Pressed wood
Wood chip materials or chipboard in the broader sense are wood-based materials, which are made from wood chips and a synthetic resin glue under heat and pressure. Chipboard is the world's most widely used type of wood materials. Besides wood, to a minor extent also alternative board materials such as flax shives, bagasse, and used to a limited extent, bamboo or straw.
Are used the wood chip materials in furniture and interior design. Approximately 50% of particleboard manufactured in Germany are made into furniture. They are suitable, depending on the resistance of the glue for moist places.
Production
The simplified manufacturing process of the particle board is as follows:
The raw material of wood ( mainly coniferous ) is crushed by hackers and chipper for chips. ( Middle layer 4-6% topsheet 1-8 %) for the gluing and the subsequent presses the chips a required set humidity require. Because the chips will not normally satisfy these requirements, they need to be dried. The drying process is dependent on the parameters of wood, particle size, bulk density and initial moisture content.
After drying, the chips are mechanically sifted. Larger chips are used in the middle layer, finer in the top layer. By screening the chips can be glued to their use accordingly. The gluing process includes the following steps: preparing the glue mixture, dosage of chips and glue and mixing of chips and glue.
After gluing the chips are scattered to form a web. This is then compressed under the action of high temperatures (approx. 200 ° C) plates. Old presses are designed as single or multi- stage presses, but modern systems operate in continuous mode of operation, that is, as an endless belt presses. After pressing, the panels are conditioned (storage over a week to compensate for moisture and heat in the plate), trimmed and sanded.
Chipboard is made mainly of coproducts of wood processing.
Classification
We distinguish the following sub- types:
- Flat pressing plate (P1 -7), commonly referred to as chipboard Single-ply
- Three-layer plate
- Multilayer board
- Light flat pressing plate
- Extruded tube plate ( ET - Extruded Tubular )
- Extruded full plate ( ES- Extruded Solid)
Adhesives
As adhesive systems, especially systems comprising various combinations of urea, melamine and phenol-formaldehyde adhesives are used. Additionally, with the polymeric isocyanate ( PMDI) -based plates. The adhesives are particularly characterized by different water and hot water resistance, and thus determine the durability of particleboard products.
The simplest and most common type of particle board (not resistant to swelling ) is prepared with the best priced adhesive system, the urea -formaldehyde glue, just UF adhesive ( U for urea = urea formaldehyde and F ). For swelling resistant types are melamine-containing urea adhesives, short MUF adhesives ( M for melamine ) are used. Particularly high-quality plates are made with PMDI, these plates are, however, priced much higher.
When using adhesives Verleimungsarten following are distinguished:
The terms V20 and V100 according to DIN 68763 were replaced by seven types of plates according to DIN EN 312 and identical technical categories of EN 13986th For disks with wood preservatives against fungal attack by the former type V100G is no CE marking according to DIN 13986 possible. These drives require a general building approval.
Economic Importance
Wood chip materials are the most economically important wood-based materials in Europe. They make up about ¾ of the total production. 2008 34.5 million m3 and 3.3 million m3 of chipboard OSB were produced in Europe. In Germany, the production of particleboard in 2008 was 7.5 million m3, of which about 1 million m3 of OSB. In the wake of the financial and economic crisis, the chipboard production in Germany fell by 6-7 %, in Europe by 8-9% over the previous year.
Emission classes
It is less than 10 % share in the adhesive chipboard. Nevertheless, this small amount plays a major role in the development of toxic substances. Curing the adhesives after a while, including the pungent-smelling gas, formaldehyde is free. To be the resulting health hazards be kept as low as possible chipboard divided into three emission classes.
Development
For several years trying adhesive systems with lignin ( natural glue in wood, which is a by -product of paper production) and other adhesives ( for example, cross-linked polyurea ) to develop and thus to reduce the health burden.