thumb|upright=1.35|A sample of 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 generally denser than plywood. It is made up of separated fibre but can be used as a building material similar in application to plywood. It is stronger and denser than particle board.

The name derives from the distinction in densities of fibreboard. Large-scale production of MDF began in the 1980s, in both North America and Europe.

Over time, the term "MDF" has become a generic name for any dry-process fibreboard.

Physical properties

MDF is typically made up of 82% wood fibre, 9% urea-formaldehyde resin glue, 8% water, and 1% paraffin wax. The density is typically between . The range of density and classification as light-, standard-, or high-density board is a misnomer and confusing. The density of the board, when evaluated in relation to the density of the fibre that goes into making the panel, is important. A thick MDF panel at a density of may be considered as high density in the case of softwood fibre panels, whereas a panel of the same density made of hardwood fibres is not regarded as so. The evolution of the various types of MDF has been driven by differing need for specific applications.

Types

The different kinds of MDF (sometimes labeled by colour) are:

  • Ultralight MDF plate (ULDF)
  • Moisture-resistant board is typically green
  • Fire retardant MDF is typically red or blue

In Europe, MDF is classified for use by the standard EN 622-5, such as load-bearing for general dry or humid conditions. The light and ultralight MDF are also classified by EN 622-5 for general (non-load-bearing) use.

{| class="wikitable"

|+

!EN 622 classification

!Use

|-

|MDF

|General purpose board for dry conditions

|-

|MDF.H

|General purpose board for humid conditions

|-

|MDF.LA

|Load-bearing boards for dry conditions

|-

|MDF.HLS

|Load-bearing boards for humid conditions

|-

|MDF.RWH

|Board for rigid underlays in roofs and walls

|}

Although similar manufacturing processes are used in making all types of fibreboard, MDF has a typical density of 600–800&nbsp;kg/m<sup>3</sup> or 0.022–0.029&nbsp;lb/in<sup>3</sup>, in contrast to particle board (500–800&nbsp;kg/m<sup>3</sup>) and to high-density fibreboard (600–1,450&nbsp;kg/m<sup>3</sup>). In addition, MDF typically has an MOR of 40 MPa and an MOE of 3 GPa. 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.

Manufacturing

thumb|upright=1.35|Development of the worldwide production of MDF by region 1995-2021.

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.

Chip production

The trees are debarked after being cut. The bark can be sold for use in landscaping or used as biomass fuel 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 four to 16 blades. Any resulting chips that are too large may be rechipped; undersized chips may be used as fuel. The chips are then washed and checked for defects. Chips may be stored in bulk, as a reserve for manufacturing. However, MDF is not entirely isotropic since the fibres are pressed tightly together through the sheet. Typical MDF has a hard, flat, smooth surface that is suitable for applying a veneer, as it does not have a grain that will telegraph through the veneer as can happen with plywood. A so-called "premium" MDF is available that features more uniform density throughout the thickness of the panel.

MDF may be glued, doweled, or laminated. Typical fasteners are T-nuts and pan-head machine screws. Smooth-shank nails do not hold well, and neither do fine-pitch screws, especially in the edge. Special screws are available with a coarse thread pitch, but sheet-metal screws also work well. MDF is not susceptible to splitting when screws are installed in the face of the material, but due to the alignment of the wood fibres, may split when screws are installed in the edge of the board without pilot holes.

Advantages

  • Denser than plywood and chipboard
  • Consistent in strength and size
  • Shapes well
  • Stable dimensions (less expansion and contraction than natural wood)
  • Takes paint well
  • Takes wood glue well
  • High screw pull-out strength in the face grain of the material
  • Flexible

Disadvantages

  • Low-grade MDF may swell and break when saturated with water
  • May warp or expand in humid environments if not sealed
  • May release formaldehyde, which is a known human carcinogen and may cause allergy, eye and lung irritation when cutting and sanding
  • Dulls blades more quickly than many woods: Use of tungsten carbide-edged cutting tools is almost mandatory, as high-speed steel dulls too quickly.
  • Though it does not have a grain in the plane of the board, it does have one into the board. Screwing into the edge of a board will generally cause it to split in a fashion similar to delaminating.

Applications

thumb|right|200px|[[Loudspeaker enclosure being constructed out of MDF]]

MDF is often used in school projects because of its flexibility.

Slatwall panels made from MDF are used in the shop fitting industry.

MDF is primarily used for indoor applications due to its poor moisture resistance. It is available in raw form, or with a finely sanded surface, or with a decorative overlay.

MDF is also usable for furniture such as cabinets, because of its strong surface.

MDF's density makes it a useful material for the walls of pipe-organ chambers, allowing sound, particularly bass, to be reflected out of the chamber into the hall.

Interior trim and mouldings

MDF is widely used for painted interior trim, including skirting (base) boards, architraves and window boards, because its smooth, knot-free surface can be machined into crisp profiles and accepts paint evenly.

According to the British Woodworking Federation, MDF mouldings are commonly supplied factory-primed, which shortens on-site finishing time and improves surface quality.

"Homebuilding & Renovating" magazine also describes MDF trim as “a robust and affordable solution” that resists warping and swelling better than many softwoods.

Safety concerns

thumb|MDF dust collector

When MDF is cut, a large quantity of dust particulate is released into the air.

Formaldehyde resins are commonly used to bind together the fibres in MDF, 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. Urea-formaldehyde is always being slowly released from the edges and surface of MDF. When painting, coating all sides of the finished piece is a good practice to seal in the free formaldehyde. Wax and oil finishes may be used as finishes, but they are less effective at sealing in the free formaldehyde.

According to International Composite Board Emission Standards<!-- (ICBES) -->, three European formaldehyde classes are used, E0, E1, and E2, based on the measurement of formaldehyde emission levels. For instance, E0 is classified as having less than 3&nbsp;mg of formaldehyde out of every 100&nbsp;g of the glue used in particleboard and plywood fabrication. E1 and E2 are classified as having 9 and 30&nbsp;mg of formaldehyde per 100&nbsp;g of glue, respectively. 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.

Veneered MDF

Veneered MDF provides many of the advantages of MDF with a decorative wood veneer surface layer. In modern construction, spurred by the high costs of hardwoods, manufacturers have been using veneered MDF instead of hardwood. One common type uses oak veneer. Making veneered MDF is a complex procedure, which involves taking a slice of hardwood about thick and then, through high pressure and stretching, wrapping it around a profiled MDF board. This is successful only when the MDF has a simple profile; if the thin wood layer is forced into more bends and angles, it will break as it dries.

See also

  • Oriented strand board <!-- (OSB) -->
  • Hardboard
  • Solid wood
  • Natural Fibre Board

References

Sources

Further reading

  • English, Brent, John A. Youngquist, and Andrzej M. Krzysik, Lignocellulosic Composites in Gilbert, Richard D., ed. Cellulosic polymers, blends and composites. New York: Hanser Publishers: 115–130; 1994. Chapter 6
  • ASTM D5651 - 95a(2008) Standard Test Method for Surface Bond Strength of Wood-Base Fiber and Particle Panel Materials