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Kodi zipangizo za polyurethane zimagonjetsedwa ndi kutentha kwakukulu? Kawirikawiri, polyurethane sichigonjetsedwa ndi kutentha kwakukulu, ngakhale ndi dongosolo la PPDI lokhazikika, malire ake otentha amatha kukhala pafupifupi 150 °. Polyester wamba kapena polyether mitundu sangathe kupirira kutentha pamwamba 120 °. Komabe, polyurethane ndi polima wa polar kwambiri, ndipo poyerekeza ndi mapulasitiki wamba, imakhala yosamva kutentha. Choncho, kufotokozera kutentha kwa kutentha kwapamwamba kwambiri kapena kusiyanitsa ntchito zosiyanasiyana ndizofunikira kwambiri.
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Ndiye kodi kukhazikika kwamafuta azinthu za polyurethane kungasinthidwe bwanji? Yankho lofunikira ndikuwonjezera kristalo wazinthu, monga PPDI isocyanate yomwe tatchula kale. Chifukwa chiyani kukulitsa kristalo wa polima kumapangitsa kuti kutentha kwake kukhale kokhazikika? Yankho limadziwika kwa aliyense, ndiye kuti, kapangidwe kake kamatsimikizira katundu. Lero, tikufuna kuyesa kufotokoza chifukwa chake kusintha kwa kapangidwe ka maselo kumabweretsa kusintha kwa kukhazikika kwa kutentha, lingaliro loyambira likuchokera ku tanthauzo kapena kalembedwe ka 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.
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Mphamvu yaulere ya Gibbs ndi lingaliro lamphamvu mu thermodynamics, ndipo kukula kwake nthawi zambiri kumakhala kofanana, mwachitsanzo, kusiyana pakati pa zikhalidwe zoyambira ndi zomaliza, kotero chizindikiro △ chimagwiritsidwa ntchito patsogolo pake, popeza mtengo wathunthu sungathe kupezedwa mwachindunji kapena kuyimiridwa. Pamene △G ichepa, mwachitsanzo, ikakhala kuti palibe, zikutanthauza kuti mankhwala amatha kuchitika mwadzidzidzi kapena kukhala abwino pazochitika zinazake. Izi zitha kugwiritsidwanso ntchito kudziwa ngati zomwe zimachitikazo zilipo kapena zitha kusinthidwa mu thermodynamics. Digiri kapena kuchuluka kwa kuchepetsa kumatha kumveka ngati kinetics ya zomwe zimachitika. H kwenikweni ndi enthalpy, yomwe imatha kumveka ngati mphamvu yamkati ya molekyulu. Zitha kuganiziridwa kuchokera ku tanthauzo lapamwamba la zilembo zaku China, monga momwe moto ulibe

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S imayimira entropy ya dongosolo, lomwe limadziwika bwino ndipo tanthauzo lenileni ndilomveka bwino. Imakhudzana kapena kufotokozedwa molingana ndi kutentha kwa T, ndipo tanthauzo lake lalikulu ndi kuchuluka kwa chisokonezo kapena ufulu wa kachitidwe kakang'ono kakang'ono kakang'ono. Panthawiyi, bwenzi laling'ono loyang'anitsitsa likhoza kuzindikira kuti kutentha kwa T kumakhudzana ndi kukana kwa kutentha komwe tikukambirana lero kunawonekera. Ndiloleni ndingoyang'ana pang'ono za lingaliro la entropy. Entropy ikhoza kumveka mopusa ngati yosiyana ndi crystallinity. Kukwera kwa mtengo wa entropy, m'pamenenso ma cell amasokonekera komanso osokonekera. Mapangidwe a mamolekyuwa akakwera, m'pamenenso kuwala kwa mamolekyu kumakhala bwino. Tsopano, tiyeni tidule kagawo kakang'ono pampukutu wa rabara wa polyurethane ndikuwona bwalo laling'ono ngati dongosolo lathunthu. Unyinji wake umakhala wokhazikika, poganiza kuti lalikululo limapangidwa ndi mamolekyu 100 a polyurethane (kwenikweni, alipo N ambiri), popeza kuchuluka kwake ndi kuchuluka kwake sikunasinthe, titha kuyerekeza △G ngati mtengo wocheperako kwambiri kapena pafupi kwambiri ndi ziro, ndiye kuti fomula yaulere ya Gibbs imatha kusinthidwa kukhala ST = H, tropy ndi T ndi kutentha kwa T. Ndiko kuti, kukana kutentha kwa polyurethane lalikulu lalikulu ndi lofanana ndi enthalpy H ndi inversely proportional kwa entropy S. Inde, iyi ndi njira pafupifupi, ndipo ndi bwino kuwonjezera △ pamaso (zopezedwa mwa kuyerekezera).
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Sizovuta kupeza kuti kusintha kwa crystallinity sikungathe kuchepetsa mtengo wa entropy komanso kuonjezera mtengo wa enthalpy, ndiko kuti, kuwonjezeka kwa molekyulu pamene kuchepetsa chiwerengero (T = H / S), chomwe chikuwonekera chifukwa cha kuwonjezeka kwa kutentha kwa T, ndipo ndi imodzi mwa njira zothandiza kwambiri komanso zofala, mosasamala kanthu kuti T ndi kutentha kwa magalasi kapena kutentha kosungunuka. Chomwe chiyenera kusinthidwa ndi chakuti kukhazikika ndi crystallinity ya monomer molecular structure ndi nthawi zonse ndi crystallinity ya kulimba kwa maselo pambuyo pophatikizana kumakhala mzere, womwe ukhoza kukhala wofanana kapena womveka bwino. The enthalpy H makamaka imathandizidwa ndi mphamvu ya mkati mwa molekyulu, ndipo mphamvu ya mkati mwa molekyulu ndi chifukwa cha mitundu yosiyanasiyana ya maselo osiyanasiyana amphamvu, ndipo mphamvu yamagetsi ndi mphamvu ya mankhwala, mawonekedwe a maselo ndi okhazikika komanso olamulidwa, zomwe zikutanthauza kuti mphamvu ya maselo ndi apamwamba, ndipo n'zosavuta kupanga zochitika za crystallization, monga madzi oundana mu ayezi. Kupatula apo, tangoganizani mamolekyu 100 a polyurethane, mphamvu yolumikizana pakati pa mamolekyu 100 idzakhudzanso kukana kwamafuta a wodzigudubuza ang'onoang'ono, monga zomangira za hydrogen, ngakhale sizili zamphamvu ngati zomangira zamagulu, koma chiwerengero cha N ndi chachikulu, chodziwika bwino cha mamolekyulu a hydrogen chomangira amatha kuchepetsa kuchuluka kwa mamolekyu kapena kuletsa mamolekyu ang'onoang'ono, kuletsa mamolekyu ang'onoang'ono a hydrogen. kutentha kukana.