Fluoropolymer Additives

286 Pages·2012·39.85 MB·English

by  Sina Ebnesajjad and Richard Morgan (Auth.)

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FLUOROPOLYMER ADDITIVES
Sina Ebnesajjad, PhD, President
Fluoro Consultants Group, LLC
Richard A. Morgan, PhD, President
Morgan Associates
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Preface
The aim of the present book, as with the previous A note indicating the specific errors to the publisher,
volumesinthePDLFluorocarbonSeries,istocompile for the purpose of correction offuture editions, would
in one place a working knowledge of the polymer be much appreciated.
chemistry, physics, and properties of fluoropolymer The present volume deals with an important but
additives with descriptions of commercial processing little noticed group of products called fluoropolymer
and applications techniques. additives. Their use has proliferated in the last three
Thebookfocusesonbeingapracticalguideanddata decades because of the unique properties that they
source as well as a reliable reference for learning the imparttothehostmaterialtowhichtheyareadded.We
basics for the practitioners of applications or research hope this book is useful to those who are in search of
involving fluoropolymer additives. The references lis- information, as we were when we began our fluorine
ted at the end of each chapter serve as both bibliog- careers some decades ago.
raphy and additional reading material. Review papers The authors wish to thank all the companies which
are helpful as a starting point for finding additional have generously contributed data and illustrations to
references for concentrated reading in a selected area. thisbook.MissKristinN.Drossisthankedforediting
None of the views or information presented in this Chapters 1e5.
book reflects the opinion of any of the companies or
individuals who have contributed to the book. If there SinaEbnesajjad
areerrors,theyareoversightonthepartoftheauthors. RichardMorgan
xiii
1 Introduction
1.1 Introduction imparts to compounds that contain it, is responsible
for the importance of the field and for its constant
Aside from a short description of additives, this ‘‘reinvention’’. Thus, in spite of the immense
chapter is devoted to describing fluorine properties contributions of fluorine chemistry to various tech-
and preparation, inorganic and organic fluorine nologies of the last century, the current period, i.e.,
chemistry, biologically active compounds, and the the beginning of the 21st century, can authentically
naturaloccurrenceoffluorine.Specificallyspeaking, beconsidereda‘‘renaissance’’periodforthefieldof
organic fluorine chemistry provides a useful back- fluorine chemistry, where renaissance, in particular,
ground for fluorinated additives, particularly fluo- is defined as ‘‘a period characterized by vigorous
ropolymer additives. Some readers may rightfully activity along literary, artistic, or other lines’’ [2].
feelthattheauthorhasgoneoverboardindiscussing After reading this chapter, the reader should be
fluorine and its chemistry. Yet, this introductory equipped with a working knowledge of fluorine
chapterisnotaprerequisiteforunderstandingtherest compounds, including fluoropolymers, disregard-
of this book. Each chapter can be studied indepen- ing all prior knowledge of the subject. Even
dently of others. though the scope of the coverage of fluorinated
A typical dictionary defines an additive as “a materials has been limited to fluoropolymers in
substance added in small amounts to something else this book, every fluorinated compound is poten-
to improve, strengthen, or otherwise alter it”. There tially an additive. The nature of possible applica-
are vast numbers of additives incorporated in mate- tions may be unknown at present but the potential
rials to enhance and modify their performances or use exists.
characteristics and render them more useful.
Table 1.1 shows a lengthy, though probably incom-
plete,listofadditivetypes.Generally,themodifying 1.2 Uniqueness of Fluorine
effectofadditivesiseitherchemicalorphysical.For
example, adding a few parts of a laser marking What sets fluorine apart from other halogens?
additive, such as titanium dioxide, to a plastic, cata- Technically speaking, the term “halogen” provides
lyzes the incident laser beam, and the plastic little descriptive value in scientific and technolog-
substrateiscarbonizedaccordingtoaprintedpattern. ical discussions. The common characteristic of
A matting additive, such as silica powder, when halogens is that they all have seven electrons in the
added to a plastic film, can drastically decrease its outer shell of their atomic structure. They all have
gloss.Lasermarkingadditiveshasachemicalimpact a valence of (cid:1)1 in their reactions with hydrogen
whilst silica acts physically. and metals. The reactivity of halogens decreases
The presence of fluorine in any compound sets it from the top (fluorine) to the bottom of the column.
apartfromallothers.F isnotonlythemostreactive The McGraw-Hill Encyclopedia of Chemistry [3]
2
halogen,butalso,arguably,themostreactiveelement describes the differences among halogens:
on the periodic table, combining with all other “Although halogens generally undergo the same
elements,exceptthelighternoblegases,He,Ne,and types of reactions, the extent and ease with which
Ar [1]. Fluorine is unique because of its electronic these reactions occur vary markedly. Fluorine in
structureandforbeingthemostelectronegativeofall particular has the usual tendency of the lightest
elements.Indeed,thereisahealthyrangeofresearch memberofafamily ofelementstoexhibitreactions
anddevelopmentactivitiesaimedatthedevelopment not comparable to the other members.”
of new fluorine compounds. The singular nature of Fluorine forms an extremely strong bond with
thefluorineatom,combinedwiththeuniquephysical otherelements,suchascarbon,becauseitisthemost
and chemical properties that the fluorine substituent electronegativeofallelements.Thecarbonefluorine
FluoropolymerAdditives.DOI:10.1016/B978-1-4377-3461-4.00001-5
Copyright(cid:1)2012ElsevierInc.Allrightsreserved. 3
4 FLUOROPOLYMER ADDITIVES
Table1.1 List of Additive Types Table 1.1 List ofAdditive Typesdcont’d
Acid scavenger Gel inhibitor
Adhesion promoter Heat stabilizer
Antifoaming agent (foam suppressant) Hydrophilic agent
Antifogging agent Impactmodifier
Antioxidant Infrared filter
Antiozonant Inhibitor
Antislip agent Lasermarkingadditive
Antistatic agent Leveling agent
Antitack(antiblock) agent Light stabilizer/UV absorber
Biocide/antibacterialagent Lubricants &waxes
Blowing/foaming agent Matting/gloss agent
BOPP film modifier Melt strengthenhancer
Carbonblack Metaldeactivator
Chain extender Nucleating agent
Chelating agent/complexingagent Organicpigment
Clarifying agent Oxygen absorber
Cling agent Peptizer
Couplingagent/compatibilizer Photoinitiator
Crosslinking catalyst/accelerator/initiator Photoselectiveagent (agriculture)
Crosslinking orcuring agent/hardener Plasticizer
Defoamer Polymerization inhibitor
Deodorant Polymerization initiator
Desiccant Processingaid
Dispersing agent Release agent
Emulsifier Slip agent
Fibers (extenderreinforcer) Solvent
Filler/fiber conductive Styrene suppressant
Fillers (reinforcer/extender) Tackifier
Flame retardant/smoke suppressant Thickening agent
Flatting (gloss control) agent Thixotropic agent
Flexibilizer Titanium dioxide
Fluorescentwhitening agent Viscositymodifier
Fragrance Vulcanizing agent
Fresh keeping agent Wetting agent
Continued
1: INTRODUCTION 5
bond (CeF) is the fundamental reason that poly- Table 1.2 EffectofIncrease in Fluorine Contentof
tetrafluoroethyleneisoneofthemoststableandinert Polymers
plastics known to man. Yet, tetrafluoroethylene is
Property Impact
highly explosive, adding to the diversity of the fluo-
rine effect. A key point is made in the McGraw-Hill Chemical resistance Increases
Encyclopedia of Chemistry about the stability of Melting point Increases
halogenated compounds: “Organic halogen
Coefficient offriction Decreases
compounds generally show progressively increased
Thermal stability Increases
stability in the order iodine, bromine, chlorine and
fluorine.” Dielectric constant Decreases
Itisclearthatfluorineisaspecialelementbeyond
Dissipation factor Decreases
all others. It is relatively easy to substitute fluorine
Volume andsurface resistivity Increase
for hydrogen (and other elements) in organic
compounds because of its extreme affinity for grab- Mechanical properties Decrease
bing electrons. Substituting fluorine for hydrogen in Flame resistance Increases
achemicalcompoundgivesrisetoavarietyofunique
Resistance to weathering Increases
and useful effects. Examples include increased
polarity, decreased polarity, chemical activity,
chemical neutrality, increased biological activity for 1.3 Fluorine Characteristics
pharmaceuticals and agrochemicals, greater thermal
and oxidative stability, and increased chemical Fluorine ranks 13th in abundance among the
resistance. Earth’s rocks, present at an average concentration of
An interesting example is fluorination of 0.1% by weight [4]. Fluorine abundance is 0.08%,
polyolefin film surface. Slight fluorination renders compared to 0.05% in the Earth’s lithosphere [5].
the neutral surface of a polyolefin film polar. Fluorine is considered the most dominant halogen
Further increases in the fluorine content of the when the whole Earth is considered.
surface result in total neutrality of the film The most abundant natural sources of fluorine are
surface. In practice, slight fluorination of poly- fluorspar (CaF ) and cryolith (also called cryolite
2
olefin surfaces is used to make them adherable. (Na AlF )). The enamel of teeth is very hard, and
3 6
The inside surface of plastic pesticide and mechanically strong, and has long-term durability,
herbicide bottles is fluorinated extensively to mainly because of fluoroapatite (Ca (PO ) F or
5 4 3
prevent permeation of agents, which could result 3Ca (PO ) .CaF ) and hydroxyapatite being its
3 4 2 2
in loss of material and unsafe conditions. Some- major components. Fluoride is considered a trace
times, fluorine is mixed with the blow molding element because only small amounts are present in
gas in order to combine the bottle fabrication and thebody(about2.6ginadults),andbecausethedaily
fluorination steps. requirement for maintaining dental health is only
A number of partially and fully fluorinated poly- afewmilligramsaday.About95%ofthetotalbody
mers have been developed because of the unique fluoride is found in bones and teeth. Fluoride’s
effect of fluorine on their properties. Some of the primary function in the human body is to strengthen
common polymer chemistries include polyolefins, the bones and it is known to prevent tooth decay.
fluorinated elastomers, polymethyl siloxane, acrylic Experts contend that fluoride strengthens the teeth’s
and methacrylic polymers, and perfluorether poly- enamel by strengthening the mineral composition of
mers. The impact of increasing the fluorine content the teeth themselves [6,7].
of olefinic polymers on their properties is listed in About40%offluorspar[4]isusedasmetallurgical
Table 1.2. fluxinthesteelindustry,someofwhichisrecovered
One can simply conclude that fluorinated as syntheticfluorspar.The highestgrade of fluorspar
compounds have varied and unusual properties, (>97% CaF ) is reacted with sulfuric acid for the
2
a number of which are quite useful to the develop- production of HF, which is the starting point of
ment of commercial materials for a broad range of organic fluorinated compounds. Some fluorspar is
applications, including plastics, electronics, agricul- consumed in uranium processing, petroleum alkyl-
ture, pharmaceuticals, and medicine. ation, and stainless steel pickling [8].
6 FLUOROPOLYMER ADDITIVES
Fluorine is a gas with a greeneyellow color, trifluoride (DAST) transforms hydroxyl and carbonyl
a boiling point of (cid:1)188.1(cid:3)C, and a melting point of groupsintoCFandCF moieties,whiletriethylamine
2
(cid:1)219.6(cid:3)C [9]. Its pungent odor is perceptible at tris-hydrofluoride provides a pH neutral, non-volatile
a concentration of 10parts per million. Fluorine is equivalent of hydrogen fluoride and is a source of
highly toxic, corrosive, and oxidizes nearly every fluoride ions for various nucleophilic reactions. In
element,includingnoblegasesxenonandkrypton.In addition,trifluoromethyltrimethylsilane,CF SiMe ,is
3 3
contrast to HF, dry fluorine does not etch glassware ausefulCF sourcethatreactswithcarbonylsystems
3
but reacts with hot platinum and gold. To reduce its to give trifluoromethylated alcohol derivatives.
reactivity and hazard, fluorine is diluted with Thesearchforeffectiveandimprovedfluorinating
nitrogen; a 10% F in nitrogen can be stored and and perfluoroalkylating reagents is ongoing. At the
2
transported in passivated steel bottles. University of York, the Green Chemistry Group [11]
Some basic facts about fluorine are given in have developed efficient one-pot syntheses of fluo-
Table 1.3. rine-containing aromatic systems. Moreover, con-
verting chlorofluorocarbons (CFCs) to useful
1.3.1 Fluorination productsisnowthefocusofmuchindustrialattention.
Forintroducingfluorineatomsintoparticulartarget 1.3.2 Reactivity e An Extreme
molecules, researchers are now well served by
Element
a variety of commercially available, easy-to-use,
fluorinating agents. Selectfluor(cid:3), developed at the As has often been stated, fluorine is truly a ma-
University of Manchester Institute of Science and terial of extremes [12]. Fluorine is the most reactive
Technology (UMIST) and manufactured by Air element known to man. It reacts with nearly every-
Products in the US [10], is perhaps the best-known thing, including glass. Noble gases such as xenon,
electrophilic fluorinating agent. Pharmaceutical and krypton, and gold and platinum are no excep-
researchers routinely use the reagent, for example, tions; all react with fluorine. Moissan [13] has been
when fluorinating steroids. Diethylaminosulfur creditedwiththefirstsynthesisoffluorine.Hereisan
experiment that he conducted to illustrate the
extreme reactivity of fluorine.
Table1.3 Basic facts about fluorine
Oil of turpentine, in the solid state, is attacked by
Natural abundance liquidfluorine.Toperformthisexperiment,alittleoil
ofturpentinewasplacedatthebottomofaglasstube
Earth’scrust:950ppm
surrounded by boiling liquid air. As soon as a small
Important minerals:Fluorspar CaF ;
2 quantity of fluorine was liquefied on the surface of
ApatiteCa (PO ) F;CryoliteNa AlF (Cl130ppm)
5 4 3 3 6 the solid, combination took place with explosive
Ocean: 1.3ppm (Cl18,000ppm) force. After each explosion, the current of fluorine
Essentialelement: 0.3e0.5mg/day for humans; gas was kept up slowly, a fresh quantity of liquid
a human body (70kg)contains 2.6g fluorine fluorine was formed, and the detonations succeeded
Bond distance toC: CH eF 1.39A˚ (CH eCl each other at intervals of 6e7min. Finally, after
3 3
1.77A˚) a longer interval of about 9min, the quantity of
fluorine formed was sufficient to cause, at the
BonddissociationenergyfromC:CH eF116kcal/
mol (CH eCl 81kcal/mol) 3 moment of reaction, the complete destruction of the
3
apparatus. In several of these experiments, a little
Fluorineformsthestrongestsinglebondtocarbon
liquidfluorineaccidentallyfellonthefloor;thewood
(and other elements)
instantly caught fire.
Hammetts parameters
F: s 0.06;s 0.34 1.3.3 Preparation of Fluorine
p m
CF :s 0.54; s 0.43 Interest in fluorine is literally centuries old, even
3 p m
SO CF :s 0.96; s 0.83 thoughitssuccessfulpreparationisrelativelyrecent.A
2 3 p m
18F:T ¼109.8min; bþ¼1.655MeV numberofunsuccessfuleffortstopreparefluorinewere
1/2 made in the past. In 1529, Georigius Agricola
Application in positron emissiontomography (PET)
describedtheuseoffluorspar(CaF )asaflux.In1670,
2
1: INTRODUCTION 7
Schwandhard found that glass was etched when synthesis of the first isolable compound of a noble
exposed to fluorspar treated with acid. Fluorine was gas. Neil Bartlett, at the University of British
one of the last elements to be isolated, due to its Columbia, Canada, showed that PtF will oxidize
6
þ (cid:1)
voraciousreactivity.In1764,MargraffsynthesizedHF xenontogenerateanionicsolid[XeF] [PtF ] .This
6
by reacting sulfuric acid and fluorspar. The extreme work opened up a new era in inorganic chemistry,
redox potential of fluorine prevented its synthesis which continues to the present day. For theorists,
becauseofthelackofasuitableoxidant[9].Theplight compounds such as XeF , XeF , and XeF , and ions
2 4 6
ofthescoresofchemistspoisonedandkilledbyfluo- derived from them, have acted as test molecules for
rinehasbeenlikenedtomaulingbyatiger[14]. ideasonbondingandstructure.Forexperimentalists,
The eminent French chemist Henri Moissan first these molecules provide the starting point for
prepared fluorine onJune 26, 1886. Heused Fremy’s other xenon-element compounds, and examples of
salt (after the venerable French chemist Edmond compounds containing xenoneoxygen, xenoneni-
Fremy, 1814e1894) technique to make and isolate trogen,andxenonecarbonbonds,suchasXe(C F ) ,
6 5 2
pure fluorine by the electrolysis of KF in anhydrous are now known [17].
hydrofluoric acid. Moissan performed electrolysis of In2000,attheFreieUniversita¨tofBerlin,Konrad
a1:12mixtureofKFandHFinaU-shapedplatinum Seppelt’s group [18] synthesized the [AuXe ]2þ
4
(cid:3)
tube cooled at 23 C in a MeCl bath. Henri Moissan cation, the first true compound to contain bonds
was awarded the Nobel Prize in chemistry in 1906. between xenon and a metal. Their reaction involves
Christe synthesized elemental fluorine purely chemi- asuper-acidmediumeasolventsystemthatismore
cally in 1986 [15]. The reaction has two main steps acidic than pure H SO e based on a mixture of HF
2 4
(Fig.1.1):first,potassiumhexafluoropermanganateis and SbF . What is surprising is that the generally
5
derived from the reaction of hydrofluoric acid, unreactive,noblemetalgoldshouldbethefirstmetal
hydrogen peroxide, and potassium permanganate. In to be found to bond to a noble gas. Even more
the second step, a displacement reaction takes place extraordinary is that the metal cation is sufficiently
between antimony pentafluoride and potassium hexa- stable and that researchers have determined its
(cid:3)
fluoropermanganateat150 C,liberatingfluorinegas. structure by single crystal diffraction.
TheprincipleofMoissan’selectrolyticpreparation Noble gas chemistry is dominated by compounds
of fluorine is still in use for industrial manufacture. of xenon, with a much smaller number of krypton-
Another technique for fluorine preparation is the containing analogs being isolable. Meanwhile, the
electrochemical method (Fig. 1.2). quest for compounds of the lighter noble gases,
which are expected to be much less stable, relies on
the use of specialist techniques. In 2002, Markku
1.3.4 Inorganic Chemistry
Ra¨sa¨nen and colleagues at Helsinki University
Nearly 40 years ago, the extreme reactivity of reported[19]trappingHFinanexcessofsolidargon
fluorineandits compoundswasdemonstratedbythe or krypton at 7K to give a HF matrix isolated in
Figure 1.1 Moissan’s reactions for fluorine synthesis [16].
8 FLUOROPOLYMER ADDITIVES
Anode connection composing the Polovtsian Dances from the great
opera Prince Igor (later finished by Nikolai
F outlet
2
Rimsky-Korsakov and Aleksandr Glasunov) while
HF inlet H outlet
2 synthesizing benzoylfluoridebythereplacementof
chlorine in benzoyl chloride using Fremy’s salt
(KFþHF) [9]. This reaction, known as Halex
Cell cover
(short for halogen exchange), remains the most
Electrolyte importantcommercialroutetothesynthesisofCeF
level
bonds [21].
Fluoroaromatics were better understood in the
Gas
separation skirt latter part of the nineteenth and early part of the
twentieth centuries. Aliphatic fluorine chemistry
lagged behind until the pioneering work of the
Carbon anode Belgian chemist Frederic Swarts. He carried out
halogen exchange on polychlorides and poly-
bromides using antimony trifluoride and bromine
Cooling jacket
(SbF þBr ). Swarts demonstrated that dehaloge-
3 2
nation using Zn and dehydrohalogenation using
K CO would preferentially eliminate halogens
2 3
Steel cathode other than fluorine, forming fluorinated olefins.
Swarts has been credited with the first synthesis of
2HF F + H
2 2 CCl F by Midgley and Henne of the Frigidaire
2 2
Figure 1.2 Schematic diagram of an electrolytic Co.(partofGeneralMotors),whopioneeredtheuse
fluorine-generating cell [11].
of fluorinated hydrocarbons in the refrigeration
industry [21].
TheyearsbeforeandduringWorldWarIIbrought
a noble gas. The laser irradiation of these frozen
importantadvancestoorganicfluorinechemistrythat
samples results in the breaking of some of the HeF
facilitatedtheuseoffluorocarbons.Thediscoveryof
bonds and generates the new species HArF and
the catalytic activity of HgF by Simons and Block
HKrF,whicharedetectedbyspectroscopicmethods. 2
[21],whichallowednon-explosivereactionofcarbon
Asexpected,thesecompoundsareveryunstable,and
and fluorine, paved the way for the synthesis of
above 27K, they begin to decompose. But, they
saturated perfluorohydrocarbons. These compounds
clearlydemonstratetheabilityoffluorinetoactasan
resisted the highly reactive UF and were used as
“enabler” for novel and exciting species. This is 6
buffer fluids in the gas-diffusion process of the
evident not just in noble gas chemistry, but in many
Manhattan Project in the early 1940s.
otherareasofinorganicchemistry,andwillcontinue
The discovery of polytetrafluoroethylene by Roy
for a long time to come.
Plunkett of DuPont in 1938 was the beginning of
the fluoropolymers era in earnest. He was exper-
1.3.5 Organic Chemistry
imenting with tetrafluoroethylene (TFE), looking
Carbon forms its strongest bondwith fluorine and for a synthetic route to a useful refrigerant
the credit for demonstrating the stability of the CeF (CClF2eCHF2).Theeffortwasspurredbythedesire
bondgoestotheFrenchchemistsDumasandPeligot, to create safe, non-flammable, non-toxic, colorless,
who heated dimethyl sulfatewith potassium fluoride andodorlessrefrigerants.OnthemorningofApril6,
and obtained methyl fluoride (Eqn (1.1)) [9]: 1938, when Plunkett checked the pressure on
a cylinder of TFE that he was certain was full, he
ðCH OÞ SO þ2KF/2CH FþK S O (1.1) found no pressure, yet the cylinder had not lost
3 2 2 3 2 2 4
weight. Careful removal yielded a few grams of
The first nucleophilic replacement of another a waxy-looking white powder e the first polymer of
halogen by fluorine has been attributed to an tetrafluoroethylene. The slippery PTFE could not be
unfathomable genius, the Russian musician and dissolved in any solvent, acid, or base and, upon
chemist Alexander Borodin [20]. He was probably melting, formed a stiff clear gel without flow. At