Study On Anti-aging Performance Of Polyurethane/Conjugated Organic Compounds Composites

The molecular structure of polyurethane elastomer contains carbamate,isocyanate,ureido and biuret groups,when polyurethane were exposed to ultraviolet light,C-N bond of carbamate were cleavaged and generated amino radical and alkyl radical after irradiating with ultraviolet,then amino radical formed intermediates and genetrating azo-compounds containing chromophore through losing hydrogen,thus appeared different colors;amino radical connected with benzene ring can generate quinone after losing a hydrogen radical and exhibit orange or orange red;then ureido in hard segments can generate chromophore by oxidation,which lead to yellowing of polyurethane;molecule rearrangement of polyurethane after absorbing ultraviolet light also may lead to yellowing of polyurethane,As a result,mechanical properties and other properties were deteriorated.Some studies used antioxidants and light-stabilizers so as to inhibit aging or yellowing of polyurethane.In view of the molecular structure of carotenoids contains multiple conjugated olefinic bond:β-carotene contains 11 Π-electron conjugated double bond and vitamin A acetate contains 5 π-electron conjugated double bond,its structure are able to clear free radicals,absorb ultraviolet light and has ability of weather resistance,besides,it is non-toxic and environmental friendly.In this paper,organic compounds of vitamin A acetate and β-carotene containing conjugated double bonds were used as additives in polyurethane,and UV resistance and aging resistance of composites were investigated.Modified polyether polyurethane were prepared using polymer polyol(PCL,PEA,PTMG),diisocyanate(TDI),3,5-dimethylhiotol-uenediamine(DMTDA)as raw materials,vitamin A acetate and β-carotene as additives by prepolymer method.The modified PUs were aged by ultraviolet light and characterized by chromatism analysis,UV spectral analysis,mechanical test,solvent swelling resistance test,dynamic mechanical analysis(DMA).Chromatism analysis showed that the conjugated organic compounds can inhibit yellowing of polyurethane materials in the UV environmentMechanical test showed that changes of tensile strength and elongation of polyurethane/conjugated organic compounds composites was smaller than that of pure PU after UV aging,which illustrated that the addition of conjugated organic compounds can improve anti-ultraviolet properties of polyurethane material.UV spectra showed that the absorption intensity and peak position of polyurethane material were changed in ultraviolet radiation,then the different ultraviolet absorption spectra in different aging times indicated that conjugated organic compounds can inhibit the aging of polyurethane.Solvent resistance resusts showed that some of the olefinic bonds in conjugated organic compounds were breaked and formed more crosslink with polyurethane chains after irradiation of UV,therefore the solvent resistance were improved.Dynamic mechanical analysis(DMA)results showed that aggregation phase of multiple polyurethane between soft and hard segments in PU composites modified with conjugated organic compounds were changed,and the degree of microphase separation were also changed.Olefinic bonds in conjugated organic compounds were breaked after absorption of ultraviolet in aging process and crosslinked with polyurethane chain again,which can protect PU composites accordingly.