Lub degradation ntawm PVC feem ntau yog tshwm sim los ntawm decomposition ntawm active chlorine atoms nyob rau hauv lub molecule nyob rau hauv cua sov thiab oxygen, uas ua rau zus tau tej cov HCI. Yog li ntawd, PVC cov cua sov stabilizers feem ntau yog cov sib txuas uas tuaj yeem ruaj khov cov tshuaj chlorine atoms hauv PVC molecules thiab tiv thaiv lossis lees txais kev tso tawm ntawm HCI. R. Gachter et al. cais cov teebmeem ntawm cov cua sov stabilizers raws li kev tiv thaiv thiab kho. Cov qub muaj lub luag haujlwm ntawm kev nqus HCI, hloov cov tshuaj chlorine tsis ruaj khov, tshem tawm cov khoom siv hluav taws xob, thiab tiv thaiv tsis siv neeg oxidation. Hom kev kho tom kawg yog txhawm rau ntxiv rau cov qauv polyene, hnov mob nrog cov khoom tsis txaus ntseeg hauv PVC, thiab rhuav tshem cov carbocations. Tshwj xeeb, raws li hauv qab no:
(1) Absorb HC1 rho tawm los ntawm PVC los inhibit nws tus kheej catalytic kev ua si. Cov khoom xws li cov ntsev ntsev, organic acid hlau soaps, organotin tebchaw, epoxy compounds, amines, hlau alkoxides thiab phenols, thiab hlau thiols tuaj yeem ua rau tag nrho cov tshuaj HCI los tiv thaiv HCI cov tshuaj tiv thaiv ntawm PVC.
Me (RCOO) 2+2HCI MeCl+2RCOOH
(2) Hloov lossis tshem tawm yam tsis ruaj khov xws li allyl chloride atoms lossis tertiary carbon chloride atoms hauv PVC molecules, thiab tshem tawm qhov pib ntawm HCI tshem tawm. Yog hais tias cov tin atoms ntawm cov organic tin stabilizers koom tes nrog cov chlorine atoms tsis ruaj tsis khov ntawm PVC molecules, thiab cov sulfur atoms hauv organic tin koom tes nrog cov carbon atoms hauv PVC, cov sulfur atoms hauv lub cev sib koom ua ke hloov nrog cov tshuaj chlorine tsis ruaj khov. Thaum HC1 tam sim no, kev sib koom ua ke sib faib, thiab pawg hydrophobic ruaj khov nrog cov pa roj carbon atoms hauv PVC molecules, yog li inhibiting kev cuam tshuam ntxiv ntawm HCI tshem tawm thiab tsim ob daim ntawv cog lus. Ntawm cov tshuaj soaps hlau, zinc xab npum thiab lub lauj kaub xab npum muaj qhov hloov pauv sai tshaj plaws nrog cov tshuaj chlorine tsis ruaj khov, cov xab npum barium yog qhov qeeb tshaj plaws, calcium xab npum yog qeeb dua, thiab cov hmoov txhuas yog nyob hauv nruab nrab. Nyob rau tib lub sijhawm, cov hlau chloride tsim muaj qhov sib txawv ntawm cov nyhuv catalytic ntawm kev tshem tawm HCI, thiab lawv lub zog yog raws li hauv qab no:
ZnCl> CdCl>> BaCl, CaCh> R2SnCl2 (3) yog ntxiv rau ob daim ntawv cog lus thiab sib txuas ob daim ntawv cog lus los tiv thaiv kev txhim kho ntawm cov qauv polyene thiab txo cov xim. Unsaturated acid ntsev los yog complexes muaj ob daim ntawv cog lus, uas dhau mus rau ib tug diene ntxiv cov tshuaj tiv thaiv nrog PVC molecules, yog li cuam tshuam lawv covalent qauv thiab inhibiting xim hloov. Tsis tas li ntawd, cov xab npum hlau yog nrog los ntawm kev hloov pauv ntawm ob daim ntawv cog lus thaum hloov allyl chloride, ua rau muaj kev puas tsuaj rau cov qauv polyene thiab yog li inhibiting xim hloov.
(4) ntes cov dawb radicals los tiv thaiv oxidation tsis siv neeg. Yog tias ntxiv phenolic heat stabilizers tuaj yeem thaiv qhov kev tshem tawm ntawm HC1, nws yog vim tias hydrogen atom dawb radicals muab los ntawm phenols tuaj yeem ua ke nrog cov degraded PVC macromolecular dawb radicals, tsim ib yam khoom uas tsis tuaj yeem hnov mob nrog oxygen thiab muaj thermal stabilization nyhuv. Cov cua sov stabilizer no tuaj yeem muaj ib lossis ntau yam teebmeem.
Lub sij hawm xa tuaj: Mar-29-2024
