| Polymers which have the advantages of light quality,high strength,good corrosion resistance and other excellent performance are being widely used in the various walks of life.As one of the most important members of polymers,synthetic rubber will undergo a certain degree of aging during the process of transportation,storage and use,which will seriously affect the service life of rubber.Studying the aging mechanism of rubber can help us understand the aging behavior of rubber fundamentally,so as to provide a theoretical basis for the development of more efficient and reliable anti-aging technology.In this paper,1H-NMR,FT-IR and UV-Vis were used to study the UV aging,thermal oxidative aging and natural aging of EPDM(EPDM 3110M and 9950,the latter had higher propylene content than the former).The anti-aging effect of UV absorbent UV-531,antioxidant RD and MB were evaluated,the relationship between natural aging and artificial accelerated aging was established innoatively,and the following conclusions were obtained.1.UV agingEPDM had poor anti-UV aging performance,so the UV light stabilizer needed to be added into EPDM products to improve its anti-UV aging performance.UV aging started from the tertiary hydrogen of the propylene chain segment,it firstly produced hydroperoxides in the process of aging and then other oxygen-containing products produced in further aging process;The anti-UV aging performance of EPDM improved obviously after adding 5‰ UV-531.The lifetime of a-H of double bond in third monomers extended from 1 h to 8 h.The effective time for UV-531 was 8 h,and its content reduced gradually during the UV aging process;The more propylene content in EPDM,the worse the anti-UV aging performance of EPDM.The anti-UV aging performance of 3 samples showed the following order of quality:EPDM 3110Muv>EPDM 3110M>EPDM 9950;The degradation reaction was dominant during the UV aging process of EPDM,and the sample reduced continuously due to the escaped of small molecular products;The UV aging equations(equations 2.1?2.6)were established under the experimental conditions.2.Thermal oxidative agingEPDM had good resistance to thermal oxidative aging.There were no obvious changes in the chemical structure of EPDM 3110M and 9950 after aging at 100?C for 20 d and 17 d,respectively;There was an "induction period" during the thermal oxidative aging of EPDM,it was meant to say that the thermal oxidative aging needed to accumulate a certain amount of energy.During the "induction period",a small amount of ?-diketone produced,no crosslinking structure was founded in the samples;The thermal oxidative aging properties of EPDM improved significantly after adding 5‰ of antioxidant RD and MB.The "induction period" of EPDM 3110M,EPDM 9950,EPDM 3110MRD and EPDM 3110MMB at 130? were 4?5 d,1 d,>20 d,17?20 d,respectively;The thermal oxidative aging properties of 4 samples showed the following order of quality:EPDM 3110MRD>EPDM 3110MMB>EPDM 3110M>EPDM 9950;After the "induction period",the sample aged rapidly.The tertiary hydrogen of the propylene chain segment on the main chain was fractured,it firstly produced hydroperoxides in the process of aging and then other oxygen-containing products produced in further aging process.The samples cross-linked seriously and the color got deepens gradually;The thermal oxidative aging equations(equations 3.1?3.4)were established under the experimental conditions.3.Natural agingEPDM had poor resistance to natural aging.At 10 d after natural aging,the chemical structure of EPDM changed obviously.So the UV light stabilizer needed to be added into EPDM products to prolong its service life;The natural aging behavior of EPDM was similar to that of UV aging,and followed the same aging mechanism;The natural aging performance of EPDM improved obviously after adding 5 ‰UV-531.The effective time for UV-531 was 8 h,and its content reduced gradually during the natural aging process;The natural aging properties of 3 samples showed the following order of quality:EPDM 3110Muv>EPDM 3110M>EPDM 9950;The natural aging equations(equations 4.1?4.10)were established under the experimental conditions,and we could use the natural aging equations to identify the utility time of sample that had been used in the natural environment.The dependent equations(equations 4.11?4.18)between natural aging and artificial accelerated aging were established,which could be used to predict the service life of rubber;Under the experimental condition,artificial UV aging 7 h was equivalent to 20 d for natural aging,and 36 h of artificial UV aging was equivalent to 210 d of natural aging.Artificial thermal oxidative aging(130?)5d was equivalent to 70 d for natural aging;The differences between aging of styrene butadiene rubber(SBR)and ethylene propylene diene monomer(EPDM)were compared.The fundamental reason was that their chemical structure was different,resulting in the different aging products were formed.Aging was always caused by oxidation reaction of weaker links in their chemical structure(active H),and then evolved into active center of aging. |
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