Polyvinyl fluoride
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| Names | |
|---|---|
| IUPAC name
poly(1-fluoroethylene)[1]
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| Other names
poly(vinyl fluoride)
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| Identifiers | |
| Abbreviations | PVF |
| ChEBI | |
| ChemSpider |
|
| MeSH | polyvinyl+fluoride |
CompTox Dashboard(EPA)
|
|
| Properties | |
| (C2H3F)n | |
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).
| |
Polyvinyl fluoride(PVF) or –(CH2CHF)n– is apolymermaterial mainly used in theflammability-lowering coatings of airplane interiors andphotovoltaic modulebacksheets.[2]It is also used inraincoatsand metal sheeting. Polyvinyl fluoride is athermoplasticfluoropolymerwith a repeatingvinyl fluorideunit, and it is structurally very similar topolyvinyl chloride.
History
[edit]The PVF-basedfilmwas first commercialised in 1961 byDuPontunder the name Tedlar.[3][4]
Polymerization
[edit]The most widely usedpolymerizationsof VF are inaqueous suspensionsoremulsions.Highpressuresare required because of theVFvolatility.The highelectronegativityoffluorinemakes thepolymerizationmore difficult when compared to othervinyl halides.[4]Thepolymerizationtemperaturesrange from 50 °C to 150 °C and can affect thecrystallinity,melting pointandbranchingof the product.Initiationis done byperoxidesorazo compounds.[3]
Theresonance stabilizationof thepropagatingintermediate(VFradical) is poor, which often leads tomonomerreversals,branchingandchain-transfer reactions.The presence ofimpuritiesgreatly affects themolecular weightandthermal stabilityof the product, as theVFradicalis highly reactive. This also limits the choice ofpolymerizationmediums,surfactants,initiatorsor other additives.[4]
Suspension polymerization
[edit]TheliquidVFissuspendedinwaterand stabilized either bywater-solublepolymersbased oncelluloseorpolyvinyl alcohol.Inorganicsaltscan also act as stabilizers. Thesuspension polymerizationis usuallyinitiatedbyorganic peroxides(eg diisopropyl peroxydicarbonate), butUV lightorionizing radiationcan also be used. However, when there are noradicalspresent, theUV radiationdecomposestheVFintoacetyleneandHF.[4]
Emulsion polymerization
[edit]Emulsion polymerizationcan be done at highly reducedpressuresand lowertemperaturescompared tosuspension polymerization.The improved process control andreaction heatremoval lead to increase inmolecular weight,rate of reactionandyield.Fluorinatedsurfactantssuch asperfluorinatedcarboxylic acidsmaintain a highrate of reactioneven after 40%conversion,they arethermallyandchemically stableand their incorporation does not impair PVF properties. Otheremulsifiers(fatty alcoholsulfates,alkane sulfonates etc) are not as effective.[4]
Processing
[edit]PVF is usually converted intothin filmsandcoatings.However, due to its hydrogen bonds andcrystallinity,atemperatureabove 100 °C is necessary to dissolve PVF in latentsolvents.The processing bymelt extrusiondepends on the latentsolvationof PVF in highlypolarsolventsand its subsequentcoalescence.The incorporation of additives (plasticizers,pigments,stabilizersetc.) is done bydispersionwith PVF in the latentsolvent.Thesolventisevaporatedafterextrusion.[4]
To create biaxially orientedfilms,the PVFdispersedinsolventmust be trailed by bothtransverse directionsand biaxial orientations, which results in highertensile strength.The unoriented films are also slightly stretched aftercasting.They are more compliant andformableand exhibit higherelongation at breakthan the oriented films.[5]
Properties
[edit]The majority of linkages in PVF are head-to-tail, and only 12-18 % of linkages are head-to-head. These irregularities are probably the cause of the variations inmelting point,which ranges from 185 °C to 210 °C. Thecrystallinityof PVF ranges from 20 to 60%, depending on thepolymerizationmethod and thermal history of thepolymer.It has been found that lowerpolymerizationtemperatureleads to a decrease in head-to-head linkages and subsequently increase inmelting pointsince the highly regular structures display highercrystallinity.As forstereoregularity,PVF is mostlyatacic,but this does not significantly affect themelting point.The commercialatacticPVFfilmshows amelting pointpeak at 190 °C.[3][4][5]
Several transition phases occur below themelting point,mainly at lowerTgfrom -15 to ‑20 °C, and at upperTgwith the temperature range of 40 to 50 °C.[6]
PVF isinsolublein commonsolventsbelow 100 °C. When thetemperatureis raised, it becomessolubleinpolarsolvents(amides,ketonesetc.). At roomtemperature,the PVFfilmsare resistant to bothacidsandbasesas well asaliphatic,aromaticandalcoholliquids.[3]
Thethermal stabilityof PVF is better than that of othervinyl halidepolymers,reportingbackbonecleavageandHFloss in aninert atmosphereat 450 °C, while inairtheHFloss occurs at 350 °C.[4]
Safety
[edit]Since PVF has exceptionalthermal stability,it is far safer thanPVC,which degrades more easily. If PVF degradation happens, the highly reactiveHF acidis generated but is quickly absorbed into the surrounding materials and dissipates.[7]
Themonomer,VFisflammableand highly reactive, forms anexplosivemixture withairand is classified as "probablycarcinogenictohumans".[7]
PVF has not caused anyskinreaction ortoxic effects,although after excessive exposure thefluoridecontent inurineincreased. The overheating of PVF products may result in interaction with the additives such aspigmentsorfillers,which may pose as an additional risk. Some formulations of the Tedlarfilmsmay containheavy metalcompounds, which can be present industcreated by secondary operations (egsanding).[7]
Exterior and interior PVF finishes do not create an additional danger regardingfirein residential and industrial buildings, because thecarbon monoxidecreated by thecombustionof otherconstruction materialsis far more dangerous.[7]
Application
[edit]The main applications of PVF are protective and decorativecoatings,thanks to itsthermal stability,and generalinertnesstowardschemicals,corrosivesandstaining agents.There are two ways to apply PVF, either as a preformed film (laminating) or fromdispersion(coating). Thesecoatingscan betransparentorpigmented.[4]
In theautomotive industry,PVFprimeris used to improvepaintadhesion,while in theaerospace engineeringindustry, the PVF film is applied toinsulatingbags containingglass fibre,which are used on exteriorairplanewalls, incargo spaceandair condition ducts.[4]
On the top ofphotovoltaic cells,thetransparentPVFfilmprotects againstmoisture,while thewhite-pigmentedfilmis used on their bottom surface.[4]
PVFfilmsare non-adheringtophenolic,acrylicandepoxy resinsand can be therefore used as releasefilms,usually in high-temperature processing of theseresins.[4]
Related compounds
[edit]- Vinyl fluoride
- PVC (polyvinyl chloride)
- PVDF (polyvinylidene fluoride)
- PTFE (polytetrafluoroethyleneor Teflon)
References
[edit]- ^"poly(vinyl fluoride) (CHEBI:53244)".RetrievedJuly 14,2012.
- ^"Tedlar PVF".Archived fromthe originalon 2014-02-24.Retrieved2008-06-12.
- ^abcdHintzer, Klaus; Zipplies, Tilman; Carlson, D. Peter; Schmiegel, Walter (2014-01-31). "Fluoropolymers, Organic".Ullmann's Encyclopedia of Industrial Chemistry:1–55.doi:10.1002/14356007.a11_393.pub2.
- ^abcdefghijklEbnesajjad, Sina (2011-07-15). "Vinyl Fluoride Polymers (PVF)".Encyclopedia of Polymer Science and Technology.doi:10.1002/0471440264.pst388.pub2.
- ^abAlaaeddin, M. H.; Sapuan, S. M.; Zuhri, M.Y.M; Zainudin, E.S; AL-Oqla, Faris M. (2019-05-01)."Polyvinyl fluoride (PVF); Its Properties, Applications, and Manufacturing Prospects".IOP Conference Series: Materials Science and Engineering.538(1): 012010.doi:10.1088/1757-899X/538/1/012010.ISSN1757-8981.
- ^Alaaeddin, M. H.; Sapuan, S. M.; Zuhri, M.Y.M; Zainudin, E.S; AL-Oqla, Faris M. (2018-11-06)."Properties and Common Industrial Applications of Polyvinyl fluoride (PVF) and Polyvinylidene fluoride (PVDF)".IOP Conference Series: Materials Science and Engineering.409:012021.doi:10.1088/1757-899X/409/1/012021.ISSN1757-899X.
- ^abcdEbnesajjad, Sina (2013).Polyvinyl fluoride: technology and applications of PVF.PDL handbook series. Amsterdam Boston: Elsevier.ISBN978-1-4557-7885-0.