Document rxObG3QgEX6Z6BZZ48RO5xEeG
Request for Derogation or Exemption for PFAS Fluoropolymers Used in Gas Sensors
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Contents
List of Abbreviations and Tradenames .......................................................................................... 3 Abbreviations ...................................................................................................................................... 3 Trade names........................................................................................................................................ 3
Background ................................................................................................................................. 3 Who is CoGDEM? ................................................................................................................................ 3 Objectives of this Report..................................................................................................................... 4
Sectors and Sub-uses.................................................................................................................... 4 Materials and Volumes ....................................................................................................................... 5 Table 1 Annual usage of fluoropolymers for gas sensors ................................................................... 5
Alternative Options and Current Status......................................................................................... 5 Alternative Materials .......................................................................................................................... 5 General comments: alternatives for ePTFE for gas porous substrates and solid barriers .............. 5 Expanded Polypropylene ................................................................................................................ 6 Expanded Polyethylene................................................................................................................... 6 Acrylic Copolymer ........................................................................................................................... 6 Polyether-ether-Ketone (PEEK) ....................................................................................................... 6 Polyurethanes (PU) ......................................................................................................................... 7 Ceramics.......................................................................................................................................... 7 Alternatives to Fluoroelastomers as gaskets O-rings and sealants ..................................................... 7 Alternatives to Fluoroether greases and Nafion ................................................................................. 7
Emissions..................................................................................................................................... 7 Derogation and Exemption Submissions ....................................................................................... 8
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List of Abbreviations and Tradenames
Abbreviations
BSI
British Standards Institute, the UK Standards Body
CEG
coal, electricity and gas industry
CENELEC European Committee for Electrotechnical Standardisation
CO
Carbon monoxide
CoGDEM Council for Gas Detection and Environmental Monitoring
ETFE
Ethylene Tetrafluoroethylene
ePTFE
Expanded PTFE, also termed gas porous PTFE when used for gas sensors
FEP
Fluorinated Ethylene propylene
HSE
UK Health and Safety Executive
IEC
International Electrotechnical Commission
ISO
International Standards Organisation
PFA
Per Fluoro Alkoxy Alkane
PFPE
Per Fluoro Poly Ether
PTFE
Polytetrafluoroethylene, the most common fluoroplastic with a very high melting
point, excellent chemical resistance and very low surface energy
PVDF
Poly Vinylidene Fluoride
Trade names
KalrezTM perfluroelastomer from Dupont
VitonTM Fluoropolymer made of Fluorine Kautschuk Material (FKM), sold by Chemours. Similar
FKM
materials include Dai-ElTM from Daikin, DyneonTM from 3M, TechnoflonTM from Solvay
and ElaflorTM from HaloPolymer.
FomblinTM Perfluoroether (PFPE) from Solvay. Other suppliers include DuPont MolykoteTM and
Castrol BraycoatTM.
FluonTM PTFE ETFE or PFA fluoropoplastic from AGC Chemical. There are many other global
manufacturers of PTFE, ETFE or PFA.
NafionTM Sulfonated tetrafluoroethylene, manufactured by Chemours.
Background
Who is CoGDEM?
The Council for Gas Detection and Environmental Monitoring (CoGDEM) was founded in 1974 by the UK's leading gas detection manufacturers as a trade association; CoGDEM's activities are wholly financed by its members . CoGDEM is the co-ordinating body of the gas detection, gas analysis and environmental monitoring Industries, representing the collective interest to Government, EC Commission, BSI, and other trade and professional bodies.
An original objective was to be represented on BSI committees involved in gas detection and to address issues raised by the Coal, Electricity, Gas (CEG) committee's draft gas detection standard. CoGDEM joined BSI committee GSE/29 (now EXL/31/1) which created BS 6020 for flammable gas detectors.
CoGDEM now sits on the sub-committees that have worked, or continue to work on flammable and toxic gas safety and air quality standards. CoGDEM is represented on CENELEC, ISO and IEC committees , drafting documents used to create EN and global IEC and ISO standards. CoGDEM has good relations with the UK Health & Safety Executive (HSE) and others, and contributes to reducing the number of incidents and improving the standard of available gas detection equipment for both industrial safety and domestic CO alarms in residences.
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CoGDEM membership includes more than 50 companies (www.cogdem.org.uk); most of the member companies have global sales networks and many have multinational manufacturing sites. CoGDEM have engaged the services of Graham Wardman of SSC Consulting Ltd, to make this submission (and the later submission in September) on their behalf.
Objectives of this Report
To present data from the Gas Detection and Environmental Monitoring Industries on the usage of PFAS chemicals and materials within the range of Gas Detectors and Environmental Monitoring equipment sold by Companies within the Trade Industry. We will use this data from our members to present an initial derogation listing by PFAS chemical family, for inclusion in the full Socio-Economic review in September.
Sectors and Sub-uses
There is no exact sector that matches the production and use of Gas Sensors, but the closest sector is under Medical Devices (Annex E.2.9.), sub -use "Diagnostic Laboratory Testing". There are generally two types of sensors:
Domestic sensors (eg. carbon monoxide) - a price sensitive market, requiring simpler design and fewer PFAS compounds
Industrial Sensors (eg. gas-specific sensors) - a more specialist market with more complex designs and a larger variety of PFAS materials to resist more harsh environments and ensure good data quality.
Three classes of PFAS materials are used in gas sensors: 1. Fluoroplastics (eg. PTFE); used for their very low surface energy, wide chemical and temperature resistance, both in porous form (dust filters and gas porous membranes) and as solid substrates as barriers in gas sensors. Machined parts and low surface energy tubing are also fluoroplastics, typically PTFE, PVDF or FEP. ICI Fluon and PTFE granules from other suppliers are used as a carrier and dispersant for the electrocatalyst on the electrodes.
2. Fluoroelastomers (eg. Viton); used to seal internal sections of the gas sensor from other sections, or to seal with external components, for situations requiring low surface energy and chemical and temperature resistance.
3. Fluoroether greases (eg. Fomblin); comprising short chains, these greases are hydrophobic and oleophobic with excellent chemical and temperature resistance. Nafion is a specialist sulfonated PTFE with the unique properties of ion transport and is often used to regulate humidity in flowing gas.
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Materials and Volumes Table 1 Annual usage of fluoropolymers for gas sensors
Fluoroplastics for Gas Sensors
expanded PTFE
dust filters
solid PTFE
General Purpose Fluoroplastics Fluoro-
elastomer
Gas tubing machinings Fluoro disp, powder
gasskets
Fluoroethers
grease & Nafion
Units
m2
m2
m2 linear m
kg
kg
kg
kg
Conversion
256g/m2
6g/m2 425 g/m2 345 g/m
N/A
N/A
N/A
N/A
Industrial Sensor Mfr 1
1,300
1,700
450
1,800
80
170
400
45
Safety Sensor Mfr 2
900
1,400
350
1,700
40
130
200
25
Sensor Mfr 3
800
1,500
400
600
50
150
150
20
Sensor Mfr 4
400
300
350
75
25
60
100
10
Sensor Mfr 5
1,000
2,000
220
9,000
1,000
50
50
Sensor Mfr 6
1,000
900
200
0
15
50
8
Sensor Mfr 7
300
900
180
600
25
130
12
Sensor Mfr 8
2,000
2,000
500
0
50
100
25
Sensor Mfr 9
75
160
25
TOTAL
7,700 10,775
2,650 13,935
1,310
510
1,180
195
TOTAL kg
1,971
65
1,126
4,808
1,310
510
1,180
195
% market
90
90
80
90
90
60
80
80
CoGwDhEoM kg
2,190
72
1,408
5,342
1,456
850
1,475
244
Domestic AlraeTrpOmoTrMAteLfdr 1
550
4.6
CO
Alarm Mfr 2
470
Alarms Alarm Mfr 3
3,000
9.6
TOTAL
4,020
TOTAL kg
1,029
14.2
% market
60
40
CoGwDhEoM kg
1,715
36
rGeTpROoATrANteLDd
3,905
72
1,408
5,342
1,456
886
1,475
244
TOTAL kg
Alternative Options and Current Status
Gas sensors are often used in safety critical situations. Domestic carbon monoxide detectors are an
obvious human safety application, but there are also industrial safety related applications, including
gas monitoring in confined spaces for oxygen, and combustible and toxic gases; gas sensors are also
used for similar human safety risk mitigation.
Oxygen, and carbon dioxide sensors are also used in medical respiration equipment, such as capnographs (used to monitor sedation in operating theatres).
Alternative Materials
General comments: alternatives for ePTFE for gas porous substrates and solid barriers Alternatives to PTFE and expanded PTFE (ePTFE) have been identified that can meet some but not all of the attributes required for gas sensing applications.
The alternatives listed below are not drop-in substitutes for ePTFE, PTFE or other fluoropolymers. Each would need significant further development before it could be substituted for fluoropolymers in gas sensors. Ultimately, gas detection manufacturers rely upon their material suppliers for this development, but indications from the raw material Suppliers are that replacements for these unique family of PFAS will be cost prohibitive and have timescales longer than the proposed maximum derogation period, before replacement technologies become commercially available. Realistically, it is uncertain whether the PTFE alternatives known today will be capable of achieving equivalent
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technical performance while meeting all relevant regulatory standards. Therefore, replacing PTFE in electrochemical gas sensors in a specified time frame is not feasible.
Note that we have focused our evaluation of ePTFE/fluoropolymer for use in electrochemical gas sensor applications and as dust filters for all gas sensors. While some fluoropolymers are used in other gas sensor technologies, the large majority of fluoropolymer usage is in amperometric electrochemical gas sensors. A blanket prohibition on PFAS would require a similar evaluation of other components of gas detection technology, which may also currently rely on PTFE or other PFAS.
Electrolyte leakage of gas porous (expanded) substrates can occur by seeping through microcracks that develop during use, especially during thermal cycling. This failure mechanism has been conquered with ePTFE and would require a very long time of material development and extended safety field trials for any alternative material to meet safety reliability requirements.
PTFE and similar fluoroplastics can withstand high processing temperatures. Electrochemical gas sensor electrodes require one, two or three elevated temperature stages, depending on the manufacturing method. These sintering/ bonding/sealing operations require temperatures in excess of 150C, which either eliminates certain alternative materials or requires new sensor designs and electrode manufacturing operations that would already be used now if they were able to meet performance requirements. Developing new low temperature designs and processes for alternative materials will be a significant challenge.
Expanded Polypropylene Expanded polypropylene membranes are hydrophobic, but with a higher surface energy than PTFE, limiting their use as gas porous substrates.
Unlike PTFE, they are not resistant to the electrolytes used in gas sensors, specifically sulfuric or phosphoric acid. If they are manufactured as thicker substrates to improve lifetime in these electrolytes, the gas diffusion and hence response time slows to a point that the gas sensor does not respond fast enough to provide a safe alarm.
Expanded polypropylene lacks the thermal stability of fluoropolymers; the melting point of polypropylene is 160C versus 325C for PTFE.
While there may be the potential to improve the chemical resistance and possibly the thermal stability of expanded polypropylene via "surface cross-linking" this process may reduce the ability of this material to be recycled.
Expanded Polyethylene With a melting point of only 120C, expanded polyethylene lacks the thermal stability required
for manufacturing.
Acrylic Copolymer The hydrophobicity and porosity of acrylic copolymer membranes are equivalent to that of PTFE
and other fluoropolymers. For this reason, acrylic copolymer membranes have been used successfully in medical device applications requiring such properties. The critical limitation is its chemical incompatibility with strong acids, which will limit its use with the electrolytes within electrochemical gas sensors
Polyether-ether-Ketone (PEEK) PEEK offers good temperature and chemical stability that may make it more suitable for direct,
prolonged contact with corrosive electrolytes.
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The main limitation is the high surface energy, so they can be used as internal barriers but not as gas porous substrates.
Polyurethanes (PU) Similar to PTFE, polyurethane has both high thermal stability and hydrophobic behaviour. Again,
the critical limitation is its chemical incompatibility with strong acids, which will limit its application with the electrolytes within electrochemical gas sensors. Polyurethane is also susceptible to degradation by repeated exposure to certain toxic acidic-type gases including hydrogen cyanide (HCN), hydrochloric acid (HCl), chlorine (Cl2), sulfer dioxide (SO2)
Ceramics Some electrochemistry research has been published on ceramic membranes subjected to
hydrophobic surface treatment, which offer good temperature and chemical stability. However, this technology is not mature and has not yet been implemented on a commercial
scale and mechanical properties need improving to meet commercial gas sensor reliability requirements. Further development and investigation are required to fully understand its manufacturability and durability for industrial applications.
Alternatives to Fluoroelastomers as gaskets O-rings and sealants
Fluoroelastomers are used to seal components inside the gas sensor and in the sampling lines between the sensor and tubing, pump, etc.
Alternative materials may be used when measuring inert gases that are non-reactive or not acidic, but where gases will react on many surfaces (ozone, nitrogen dioxide, chlorine, sulfur dioxide, hydrogen sulfide) then chemically inert seals must be used. Manufacturers of Digital Mass Flow Controllers (DMFCs) usually provide two grades of DMFCs for gas control: normal seals for many gases and Kalrez fluoroelastomer seals for reactive and acidic gases. Manufacturers have not found a satisfactory alternative to expensive fluoroelastomers when using with reactive or acidic gases, so likewise, replacing fluoroelastomers in gas sensor applications will be a technical challenge that to date has not been achieved,
Alternatives to Fluoroether greases and Nafion
Specialist fluoropolymers can be found as greases inside of gas sensors because of their ability to withstand the extreme acidic conditions. These fluoro-greases also maintain the correct viscosity over the wide temperature range from -40C to +60C, a requirement that again will take time to provide a formulation with low viscosity-temperature dependence.
Nafion is a unique PFAS, used in many applications including humidity control. This material has been used in very small quantities (a few tons annually) by many industries, including industrial and air quality gas direction. Although a replacement material does not exist, it is possible for a company to explore a non-PFAS alternative, although with such a small demand volume, few competent companies would support this focused research for such a small market.
Emissions
PFAS emissions can be separated into emissions during manufacture, during use and when disposed.
Fluoropolymers are by definition polymerized materials with monomers as the feedstock. Due to their use at high temperatures and in highly reactive media, fluoropolymers almost universally do not have fillers or additives, so the only emissions generated during manufacture are vapours from
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the monomers and monomer leakage or waste monomer disposal which may find its way into groundwater, depending on the supplier's best practice. This trade association is not capable of commenting on the generated emissions of PTFE and other fluoropolymers during polymerization. Any post-processing such as micro-tearing of Gore or film/ tube extrusion should not generate any significant gas emissions. Emissions during use of fluoropolymers will be effectively nil. These expensive materials are used because they do not emit by-products, degrade naturally or dissolve in water. Emissions during disposal depend on the method of disposal. If the PFAS is being dispersed in a landfill then it will not break down for many years but also it will not leach into the soil or groundwater, nor will it degas or generate aerosols. However, if the fluoropolymer is to be incinerated then noxious and toxic fumes, for example HF, can be generated and must be scrubbed as is normal practice when controlling stack emissions. The level of emissions depends on the competency and best practice of the incinerator operator.
Derogation and Exemption Submissions
The following Risk Options are requested: Fluoroplastics (eg. PTFE); it is requested that this family of products are exempted from this regulation completely for use in Gas Sensors. Fluoroelastomers (eg. Viton); it is requested that this family of products are exempted or that we have a 12 year derogation in which to prove out the alternatives with Suppliers. Fluoroether greases (eg. Fomblin); it is requested that this family of products are exempted or that we have a 12 year derogation in which to prove out the alternatives with Suppliers.
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