轮胎氧化课件

AREVIEWOF

RUBBER

OXIDATIONTheagingofrubbercausedbyoxidativedegradationleadstothedeteriorationinthephysicalandmechanicalpropertiesofvulcanizedrubbers.Thecriticalreviewwillcoverthemajordevelop-mentsinourunderstandingoftheoxidationofrubbers.ThemechanismsrelativetooxidationofrubberMethodsofprotectionThemechanismsrelativetooxidationofrubberR•+O2→RO2•(1)RO2•+RH→ROOH+R•(2)ROOH→RO•+•OH(3)RO•+RH→ROH+R•(4)RH+•OH→H2O+R•(5)RO2•+RO2•→ROOR(stable)+O2(6)auto-acceleratedoxidationThemechanismsrelativetooxidationofrubberthelossofunsaturationofα,β-unsaturated

oxidizedproductsthroughcrosslinking:x-CH=CH-CH2-x-CH-CH-CH2-

→

׀

׀

-CH2-CH=CH-CH2--CH2-CH-CH-CH2-with:x=-C-,-C-OH,-C-,-C-H

׀

׀׀׀׀׀׀OHOOOoxidativecrosslinkingreactionThemechanismsrelativetooxidationofrubbertheformationofanetherlinkagethroughphotooxidation:

CH3CH3

׀׀•C=C-CH-CH=C-CH2-

→-CH-CH=C-CH2-------→

׀

׀

+H•OOHO•

CH3׀-CH-CH=C-CH2-

׀O׀-C-CH-׀׀oxidativecrosslinkingreaction

HowtopreventtheagingofrubberBCABlockMethodReactionMethodPPDMethodsofprotection

Methodsofprotection——BlockMethod

Theblockmethod(protectivefilm)reliesonthestabilizerfilmformedatthesurfaceofrubberthatpreventsozoneattackontherubber.wax

Methodsofprotection——BlockMethod

Thekeyeffectsofawaxinrubberhavebeensummarizedasthefollowing:Awaxprotectsbybloomingtothesurfacetoformafilmofhydrocarbonswhichisimpervioustoozone.Protectionisachievedonlywhenthefilmisthickenoughtoprovideabarriertoozone.Thickerfilmsensurelongerprotection.Thicknessofbloomedfilmdependsonboththesolubilityanddiffusionrateofwaxinrubber.Microcrystallinewaxesperformbetterathighertemperature,sincehighertemperaturesincreasetheirmobilityandhencetheirrateofmigrationtothesurface.Itiscommonpracticetoblendparaffinandmicrocrystallinewaxestogethertoachievean"allseason"orwiderangeoftemperatureprotectionagainstozone.

Methodsofprotection——

ReactionMethod

Studieshaveshownthatthefollowingfeaturesofp-phenylenediaminescontribute:1)ahigherrateofreactionwithozonethanthatshownbytherubber;2)diffusionoffreshantiozonantstotheexposedsurfaceonceaconcentrationgradlenthasbeenestablished;3)formationofasurfacefilm,whichrecentspectroscopicanalyseshaveconfirmedconsistsoftheozonationreactionproductsofthep-phenylenediamine.

Methodsofprotection——PPDN,N'-substitutedp-phenylenediamines(PPD)arewidelyusedantioxidantagentsfordienerubbers.Ithasbe