Ib txoj hauv kev kom nkag siab txog qhov cuam tshuam ntawm fluorine yog tshawb nrhiav qhov sib txawv ntawm linear polyethylene (PE) thiab PTFE uas yog qhov kawg ntawm fluoropolymer ntawm cov khoom thiab cov yam ntxwv.
Muaj qhov sib txawv tseem ceeb ntawm cov khoom ntawm PE thiab PTFE:
- * PTFE yog ib qho ntawm cov khoom siv hluav taws xob qis tshaj plaws
- *PTFE yog cov tshuaj tiv thaiv zoo tshaj plaws polymer
- *PTFE yog ib qho ntawm cov thermally ruaj khov polymers
- *Melting point thiab lub ntiajteb txawj nqus ntawm PTFE yog ntau tshaj ob npaug ntawm polyethylene
PTFE thiab PE qhov sib txawv yog vim qhov sib txawv ntawm CeF thiab CeH daim ntawv cog lus.Qhov sib txawv ntawm cov khoom siv hluav taws xob thiab qhov ntau thiab tsawg ntawm F thiab H ua rau cov kev soj ntsuam hauv qab no:
- *F yog qhov feem ntau electronegative ntawm tag nrho cov ntsiab lus (4 Paulings)
- *F muaj cov khoom siv hluav taws xob tsis sib koom
- *F yog hloov dua siab tshiab rau Fe
- *Bond zog ntawm CeF siab dua CeH
- *F yog loj dua H
Lub electronegativity ntawm carbon ntawm 2.5 Paulings yog me ntsis siab dua li ntawm hydrogen thiab qis dua cov electronegativity ntawm fluorine.Yog li ntawd, qhov polarity ntawm CeF daim ntawv cog lus yog qhov sib txawv ntawm CeH daim ntawv cog lus, thiab CeF daim ntawv cog lus yog ntau polarized.Nyob rau hauv daim ntawv cog lus CeF, fluorine kawg ntawm daim ntawv cog lus tsis zoo raug them piv rau CeH daim ntawv cog lus uas cov pa roj carbon tsis zoo.
Qhov sib txawv ntawm daim ntawv cog lus polarity ntawm CeH thiab CeF cuam tshuam rau cov txheeb ze ruaj khov ntawm kev sib haum xeeb ntawm ob txoj hlua polymer.Crystallization ntawm polyethylene yuav siv sij hawm qhov chaw nyob rau hauv ib tug planar thiab trans conformation.PTFE tuaj yeem raug yuam kom ua raws li qhov sib txawv ntawm qhov siab heev.PTFE, qis dua 19 C, crystallizes raws li ib tug helix nrog 0.169 nm ib qho kev ncua deb: nws yuav siv sij hawm 13 C atoms rau 180 tig kom tiav.Tshaj 19 C, qhov kev ncua deb nce mus rau 0.195 nm uas txhais tau hais tias 15 carbon atoms xav tau rau 180 tig.Nyob rau saum toj 19 C, cov chains muaj peev xwm ntawm angular hloov chaw, uas nce siab tshaj 30 C mus txog rau lub melting point (327 C).
Kev hloov pauv ntawm F rau H hauv CeH daim ntawv cog lus txhawb nqa lub zog ntawm 99.5 kcal / mole rau CeH daim ntawv cog lus rau 116 kcal / mole rau CeF daim ntawv cog lus.Yog li ntawd, thermal stability thiab tshuaj tiv thaiv ntawm PTFE yog siab dua PE vim hais tias ntau zog yuav tsum tau ua txhaum CeF daim ntawv cog lus.Lub polarity thiab lub zog ntawm CeF daim ntawv cog lus ua rau F atom abstraction mechanism rau branching nyuaj.Nyob rau hauv sib piv, heev branched polyethylene (> 8 ceg ntawm 100 carbon atoms) tuaj yeem ua ke.Branching mechanism ua ib lub cuab tam los kho crystallinity yog tsis zoo rau PTFE.Es tsis txhob comonomers nrog cov pab pawg neeg yuav tsum tau polymerized nrog TFE.
Crystallinity ntawm PTFE tsis-melted yog nyob rau hauv ntau ntawm 92e98%, raws li ib tug unbranched saw qauv.FEP, ib copolymer ntawm TFE thiab HFP, muaj ib tug li-polymerized crystallinity ntawm 40e50%.Hauv FEP, cov pab pawg CF3 muaj kev sib koom ua ke rau cov pa roj carbon tertiary uas tsis tshua muaj thermally ruaj khov dua li cov pa roj carbon monoxide thawj thiab theem nrab.Degradation curves qhia degradation pib kub ntawm 300 C rau FEP (0.02% poob phaus) thiab 425 C rau PTFE (0.03% poob phaus).
Post lub sij hawm: Sep-25-2020