Study On The Aging Of Natural Rubber And Isoprene Rubber

Rubber material is a kind of polymer material with high elasticity and viscoelasticity.Among them,natural rubber(NR)has become the most widely used universal rubber in the world with its excellent comprehensive performance.Due to the imbalance of supply and demand of natural rubber and the continuous development of the rubber industry.Isoprene rubber(IR),which is similar to NR,has become a perfect substitute for natural rubber.However,in actual use and storage,they're inevitable to be influenced by various environmental factors,such as oxygen,light and heat,which result in poor performance after aging.Therefore,the study of aging failure mechanism of rubber has always been an important issue in the field of polymer materials.For NR and IR,among all related researches so far,not many work has been done on the aging mechanism and microscopic analysis,the differences in aging behavior between them even less.So does the relationship between artificial aging and natural aging.In this paper,1H-NMR,FT-IR and UV-Vis were used to study the aging of natural rubber and isoprene rubber.All results were covered as follows:1.Study on UV aging.After UV aging of NR and IR,it was concluded that,IR was inferior to NR in its ability of resistance to UV;Non-rubber hydrocarbons such as proteins contained in NR reduced the aging,this kind of components also effectively reduced the influence of UV on the double bonds in molecular structure,it also reduced the generation of new radicals.The mechanism of NR and IR UV aging was as follows:a-H of double bond was oxidized to peuoxide alcohol firstly,with double bond of main chain ruptured at the same time,and then to alcohols,aldehydes,ketones,esters or generated small molecule compounds by degradation,and ?,?-unsaturated conjugated structure was formed during UV aging.2.Study on the thermal oxidation agingAfter thermal oxidative aging of NR and IR under the temperature of 80?,100? and 120? it was concluded that,the ability of resistance to thermal oxidation of NR was better than IR's;Their molecular structures showed no obvious change under 80?,but the changes of molecular structures under 100? were slower than the changes under 120?.This suggested that temperature rising accelerated the process of thermal oxidative aging.Non-rubber hydrocarbons such as proteins contained in NR also reduced the thermal oxidative aging,this kind of components also effectively reduced the influence of UV on the double bonds and a-H in molecular structures,it also reduced the generation of new radicals.Thermal oxidative aging mechanism was similar to the UV aging mechanism:at first a-H of double bond was oxidized to peuoxide alcohol,with double bond of main chain ruptured at the same time,and then to alcohols,aldehydes,ketones,esters or generated small molecule compounds by degradation,and ?,?-unsaturated conjugated structure was formed during thermal oxidative aging.3.Study on chemical media agingAfter chemical media aging of NR and IR in the solution of 5%H2O2,5%KMnO4,5%HCl and 5%NaOH,it was concluded that,the ability of IR to resist these four solutions was strong.The ability of NR to resist 5%KMnO4 was poor,to resist 5%H2O2 was a bit better,and in 5%HCl it showed strong.Non-rubber hydrocarbons such as proteins contained in NR showed poor ability of resistance to 5%NaOH,the rubber hydrocarbon components were not affected much.During the aging of NR in H2O2,at first a-H of double bond was oxidized to peroxide alcohol,and then to aldehyde,with the rupture of main chain at the same time,then the decarboxylic reaction followed.During the aging of NR in KMnO4,the double bond of main chain ruptured firstly,then vicinal diol componds formed.Non-rubber hydrocarbon components such as proteins in NR made the rubber more vulnerable,while IR had no such problems.During HCl aging,most of NR reacted with the addition of unsaturated double bonds to HCl,and also a small part of them reacted by the way that a-H of double bond was oxidized to peuoxide alcohol,then to?,?-unsaturated carbonyl compounds,and then reacted with the addition of unsaturated double bonds to HCl.4.Study on natural agingAfter aging of NR and IR for 18 months in Xiamen,the results showed that,during natural aging,UV made a greater impact,and then thermal oxdation and UV worked together.The ability of resistance to natural aging of NR was stronger than IR's,Non-rubber hydrocarbons such as proteins contained in NR also reduced the natural aging,this kind of components effectively reduced the influence of naural aging on the double bonds in molecular structure,and reduced the generation of new radicals.During the natural aging,the mechanism showed that a-H of double bond was oxidized to peuoxide alcohol,with the double bond of main chain ruptured at the same time,and then to alcohols,aldehydes,ketones,esters or generated small molecule compounds by degradation,and ?,?-unsaturated conjugated structure was formed during UV aging;The curves of UV aging,100 ? and 120 ? thermal oxidative aging,and natural aging were built.The correlation between artificial aging and natural aging were built innovatively,which provided some academic bases and references for the aging study and service life prediction of NR and IR.