1
Kodi zinthu zopangidwa ndi polyurethane zimapirira kutentha kwambiri? Kawirikawiri, polyurethane siimalimbana ndi kutentha kwambiri, ngakhale ndi makina wamba a PPDI, kutentha kwake kwakukulu kumatha kukhala pafupifupi 150°C. Mitundu ya polyester wamba kapena polyether singathe kupirira kutentha kopitilira 120°C. Komabe, polyurethane ndi polima wozungulira kwambiri, ndipo poyerekeza ndi mapulasitiki wamba, imalimbana kwambiri ndi kutentha. Chifukwa chake, kudziwa kutentha komwe kumafunika kuti kutentha kukhale kolimba kapena kusiyanitsa kugwiritsa ntchito kosiyanasiyana ndikofunikira kwambiri.
2
Ndiye kodi kukhazikika kwa kutentha kwa zinthu za polyurethane kungawongoleredwe bwanji? Yankho loyambira ndikuwonjezera kukhazikika kwa kristalo kwa zinthuzo, monga isocyanate ya PPDI yodziwika bwino yomwe yatchulidwa kale. Nchifukwa chiyani kuwonjezera kukhazikika kwa kristalo ya polymer kumawonjezera kukhazikika kwake kwa kutentha? Yankho lake limadziwika ndi aliyense, ndiko kuti, kapangidwe kake kamasankha katundu. Masiku ano, tikufuna kuyesa kufotokoza chifukwa chake kusintha kwa kayendedwe ka mamolekyulu kumabweretsa kusintha kwa kukhazikika kwa kutentha, lingaliro loyambira likuchokera ku tanthauzo kapena njira ya Gibbs free energy, mwachitsanzo △G=H-ST. Mbali yakumanzere ya G imayimira mphamvu yaulere, ndipo mbali yakumanja ya equation H ndi enthalpy, S ndi entropy, ndipo T ndi kutentha.
3
Mphamvu ya Gibbs free ndi lingaliro la mphamvu mu thermodynamics, ndipo kukula kwake nthawi zambiri kumakhala ndi mtengo woyerekeza, mwachitsanzo kusiyana pakati pa ma values ​​oyambira ndi otsiriza, kotero chizindikiro △ chimagwiritsidwa ntchito patsogolo pake, chifukwa mtengo wokwanira sungapezeke kapena kuimiridwa mwachindunji. Pamene △G ikuchepa, mwachitsanzo pamene ili yoipa, zikutanthauza kuti reaction ya mankhwala ikhoza kuchitika mwadzidzidzi kapena kukhala yabwino pa reaction inayake yomwe ikuyembekezeredwa. Izi zingagwiritsidwenso ntchito kudziwa ngati reaction ilipo kapena ikusinthika mu thermodynamics. Mlingo kapena liwiro la kuchepetsa lingathe kumvedwa ngati kinetics ya reaction yokha. H kwenikweni ndi enthalpy, yomwe ingamvedwe ngati mphamvu yamkati ya molekyulu. Itha kuganiziridwa kuchokera ku tanthauzo la pamwamba la zilembo zaku China, chifukwa moto si

4
S ikuyimira entropy ya dongosolo, yomwe imadziwika bwino ndipo tanthauzo lenileni ndi lomveka bwino. Ikugwirizana kapena kufotokozedwa malinga ndi kutentha kwa T, ndipo tanthauzo lake loyambirira ndi kuchuluka kwa chisokonezo kapena ufulu wa dongosolo laling'ono la microscopic. Pakadali pano, mnzake wamng'ono wowonera mwina adazindikira kuti kutentha kwa T kokhudzana ndi kukana kutentha komwe tikukambirana lero kwawonekera. Ndiloleni ndingolankhula pang'ono za lingaliro la entropy. Entropy imatha kumveka mopusa ngati yosiyana ndi kristalo. Mtengo wa entropy ukakwera, kapangidwe ka mamolekyulu kamakhala kosokonezeka komanso kosokonezeka. Kapangidwe ka mamolekyulu kakakhala kokwera, kristalo ya mamolekyulu imakhala yabwino. Tsopano, tiyeni tidule sikweya yaying'ono kuchokera pa mpukutu wa rabara wa polyurethane ndikuiona sikweya yaying'ono ngati dongosolo lathunthu. Kulemera kwake kuli kokhazikika, poganiza kuti sikweyayi imapangidwa ndi mamolekyu 100 a polyurethane (kwenikweni, pali N ambiri), popeza kulemera kwake ndi voliyumu yake sizisintha kwenikweni, tikhoza kuyerekeza △G ngati mtengo wochepa kwambiri wa manambala kapena pafupi kwambiri ndi zero, ndiye kuti njira ya Gibbs free energy ingasinthidwe kukhala ST=H, pomwe T ndiye kutentha, ndipo S ndiye entropy. Ndiko kuti, kukana kutentha kwa sikweya yaying'ono ya polyurethane kuli kofanana ndi enthalpy H ndipo kumagwirizana ndi entropy S. Zachidziwikire, iyi ndi njira yoyerekeza, ndipo ndibwino kuwonjezera △ isanafike (yomwe imapezeka poyerekezera).
5
Sikovuta kupeza kuti kusintha kwa crystallinity sikungochepetsa entropy yokha komanso kumawonjezera enthalpy value, kutanthauza kuti, kuwonjezera molekyulu pamene mukuchepetsa denominator (T = H/S), zomwe zimadziwika bwino pakuwonjezeka kwa kutentha kwa T, ndipo ndi imodzi mwa njira zothandiza kwambiri komanso zodziwika bwino, mosasamala kanthu kuti T ndi kutentha kwa kusintha kwa galasi kapena kutentha kosungunuka. Chomwe chiyenera kusinthidwa ndikuti kukhazikika ndi crystallinity ya kapangidwe ka molekyulu ya monomer komanso kukhazikika ndi crystallinity yonse ya kulimba kwa molekyulu yayikulu pambuyo pa kusonkhana kwenikweni ndi mzere, zomwe zitha kukhala zofanana kapena kumveka mwanjira yolunjika. Enthalpy H imathandizidwa makamaka ndi mphamvu yamkati ya molekyulu, ndipo mphamvu yamkati ya molekyulu ndi zotsatira za kapangidwe ka molekyulu kosiyana ka mphamvu ya molekyulu, ndipo mphamvu ya molekyulu ndi mphamvu ya mankhwala, kapangidwe ka molekyulu ndi kokhazikika komanso kolinganizidwa, zomwe zikutanthauza kuti mphamvu ya molekyulu ndi yokwera, ndipo ndikosavuta kupanga zochitika za crystallization, monga madzi omwe amaundana kukhala ayezi. Kupatula apo, tangoganiza kuti mamolekyu 100 a polyurethane, mphamvu zolumikizirana pakati pa mamolekyu 100 awa zidzakhudzanso kukana kutentha kwa chozungulira chaching'ono ichi, monga ma bond a hydrogen enieni, ngakhale kuti si olimba ngati ma bond a mankhwala, koma nambala N ndi yayikulu, khalidwe lodziwikiratu la cholumikizira cha hydrogen chochulukirapo lingathe kuchepetsa kuchuluka kwa chisokonezo kapena kuletsa kuyenda kwa molekyulu iliyonse ya polyurethane, kotero cholumikizira cha hydrogen ndi chothandiza pakukweza kukana kutentha.