Synthetic Polymers: Polyesters, Polyethers, Polysulfones, and Other Polymers

Abstract

Commercial use of polyester resins dates from the early twentieth century, when alkyd resins were first used in surface coatings. The polyesters are found today as fibers, films, laminating resins, molding resins, and engineering plastics. Many of the high molecular weight polyethers are used as engineering plastics, as are the polysulfides and the polysulfones. Important properties of these compounds and production data for the general categories are provided. Processing techniques vary widely and are discussed in the sections in this chapter. Although toxicity data for some of these polymers are limited, information is discussed in the sections in this chapter. In many cases, the finished polymers are associated with low toxicity. However, some chemicals within the finished products have been known to migrate from the polymers (although usually in small amounts). Further, some of the polymers described in this chapter are used in biomedical equipment, including grafts and other implants, dialysis membranes, or as vehicles for intravenous injections, and there may be toxicity associated with these uses. For specific medical applications, any risks should be weighed against benefits derived from the products. Consultation with medical professionals is necessary before deciding on whether to use particular devices. Certainly some of the highest potentials for concern associated with these polymers are for workers at manufacturing or processing sites. Workers may be exposed to volatile chemicals (e.g., monomers, flame retardants, additives) generated during processing of flammable solvents, elevated temperatures, or fires. Workers may also be exposed to dust or particulates generated in the manufacturing and processing of polyester fibers. Finally, explosion hazards might be possible where static charges are generated (e.g., during physical processing of polyester films over rollers) where flammable materials are used. Industrial hygiene concerns with these polymers depend on the type of resin. Examples of such concerns include the following: significant quantities of styrene may be released during the fabrication of unsaturated polyester resins; particulates that have biologically significant consequences when inhaled in large amounts may be generated in the manufacturing and processing of polyester fibers; processing of polyoxymethylene in a poorly ventilated space may release biologically significant amounts of formaldehyde into the adjacent atmosphere; or sulfur-containing engineering resins may yield hydrogen sulfide or sulfur dioxide if heated to decomposition temperatures. The chemical inputs typically used to synthesize each of the polymers as well as relevant additives are discussed in the sections in this chapter. Toxicity data for most of these inputs can be found in other chapters of this edition of Patty's Industrial Hygiene and Toxicology. No specific standards are known that pertain to ordinary industrial use of the finished polymeric products. However, there may be occupational exposure limits for the chemicals used to synthesize or process these polymers. In addition, there are occupational exposure limits for dust and particles that may be applicable. There are also several examples of general protection measures that might be required such as using a continuous supply of fresh air to the workplace together with removal of processing fumes through exhaust systems is recommended. Also, processing fume condensates that are toxic or are fire hazards should be removed periodically from exhaust hoods, ductwork, and other surfaces by individuals using appropriate personal protection. Ventilation requirements must be locally determined to limit exposure to materials at their point of use. Use of proper personal protection while cleaning or handling condensates and plastic processing fumes should be observed. The polymers described in this chapter have generally little or no data on toxicity from burning. The toxicological aspects of plastic combustion products can be very complex in part because it is very difficult to simulate real-world environments under controlled conditions. Also, depending on a variety of factors, the qualitative and quantitative nature of chemicals present in the combustion product mixtures will vary. Some factors that may contribute to toxicity of combustion products of these polymers include increase of carbon monoxide and carbon dioxide, decrease of oxygen, and the presence of irritant gases. The primary effects from fires are often asphyxia due to oxygen deficiency, poisoning from carbon monoxide, heat damage to tissues, and irritation of the respiratory tract by combustion gases. Some polymers are used in packaging (or directly in food), and clearances for direct or indirect food contact applications are listed under Title 21 of the Code of Federal Regulations, and are listed in the sections in this chapter. Other polymers have been approved for use in specific medical devices that may be implanted in the body or used in dialysis machines. Keywords: Additives; alkyd resins; allyl polymers; combustion products; fire smoke; linear terephthalate polymers; personal protection; polycarbonates; polyethers; polyphenylene sulfide; polysulfones; processing fumes; sulfur polymers; synthetic fibers; thermal degradation; unsaturated polyester resins