Preparation And Characterization Of Polyurethane/gelatin Copolymers And Its Filming Performance

As one kind of protein materails, gelatin possesses a wide variety of sources,and lower price. But in the extraction process, gelatin is always subject tocomplex physical and chemical processing causing many damages such asdestruction of the triple helix structure, hydrolysis of the peptide bonds, smallergelatin molecule, wide molecular weight distribution, crisp, lower water resistantand lower elongation break. In this paper gelatin was modified by polyurethanethrough chemical reaction to improve the performance of gelatin. Polyuerthaneprepolymer was produced by PCDL, TDI, DMPA, and BDO. Thensalicylaldehyde was bonded to the main chain of waterborn polyuerthaneprepolymer. Finally, the polyurethane/gelatin copolymer was prepared by thereaction of–NH2on the chain of gealtin with–CHO on the chain of waterbornpolyurethane prepolymer.Waterborn polyuerthane films and emulsions prepared in the excessive existof–NCO showed better performance.The effects of reaction temperature,reaction time, DMPA dosage, the isocyanate index before adding chain extender,various chain extender and different hard segment content on the performance ofwaterborn polyurethane emulsion and latex film were studied. The influences ofneutral degree and water dosage on the the phase transition were investigated.The prepolymer was also characterized by FTIR and GPC, the results showedthat salicylaldehyde was successfully introduced to the prepolymer chain and thenumber-average molar mass of the prepolymer was8982.The impacts of pH value and substance concentration on copolymerizationwere explored. It was found that when the pH value raged between5to8and thesubstance concentration was less than20%, a stability copolymer emulsion withan average zata potential of-27.7mV and an average particle size of504nm wasobtained. With the WPU dosage increased to50%, the elongation at break of thecopolymer latex film reached up to550%, the breaking strength decreased down to36Mpa, the contact angle of the copolymer latex films increased to73.6o, thewater absorption rate decreased to70%, the toluene absorption rate increased to26%. FTIR analysis showed that–NH2on the gelatin chain participated in thechemical reaction in the copolymerization process. GPC analysis showed that thenumber-average molecular mass of the obtained copolymer was19124indicatingthat WPU had been successfully bonded to gelatin chains. Thermal analysisindicated that the thermal stability of the copolymer had been greatly improvedcompared to that of gelatin. The lower glass temperature value (66oC) of thecopolymer characterized by DSC demonstrated that the polyurethanecomponents played a role as plasticizer in the copolymer compound. XRDanalysis showed that the degree of crystallinity decreased with the increasingWPU dosage, and when the WPU dosage reached up to50%, crystallinity of thecopolymer decreased to2%. AFM was also been used to characterize theaggregation structure and the surface topography of the products and it wasfound that a great change in the phase diagram and a rough surface of the latexfilm had generated from copolymerization.Finally, the finishing performance of the products was studied, the resultsinvestigated that water resistance and wet-dry rubbing resistance of the coatingwere significantly improved by modificating gelatin by polyurethane. Thewonderful water vapor permeability properties of protein materials was wellretained after copolymerization.