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MDF Sample

A sample of MDF

Medium-density fiberboard (MDF) is an engineered wood product formed by breaking down hardwood or softwood residuals into wood fibers, often in a defibrator, combining it with wax and a resin binder, and forming panels by applying high temperature and pressure.[1] MDF is more dense than plywood.

It is made up of separated fibers, (not wood veneers) but can be used as a building material similar in application to plywood. It is much more dense than normal particle board.

The name derives from the distinction in densities of fiberboard. Large-scale production of MDF began in the 1880s [1].[citation needed]

TypesEdit

There are different kinds of MDF, which are sometimes labeled by colour:

  • Moisture resistant is typically green
  • Fire retardant MDF is typically red or blue
  • Nuclear resistant is yellow.

Although similar manufacturing processes are used in making all types of fiberboard, MDF has a typical density of 600-800 kg/m³ or .022-.029 lbs/in3, in contrast to particle board (160-450 kg/m³) and to high-density fiberboard (600-1450 kg/m³).

Another addition to the MDF range is a product named FX-Platform, produced by Norbord. It is a softwood plywood core, laminated on both sides with MDF, giving it working properties containing the advantages of both plywood and MDF.[2] This product has met the acceptance criteria for compliance with the ANSI/HPVA HP-1-2004 Section 3.12 Formaldehyde Emission Requirements for industrial panels.[3]

ManufactureEdit

2005mdf

Medium-density fiberboard output in 2005

In Australia 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 fibers.

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, and will be heated for 30-120 seconds to soften the wood; they are then fed into a defibrator which maintains high pressure and temperature. The pulp that exits from the defibrator is fine, fluffy, and light in weight and in colour.

From the defibrator the pulp enters a blowline where it is joined with wax (to improve moisture resistance) and resin (to stop the pulp from forming bundles). The material expands in size and is then heated by heating coils. When it comes out it may be stored in bins for an indefinite length of time.

After this drying period the board goes through a "Pendistor" process which creates 230-610 mm thick boards. Then it is cut and continues to the press. Here it is pressed for a few minutes, to make a stronger and denser board.

After pressing, MDF is cooled in a star dryer, trimmed and sanded. In certain applications, boards are also laminated for extra strength.

The Environmental Impact of MDF has greatly improved over the years.[citation needed] Today many MDF boards are made from a variety of materials. These include other woods, scrap, recycled paper, bamboo, carbon fibers and polymers, steel, glass, forest thinning 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 fibers because they are a fast growing renewable resource.

Comparison to natural woodsEdit

Benefits of MDFEdit

  • Is an excellent substrate for veneers.
  • Is becoming an environmentally friendly product.
  • Some varieties are less expensive than many natural woods
  • Isotropic (its properties are the same in all directions as a result of no grain), so no tendency to split
  • Consistent in strength and size
  • Flexible. Can be used for curved walls or surfaces.
  • Shapes well.

Drawbacks of MDFEdit

  • More dense than plywood or chipboard (the resins are heavy)
  • Swells and breaks when saturated with water
  • May warp or expand if not sealed
  • Contains urea-formaldehyde which may cause eye and lung irritation when cutting and sanding
  • Dulls blades more quickly than many woods
  • 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.
  • Subject to significant shrinkage in low humidity environments.
  • Trim (i.e. baseboards) comes pre-primed but this is insufficient for fine finish painting. Painting with latex paints is difficult due to rapid water absorption. Most finishes appear uneven and nail holes tend to pucker somewhat.

Recent developmentsEdit

A fairly recent development is flexible MDF sheets made by BendyMDF. These are sheets scored with multiple slots so that the material can easily be formed into curved shapes and then fixed.

Applications Edit

Medium density fiberboard

Loudspeaker enclosure being constructed out of MDF

MDF is often used in school projects because of its flexibility. It is also often used in loudspeaker enclosures, due to its increased weight and rigidity over normal plywood. Slatwall Panels made from MDF are used in the shop fitting industry.

Safety aspects of MDF Edit

When MDF is cut, a large quantity of dust particles is released into the air. It is important that a respirator be worn and the wood be cut in a controlled and ventilated environment. It is a good practice to seal the exposed edges to limit the emissions from the binders contained in this material.

Formaldehyde resins are commonly used to bind MDF together, and testing has consistently revealed that MDF products emit urea formaldehyde and other volatile organic compounds that pose health risks at sufficient concentrations, for at least several months after manufacture.[4][5][6][7][8] Urea formaldehyde is always being slowly released from the surface of MDF. When painting it is good idea to coat the whole of the product in order to seal in the urea formaldehyde. Wax and oil finishes may be used as finishes but they are less effective at sealing in the urea formaldehyde.[9]

Whether these chronic emissions of formaldehyde reach harmful levels in real-world environments is not yet fully determined. The primary concern is for the industries using formaldehyde. As far back as 1987 the U.S. EPA classified it as a "probable human carcinogen" and after more studies the WHO International Agency for Research on Cancer (IARC), in 1995, also classified it as a "probable human carcinogen". Further information and evaluation of all known data led the IARC to reclassify formaldehyde as a "known human carcinogen"[10] associated with nasal sinus cancer and nasopharyngeal cancer, and possibly with leukemia in June 2004.[11]

ReferencesEdit

NotesEdit

Reference SourcesEdit

External linksEdit

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