Makhalidwe a Cellulose Ethers

Ma ether a cellulosendi gulu la ma polima achilengedwe osinthidwa ochokera ku cellulose, biopolymer yochuluka kwambiri padziko lonse lapansi. Monga zotumphukira za cellulose, ma ether a cellulose amasunga mawonekedwe oyambira a cellulose pomwe amaphatikiza magulu a ether omwe amakhudza kwambiri kusungunuka kwawo, khalidwe la rheological, kukhazikika kwa kutentha, ndi reactivity ya mankhwala. Zipangizozi zimagwiritsidwa ntchito kwambiri m'mafakitale kuyambira mankhwala ndi chakudya mpaka zomangamanga ndi chisamaliro chaumwini, chifukwa cha kuphatikiza kwawo kwapadera kwa katundu.

1. Cellulose: Kapangidwe ka Msana

Cellulose ndi polysaccharide yolunjika yopangidwa ndi mayunitsi a β-D-glucose olumikizidwa ndi ma bond a β-1,4-glycosidic. Gawo lililonse la shuga limazunguliridwa 180° poyerekeza ndi oyandikana nawo, zomwe zimapangitsa kuti unyolo ukhale wokonzedwa bwino komanso wotambasuka. Ma unyolo awa amapanga ma bond amphamvu a hydrogen pakati pa mamolekyulu, ndikupanga kapangidwe kolimba komanso kofiira. Gawo lililonse la anhydroglucose (AGU) mu cellulose lili ndi magulu atatu a hydroxyl (–OH), omwe ali pamalo a C2, C3, ndi C6. Magulu a hydroxyl awa ndi ogwirizana kwambiri ndipo amagwira ntchito ngati malo oyambira kusintha mankhwala.

2. Kutulutsa kwa Cellulose

Ma cellulose ether amapangidwa pochita zinthu ndi ma alkylating agents pamene pali maziko olimba, omwe nthawi zambiri amakhala sodium hydroxide. Njira imeneyi imalowa m'malo mwa magulu a hydroxyl a cellulose ndi magulu osiyanasiyana a ether monga methyl (–CH₃), hydroxyethyl (–CH₂CH₂OH), kapena carboxymethyl (–CH₂COOH). Njira yodziwira zinthu imakhudza kuyambitsa ma hydroxyls a cellulose kuti apange ma ayoni a alkoxide, omwe kenako amachita zinthu ndi etherifying agent.

Mtundu wa cholowa m'malo chomwe chayambitsidwa umasankha gulu la ether ya cellulose. Mwachitsanzo:

Methylcellulose (MC)- M'malo mwake ndi magulu a methyl.

Hydroxyethylcellulose (HEC)- M'malo mwake ndi magulu a hydroxyethyl.

Carboxymethylcellulose (CMC)- M'malo mwake amalowetsedwa ndi magulu a carboxymethyl.

Hydroxypropylcellulose (HPC)- M'malo mwake ndi magulu a hydroxypropyl.

Ethylcellulose (EC)- M'malo mwake ndi magulu a ethyl.

Chilichonse mwa zinthuzi chimapereka zinthu zinazake, monga kusungunuka kwa madzi, kupangika kwa filimu, kukhuthala, ndi kutentha, zomwe zimapangidwa kuti zigwirizane ndi ntchito zinazake.

3. Degree of Substitution (DS) ndi Molar Substitution (MS)

Chimodzi mwa zinthu zofunika kwambiri pa kapangidwe ka ma cellulose ethers ndi digiri ya kusintha (DS), yomwe imatanthauza kuchuluka kwa magulu a hydroxyl pa unit iliyonse ya shuga yomwe yasinthidwa ndi magulu a ether. Popeza pali magulu atatu a hydroxyl pa AGU iliyonse, DS yayikulu ndi 3.

Ma ether ena a cellulose, monga hydroxyethylcellulose kapena hydroxypropylmethylcellulose, amakhudza unyolo wam'mbali womwe ungakhale ndi magulu ena a hydroxyl. Pazochitika zotere, molar substitution (MS) imagwiritsidwanso ntchito pofotokoza kuchuluka kwa ma moles a magulu olowa m'malo omwe ali pa AGU iliyonse. MS imatha kupitirira 3 chifukwa imapangitsa kuti etherification yowonjezera ikhale pa unyolo wolowa m'malo.

DS ndi MS zimakhudza kwambiri kusungunuka, kukhuthala, ndi kutentha kwa ma cellulose ethers. DS yapamwamba nthawi zambiri imasintha kusungunuka m'madzi kapena zosungunulira zachilengedwe ndipo imasintha khalidwe la gelation. Mwachitsanzo, low-DS carboxymethylcellulose sisungunuka m'madzi, pomwe mitundu ya high-DS imasungunuka mosavuta.

4. Madera Osaoneka ndi Maso ndi Makristalo

Maselo opangidwa ndi ma crystalline achilengedwe amakhala ndi kapangidwe ka semi-crystalline, kopangidwa ndi madera opangidwa ndi ma crystalline okonzedwa bwino omwe ali ndi madera osakonzedwa bwino. Madera opangidwa ndi ma crystalline amakhazikika chifukwa cha hydrogen bonding yayikulu komanso kuyanjana kwa van der Waals, zomwe zimapangitsa kuti asagwirizane ndi kusintha kwa mankhwala.

Machitidwe a etherification nthawi zambiri amapezeka mosavuta m'madera opanda mawonekedwe, komwe unyolo wa cellulose umapezeka mosavuta. Pamene kusinthana kukupita patsogolo, madera a crystalline amasokonezeka, zomwe zimawonjezera kuchuluka kwa amorphous ndipo, motero, kusungunuka kwa cellulose ether m'madzi kapena zosungunulira. Kusintha kumeneku kuchokera ku kapangidwe ka crystalline kupita ku amorphous ndi kusintha kwakukulu kwa kapangidwe kake pakupanga cellulose ethers.

5. Kusungunuka ndi Kusinthasintha kwa Madzi

Kusintha kwa kapangidwe ka cellulose kudzera mu etherification kumasintha hydrophilicity yake. Kutengera mtundu ndi kuchuluka kwa magulu olowa m'malo, ma cellulose ether amatha kusungunuka m'madzi, organic solvents, kapena zonse ziwiri. Mwachitsanzo:

Methylcellulose imasungunuka m'madzi ndipo imasunga kutentha kwa gelation.

Ethylcellulose sisungunuka m'madzi koma imasungunuka m'zinthu zachilengedwe monga ethanol ndi toluene.

Hydroxyethylcellulose ndi hydroxypropylcellulose zimakhala ndi hydrophilic kwambiri komanso zimasungunuka m'madzi.

Kuwonjezeka kwa kusungunuka kwa ma cellulose ethers kumachitika chifukwa cha kusokonekera kwa ma hydrogen bonding pakati pa mamolekyulu mu cellulose yachilengedwe komanso kuyambitsa magulu a hydrophilic ether, omwe amatha kupanga ma hydrogen bond atsopano ndi mamolekyu amadzi.

6. Katundu wa Mafupa ndi Kulemera kwa Mamolekyulu

Maonekedwe osinthira ma cellulose chains samakhudza kusungunuka kokha komanso kukhuthala ndi kusinthasintha kwa mayankho amadzi. Ma cellulose ether nthawi zambiri amakhala ma polima olemera kwambiri, ndipo mayankho awo amasonyeza khalidwe la pseudoplastic (kuchepetsa kumeta), lomwe ndi lofunika kwambiri pogwiritsira ntchito monga utoto, zokhuthala chakudya, ndi mankhwala.

Kukhuthala kumawonjezeka ndi kulemera kwa mamolekyulu ndi kuchuluka kwa polymerization koma kumakhudzidwanso ndi DS ndi MS. Ma ether a cellulose omwe amasinthidwa kwambiri nthawi zambiri amakhala ndi kusinthasintha kwakukulu kwa unyolo komanso kuchepa kwa kuyanjana kwa ma interchain, zomwe zimapangitsa kuti kukhuthala kukhale kochepa pamlingo womwewo poyerekeza ndi mitundu yochepa yosinthidwa.

7. Kukhazikika kwa Kutentha ndi Mankhwala

Kusungunuka kwa ether kumawonjezera kukhazikika kwa kutentha ndi mankhwala a cellulose. Magulu a ether omwe amasinthidwa amapereka chitetezo cha steric ku kuwonongeka kwa hydrolytic ndi oxidative. Komabe, khalidwe la kutentha limasiyana malinga ndi mtundu wa cholowa m'malo:

Methylcellulose ndi hydroxypropylmethylcellulose zimawonetsa kutentha kwa gelation, njira yosinthika pomwe maunyolo a polima amasonkhana akatenthedwa ndikupanga gel.

Ethylcellulose siigwira ntchito ngati jeli ikatenthedwa koma imasunga kapangidwe kake bwino pa kutentha kwakukulu.

Kukana kwa mankhwala ku ma acid ndi ma bases kumawonjezekanso mu ma cellulose ethers, makamaka omwe ali ndi DS yapamwamba. Komabe, carboxymethylcellulose imakhala yogwirizana kwambiri ndi pH chifukwa cha magulu ake a anionic carboxyl.

8. Kapangidwe ndi Kapangidwe ka Mamolekyulu

Ngakhale kuti cellulose ndi polima yolunjika, kuyambitsidwa kwa magulu akuluakulu a ether kungayambitse kupota kwa unyolo kapena nthambi zina, kutengera kukula ndi kusinthasintha kwa zinthu zolowa m'malo. Kusintha kwa kapangidwe kameneka kumakhudza khalidwe la yankho ndi mphamvu zopangira filimu ya ma ether a cellulose. Kugawidwa kwa malo kwa zinthu zolowa m'malo mwa unyolo wa polima kumakhudzanso kuyanjana kwa mamolekyulu ndi kugwirizana ndi ma polima ena kapena zowonjezera.

9. Makhalidwe Ogwira Ntchito Ochokera ku Kapangidwe kake

Makhalidwe apadera a ether a cellulose amawapangitsa kukhala zipangizo zogwirira ntchito zosiyanasiyana. Zitsanzo zina zodziwika bwino ndi izi:

Kupanga filimu: Chifukwa cha kulemera kwawo kwa mamolekyulu ndi kuyanjana kwa unyolo, ma cellulose ether amapanga mafilimu osinthasintha, owonekera bwino omwe amagwiritsidwa ntchito popaka ndi kulongedza.

Kutulutsa mankhwala kolamulidwa: Mphamvu zopangira gel ndi kutupa kwa ma cellulose ethers zimagwiritsidwa ntchito m'mapiritsi a mankhwala kuti mankhwala aperekedwe nthawi zonse.

Kusakaniza ndi kuyimitsidwa: Kulinganiza kwa hydrophilic-lipophilic komwe kumaperekedwa ndi zinthu zinazake kumathandiza kuti ma cellulose ethers azikhazikika mu emulsions ndi kuyimitsidwa.

Kumamatira ndi kumamatira: Kuthekera kwawo kupanga ma hydrogen bond ndi zinthu zina kumapangitsa kuti ma cellulose ethers akhale abwino kwambiri pomanga, kupanga zinthu zadothi, ndi zinthu zamapepala.

Themakhalidwe a kapangidwe ka ethers a cellulose—zomwe zimafotokozedwa ndi mawonekedwe awo a etherification, kuchuluka kwa kusintha, kapangidwe ka mamolekyulu, ndi mawonekedwe ake enieni—ndizofunikira kwambiri pakugwira ntchito kwawo m'njira zosiyanasiyana. Kudzera mu kusintha kwa mankhwala kolamulidwa kwa cellulose yachilengedwe, n'zotheka kukonza kusungunuka, kukhuthala, kutentha, komanso kugwirizana ndi zinthu zina. Pamene mafakitale akupitiliza kufunafuna njira zina zokhazikika komanso zowola m'malo mwa ma polima opangidwa, kufunika ndi kufunikira kwa ma ether a cellulose kukuyembekezeka kukula, zomwe zimapangitsa kumvetsetsa bwino ubale wawo ndi ntchito kukhala kofunikira kwambiri.