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1、Lesson13PulpbleachingBleachingisthetreatmentofwoodandotherlignocellulosicpulpswithchemicalagentstoincreasetheirbrightness.Brightnessisincreasedbydecolorizingordissolvingthecoloredcomponentsinpulp,primarilylignin.Twoapproachesareusedinthechemicalbleachingofpulps.bleachv.漂白lig
2、nocellulosic木质纤维素的agent【化学】药剂brightness亮度decolorizevt.使脱色dissolvevt.使溶解componentn.组分Lesson13PulpbleachingOneistoalmosttotallyremoveresiduallignin,whichisusedforbleachingofchemicalpulpsandleadstogreaterfiber-fiberbondingstrengthinpaperbutweakerfibersduetothestrongchemicalused
3、todecreasethelengthofcellulosemolecules.Theotherapproachistoutilizechemicalsthatselectivelydestroysomeofthechromophoricgroupsinmechanicalpulps,whichisreferredtoaslignin-preservingorbrightening.residual残余的，剩余的bondv结合，使粘合strength强度chemical化学药品molecule分子chromophoric发色的，发色团的grou
4、p基团，基mechanicalpulp机械浆brightening显白，显亮Lesson13PulpbleachingSinceligninisacomplexmoleculewithdifferentlinkages,thebreakageofvarioustypesofbondsrequirestheuseofdifferentchemicals.Therefore,allthecoloredmaterialinpulpscannotbeeliminatedbyanysinglechemicalandbleachingisamulti-st
5、epprocess.complex复杂的，多元的linkage【化】键合，成键Lesson13PulpbleachingTheprincipalcommercialbleachingchemicalsconsistsoftheoxidants:chlorine(C),oxygen(O),hypochlorite(H),chlorinedioxide(D),hydrogenperoxide(P),andozone(Z);theonlyreductant:hydrosulfite;andtheonlyalkali:sodiumhydroxide(E
6、,orcausticextraction).oxidant氧化剂chlorine氯oxygen氧气hypochlorite【化】次氯酸盐chlorinedioxide二氧化氯hydrogenperoxide过氧化氢ozone【化】臭氧reductant还原剂hydrosulfite【化】亚硫酸氢盐alkali碱sodiumhydroxide氢氧化钠causticextraction碱抽提Lesson13PulpbleachingItispossibletorankeachoftheoxidizingchemicalsforeconomy,sel
7、ectivity,andparticlebleaching,althoughitmustberememberedthattheparticularconditionsofusewillgreatlyeffectonranking.Therankingsare:Economy:O>C>D>H>P>Z;Selectivity:DelignificationD>C>O>ZBrightening:D,P>HParticlebleaching:D>H,C,O,P>Zdelignification脱木素作用Lesson13PulpbleachingBeca
8、useoftheirgreatereconomy,chlorineandoxygenareusedintheearlystagesofbleachin
