Future feedstocks for mdf production

Global wood based panel consumption is on the rise and new investments in mills are being made to meet these demands. However, with increased demand for MDF, and competition from the biomass energy sector, there are growing concerns over the future availability of wood.

Over the last 20-plus years, the BioComposites Centre has researched the use of a variety of biomass feedstocks for MDF production. This work is driven by commercial and environmental concerns. Commercial drivers include the securing of new feedstocks to mitigate against reductions in wood supply and diversification of markets. Environmental concerns, such as the need to make better use of co-products/waste from other sectors, and the need to increase recycling, were also important factors.

In the early 1990s the Centre undertook a comprehensive study to determine the suitability of selected agricultural raw materials (ARMs) as feedstock for MDF production. The ARMs selected for investigation were: wheat straw, linseed straw, miscanthus, coppice poplar and hemp.

Some of the main objectives of the study were to determine optimum ARM addition levels and resin content to optimise MDF quality. The study also looked at the viability of a supply chain between the agricultural community and panel industry. Using the pilot scale refiner, MDF fibre was produced from the ARMs and then blended with wood fibre and urea formaldehyde (UF) resin. Low-to-moderate levels of wood substitution were tested (20% and 40%).

The results suggested that all of the materials would be suitable with wood substitution levels of up to 20% without any significant loss in quality. Some modest reductions in panel properties were evident at 40% wood substitution levels for some materials and full wood substitution was only possible with either coppice poplar or miscanthus.

It was also possible to refine wheat straw alone, but attempts to manufacture UF-bonded straw panels were unsuccessful, even when using high levels of UF resin and a catalyst.

The fact that panels could only be made using MDI (isocyanate) resins was a key issue for straw. This is because the wax present on the surface of the straw significantly reduces the bonding ability of UF resins.

The study also looked at storage of materials over a year, either protected or unprotected. Results suggested that this did not appear to have a significant effect on panel properties, so stock piles of ARMs after harvest would be possible.

Feedback from the industry suggested that the more promising ARMs would potentially be considered as alternatives. However, it was apparent that they would only be considered if they could be supplied at an equal or lower cost than that of wood, coupled with assurances in terms of security of supply and quality. The industry also wanted more information on the likely longterm effects on the production processes themselves, as the higher levels of silica and extractives could cause problems with equipment wear.

Research on feedstocks for MDF production at the Centre is now focused on the use of recycled MDF.

Significant volumes of waste MDF are available from post- and pre-consumer sources. This is a potentially valuable source of fibres that is currently not utilised. A number of technologies have looked at this in the past, but these were based on batch processes, with high pressures and energies, so were not affordable.

However, recent developments by MDF Recovery Ltd – and full scale trails at some of the largest European panel manufacturers – has successfully demonstrated that it is viable and that production cost savings can be achieved. Combined with a market pull from the shopfitting and retail sectors for recycled products, and regulators promoting circular economies in manufacturing, the availability