The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Influence of Moisture and Substrate on the Emission of Volatile Organic Compounds from Wall Structures
Leif Wirtanen
Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Civil and Environmental Engineering for public examination and debate in Auditorium R3 at Helsinki University of Technology (Espoo, Finland) on the 27th of January, 2006, at 12 o'clock noon.
Dissertation in PDF format (ISBN 951-22-8052-3) [3611 KB]
Dissertation is also available in print (ISBN 951-22-8011-6)
Abstract
Volatile organic compounds, VOCs, are released from a multitude of different polymer-based building materials. They can cause adverse health effects such as irritation of eyes, nose and throat, headache, fatigue, dizziness, sinus congestion, allergic reactions, and respiratory infections. This study concentrates on the influence of moisture and substrate on the emissions of VOCs from common wall structures. The structures are made up of primers and paints or adhesives applied onto either gypsum board or a combination of filler and plaster (or a single layer of plaster) which is applied onto calcium silicate bricks. An inert substrate, glass, is used as a reference substrate for single layers of paints, adhesives or plasters, and combinations of primer and paint and filler and plaster.
The experimental section of this study is preceded by a literature review where the different factors affecting the emission process is dealt with. The literature review also includes the elaboration of a mathematical model describing the emission process.
Small environmental chambers were developed for the experiments. The relative humidity of the air introduced into the chambers, the air exchange rate, and the air flow velocity over the sample surfaces could be easily controlled. Samples were exposed to different moisture conditions by adjusting the relative humidity of the air introduced into the chambers and by the use of different substrates. The emitted compounds were collected both from the chamber air and from the surface of the samples by using a Field and Laboratory Emission Cell into stainless steel tubes containing Tenax TA adsorbent.
Other tests performed in this study included infrared spectroscopy, mercury intrusion porosimetry, microscopy, and the determination of pH. These tests were mainly performed to derive additional information on the chemical and physical characteristics of the materials studied.
The experimental results demonstrated that the emission of VOCs from a surface layer is affected especially by the substrate, primer included, and by the drying process of both the substrate and the surface layer. The use of gypsum board as a substrate for either combinations of primer and paint or adhesives resulted in the lowest emission rates, while the use of a combination of filler and plaster or a single layer of plaster applied onto calcium silicate brick as a substrate resulted either in higher or lower emission rates compared with the glass (reference substrate) depending on the emission characteristics of the combination of filler and plaster. The experimental results indicated also that a high relative humidity prolongs the drying process, thus affecting the emissions because of interactions of water molecules with other emitting compounds. The consequence of this is that different compounds are emitted at different points of time.
There was a statistically significant difference after the samples had reached moisture equilibrium only in the emission rate of aldehydes at RH 20 % and RH 80 % target relative humidities for samples collected from the test chambers. The emission rate was higher for the higher humidity environment. This result applied only when different combinations of primer and paint were spread onto glass plates.
The experimental results additionally confirmed that TVOC, the total amount of VOCs being released, is not a good estimate of the behaviour of the emission of single compounds, since their behaviour, as regards relative humidity, can not always be determined based on TVOC-values. Nevertheless, it has been proven that it is possible to reach low emission rates, i.e. TVOC-values < 30 µg/m2·h, in less than two weeks with an appropriate choice of materials and by ensuring good drying conditions.
Keywords: volatile organic compounds, VOC, emission, moisture, substrate, primer, paint, adhesive, gypsum board, filler, plaster
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© 2006 Helsinki University of Technology
Last update 2011-05-26