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5. Most Commonly Used Recycling Options 5.1. Mulches, Animal Bedding, Play Surfaces, and Cat Litter
For waste wood in the UK, two markets which use the cleanest grade of wood are found in agriculture (as bedding for livestock or for equine applications such as arenas and gallops) and in horticulture (as mulch). These are long-standing markets and the quantity of material entering these products is relatively stable, with only Category A wood accepted. Once the mulch or equine surface material is produced, the wood has a relatively short lifespan and moves rapidly to landfill, composting, or degradation in service. Another minority product is wood pellet cat litter. This also requires high cleanliness of wood feedstock, so it can only be formed from a small proportion of the available recycled wood resource. The cat litter product also has a short residence time. 5.2. Wood-Based Panels Wood-based panels have been one of the most significant options for recovered wood for a long time, with the bulk of usage in particleboard. Vis et al. [63] indicated that the recycled wood entering particleboard varied between 100% in Italy; 50% in Belgium, the United Kingdom, and Denmark; 15–30% in Germany, France, and Spain; and 0% in Switzerland. The proportion in the UK has diminished in the past few years as demand for bioenergy has increased. The production of wood-based panels in the UK in 2022 was 3.5 million m 3 using 1.0 million tonnes of recycled wood, but 1.2 million green tonnes of roundwood and 1.2 million green tonnes of sawmill residues [10]. However, panel production remains an important part of the circular economy for wood materials in many European countries, as reflected in the recent European Parliament statement [19]. While particleboard is the most common panel to contain recycled material, there is scope to produce medium-density fibreboard (MDF) as well. This product uses pressurised refining technology to transform chips of recycled wood into thermomechanical pulp fibres (TMP). However, it is essential that the feedstock is sufficiently clean and free from solid contaminants (metals and inorganics). After refining, the TMP fibre can be used to form MDF or other fibreboards such as high-density fibreboard (HDF) or hardboard. There is also limited scope for incorporating recycled wood into other panels such as oriented strand board (OSB), as demonstrated by the recent development of a five-layer OSB panel by Kronospan, produced in Luxemburg. However, the strands that are used to form the OSB need to have a long thin shape, allowing good transfer of load for this structural panel product. To recycle solid wood into strands for OSB would require a different stranding process, and while it is not impossible to imagine, it has not been widely investigated. Again, this relates to concerns about the contamination of recycled wood with solid particles, which could damage the cutting knives, or concerns about the suitability of infeed material. In the most common demolition practice wood is broken up during demolition rather than removed sequentially in long lengths. Large fractures at multiple points in the timber would reduce the potential yield of strands for OSB. Consumption of panel products in the UK is significantly larger than manufacture capacity: 1.25 million m 3 plywood (100% import); 3.38 million m 3 particleboard and OSB (30% import); and 1.69 million m 3 MDF and fibreboard (53% import) in 2022 [10]. Based on strong demand, there is scope for expansion and for this to incorporate additional recycled feedstock. Wood-based panels, therefore, represent a substantial market for recycled wood and recycled fibre if recycling practices continue to develop, and feedstock is sufficiently clean.
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