Styrene emissions

The UP industry reacted by developing so-called LSE (low styrene emission)- and LSC (low styrene content) resins. An LSE resin contains paraffin or wax in such a concentration that upon only a little styrene evaporation it forms a thin barrier film on top of the laminate, curtailing styrene emission. However, one aspect that warrants attention is the interlaminar adhesion of parts built up from several laminate layers. Note that these LSE resins are only active in the static state when the surface of the laminate is at rest. During processing, when the surface is regularly disturbed, the effect of the film-forming additive is far less. 

The most obvious way to reduce styrene emission is to use another monomer. However, there appears to be no real alternative that fulfills all the technical and economical requirements as well as being less toxic, and consequently styrene is at most partially replaced in some cases. 

Other elements which alone, or in combination, will contribute to less styrene emission/exposure in the workplace are  

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The primary UPR end markets are construction, automotive, and marine industries widi applications such as house paneling, tub and shower applications, chemical-resistant storage tanks, pultruded profiles, and fiberglass composite boat hulls. The UPR industry is mature, with a world production close to 1.7 million tons (Table 2.2), but must face two important issues increasingly strict regulations for styrene emissions and poor recycling potential for polyester thermosets.48 49... 

Methods for achieving low styrene emissions in the unsaturated polyester resin industry are discussed. The necessity for new formulations to maintain the same mechanical properties as the previous ones is considered. The environmental requirements and working conditions that make essential the development of new formulations and processes that reduce volatile emissions are examined. The need for factories to adopt alternative technologies in order to comply with the latest environmental restrictions is discussed. 12 refs. 

The current state of play with regard to legislative issues relating to styrene emissions in the composites workshop... 

The effects of amendments to the Environmental Protection Act (1990), which relate to pollution control and styrene emissions from installations, on UK fibre reinforced plastics processors are examined. Possible cost-effective abatement solutions are briefly considered. 

Intentions by the EPA to more tightly regulate the emission of hazardous air pollutants through maximum-achievable-control-technology standards are briefly reported with reference to styrene emissions. The regulation would require that any facility that emits more than 100 tons of styrene annually, should retrofit with expensive ventilation equipment, and that a new facility of any size would have to install the same type of equipment. The composites industry considers this to be an expensive standard, which could put companies out of work. 

A schematic of a rotary concentrator is shown in Fig. 9. The wheel rotates slowly (1-3 rotations per hour) with about 90% of its face exposed to the incoming air stream. The remainder of the face is in a regeneration sector where a counterflow of hot air desorbs the VOCs for subsequent incineration. The rotary adsorber increases the VOC concentration by a factor of 100, so there is little need for supplemental fuel in the small oxidizer that can be used to destroy the VOCs. This technology has been used for the removal of styrene emissions in the plastics molding industry. The process is also used with automotive paint booths where modular rotary concentrators and a regenerative thermal oxidizer are used to capture and destroy VOCs. 

Styrid. [Specialty Prods.] Woven glass fiber polyimide qx>xy lamintes styrene emissions reducer for fiberglass molding. 

If a dangerous compound cannot be replaced for technical reasons, sometimes there is a possibility to use it in a form which creates minor amounts of emissions. Powdery materials may be replaced by granules, pellets, solutions, or molten materials. For example, unsaturated polyester resins have been available for many years in a form giving low styrene emissions due to paraffin additives. 

The polymer is dissolved in styrene or a monomer containing vinyl unsaturated. With heat and a chemically activated free radical initiation, the polyester and the reactive diluent crosslink to form a 3-D nonmelting network. The reaction occurs at 170-200C (338-390F), with components in roughly equal molecular ratio and water eliminated. The polyester is then dissolved in stabilized comonomers. Protected from light, the resin has a shelf life of about six months. Thirty percent styrene usually serves as comonomer solvent. In response to growing unease about the presence of styrene vapor at the workplace, low-styrene emission types have been introduced in recent years. 

As with TS polyester resins, the VE resin is diluted with 30-50% styrene, to give usable consistency and, during fabrication, part of the styrene evaporates into the workplace atmosphere. Low styrene emission (LSE) resins are used (Table 3.19). Traditionally, the route is to introduce a wax-based additive, which seals the surface as soon as lamination is completed, so preventing evaporation, but this technique can also reduce the effectiveness of the bonding between layers, leading to possible delamination. 

Table 3.19 Typical properties of vinyl ester standard and low styrene emission (LSE) resins...

A low-pressure glass fiber polyester spray plant also gives low styrene emission and little mist formation. Resin and hardener are mixed and an automatic pump delivers safe exact proportions of peroxide from original containers, no peroxide being dispersed in the air. The German Technical Monitoring Service has confirmed an emission of only 5 ppm and low-pressure equipment with internal mixing also ensures that no peroxide is freely dispersed into the air. 

All types of RP molding should be carried out in a controlled environment. This is essential where TS polyester resins are being processed and there may be risk of over-exposure to styrene emissions, and is advisable also when working with TPs, because of heat build-up from machines, the effect of sudden drops in temperature (as, for example, when doors are left open), and the removal of fumes. 

Miller, B., Styrene Emissions from Open Molds, PW, p. 39, Jan. 1989. 

Open mold methods (hand lay-up and spray-up methods) are most commonly used. In addition, the products often have large surface areas and large styrene vapor emissions take place. The emission depends on the type of resin used. While the mean evaporation loss of styrene was 11.6% for conventional resins, it was only 4.4% for the low styrene emission (LSE) resins containing volatilization inhibitors. ... 

C.M. Nunez, G.H. Ramsey, M.A. Bahner, and C.A. Clayton, An Empirical Model to Predict Styrene Emissions from Fiber-Reinforced Plastics Fabrication Processes, J. Air cfe Waste Management Assoc., 49, 1168-1178(1999). 

Case Styrene Emissions from Composite Manufacture A sector of the plastics industry presently nnder review by the EPA is that of composites. When final, the regulatory action by the agency is expected to reduce related air emissions by 14,500 tons per year (a reduction of 65% over... 

General polyesters are usually orthophthalic acid based resins, which are used in applications based on open moulds and hand and spray lay-up moulding. Resins with a low level of styrene emission are ideal for these applications. 

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