Cellulose derivatives yog tsim los ntawm esterification los yog etherification ntawm hydroxyl pawg nyob rau hauv cellulose polymers nrog tshuaj reagents. Raws li cov yam ntxwv ntawm cov khoom siv tshuaj tiv thaiv, cellulose derivatives tuaj yeem muab faib ua peb pawg: cellulose ethers, cellulose esters, thiab cellulose ether esters. Cov cellulose esters uas tau siv ua lag luam yog: cellulose nitrate, cellulose acetate, cellulose acetate butyrate thiab cellulose xanthate. Cellulose ethers muaj xws li: methyl cellulose, carboxymethyl cellulose, ethyl cellulose, hydroxyethyl cellulose, cyanoethyl cellulose, hydroxypropyl cellulose thiab hydroxypropyl methyl cellulose. Tsis tas li ntawd, muaj ester ether sib xyaw derivatives.
Cov khoom siv thiab siv Los ntawm kev xaiv cov khoom siv hloov pauv thiab cov txheej txheem tsim, cov khoom tuaj yeem yaj hauv dej, dilute alkali tov lossis organic hnyav, lossis muaj cov khoom siv thermoplastic, thiab tuaj yeem siv los tsim cov tshuaj fibers, films, zaj duab xis hauv paus, plastics, insulating. cov ntaub ntawv, txheej, slurry, polymeric dispersant, khoom noj khoom haus additives thiab tshuaj txhua hnub. Cov khoom ntawm cellulose derivatives muaj feem xyuam rau qhov xwm ntawm cov neeg hloov pauv, qib DS ntawm peb pawg hydroxyl ntawm cov piam thaj hauv pawg tau hloov pauv, thiab kev faib tawm ntawm cov neeg hloov pauv raws li cov saw hlau macromolecular. Vim yog qhov tsis sib xws ntawm cov tshuaj tiv thaiv, tshwj tsis yog cov khoom hloov pauv tsis sib xws thaum tag nrho peb pawg hydroxyl hloov pauv (DS yog 3), lwm yam (homogeneous cov tshuaj tiv thaiv lossis cov tshuaj tiv thaiv heterogeneous), peb txoj haujlwm sib txawv hauv qab no tau txais: Cov khoom sib xyaw nrog unsubstituted glucosyl pawg: ① monosubstituted (DS yog 1, C, C los yog C txoj hauj lwm yog hloov, qauv qauv pom cellulose); ② disubstituted (DS yog 2, C, C, C, C los yog C, C txoj hauj lwm raug hloov); ③ hloov pauv tag nrho (DS yog 3). Yog li ntawd, cov khoom ntawm tib cellulose derivative nrog tib tus nqi hloov pauv kuj yuav txawv heev. Piv txwv li, cellulose diacetate ncaj qha esterified rau DS ntawm 2 yog insoluble nyob rau hauv acetone, tab sis cellulose diacetate tau los ntawm saponification ntawm tag nrho esterified cellulose triacetate tuaj yeem yaj tag hauv acetone. Qhov no heterogeneity ntawm kev hloov pauv yog cuam tshuam nrog cov cai yooj yim ntawm cellulose ester thiab cov tshuaj tiv thaiv etherification.
Txoj cai tseem ceeb ntawm cellulose esterification thiab etherification cov tshuaj tiv thaiv nyob rau hauv cellulose molecule, txoj hauj lwm ntawm peb hydroxyl pawg nyob rau hauv cov piam thaj yog sib txawv, thiab cov kev cuam tshuam ntawm cov uas nyob ib sab substituents thiab steric hindrance kuj txawv. Cov txheeb ze acidity thiab degree ntawm dissociation ntawm peb pawg hydroxyl yog: C> C> C. Thaum cov tshuaj tiv thaiv etherification yog ua nyob rau hauv ib qho nruab nrab alkaline, pawg C hydroxyl reacts ua ntej, ces cov C hydroxyl pawg, thiab thaum kawg cov C thawj hydroxyl pawg. Thaum cov tshuaj tiv thaiv esterification tau ua nyob rau hauv ib qho acidic nruab nrab, qhov nyuaj ntawm cov tshuaj tiv thaiv ntawm txhua pawg hydroxyl yog opposite rau qhov kev txiav txim ntawm cov tshuaj tiv thaiv etherification. Thaum reacting nrog ib tug loj hloov reagent, steric hindrance nyhuv muaj ib tug tseem ceeb lub luag hauj lwm, thiab C hydroxyl pab pawg neeg nrog ib tug me me steric hindrance nyhuv yog yooj yim rau react dua cov C thiab C hydroxyl pawg.
Cellulose yog crystalline natural polymer. Feem ntau ntawm cov tshuaj esterification thiab etherification yog cov tshuaj tiv thaiv heterogeneous thaum cov cellulose tseem khov. Lub xeev diffusion ntawm cov tshuaj tiv thaiv reagents rau hauv cellulose fiber yog hu ua qhov ncav cuag. Kev sib xyaw ua ke ntawm thaj tsam crystalline yog nruj nruj, thiab cov reagent tuaj yeem tsuas yog diffuse mus rau crystalline nto. Kev sib xyaw ua ke hauv cheeb tsam amorphous yog xoob, thiab muaj ntau pawg hydroxyl dawb uas yooj yim rau kev sib cuag nrog cov tshuaj reagents, muaj kev nkag tau yooj yim thiab cov tshuaj tiv thaiv yooj yim. Feem ntau, cov khoom siv raw nrog cov crystallinity siab thiab loj siv lead ua loj tsis yooj yim rau kev hnov mob li raw cov ntaub ntawv uas tsis tshua muaj crystallinity thiab siv lead ua me me. Tab sis qhov no tsis yog tag nrho, piv txwv li, acetylation tus nqi ntawm qhuav viscose fibers nrog qis crystallinity thiab me crystallinity yog ho qis dua cov paj rwb fiber ntau nrog crystallinity ntau dua thiab loj crystallinity. Qhov no yog vim qee cov ntsiab lus hydrogen bonding yog tsim los ntawm cov polymers uas nyob ib sab thaum lub sij hawm ziab, uas cuam tshuam cov diffusion ntawm reagents. Yog tias cov dej noo hauv cov khoom siv cellulose ntub yog hloov los ntawm cov kuab tshuaj loj dua (xws li acetic acid, benzene, pyridine) thiab tom qab ntawd qhuav, nws cov reactivity yuav zoo dua, vim tias ziab tsis tuaj yeem tshem tawm cov kuab tshuaj, thiab qee qhov loj dua. cov molecules yog daig nyob rau hauv "qhov" ntawm cellulose raw khoom, tsim thiaj li hu ua muaj cellulose. Qhov kev ncua deb uas tau nthuav dav los ntawm qhov o tsis yooj yim rau kev rov qab los, uas yog qhov zoo rau kev nthuav dav ntawm cov tshuaj reagents, thiab txhawb cov tshuaj tiv thaiv tus nqi thiab kev sib txuam ntawm cov tshuaj tiv thaiv. Vim li no, nyob rau hauv cov txheej txheem ntau lawm ntawm ntau yam cellulose derivatives, yuav tsum muaj kev kho mob o. Feem ntau, dej, kua qaub los yog ib qho concentration ntawm alkali tov yog siv los ua tus neeg sawv cev o. Tsis tas li ntawd, qhov nyuaj ntawm cov tshuaj tiv thaiv ntawm cov kua dej dissolving nrog tib lub cev thiab tshuaj ntsuas ntsuas yog feem ntau sib txawv, uas yog tshwm sim los ntawm morphological yam tseem ceeb ntawm ntau hom nroj tsuag los yog hlwb nrog txawv biochemical thiab structural functions nyob rau hauv tib cov nroj tsuag. ntawm. Thawj phab ntsa ntawm txheej txheej ntawm cov nroj tsuag fiber ntau cuam tshuam kev nkag mus ntawm cov tshuaj reagents thiab retards tshuaj lom neeg cov tshuaj tiv thaiv, yog li nws yog ib qho tsim nyog yuav tsum siv cov xwm txheej zoo sib xws hauv cov txheej txheem pulping los rhuav tshem cov thawj phab ntsa txhawm rau kom tau txais cov ntaub so ntswg zoo dua. Piv txwv li, bagasse pulp yog cov khoom siv raw nrog tsis zoo reactivity nyob rau hauv zus tau tej cov viscose pulp. Thaum npaj viscose (cellulose xanthate alkali tov), ntau cov pa roj carbon disulfide tau noj ntau dua li paj rwb linter pulp thiab ntoo pulp. Qhov pom tus nqi qis dua li ntawm viscose npaj nrog lwm cov pulps. Qhov no yog vim lub hauv paus phab ntsa ntawm cov piam thaj fiber ntau tsis tau raug puas tsuaj thaum lub sij hawm pulping thiab kev npaj ntawm alkali cellulose los ntawm cov pa txoj kev, uas ua rau muaj teeb meem nyob rau hauv yellowing cov tshuaj tiv thaiv.
Pre-hydrolyzed alkaline bagasse pulp fibers] thiab Daim duab 2 [bagasse pulp fibers tom qab alkali impregnation] yog electron microscope scanning dluab ntawm lub nto ntawm bagasse pulp fibers tom qab pre-hydrolyzed alkaline txheej txheem thiab pa alkaline impregnation raws li, tus qub tseem tuaj yeem pom. clear pits; nyob rau hauv lub tom kawg, txawm hais tias lub pits ploj vim o ntawm alkali tov, thawj phab ntsa tseem npog tag nrho cov fiber. Yog hais tias "thib ob impregnation" (ib txwm impregnation ua raws li ib tug thib ob impregnation nrog ib tug dilute alkali tov nrog ib tug loj o nyhuv) los yog dip-sib tsoo (ntau impregnation ua ke nrog txhua yam sib tsoo) txheej txheem, yellowing cov tshuaj tiv thaiv tuaj yeem ua tau zoo, viscose pom tus nqi yog kho tau zoo heev. Qhov no yog vim hais tias ob qho tib si saum toj no ob txoj kev tuaj yeem tev tawm ntawm cov phab ntsa, nthuav tawm cov txheej txheem sab hauv ntawm cov tshuaj tiv thaiv yooj yim, uas yog qhov tsim nyog rau kev nkag mus ntawm cov tshuaj reagents thiab txhim kho cov tshuaj tiv thaiv kev ua tau zoo (Daim duab 3 [secondary impregnation ntawm bagasse pulp fiber. ], Fig. Sib tsoo Bagasse Pulp Fibers]).
Nyob rau hauv xyoo tas los no, cov kuab tshuaj tsis muaj dej uas tuaj yeem yaj cov cellulose ncaj qha tau tshwm sim. Xws li dimethylformamide thiab TSIS MUAJ, dimethyl sulfoxide thiab paraformaldehyde, thiab lwm cov kuab tshuaj sib xyaw, thiab lwm yam, pab kom cov cellulose tau txais cov tshuaj tiv thaiv homogeneous. Txawm li cas los xij, qee qhov kev cai lij choj uas tau hais los saum toj no ntawm cov kev tawm tsam tawm ntawm theem tsis siv lawm. Piv txwv li, thaum npaj cellulose diacetate soluble nyob rau hauv acetone, nws tsis yog yuav tsum tau undergo hydrolysis ntawm cellulose triacetate, tab sis tuaj yeem ncaj qha esterified kom txog thaum DS yog 2.
Post lub sij hawm: Feb-27-2023