Processes are being developed to recycle medium density fiberboard, giving a second life to a material once considered unrecyclable.
Medium density fiberboard (MDF) is a success story. Barring the odd regional dip during the recent economic crisis, the production of MDF has increased every year for three decades. Its versatility as a material for furniture, shop fitting and construction applications has seen demand for the product mirror the growth in economic development globally. The most prominent regions for production are Europe and China although strong growth is being witnessed in South America and Southeast Asia.
MDF has, however, seen its fair share of criticism from environmentalists. High levels of formaldehyde within resins were typical when MDF was in its infancy. PVC (polyvinyl chloride) was often applied to boards via edge bands or surface finishes, particularly for furniture applications. MDF production itself was seen as power hungry and polluting. A great deal of investment has been made in advanced manufacturing techniques to mitigate many of these concerns. Initiatives in the field of bio-resins will ensure that environmental efficacy continues to improve.
The one key aspect to this material that still sets it apart from other wood based material streams is its perceived lack of recyclability. MDF was conceived in an era that had minimal regard for recycling. Functionality and in-service performance were the critical design parameters of the day. With a global production capacity now exceeding 80 million cubic meters, it is apparent that a solution for the effective recycling of MDF must be adopted.
MDF can of course be burnt and in many countries it is blended with other wood wastes to form biomass fuels from which energy can be recovered. The demand for this type of power station is on the increase because wood is classified as a renewable fuel. Sovereign states seem intent on ignoring waste management hierarchies in their somewhat desperate attempts to meet their obligations as defined under international treaties such as Kyoto.
In some territories, regulatory control exists to prevent MDF being burnt in all but the most sophisticated of incineration facilities. Unfortunately in other regions, the material is often burnt without energy recovery and is used for factory space heating which is a seasonal requirement at best. Worse still is the continued landfilling of this material, a practice that remains prevalent in the U.K.
MDF Recovery Ltd. (MDFR), a start-up company based in Wales, U.K. has an answer, not only for enhancing the sustainability of the life-cycle of MDF but also for adding value to the MDF manufacturing process and to those industries that might wish to utilize a recycled cellulosic fiber source.
MDFR was established in 2009, but one of its founding directors, Craig Bartlett has been associated with technology development for MDF recycling since the year 2000, when he worked at the U.K.’s Furniture Industry Research Association. He feels that current market conditions now allow the re-working of waste generated internally by MDF manufacturers to be highly cost-effective, even when considering the energy savings associated with burning the waste on-site. MDFR, in collaboration with a European MDF producer, constructed a basic waste evaluation tool that suggested that additional annual profits of £2.6 million could be made by re-working waste and ‘B’ grade boards instead of burning them or selling them at reduced cost. Payback on investment of less than 18 months would be possible for those MDF manufacturers that chose to adopt the technology.
The technology also allows for waste MDF from commercial and industrial sources (including customers) to be brought onsite and recycled back into high quality fibers that are suitable for re-integration into the MDF manufacturing process. The value to be gained from such a practice will only increase as manufacturers are subjected to ever increasing price pressure on virgin timber raw materials.
How It Works
MDF Recovery was keen to ensure that its solution was robust, simple and efficient. The approach was adapted from the food processing industry and utilizes a technology known as ohmic (Joule) heating to degrade and break apart the resin bonds that glue the wood fibers together.
The technology involves passing an electric current directly through the material, causing its whole bulk to be heated due to its own natural electrical resistance. This enables rapid and uniform heating of both liquids and particulates without the use of hot heat transfer surfaces and avoids the creation of damaging ‘hot spots’ in the slurry.
The recycling is achieved by soaking the pre-shredded MDF chips within a liquid medium and then heating to around 90 degrees Celcius. At this temperature the bonding resin is hydrolyzed, freeing the wood fibers for effective recovery and re-use.
Once the MDF chips are wet, an electric current can flow though them, causing them to heat much more rapidly than would occur through simple heat conduction. In addition, the temperature within the particulates can rise above 100 degrees Celcius, causing the MDF to split and expand, allowing more rapid ingress of water and the rate of hydrolysis to increase.
This leads to a fast processing rate with minimal water usage and at high efficiency.
Previous attempts to recycle MDF have been made. A batch process utilizing an autoclave was designed in Germany in the mid 1990s, with a continuous microwave-based approach being proposed in the U.K. as recently as 2007. Neither were perfect, batch processing is not suitable for re-integrating fibers into the MDF manufacturing process with plants running at 30-40 tons per hour and microwaving is an inefficient method of heating.
There are many compelling reasons for recycling MDF at the end of its first user life. The principal barrier to doing so has until now been technological. The most apparent market for the MDFR process is within MDF manufacture itself. There are over three hundred production plants operating worldwide, all of which are competing for virgin timber feed stocks with the biomass fuel and other wood using industries. Sixty million tons of timber are required each year for MDF production alone.
The MDFR technology can be retro-fitted to existing plants or designed into new lines. The re-processing of internal waste generated during MDF manufacture could reduce the annual dependence on virgin timber by 1.8 million tons to 3.6 million tons (3 percent to 6 percent of throughput). It makes for a very elegant closed loop recycling solution for the MDF industry. The technology works just as well for particleboard although recycled feed stocks are already common for this product.
MDF Manufacture: This offers the largest potential market for recycled fibers. The specification for incoming fibers is quite exacting as manufacturers seek to maintain a consistency of quality output from their production lines. With this in mind, MDFR sought external validation of the quality of its recovered fibers. Working closely with the BioComposites Centre at the University of Wales, Bangor, MDFR subjected its fibers to rigorous quality assessment.
The recovered fibers were analyzed under a scanning electron microscope to confirm that they retained their structural integrity and that they remained undamaged by the recycling operation. The results showed that the fibers are of a suitable quality for this application.
Although a degree of engineering will be required, the obvious point of entry for the introduction of these recovered fibers into the continuous manufacturing process is just before the blowline. The recovered fibers (introduced at an appropriate and controlled moisture content) will then be resinated alongside the virgin fibers already contained within the system. A virgin fiber substitution rate of 20 percent is considered most appropriate and practicable but niche products containing 100 percent recovered fiber are seen as commercially attractive as they offer a ‘no added formaldehyde’ option when combined with the addition of bio-resins.
Thermal Insulation Products: Mineral wool is by far and away the dominant material used for thermal insulation. It is however, dogged by concerns over its environmental impact (high embedded energy) and lack of ‘user-friendliness’ during installation—in some forms it can prove unpleasant to work with.
The use of cellulosic material for insulation is increasing but commands less than 5 percent of the overall market at present. Cellulosic materials already in use include overprint newspaper and wood fibers. Recycled newspaper is particularly suitable for loose blown applications whereas wood fibers are used as flexible mats or semi-solid batts. MDFR’s recovered MDF fibers have been trialed in loose blown products and have been shown to improve the in-service performance of the product when used in substitution rates of between 25 percent and 50 percent.
Further development is under way to incorporate recycled MDF fibers into flexible mats that will offer class-leading performance in combination with excellent handling characteristics and competitive pricing.
Wood Plastic Composites (WPCs): The major markets for these products are North America and Continental Europe although production is growing in other parts of the world. Garden decking, street furniture and increasingly construction profiles are the most common product types produced.
WPCs are usually made with a mix of virgin or natural polymer together with fine wood particles (wood flour). The mixture is typically extruded into the desired profile although pre-pelletizing the mix before further extrusion has been shown to offer some manufacturing advantages.
The current wood content used in WPCs has a particle size of less than 500 microns. MDFR’s fibers are typically in the range of 0.5 to 3 millimeters. A successful introduction of recycled MDF fibers into WPCs will allow for light weighting of products to take place whilst retaining strength. MDF Recovery is undertaking trials in the U.K. which involve pelletizing the fiber/polymer mix before extrusion.
Other Industrial Applications: There are numerous industrial product applications for which recycled MDF fibres can be used. These include spill sorbents, horticultural growth media (hydroseeding, grow bags and hydroponic substrates), industrial fillers and bitumen additives (flow aids).
MDF Recovery has secured U.K. patent protection for its process. The Welsh government has provided grant funding to assist the company with securing protection in other territories around the world during 2012. The process, having been proven by an independent engineering research company, will now be up-scaled with the construction of a pilot sized demonstration unit.
The economic and environmental benefits that this technology offers to the MDF industry are clear. However, the demonstrator is needed to mitigate the risk involved in investing in such a novel process. The high quality fibers produced by this plant are designed to show that the technology can operate at a commercially relevant scale. Further negotiations will then take place with MDF manufacturing groups to ensure that the technology is rolled out in the most effective manner.
Outside of the U.K., the principal commercialization mechanism adopted by MDFR will be the issuing of licenses to utilize the technology. However, within the U.K., MDFR will operate its own fiber processing plants. The company is partnering with a waste management firm that will issue long term supply contracts for the provision of MDF waste. Several regional plants are planned.
This story was submitted on behalf of MDF Recovery Ltd (MDFR), Wales, U.K.