专外-专业外语chapter7manufactured cellulosic fibers

Joseph’sIntroductory

TextileScience(6thEd.)XudongYang杨旭东

Ch.7ManufacturedCellulosicFibersWordslistKeywords全部Newwords3，6，7，12，13，21，22，26，34-36，46，48，50,57，58，62。Today,threecellulosicfibers,withquitedifferentproperties,aredefinedbytheTFPIA.Theyareacetate(醋酯纤维),triacetate（三醋酯纤维）,andrayon:acetate—amanufacturedfiberinwhichtheformingsubstanceiscelluloseacetate(醋酸盐）.Wherenotlessthan92%ofthehydroxylgroups（羟基）areacetylated（乙酰化的）,thetermtriacetatemaybeusedasagenericdescriptionofthefiber.Rayon-amanufacturedfibercomposedofregeneratedcellulose,aswellasmanufacturedfiberscomposedofregeneratedcelluloseinwhichsubstitutents（替代物）havereplacednotmorethan15%ofthehydrogensofthehydroxylgroupsCommercialDevelopmentRAYONViscose（粘胶）Rayon:它是由纤维素纤维黄原酸盐溶于氢氧化纳而制得的。CuprammoniumRayon铜氨纤维:它是溶于含氨的氧化铜溶液中的纤维素经沉淀生产出的絮萦长丝，即为铜氯絮萦纤维Solvent-SpunRayon:TencelHistorically,twomethodsofrayonproduction,theviscose(粘胶)andcuprommonium（铜氨）processes，havebeencommercialized.(商品化)Lyocell纤维是英国考陶尔兹公司和奥地利兰精公司分别于20世纪90年代开发的新型纤维素纤维。国外Lyocell纤维的应用已非常普遍，技术较成熟，而国内尚属开发应用阶段。Lyocell是纤维的学名，商品名叫Tencel,我国俗称天丝。它是采用全新溶剂在制造过中可回收，产品使用后的废品可生化降解，所以称之为“21世纪的绿色纤维”。Lyocell纤维的横截面呈圆形，聚合度、结晶度高，初始模量、湿模量高；具有高强、低伸、干湿强度相仿、刚性强、表面光滑而干燥、收缩率低及呈原纤化特征；吸湿性、舒适性、光泽性、染色性及生物降解性、尺寸稳定性都相当优良。Lyocell纤维可以纯纺，也可与棉、麻、毛、丝或合成纤维混纺，制成品种繁多的各种特色的机织物和针织物，提高和改善织物的性能，适应各种时尚潮流。FiberProductionPULPFORMATIONWoodpulpandcottonlinters(棉仔绒，棉短绒)arethetwomajorsourcesofpurifiedcelluloseformanufacturingacetateandrayon.Woodpulpisproducedfromtimber（木材、木料）Afterthebarkisremoved,thewoodischippedintoverysmallpieces.Thewoodchipsaretreatedwithcalciumbisulphite（亚硫酸钙）andthensteamedunderpressureforseveralhours.Thewoodposes,andapurifiedformorCelluloseisproduced.Thepulpisbleachedwithhypochlorite（次氯酸盐）andpressedintoasheetofpulp,whichesthestartingproductforfibermanufacturing.Sheetpulpissomewhatsofterandlessdensethanproductssimilarinformcalledpaperboard(纸板)andblottingpaper（吸墨纸）.ViscoseRayonFigure7.2isthebasicflowdiagramforviscoserayonproduction,Theprincipalrawmaterialforviscoserayonisarefined（提炼的）gradeofwoodpulp.Sheetsofcellulosepulp,about0.6meter(2ft)square,aresteeped（浸渍）ina17.5percentsolutionofsodiumhydroxide（NaOH）untilthecelluloseisconvertedtoalkalicellulose.FlowchartThealkalizedsheetsarethenshredded（粉碎）tocrumbs（碎屑）andagedforvaryingperiodsoftimeuptothreedays.Theaging（老化，熟化）processinvolvesachemicalreactionbetweenalkaliandoxygenintheair,whichreducesthelengthofthecellulosepolymerchainfromhighdegreeofpolymerizationtoalowerdp,suitableforthedesiredtypeofrayontobemade.Thereactiontimeintheagingprocessdependsonthestartingdpofthepulp,thechemicalreactivityofthespecificpulpused,thepresenceofacatalyst,andtemperature.Afteraging,thealkalicellulosecrumbsarereactedwithcarbondisulfide(二硫化碳).Uptothispointthesodacellulose（碱纤维素）hasbeenwhite,butthecarbondisulfidechangesittoabrightorangeproductcalledsodiumcellulosexanthate黄原酸纤维素钠.Thexanthatecrumbisdissolvedindilutesodiumhydroxide(5to8percentNaOH)andformsaviscous(粘液hencethenameviscose),honey-coloredliquid(Figure7.3).Thissolutionisageduntilitreachesthecorrectdegreeofcoagulation（凝结）forspinnabilityatspecifiedconditions.Therelationshipbetweendegreeofcoagulationandspinbathconditionsinfluencesthekindofproductobtainedandisakeyelementinthe“art”ofmanufacturingrayonfibers.Keyfactorsinviscoseproductionincludeconcentration（浓度）,degreeofpolymerizationofthecellulose,thepresenceofadditives,temperature,andtheamountofreversereactionofxanthate（黄酸盐）thathasoccurredpriortospinning.Theviscoseisfilteredanddeaerated(脱氧，脱泡).deliveredtothespinningpumps,andforced,byindividualpumpsforeachspinnerette,intoanacidbath.Thebathandspinningconditionsforviscoserayonarecontrolledcarefullytomaintainfiberquality.Thespinbathforviscoserayoncontainssulfuricacid(H2SO4硫酸),sodiumsulfate(Na2SO4硫酸钠)water,andcertainadditivessuchasglucose(葡萄糖)andzincsulfate（硫酸锌）.Thecomposition（混合，构成）andtemperatureofthespinbathinfluencetheratesofcoagulationofcellulosexanthateanditssubsequentregenerationtocellulose.Thesefactorsalsoinfluencethecrosssectionandwhetherornotalatent（潜在的）crimpcanbeimparted（给予）tothefinalfiber.Sodiumsulfateistheprimarycoagulationmedium.Theacidneutralizes（中和）excesscaustic(苛性碱)intheviscoseandcoagulatesthecellulosexanthatefilaments.Zincsulfatemoderatestherateofregenerationbyslowingtheprocess.Thecellulosexanthatefilamentsarewithdrawn（退绕）continuouslyfromtheacidbathandarefurthertreatedwithwarmdiluteacidtoforceregenerationofthecellulosexanthatebacktopurecellulose,withthereleaseofcarbondisulfide(二硫化碳),Thefilamentsarestretched,ordrawn,duringtheregenerationstep.Thedegreeofdrawingcontrolsfibertenacityandmodulus。Highdrawratiosareusedtoproducehightenacityandhigh-wet-modulusviscoseThesetwosteps,coagulationandregeneration,makeupthewetspinningprocessforrayon.Afterregenerationthefilamentsarethoroughlywashedtoremoveanyimpuritiesthatmightbestucktothem.Theyareeithercombineddirectlyintofilamentyarnsorcutintoshortlengthsforspinningstapleyarns.ACETATEThepretreatedcelluloseistransferredtokneading(混合，搅拌)machinescalledacetylators（乙酰化器）,whereaceticanhydride（乙酸酐）isadded.STRESS-STRAINRELATIONSAcomparisonofthetenacityandelongationofseveralcellulosicFibersmaybemadebystudyingthestress-straincurvesofsomeofthemajorfibers(Figure7.8).Becauseacetatefibershavefewerassociativeforcesbetweenthemolecularchainsthanrayonfibers,acetatefibersgenerallyhavelowertenacities.Themanufacturedcellulosefiberstendtolosestrengthwhenwet.Thehigh-wet-modulusfibersdonotloseasmuchstrengthasregularrayons.asshowninTable7.2Awiderangeofstress-straincharacteristicsisavailableinmanufacturedcellulosicfibers.Bylookingatthestress-straincurvesofthefibers,therelativetoughness（韧性）andresilience(弹性恢复力)ofaseriesoffiberscanbedetermined.Ingeneral,cellulosicfibershavepoorresiliencyandmustbetreatedwithspecialfinishestoimprovetheirrecoveryfromwrinkling（起皱）,crushing（压痕）,andcreasing（折痕）.Triacetatefibershavethebestresiliencyofthecellulosicfibers.