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Safety, Hygiene, Disposal, Recycling of Fluoropolymer Films
8 Safety, Hygiene, Disposal, Recycling of Fluoropolymer Films 8.1 Safety, Hygiene, and Disposal of Fluoropolymer Films 8.1.1
Toxicology of Fluoroplastics
Fluoroplastics are chemically very stable and inert. However, they can produce toxic compounds if overheated. Precautions should be taken to remove any degradation fragments produced during the processing and fabrication of parts from them. Filled or compounded resins contain pigments, surfactants, and other additives to modify the properties of the polymers. These additives may present some hazards in the processing of the compounded resins. For example, aqueous dispersions of fluoropolymers frequently contain surfactants that may produce adverse physiological symptoms. Such hazards should be considered by themselves and in conjunction with fluoropolymers [1]. Safety information provided by manufacturers of the additives and the compounds should be consulted.
8.1.2
Thermal Behavior of Fluoroplastics
During usual processing, fluoroplastics are heated to high temperatures and degraded to some extent. The extent of degradation and the type of degradation products depend on variables, such as temperature, presence of oxygen, physical form of the article, duration of exposure to the temperature, and presence of additives. The products of decomposition of fluoropolymers fall into three categories: fluoroalkenes, oxidation products, and particulates of low molecular weight fluoropolymers. A major product of oxidation of PTFE is carbonyl fluoride that is highly toxic and hydrolyzes into hydrofluoric acid and carbon dioxide. At 450 C (842 F) in the presence of oxygen, PTFE degrades into carbonyl fluoride and hydrofluoric acid. At 800 C (1472 F), tetrafluoromethane is formed [1]. It is important to follow the recommendations and specifications of the
Applications of Fluoropolymer Films. DOI: https://doi.org/10.1016/B978-0-12-816128-9.00008-8 © 2020 Elsevier Inc. All rights reserved.
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Table 8.1 Maximum Continuous Use and Processing Temperatures of Common Fluoroplastics.
Polymer
Maximum Continuous Use Temperature ( C)
PTFE PFA FEP ETFE ECTFE PCTFE PVF PVDF
260 260 205 150 150 120 107 120
Typical Processing Temperature ( C) 380 380 360 310 280 265 193 230
suppliers of resins and parts. The Guide to Safe Handling of Fluoropolymer Resins, published by the Society of Plastics Industry, Inc. (see Table 8.1), specifies the maximum continuous use and processing temperatures for selected fluoroplastics [2]. Operation of processing equipment at high temperatures may result in the generation of toxic gases and particulate fume. The best known adverse effect on humans is polymer fume fever. This temporary flu-like condition, lasting typically 24 hours causes fever, chills, and occasionally coughs. It is further enhanced by tobacco smoking. It has been suggested that no health hazards exist, if the fluoroplastics are heated at temperatures below 300 C (572 F) [3]. Details on health hazards of decomposition products of fluoropolymers are in Refs. [2,3]. These risks prompted the establishment of exposure limits by various regulatory agencies (see Table 8.2) [4]. There are a number of measures that can be taken to reduce and control the exposure of personnel to monomers and decomposition products during the processing of fluoroplastics. These include ventilation, spillage cleanup, equipment cleanup, proper maintenance, and elimination of fire hazard. The personnel involved in the processing should wear protective clothing, maintain strict personal hygiene, and be made aware of incompatibility of specific materials [5]. Processing and fabrication to finished products may be hazardous, because often very high processing temperatures are used. Depending
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Table 8.2 Exposure Limit Types. Limit
Type
Source
PEL
Legal OEL
TLV
REL
US Code of Federal Regulations, Title 29, Part 1910 (29 CFR 1910) American Conference of Governmental Industrial Hygienists or NIOSH
NIOSH, National Institute for Occupational Safety and Health; OEL, occupational exposure limit; PEL, permissible exposure limit; REL, recommended exposure limit; TLV, threshold limit values. Source: Data from The Society of Plastics Industry, The Guide for Safe Handling of Fluoropolymer Resins, fourth ed., The Society of Plastics Industry, Washington, DC, 2005.
on a specific process, fumes may not be present in the amounts to affect the personnel, but protection, such as protective clothing and gloves, should be used [5].
8.1.3
Medical Applications of Fluoroplastics
Because of their inertness and relative purity, some fluoroplastics, for example, certain grades of PTFE, are used in medical applications. In such cases, Federal Food and Drug Administration most often reviews and approves the entire medical device, not its components, such as specific parts or resin used. Resin suppliers have strict specific policies about the use of their resins in medical devices [5].
8.1.4
Food Contact
Fluoropolymer resins are covered in the United States by Federal Food, Drug and Cosmetic Act, 21 CFR & 177.1380 & 177.1550 and in the European Union by the EC Directive 90/128 [5]. Several fluoroplastics, such as PTFE, PFA, and FEP, have been approved by FDA for contact with food. Additives, such as stabilizers, antioxidants, pigments, and others, must be approved to meet the food-additive regulations if they have no prior clearance [5].
142
APPLICATIONS
OF
FLUOROPOLYMER FILMS
8.1.5 Environmental Protection and Disposal Methods for Fluoroplastics The preferred methods for disposing fluoroplastics are recycling and reusing them. This subject is covered in more detail in Section 8.2. Landfilling of fluoroplastics is permitted in some cases by local regulations because they are environmentally stable and contain no harmful substances. This is justified if there is no valid recycling or incineration. When disposing suspensions and dispersions, solids should be removed from the liquids and then disposed off. Incineration can be used only when the incinerator is equipped by a scrubber for removing hydrogen fluoride, hydrogen chloride, or other acidic products of combustion. If the scrap contains pigments, additives, and solvents, it should be handled in a manner to meet local regulations for nonfluoropolymer ingredients. Some of the mixtures may require compliance with local regulations for hazardous materials [6].
8.2 Recycling of Fluoropolymer Films As with any raw material, recycling of fluoropolymers is very important. Most melt-processible fluoropolymers can be reprocessed in a fashion similar to other thermoplastics. With PTFE the situation is more complicated. Because of its high melt viscosity, it is difficult to remelt and mix with virgin material, particularly if it contains mineral fillers. Nevertheless, a significant amount of PTFE production scrap is being reused by cleaning, grinding, and using in that form for ram extrusion [7]. Currently, most PTFE scrap (mainly residues from machining operations) is processed by radiation, being exposed to doses up to 400 kGy to reduce the molecular weight drastically and to obtain micropowders [8]. The most common process employs an electron-beam processor, although gamma radiation can also be used. High-molecular-weight PTFE can also be converted into micropowders by thermal or shear degradation [8]. A process involving chemical recycling of PTFE using fluidized bed has been developed and patented [9,10]. The optimum temperature is in the range of 545 C 600 C (1013 F 1112 F), and the main decomposition products are tetrafluoroethylene (TFE), hexafluoropropene (HFP), and cyclo-perfluorobutane (c-C4F8). The most important advantages of this process are that the monomers produced can be purified before repolymerization, which
8: SAFETY, HYGIENE, DISPOSAL, RECYCLING
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FLUOROPOLYMER FILMS
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allows the production of a more valuable product, and that the process is continuous [9]. Another continuous process is the pyrolysis of PTFE scrap in a reactor heated by radiofrequency induction to 600 C 900 C (1112 F 1652 F). The products are TFE, HFP, and c-C4F8. The yield is in excess of 94% [11]. The use of reprocessed (reground) PTFE resin has limitations. For one thing, it exhibits markedly lower tensile strength and elongation than virgin PTFE. Reprocessed material creeps up to 25% more than virgin resin and contains twice the void content [12]. Because of porosity and larger number of voids, its dielectric strength is lower than that of the virgin PTFE. Thus the use of reprocessed material is limited to such applications, where cost is an important consideration and lower performance is sufficient for the application.
References [1] S. Ebnesajjad, P.R. Khaladkar, Fluoropolymers Applications in Chemical Processing Industries, William Andrew, Inc, Norwich, NY, 2005, p. 385. [2] The Society of Plastic Industry, Inc., The Guide to Safe Handling of Fluoropolymers Resins, The Society of Plastic Industry, Inc., 1988. [3] C.A. Rose, Environmental and Occupational Medicine, second ed., Little, Brown and Co., Boston, 1992, p. 373. [4] The Society of Plastics Industry, The Guide for Safe Handling of Fluoropolymer Resins, fourth ed., The Society of Plastics Industry, Washington, DC, 2005. [5] S. Ebnesajjad, P.R. Khaladkar, Fluoropolymers Applications in Chemical Processing Industries, William Andrew, Inc, Norwich, NY, 2005, p. 391. [6] S. Ebnesajjad, Fluoroplastics, Melt-Processible Fluoropolymers, vol. 2, William Andrew, Inc, Norwich, NY, 2003, p. 547. [7] B.J. Lyons, in: J. Scheirs (Ed.), In Modern Fluoropolymers, John Wiley and Sons, Ltd, Chichester, 1997, p. 340. [8] S.V. Gangal, in: H.F. Mark, J.I. Kroschwitz (Eds.), Encyclopedia of Polymer Science and Engineering, vol. 16, John Wiley and Sons, New York, 1989, p. 597. [9] C.H. Simon, Kaminski, Polym. Degrad. Stabil. 1998 (62) 1. [10] German Patent DE 4334015 A1. [11] I.J. Van der Walt, US Patent 6,797,913 to South African Energy Corporation, September 2004. [12] S. Ebnesajjad, V. Lishinsky, Machine Design, February 1999, p. 82.
Toxicology of Fluoroplastics
Fluoroplastics are chemically very stable and inert. However, they can produce toxic compounds if overheated. Precautions should be taken to remove any degradation fragments produced during the processing and fabrication of parts from them. Filled or compounded resins contain pigments, surfactants, and other additives to modify the properties of the polymers. These additives may present some hazards in the processing of the compounded resins. For example, aqueous dispersions of fluoropolymers frequently contain surfactants that may produce adverse physiological symptoms. Such hazards should be considered by themselves and in conjunction with fluoropolymers [1]. Safety information provided by manufacturers of the additives and the compounds should be consulted.
8.1.2
Thermal Behavior of Fluoroplastics
During usual processing, fluoroplastics are heated to high temperatures and degraded to some extent. The extent of degradation and the type of degradation products depend on variables, such as temperature, presence of oxygen, physical form of the article, duration of exposure to the temperature, and presence of additives. The products of decomposition of fluoropolymers fall into three categories: fluoroalkenes, oxidation products, and particulates of low molecular weight fluoropolymers. A major product of oxidation of PTFE is carbonyl fluoride that is highly toxic and hydrolyzes into hydrofluoric acid and carbon dioxide. At 450 C (842 F) in the presence of oxygen, PTFE degrades into carbonyl fluoride and hydrofluoric acid. At 800 C (1472 F), tetrafluoromethane is formed [1]. It is important to follow the recommendations and specifications of the
Applications of Fluoropolymer Films. DOI: https://doi.org/10.1016/B978-0-12-816128-9.00008-8 © 2020 Elsevier Inc. All rights reserved.
139
140
APPLICATIONS
OF
FLUOROPOLYMER FILMS
Table 8.1 Maximum Continuous Use and Processing Temperatures of Common Fluoroplastics.
Polymer
Maximum Continuous Use Temperature ( C)
PTFE PFA FEP ETFE ECTFE PCTFE PVF PVDF
260 260 205 150 150 120 107 120
Typical Processing Temperature ( C) 380 380 360 310 280 265 193 230
suppliers of resins and parts. The Guide to Safe Handling of Fluoropolymer Resins, published by the Society of Plastics Industry, Inc. (see Table 8.1), specifies the maximum continuous use and processing temperatures for selected fluoroplastics [2]. Operation of processing equipment at high temperatures may result in the generation of toxic gases and particulate fume. The best known adverse effect on humans is polymer fume fever. This temporary flu-like condition, lasting typically 24 hours causes fever, chills, and occasionally coughs. It is further enhanced by tobacco smoking. It has been suggested that no health hazards exist, if the fluoroplastics are heated at temperatures below 300 C (572 F) [3]. Details on health hazards of decomposition products of fluoropolymers are in Refs. [2,3]. These risks prompted the establishment of exposure limits by various regulatory agencies (see Table 8.2) [4]. There are a number of measures that can be taken to reduce and control the exposure of personnel to monomers and decomposition products during the processing of fluoroplastics. These include ventilation, spillage cleanup, equipment cleanup, proper maintenance, and elimination of fire hazard. The personnel involved in the processing should wear protective clothing, maintain strict personal hygiene, and be made aware of incompatibility of specific materials [5]. Processing and fabrication to finished products may be hazardous, because often very high processing temperatures are used. Depending
8: SAFETY, HYGIENE, DISPOSAL, RECYCLING
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FLUOROPOLYMER FILMS
141
Table 8.2 Exposure Limit Types. Limit
Type
Source
PEL
Legal OEL
TLV
REL
US Code of Federal Regulations, Title 29, Part 1910 (29 CFR 1910) American Conference of Governmental Industrial Hygienists or NIOSH
NIOSH, National Institute for Occupational Safety and Health; OEL, occupational exposure limit; PEL, permissible exposure limit; REL, recommended exposure limit; TLV, threshold limit values. Source: Data from The Society of Plastics Industry, The Guide for Safe Handling of Fluoropolymer Resins, fourth ed., The Society of Plastics Industry, Washington, DC, 2005.
on a specific process, fumes may not be present in the amounts to affect the personnel, but protection, such as protective clothing and gloves, should be used [5].
8.1.3
Medical Applications of Fluoroplastics
Because of their inertness and relative purity, some fluoroplastics, for example, certain grades of PTFE, are used in medical applications. In such cases, Federal Food and Drug Administration most often reviews and approves the entire medical device, not its components, such as specific parts or resin used. Resin suppliers have strict specific policies about the use of their resins in medical devices [5].
8.1.4
Food Contact
Fluoropolymer resins are covered in the United States by Federal Food, Drug and Cosmetic Act, 21 CFR & 177.1380 & 177.1550 and in the European Union by the EC Directive 90/128 [5]. Several fluoroplastics, such as PTFE, PFA, and FEP, have been approved by FDA for contact with food. Additives, such as stabilizers, antioxidants, pigments, and others, must be approved to meet the food-additive regulations if they have no prior clearance [5].
142
APPLICATIONS
OF
FLUOROPOLYMER FILMS
8.1.5 Environmental Protection and Disposal Methods for Fluoroplastics The preferred methods for disposing fluoroplastics are recycling and reusing them. This subject is covered in more detail in Section 8.2. Landfilling of fluoroplastics is permitted in some cases by local regulations because they are environmentally stable and contain no harmful substances. This is justified if there is no valid recycling or incineration. When disposing suspensions and dispersions, solids should be removed from the liquids and then disposed off. Incineration can be used only when the incinerator is equipped by a scrubber for removing hydrogen fluoride, hydrogen chloride, or other acidic products of combustion. If the scrap contains pigments, additives, and solvents, it should be handled in a manner to meet local regulations for nonfluoropolymer ingredients. Some of the mixtures may require compliance with local regulations for hazardous materials [6].
8.2 Recycling of Fluoropolymer Films As with any raw material, recycling of fluoropolymers is very important. Most melt-processible fluoropolymers can be reprocessed in a fashion similar to other thermoplastics. With PTFE the situation is more complicated. Because of its high melt viscosity, it is difficult to remelt and mix with virgin material, particularly if it contains mineral fillers. Nevertheless, a significant amount of PTFE production scrap is being reused by cleaning, grinding, and using in that form for ram extrusion [7]. Currently, most PTFE scrap (mainly residues from machining operations) is processed by radiation, being exposed to doses up to 400 kGy to reduce the molecular weight drastically and to obtain micropowders [8]. The most common process employs an electron-beam processor, although gamma radiation can also be used. High-molecular-weight PTFE can also be converted into micropowders by thermal or shear degradation [8]. A process involving chemical recycling of PTFE using fluidized bed has been developed and patented [9,10]. The optimum temperature is in the range of 545 C 600 C (1013 F 1112 F), and the main decomposition products are tetrafluoroethylene (TFE), hexafluoropropene (HFP), and cyclo-perfluorobutane (c-C4F8). The most important advantages of this process are that the monomers produced can be purified before repolymerization, which
8: SAFETY, HYGIENE, DISPOSAL, RECYCLING
OF
FLUOROPOLYMER FILMS
143
allows the production of a more valuable product, and that the process is continuous [9]. Another continuous process is the pyrolysis of PTFE scrap in a reactor heated by radiofrequency induction to 600 C 900 C (1112 F 1652 F). The products are TFE, HFP, and c-C4F8. The yield is in excess of 94% [11]. The use of reprocessed (reground) PTFE resin has limitations. For one thing, it exhibits markedly lower tensile strength and elongation than virgin PTFE. Reprocessed material creeps up to 25% more than virgin resin and contains twice the void content [12]. Because of porosity and larger number of voids, its dielectric strength is lower than that of the virgin PTFE. Thus the use of reprocessed material is limited to such applications, where cost is an important consideration and lower performance is sufficient for the application.
References [1] S. Ebnesajjad, P.R. Khaladkar, Fluoropolymers Applications in Chemical Processing Industries, William Andrew, Inc, Norwich, NY, 2005, p. 385. [2] The Society of Plastic Industry, Inc., The Guide to Safe Handling of Fluoropolymers Resins, The Society of Plastic Industry, Inc., 1988. [3] C.A. Rose, Environmental and Occupational Medicine, second ed., Little, Brown and Co., Boston, 1992, p. 373. [4] The Society of Plastics Industry, The Guide for Safe Handling of Fluoropolymer Resins, fourth ed., The Society of Plastics Industry, Washington, DC, 2005. [5] S. Ebnesajjad, P.R. Khaladkar, Fluoropolymers Applications in Chemical Processing Industries, William Andrew, Inc, Norwich, NY, 2005, p. 391. [6] S. Ebnesajjad, Fluoroplastics, Melt-Processible Fluoropolymers, vol. 2, William Andrew, Inc, Norwich, NY, 2003, p. 547. [7] B.J. Lyons, in: J. Scheirs (Ed.), In Modern Fluoropolymers, John Wiley and Sons, Ltd, Chichester, 1997, p. 340. [8] S.V. Gangal, in: H.F. Mark, J.I. Kroschwitz (Eds.), Encyclopedia of Polymer Science and Engineering, vol. 16, John Wiley and Sons, New York, 1989, p. 597. [9] C.H. Simon, Kaminski, Polym. Degrad. Stabil. 1998 (62) 1. [10] German Patent DE 4334015 A1. [11] I.J. Van der Walt, US Patent 6,797,913 to South African Energy Corporation, September 2004. [12] S. Ebnesajjad, V. Lishinsky, Machine Design, February 1999, p. 82.