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In addition to the industrial electricity and heat systems, some recycled wood can be incorporated into pellets and briquettes for the consumer market. Kindling might also be formed from short lengths and narrow dimension solid wood residues. All of these options require clean recycled wood to ensure the wood fuel is not harmful. Heavy metals, such as CCA-treated wood would not be suitable within the domestic wood pellet stoves or wood burning stoves commonly used by the public. However, reliance on burning waste wood for energy recovery may be premature, in that it cuts short the options for materials cascading through multiple uses prior to eventual incineration [56]. This topic will be further considered later as it provides the context in which the different recycling options operate.
6. Emerging Practice in Reusing or Recycling Timber 6.1. Reuse in Construction
There is growing interest in the process of reclaiming solid wood for recycling into first generation products such as glulam and CLT [65,75,76]. However, this requires the solid wood to be removed from buildings in a form that does not decrease its length or cause damage. This returns to the key themes when developing markets for waste wood from construction—detection and removal of fasteners and fixings, and potential contamination from paints or treatments used during the first life of the product. A portion of reclaimed wood is recovered during demolition, if particularly old or valuable, and then stored and marketed by salvage merchants, and specialist architectural dealers. In the majority of cases, however, demolition teams prefer to break wood up during demolition, rather than deconstruct the building to reclaim the timber. The exception is where the client specifically requests the deconstruction method, or where the value of the timber beams or trusses is sufficiently high to make it worth the cost. The focus on material shortages and circular economy principles has led to new research to use reclaimed demolition wood for new applications. One example is the manufacture of CLT and glulam from reclaimed timber [65,75]. This requires good metal detection prior to resawing into the new unit dimensions for the lamellae. It has also been demonstrated that timing and storage are essential to being able to respond rapidly when timber is available and to hold stocks until sufficient material is gathered for manufacture of the laminated timber. 6.2. Wood Fibre Insulation The emergence of technologies for recycling MDF into a fibrous feedstock [70] opens the opportunity for wood fibre insulation to use this recycled fibre. A company in Wales is working with MDF Recovery to develop a loose fill product, Pillo, with excellent thermal insulating properties [77]. The product could be deployed in timber framed housing panels or as a cavity wall insulation option. Previous studies have considered the use of sawdust and shavings, or the creation of wood fibre from chipped waste, or used paper fibre [78,79]. 6.3. Wood Plastic Composites Wood plastic composites (WPCs) are a blend of wood particles or wood fibres in a thermoplastic matrix. WPCs often use virgin timber or sawdust from primary manufacture to ensure a consistent chemical composition and particle dimensions to aid uniformity in manufacturing. The feedstock can be sawmill residues, and hardwood material is preferred, to minimise the off-gassing of terpene volatiles which would occur from softwood timbers [80]. Such feedstocks also help to ensure consistent particle sizes and easy milling. In some cases co-location of WPC manufacture with existing wood processing industries is beneficial, if these are generating sawdust or planer shavings as waste. However, there
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