Interactions between volatile organic compounds and natural building materials

Abstract

There is increasing concern regarding the indoor air quality of energy efficient buildings. Indoor air pollutants, such as volatile organic compounds (VOCs) and particulates, commonly found in buildings, can be harmful to human health. Interior materials are known to be one of the main contributors to poor indoor air quality. There is a need to develop natural materials and systems in order to minimise the level of indoor air pollutants, or even reduce them to near zero through the use of VOC-free emitters and exploitation of the sink effect for airborne pollutants. Natural building materials are considered to possess low embodied energy and are environmentally-friendly.The aim of this research was to investigate the physical and chemical interactions between natural building materials and VOCs in new or refurbished buildings (e.g. dwellings, offices, hospitals, schools and retail outlets). Key to this was the identification of low VOC emission materials with the added benefit of passively improving the indoor air quality. Comprehensive chemical and physical characterisation of materials was undertaken in order to understand the mechanisms involved in the capture of VOCs by three classes of natural building materials: insulation, coatings and wood panels.In order to understand the interactions between VOCs and building materials, adsorption and desorption experiments were carried out in laboratory-scale environmental chambers and in a real size room with a volume of 30 m3, all with controlled temperature, relative humidity and air flow-rate. Four organic pollutants commonly found in indoor environments were selected for this study according to their physico-chemical properties: formaldehyde, toluene, limonene and dodecane. In the first stage of this research, TVOC and formaldehyde emissions from 18 commercially available natural building materials were analysed (six insulation materials, six coatings and six wood-based panels). These materials included natural wool, hemp fibres, wood fibres, gypsum, lime mortars, clay-based plasters and wood-based plasters. Four of these materials were selected to investigate their adsorption and desorption behaviour towards the selected organic pollutants. It was observed that, in general, all natural building materials showed very low, or even zero, VOC emissions. In the case of formaldehyde, this organic pollutant was found to be emitted by the wood-based panels due to the formaldehyde-based resins used to glue the wood fibres. In the case of coated wood panels, the resin impregnated paper coating was shown to act as a barrier to formaldehyde emission and as a result this showed lower emission levels compared to an equivalent uncoated material. With regard to the adsorption and desorption behaviour it was observed that highly porous materials such as lime mortar and MDF panels have good capacity to remove VOCs and formaldehyde from the indoor air due to their high surface area. They allow the diffusion of the organic pollutants through their bigger pores. Natural wool, classed as an insulation material, showed good affinity to adsorb formaldehyde due to chemisorption by the proteins present in the fibres.The later stages of this research involved the investigation of the adsorption/desorption behaviour of newly developed natural building materials incorporating bio-based additives with optimised capacity to remove VOCs from the air. The incorporations were as follows: walnut shell within MDF panels; hemp sheaves, pumice and brick powder within clay-based plasters; and cellulose flakes, natural wool and photocatalytic TiO2 particles within lime mortar. The combination of two materials was also used because of the affinity of each material with different VOCs, for example the incorporation of natural wool in a lime mortar formulation.The outcomes of this research demonstrate that, if careful consideration is given to materials selection when constructing a new building or during a refurbishment process, the old judgment “building materials are the main contributors to a poor indoor air quality” is not true. This is achieved by selecting materials with low- or zero-VOC emissions and with the capacity to remove organic pollutants from the indoor air. Therefore, these materials contribute to a better indoor air quality by releasing low or negligible emissions and by facilitating the removal of airborne pollutants.

Date of Award	21 Aug 2017
Original language	English
Awarding Institution	University of Bath
Sponsors	BRE Trust
Supervisor	Richard Ball (Supervisor), Martin Ansell (Supervisor) & Andy Dengel (Supervisor)