Document rpdMXN16NxEoke1Vg5oJRvJe
Processing additives for polyethylene
CONTENTS
ExxonMobil Petroleum & Chemical BV (EMPC) Comments on Annex XV restriction report on perand polyfluoroalkyl substances (PFAS)
Processing additive for polyethylene
Processing additive for polyethylene
21 September 2023 Project No.: 0691418
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ExxonMobil Petroleum & Chemical BV (EMPC) Comments on Annex XV restriction report on perand polyfluoroalkyl substances (PFAS)
Clean Agents in Fire Suppression Systems
0691418
21 September 2023
FINAL
Tom Persich, Giulio Bracalente, Jo Lloyd
ExxonMobil Petroleum & Chemical BV
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Signature Page
21 September 2023
ExxonMobil Petroleum & Chemical BV (EMPC) Comments on Annex XV restriction report on per-and polyfluoroalkyl substances (PFAS)
Processing additive for polyethyleneProcessing additive for polyethylene
ExxonMobil Petroleum & Chemical BV (EMPC) Comments on Annex XV restriction report on per-and polyfluoroalkyl substances (PFAS)
Jim Davidson Partner ERM
Jo Lloyd Technical Partner ERM-EMEA
Environmental Resources Management Southwest, Inc. 840 West Sam Houston Parkway North, Suite 600 Houston, Texas 77024
Copyright 2023 by each of ERM Worldwide Group Ltd and/or its affiliates ("ERM") and ExxonMobil Petroleum & Chemical BV and its affiliated companies ("ExxonMobil"). All rights reserved. No part of this work may be reproduced or transmitted in any form, or by any means, without the prior written permission of both ERM and ExxonMobil.
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CONTENTS
1. EXECUTIVE SUMMARY ................................................................................................................... 1
2. BACKGROUND INFORMATION....................................................................................................... 3
3. OVERVIEW OF USE ......................................................................................................................... 5
3.1 Sectors and Sub-uses......................................................................................................................... 5 3.2 Performance requirements .................................................................................................................. 9 3.3 Safety and sustainability considerations related to the use PPA...........................................................10
3.3.1 3.3.2
PE processing and Service life ...........................................................................................12 End of Life .........................................................................................................................12
4. OVERVIEW OF POTENTIAL ALTERNATIVES ............................................................................... 14 4.1 Introductory Note ...............................................................................................................................14 4.2 Annex XV Restriction Report proposed alternatives ............................................................................14 4.3 Availability of alternatives ...................................................................................................................15
4.3.1 Safety considerations related to alternatives .......................................................................15
4.4 Summary...........................................................................................................................................17
5. SOCIO-ECONOMIC ANALYSIS...................................................................................................... 18
5.1 Introductory Note ...............................................................................................................................18 5.2 Continued use scenario (aligned with preferred derogations)...............................................................19
5.2.1 5.2.2 5.2.3
Introduction and scenario definition ....................................................................................19 Market and business trend considerations ..........................................................................19 Risks associated with continued use...................................................................................20
5.3 Non-derogation scenario ....................................................................................................................20
5.3.1 5.3.2
Introduction and scenario definition ....................................................................................20 Societal costs associated with a non-derogation scenario ...................................................20 5.3.2.1 Impacts for ExxonMobil......................................................................................20 5.3.2.2 Impacts on plastic usage....................................................................................20 5.3.2.3 Impacts to downstream stakeholders..................................................................20
6. SUMMARY...................................................................................................................................... 22
APPENDIX 1 ............................................................................................................................................... 1
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List of Tables Table 3-1: Toughness properties of different polyethylene families ............................................................... 7 Table 3-2: characterization of PVDF and PVDF-HFP against PLC criteria, extracted from S. Korzeniowski et al (2023) .................................................................................................................................................... 11 Table 3-3: Availability of fluoropolymer PVDF from polyethylene matrix in water...........................................11 Table 4-1: Materials evaluated as alternatives to fluoropolymers ................................................................ 15 Table 4-2: GHS classification of the alternatives tested as PPA substitute.................................................. 15 List of Figures Figure 3-1: Melt flow profile of linear molecules through a narrow opening without using a processing aid.... 7 Figure 3-2: Melt fracture in polyethylene film without using a processing aid (left) and film without melt fracture (right) (source: ExxonMobil) ............................................................................................................ 8 Figure 3-3: Melt flow profile of polymer using a PPA with a fluoropolymer processing aid ............................. 9 Figure 3-4: Evolution of post-consumer plastics waste treatment................................................................ 13 Figure 5-1: European production of PE in 2021.......................................................................................... 19
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Acronyms and Abbreviations
CAGR ECETOC ECHA EDPM EEA EIF EMPC FP GHS HDPE JRC LDPE LLDPE MDPE MD Tear MFE OECD
PAO PE PFAS PFCA PLC PPA PVDF PVDF-HFP RMM R&D SEA TD Tear
Compound Annual Growth Rate Centre for Chemical Safety Assessment European Chemical Agency Ethylene Propylene Diene M-class rubber European Economic Area Entry In Force ExxonMobil Petroleum & Chemical BV Fluoro Polymer Global Harmonized System High Density Polyethylene Joint Research Centre Low Density Polyethylene Linear Low Density Polyethylene Medium Density Polyethylene Machine Direction Tear Melt Fracture Elimination Organisation for Economic Co-operation and Development Poly-Alpha Olefin Polyethylene Per- and Polyfluoroalkyl Substance Polyfluoroalkyl Carboxylic Acids Polymer of Low Concern Polymer Processing Aids Poly Vinylidene Fluoride Poly Vinylidene Fluoride and HexaFluoroPropylene Risk Management Measures Research & Development Socioeconomic Assessment Transverse Direction Tear
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1. EXECUTIVE SUMMARY
This response is submitted on behalf of ExxonMobil Petroleum & Chemical BV ("EMPC"). For the purpose of this submission, EMPC is acting in its own name and in name and on behalf of the other affiliates potentially affected by the proposed REACH restriction (hereafter referred to as "ExxonMobil"). EMPC is a subsidiary of Exxon Mobil Corporation and part of the ExxonMobil group of companies ("ExxonMobil Group").
Processing aid is a general term that refers to several different classes of materials used to improve the processability and handling of high-molecular-weight polymers. ExxonMobil uses polymer processing aids (PPA) consisting of fluoropolymers (FP) in the processing of Polyethylene (PE) materials. PE is then globally supplied to end users for different applications including users in the European Economic Area (EEA).
By adding the PPA in low concentration (below 1000 ppm), the PE materials are prevented from forming "melt fracture". This improvement translates into higher mechanical performance, meeting the technical criteria and specifications of different end-use applications, and increases the durability and the recyclability of PE materials.
ExxonMobil has evaluated different alternatives to the use of FP as PPA. None of the materials evaluated offered a complete 100% option to replace fluoropolymers in commercial applications. Most of assessed alternatives did not eliminate melt-fracture, and in many cases the neck-in (final film width relative to die opening width) was too high, resulting in a film that is too narrow. This is aligned with the general conclusions provided by other submitters during this public consultation. Despite the alternatives reported by the restriction proposal submitters, it is ExxonMobils opinion that both boron nitride and polyethylene waxes do not meet the required technical specifications and cannot be considered alternatives as processing aids.
Both PE and FP processing aid meet the OECD (Organisation for Economic Co-operation and Development) definition of Polymer of Low Concern (PLC). FP are demonstrated not to break down into smaller PFAS molecules under normal environmental exposure. FP are unlikely to migrate from PE and along with its very high molecular weight (> 1000 daltons) make FP not bioavailable and a nondispersive application.
The use of PE is often seen as more favourable in packaging than alternatives such as metal, paper, or glass. High performance PE, which requires FP as a processing aid allows for significantly reduced packaging weight and has greater ability to incorporate mechanically recycled polymer. FP facilitate the use of mechanically recycled polymer.
In the current non-derogation scenario, ExxonMobil would not be able to produce and supply PE with the required technical standards that the wide downstream users expected for their packaging applications. Following the standard timelines of regulatory processes, a non-derogation scenario would then imply that ExxonMobil is not able to use FP in the processing of PE immediately once the restriction enters into force.
In a non-derogation scenario, a significant impact is expected for ExxonMobils customers of PE materials, such as the packaging industry and their customers, construction sector, automotive industry, manufacturers of electrical and electronic equipment and the general public or end-users of the associated items. Given the significant market share of ExxonMobils PE a supply chain disruption could possibly result as there would be insufficient product available to satisfy all customers' needs.
It is well demonstrated that the use of FP as a processing aid in the production of PE has enabled the PE film value chain in 2021 to avoid approximately 1.3 million tons of global plastic consumption when compared to year 2010.1 A ban on the use of FP as an aid in the production of PE materials would
1 ExxonMobil internal data
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jeopardize this significant saving in plastic consumption and would run counter to the objectives of the EU plastics strategy2. As a conclusion, and considering the high difficulty in identifying an alternative to fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE), ExxonMobil would request that a time un-limited derogation be included as per the wording below:
The use of fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE) Nevertheless, work on alternatives is ongoing, in an effort to improve the environmental footprint of the products, along with the overall performance of Polymer Processing Additives (PPA) used in the processing of polyethylene (PE). As such, and to capture the possibility that an alternative is identified in the future, the validity of the time-unlimited derogation can be re-evaluated at regular intervals, depending on the status and availability of alternative additives. This report details the use fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE), as well as the required technical feasibility criteria and an overview of potential alternatives. Potential for substitution are discussed, as are the safety considerations. The report concludes with a socio-economic analysis which covers both the scenario where use continues, and that where the no derogation applies.
2 https://environment.ec.europa.eu/strategy/plastics-strategy_en
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2. BACKGROUND INFORMATION
Exxon Mobil Corporation manages an industry-leading portfolio of resources, and is one of the largest integrated fuels, lubricants and chemical companies in the world. The ExxonMobil Group evolved an operating model and global organization to better leverage the scale of its increasingly integrated company and global brands. There are three core businesses with operations around the world3:
Upstream business - Focused on strengthening energy security by expanding low-cost-of-supply, highreturn oil and natural gas operations.
Product Solutions business - Integrating downstream and chemicals operations to develop lower emission fuels and innovative products needed by modern society.
Low Carbon Solutions Business - Helping lower emissions by providing solutions to industrial and commercial customers in growing markets for carbon capture and storage, hydrogen and biofuels.
ExxonMobils history of operating in Europe is more than a century long and Europe has played an important role in some of the key milestones that marked their development into a manufacturer of the products that drive modern transportation, power cities, lubricate industry and provide petrochemical building blocks that lead to thousands of consumer goods.
The ExxonMobil Group's Corporate brands include:
Esso: Customers around the world have come to respect and rely on Esso-branded fuels, services and lubricants for their personal and business needs;
Exxon: Customers have also come to respect and rely on Exxon-branded fuels, services and lubricants for their personal and business needs;
Mobil: Marketed around the world, Mobil is known for performance and innovation. Mobil is recognised for its advanced technology in fuels, lubricants and services; and
ExxonMobil Chemical: There is a broad portfolio of petrochemical product brand and service solutions. These products play a key role in enabling the manufacture of affordable, sustainable and safe products that are helping meet the growing demands of an increasing global population.
With specific regard to chemicals and specialties, it has manufacturing capacity in every major region of the world, serving large and growing markets. More than 90 percent of the company's chemical capacity is integrated with refineries or natural gas processing plants4:
The portfolio includes product and services (branched alcohols, branched higher olefins, butyl, EPDM rubber, linear alpha olefins, neo acids, plasticisers, polyethylene, polymer modifiers, polyolefin plastomers and elastomers, polypropylene, solvents & fluids, synthetic base stocks, tackifiers, transformer oils and thermoset systems);
The industrial sectors supplied include: adhesives and sealants, agriculture, automotive, building and construction, compounding, consumer products, healthcare & medical, hygiene and personal care, industrial applications, energy, packaging, synthetic base stocks.
3 https://corporate.exxonmobil.com/who-we-are/our-global-organization#Aglobalcompany 4 https://www.exxonmobilchemical.com/en/
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This document is being submitted by ExxonMobil in response to the public consultation on the universal PFAS restriction proposal, which was initiated by ECHA and runs until 25 September 2023. The ExxonMobil Group does not manufacture per-and polyfluoroalkyl substances (PFAS). As part of their response, ExxonMobil wants to present relevant data on the uses and applications of certain PFAS and respond to ECHA's public consultation questions, which are applied in a number of products in industry sectors and applications including, but not limited to, the uses identified in this report. ExxonMobil will be submitting reports covering the following uses: Fluoropolymer use in upstream, refining, and petrochemical manufacturing Aviation hydraulic fluid additive Additives in lubricants Processing additive for polyethylene Clean agent in fire suppression systems Please note that the information able to be submitted at this juncture is incomplete. The scope and potential impact of the proposed restriction is unprecedented and open-ended. Many thousands of substances would be subject to the restriction, and few of these substances are identified in the proposal on an individual basis. Accordingly, more time would be needed to do a more comprehensive and complete assessment. Due to the absence of identification of the individual substances that are in scope of the proposed restriction, the current assessment has been limited to those substances that are known to be used by ExxonMobil and are within the proposed restriction's scope. ExxonMobil reserves our rights in this context. The information provided will describe in detail the sectors and sub-uses involved and the potential impact of the current restriction proposal, demonstrating the necessity of the use of certain PFAS in these applications, the potential for substitution, and the importance of the use, and continued use, with specific regard to the European Economic Area (EEA).
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3. OVERVIEW OF USE 3.1 Sectors and Sub-uses
Exxon Mobil Corporation is one of the largest integrated fuels, lubricants and chemicals companies globally. Its business encompasses all aspects of the oil and gas industry, including Upstream, Products Solutions (including downstream and chemicals), and Low Carbon Solutions. The value chain of ExxonMobil businesses extends to end users of products and services, which can be found across all industry sectors in the EEA, including, but not limited to, automotive and aerospace, building and construction, chemical processing, including agrochemicals and pharmaceuticals, packaging.
Polyethylene (PE) is the world's largest volume thermoplastic product family. Polyethylene applications include, but are not limited to, flexible food packaging, rigid food packaging (bottles and containers), nappy and feminine care product back sheeting, collation shrink film, pallet wrap stretch film, stretch hood film, household and industrial chemicals (HIC) packaging, nonwoven fabrics, medium and heavy-duty sacks, greenhouse films, geomembranes, pressure and non-pressure pipes.
Polyethylene has evolved since its discovery in the 1930s. Early resins, termed Low Density Polyethylene (LDPE) were highly branched molecules. This high branching content made LDPE easy to convert into usable articles, e.g., films, but made the polymer relatively weak in terms of mechanical properties. The process used to make these polymers was termed the "high-pressure" process because it required an energy-intensive reactor environment of 30,000 to 50,000 psi. Subsequent versions of polyethylene - High Density Polyethylene (HDPE), created in the 1950s, Linear Low-Density Polyethylene (LLDPE), created in the 1970s - were linear molecules (no long chain branching) which made them more difficult to convert into usable articles, but provided much improved mechanical properties. These improved mechanical properties allowed for significant reduction in the amount of polyethylene required for an application - commonly called "downgauging." The processes used to manufacture these molecules - slurry, solution, and gas-phase processes, required much less energy than the high-pressure processes. The evolution of polyethylene continued into the 1990s and through to current day with the development of high-performance families made with metallocene-based and other single-site catalysts. The use of these catalysts allowed for the design of polyethylene with much higher performance in mechanical properties and continued downgauging of applications, including the reduction of packaging thickness as required, for example, by the technical standard EN13428:2005.
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Table 3-1 shows the improvement in mechanical properties for films made from different polyethylene families, at approximately the same molecular weight (as measured by melt index). The trends show that overall toughness and potential for less material use in end-use applications improves with narrower molecular weight distributions. The development of linear molecules created products with improved mechanical properties with more economic and energy efficient processes. However, as also noted below, the linear nature of these molecules made them more difficult to convert into usable articles.
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Table 3-1: Toughness properties of different polyethylene families
Toughness properties
PE Family
LDPE
HDPE
LLDPE
mLLDPE
Melt Index (g/10 min) Density (g/cm3) Dart Impact (g) MD (Machine Direction) Tear (g) TD (Transverse Direction)Tear (g) Puncture Energy (J) MD Tensile Strength (MPa) TD Tensile Strength (Mpa) Molecular Weight Distribution
1.1 0.919 120 270
90 2.1 31 24 Broad
0.7 0.961 < 30
10 200 --60 31 Broad
1.0 0.917 170 310 710
3.4 50 47 Narrow
1.0 0.918 550 220 370
5.5 60 60 Very Narrow
Test Methods: Melt Index - ASTM D1238, Density - ASTM D792, Dart Impact - ASTM1709A, Tear - ASTM D1922, Puncture -
ExxonMobil Method, Tensile Strength - ASTM D882.
Polyethylene is typically manufactured and sold as pellets, usually with 5 mm or less diameter. To convert these pellets into a usable article, they are melted, compressed and pushed through a relatively small opening called a die. The linear nature of these molecules means that their viscosity is not significantly impacted by shear rate, therefore when they are pushed through a die with a narrow opening at high shear, there is a large difference in the melt flow profile as shown in Figure 3-1.
Figure 3-1: Melt flow profile of linear molecules through a narrow opening without using a processing aid5
Molten polymer flows more easily in the centre and tends to drag at the die interface. Eventually, the elastic nature of the polymer will cause the material at the die interface to "snap back" in the direction of flow. The resultant effect of this "snap back" is a surface imperfection called "melt fracture" which is not only visually
5 Picture from ExxonMobil's internal document
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unappealing, but also causes mechanical weak points in the article manufactured and potentially preventing the proper application and compliance with labelling requirements of end products (es: labelling of batch code). An example of melt fracture in a film without processing aid is shown in Figure 3-2.
Figure 3-2: Melt fracture in polyethylene film without using a processing aid (left) and film without melt fracture (right) (source: ExxonMobil)6 From a mechanical integrity standpoint, it is very important that polyethylene can be processed without melt fracture. Indeed, melt fracture can occur in films, bottles, pipes and other applications. In the 1960s, it was learned that the addition of fluoropolymers to polyethylene as additives in low concentrations could eliminate melt fracture in the fabrication of finished articles. The fluoropolymer "coated" the metal die wall and decreased the shear experienced by the polymer melt. Lower shear at the wall results in a more uniform melt flow as shown in Figure 3-3. Materials used to improve the processing of polyethylene became known as Polymer Processing Aids (PPA)7.
6 Picture from ExxonMobil's internal document 7 ExxonMobil proprietary information
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Figure 3-3: Melt flow profile of polymer using a PPA with a fluoropolymer processing aid8
The use of fluoropolymer processing aids allows for the processing of polyethylene with narrow molecular weight distributions and high molecular weights at favourable commercial output rates.
An additional application of fluoropolymers in polyethylene is to reduce the build-up of exuded material from molten polymer flows onto die surfaces, known in the industry as die lip build-up. Die lip build-up is commonly found to be low molecular weight polyethylene and/or additives that migrate from molten polyethylene. Through normal manufacturing conditions, it can aggregate at the die exit and eventually impinge on the molten flows causing undesired imperfections on the film surface, known in the industry as die lines. Die lines can affect the aesthetics of a film, making it unusable for packaging applications, and if severe enough, can negatively impact mechanical properties. To eliminate die lip build-up, operators must shut down their equipment for cleaning, which results in lost production and poorer process economics. Fluoropolymers in polyethylene help prevent die lip build-up by creating a "non-stick" surface coating on the die, as a result allowing operators to run their equipment for longer periods of time before cleaning.
If fluoropolymer processing aids were not derogated, a converter could theoretically process these high performing polyethylene resins but at either:
(1) excessively slow output rates which limits production capacity requiring additional capital investment to meet consumer demand, and proportionally more energy consumed per finished part; or
(2) at much higher processing temperatures which risks the degradation of polyethylene and subsequently poorer performance.
According to ExxonMobil internal data, the use of high performance polyethylene, which incorporates fluoropolymers for processing, has allowed an average reduction of film thickness across 30 film segments of 2-3% per year as from year 2010. In 2021, this performance improvement enabled the film value chain to avoid approximately 1.3 million tons of global plastic consumption when compared to year 2010.9
3.2 Performance requirements
Processing aids is a general term that refers to several different classes of materials used to improve the processability and handling of high-molecular-weight polymers. The benefits are mainly obtained at the stage of melting the host polymer. Two main groups of processing aids are lubricants and fluoropolymerbased additives. Each has a distinct effect on the polymer melt, and they are used in different ways (Drobny, 2014) 10:
Lubricants are used in polymer processing to lower melt viscosity or to prevent polymers from sticking to metal surfaces. Internal lubricants act intermolecularly, making it easier for polymer chains to slip past one another. Lowering viscosity improves polymer flow. Materials used as lubricants include metal soaps, hydrocarbon waxes, polyethylene, amide waxes, fatty acids, fatty alcohols, and esters.
Fluoropolymer-based processing aids can be:
8 Picture from ExxonMobil's internal document 9 ExxonMobil internal data 10 Jiri George Drobny, in Handbook of Thermoplastic Elastomers (Second Edition), 2014. https://www.sciencedirect.com/topics/engineering/processing-aid
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- homopolymer: polyvinylidene fluoride (PVDF) (CAS: 24937-79-9), or - copolymers: vinylidene fluoride and hexafluoropropylene (PVDF-HFP) (CAS: 9011-17-0). Some materials used may be referred to as "fluoroelastomers". The most pronounced effect of fluoropolymer processing aids is the elimination of the melt fracture during polymer extrusion. The second major function of fluoropolymer processing aids is the prevention of die lip build-up, which can cause imperfections in film quality resulting in product losses, and lost downtime needed for cleaning.
Fluoropolymer processing aids are very effective in their role for melt fracture elimination such that amounts needed are typically 1000 ppm or less.
3.3 Safety and sustainability considerations related to the use PPA
In this section we present generic considerations related to safety and sustainability related to PPA in PE.
PPA as Polymer of Low Concern According to recent publications (Henry, 2018)11 (Korzeniowski et al, 2023)12, 96% of commercial fluoropolymers meet the OECD criteria on `polymers of low concern' and are not expected to pose environmental and human health concerns (or hazard). The PLC criteria entails physicochemical properties, such as molecular weight, which determine bioavailability and warn of potential hazard. PLC criteria were developed over time within regulatory frameworks around the world as an outcome of chemical hazard assessment processes, which identified physical-chemical properties of polymers that determine polymer bioavailability and thereby report a polymer's potential hazard. Table 3-2 below, extracted from S. Korzeniowski et al (2023), reports the characterization of PVDF and PVDF-HFP against PLC criteria.
11 Henry, B., Carlin, J., Hammerschmidt, J., Buck, R. C., Buxton, L., Fiedler, H., Seed, J., & Hernandez, O. (2018). A critical review of the application of polymers of low concern and regulatory criteria to fluoropolymers. Integrated Environmental Assessment and Management, 14(3), 316-334. https://doi.org/10.1002/ieam.4035 12 S. Korzeniowski and all - A Critical Review of the Application of Polymer of Low Concern Regulatory Criteria to Fluoropolymers II: Fluoroplastics and Fluoroelastomers - Integrated Environmental assessment and Management htttps://setac.onlinelibrary.wiley.com/doi/10.1002/ieam.4646.
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Table 3-2: characterization of PVDF and PVDF-HFP against PLC criteria, extracted from S. Korzeniowski et al (2023)
According to the studies, both PVDF and PVDF-HFP meet the PLC criteria.
Bioavailability studies conducted by a third party for ExxonMobil show that fluoropolymer PVDF does not migrate from a polyethylene matrix in fresh or sea water environments.
Table 3-3 Availability of fluoropolymer PVDF from polyethylene matrix in water13
Time
2 hours 1 day 3 days 7 days 10 days
Analyte (Moderate Hard Water) PVDF
None detected None detected None detected None detected None detected
Analyte (Instant Ocean) PVDF
None detected None detected None detected None detected None detected
13 ExxonMobil's data
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20 days 30 days
None detected None detected
3.3.1 PE processing and Service life
None detected None detected
Regarding the emission control during manufacturing of PPA, ExxonMobil is not a manufacturer of this PFAS, so they do not control the emissions at that phase. Any discussion on emissions at the production stage is best to be presented by the manufacturer.
With regard to the emission control during the PE processing, all the ExxonMobil sites, both inside and outside the EEA (European Economic Area), apply Risk Management Measures to minimise the potential release of PPA, complying with the technical requirements requested by occupational and environmental legislation.
According to the latest available data of Plastics Europe (2022)14, plastic production in Europe is mainly related to packaging (39.9%), followed by building and construction items (19.8%), automotive components (19.8%), electrical and electronic equipment (6.2%) and household leisure and sports (4.1%).
With specific regard to hexafluoropropylene (HFP) and according to ECETOC (Centre for chemical safety assessment, 2005)15, the potential release to the environment during the service life of the plastic is expected to be negligible.
3.3.2 End of Life
Regarding waste management, energy recovery is the most frequent option to dispose of plastic waste (42.6%), followed by recycling (32,5%) and landfill (24.9%). More specifically, the evolution of the postconsumer plastic waste treatment is shown in Figure 3-4.16,17.
14 https://plasticseurope.org/wp-content/uploads/2022/10/PE-PLASTICS-THE-FACTS_V7-Tue_19-10-1.pdf 15 ECETOC JACC No. 48 https://www.ecetoc.org/wp-content/uploads/2014/08/JACC-048.pdf 16 https://www.europarl.europa.eu/news/en/headlines/society/20181212STO21610/plastic-waste-and-recycling-in-the-eu-facts-andfigures 17 https://plasticseurope.org/wp-content/uploads/2022/10/PE-PLASTICS-THE-FACTS_V7-Tue_19-10-1.pdf
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Figure 3-4: Evolution of post-consumer plastics waste treatment
According to this trend, the recycling option for plastic waste has experienced the highest growth in the period 2006-2020, either in terms of quantity (+117%) and investment (+5,7%). To achieve EU net-zero and circularity ambitions, if the right enabling conditions are in place, this trend would be expected to be consolidated during the next years, including the re-use option. A high quality secondary raw material is one that can be used in subsequent manufacturing processes in place of high-quality virgin material. For a secondary raw material to be used in place of virgin material, it would need to meet regulatory standards, such as limitations on substances harmful to health or the environment (JRC, 2020)18. With this regard, a high performance and good mechanical properties of plastic material, are also required to facilitate the use of mechanical recycled plastic and achieve the recycling target.
18 Quality of recycling: Towards an operational definition. JRC, 2020
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4. OVERVIEW OF POTENTIAL ALTERNATIVES
4.1 Introductory Note
The assessment of potential alternatives is based on the recommendations found in `ECHA's Guidance on Analysis of Alternatives under REACH Authorisations', published in 202119.
Basically, the workflow encompasses to first describe the functionality of the PFAS substance in the particular use, followed by the analysis of the performance of alternatives requires. The latter requires indepth experience of the characteristics of such alternatives to determine the extent to which such hypothetical candidates fall short in substituting away for the use of the PFAS substance.
This effort required in-house technical expertise within ExxonMobil to review the status of readiness for the suitability/unsuitability of potential alternative substances. Particular attention is paid to the research efforts in the past years. A literature search on further alternatives based on publicly available information has also been carried out. The analysis has been carried out in a scientifically sound manner and encompasses the following key assessed dimension:
Description of the functionality in the particular use and the technical feasibility criteria;
Efforts made to identify alternatives, including own R&D efforts, if any, and other publicly available information;
Identification and shortlisted alternatives;
Assessment of shortlisted alternatives, which includes: availability, safety considerations as technical and economic feasibility of the assessed alternative.
4.2 Annex XV Restriction Report proposed alternatives
In the Annex XV Restriction Report of the proposed PFAS restriction both boron nitride and polyethylene wax are suggested as viable alternatives to fluoropolymers as polymer processing aids of polyethylene.
Boron nitride was proposed as a processing aid and as an alternative to fluoropolymers in the 1990s. It could not be demonstrated to have the same efficacy as a processing aid and it does nothing to prevent or minimize die lip build up. Additionally, the commercial form of boron nitride raises concerns for dispersion issues due to particle sizes which can impact optical and mechanical properties. Boron nitride is available in a form of a powder which would be causing issues during feeding into PE reactors. Cost of boron nitride is significantly higher than that of fluoropolymers. The lack of performance relative to fluoropolymers as processing aids is evident in that it is not used in any known commercial polyethylene applications.
Polyethylene waxes would only serve to broaden the effective molecular weight of the polyethylene polymer in use. The lower molecular weight of the waxes may serve to modify melt viscosity, but as a result of their lower molecular weight and subsequent fewer molecular entanglements, the waxes are more likely to bloom from the polymer matrix and be available for migration into the article being packaged. The lower molecular weight species in the waxes are also more likely to exude from the molten polymer during extrusion causing more die lip build up than other alternatives.
Therefore, ExxonMobil differs with the dossier submitters and is of the opinion that both boron nitride and polyethylene waxes do not meet required technical specification and cannot be considered alternatives as processing aids.
19 How to apply for authorisation_v1_corrected (europa.eu)
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4.3 Availability of alternatives
ExxonMobil has evaluated different materials20 as potential fluoropolymer alternatives. Tests were conducted at additive loadings equal to or greater than those found for fluoropolymers. Results are shown in the table below. To date, an alternative material that provides the same level of melt fracture elimination and die lip build-up prevention as fluoropolymers has not been identified. Most materials evaluated did not eliminate melt fracture, and in an unexpected outcome, it was observed in many cases the neck-in (final film width relative to die opening width) was too high (resultant film was too narrow). None of the materials evaluated offered a complete 100% effective "drop-in" option to replace fluoropolymers in a commercial application.
Table 4-1: Materials evaluated as alternatives to fluoropolymers
Material Calcium stearate Zinc stearate Silicone Ethylene bis(stearamide) n,n' - ethylenebisoleamide Erucamide PE wax PAO Ethoxylated Sorbitan Monostearate Polyethylene glycol
CAS 1592-23-0 557-05-1 18023-33-1 110-30-5 110-31-6 112-84-5 68441-17-8 68649-11-6 9005-67-8
Number
25322-68-3
Note: MFE - melt fracture elimination
Outcome Poor MFE; high neck-in Poor MFE; high neck-in Incomplete MFE; high neck-in Poor MFE; high neck-in Poor MFE; high neck-in Poor MFE; high neck-in Poor MFE; high neck-in Incomplete MFE; high neck-in High neck-in
OK MFE; deficient to fluoropolymer in die lip build up
It is noted in Appendix E of the proposed restriction that "despite the identification of alternatives, 7 out of 8 respondents to the 2nd stakeholder consultation considered that alternatives to PFAS were not technically feasible as substitutes."21
4.3.1 Safety considerations related to alternatives
Table 4-2 reports the GHS (Global Harmonized System) classification of the alternatives tested as Polymer Processing Aids (PPA) substitute.
Table 4-2: GHS classification of the alternatives tested as PPA substitute
Material
Calcium stearate
CAS Number
1592-23-0
CLP
Annex VI
Not listed
GHS self-classification*
H319 (97.11%): Causes serious eye irritation [Warning Serious eye damage/eye irritation]
20 ExxonMobil's proprietary information 21 Annex XV Restriction Report, Proposal for a Restriction, Per and Polyfluoroalkyl Substances (PFASs), European Chemicals Agency, 7 February 2023, Appendix E (page 148).
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Zinc stearate
557-05-1 Not listed
Silicone Ethylene bis(stearamide)
18023-33-1 110-30-5
Not listed Not listed
n,n' ethylenebisoleamide Erucamide
110-31-6 112-84-5
Not listed Not listed
PE (Poly-Ethylene) wax* PAO (Poly-alpha olefins)
68441-17-8 Not listed 68649-11-6 Not listed
Ethoxylated Sorbitan Monostearate Polyethylene Glycol
9005-67-8 Not listed 25322-68-3 Not listed
* according to PubChem database
H335 (100%): May cause respiratory irritation [Warning Specific target organ toxicity, single exposure; Respiratory tract irritation]22 H335 (73.44%): May cause respiratory irritation [Specific target organ toxicity, single exposure; Respiratory tract irritation] H400 (79.68%): Very toxic to aquatic life [Hazardous to the aquatic environment, acute hazard] H413 (58.51%): May cause long lasting harmful effects to aquatic life [Hazardous to the aquatic environment, long-term hazard]23 H226 (100%): Flammable liquid and vapor [Flammable liquids]24
H312 (33.11%): Harmful in contact with skin [Acute toxicity, dermal] H315 (42.92%): Causes skin irritation [Skin corrosion/irritation] H317 (18.72%): May cause an allergic skin reaction [Sensitization, Skin] H319 (47.95%): Causes serious eye irritation [Serious eye damage/eye irritation] H335 (42.92%): May cause respiratory irritation [Specific target organ toxicity, single exposure; Respiratory tract irritation] Not Classified25
H315 (99.52%): Causes skin irritation [Skin corrosion/irritation] H319 (99.52%): Causes serious eye irritation [Serious eye damage/eye irritation] H335 (99.52%): May cause respiratory irritation [Specific target organ toxicity, single exposure; Respiratory tract irritation]26 Not Classified 27
H304 (99.9%): May be fatal if swallowed and enters airways [Aspiration hazard] H332 (95.14%): Harmful if inhaled [Acute toxicity, inhalation]28 Not Classified 29
Not Classified
Most of tested alternatives present short-term hazards for human health (Calcium stearate, Zinc stearate, Ethylene bis(stearamide), Erucamide and PAO, and one alternative (Zinc stearate) has been classified as chronic hazard for the environment.
22 https://pubchem.ncbi.nlm.nih.gov/compound/Calcium-stearate#section=Safety-and-Hazards 23 https://pubchem.ncbi.nlm.nih.gov/compound/11178#section=Safety-and-Hazards 24 https://pubchem.ncbi.nlm.nih.gov/compound/87409#section=Safety-and-Hazards 25 https://pubchem.ncbi.nlm.nih.gov/#query=110-30-5 26 https://pubchem.ncbi.nlm.nih.gov/#query=68441-17-8 27 https://pubchem.ncbi.nlm.nih.gov/compound/24847855#section=Safety-and-Hazards 28 https://pubchem.ncbi.nlm.nih.gov/compound/530173#section=Safety-and-Hazards 29 https://echa.europa.eu/it/information-on-chemicals/cl-inventory-database/-/discli/details/64127
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In response to the evaluation of potential alternatives, 90%30 of the downstream converting companies surveyed have undertaken efforts to identify potential alternatives to fluoropolymer used as a polymer processing aid in polyethylene. Of the companies that have identified an alternative and have tested the alternative, only 22% had partial success. The primary explanation for the alternative not being successful was the processing time was not comparable with the standard (too short) and the alternative did not meet quality requirements. Furthermore, the majority of companies noted that without a processing aid that matches the performance and properties of the fluoropolymer they cannot achieve the current film properties and the productivity of the process, further commenting that it was possible for films and finished packaging material to be reformulated, but such reformulation is not trivial to implement in the market of packaging.
4.4 Summary
If fluoropolymer processing aids are restricted for use, polyethylene producers could make polymers that are easier to process but would have poorer mechanical properties. Weaker mechanical performance would require thicker films and parts to have the same mechanical performance, increasing the amount of plastic used as well as increasing the energy required to transport articles and consumer goods, which can potentially lead to increased plastic waste. Weaker polymers would also limit the amount of mechanically recycled plastic that can be viably incorporated into a finished article. Polyethylene with high performance and good mechanical properties facilitates the use of mechanical recycled plastic.
30 Based on third-party anonymous survey conducted on behalf of the ExxonMobil
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5. SOCIO-ECONOMIC ANALYSIS
5.1 Introductory Note
This socioeconomic impact assessment compares two scenarios, the `continued use scenario' and `nonderogation scenario':
The `continued use scenario' considers a scenario whereby requested derogations for uses are granted (i.e. the company can `continue using' fluoropolymers where required), which means that the use of fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE), can continue. The continued use scenario does not assume that all uses will continue indefinitely, and
The `non-derogation scenario' considers a scenario whereby the restriction is implemented in its current form, and i.e. no derogations will be applicable to the use of fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE)
From a geographical scope, emphasis has been placed predominantly upon describing the nature of impacts inside the EEA. This is based on clear information from ECHA's original SEA restrictions guidance, which highlights that "In setting the geographical coverage and undertaking the assessment of impacts, it should be kept in mind that the final comitology decision... on whether or not to grant an authorisation will most likely focus mainly on impacts inside the EU. As a consequence, it is recommended that the emphasis be placed on describing and possibly quantifying what happens inside the EU"31
Whilst the key focus of the SEA is considered to be EEA society as a whole, information is also provided regarding higher level direct impacts to ExxonMobil and its customers. This is in order to provide clarity regarding wider downstream and societal impacts. For example, in certain instances, direct impacts to ExxonMobil can also be associated with indirect impacts that will impact EEA society more widely. Such instances include direct job losses to ExxonMobil within the EEA associated with the non-derogation scenario having an indirect effect on unemployment more widely within the EEA.
It is also noted that whilst efforts have been made to quantify impacts where possible, the analysis of impacts is also described qualitatively.
ExxonMobil understands that the Annex XV restriction proposal it itself presented mainly in qualitative terms. For example, the restriction proposal highlights that "benefits to human health are evaluated qualitatively as data is limited, or missing, to assess (i) the hazard of many of the individual PFASs".
Importantly, the proposal also highlights that "as specific information on costs of a ban of PFASs for the different actors associated with the addressed uses was scarce and mainly qualitative, the derogations and their duration were mainly based on the availability and applicability of alternatives to PFASs". ExxonMobil wishes to add that whilst the scope of applicable derogations to ExxonMobil within the restriction proposal is limited, significant information has been provided in the above analysis of alternatives which conclusively highlights the significant lack of technical and economic feasibility for substitution of fluoropolymers over a series of timeframes (associated with each of the uses in question). In this regard, the current SEA is provided to further support ExxonMobil's requests for derogations as summarised in Section 6 of this report.
31 ECHA (2008): Guidance on Socio-Economic Analysis - Restrictions Available at: https://www.echa.europa.eu/documents/10162/2324906/sea_restrictions_en.pdf/2d7c8e06-b5dd-40fc-b646-3467b5082a9d.
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5.2 Continued use scenario (aligned with preferred derogations) 5.2.1 Introduction and scenario definition
Regarding the use of processing aids, the PFAS restriction proposal includes a specific derogation for the use of polymerisation aids in the production of polymeric PFASs until 6.5 years after EiF. This derogation proposal does not cover the use of PPA in the processing of PE materials. As discussed in section 4, there are currently no technically feasible alternatives available to substitute FP as PPA. This concern is further confirmed by the stakeholder consultation mentioned in Annex E of the restriction proposal, regarding to the production of plastic films for packaging applications. A wider derogation would be required to ensure that PE materials meeting high technical standards, can be produced and imported in the EEA. The proposed time un-limited derogation would thus be as below:
The use of fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE).
5.2.2 Market and business trend considerations
According to Plastic Europe (2022)14 European sales of PE experienced a decrease in 2020, followed by rebound in 2021 as production increased to 57.2 million tonnes in 2021, which included a 12.4% of plastic production from polymerisation and production of mechanically recycled plastics. Of the total volume, PE Low Density, PE-Linear Low Density represented 14.7% (8,41 million tons/year), while the PE-High Density, PE-Medium Density represented 9,3% (5,32 million tons/year). PE accounted for a total share of 24% (13,73 million tons/year). Figure 5-1 shows the European production of PE in 202114
Figure 5-1: European production of PE in 2021
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5.2.3 Risks associated with continued use
As described in section 3, both the PVDF and the PVDF-HFP used as PPA in the processing of PE by ExxonMobil, meet the criteria of PLC. While the investigation of potential emission during the manufacturing process is out of the scope of this document, ExxonMobil applies the Risk Management Measures during the processing of PE to minimise and eliminate any release of PPA. Considering the low concentration of PPA remaining in the finished PE articles and the low probability of release of PPA from PE matrix during the service life, the risk for human health and environment associated with continued use of PVDF and the PVDF-HFP as PPA, is considered negligible.
5.3 Non-derogation scenario
5.3.1 Introduction and scenario definition
If the proposed derogation does not change and a derogation for the use of FP as PPA in the processing of PE is not included, it would mean ExxonMobil would not be able to supply PE with the required technical standards that the wide downstream users expected for their packaging applications. Following the standard timelines of regulatory processes, the PFAS restriction will come into force, a non-derogation scenario would then imply ExxonMobil is not able to use FP in the processing of PE immediately once the restriction enters into force. The use of FP as processing aids allows PE with narrow molecular weight distributions and high molecular weights to be successfully processed giving commercially favourable production yields. If fluoropolymer processing aids were not derogated, ExxonMobil may be forced to use a converter to process these high performing polyethylene resins, however this would slow the production output rates resulting in the following consequences:
Limiting production capacity requiring additional capital investment to meet consumer demand, and proportionally more energy consumed per finished part.
Requiring much higher processing temperatures which risks the degradation of PE and subsequently poorer performance.
5.3.2 Societal costs associated with a non-derogation scenario
5.3.2.1 Impacts for ExxonMobil
Given the significant market share of ExxonMobils PE a supply disruption could possibly result which would impact the production and packaging of items in a number of industries and sectors. Additionally, it would be expected to have increased costs associated with operations, such as but not limited to energy costs.
5.3.2.2 Impacts on plastic usage
According to ExxonMobil internal data, the use of high-performance PE, which is produced by adding FP in the processing, has allowed an average reduction of film thickness across 30 film segments of 2-3% per year as from year 2010.
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In 2021, this performance improvement has enabled the film value chain to avoid approximately 1.3 million tons of global plastic consumption when compared to year 2010.32 It is without doubt that a ban on the use of FP as an aid in the production of PE materials would jeopardize this significant saving in plastic consumption and would run counter to the objectives of the EU plastics strategy which supports more sustainable and safer consumption and production patterns for plastics.
According to the latest available data of Plastics Europe (2022)33, in Europe the plastic production is mainly related to packaging (39.9%), followed by building and construction items (19.8%), automotive components (19.8%), electrical and electronic equipment (6.2%) and household leisure and sports (4.1%).
It should be noted that in plastic recycling, high performance and good mechanical properties of the plastic material are also required to facilitate the use of mechanically recycled plastic and achieve the recycling target. Therefore, as noted by the JRC report on quality of recycling 34, a high-quality secondary raw material is one that can be used in subsequent manufacturing processes instead of the high-quality virgin raw material. Equally important is that to use a secondary raw material instead of virgin material, it would be necessary to comply with regulatory standards, such as the limitations of substances harmful to health or the environment.
5.3.2.3 Impacts to downstream stakeholders
The main impacts in such a scenario will be for ExxonMobils PE customers, which can be directly related to the packaging industry and their customers, construction sectors, automotive industry, manufacturers of electrical and electronic equipment and consequently the general public and end-users of the associated items. A ban in the use of FP as processing aid in the production of PE materials could have significant impact in the operations of downstream users relying on ExxonMobils supply, which would have to stop as the restriction proposal enters into force. Given the significant market share of ExxonMobils PE a supply disruption could possibly result which would impact the production and packaging of items in a number of industries and sectors.
32 ExxonMobil internal data 33 https://plasticseurope.org/wp-content/uploads/2022/10/PE-PLASTICS-THE-FACTS_V7-Tue_19-10-1.pdf 34 Quality of recycling: Towards an operational definition. JRC, 2020
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6. SUMMARY
Processing aid is a general term that refers to several different classes of materials used to improve the processability and handling of high-molecular-weight polymers. ExxonMobil uses Polymer Processing Aids (PPA) consisting of Fluoropolymers in the processing of Polyethylene (PE) materials. PE is then globally supplied to end users for different applications including the European Economic Area (EEA).
By adding the PPA in low concentration (below 1000 ppm), the PE materials is prevented from forming "melt fracture". This improvement translates into higher mechanical performances, meeting the technical criteria and specifications of different end-use applications, and increases the durability and the recyclability of PE materials.
ExxonMobil has evaluated different alternatives to the use of FP as PPA. None of the materials evaluated offered a complete 100% effective option to replace fluoropolymers in commercial applications. This is aligned with the general conclusions provided by W. L. Gore & Associates during this public consultation35. Most of assessed alternatives did not eliminate melt-fracture, and in many cases the neck-in (final film width relative to die opening width) was too high, resulting in a film is too narrow. Despite the alternatives reported by the restriction proposal submitters, it is ExxonMobil's analysis shows that both boron nitride and polyethylene waxes do not meet the required technical specifications and cannot be considered alternatives as processing aids.
Both PE and FP processing aid meet the OECD definition of Polymer of Low Concern (PLC). FP are demonstrated not to break down into smaller PFAS molecules under normal environmental exposure. FP are unlikely to migrate from PE and along with its very high molecular weight (> 1000 daltons) make FP not bioavailable and a nondispersive application.
The use of PE is often seen as more favourable in packaging than alternatives such as metal, paper, or glass. High performance PE, which requires FP as a processing aid allows for significantly reduced packaging weight and has greater ability to incorporate mechanically recycled polymer. FP facilitate the use of mechanically recycled polymer.
In the current non-derogation scenario, ExxonMobil would not be able to supply PE with the required technical standards that the wide downstream users expected for their packaging applications. Following the standard timelines of regulatory processes, the PFAS restriction will come into force, a non-derogation scenario would then imply that ExxonMobil is not able to use FP in the processing of PE immediately once the restriction entry into force.
In a non-derogation scenario, a significant impact is expected for ExxonMobils customers of PE materials, such as the packaging industry and their customers, construction sector, automotive industry, manufacturers of electrical and electronic equipment and the general public or end-users of the associated items. Given the significant market share of ExxonMobils PE a supply chain disruption could possibly result as there would be insufficient product available to satisfy all customers' needs.
It is well demonstrated that the use of FP as processing aid in the production of PE has enabled the PE film value chain in 2021 to avoid approximately 1.3 million tons of global plastic consumption when compared to year 2010. A ban on the use of FP as an aid in the production of PE materials would jeopardize this significant saving in plastic consumption and would run counter to the objectives of the EU plastics strategy.
35 PFAS restriction proposal_Pt. 13, comments 4289
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As a conclusion, and considering the high difficulty in identifying an alternative to fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE), ExxonMobil would request that a time un-limited derogation be included as per the wording below:
The use of fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE). Nevertheless, work on alternatives is ongoing, in an effort to improve the environmental footprint of the products, along with the overall performance of Polymer Processing Additives (PPA) used in the processing of polyethylene (PE). As such, and to capture the possibility that an alternative is identified in the future, the validity of the time-unlimited derogation can be re-evaluated at regular intervals, depending on the status and availability of alternative additives. This report details the use fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE), as well as the required technical feasibility criteria and an overview of potential alternatives. Potential for substitution are discussed, as are the safety considerations. The report concludes with a socio-economic analysis which covers both the scenario where use continues, and that where the no derogation applies.
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APPENDIX 1: POLYETHYLENE WITH FLUOROPOLYMER SAFETY POSITION PAPER
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An Advocacy Case for the Continued Use of Fluoropolymers as Polymer Processing Aids in Polyethylene
Authors: Dr. Allison L. Isola, Senior Toxicologist, ExxonMobil Biomedical Sciences, Inc. Dr. Cynthia A. Mitchell, Principal, Regulatory Compliance Advisor, ExxonMobil Technology and Engineering Company Dr. David M. Simpson, Senior Polymer Advocacy Advisor, ExxonMobil Product Solutions Company Ing. Severine Beauchet, Global Sustainability and Regulatory Affairs Manager Fluoropolymers, Arkema Corporation
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DOCUMENT BOUNDARY
This document discusses the safe use of polyethylene with fluoropolymer added as a polymer processing aid. Its scope is defined as the processing of polyethylene into finished articles and the use of those articles under normal conditions in their intended applications. End-of-life scenarios are outside the scope of this document and are not included for consideration.
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EXECUTIVE SUMMARY
In early 2023, 5 EU member states released a REACH Article XV Restriction Proposal to significantly restrict the use of per- and polyfluoroalkyl substances (PFAS) in many applications. One of the specific applications proposed for restriction is the use of fluoropolymers as polymer processing aids in polyethylene.
This document will show that:
- Polyethylene meets the OECD definition of a Polymer of Low Concern (PLC). - The fluoropolymers used as polymer processing aid meet the OECD definition of Polymer of Low
Concern (PLC) - Fluoropolymers used as polymer processing aids do not break down into smaller PFAS molecules
under normal environmental exposure. - Fluoropolymers are unlikely to migrate from polyethylene and are of very high molecular weight
(>> 1000 daltons), and therefore are not bioavailable, making this a nondispersive application. - Boron nitride and polyethylene wax, alternatives currently suggested for use instead of
fluoropolymers, do not have the same level of application effectiveness and potentially have their own hazards. - High performance polyethylene, which typically requires fluoropolymer as a processing aid allows for significantly reduced packaging weight and has greater ability to incorporate mechanically recycled polymer. - Fluoropolymers facilitate the use of mechanically recycled industrial or post-consumer polymer.
As a conclusion, and considering the high difficulty in identifying an alternative to fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE), ExxonMobil would request that a time un-limited derogation be included as per the wording below:
The use of fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE)
Nevertheless, work on alternatives is ongoing, in an effort to improve the environmental footprint of the products, along with the overall performance of Polymer Processing Additives (PPA) used in the processing of polyethylene (PE). As such, and to capture the possibility that an alternative is identified in the future, the validity of the time-unlimited derogation can be re-evaluated at regular intervals, depending on the status and availability of alternative additives.
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POLYETHYLENE: A POLYMER OF LOW CONCERN
Assessment of polyethylene as a Polymer of Low Concern (PLC)
Specific, widely accepted assessment criteria for polymers of low concern (PLCs) have been described previously [1] and are based on factors that have been determined to be predictive of potential health and environmental hazards of polymers. Here, we compare the assessment criteria to the characteristics of a polyethylene polymer to determine if they satisfy the requirements to be considered a PLC. The polymer characteristics assessed here are representative of a barefoot (additive-free) polyethylene polymer, more specifically ethylene hexene copolymers (CAS# 25213-02-9). For this class of polyethylene, the terminology in Table 1 applies.
Name
Description
VLDPE, mVLDPE, ULDPE
Metallocene-catalyzed very low
density polyethylene
LLDPE, mLLDPE
Linear low density Polyethylene,
metallocene catalyzed LLDPE
Table 1. Polyethylene Description and Density Range
Density Range (g/cc) 0.905 - 0.915
0.915 - 0.940
Polymer Structural and Elemental composition The polymer composition criterion requires that the structure and elemental composition of the polymer be identified. The polymer must have a Chemical Abstracts [CAS] number and must have C, H, Si, S, F, Cl, Br or I covalently bound to C.
Polyethylene satisfies the PLC criterion of polymer composition. Ethylene, the simplest of olefins (CH2=CH2), is polymerized to form polyethylene homopolymer (CAS# 9002-88-4). Linear low density polyethylene (LLDPE) is produced by copolymerization of ethylene with alpha-olefins such as 1-butene, 1-hexene, and 1-octene as the most common comonomers. LLDPE consists of long polymer chains with short chain branches of ethyl, n-butyl, and n-hexyl groups respectively. The structure of LLDPE produced by the copolymerization of ethylene with 1-hexene (CAS# 25213-02-9) is provided in Figure 1.
Figure 1. Structure of LLDPE formed by the copolymerizarion of ethylene with 1-hexene
Elemental requirements in order to be a PLC differ across jurisdictions, however, consistently polymers containing only Carbon and Hydrogen atoms are considered of low concern. Polyethylene only contains these elements and are thus considered to satisfy this PLC criteria across jurisdictions.
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Molecular weight (MW), number average molecular weight (Mn), MW distribution (MWD), and % oligomer <1000 Da Polyethylene is one of the most commonly used polymers for food containers and packaging thus it has been evaluated for safety in various publications [2 - 6]. Polyethylene is created from ethylene and is commonly polymerized with comonomers of 1-butene, 1-hexene, or 1-octene of varied content. The oligomers found in polyethylene consist of a mix of linear and branched structures, saturated and unsaturated hydrocarbons [2]. Several C6 linear low density polymers (LLDPE) were characterized employing High Temperature Gel Permeation Chromatography. The instrument was equipped with a multiple channel band filter based Infrared detector ensemble IR45 (PolymerChar GPC-IR).The number average molecular weight of these copolymers varied from approximately 20,000 to 50,000 Da. The average molecular weight of these copolymers ranged from approximately 50,000 to 116,000 Da and the molecular weight distribution (Mw/Mn) was on average 2 to 3. The standard test method to evaluate mid to high molecular weight polymers was modified to evaluate the trace amounts of substances including oligomers < 1000 Da. The standard deviation of the test method is about 0.2. The measured samples contained material < 1000 Da ranged from 0.3 to 0.7 % depending on grade and measured Mn. Material < 500 Da ranged from 0.2 to 0.4 % also dependent upon grade and measured Mn. A representative C6 linear low density copolymer at the low end of the molecular weight range is provided in Figure 2. These results meet the OECD Polymer of Low Concern Criteria (< 5% for < 1000 Da oligomers, < 2 % for < 500 Da oligomers).
Figure 2. A linear low density polyethylene copolymer (LLDPE) molecular weight distribution from high temperature gel chromatography.
Reactive functional groups and RFG ratio to MW A reactive functional group (RFG) is defined as a chemical moiety that can be reasonably anticipated to undergo a chemical reaction. Substances containing a high concentration of RFGs (or high RFG ratio to
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MW) can be associated with human health hazards and environmental effects. Polyethylene does not contain any RFGs, thus no RFG ratio to MW, and therefore satisfies this assessment criteria to be considered a PLC.
Low MW leachables Low molecular weight leachables are molecules that have the ability to migrate out of the polymer. Because the polyethylene assessed here contains no additives, the substances with the potential to migrate could be residual monomers or oligomers or other chemicals used in the manufacturing process such as catalyst residues. Presence of these substances in the PE polymer would be a result of incomplete polymerization of monomers (in this case ethylene and 1-hexene), or from possible degradation that can occur in normal processing.
These LMW leachables are important to understanding the potential hazard to health and the environment due to the migration potential out of the polymer, potentially capable of crossing biological membranes, and the ability to interact with biomolecules.
It has been provided that polymers with < 1 % Mw < 1000 Da and low water extractivity are not capable of causing systemic effects [7]. By the GPC-4D results noted above, the content of material < 1000 Da is less than 1 %.
Further, in a migration experiment, the concentration of oligomers < 1000 Da found to migrate in a 95 % ethanol solution at 40 oC for 10 days was < 160 ppm for a worst-case linear low density polymer. This would be considered a worst-case type of LLDPE sample for a migration experiment due to the relatively low density (0.908 g/cc) and number average molecular weight (Mn) (approximately 30,000 Da) compared to other LLDPEs in this class.
Residual monomer content is also important in determining if a material qualifies as a PLC. Studies on LLDPE were performed and showed minimal migration of monomers. Briefly, the specific migration of 1hexene in the same polymer by total immersion in rectified olive oil with exposure conditions of 10 days at 40 oC (migration simulants and conditions as detailed in EU Regulation No 10/2011) was <0.5 ppm. A range of LLDPE polymers were tested under the same conditions and all were less than 1 ppm or registered as a non-detect. The specific migration limit given in EU Regulation No 10/2011 for 1-hexene is 3 mg/kg of foodstuff. Migration simulants and conditions as detailed in EU Regulation No 10/2011 were used. Additionally, in a safety review, PE was evaluated, and no residual ethylene is detected in PE due to the manufacturing process removal, additionally, catalyst residuals of high-density (low-pressure) Polyethylene can be reduced to 0.002% to 0.003% by washing [3].
Typically, low weight molecular leachables such as catalyst residues are at sub-impurity (~0.5 ppb) levels in PE, are thus not of concern. Polyethylene satisfies the PLC criterion for low MW leachables.
Water and lipid solubility and the octanol-water partition coefficient Water solubility is a characteristic of a substance that determines the extent to which it will dissolve in water. According to the OECD, polymers with an intermediate water solubility value (10-10,000 mg/L) may pose a health concern when compared to polymers with low water solubility (<10mg/L) show low potential for health concerns [8]. Unlike water-soluble polymers such as polyethylene glycol, polyacrylamides, polyacrylic acid copolymer, and polyvinyl alcohol, PE is not soluble in water. PE is an
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inert material and has been shown to have negligible degradation and weight loss when kept in moist soil for up to 32 years [9].
The lipid solubility, or lipophilicity, of a substance is associated with the octanol-water partition coefficient (Kow). A substance with a high Kow has a higher lipophilicity and a higher potential to bioaccumulate or bioconcentrate, resulting in a potential impact on human health and the environment. For high molecular weight materials, such as PE, the molecular weight is too high to partition into lipid, which is the purpose of using octanol as a surrogate measure. Additionally, any measured or calculated value much higher than a ~ log(Kow) value of 10 is prone to large errors.
Therefore, the water and lipid solubility of polyethylene satisfies the criteria for a polymer of low concern.
Stability Abiotic stability PE is highly stable under abiotic conditions. Multiple characteristics of PE contribute to its stability; insolubility in water, hydrophobicity due to its linear carbon atom backbone, degree of crystallinity and high molecular weight [10 - 12].
Biotic stability: aerobic, anaerobic, and in vivo In order to understand the stability of PE under biotic conditions, polymers are assessed by the degradability in the presence (aerobic) or absence (anaerobic) of oxygen both inside (in vivo) and outside (in vitro) of an organism. In vivo degradation utilizes biological processes involving bacteria, enzymes and oxidants present within the organism. Polyethylene is biologically inert and is not readily biodegradable under aerobic or anaerobic conditions. There is a general understanding in the literature that the biodegradation process of PE is extremely slow, and that the utilization of PE by microorganisms is limited by the high molecular weight, insolubility and lack of functional groups [13].
Thermal stability When used as intended and under normal use conditions are thermally stable. The temperature at which the rate of polymerization and depolymerization are equal is the ceiling temperature. Above this temperature, depolymerization will occur and the polymer reverts to monomer. For polyethylene, this temperature is 610 oC [14]. Typical processing temperatures for LLDPE indicated here range from 200 to 220 oC with a few exceptions where processing temperatures can approach 240 oC. This data supports thermal stability under typical use conditions and are therefore unlikely to depolymerize under conditions of normal use.
Therefore, the stability (abiotic, biotic and thermal) of polyethylene satisfies the criteria for a polymer of low concern.
Conclusion
This review has summarized data for polyethylene products that support the conclusion that polyethylene satisfies the requirements in order to be considered a polymer of low concern. The data reviewed here supports that polyethylene product characteristics are well defined and should be considered of low hazard to human health and the environment.
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[7] BIO by Deloitte. 2015. Technical assistance related to the review of REACH with regard to the registration requirements on polymers Final report prepared for the European Commission (DG ENV), in collaboration with PIEP.
[8] [OECD] Organisation for Economic Co-operation and Development. 2009. Data analysis of the identification of correlations between polymer characteristics and potential for health or ecotoxicological concern. OECD Task Force on New Chemicals Notification and Assessment, Expert Group Meeting on Polymers; 2007 Mar; Tokyo, Japan. Paris (FR).
[9] Otake Y, Kobayashi T, Asabe H, Murakami N, Ono K (1995) Biodegradation of low density polyethylene, polystyrene, polyvinyl chloride, and urea formaldehyde resin buried under soil for over 32 years. J Appl Polym Sci 56:1789-1796.
[10] Restrepo-Florez JM, Bassi A, Thompson MR (2014) Microbial degradation and deterioration of polyethylene-a review. Int Biodeterior Biodegradation 88:83-90.
[11] Tokiwa Y, Calabia B, Ugwu C, Aiba S (2009) Biodegradability of plastics. Int J Mol Sci 10:3722-3742.
[12] Webb HK, Arnott J, Crawford RJ, Ivanova EP (2013) Plastic degradation and its environmental implications with special reference to poly(ethylene terephthalate). Polymers 5:1-18.
[13] Juan-Manuel Restrepo-Flrez, Amarjeet Bassi, Michael R. Thompson, Microbial degradation and deterioration of polyethylene - A review, International Biodeterioration & Biodegradation, Volume 88, 2014, Pages 83-90, ISSN 0964-8305, https://doi.org/10.1016/j.ibiod.2013.12.014.
[14] Stevens, M.P. (1999). Polymer Chemistry an Introduction (3rd ed.). New York: Oxford University Press. pp. 193-194.
8
FLUOROPOLYMER: A POLYMER OF LOW CONCERN
96% of commercial fluoropolymers meet the OECD criteria on `polymers of low concern' and are not expected to pose environmental and human health concerns (or hazard) based on the current available data [1, 2]. This include PVDF and many other fluoropolymers. The PLC criteria include physicochemical properties, such as molecular weight, which determine bioavailability and warn of potential hazard. PLC criteria were developed over time within regulatory frameworks around the world as an outcome of chemical hazard assessment processes, which identified physical-chemical properties of polymers that determine polymer bioavailability and thereby report a polymer's potential hazard. For example, many of the physicochemical properties, such as MW, limit the ability of a polymer to cross the cell membrane and therefore limit its bioavailability [3]. An OECD expert group on polymers reached consensus on these criteria and their respective metrics, documenting the data required for a polymer to qualify as a PLC to human health and the environment (OECD, 1993). Subsequently, an additional OECD work group concurred that PLC have "insignificant environmental health and human health impacts" (OECD, 2009). All data to prove the compliance of fluoropolymers and especially PVDF with OECD PLC criteria [1,2] have been generated and are available in a peer-reviewed published article.
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Leachables and Monomer content
The SEC characterization determined the weight fraction below 1000Da to be under 1% maximum and more generally below 0.5% +/- 0.3%. No change of this fraction is significantly seen after different kind of ageing conditions (heat, in water, etc). Water used for ageing shows no detection of Mw<1000 Da with NMR 19F with a limit of detection of less than 500 ppm. Therefore, low molecular weight oligomers that might be present in the polymer are not extractable.
This was confirmed as polymer pellets have no active leachables as tested by USP Class VI and ISO 10993. Additionally, residual monomers were detected under 50 ppb in all polymer samples tested (different grades of homopolymers and copolymers) by Dynamic or Static HS-GC/MS (method selected can change depending on the grade tested). The headspace is generated at 150 C during 20min. The limit of quantification may vary depending on the sample characteristic and the chosen technique adapted to this sample. Several samples demonstrate even a residual monomer content <10pbb w/w. Using the limit of quantification instead of actually detected monomer the ratio of limit of quantification to molecular weight is estimated at or below 10-13.
Aging in different conditions
No degradation of the polymer was observed nor leach-out in the liquid environment (measured by GPC analysis) in air, water, high temperature, in N2 atmosphere, in acidic conditions, under UV exposure, for 4 months.
Samples of different grades of PVDF (pellets and transformed pieces), have been tested after 1000h UV exposure. The samples have been tested by SEC (similar method than the one mentioned for Molecular Weight characterization). No significant difference before/after ageing has been observed in molecular weight distribution. The same conclusion for the % of Mn<1000 Da, in both cases the value was <0.25 %. The product remains stable and no leachables are generated. Physical properties were unchanged as well.
Similar conclusions are observed after ageing in different conditions of pellets and test pieces for homopolymer and copolymer: 744h @90 C in air, 744h@140 C in air, 742h @90 C in dinitrogen, 744h @60 C in HCl, 744h @90 C for homopolymers in water and @60 C for copolymer in water. The cited testing conditions have demonstrated the stability of the polymer at high T and in oxidative, acidic environment. In each case, the % of Mw<1000 Da is below 0.25 %. There was no difference in the mass distribution observed when we compare before and after ageing. In addition, when tested in water, the water used for ageing shows no detection of Mw<1000 Da with NMR 19F with a limit of detection of less than 500 ppm.
The hydrolysis resistance was demonstrated via the existence of the ISO10931 standard regarding Plastics piping systems for industrial applications -- Poly(vinylidene fluoride) (PVDF) -- Specifications for components and the system. The thermal degradation resistance has also been demonstrated by several references [4,5].
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Aerobic Biodegradability
We tested PVDF according to OECD Guideline 301F for 60 days and found no degradation of the polymer and no leach-out of smaller molecules in the environment. The small molecules have been tested in the environment of testing through SEC characterization
Anaerobic biodegradability
The product has been tested by a third party at 37C according to ASTM D5511 with cryogenic grinding products (<1mm), for 90 days, designed to represent more than 6 years of landfilling. As a result, no degradation and no leach-out of small molecules in the environment was observed. The small molecules have been tested in the environment of testing through SEC characterization
These recognized testing methods and associated results demonstrate the non-degradation of PVDF produced without the use of PFAS surfactants in the environment and no leach out of small molecules in the environment. Non degradation is a strong advantage during the use phase as it is a synonym of safety and durability. Non degradation means no release of small molecules during our product lifetime. This in turn reinforces the importance of managing its end of life.
Toxicology Testing
Toxicological information on homopolymer PVDF is available on the Japanese Existing Chemicals Database (National Institute of Health (NIHS)/Japan) as well as in a publication [6] The summary of a combined repeated dose toxicity and reproductive and developmental toxicity screening study and developmental toxicity (OECD guideline 422) in rats did not report any adverse effects after standard investigations conducted (haematobiochemical and urinary analyses including thyroid hormones, clinical thyroid hormones, clinical, functional and neurobehavioural battery, macroand microscopic examination of organs microscopic examination of organs) up to the highest dose tested orally (1000 mg/kg/d). The significant increase in relative and absolute pituitary weights in females given 1000 mg/kg/day was not considered adverse in the absence of histological abnormalities or effects on endocrine organs.
The second part of this study evaluated the reproductive capabilities of the animals (estrous cycles, sperm parameters, mating, conception...) as well as embryo development, parturition and also examined the parturition and also examined the litters. Exposure to the PVDF homopolymer did not have reproductive parameters of males and females, nor did it have any adverse effect on development. Therefore, the No Observed Adverse Effect Level (NOAEL) for systemic and reproductive/developmental for systemic and reproductive/developmental effects was set at 1000 mg/kg/d. This concentration is the maximum limit concentration that can be used in regulatory repeated toxicity and repeated toxicity and reproduction studies.
The genotoxic potential of homopolymeric PVDF was assessed in vitro using a bacterial reverse mutation assay mutation assay (Ames test) according to OECD 471 and a chromosomal aberration assay chromosomal aberration test in mammalian cells according to OECD 473. Both tests gave negative results with or without metabolic activation indicating the absence of genotoxic potential of PVDF.
PVDF is approved according to a list of particularly demanding international standards. These include, but are not limited to, the following :US Food contact - EU Food contact - ISO 10993 et USP Biocompatibility
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- NSF standard 61 for potable water systems
It has demonstrated the stability after a simulation of more than 6 years of landfilling (OECD Guideline 301F) with no degradation of the polymer and no leach-out of smaller molecules in the environment observed [1,2].
Ecotoxicology Testing
With respect to mobility, bioavailability and (eco)toxicity, PVDF is a polymer of high molecular weight and insoluble in water. The high molecular weight prevents the PVDF to penetrate cell membrane and so PVDF is not bioavailable.
Studies conducted on fluoropolymer in a polyethylene matrix in aqueous environments. LLDPE dosed with 1200 ppm PVDF (a typical formulation) was placed in moderate hard water and simulated seawater at ambient conditions. Even at the extent of the experiment (30 days), no detectable migration of fluoropolymer from the matrix (LOD 1 ppm, LOQ 2.5 ppm) was observed [7].
Timepoint
Moderate Hard Water
2 hours
None detected
1 day
None detected
3 days
None detected
7 days
None detected
10 days
None detected
20 days
None detected
30 days
None detected
Table 1. No detectable migration of fluoropolymer from LLDPE matrix
Simulated Seawater None detected None detected None detected None detected None detected None detected None detected
An assessment of bioaccumulation and mobility properties of PVDF was performed, by using the US EPA EPISUITE, a software recommended in ECHA Guidance [4].
Overall, it was found that as the number of monomer units in the chain increases, the LogKow and LogKoc values increase while the bioconcentration factors (BCF) values decrease.
No bioaccumulation is expected if there are more than 5 monomers units in the chain, since the molecules would be too big to cross biological membranes. As PVDF is insoluble in water, some ecotoxicological evaluation methods could not be performed. However, PVDF insolubility limits the mobility capacity of those polymers. With more than 2 monomers unit in the chain, PVDF is not expected to be mobile, where a Log Koc < 2 indicates mobility and Log Koc < 3 high mobility.
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References
[1] S. Korzeniowski and all - A Critical Review of the Application of Polymer of Low Concern Regulatory Criteria to Fluoropolymers II: Fluoroplastics and Fluoroelastomers - Integrated Environmental assessment and Management - htttps://setac.onlinelibrary.wiley.com/doi/10.1002/ieam.4646. [2] S. Korzeniowski and all - A Critical Review of the Application of Polymer of Low Concern Regulatory Criteria to Fluoropolymers II: Fluoroplastics and Fluoroelastomers -Supplemental Data - Integrated Environmental assessment and Management htttps://setac.onlinelibrary.wiley.com/doi/10.1002/ieam.4646 [3] Kostal, 2016; Lipinski et al., 2001; USEPA, 2012 [4] S. Zulfiqar and al. Study of the thermal degradation of polychlorotrifluoroethylene, poly(vinylidenefluoride) and copolymers of chlorotrifluoroethylene and vinylidene fluoride, In Polymer Degradation and stability 43(1994) 423-430 - Elsevier. [5] Laurence W. McKeen - Book - The Effect of Long Term Thermal Exposure on Plastics and Elastomers - 2014. [6] Bull. Natl Inst. Health Sci. 138, 33-39 (2020). [7] ExxonMobil data from tests conducted by third party lab.
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PURPOSE OF PROCESSING AIDS IN POLYETHYLENE PRODUCTION
Polyethylene is the world's largest volume thermoplastic product family. It is used daily in many applications that impact the lives of people around the world. Polyethylene applications include, but are not limited to flexible food packaging, rigid food packaging (bottles and containers), diaper and feminine care product backsheeting, collation shrink film, pallet wrap stretch film, stretch hood film, household and industrial chemicals (HIC) packaging, nonwoven fabrics, medium and heavy duty sacks, greenhouse films, geomembranes, pressure and non-pressure pipes.
Polyethylene has evolved since its discovery in the 1930s. Early resins, termed Low Density Polyethylene (LDPE) were highly branched molecules. This high branching content made LDPE easy to convert into usable articles, e.g. films, but made the polymer relatively weak in terms of mechanical properties. The process used to make these polymers was termed the "high-pressure" process because it required a very energy-intensive reactor environment of 30,000 to 50,000 psi. Subsequent versions of polyethylene - High Density Polyethylene (HDPE), created in the 1950s, Linear Low Density Polyethylene (LLDPE), created in the 1970s - were linear molecules (no long chain branching) which made them more difficult to convert into usable articles, but provided much improved mechanical properties. These improved mechanical properties allowed for significant reduction in the amount of polyethylene required for an application - commonly called "downgauging." The processes used to manufacture these molecules - slurry, solution, and gas-phase processes, required much less energy than the high pressure processes
The evolution of polyethylene continued into the 1990s and through current day with the development of high performance families made using metallocene-based and other single-site catalysts. The use of these catalysts allowed for the design of polyethylene with much higher performance in mechanical properties and continued downgauging of applications.
Table 1 shows the improvement in mechanical properties for films made from different polyethylene families, at approximately the same molecular weight (as measured by melt index). The trends show that overall toughness, and potential for less material usage in end-use applications, is improved at narrower molecular weight distributions.
PE Family
LDPE
HDPE
LLDPE
mLLDPE
Melt Index (g/10 min)
1.1
0.7
1.0
1.0
Density (g/cm3)
0.919
0.961
0.917
0.918
Dart Impact (g)
120
< 30
170
550
MD Tear (g)
270
10
310
220
TD Tear (g)
90
200
710
370
Puncture Energy (J)
2.1
---
3.4
5.5
MD Tensile Strength (MPa)
31
60
50
60
TD Tensile Strength (MPa)
24
31
47
60
Molecular Weight Distribution
Broad
Broad
Narrow
Very Narrow
Test Methods: Melt Index - ASTM D1238, Density - ASTM D792, Dart Impact - ASTM1709A, Tear - ASTM D1922, Puncture - ExxonMobil
Method, Tensile Strength - ASTM D882.
Table 1. Toughness properties of different polyethylenes [1].
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As noted above, the development of linear molecules created products with improved mechanical properties with more economic and environmentally-friendly processes. However, as also noted above, the linear nature of these molecules made them more difficult to convert into usable articles. Polyethylene is typically manufactured and sold as small pellets (nurdles), usually with 5 mm or less diameter. To convert these pellets into a usable article, they are melted, compressed and pushed through a relatively small opening called a die. The linear nature of these molecules means that their viscosity is not significantly impacted by shear rate, therefore when they are pushed through a die with a narrow opening at high shear, there is a large difference in the melt flow profile as shown in Figure 1.
Figure 1. Melt flow profile of linear molecules through a narrow opening. Molten polymer flows more easily in the center and tends to drag at the die interface. Eventually, the elastic nature of the polymer will cause the material at the die interface to "snap back" in the direction of flow. The resultant effect of this "snap back" is a surface imperfection called "melt fracture" which is not only visually unappealing, but also causes mechanical weak points in the article manufactured. An example of melt fracture in a film is shown in Figure 2.
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Figure 2. Example of melt fracture in polyethylene film (ExxonMobil photo). Melt fracture can occur in films, bottles, pipes and other applications. It is very important from a mechanical integrity standpoint as well as aesthetics, that we are able to convert polyethylene without melt fracture. In the 1960s, it was learned that the addition of fluoropolymers to polyethylene as additives in low concentrations could eliminate melt fracture in the fabrication of finished articles. The fluoropolymer "coated" the metal die wall and decreased the shear experienced by the polymer melt. Lower shear at the wall results in a more uniform melt flow as shown in Figure 3. Materials used to improve the processing of polyethylene became known as Polymer Processing Aids (PPA).
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Figure 3. Melt flow profile of polymer using a PPA.
The use of fluoropolymer processing aids allows for the processing of polyethylene with narrow molecular weight distributions and high molecular weights at favorable commercial output rates. If fluoropolymer processing aids are disallowed, a converter could theoretically process these high performing polyethylene resins but at either (1) excessively slow output rates which limits production capacity requiring additional capital investment to meet consumer demand, and proportionally more energy consumed per finished part; or (2) at much higher processing temperatures which risks the degradation of polyethylene and subsequently poorer performance.
If fluoropolymer processing aids are disallowed for use, polyethylene producers could make polymers that are easier to process, but would have poorer mechanical properties. Weaker mechanical performance would require thicker films and parts to have the same mechanical performance, increasing the amount of plastic used, increasing the energy required to transport articles and consumer goods, and potentially leading to increased plastic waste. Weaker polymers would also limit the amount of mechanical recycle plastic that can be viably incorporated into a finished article. Polyethylene with high performance and good mechanical properties facilitates the use of mechanical recycle plastic.
An additional application of fluoropolymers in polyethylene is to reduce the build-up of exuded material from molten polymer flows onto die surfaces, known in the industry as die lip build-up. Die lip build-up is commonly found to be low molecular weight polyethylene and/or additives that migrate from molten polyethylene. Through normal manufacturing conditions, it can aggregate at the die exit and eventually impinge on the molten flows causing undesired imperfections on the film surface, known in the industry as die lines. Die lines can affect the aesthetics of a film, making it unusable for packaging applications, and if severe enough, can negatively impact mechanical properties. To eliminate die lip build-up, operators must shut down their equipment for cleaning, which results in lost production and poorer process economics. Fluoropolymers in polyethylene help prevent die lip build-up by creating a "non-stick" surface coating on the die, as a result allowing operators to run their equipment for longer periods of time before cleaning.
The use of high performance polyethylene (incorporating fluoropolymer for processing) has allowed an average reduction of film thickness across 30 film segments of 2-3% per year from the year 2010. By the
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year 2021, this performance improvement enabled the film value chain to avoid approximately 1.3 million tons of plastic consumption from the 2010 reference [2].Reducing thickness, also known as downgauging, in product applications has many important impacts. First, we use less raw materials per package resulting in savings in natural resources and energy usage. Lighter packaging can also result in more packages per shipment resulting in energy savings in transportation. Polyethylenes with higher mechanical performance can make stronger packaging resulting in fewer package failures in shipping and handling with less product loss.
On 30 November 2022, the European Commission released a proposal on reducing packaging and packaging waste (PPWR) [6]. Within, there are goals of increasing recycle content from 10-35% in polyethylene in the year 2030 and increasing to 50-65% by the year 2040. It also states that "packaging should be designed, manufactured and commercialised in such a way as to allow for its re-use or highquality recycling, and to minimise its impact on the environment during its entire life-cycle and the life cycle of products, for which it was designed."[3]
Efficient mechanical recycling of post-industrial and post-consumer polyethylene film remains a challenge in the industry today in part due to the variability of incoming film feed streams. Different additive packages in different PE film sources, different viscosities, and variability in thermal degradation of the PE resin can make mechanical recycling more challenging. Previous studies have shown that both melt fracture elimination and pressure reduction are observed when PVDF is added to a recycled PE film process. This data suggests that film converters looking to increase recycled PE output, or the percent of recycled PE content in their process, can consider adding PVDF to increase their processing efficiency. [4]
A separate study by Seiler et al. has shown that if film converters are blending recycled polyethylene content with virgin polyethylene, they can consider increasing the ratio of recycled to virgin PE resin, and still produce a product that meets the performance requirements of a given application, by also adding PVDF to the process. PVDF can help increase the total output for a film converter so they can run more PE resin on the same equipment, without the need to invest in additional processing equipment. [5]
REFERENCES
[1] ExxonMobil data
[2] ExxonMobil data
[3] Regulation of the European Parliament and of the Council on Packaging and Packaging Waste, amending Regulation (EU) 2019/1020 and Directive (EU) 2019/904, and repealing Directive 94/62/EC.
[4] R. Lowrie, et al, The Effect of Fluorinated Thermoplastic Processing Aids in Film Processing of Recycled Polyethylene Resins, 2022 Plastics Industry Fluoropolymers Conference.
[5] D.A. Seiler, et al, Study of the Positive Effects Seen When Using Fluorinated Polymer Processing & Recycling Aids (PPRA) in Reprocessed LLDPE. 2022 SPE Polyolefins Conference.
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19
ALTERNATIVES
In the Annex XV Restriction Report for the proposed PFAS restriction, both boron nitride and polyethylene wax are suggested as viable alternatives to fluoropolymers as polymer processing aids.
Boron nitride was proposed as a processing aid and as an alternative to fluoropolymers in the 1990s. It could not demonstrated to have the same efficacy as a processing aid and it does nothing to prevent or minimize die lip build up. Additionally, the commercial form of boron nitride raises concerns for dispersion issues due to particle sizes which can impact optical and mechanical properties. Cost of boron nitride is significantly higher than that of fluoropolymers. The lack of performance relative to fluoropolymers as processing aids is evident in that it is not used in any known commercial polyethylene applications. Additionally, boron nitride has shown to have potential human health hazards [1].
Polyethylene waxes would only serve to broaden the effective molecular weight of the polyethylene polymer in use. The lower molecular weight of the waxes may serve to impact melt viscosity, but as a result of their lower molecular weight and subsequent fewer molecular entanglements, the waxes are more likely to bloom from the polymer matrix and be available for migration into the article being packaged. The lower molecular weight species in the waxes are also more likely to exude from the molten polymer during extrusion causing more die lip build up than other alternatives. Our tests (below) indicate that is ineffective in eliminating melt fracture.
ExxonMobil has evaluated several different materials [2] as potential fluoropolymer alternatives. Tests were conducted at additive loadings equal to or greater than those found for fluoropolymers. Results are shown the table below. To date an alternative material that provides the same level of melt fracture elimination and die lip build-up prevention as fluoropolymers has not been identified. Most materials evaluated did not eliminate melt fracture, and in an unexpected outcome, it was observed in many cases the neck-in (final film width relative to die opening width) was too high (resultant film was too narrow). None of the materials evaluated offered a complete "drop-in" option to replace fluoropolymers in a commercial application.
Material Calcium stearate Zinc stearate Silicone Ethylene bis(stearamide) n,n' - ethylenebisoleamide Erucamide PE wax PAO Ethoxylated Sorbitan Monostearate Polyethylene glycol
MFE - melt fracture elimination
CAS Number 152-23-0 557-05-1
18023-33-1 110-30-5 110-31-6 112-84-5
68441-17-8 68649-11-6 9005-67-8
25322-68-3
Outcome Poor MFE; high neck-in Poor MFE; high neck-in Incomplete MFE; high neck-in Poor MFE; high neck-in Poor MFE; high neck-in Poor MFE; high neck-in Poor MFE; high neck-in Incomplete MFE; high neck-in High neck-in
OK MFE; deficient to fluoropolymer in die lip build up
Table 1. Materials evaluated as alternatives to fluoropolymers. [ExxonMobil information]
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It is noted in Appendix E of the proposed restriction for this application that "[d]espite the identification of alternatives, 7 out of 8 respondents to the 2nd stakeholder consultation considered that alternatives to PFAS were not technically feasible as substitutes." [3]
REFERENCES
[1] M.M. Fiume, W. F. Bergfeld, et al, Safety Assessment of Boron Nitride as Used in Cosmetics, International Journal of Toxicology, Vol. 23, Issue 3, https://doi.org/10.1177/1091581815617793. [2] ExxonMobil information [3] Annex XV Restriction Report, Proposal for a Restriction, Per and Polyfluoroalkyl Substances (PFASs), European Chemicals Agency, 7 February 2023, Appendix E (page 148).
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SUMMARY
The Annex XV Restriction Report for the proposed PFAS restriction published on 7-February 2023 shows no derogation for the use of fluoropolymers as polymer processing aids (PPA) in polyethylene. The authors here have provided evidence that both polyethylene and the fluoropolymers used as a PPA in their production meet the OECD definition of Polymers of Low Concern. The use of fluoropolymers as PPA in polyethylene is not a dispersive application, i.e. there is not risk to the environment, humans, or wildlife because the fluoropolymer is not extracted from the polyethylene matrix under normal environmental exposure. Polyethylene mechanical properties have evolved and improved through the years allowing for the significant downgauging of packaging applications. Fluoropolymers make the conversion of polyethylene at high commercial rates possible, while saving energy and industrial investment. Intensive research efforts shown herein demonstrate that replacing fluoropolymers as a PPA is extremely difficult due to the unique properties that fluoropolymers bring to the application. The two alternatives cited in the restriction proposal are not as effective as fluoropolymers in melt fracture elimination, processability, or die lip build-up prevention. Neither are in commercial use today, although they have been commercially available for over 30 years. The authors strongly urge the Socio-Economic Assessment Committee to reconsider the proposed "no derogation" for fluoropolymers in PPA. The case has been made that fluoropolymers in polyethylene are not a safety hazard, are not bioavailable, are not easily replaceable, and are needed to achieve future sustainability targets. As a conclusion, and considering the high difficulty in identifying an alternative to fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE), ExxonMobil would request that a time un-limited derogation be included as per the wording below:
The use of fluoropolymers as Polymer Processing Additives (PPA) used in the processing of polyethylene (PE)
Nevertheless, work on alternatives is ongoing, in an effort to improve the environmental footprint of the products, along with the overall performance of Polymer Processing Additives (PPA) used in the processing of polyethylene (PE). As such, and to capture the possibility that an alternative is identified in the future, the validity of the time-unlimited derogation can be re-evaluated at regular intervals, depending on the status and availability of alternative additives.
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