In the rest of the world the product is known as particleboard, but in the UK the product has been known traditionally as wood chipboard. However, with the advent of European standardisation and greater trade with European countries the term particleboard should now be used in the UK; care should be taken to distinguish between particleboard and particleboard made from vegetable fibres such as flax, straw and bagasse (flaxboards according to EN 15197 are dealt with separately in this document). Particleboard is an engineered wood-based sheet material in which wood chips are bonded together with a synthetic resin adhesive.
The particleboard industry in the UK dates from the nineteen forties and originated in a time of austerity with the purpose of utilising waste timber. Over the years the application of new technologies in both production and control, together with the production of tailor-made chips from solid softwood, as well as the use of more sophisticated resin systems has led to the production of huge quantities of a range of panels having a known and reproducible performance.
Wood chips comprise the bulk of particleboard and are prepared in a mechanical chipper generally from coniferous softwoods principally spruce, though pine and fir and hardwoods, such as birch, are sometimes used. Particleboards may also incorporate a large proportion from recycled sources (up to 95% plus but generally around 40%). These chips are generally bound together with synthetic resin systems such as urea- formaldehyde (UF) or melamine urea-formaldehyde (MUF), though phenol- formaldehyde (PF) and polymeric methylene di-isocyanate (PMDI) are used by a few manufacturers.
The binding system employed depends on the end use intended and the grade of the product. The most common resin employed is urea-formaldehyde, but this is only suitable for use in dry conditions: the other three resin systems confer a measure of moisture resistance to the composite.
Typical constituents of a particleboard are of the order (by mass) of 83-88% wood chips, 6-8% formaldehyde based resin or 2-3% PMDI, 5-7% water, and 1-2% paraffin wax solids.
Raw material in the form of either virgin wood or reclaimed wood is chipped, dried and graded into different sizes. Resin is added to the chips and a mat is formed, this would normally have fine chips on the surfaces with coarse chips in the centre. This mat will then be hot pressed either with what is known as a multi-daylight or daylight press which are batch presses or a continuous press. The heat involved and the time in the hot press will cure the resins so that they bind the chips together forming a board with the desired properties (e.g. strength, density etc...). All of the manufacturing processes are usually controlled by complex computer systems that enable the operators to reproduce the same quality with consistency and accuracy on a 24 hour basis. Once the boards are conditioned and cut to size, they will be tested to prove compliance with the relevant specification and claims.
In the UK all the particleboard mills use their own process derived wood fuels to generate process heat. This means that as much as 55% of the heat requirement for production is currently derived from renewable sources.
The special properties of particleboard have several advantages in a wide range of construction and furniture applications. Thus, its good mechanical performance which is the same along and across the panel, and its availability in large sizes renders it appropriate for use as floor decking, either on timber joists, or as a floating floor system. Different grades of the product are available for different environmental conditions and different levels of loading, ranging from domestic to industrial usage including both platform and raised access floors. The higher grades also find widespread use in industrial storage systems. Guidance on the use of load-bearing grades of particleboard in floors, walls and roofs is given in DD CEN/TS 12872.
Large quantities of particleboard are also used in the manufacture of kitchen units and worktops, and in dining-room and bedroom units; these generally have a veneered or laminated finish.
Particleboard is commonly used in furniture and worktops (Grades P1, P2, P3) and structural flooring (Grades P4, P5, P6 & P7).
Oriented Strand Board (OSB)
Compared with many other types of panel products, OSB is a relative newcomer, first developed about twenty five years ago. Over the last decade a phenomenal increase in capacity has occurred and in 2008 world capacity was approximately 25 million m3 produced from nearly 60 mills; European capacity in 2008 was about 3.3 million m3.
OSB is an engineered wood-based sheet material in which relatively long strands of wood are bonded together with a synthetic resin adhesive. Sometimes in all three layers, but usually in only the outer layers of these three-layer panels, the strands are orientated in a particular direction. However, there is quite a large degree of variability in this orientation among adjacent strands in the panels from any one production line as well as between panels from different producers.
Composition and manufacturing process
The timbers used in OSB manufacture include both softwoods (spruce, pine) and hardwood (aspen). Wood strands are cut tangentially from debarked logs which are held longitudinally against rotating knives. The ribbon of flakes produced is usually about 75mm wide and this breaks up on handling to produce individual flakes which are 75mm along the grain and from 5 to 50mm across the grain.
After drying, these flakes are generally sprayed with a synthetic resin, though one or two mills employ powdered resins. One of the important points in OSB manufacture is the removal of fines prior to resin application: this results in the use of lower amounts of resin in OSB (2-3%) compared with other resin bonded panel products.
The three main adhesives used in the production of OSB are phenol formaldehyde (PF), Isocyanates (MDI or PMDI) and melamine urea formaldehyde (MUF). These are either used on their own or the core and the surface layers may use two different types of adhesive.
All these resins confer a measure of moisture resistance to the composite.
In the formation of the mat the strands are aligned either in each of the three layers of the panel, or, more frequently, in only the outer two layers. The degree of orientation varies widely within any one panel, and also in panels from different manufacturers; thus, in panels from different manufacturers it is possible to obtain ratios of property levels in the machine- to cross-direction of 1.25:1 to 2.5:1, thereby emulating the ratios found in plywood.
The boards are subsequently pressed with heat to cure the adhesive and compress the strands to form a compact and dense product to the desired thickness.
There may be a sanding process following pressing and therefore it is possible to obtain sanded boards as well as un-sanded versions.
Because of its lay-up and composition, OSB is primarily a panel for construction and is widely used for flooring, flat roof decking and wall sheathing but is used in furniture where it is not seen. Different grades of the product are available for different levels of loading and different environmental conditions. Guidance on the use of OSB in these load-bearing applications is given in DD CEN/TS 12872. Generally, for the same loading conditions, a thinner board of OSB can be used than a load-bearing particleboard.
There are currently “deemed to satisfy” tables for domestic floor and roof applications in BS 8103-3 (Code of practice for timber floors and roofs for housing), for plywood and particleboard. However there is no deemed to satisfy route for non-domestic floor applications at present.
Large quantities of OSB are also used for sarking and industrial packaging and in the construction of site hoardings and pallet tops.
Dry process fibreboard ('MDF')
MDF is an engineered wood-based sheet materials made by bonding together wood fibres with a synthetic resin adhesive. MDF is a dry process fibreboard which is a generic term so called by virtue of the manufacturing process. A typical process involves reducing wood down to small chips, which are then thermally softened and mechanically refined into fibres, which are then mixed with a synthetic resin adhesive. The resinated fibres are dried and then formed into a mattress ready for pressing. The mattress is pressed between heated polished press plates to the desired thickness. For thick boards more than one mattress may be 'piggy backed' together.
Since 1966 when the first MDF was produced commercially in Deposit, New York State, USA, the market for MDF has increased dramatically world-wide. The first MDF was produced in Europe in 1973 and today European production capacity rivals that in the USA, with 12.5 million cubic metres per annum produced in 2008. Because of its availability in a wide range of thicknesses and the ability to be machined and finished to a high standard, dry process fibreboards have been accepted in a wide range of applications both in construction and also furniture, where in both cases it has substituted solid timber and also other wood-based panels in particular applications.
Around the world there will be many different classification systems under different countries standardization systems, in Europe this would be EN 622-1 and EN 622-5 for MDF in order to easily prove compliance with the requirements for the Construction Products Directive when used in construction applications. It is also possible to obtain product that has not been made according to a standard or indeed uncertified product, but if this is the case correct specification is a must. There are many different end use requirements depending where the product is to be used (e.g. Building Regulations).
The development of value added variants with enhanced mechanical performance and improved performance in the presence of moisture (including for exterior use) and fire have further aided the applications available.
MDF can be manufactured with either softwood or hardwood species. The majority of MDF manufactured is composed mainly of softwood although some individual brands may contain a higher percentage of temperate hardwood depending on the location of the factory to the local forest resource.
The constituents of a typical standard MDF manufactured in the United Kingdom or Ireland are 82% virgin wood fibre (wholly or mainly softwood), 10% synthetic resin binder, 7% water, less than 1% paraffin wax solids and less than 0.05% silicon. The most common binder is urea-formaldehyde (service class 1 or 'dry') although depending on the grade and end use of the product other binders may be used, i.e. melamine urea-formaldehyde, phenolic resins and polymeric methylene di-isocyonate (PMDI) which are generally applied in boards that require an improved moisture resistance.
The raw material used is often forest thinning, undersize sawmill stock up to about 200mm in diameter and sawmill residues that are initially chipped to approximately 20mm squares that are 3-4mm thick. This goes through a screening process to remove large particles and any metal. The next stage in the process is to reduce the chips into fibres. The chips are subjected to steam under pressure which softens the lignin in the wood. The most common method of producing fibres is by using a defribrator which breaks up the softened chips between two revolving segmented discs.
The next stage is to add resin to the fibres. This is done by blowing fibres down a pipe which can be 1m wide and as long as 90m. In the pipe the defribrated fibres are first dried, once dried resin is added to the fibres. The resin is blown into the pipe and coats the fibres as they pass or this carried out in a separate chamber. Dried and resinated fibres are the fed onto a conveyor belt to form the mat. The mat can be as much as 500mm or greater to begin with but is gradually reduced in size before final pressing. The final pressing stage is carried out under heat and pressure for a predetermined length of time. Once pressed, boards are conditioned and cut to size.
Due to the particular machining and finishing attributes combined with good working properties and its availability in a wide range of sheet thicknesses and sizes, MDF finds application in a wide range of construction and furniture applications. It is used increasingly for interior design and building applications such as skirtings and architraves, windowboards, wall linings, and decorative facades, as well as the core material for some floorings.
MDF can be cut without breakout or splintering and it can be profiled on the edges and surfaces. The smooth and relatively dense surface provides an excellent base for painting, veneering and laminating. Consequently MDF is used extensively in furniture production, and with the range of value added variants, its use is being extended into shopfitting and display, interior fitments, exterior application (e.g. signage and shop fronts) as well as components within numerous other products.
Wet process fibreboards
('Hardboard', 'Mediumboard', Softboard')
Wet process fibreboards are part of the fibreboard family as are dry process fibreboards but differ in the way that they are produced. Wet process boards are generally produced without the addition of a synthetic resin but are formed very much like paper to make a board.
Wet process fibreboards can be classified according to their density:
Hardboards > 900kg/m3
Mediumboards* > 400kg/m3 to <900kg/m3
Softboards > 230kg/m3 to <400kg/m3
*Mediumboards (which should not be confused with Medium Density Fibreboard - MDF) can be sub-divided into:
Low density mediumboards 400kg/m3 to <560kg/m3
High density mediumboards 560kg/m3 to <900kg/m3
Composition & Manufacturing process
Wet process fibreboards can be made using either softwood or temperate hardwood species (or both) (some low density mediumboards are made from recycled paper fibre). Wood chips are thermally softened in water and then mechanically refined into fibres. The wet fibres are formed into a mat which is either rolled (softboards), or rolled and then pressed, at a high temperature to the desired thickness. The primary bond is generally derived from the felting together of the fibres and their inherent adhesive properties although in some instances a synthetic adhesive may be added to the fibres. Other additives such as wax, bitumen emulsion, natural oil, fire retardant chemicals may be added.
The differentiating feature between a wet process and dry process fibreboard is that the wet process fibreboards have a fibre moisture content of more than 20% at the forming stage whereas dry process fibreboards have a fibre moisture content of less than 20% at the forming stage and they are produced with the addition of a synthetic resin binder.
Wet process fibreboards find use in a wide range of construction and furniture related applications.
Hardboards are used in furniture as drawer bottoms and unit backs; door facings, caravan interiors, floor coverings as well as being used in shopfitting and display work. Standard hardboard is generally not recommended for exterior use or for use in areas subject to direct wetting or high humidity conditions. Enhanced performance hardboards can be used for applications where higher strength properties and resistance to abrasion above that of standard hardboard is required. These boards find applications as components within structural members (e.g. I beams) exterior applications such as soffits and signage and for uses in packaging, agriculture and flooring overlays.
Low density mediumboards have particular application as pinboards and as components of partitioning systems. They can also be found in shopfitting and display applications and as a floor underlay material. High density mediumboards have been used as wall and ceiling lining boards and as a sheathing material in timber frame construction, however, their use today in the UK is limited.
Like mediumboards, the range of applications for softboards today has diminished, however, they do find application as pinboards, underlay materials and as an acoustic absorbent. Impregnated softboards are used as a sheathing material in timber frame construction and as a protective overlay in some forms of flat roofing. In pitched roof construction in Scotland impregnated softboards are used as a sarking material and heavily impregnated brands find application as expensive joint fillers.
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