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5.3. Recycling Wood-Based Panels into New Wood-Based Panels Hydrolysis can be used to break down urea-formaldehyde (UF) resins in wood panel waste, liberating the chips or fibres [5,45,66]. This process can also help mitigate the release of formaldehyde in the next generation of product. Various factors such as temperature, pressure, and steam ratio can affect the hydrolysis process [67,68]. Whilst this has been the subject of research for some years [5,69], one company has recently commercialised a technology to recover fibres from MDF panels and return these fibres back into MDF manufacture. MDF Recovery have patented technologies for the separation of fibres from boards and have proven their use in the remanufacture of MDF boards with similar board properties and emission profiles to those of virgin boards [6]. This technology is now scaled up and commercially available [70]. A parallel development has been the use of steam and pressure to hydrolyse the resin, and Unilin are trialling the technology at their mill in France [71]. An alternative approach is mechanical disintegration, although this is reported to degrade the size and quality of the particles [7]. Surface-laminated panels present an additional challenge and were studied by Hong et al. [72]. Four different laminate types on MDF were investigated in a hydrolysis system. The recycled fibre was used in the core of three-layer MDF panels, and their properties evaluated. The lowest strengths were seen for the polyester coating laminates, and it was suggested this might relate to the different alkaline buffer capacity of this laminate type affecting resin cure [72]. The literature suggests a lack of research on the production of plywood and OSB from wood waste [28,73]. This is because of difficulty in processing wood waste into suitable veneers for plywood or strands for OSB. The process would be at great risk of contaminants shattering any blades used in slicing the veneers of strands. Complex sorting would be required to ensure suitable material was prepared for strand manufacture if OSB production were to be pursued. Further research could address this challenge, as contaminant recognition and removal technologies continue to advance. However, the idea of recycling OSB into new panels of OSB is limited by the resins that are most commonly used in this panel type being resistant to hydrolysis. OSB is typically an exterior product or used in humid environments, so water-resistant resin types are used, preventing recycling through the hydrolysis-based technologies [45]. It would also be beneficial to evaluate the economic viability of innovative recycling and processing methods to maximise adoption and contribution to a circular economy in the timber industry. 5.4. Wood for Biomass Energy or Heat The other primary option for disposal of waste wood is burning for energy recovery. It was noted above that this is currently the destination of 63% of the UK’s recycled wood [15]. There has been steady policy support for renewable energy generation within the UK (from the UK Renewable Energy Strategy in 2009 up to the current Clean Power 2030 action plan). Wood as a fuel contributes to electricity generation and heat generation. The Biomass Strategy indicates that biomass contributed to 11% of the UK’s electricity supply [74]. While not all of this is from recycled wood, it indicates the scale of expansion which has occurred in the sector in the past decades. Many energy generation systems can handle only clean wood or clean agri-crop residues such as straw, miscanthus, and short rotation coppice. However, there has been expansion in the number of sites licenced to handle waste wood. Such incinerators operate with greater controls and measures to control emissions from burning timber containing preservative treatments, paints, or other potentially problematic components and are compliant with Chapter IV of the Industrial Emission Directive.
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