In Australia and New Zealand, the main species of tree used for MDF is plantation-grown radiata pine; but a variety of other products have also been used, including other woods, waste paper and fibres.
The trees are debarked after being cut. The bark can be sold for use in landscaping, or burned in on-site furnaces. The debarked logs are sent to the MDF plant, where they go through the chipping process. A typical disk chipper contains 4–16 blades. Any resulting chips that are too large may be re-chipped; undersized chips may be used as fuel. The chips are then washed and checked for defects.
The chips are then compacted using a screw feeder, are heated/steamed for 30–120 seconds to soften the wood, then joined with liquefied wax and fed into a defibrator. The defibrator maintains a high pressure and temperature while grinding the wood chips into a pulp.
From the defibrator, the pulp enters a blowline, where it is joined with resin, often urea-formaldehyde. The wax improves moisture resistance and the resin initially helps reduce clumping, but ultimately is the primary binding agent. The material dries quickly when it enters an expansion chamber and expands into a fine, fluffy and lightweight fibre that is stored until needed at the forming line.
Dry fibre gets sucked into the top of a pendistor, which evenly distributes fibre into a uniform mat below it, usually of 230–610 mm thickness. The mat is pre-compressed and either sent straight to a continuous hot press or cut into large sheets for a multi-opening hot press. The hot press activates the bonding resin and sets the strength and density profile.
After pressing, MDF is cooled in a star dryer or cooling carousel, trimmed and sanded. In certain applications, boards are also laminated for extra strength.
The Environmental Impact of MDF has greatly improved over the years. Today, many MDF boards are made from a variety of materials. These include other woods, scrap, recycled paper, bamboo, carbon fibres and polymers, forest thinnings and sawmill off-cuts.
As manufacturers are being pressured to come up with greener products, they have started testing and using non-toxic binders. New raw materials are being introduced. Straw and bamboo are becoming popular fibres because they are a fast-growing renewable resource.