Medium-density fibreboard

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A sample of MDF MDF Sample.jpg
A sample of MDF

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. [1] 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. [2]

Contents

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. [3]

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. [4] The density is typically between 500 and 1,000 kg/m3 (31 and 62 lb/cu ft). [5] 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 700–720 kg/m3 (44–45 lb/cu ft) 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:

Although similar manufacturing processes are used in making all types of fibreboard, MDF has a typical density of 600–800 kg/m3 or 0.022–0.029 lb/in3, in contrast to particle board (500–800 kg/m3) and to high-density fibreboard (600–1,450 kg/m3).

Manufacturing

Development of the worldwide production of MDF by region 1995-2021.
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Africa
Asia
Europe
North America
Latin America
Oceania MDF-Production by Regions.jpg
Development of the worldwide production of MDF by region 1995-2021.
  Africa
  Asia
  Europe
  North America
  Latin America
  Oceania

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. [7]

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. [7]

Fibre production

Compared to other fibre boards, such as Masonite, MDF is characterised by the next part of the process, and how the fibres are processed as individual, but intact, fibres and vessels, manufactured through a dry process. [7] 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. [7] A typical defibrator consists of two counter-rotating discs with grooves in their faces. Chips are fed into the centre and are fed outwards between the discs by centrifugal force. The decreasing size of the grooves gradually separates the fibres, aided by the softened lignin between them. [7]

From the defibrator, the pulp enters a blowline, a distinctive part of the MDF process. This is an expanding circular pipeline, initially 40 mm in diameter, increasing to 1500 mm. Wax is injected in the first stage, which coats the fibres and is distributed evenly by the turbulent movement of the fibres. A urea-formaldehyde resin is then injected as the main bonding agent. The wax improves moisture resistance and the resin initially helps reduce clumping. 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. This fibre may be used immediately, or stored. [7]

Sheet forming

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 precompressed and either sent straight to a continuous hot press or cut into large sheets for a multiple-opening hot press. The hot press activates the bonding resin and sets the strength and density profile. The pressing cycle operates in stages, with the mat thickness being first compressed to around 1.5 times the finished board thickness, then compressed further in stages and held for a short period. This gives a board profile with zones of increased density, thus mechanical strength, near the two faces of the board and a less dense core. [7]

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.[ citation needed ] 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 nontoxic binders. New raw materials are being introduced. Straw and bamboo are becoming popular fibres because they are a fast-growing, renewable resource.

Comparison with natural woods

MDF does not contain knots or rings, making it more uniform than natural woods during cutting and in service. [8] 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 makes it ideal for veneering, as no underlying grain is available to telegraph through the thin veneer as 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. [9] 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

Disadvantages

Applications

Loudspeaker enclosure being constructed out of MDF Medium density fiberboard.jpg
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. [12]

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.

Safety concerns

MDF dust collector Wood dust collector.jpg
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. [13] [14] [15] 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. [8]

Whether these constant emissions of formaldehyde reach harmful levels in real-world environments is not fully determined. The primary concern is for the industries using formaldehyde. 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". 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 leukaemia in June 2004. [16]

According to International Composite Board Emission Standards, 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 mg of formaldehyde out of every 100 g of the glue used in particleboard and plywood fabrication. E1 and E2 are classified as having 9 and 30 g of formaldehyde per 100 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. [17]

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 adopting this approach to achieve a high-quality finishing wrap covering over a standard MDF board. One common type uses oak veneer. [18] Making veneered MDF is a complex procedure, which involves taking a slice of hardwood about 1–2 mm thick and then, through high pressure and stretching methods, wrapping them around the profiled MDF boards. This is possible only with simple profiles; otherwise, when the thin wood layer dries, it breaks at bends and angles.

See also

Related Research Articles

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Formaldehyde ( for-MAL-di-hide, fər-) (systematic name methanal) is an organic compound with the chemical formula CH2O and structure H−CHO, more precise H2C=O. The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as aqueous solutions (formalin), which consists mainly of the hydrate CH2(OH)2. It is the simplest of the aldehydes (R−CHO). As a precursor to many other materials and chemical compounds, in 2006 the global production of formaldehyde was estimated at 12 million tons per year. It is mainly used in the production of industrial resins, e.g., for particle board and coatings. Small amounts also occur naturally.

<span class="mw-page-title-main">Plywood</span> Manufactured wood panel made from thin sheets of wood veneer

Plywood is a composite material manufactured from thin layers, or "plies", of wood veneer that are glued together with adjacent layers, having both glued with each other at right angle or at 90 degrees angle. It is an engineered wood from the family of manufactured boards, which include medium-density fibreboard (MDF), oriented strand board (OSB), and particle board.

<span class="mw-page-title-main">Engineered wood</span> Range of derivative wood products engineered for uniform and predictable structural performance

Engineered wood, also called mass timber, composite wood, human-made wood, or manufactured board, includes a range of derivative wood products which are manufactured by binding or fixing the strands, particles, fibres, or veneers or boards of wood, together with adhesives, or other methods of fixation to form composite material. The panels vary in size but can range upwards of 64 by 8 feet and in the case of cross-laminated timber (CLT) can be of any thickness from a few inches to 16 inches (410 mm) or more. These products are engineered to precise design specifications, which are tested to meet national or international standards and provide uniformity and predictability in their structural performance. Engineered wood products are used in a variety of applications, from home construction to commercial buildings to industrial products. The products can be used for joists and beams that replace steel in many building projects. The term mass timber describes a group of building materials that can replace concrete assemblies.

<span class="mw-page-title-main">Oriented strand board</span> Engineered wood particle board

Oriented strand board (OSB) is a type of engineered wood similar to particle board, formed by adding adhesives and then compressing layers of wood strands (flakes) in specific orientations. It was invented by Armin Elmendorf in California in 1963. OSB may have a rough and variegated surface with the individual strips of around 2.5 cm × 15 cm, lying unevenly across each other, and is produced in a variety of types and thicknesses.

<span class="mw-page-title-main">Thermosetting polymer</span> Polymer obtained by irreversibly hardening (curing) a resin

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<span class="mw-page-title-main">Phenol formaldehyde resin</span> Chemical compound

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<span class="mw-page-title-main">Bamboo floor</span> Type of flooring

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<span class="mw-page-title-main">Particle board</span> Pressed and extruded wood product

Particle board, also known as particleboard, chipboard, and low-density fiberboard, is an engineered wood product manufactured from wood chips and a synthetic resin or other suitable binder, which is pressed and extruded. Particle board is often confused with oriented strand board, a different type of fiberboard that uses machined wood flakes and offers more strength.

<span class="mw-page-title-main">Hardboard</span> Type of fiberboard (engineered wood product)

Hardboard, also called high-density fiberboard (HDF), is a type of fiberboard, which is an engineered wood product. It is used in furniture and in the construction industry.

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<span class="mw-page-title-main">Laminated veneer lumber</span> Engineered Wood Product used in wood frame construction

Laminated veneer lumber (LVL) is an engineered wood product that uses multiple layers of thin wood assembled with adhesives. It is typically used for headers, beams, rimboard, and edge-forming material. LVL offers several advantages over typical milled lumber: Made in a factory under controlled specifications, it is stronger, straighter, and more uniform. Due to its composite nature, it is much less likely than conventional lumber to warp, twist, bow, or shrink. LVL is a type of structural composite lumber, comparable to glued laminated timber (glulam) but with a higher allowable stress. A high performance more sustainable alternative to lumber, Laminated Veneer Lumber (LVL) beams, headers and columns are used in structural applications to carry heavy loads with minimum weight.

Urea-formaldehyde (UF), also known as urea-methanal, so named for its common synthesis pathway and overall structure, is a nontransparent thermosetting resin or polymer. It is produced from urea and formaldehyde. These resins are used in adhesives, plywood, particle board, medium-density fibreboard (MDF), and molded objects. In agriculture, urea-formaldehyde compounds are one of the most commonly used types of slow-release fertilizer.

<span class="mw-page-title-main">Kitchen cabinet</span> Kitchen furniture

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<span class="mw-page-title-main">Wood veneer</span> Thin slices of wood

In woodworking, veneer refers to thin slices of wood and sometimes bark that typically are glued onto core panels to produce flat panels such as doors, tops and panels for cabinets, parquet floors and parts of furniture. They are also used in marquetry. Plywood consists of three or more layers of veneer. Normally, each is glued with its grain at right angles to adjacent layers for strength. Veneer beading is a thin layer of decorative edging placed around objects, such as jewelry boxes. Veneer is also used to replace decorative papers in wood veneer HPL.

Wood glue is an adhesive used to tightly bond pieces of wood together. Many substances have been used as glues. Traditionally animal proteins like casein from milk or collagen from animal hides and bones were boiled down to make early glues. They worked by solidifying as they dried. Later, glues were made from plant starches like flour or potato starch. When combined with water and heated, the starch gelatinizes and forms a sticky paste as it dries. Plant-based glues were common for books and paper products, though they can break down more easily over time compared to animal-based glues. Examples of modern wood glues include polyvinyl acetate (PVA) and epoxy resins. Some resins used in producing composite wood products may contain formaldehyde. As of 2021, “the wood panel industry uses almost 95% of synthetic petroleum-derived thermosetting adhesives, mainly based on urea, phenol, and melamine, among others”.

<span class="mw-page-title-main">Fiberboard</span> Engineered wood product made out of wood fibers

Fiberboard or fibreboard is a type of engineered wood product that is made out of wood fibers. Types of fiberboard include particle board or low-density fiberboard (LDF), medium-density fiberboard (MDF), and hardboard or high-density fiberboard (HDF).

<span class="mw-page-title-main">Edge banding</span> A material or process used in finish carpentry

Edge banding or edgebanding is the name of both a process and an associated narrow strip of material used to create durable and aesthetically pleasing trim edges during finish carpentry. Edge banding is used to cover the exposed sides of materials such as plywood, particle board, or MDF, increasing durability and giving the appearance of a solid or more valuable material.

Plyboo is one of the brands owned by Smith&Fong Co., a privately held building materials company based in San Francisco. Plyboo was launched as a brand in 1993 by Smith&Fong, the first U.S. company to sell imported bamboo flooring in North America. Although Smith&Fong Co. is the parent company, Plyboo has come to be how the company is primarily identified.

<span class="mw-page-title-main">Molded plywood</span>

Molded plywood is the term for two- or three-dimensionally shaped products from multiple veneer layers that are glued together through heat and pressure in a pressing tool. The veneer layers are arranged crosswise at an angle of 90 degrees. Molded wood is used for flat furniture components such as seats, backrests and seat shells. When the veneer layers are arranged in the same direction, it is called laminated wood. It is used for armrests and chair frames. After pressing, the blanks are processed mechanically. A particular feature is the ability to produce different variations of shapes from the blanks. Due to its immense strength and low weight, molded wood is particularly suitable for interior decoration, seating furniture, bed slats, skateboards and vehicle construction.

References

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  15. "ALDEHYDE EMISSIONS FROM PARTICLEBOARD AND MEDIUM DENSITY FIBERBOARD PRODUCTS" (PDF). Fpl.fs.fed.us. Retrieved 17 January 2018.
  16. "Formaldehyde and Cancer Risk". National Cancer Institute. 10 June 2011. Retrieved 17 January 2018.
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Further reading