Handbook of Solvents - George Wypych - ChemTech - Ventech!

1240 Tilman Hahn, Konrad Botzenhart, Fritz Schweinsberg, Gerhard Volland
18.3.3 EMISSION OF SOLVENTS
18.3.3.1 Emission
Solvents are usually the most significant emission products coming from building materials
and interior furnishings. 2,5,6,13 All painted products are potential sources of emission.
Even the so-called “bio” paints or natural paints emit various substances, 5 e.g., mineral varnishes,
natural oils and even synthetic terpene-like compounds.
Depending on the products and the components which make them up, the various parameters
listed below can determine the emission and behavior of solvents in ambient air
from paints and varnishes: 2,5,6
• Film formation. During the film formation stage solvents are emitted. The emission
rate is directly proportional to the VOC concentrations in the product and inversely
proportional to the film thickness (first order of kinetics). When the film has
completely formed, the emission is controlled by diffusion processes, the emission
rate is now inversely proportional to the square of the film thickness.
• Application of the paints and varnishes, methods of application of the paint or
varnish, e.g. speed of application of the paint.
• Characteristics of solvents in paints and varnishes, e.g., volatility (boiling point),
dynamic characteristics of evaporation and concentrations. Substances having a
low boiling point evaporate fast, mostly during application and cause a rapid skin
formation. Thus the risk of exposure is mainly with the painters. Medium boilers
allow the surface to remain open for a while (evaporation of volatile products). The
evaporation of substances with a high boiling point is slow, taking several weeks or
months after application, resulting in exposure to the building occupants.
• Characteristics of other compounds in paints and varnishes (e.g., relationship of
binders to solvents, possible reactions between solvents and other compounds).
• Characteristics of surfaces which have been painted (e.g., area, structure of
surface).
• Characteristics of emission processes, e.g., type of emissions (e.g., diffusion),
dynamics of emissions (constant of evaporation), interrelations (e.g., diffusion and
back diffusion).
The quantitative assessment of emission processes can be described with various
models. The usefulness of these models differs. Some models describe these processes
very well, as proven by various experiments or measurements (e.g., test chambers). Basic
equations which describe emission processes are shown in Table 18.3.3.
The emission processes of solvents from paints and varnishes can be divided into two
phases: 2,5,6
1. Emissions during application of paints. This deals with complex interrelations dependent
on various parameters.
2. Emissions after application process. Here the course is governed by complex emission
processes dependent on various parameters (e.g., film formation, surface area).
Most solvent products, especially organic solvents and some additives, emitted from
paints and varnishes are VOCs. The largest components of VOCs are solvents, e.g.,
aliphatic and aromatic hydrocarbons, alcohols, amines, acids, aldehydes, esters, ketones,
terpenes. The definition of the term VOC varies, a standard definition is published by CEN
(European Committee for Standardization): 1 VOCs are any organic liquids and/or solids
that evaporate spontaneously at the prevailing temperature and pressure of the atmosphere.