Basic Chemical Reactions ntawm Polyurethane Ua Npuas Ncauj
Polyurethane qee zaum hu ua PU, uas yog lub ntsiab lus ntawm polyurethane. Raws li lub npe qhia, nws muaj npe tom qab cov urethane tsim los ntawm cov tshuaj tiv thaiv ntawm isocyanate thiab hydroxyl compound raws li nws cov yam ntxwv saw txuas. Tab sis qhov tseeb, muaj ntau yam tshuaj lom neeg cuam tshuam nrog polyurethane, tshwj xeeb tshaj yog polyurethane ua npuas ncauj, thiab tsis muaj ntau qhov kev cuam tshuam tseem ceeb uas muaj kev cuam tshuam tiag tiag. Feem ntau ntawm cov tshuaj tiv thaiv ntawm polyurethane muaj feem xyuam rau cov tshuaj lom neeg ntawm isocyanate NCO hauv isocyanates. NCO tsis tuaj yeem tsuas yog hnov mob nrog hydroxyl tebchaw los tsim cov carbamates, tab sis kuj ua rau lwm cov "active hydrogen" tebchaw los tsim cov tshuaj sib txawv. Li no hloov cov qauv tshuaj thiab cov khoom siv ntawm polyurethane.
Cov pab pawg neeg nquag ntawm isocyanate yog isocyanate NCO. Cov qauv hluav taws xob ntawm NCO qhia tau hais tias nws muaj zog resonance nyhuv. Cov tshuaj tiv thaiv ib txwm yog tsuas yog cov tshuaj tiv thaiv ntxiv ntawm carbon-nitrogen ob daim ntawv cog lus. Cov tebchaw nrog cov nquag hydrogen ua ntej tua cov nitrogen atom ntawm NCO, thiab lwm cov atoms txuas nrog cov nquag hydrogen yog ntxiv rau cov pa roj carbon atom ntawm isocyanate carbonyl pawg. Lub active hydrogen compound yog hais txog ib tug compound uas yuav hloov tau ib hydrogen atom los ntawm metallic sodium, feem ntau suav nrog hydroxyl-muaj cawv, amino-muaj amines, dej, thiab lwm yam.
Cov tshuaj tiv thaiv tseem ceeb ntawm polyurethane tuaj yeem muab faib ua cov tshuaj tiv thaiv polymerization, cov tshuaj tiv thaiv foaming thiab cross-linking cov tshuaj tiv thaiv raws li lawv txoj haujlwm.
1. Polymerization
Qhov ntawd yog (1) cov tshuaj tiv thaiv ntawm isocyanate thiab hydroxyl
NCO ntawm isocyanate reacts nrog hydroxyl OH ntawm cawv (feem ntau polyether, polyester los yog lwm yam polyol) los tsim polyurethane.
2. Cov tshuaj tiv thaiv ua npuas ncauj
cov tshuaj tiv thaiv ntawm isocyanate thiab dej
NCO ntawm isocyanate reacts nrog dej los tsim tsis ruaj tsis khov carbamic acid ua ntej, uas yog tom qab ntawd decomposed rau hauv amine thiab carbon dioxide.
3. Kev sib txuas lus sib txuas
Xws li (3) allophanate cov tshuaj tiv thaiv thiab (4) cov tshuaj tiv thaiv biuret
Cov hydrogen ntawm nitrogen atom ntawm pawg urethane reacts nrog NCO ntawm isocyanate los ua ib qho allophanate. Cov hydrogen ntawm nitrogen atom ntawm urea pawg hauv diurea reacts nrog pawg isocyanate ntawm isocyanate los ua ib tug biuret.
Ob qho kev tshwm sim saum toj no (3) thiab (4) yog ob qho kev sib txuas sib txuas. Feem ntau hais lus, cov tshuaj tiv thaiv tus nqi kuj qeeb. Thaum tsis muaj catalyst, cov tshuaj tiv thaiv yuav tsum tau nqa tawm ntawm 110-130 degree . Qhov kub siab dua, qhov kev tawm tsam sai dua. Tsis tas li ntawd, vim hais tias cov allophanate thiab biuret linkers tsis ruaj khov, uas yog hais tias (3) thiab (4) yog cov tshuaj tiv thaiv rov qab.
Piv txwv li, muaj peb hom kev tshwm sim ntawm PU: cov tshuaj tiv thaiv (1) yog cov tshuaj tiv thaiv txuas ntxiv lossis cov tshuaj tiv thaiv polymerization, cov tshuaj tiv thaiv (2) yog cov tshuaj tiv thaiv roj los yog cov tshuaj tiv thaiv foaming, thiab cov tshuaj tiv thaiv (3) thiab (4) yog kev sib txuas lus sib txuas.
Nyob rau hauv cov txheej txheem foaming ntawm PU, cov tshuaj tiv thaiv no tau ua tiav ib txhij ntawm qhov kev kub ceev, thiab feem ntau ntawm cov tshuaj tiv thaiv tuaj yeem ua tiav li ntawm ob peb feeb nyob rau hauv cov xwm txheej catalyst. Thaum kawg, polyurethane ua npuas ncauj ntawm siab molecular hnyav thiab ib tug tej yam degree ntawm crosslinking yog tsim.
Cov tshuaj tiv thaiv polymerization thiab cov tshuaj tiv thaiv crosslinking yog cov tshuaj tiv thaiv tseem ceeb hauv kev tsim cov pob txha polyurethane ua npuas ncauj, uas tuaj yeem raug hu ua cov tshuaj tiv thaiv gel; Thaum cov tshuaj tiv thaiv foaming yog cov tshuaj tiv thaiv tseem ceeb rau qhov nce ntawm qhov ntim ntawm polyurethane thiab tsim cov roj qhov chaw ntawm lub hollow ua npuas ncauj qauv.
Kev txhim kho thiab kev hloov kho ntawm tag nrho cov formulations ntawm polyurethane ua npuas ncauj, nrog rau ntau yam teeb meem nyob rau hauv ua npuas ncauj ntau lawm, yog inseparable los ntawm qhov sib npaug ntawm cov tshuaj tiv thaiv gel thiab foaming.
