Medium-density fibreboard
Medium-density fibreboard (MDF) is an engineered wood product made by breaking down hardwood or softwood residuals into wood fibre, often in a defibrator, combining it with wax and a resin binder, and forming it into panels by applying high temperature and pressure.
MDF is typically made up of 82% wood fibre, 9% urea-formaldehyde resin glue, 8% water, and 1% paraffin wax.
Because it is easier to machine and has good weathering characteristics, it tends to replace particleboard in applications such as furniture, cabinet making, joinery, craft work and flooring.
[8] 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.
Where moisture resistance is desired, a proportion of eucalypt species may be used, making use of the endemic oil content of such trees.
[9] The chips are then compacted into small plugs using a screw feeder, heated for 30–120 seconds to soften the lignin in the wood, then fed into a defibrator.
The material dries quickly in the final heated expansion chamber of the blowline and expands into a fine, fluffy and lightweight fibre.
The glue and the other components (hardener, dye, urea, and so on) can be injected into blowline even at a high pressure (100 bar, 10 MPa, 1,500 psi) and the drying process continues inside a long pipe to the exit cyclones, that is connected to the heating chamber.
These include other woods, scrap, recycled paper, bamboo, carbon fibres and polymers, forest thinnings, and sawmill off-cuts.
MDF does not contain knots or rings, making it more uniform than natural woods during cutting and in service.
Formaldehyde resins are commonly used to bind together the fibres in MDF,[15] and testing has consistently revealed that MDF products emit free formaldehyde and other volatile organic compounds that pose health risks at concentrations considered unsafe, for at least several months after manufacture.
When painting, coating all sides of the finished piece is a good practice to seal in the free formaldehyde.
[10] Whether these constant emissions of formaldehyde reach harmful levels in real-world environments is not fully determined.
As far back as 1987, the United States Environmental Protection Agency classified it as a "probable human carcinogen", and after more studies, the World Health Organization's International Agency for Research on Cancer (IARC), in 1995, also classified it as a "probable human carcinogen".
All around the world, variable certification and labeling schemes are there for such products that can be explicit to formaldehyde release, such as that of Californian Air Resources Board.
In modern construction, spurred by the high costs of hardwoods, manufacturers have been adopting this approach to achieve a high-quality finishing wrap covering over a standard MDF board.
This is possible only with simple profiles; otherwise, when the thin wood layer dries, it breaks at bends and angles.
