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1、Readingmaterial:wet-chemistrytheoryWetstrengthofpaperisoftenreferredtoasrelativewet-strength,theratiobetweenwetstrengthanddrystrength.Normally,10to15%isconsideredasawet-strengthpaper.Incontrasttodrystrength,theoriginsinthehydrogenbondspresentinnaturalcellulose,wetstren
2、gthrequireswaterstable(covalent)bonds.Naturally,cellulosecontainsfewcovalentbonds,andthereforewet-strengthchemicalsarenecessary.hydrogenbond氢键covalentbond共价键-valent….价的co-共同，一起Readingmaterial:wet-chemistrytheoryPolymerresinsareoftenusedtoincreasewetstrength.Twodifferen
3、twet-strengthmechanismsexist,theprotectionmechanismandthereinforcementmechanism.Theprotectionmechanisminvolvesdiffusionofthewet-strengthpolymertothefibresurfacewhereitcross-linksthroughandaroundthefibres.Suchcross-linkednetworkspreventfibreswellingandhelpstopreservecov
4、alentbondswhenthepaperisexposedtowater.Incontrast,thereinforcementmechanismmeansthatnewbondsbetweenthewet-strengthpolymerandthefibresareformed.mechanism机理diffusion扩散cross-link交联Readingmaterial:wet-chemistrytheoryFiberchargeisanimportantfactorthatinfluencesthepapermakin
5、gprocessaswellasthepaperproperties.Cellulosefibrescontainvariousionisablegroups:carboxyl-,sulfonicacid-,phenolic-andhydroxylgroupsandarethereforenegativelychargedatallpHvalues.chargen.电荷v.使充电ionisable可离子化的group基团carboxyl羧基sulfonicacid磺酸phenolic酚的hydroxyl羟基Readingmateri
6、al:wet-chemistrytheoryUndernormalpapermakingconditions,thenegativefibrechargeisduetocarboxylandsulfonicacidgroups.Thesechargedgroupsarelocatedeitheronthefibersurfacesorinsidethecellwall;hencetheyarereferredtoassurface-andbulkcharges,respectively.Surfacechargesareimport
7、antforfibre-andpaperstrength.cellwall细胞壁bulk大小,体积,大批,respective分别的Readingmaterial:wet-chemistrytheoryAdsorptionofpolymersisusedinmanyapplications.Thedrivingforceisastrongpolymer-surfaceinteraction.Ifthesolventispoor,thenadsorptionismorefavourablethanthepolymer-solventi
8、nteraction.Aconditionformostcationicadditivesistheabilitytoadsorbtothefibresurface.Thatiswhypolymeradditivesusedinpap
