Wood-based materials are materials that are produced by chopping wood and then joining the structural elements together. The size and shape of the wood particles determine the type of wood material and its properties. The wood particles can be connected to one another with or without binders or mechanical connections.
Wood-based materials can consist of different types of shredded wood, which essentially differ in their size. The largest structural elements include sawn timber , especially boards, as well as veneers of various thicknesses. Small elements represent wood chips of different sizes (coarse to fine chips), wood chips , wood wool , wood fibers and dust. In addition to wood, other lignocellulosic materials such as cereal straw , hemp shives or miscanthus can also be used.
The properties of wood-based materials change greatly with the size and shape of the wood particles. Compared to solid wood, a number of properties change when the wood is shredded. The homogeneity of the material increases with increasing digestion, but at the same time the strength of the products decreases, the use of energy and the environmental impact increase compared to the use of solid wood. The insulation properties and the surface quality, however, improve. The requirements for the wood quality decrease the smaller the wood particles are. For example, they are significantly higher for glued laminated timber than for chipboard .
Wood-based materials in the form of panels or strands are usually produced by mixing the various types of wood particle shapes with natural and synthetic binders ( adhesives ) and, if necessary, adding further additives, for example water repellants , wood preservatives or color particles, in the course of subsequent hot pressing. The "new" or "innovative" wood-based materials are mostly processed using modern plastic technology such as extrusion or injection molding . Mechanical connections, for example using screws , dowels or tongue and groove connections, are also possible.
Types of wood materials
Due to the different structural elements used, wood-based materials can be divided into materials based on solid wood, veneer materials, chipboard materials, fiber materials and composite materials.
Solid wood materials and veneer materials
Solid wood materials or materials based on solid wood are all wood materials based on solid wood elements, especially boards or rods. In contrast, wood-based materials based on veneer consist of thin peeled veneers . Solid wood and veneered wood materials differ essentially in terms of the thickness of the wood elements used, accordingly both can be manufactured as plywood from layers that are rotated 90 ° and glued to one another or as plywood with parallel layers. In the former, the fibers of the visible surfaces run parallel on both sides. The number of layers is therefore mostly uneven.
Wood-based materials based on solid wood include:
- , One or more layers, then as a solid wood glued panels or laminated timber are querverleimt, wherein the thicker board layers. Cross laminated timber is mainly used as load-bearing wall, roof or ceiling panels. Solid wood panels with a thickness of over 12 centimeters are usually manufactured as cavity structures.
- Glued laminated timber and other board stack constructions in which the fiber orientation of the board layers is predominantly in the same direction. The boards can be simply glued or mechanically connected using nails, dowels, tongue and groove or dovetail systems.
- Stick plywood ( blockboard ) , laminated wood or other stick -shaped glued elements made of solid wood
- Solid wood elements made of cross-layered boards, which are connected by dowels and nails and are used as large structural elements, for example in house construction. Complete walls with cut-out windows and doors can be present as elements.
In the case of solid wood materials, the quality of the wood used, the type of connection, the layer structure and the direction of cut have an influence on the strength properties of the material. For example, the load-bearing capacity of laminated timber can be increased if high-strength board layers are used in the outer layers. The direction of the cut influences the dimensional stability, as it is the function of the stresses within the material.
As with solid wood materials, the division of veneered wood materials is primarily based on the panel structure, whereby in the case of veneered wood, a greater range of variation is possible due to the small thickness of the elements used. Wood-based materials based on veneer wood include:
- Veneer plywood (FU) - has a high dimensional stability due to cross-glued veneers. This includes the multiplex panels with up to 35 veneer layers.
- Laminated veneer lumber
- Veneer lumber
- Flexible plywood - usually three-ply, with the middle layer thinner than the outer one. As the name suggests, this type of plywood is easy to bend without breaking (usually up to the diameter of a wine bottle)
Veneer wood materials are mostly manufactured uncoated, but can also be coated with different materials. This includes laminate panels in particular , but also linoleum and other materials. Special veneer plywood is also painted, metal-reinforced or protected against fungicides. A special feature is the synthetic resin pressed wood (KP), in which veneer wood is impregnated with synthetic resin , especially phenolic resin , and pressed at high temperatures to form a wood-based material with very high density and strength.
Note: According to the definition in DIN 1052: 2008-12, glued laminated timber, glued laminated timber and laminated veneer lumber without transverse layers do not belong to the group of wood-based materials. All fiber-dependent properties are retained over the cross-section with the aforementioned. These materials are mostly used like solid wood as rod-shaped components. Only when the original fiber structure is changed, e.g. B. in the case of laminated veneer lumber with transverse layers or OSB panels, wood-based materials are actually created. Components made from these wood-based materials can be used as panels or discs.
Wood chip materials are made from wood chips, synthetic resin glue and additives under heat and pressure. The wood chips are extracted from solid and saw-cut wood using hackers and special chipper knives. A distinction is made between the following subspecies:
- Flat pressed board (P2), commonly referred to as chipboard
- Extrusion plate
- Chipboard molded parts
- Coarse chipboard (also called OSB board )
- Chipboard wood (LSL)
Chipboard materials are the most important wood-based materials worldwide with a wide range of applications. Accordingly, there are a large number of classification features (according to manufacture, surface, shape, size, structure or purpose) for classic particle board and OSB board and the many special applications. A standard-compliant classification can be made in accordance with EN 309.
Wood fiber materials
Wood fiber boards are made from wood fibers from sawing by-products or residual wood, but also from other fiber-containing plants such as flax or rapeseed . The structural cohesion is essentially based on the matting of the wood fibers and their natural ingredients, but polymers can also be used as binders. Depending on the manufacturing process (dry or wet web formation) and compression of the wood fibers, subgroups are distinguished:
For wood fiber boards that were manufactured using the wet process:
- The wood fiber insulation board (HFD) (also porous fiber board and "Soft Board" (SB)) is a board material of low density (230-350 kg / m³) which is used for heat and sound insulation in construction. Porous fibreboard can also be bound with bitumen .
- The means hardboard (MB) is m³, a board material with a density of 350 to 800 kg /.
- The hardboard (HB or HFH) (also called "hardboard") having a density above 800 kg / m³ is used for formwork, interior fittings, doors, furniture and packaging.
Extra hard fibreboard (HFE) has an even higher density.
For wood fiber boards that have been manufactured using the dry process:
- The medium-density fibreboard (MDF) is manufactured in a dry process. Due to its homogeneity, higher strength and better surface properties, it is increasingly replacing flat pressboard (P2).
- The high-density fibreboard (HDF) consists of wood fibers soaked with glue and pressed under pressure and heat, which are particularly highly compressed. It is used as a carrier material for high loads with low material thickness (e.g. laminate flooring ).
Low-density fibreboard without the addition of adhesive is mainly used as insulation. There are also ultra-light fibreboards (ULDF) on the market. A standard-compliant classification can be made according to EN 216.
Composite materials are characterized by the fact that they consist of different materials. They can consist of different wood fragments as well as wooden elements and other materials such as plastics and other binding agents such as resins , hardening oils , plaster of paris , concrete or paper . The type of association can also differ greatly.
Examples of wood composite materials are
- Wood plastic composites or wood-polymer materials are thermoplastically processable composite materials made of wood, plastics and additives, which are mostly processed with modern methods of plastics technology. In the GDR these composites were manufactured under the trade name Prestofol .
- Lightweight panels with high-strength top layers and a lighter core made of wood-based materials, foams, balsa wood or honeycomb (paper honeycomb panels)
- Synthetic resin press wood , also known as lignostone , is a material based on wood that is compressed in an autoclave , invented in 1915 by Fritz and Hermann Pfleumer . It is still made today from beech wood veneers pressed together with synthetic resin.
- Stone wood, a mixture of wood fibers and magnesium carbonate (magnesia) or sorel cement
- Wood concrete , Durisol and wood wool lightweight boards , mixtures of wood chips and lime or cement-based binders or magnesite
- Wood bronze , a mixture of wood fibers, glue , clay and plaster
- Linoleum , a mixture of wood flour and various other fillers and binders
Sandwich panel made from veneered hardboard and polystyrene core
Profile block made from a wood-plastic composite
- Arboform , also known as liquid wood , is a thermoplastically processable material made of lignin and cellulose, which can be processed with the established plastics processing methods such as injection molding , extrusion, pressing, deep drawing and blow molding. This innovative wood-based material has already been used in many small product series.
- Myko wood is a material made from hardwood that has been specifically degraded by a cultivated mushroom for further industrial use. The myko wood is obtained from barked round wood, mainly from beech or birch, more rarely from horse chestnut or aspen. It is tension-free, more porous, softer, lighter than untreated wood and therefore easier to impregnate and work with.
Binders and additives
Binding agents play a central role in the manufacture of wood-based materials. The binding agent content in chipboard is 8–10%, and in innovative biomaterials such as wood-plastic composites it is more than 20%. While synthetic resins containing formaldehyde are mainly used as binders in conventional wood-based materials, in Wood Plastic Composites it is i. d. Usually plastics or bio-based plastics that are less harmful to health . Binders made from renewable raw materials are in development, but still play practically no role in the wood-based materials industry. Other additives in wood-based materials can be: flame retardants , wood preservatives, water repellants, hardeners, etc.
Use of wood materials
Wood-based materials are mainly used in the construction and furniture industries. There is a wide range of applications for plywood as a building material ; wood fiber boards in particular are used as insulating materials . The furniture industry is the main buyer of chipboard - around 50% of the chipboard produced in Germany is made into furniture ( cupboards , shelves, tables, living room and seating furniture, etc.). Wood-based materials are also used in vehicle construction and as packaging material.
The wood-based panel industry includes wood fiber, chipboard, OSB panel and solid wood panel manufacturers, as well as veneer and plywood producers. In 2008 the wood-based materials industry had 15,000 direct employees. The 71 companies generated sales of around 5.6 billion euros per year. Wood-based materials are usually much cheaper than solid wood . Germany is the largest manufacturer of wood-based materials in Europe. About 10% of the forest wood in Germany is used for the production of wood-based materials. In 2008 7.5 million m³ of chipboard, approx. 1 million m³ of OSB, 3.9 million m³ of MDF and 175,000 m³ of plywood were produced. After the traditional wood-based materials in Europe and Germany for years. With the exception of Wood Plastic Composites (WPC), production in 2008 collapsed compared to the previous year: from −2% for plywood to −9.3% for MDF boards. Chipboard and OSB board production decreased by an average of 6–7%. In Europe too, wood-based panel production fell by an average of 8–9% to around 56 million m³. Only Wood Plastic Composites recorded a production increase of 78% in Germany.
There are concerns about the use of wood-based materials with regard to emissions of pollutants . Here, formaldehyde from the binders is mentioned in particular , but also volatile organic compounds (VOC), which come from the wood itself (for example terpenes ). Some manufacturers avoid formaldehyde emissions from binding agents by using formaldehyde-free adhesives (e.g. polyurethane adhesives). In addition, the numerous additives such as flame retardants , wood preservatives, water repellants or hardeners must be checked for their environmental impact. In addition to the origin of the wood for wood-based materials ( certification ), it is primarily the binders and additives that determine the sustainability of wood-based materials.
- Peter Niemz, André Wagenführ: Materials made of wood. In: André Wagenführ, Frieder Scholz (Hrsg.): Taschenbuch der Holztechnik. Specialized book publisher at Carl Hanser Verlag, Leipzig 2012; Pp. 127-259. ISBN 978-3-446-42605-4 .
- Manfred Dunky, Peter Niemz: Wood-based materials and glues. Springer Verlag, Heidelberg 2002. ISBN 3-540-42980-8 .
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- European Panel Federation (English)
- Gesamtverband deutscher Holzhandel e. V. (German)
- Description of synthetic resin lignostone
- DIY modern skis from wood
- see the article en: Brettstapel in the English Wikipedia
- Vera Krackler, Daniel Kennecke, Peter Niemz: Processing and uses of hardwood. ETH Zurich - Institute for Building Materials - Wood Physics, Zurich 2010, pages 57–59
- http://www.vhi.de/ Verband der deutschen Holzwerkstoffindindustrie (VHI): binders in wood-based materials
- http://www.bshd.eu/sites/branche.php Federal Association of Sawing and Wood Industry Germany
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