Low styrene emission

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. 

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. 

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. ... 

Pre-accelerated, low viscosity fast wet-out, thixotropic, low styrene emission, orthophthalic resin, offering good interlaminar adhesion, high heat resistance, improved water resistance and low exotherm enabling thick sections to be fabricated by either hand-lay or spray/projec ion techniques colour change on cure. Approved for food contact applications, Lloyd s and Det Norske Veritas. 

White pigmented, pre-accelerated, low viscosity, thixotropic, orthophthalic resin, offering extremely low styrene emission with good interiaminate adhesion and improved water resistance provides rapid and efficient wet-out in both hand-lay and spray/projection moulding with low exotherm in thick sections. Approved by Lloyds and Det Norske Veritas, Grade 2. 

A preaccelerated, low styrene emission, thixotropic general purpose resin free of paraffins or waxes, with reduced delamination characteristics, and containing a colour change additive to denote cure. 

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. 

Since commercialization in the mid 1980s by Byk-Chemie of the styrene evaporation suppressant BYK S 740 which was elaborated at the Industrial Chemistry Research Institute in Warsaw, Poland, some new information about low styrene-emission (LSE) UPRs was launched, cf., e.g., refs. [100,101]. 

Chem. Descrip. Block copolymer with functional groups, 70% butyl acetate Uses Stabilizer for low styrene emission additives in unsat. polyester resins Features Prevents separation of paraffin wax type additives esp. applicable in nonthixotropic unsat. polyester resins... 

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