The Aging Mechanism And Property Change Of Nitrile Rubber In H₂S Environment

Nitrile rubber?NBR?has good resistance toward oils thereby enabling the extensive use of this rubber in the oil industry.However,at present,an increasing number of oilfields have been determined to contain concentrated H₂S.H₂S act as a corrosive substance,which greatly disrupts the performance of NBR and causes the loss of rubber elasticity.In general,people attribute this performance deterioration to the corrosion of unsaturated double bonds,however they seem to neglect the effect of nitrile group and crosslink structure.Therefore,taking these factors into consideration,we conducted the following research:?1?Hydrogenated nitrile-butadiene rubber?HNBR?and butadiene rubber?BR?model compounds were used to simulate the reactive group,nitrile group and double bond,in NBR.After the corrosion tests,the content of double bond and nitrile group in rubber decreased,whereas the sulfur element increased,in addtition,crosslinking reaction occured in NBR,while HNBR and BR were not crosslinked.Therefore,it is inferred that the double bond and nitrile group of NBR was synergistically crosslinked in the H₂S environment,thereby producing sulfur crosslinked structure after corrosion.?2?Investigating the degradation of peroxide-crosslinked NBR in H₂S environment,researches found out that the vulcanizates were more susceptible to H₂S than the raw rubber.After corrosion,the increment of sulfur element in vulcanizate was much higher than that of raw rubber,and the reduction of double bond was more severe than raw rubber,which was attributed to the?-tertiary carbon structure produced by peroxide crosslinking.The?-tertiary carbon greatly activates the double bond and allyl hydrogen??–H?,thereby promoting the reaction of 1,4–polybutadiene?1,4–PB?structural units with H₂S,thereby exacerbating the corrosion of NBR,causing a serious decline in its performance.?3?Investigating the degradation of sulfur-crosslinked NBR in H₂S environment,researches found out that a great number of polysulfide crosslinks appeared in the corroded NBR,which was theoretically opposite to the crosslinked structure dominated by monosulfide and disulfide crosslinks,that could be attributed to the action of the activator Zn O.The presence of Zn O promoted the cleavage of the monosulfied and disulfide crosslink,and then the disrupted crosslinks continue to react with H₂S to produce polysulfide crosslinks,thus greatly changed the composition of the crosslinked structure in NBR.