oil is a natural unsaturated fatty acid triglyceride, its average hydroxyl functionalityis about2.7, hydroxyl value is156~165mgKOH/g. After epoxidation, the unsaturated doublebonds of the molecular formed epoxy bond. In the modified reaction of waterbornepolyurethane, both of the hydroxyl and the epoxy group crosslink with isocyanate to improvethe crosslinking degree of the waterborne polyurethane.With the increase of the amount ofepoxidized castor oil, both particle size and Zeta potential of modified waterborne polyurethane emulsion showed the trend of decreased and then increased, the water resistance of the filmincreased, thermal stability and mechanical properties was enhanced.