Hydroxypropyl methylcellulose (HPMC) yog ib qho uas tsis yog-ionic cellulose ether dav siv hauv tshuaj, khoom noj khoom haus, kev tsim kho thiab lwm yam kev lag luam, tshwj xeeb tshaj yog nyob rau hauv cov tshuaj sustained-tso ntsiav tshuaj thiab cov khoom siv hauv tsev. Txoj kev tshawb fawb txog thermal degradation ntawm HPMC tsis yog tsuas yog qhov tseem ceeb rau kev nkag siab txog kev hloov pauv kev ua haujlwm uas yuav raug ntsib thaum ua, tab sis kuj tseem ceeb heev rau kev tsim cov ntaub ntawv tshiab thiab txhim kho kev pab cuam lub neej thiab kev nyab xeeb ntawm cov khoom.
Thermal degradation yam ntxwv ntawm HPMC
Lub thermal degradation ntawm hydroxypropyl methylcellulose yog feem ntau cuam tshuam los ntawm nws cov qauv molecular, cua sov thiab nws ib puag ncig tej yam kev mob (xws li cua, av, thiab lwm yam). Nws cov qauv molecular muaj ntau cov pab pawg hydroxyl thiab ether bonds, yog li nws yooj yim rau cov tshuaj lom neeg xws li oxidation thiab decomposition ntawm qhov kub thiab txias.
Cov txheej txheem thermal degradation ntawm HPMC feem ntau muab faib ua ob peb theem. Ua ntej, ntawm qhov kub qis dua (kwv yees li 50-150 ° C), HPMC tuaj yeem ntsib qhov poob loj vim qhov poob dej dawb thiab cov dej adsorbed, tab sis cov txheej txheem no tsis cuam tshuam nrog kev rhuav tshem cov tshuaj lom neeg, tsuas yog hloov lub cev. Raws li qhov kub nce ntxiv (siab dua 150 ° C), ether bonds thiab hydroxyl pawg hauv HPMC qauv pib tawg, ua rau tawg ntawm cov saw molecular thiab kev hloov hauv cov qauv. Tshwj xeeb, thaum HPMC yog rhuab mus txog 200-300 ° C, nws pib mus rau thermal decomposition, thaum lub sij hawm lub hydroxyl pawg thiab sab chains xws li methoxy los yog hydroxypropyl nyob rau hauv lub molecule maj decompose los tsim me me molecular khoom xws li methanol, formic. acid thiab ib qho me me ntawm hydrocarbons.
Thermal degradation mechanism
Lub thermal degradation mechanism ntawm HPMC yog qhov nyuaj thiab koom nrog ntau kauj ruam. Nws cov txheej txheem degradation tuaj yeem sau tau yooj yim raws li hauv qab no: raws li qhov kub thiab txias, cov ether daim ntawv cog lus hauv HPMC maj mam tawg los tsim cov khoom me me molecular, uas tom qab ntawd ntxiv decompose tso cov khoom gaseous xws li dej, carbon dioxide, thiab carbon monoxide. Nws txoj hauv kev thermal degradation tseem ceeb suav nrog cov kauj ruam hauv qab no:
Cov txheej txheem lub cev qhuav dej: HPMC poob cov dej hauv lub cev thiab cov dej me me ntawm qhov kub thiab txias, thiab cov txheej txheem no tsis rhuav tshem nws cov qauv tshuaj.
Degradation ntawm hydroxyl pawg: Nyob rau hauv qhov kub ntawm txog 200-300 ° C, pawg hydroxyl ntawm HPMC molecular saw pib pyrolyze, tsim dej thiab hydroxyl radicals. Lub sijhawm no, methoxy thiab hydroxypropyl sab chains kuj maj mam decompose los tsim cov me me molecules xws li methanol, formic acid, thiab lwm yam.
Cov saw tseem ceeb tawg: Thaum qhov kub thiab txias ntxiv mus rau 300-400 ° C, β-1,4-glycosidic bonds ntawm cellulose cov saw tseem ceeb yuav dhau los ua pyrolysis los tsim cov khoom lag luam me me thiab cov pa roj carbon residues.
Kev tawg ntxiv: Thaum qhov kub nce siab tshaj 400 ° C, cov seem hydrocarbons thiab qee cov cellulose degraded tsis tiav yuav ua rau tawg ntxiv kom tsim tau CO2, CO thiab qee qhov me me molecular organic teeb meem.
Yam cuam tshuam rau thermal degradation
Lub thermal degradation ntawm HPMC cuam tshuam los ntawm ntau yam, feem ntau suav nrog cov hauv qab no:
Kub: Tus nqi thiab qib ntawm thermal degradation yog ze ze rau qhov kub thiab txias. Feem ntau, qhov kub thiab txias ntau dua, cov tshuaj tiv thaiv degradation sai dua thiab ntau dua qhov degradation. Hauv kev siv cov tswv yim, yuav ua li cas tswj qhov kub thiab txias ua kom tsis txhob muaj thermal degradation ntau dhau ntawm HPMC yog ib qho teeb meem uas xav tau kev saib xyuas.
Atmosphere: Tus cwj pwm thermal degradation ntawm HPMC hauv cov huab cua sib txawv kuj txawv. Nyob rau hauv huab cua lossis oxygen ib puag ncig, HPMC yog ib qho yooj yim rau oxidize, tsim cov khoom gaseous thiab carbon residues, thaum nyob rau hauv ib qho chaw inert (xws li nitrogen), cov txheej txheem degradation yog manifested li pyrolysis, tsim ib tug me me ntawm carbon residues.
Molecular Luj: Qhov hnyav molecular ntawm HPMC kuj cuam tshuam rau nws tus cwj pwm thermal degradation. Qhov siab dua qhov hnyav molecular, qhov siab dua qhov pib ntawm thermal degradation. Qhov no yog vim qhov hnyav molecular hnyav HPMC muaj cov hlua molecular ntev dua thiab cov qauv ruaj khov dua, thiab xav tau lub zog ntau dua los rhuav tshem nws cov molecular bonds.
Cov ntsiab lus noo noo: Cov dej noo hauv HPMC kuj cuam tshuam rau nws cov thermal degradation. Cov dej noo tuaj yeem txo qhov kub ntawm qhov decomposition, tso cai rau degradation tshwm sim ntawm qhov kub thiab txias.
Daim ntawv thov cuam tshuam ntawm thermal degradation
Cov yam ntxwv thermal degradation ntawm HPMC muaj qhov cuam tshuam tseem ceeb rau nws txoj kev siv. Piv txwv li, hauv kev npaj tshuaj, HPMC feem ntau yog siv los ua cov khoom tso tawm los tswj cov tshuaj tso tawm. Txawm li cas los xij, thaum ua cov tshuaj, qhov kub thiab txias yuav cuam tshuam rau cov qauv ntawm HPMC, yog li hloov qhov kev tso tawm ntawm cov tshuaj. Yog li ntawd, kev kawm nws tus cwj pwm thermal degradation yog qhov tseem ceeb heev rau kev ua kom cov tshuaj ua kom zoo thiab ua kom cov tshuaj ruaj khov.
Hauv cov khoom siv hauv tsev, HPMC feem ntau yog siv hauv cov khoom siv hauv tsev xws li cov cement thiab gypsum los ua lub luag haujlwm hauv thickening thiab dej tuav. Txij li thaum cov khoom siv hauv tsev feem ntau yuav tsum muaj qhov kub thiab txias ib puag ncig thaum siv, thermal stability ntawm HPMC kuj yog ib qho tseem ceeb rau kev xaiv cov khoom siv. Thaum qhov kub thiab txias, qhov thermal degradation ntawm HPMC yuav ua rau txo qis hauv cov khoom siv, yog li thaum xaiv thiab siv nws, nws qhov kev ua tau zoo ntawm qhov kub sib txawv feem ntau yog txiav txim siab.
Cov txheej txheem thermal degradation ntawm hydroxypropyl methylcellulose (HPMC) suav nrog ntau cov kauj ruam, uas feem ntau cuam tshuam los ntawm qhov kub, qhov chaw, qhov hnyav molecular thiab cov ntsiab lus noo noo. Nws cov thermal degradation mechanism suav nrog lub cev qhuav dej, decomposition ntawm hydroxyl thiab sab chains, thiab cleavage ntawm cov saw tseem ceeb. Cov yam ntxwv thermal degradation ntawm HPMC muaj qhov tseem ceeb ntawm daim ntawv thov hauv kev npaj tshuaj, khoom siv hauv tsev, thiab lwm yam. Yog li ntawd, kev nkag siab tob txog nws tus cwj pwm thermal degradation yog qhov tseem ceeb rau kev txhim kho cov txheej txheem tsim thiab txhim kho cov khoom ua tau zoo. Hauv kev tshawb fawb yav tom ntej, lub thermal stability ntawm HPMC tuaj yeem txhim kho los ntawm kev hloov kho, ntxiv cov stabilizers, thiab lwm yam, yog li nthuav nws daim ntawv thov teb.
Post lub sij hawm: Oct-25-2024