Particle board, also known as particleboard and chipboard, is an engineered wood product manufactured from wood chips, sawmill shavings, or even sawdust, and a synthetic resin or other suitable binder, which is pressed and extruded. Oriented strand board, also known as flakeboard, waferboard, or chipboard, is similar but uses machined wood flakes offering more strength. All of these are composite materials that belong to the spectrum of fiberboard products.
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Characteristics
Particle board is cheaper, denser and more uniform than conventional wood and plywood and is substituted for them when cost is more important than strength and appearance. However, particleboard can be made more attractive by painting or the use of wood veneers onto surfaces that will be visible. Though it is denser than conventional wood, it is the lightest and weakest type of fiberboard, except for insulation board. Medium-density fibreboard and hardboard, also called high-density fiberboard, are stronger and denser than particleboard. Different grades of particleboard have different densities, with higher density connoting greater strength and greater resistance to failure of screw fasteners.
A major disadvantage of particleboard is that it is very prone to expansion and discoloration due to moisture, particularly when it is not covered with paint or another sealer. Therefore, it is rarely used outdoors or in places where there are high levels of moisture, with the exception of some bathrooms, kitchens and laundries, where it is commonly used as an underlayment - in its moisture resistant variant - beneath a continuous sheet of vinyl flooring.
The advantages of using particleboard over veneer core plywood is it is more stable, (unless it gets wet), much cheaper to buy, and somewhat more convenient to use.
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History and development
The particleboards originated in Germany. Firstly produced particleboard is dated back to 1887, when Hubbard made so-called "artificial wood" made from wood flour and albumin based adhesive, consolidated under high temperature and pressure.
Although the use of two or three layers of wood veneer is ancient, modern 4' x 8' sheets of plywood with 5-11 core layers of veneer were invented in the early 20th century, and began to become common by the Second World War. During the war, phenolic resin was more readily accessible than top grade wood veneer in Germany, and Luftwaffe pilot and inventor Max Himmelheber played a role in making the first sheets of particleboard, which were little more than pourings of floor sweepings, wood chips, and ground up off-cuts and glue. The first commercial piece was produced during World War II at a factory in Bremen, Germany. For its production, waste material was used - such as planer shavings, offcuts or sawdust - hammer-milled into chips and bound together with a phenolic resin. Hammer-milling involves smashing material into smaller and smaller pieces until they can pass through a screen. Most other early particleboard manufacturers used similar processes, though often with slightly different resins.
It was found that better strength, appearance and resin economy could be achieved by using more uniform, manufactured chips. Producers began processing solid birch, beech, alder, pine and spruce into consistent chips and flakes; these finer layers were then placed on the outside of the board, with its core composed of coarser, cheaper chips. This type of board is known as three-layer particleboard.
More recently, graded-density particleboard has also evolved. It contains particles that gradually become smaller as they get closer to the surface
Manufacturing
Particleboard or chipboard is manufactured by mixing wood particles or flakes together with a resin and forming the mixture into a sheet. The raw material to be used for the particles is fed into a disc chipper with between four and sixteen radially arranged blades (the chips from disk chippers are more uniform in shape and size than from other types of wood chipper). The particles are then dried, after which any oversized or undersized particles are screened out.
Resin is then mist-sprayed through fine nozzles onto the particles. There are several types of resins that are commonly used. Amino-formaldehyde based resins are the best performing when considering cost and ease of use. Urea Melamine resins are used to offer water resistance with increased melamine offering enhanced resistance. It is typically used where the panel is used in external applications due to the increased water resistance offered by phenolic resins and also the colour of the resin resulting in a darker panel. Melamine Urea phenolic formaldehyde resins exist as a compromise. To enhance the panel properties even further the use of resorcinol resins typically mixed with phenolic resins are used, but this is usually used with plywood for marine applications and a rare occasion in panel production.
Panel production involves various other chemicals--including wax, dyes, wetting agents, release agents--to make the final product water resistant, fireproof, insect proof, or to give it some other quality.
The particles then pass through a mist of resin sufficient to coat all surfaces and are then layered, first into a continuous carpet. This 'carpet' is then separated into discrete, rectangular 'blankets' which will then be compacted in a cold press. A weighing device notes the weight of flakes, and they are distributed into position by rotating rakes. In graded-density particleboard, the flakes are spread by an air jet that throws finer particles further than coarse ones. Two such jets, reversed, allow the particles to build up from fine to coarse and back to fine.
The sheets formed are then cold-compressed to reduce their thickness and make them easier to transport. Later, they are compressed again, under pressures between 2 and 3 megapascals (290 and 440 psi) and temperatures between 140 and 220 °C (284 and 428 °F). This process sets and hardens the glue. All aspects of this entire process must be carefully controlled to ensure the correct size, density and consistency of the board.
The boards are then cooled, trimmed and sanded. They can then be sold as raw board or surface improved through the addition of a wood veneer or laminate surface.
Furniture design
Particle board has had an enormous influence on furniture design. In the early 1950s, particle board kitchens started to come into use in furniture construction but, in many cases, it remained more expensive than solid wood. A particle board kitchen was only available to the very wealthy. Once the technology was more developed, particle board became cheaper.
Some large companies base their strategies around providing furniture at a low price. To do this, they use the least expensive materials possible. In almost all cases, this means particle board or MDF or similar. However, manufacturers, in order to maintain a reputation for quality at low cost, may use higher grades of particle board, e.g., higher density particle board, thicker particle board, or particle board using higher-quality resins. One may note the amount of sag in a shelf of a given width in order to draw the distinction.
In general the much lower cost of sheet goods (particle board, medium density fiberboard, and other engineered wood products) has helped to displace solid wood from many cabinetry applications.
Safety
Safety concerns are two part, one being fine dust and chemicals released when particleboard is machined (e.g., sawing or routing). Occupational exposure limits exist in many countries recognizing the hazard of wood dusts. Cutting particle board can release formaldehyde, carbon monoxide, hydrogen cyanide (in the case of amino resins) and phenol (in the case of phenol-formaldehyde resins). The other concern is with the slow release of formaldehyde over time. In 1984 concerns about the initial indoor level of formaldehyde led the United States Department of Housing and Urban Development to set standards for construction of manufactured homes. Particleboard (PB), medium density fibreboard (MDF), oriented strand board (OSB), and laminated flooring have been major sources of formaldehyde emissions. In response to much consumer and woodworker pressure on the industry, PB and MDF are at least now available in "no added formaldehyde" (NAF) versions, which are not yet commonly used by 2015. Many other building materials such as furniture finish, carpeting and caulking give off formaldehyde, as well as Urea-formaldehyde foam insulation, which is banned in Canada for installation in a residential closed cavity wall. Formaldehyde is classified by the WHO as a known human carcinogen.
Source of the article : Wikipedia
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