With 4,4′-diphenyl methane diisocyanate(MDI),polyethylene glycol(PEG)and dimethylolpropionicacid(DMPA) as main raw materials,epoxy castor oil(ECO) as crosslinking modifier,the ECO modifiedWPU(waterborne polyurethane)emulsion was prepared. The research results showed that the hydroxyl and epoxygroup in ECO were participate in the synthesis reaction of WPU. The WPU film had the increasing hydrophobic,tensile strength and thermal stability,but the WPU emulsion had the increasing particle size,the poor appearan...