Abstract
Wood is one of the most sustainable, aesthetically pleasing and environmentally benign materials. Not only is wood often an integral part of structures, it is also the main source of furnishings found in homes, schools, and offices around the world. The often inevitable hazards of fire make wood a very desirable material for further investigation. As well as ignition resistance and a low heat release rate, timber products have long been required to resist burn-through and maintain structural integrity whilst continuing to provide protection when exposed to fire or heat. Various industry standard tests are thus required to ensure adequate protection from fire is provided. When heated, wood undergoes thermal degradation and combustion to produce gases, vapours, tars and char. In order to understand and alter the fire behaviour of wood, it is necessary to know in as much detail as possible about its processes of decomposition. Various thermal analysis and flammability assessment techniques are utilised for this purpose, including thermogravimetric analysis, cone calorimetry and the single burning item test. The results of such tests are often highly dependent on various parameters including changes to the gas composition, temperature, heating rate, and sample shape size. Potential approaches for fire retarding timber are reviewed, identifying two main approaches: char formation and isolating layers. Other potential approaches are recognised, including the use of inorganic minerals, such as sericrite, and metal foils in combination with intumescent products. Formulations containing silicon, nitrogen and phosphorus have been reported, and efforts to retain silicon in the wood have been successful using micro-layers of silicon dioxide. Nano-scale fire retardants, such as nanocomposite coatings, are considered to provide a new generation of fire retardants, and may have potential for wood. Expandable graphite is identified for use in polymers and has potential for wood provided coating applications are preferred.
Highlights
Wood is one of the most sustainable, aesthetically pleasing and environmentally benign materials
Cone calorimetry The cone calorimeter (ISO 5660–1 2002) is the most widely used bench-scale fire test method in use, providing a variety of quantifiable flammability parameters. It is employed as a means of predicting how a material will behave in a real fire scenario by providing the user with the heat release rate (HRR), mass loss rate (MLR), smoke production, fire spread and ignition properties
monoammonium phosphate (MAP) operates to Diammonium phosphate (DAP), and it has been reported that retentions of 15% by weight of wood of MAP increases the char production of Scots pine by 17% compared to the untreated equivalent (Nussbaum 1988)
Summary
Wood is one of the most sustainable, aesthetically pleasing and environmentally benign materials. Strong development in new technologies and products in the last decades has been observed for the fire retardant treatment of plastics and fabrics, including nanocomposites (Laoutid et al 2009) and layer by layer applications (Alongi et al 2013a). Hemicellulose and lignin are the three polymeric materials that constitute the wood cells. Cellulose forms the cell walls, and provides the tensile strength of the wood matrix. Hardwood fibres typically have higher hemicellulose content than softwood tracheids. High hemicellulose contents give rise to weak fibres In both hardwoods and softwoods, the wood in the trunk of the tree is divided into two zones, heartwood and sapwood. Both of these groups serve an important function, distinct from the other. Softwood is most commonly used by the construction industry (McDonald and Kretschmann 1999)
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