Woodbased boards

There are, in principle, three types of boarding made from ground timber: fibreboard, chipboard and cork sheeting. Plywood boards on the other hand are usually made of larger, very thin wood sheets laminated together.

Wood-based boards are mainly used for interior purposes, but can, with the use of waterproof glueing and appropriate surface treatment, also be used as external cladding. However, experience so far has shown exterior solutions to be vulnerable in harsh climate conditions (Bohlerengen, 2001). Plywood is most often exposed as internal cladding. Fibreboard and chipboard are almost exclusively used as an underlay on either floors or walls. On floors, they can provide the base for a 'floating' wooden floor or soft floor coverings; on walls and ceilings they can provide a base for wallpapering, hessian or paint. Some products are delivered from factories with these finishes already mounted. Laminate flooring is often made up of chipboard covered with a plastic laminate. Cork flooring is a soft floor covering, 3-5 mm thick and therefore dependent on a firm subfloor. The cork is often coated with a protective layer of polyvinyl chloride or polyurethane. Natural waxes can also be used.

Fibreboards are produced in porous, semi-hard and hard variations from defibrated wood fibres. The products are often glued by their own glue which forms through heating in a wet process (see page 280). But for semi-hard and hard products, small portions of additional glue are often added anyway. In the alternative dry process, the portion of glue is increased (see Table 15.9). Fibreboards produced in the dry process are widely known as medium-density fibreboard (MDF) and high-density fibreboard(HDF). MDF boards are regularly used in the production of furniture. Cork sheeting made from broken bark from the cork oak could also utilize its own glue, although additional glues are most often mixed in as well (see Table 15.9). As a non-synthetic alternative, a resin based on cashew nut oil can be used. In the laminating of plywood, additional glue is a necessity and is used to fix from 3 to 6 and more layers of wood sheeting laid across each other. Traditional chipboard is produced from ground timber waste. Oriented strand board (OSB) is a

Table 15.9 Adhesives in wood-based boards, see details on adhesives in Chapter 17

Material

Types of adhesive

Amounts of adhesive (%)

Wood fibre boards, wet process

None or Phenol-formaldehyde PF

1

Wood fibre boards, dry process

Polyurethane PU, Phenol-formaldehyde PF or Urea-formaldehyde UF

4-10

Chip board

Urea-formaldehyde UF or Phenol-formaldehyde PF

10

Oriented strand board

Methylene-diphenyl-isocyanate MDI, Phenol-formaldehyde PF, Melamin-urea-phenol-formaldehyde MUPF or Polyurethane PU

3-6

Plywood

Urea-formaldehyde UF or Phenol-formaldehyde PF

2

Cork sheeting

None, Phenol-formaldehyde PF, Polyurethane PU or Urea-formaldehyde UF

2

Note: Some products will contain several types of adhesive.

Note: Some products will contain several types of adhesive.

fairly recent version of chipboard based on wood strands. A wide range of glues are used in chipboard (see Table 15.9).

Several wood-based boards may have fire retardants, waterproofing agents and other additives; although not so much in products for indoor use. For the plastic coating of particle boards and fibreboards, mela-mine formaldehyde (MF) is usually used.

The quality of timber for veneers has to be good. Low quality raw material is used for traditional chipboard in particular. Here the use of poplar and willow is an interesting option as such species absorb more carbon dioxide per hectare and year than most other tree species (see Table 10.6). It is possible to recycle demolished chipboard into new chipboard by hydrolysis of UF adhesives with steam at 110 °C. In oriented strand boards, fresh wood is normally used. Production of fibreboard through the wet process needs mostly fresh wood where the natural glues are still available. In the production of fibreboard by the dry process method, demolition waste can be used as a basis resource. Methods have been developed for recycling used fibreboards to make new boards (Athanassiadou et al., 2005). Up to 15% of the recycled material can be mixed in with new material. To some extent, residues of the natural glues in the old material are reactivated in the process, reducing the amount of new glue required.

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