AUG 2018


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AUGUST 2018 34 CompositesWorld FEATURE / US Styrene Reduction Update manufacturers about the types of protection workers should use, and have published information employers should consider when setting exposure limits and workplace practices for employees. SIRC notes that styrene emissions are covered under the US Clean Air Amendments of 1990, which regulate air emissions of styrene and other substances classified as hazardous air pollut- ants (HAPs). Enforcement of these federal standards is done at the state level via issuance of operating permits to facilities that emit HAPs. Additionally, SIRC says nine states have established their own regulations for the chemical, using health-based emissions standards/guidelines, with a minimum of four of those states using "at least partially outdated information provided by the US EPA in the 1980s." Air-quality emissions limits can restrict manufacturers' ability to expand production of products that, for example, use styrene in the manufacturing process. Since higher production levels can mean higher emissions of styrene, manufacturers must some- times choose between trying to increase the emission limits in their air-quality permits, which can be time-consuming and costly, or switching to more-expensive, lower-emitting mate- rials or processes. "Research compiled by SIRC continues to show that styrene is unlikely to cause cancer or any other serious health impact in humans if normal safeguards are followed," adds ACMA's Schweitzer. He notes that, in any case, growing busi- nesses could find that they risk exceeding styrene or other VOC emission limits in their state operating permits, and then opt for increased use of lower-volatility resins. "However," he contends, "this would be in response to regulatory and economic consider- ations and not health concerns." Some states also have enacted legislation that seeks to limit "chemicals of concern" based on lists developed by the US EPA, NTP, the EU or other authorities. SIRC notes that "styrene often is included in such lists but has not been identified, to date, as a candidate substance for further action by any US state that has developed a list of this type." For example, in 2008, the Texas Commission on Environmental Quality (TCEQ) Review concluded that its existing "fence-line" exposure limit to styrene of 110 μg/ m 3 (based on odor detection) would be left as is. TCEQ report- edly conducted "a comprehensive review of scientific informa- tion related to styrene and styrene's potential to impact human health" and concluded that "data are inadequate for an assess- ment of human carcinogenic potential." On the other hand, California passed a ballot initiative called the Safe Drinking Water and Toxic Enforcement Act of 1986, also known as Proposition (Prop.) 65, in November 1986. at law aims to protect the state's drinking water from sources of chemical contamination "known to cause cancer, birth defects, or other reproductive harm" by maintaining and updating a list of chemicals "known in the state of California to cause cancer or reproductive toxicity" and also to provide warnings to consumers who may come into contact with products that contain the listed chemicals. e law requires manufacturers who use these chemi- cals to inform Californians about potential exposure risks. Cali- fornia EPA's Office of Environmental Health Hazard Assessment (OEHHA) announced in February 2015 that it intended to add styrene to the Prop. 65 list of chemicals of concern, based on NTP's classification of styrene in 2011. Prop. 65 has different guidelines and requirements relating to different types of contact with chemicals such as styrene: for example, occupational (job-related) exposure, environmental releases to the state's waters, and consumer exposures from use of finished products. If a consumer's estimated average daily styrene exposure (over a lifetime of 70 years) from any consumer product containing styrene is below the 27-μg/day threshold, a warning label is not required; if exposures are higher, a warning label is required. Again, according to SIRC, OEHHA established a State Public Health Goal for styrene of 0.5 ppb in drinking water, yet at the end of the state's own tests of SIDE STORY Definitions are important when discussing technology. Although often used interchangeably, the terms styrene and polystyrene refer to different materials. Preferentially called ethenylbenzene by the Interna- tional Union of Pure and Applied Chemistry (IUPAC, Zürich, Switzerland) and also known by nine other common names, styrene (C 6 H 5 CHCH 2 or C 8 H 8 ) is a thick, colorless and sweet- but strong-smelling monomer derived from benzene. Polystyrene ((C 8 H 8 ) n ), on the other hand, is a solid thermoplastic polymer made up of a great many repeating units of the styrene monomer. Notably, styrene occurs naturally in such common plants as sweetgum-genus tree sap and foodstuff, such as cinnamon, coffee beans, peanuts, beer, beef, wheat, oats, strawberries and peaches. Further, it is found in coal tar, a byproduct of coke and gas production from coal, which, itself, is formed from fossil plants. Presently, 98% of all ethenylbenzene is extracted from natural products; only 2% is currently synthesized. Polystyrene is an important polymer used to produce other ther- moplastic copolymers, including acrylonitrile butadiene styrene (ABS), styrene acrylonitrile (SAN), acrylonitrile styrene acrylate (ASA) and, of course, foam polystyrene — the latter informally and often incorrectly called by The Dow Chemical Co. (Midland, MI, US, now DowDuPont Inc.) tradename, Styrofoam. Styrenic thermoplastics are known for their excellent surface aesthetics, good stiffness and their good adhesion to both paint and plating, making them an important class of polymers for aesthetic applications in industries that range from packaging to small appliances to automotive trim. On the thermoset side of the business, styrene monomer is commonly used as a reactive diluent (solvent) in vinyl ester or unsaturated polyester resins and gel coats. "The curing reaction that transforms a liquid mixture of resin, glass, fillers and other materials into a solid, durable composite product involves the crosslinking of vinyl ester and unsaturated polyester molecules by styrene," adds John Schweitzer, senior manager with the American Composites Manufac- turers Assn. (ACMA, Arlington, VA, US). "Styrene is a uniquely capable and cost-effective reactive crosslinking agent for these resins." Styrene ≠ polystyrene: An important distinction for composites

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