Emissions behaviour of wood and wood-based materials
Wood and wood-based materials are environmentally friendly and sustainable, provided the wood is sourced and processed appropriately. Some of their emissions can be problematic. The Federal Institute for Materials Research and Testing (BAM) researched the emissions behaviour of pine wood and derived particle board products.
Wood and wood-based materials are environmentally friendly and sustainable, provided the wood was sourced and processed appropriately. Although sustainability criteria for wood have been established worldwide, there has been no comprehensive evaluation of the health-related aspects of wood-based materials. Wood-based materials as well as solid wood produce emissions of various different substances, including volatile organic compounds (VOC). A research project by BAM, the Federal Institute for Materials Research and Testing (see Publications), analysed the emissions behaviour of pine wood and the Oriented Strand Boards (OSB) which are made from this wood. The main aim was to find ways to reduce the VOC emissions from wood-based materials, and from OSBs in particular.
As concerns the health aspects of building products, the AgBB scheme classifies substances which have the lowest concentrations of interest (LCI) as problematic. In the case of OSBs, the problematic substances are unsaturated aldehydes. These compounds are formed through the oxidation of fatty acids in the production process, and pine wood has a relatively high content of these acids compared to other types of wood. Since saturated aldehydes, and hexanal in particular, are formed during fat oxidation, hexanal proved to be a good guide component for testing methods of aldehyde emissions reduction.
The OSB products of three manufacturers (4 of 6 boards) did not comply with the criteria of the AgBB scheme from among those purchased on the market between December 2007 and February 2009. Emissions of unsaturated aldehydes were the most prominent factor in this context. In addition to quantitative emissions testing, experiments were conducted to test odour impression. Test persons reported unpleasant odours in most of the samples.
In addition to the boards available on the retail market, BAM also tested boards made under special conditions in order to investigate the requirements to achieve emissions reductions. The model OSBs were produced to exact manufacturer specifications at the technology centres of the Institut für Holztechnologie Dresden (ihd) and tested by BAM in emission test chambers.
Two different trunk heights, two strand drying temperatures (coarse chips used in the production of OSBs), and three press temperatures were used to produce the OSBs. The tested press temperatures and strand drying temperatures had no verifiable influence on OSB aldehyde emissions. Although strand drying temperature was presumed to be an influencing factor, no further investigation was carried out. The antioxidants used in food technology seemed a more promising way to reduce aldehyde emissions. BAM tested this procedure in the laboratory it used to produce the OSBs. The strands were coated with mixtures of two similar antioxidants or preservatives each before drying. After drying the strands were placed in a so-called µ-Chamber, and VOC emission was measured after 24 hours.
A mixture of tartaric acid and citric acid proved to be the most effective and reduced emissions by two thirds, and emissions of hexanal and unsaturated higher aldehydes acids in particular. Emissions can thus be reduced by using rather simple means in production.
The good technical properties of the Oriented Strand Board (OSB) have made it a market leader. The potential impact on health of aldehyde emissions indoors and the odours from these substances are preventing an even more widespread use. The results of the project point out how to reduce these emissions. It is now upon the wood processing industry to transfer these results to commercial production and supply the consumer market with goods which are low in VOC and odour emissions.
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