|Reduction of styrene in the environment and the workplace||
Styrene (C8H8, CAS #100-42-5) monomer is a Volatile Organic Compound (VOC) which is an ideal cross linking agent for the unsaturated polyester resins used in commercial fibre-reinforced polymer matrix composites. More than one million tonnes of fibreglass and carbonfibre composites are manufactured each year in each of North America, Europe and Asia. Alternative monomers have been investigated, but none can match the combined performance and cost-effectiveness of styrene. Styrene evaporates from exposed uncured resin surfaces into the atmosphere during processing until the resin is fully cured.
The styrene monomer can impact on local air quality  with an odour threshold 0.08  to 0.32  parts per million (ppm) and a Photochemical Smog environmental impact classification factor (relative to ethene) of 0.412 .
Styrene is implicated in a number of health issues . The United States National Toxicology Program Report on Carcinogens 13th Edition states that “Styrene is reasonably anticipated to be a human carcinogen". That analysis is disputed by Rhomberg et al  and Collins et al . Other health effects include acute toxicity, skin and eye irritation and repeat dose toxicity. It is anticipated that styrene will be subject to a rigorous assessment in the context of the REACH (Registration, Evaluation and Authorisation of Chemicals) legislative system. Table 1 summarises the styrene odour and time weighted average occupational exposure levels (OEL).
|Odour threshold||0.08 - 0.32||1, 2|
|OEL for new build facilities in Sweden||10||8|
|Styrene Producers Association recommendation||20||9|
|Current UK voluntary code/legal OEL||50/100||10, 11|
|NIOSH (National Institute for Occupational Safety and Health)
IDLH (Immediately Dangerous to Life or Health) level
|Geometric mean for 15 minutes for workers with air purifying respirators
inside a wind turbine blade during glue wipe task
|Explosive limits (1.1-8.0%)||11000-80000||~|
Plymouth University was a prime mover in the introduction of closed mould technologies for composites manufacture during the 1990s and latterly vacuum infusion processes for larger structures [17, 18]. However, many mouldings have a cosmetic resin-rich surface finish (gel coat) which is applied to the open mould tool and allowed to partially cure before the reinforcement lamination takes place. Conventional hand gel-coating technology has been demonstrated to have significantly higher levels of styrene emission than two new closed mould processes [19, 20] developed in the FP7 InGeCt project lead by Plymouth University. For the open mould process, the average styrene levels were in the range 28-70 ppm. The two closed mould technologies significantly reduce the measured styrene levels to lie in the range 0.2-0.4 ppm. The new processes offer a reduction in average styrene emission levels of >98% (worst new/best old) with obvious benefits for worker health and the reduction of environmental burdens.
Forthcoming styrene risk assessments by the European Union, monitored by European Chemical Industry Council (CEFIC) for the chemical industry, are expected to be the major driver in the near future regarding styrene classification, labelling and use. Reduced styrene levels in the workplace are expected to improve retention of workforce personnel, minimise release to the environment and reduce odour at the factory boundary. The European Styrene Producers Association has recently [Faes, 9] recommended that Occupational Exposure Standards should be reduced to a time-weighted average (TWA) of 20 ppm which is unlikely to be achievable without in-mould gel-coating. Dependent on the REACH analysis, it may become essential to implement in-mould gel-coating to achieve styrene levels "as low as reasonably practicable" (ALARP) and permit the economic continuation of the polyester resin composites industry.
References (Plymouth University authors in bold font)