Emissions of VOCs from varnishes and paints

A substantial part of emitted materials are solvents. They preferably originate from varnishes, paints and glues. Table 18.1.1 shows a survey of the main types of varnishes referring to their average solvent content. 

Despite the introduction of water based and powder varnishes, cellulose nitrate varnishes with their high solvent content, are still widely used due to their easy application and their low prices. The current varnish application still requires the use of solvents. The chosen coating procedure determines the necessary processing viscosity, which may be adjusted in different ways  

About 10 % of the solvent remains in the varnish and it is emitted, depending on the type of solvent and varnish, wifli variable rate on their way to the eonsumers and in their living spaces. 

According to die European Commission, the furniture indusliy alone used more than 185,000 tons of solvents/year in 1994.  

Not all the VOCs enter the air, however, since remedial efforts, such as absorption and solvent reclaim, after-burning of solvents, flic use of bio-filters, result in emission reduction. 

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Wolkoff, 1998 Haghighat and de Beilis, 1998). Table 15.7, for example, shows the effects of temperature and relative humidity on the emissions of particular compounds associated with carpet, PVC flooring, sealants, varnish, and wall paint (Wolkoff, 1998). Interestingly, exposure of these samples to N2 rather than air also increased the emissions in some cases. However, using increased temperatures to bake-out buildings and hence lower the concentrations of indoor VOCs does not appear to be particularly effective. For example, Bayer (1991) reports that the total VOC concentrations from particleboard are about the same after as before a 5-day bake-out at 88°C. Similarly, significant levels of HCHO have been observed in a mobile home even after 20 years of use in a hot ambient air environment (Pitts et al., 1989 see later). 

Test chamber (volume 1 m, defined conditions temperature, humidity, air changing rates, air velocity). This is usually carried out 3 days after application of paints or varnishes by placing the products into a test chamber. The test series starts with sampling emissions of the products on defined absorption materials (Tenax, charcoal filters, activated charcoal), reconditioning and finally identification and classification of VOCs with gas chromatography. The test methods are repeated after 14 and 28 days. These test criteria permit determination of the behavior of emissions from finished products under defined conditions. 

Prodncts, snch as varnishes, lacquers, latex paints, and glnes, have large amonnts of solvents that are invariably volatilized into the atmosphere. In the United States, annual associated VOC load on the atmosphere is about 25 million tons [39]. In western Europe alone, 4 million tons of solvents are used annually with about a quarter of the annual total VOC (including biogenic emissions) attributed to solvent use. A conservative estimate of the VOC emissions from a single class of paints, the solvent-based paints used as U.S. highway markings, amounted to abont 40 million ponnds annually [40]. 

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