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Cov ntaub ntawv polyurethane puas tiv taus qhov kub siab? Feem ntau, polyurethane tsis tiv taus qhov kub siab, txawm tias muaj PPDI system ib txwm muaj, nws qhov kub siab tshaj plaws tsuas yog nyob ib puag ncig 150 °. Cov polyester lossis polyether hom ib txwm yuav tsis tuaj yeem tiv taus qhov kub siab tshaj 120 °. Txawm li cas los xij, polyurethane yog cov polymer polar heev, thiab piv rau cov yas dav dav, nws tiv taus cua sov ntau dua. Yog li ntawd, kev txhais qhov ntau thiab tsawg kub rau kev tiv taus qhov kub siab lossis kev sib txawv ntawm kev siv sib txawv yog qhov tseem ceeb heev.
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Yog li cas thiaj li txhim kho qhov ruaj khov ntawm cov khoom siv polyurethane? Cov lus teb yooj yim yog kom ua kom cov khoom siv crystallinity ntau ntxiv, xws li PPDI isocyanate uas tau hais ua ntej. Vim li cas thiaj ua kom cov polymer crystallinity ntau ntxiv txhim kho nws qhov ruaj khov thermal? Cov lus teb yeej paub rau txhua tus, uas yog, cov qauv txiav txim siab cov khoom. Niaj hnub no, peb xav sim piav qhia vim li cas kev txhim kho ntawm cov qauv molecular regularity ua rau muaj kev txhim kho hauv thermal stability, lub tswv yim yooj yim yog los ntawm kev txhais lossis cov mis ntawm Gibbs lub zog dawb, piv txwv li △G = H-ST. Sab laug ntawm G sawv cev rau lub zog dawb, thiab sab xis ntawm kab zauv H yog enthalpy, S yog entropy, thiab T yog kub.
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Lub zog Gibbs dawb yog lub tswv yim zog hauv thermodynamics, thiab nws qhov loj me feem ntau yog tus nqi sib piv, piv txwv li qhov sib txawv ntawm cov nqi pib thiab xaus, yog li lub cim △ siv nyob rau pem hauv ntej ntawm nws, vim tias tus nqi kiag li tsis tuaj yeem tau txais ncaj qha lossis sawv cev. Thaum △G txo qis, piv txwv li thaum nws tsis zoo, nws txhais tau tias cov tshuaj tiv thaiv tuaj yeem tshwm sim yam tsis tau npaj tseg lossis zoo rau qee qhov kev tiv thaiv xav tau. Qhov no kuj tseem siv tau los txiav txim siab seb qhov kev tiv thaiv puas muaj lossis rov qab tau hauv thermodynamics. Qib lossis tus nqi ntawm kev txo qis tuaj yeem nkag siab tias yog kinetics ntawm cov tshuaj tiv thaiv nws tus kheej. H yog qhov enthalpy, uas tuaj yeem nkag siab tias yog lub zog sab hauv ntawm lub molecule. Nws tuaj yeem kwv yees los ntawm lub ntsiab lus ntawm cov cim Suav, vim tias hluav taws tsis yog

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S sawv cev rau entropy ntawm lub kaw lus, uas feem ntau paub thiab lub ntsiab lus tseeb yog qhov tseeb. Nws muaj feem cuam tshuam nrog lossis qhia tawm hauv qhov kub T, thiab nws lub ntsiab lus tseem ceeb yog qib ntawm kev tsis sib haum xeeb lossis kev ywj pheej ntawm lub kaw lus me me. Ntawm lub sijhawm no, tus phooj ywg me me uas saib xyuas yuav tau pom tias qhov kub T muaj feem cuam tshuam nrog kev tiv thaiv thermal uas peb tab tom tham txog hnub no thaum kawg tau tshwm sim. Cia kuv tsuas yog hais me ntsis txog lub tswv yim entropy. Entropy tuaj yeem nkag siab ruam ua qhov txawv ntawm crystallinity. Qhov siab dua tus nqi entropy, qhov ntau dua kev tsis sib haum xeeb thiab chaotic cov qauv molecular yog. Qhov siab dua cov qauv molecular qhov kev cai lij choj, qhov zoo dua molecule crystallinity yog. Tam sim no, cia peb txiav ib lub square me me tawm ntawm polyurethane roj hmab yob thiab suav tias lub square me me ua ib lub kaw lus tiav. Nws qhov hnyav yog kho, xav tias lub square yog ua los ntawm 100 polyurethane molecules (qhov tseeb, muaj N ntau), vim nws qhov hnyav thiab ntim tsis hloov pauv, peb tuaj yeem kwv yees △G ua tus nqi lej me me lossis ze rau xoom, ces Gibbs lub zog dawb mis tuaj yeem hloov mus rau ST = H, qhov twg T yog qhov kub, thiab S yog entropy. Ntawd yog, qhov tsis kam thermal ntawm polyurethane me me square yog proportional rau enthalpy H thiab inversely proportional rau entropy S. Tau kawg, qhov no yog ib txoj kev kwv yees, thiab nws yog qhov zoo tshaj plaws los ntxiv △ ua ntej nws (tau los ntawm kev sib piv).
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Nws tsis nyuaj rau pom tias kev txhim kho ntawm crystallinity tsis yog tsuas yog txo qhov entropy tus nqi tab sis kuj nce qhov enthalpy tus nqi, uas yog, nce lub molecule thaum txo qhov denominator (T = H/S), uas yog qhov pom tseeb rau qhov nce ntawm qhov kub T, thiab nws yog ib qho ntawm cov txheej txheem zoo tshaj plaws thiab siv ntau tshaj plaws, tsis hais seb T yog qhov kub hloov iav lossis qhov kub yaj. Qhov yuav tsum tau hloov pauv yog tias qhov tsis tu ncua thiab crystallinity ntawm cov qauv molecular monomer thiab qhov tsis tu ncua thiab crystallinity ntawm cov khoom siv molecular siab tom qab sib sau ua ke yog qhov yooj yim linear, uas tuaj yeem kwv yees li sib npaug lossis nkag siab hauv txoj kev linear. Lub enthalpy H feem ntau yog pab los ntawm lub zog sab hauv ntawm lub molecule, thiab lub zog sab hauv ntawm lub molecule yog qhov tshwm sim ntawm cov qauv molecular sib txawv ntawm lub zog muaj peev xwm molecular sib txawv, thiab lub zog muaj peev xwm molecular yog lub peev xwm tshuaj lom neeg, cov qauv molecular yog ib txwm thiab txiav txim siab, uas txhais tau tias lub zog muaj peev xwm molecular siab dua, thiab nws yooj yim dua los tsim cov xwm txheej crystallization, zoo li dej condensing rau hauv dej khov. Dhau li ntawm qhov ntawd, peb tsuas xav tias muaj 100 lub polyurethane molecules, qhov kev sib cuam tshuam ntawm 100 lub molecules no kuj tseem yuav cuam tshuam rau qhov kev tiv thaiv thermal ntawm cov menyuam me me no, xws li cov hydrogen bonds, txawm hais tias lawv tsis muaj zog npaum li cov tshuaj bonds, tab sis tus lej N loj, qhov kev coj cwj pwm pom tseeb ntawm cov molecular hydrogen bond ntau dua tuaj yeem txo qhov degree ntawm kev tsis sib haum xeeb lossis txwv qhov kev txav mus los ntawm txhua lub polyurethane molecule, yog li hydrogen bond yog qhov zoo rau kev txhim kho thermal resistance.