Medium-density fibreboards

Toland, A., Bastiaans, R.J.M., Holten, A.P.C., de Goey, L.P.H. Kinetics of CO release from bark and medium density fibreboard pyrolysis, Biomass Bioenergy, submitted (2005). 

Eormaldehyde vapour treatment has been applied to improve the dimensional stability of medium-density fibreboard (MDF) (Minato elal, 1992) and albizzia waferboard (Yusuf elal, 1995c). 

Minato, K. (1993). Moisture adsorption characteristics of medium-density fibreboard and its raw wood filler treated with formaldehyde. Mokuzai Gakkaishi, 39(10), 1162-1168. 

Minato, K., Kubo, N., Norimoto, M., Sasaki, H., Sawada, M. and Yamamoto, T. (1992). Dimensional stabilisation of medium-density fibreboard by formaldehyde treatment. Mokuzai... 

Ogawa, T. and Ohkoshi, M. (1997). Properties of medium density fibreboards produced from thermoplasticized wood fibers by aUylation without adhesives. Mokuzai Gakkaishi, 43(1), 61-67. Ogiso, K. and Saka, S. (1993). Wood-inorganic composites prepared by sol-gel process II. Effects of ultrasonic treatments on preparation of wood-inorganic composites. Mokuzai Gakkasihi, 39(3), 301-307. 

Substrates include chipboard, plywood, medium-density fibreboard, hard-board, fully glued blockboard, cement-bonded particle board, mineral board, and vermiculite board. 

If wood is conditioned at 20°C and 65% relative humidity the sapwood of most timbers will equilibrate to about 12% moisture content. This corresponds to the typical moisture content of lumber in an unheated building in many temperate regions. There are exceptions. Nothofagus fusca, one of the Southern Beeches, would dry to 9.5% or so under these conditions, so drying to 12% would be inadequate (Harris, 1961). Medium density fibreboard and particleboard also equilibrate at a lower moisture content of about 8-9%. For this reason Hoadley (1979) observed that it is more logical that wood products be dried to a specified relative humidity than to a specified moisture content (Table 4.1). 

All of the above treatments, unless deliberately superficial, are not easy to apply to lumber because of the lengthy time for diffusion and reaction, or because of the difficulties in achieving effective penetration. In recent years, therefore, interest has also centred on improving the dimensional stability and durability of reconstituted panels hardboard, particleboard, medium density fibreboard and new derivatives. 

Fibres - for medium density fibreboard (MDF), high density fibreboard... 

Triboard with a thiek orientated strand eore overlaid with a layer of medium density fibreboard, so eombining exeellent strength with a smooth hard surface. 

Wood-based panels such as particleboard, oriented strand board and medium density fibreboard eonsist of particles of widely varying shape and size bonded together with an adhesive system. 

Early fibreboards were developed by taking fibre from a wet-process fibre line, drying this, mixing it with resin, and pressing it as had been done for particleboard. However, in the last three decades medium density fibreboard (MDF), a UF bonded and dry formed panel, has largely replaced the early fibreboard products. 

The major difference between the fibres used to make medium density fibreboard and the particles used to make particleboard is the greater slenderness ratio of the fibres. This is the reason why mechanical blenders designed for particleboard were not satisfactory for MDF. It is also the reason why the bulk density of fibre is low, particularly with fibres prepared from a chipped material. The fibres form networks that are quite strong, with fibres able to span considerable distances. The mats formed from such fibres hold together so that formed or even trimmed edges hold their shape. There is no requirement for tack from the resin to hold the fibre mat together. 

The various aminoplastic resins are the most important class of adhesives in the wood-based panels industry, especially for the production of particleboards and medium density fibreboard (MDF), and partly also for oriented strandboard (OSB), plywood, block-boards, and some other types of wood panels. They are also used in the furniture industry as well as in carpenters shops. 

Eethal concentration Median lethal dose Eow-density polyethylene Einear low-density polyethylene Maleic anhydride Methacrylic acid Methyl acrylate Methyl acrylate Methacrylonitrile Modified atmosphere packaging Methyl butyl ketone 2-Mercaptobenzothiazole 4,4 -Methylene dianiline Medium density fibreboard Magnesium hydroxide Methylene diisocyanate Medium density PE Monoethylhexyl phthalate Methylethyl ketone Melamine-formaldehyde Methyl isoamyl ketone... 

A relatively recent application area for pcD has been in the woodworking industry. Wood composites such as medium density fibreboard (MDF), chipboard, laminated boards with plastic coatings, for use in furniture and on floorings, and also composites, used in wall claddings and in ceilings, all tend to be highly abrasive... 

For a general introduction, see Wood adhesives - basics. Aminoplastic resins are polycondensation products of the reaction of aldehydes with compounds carrying amine or amide groups. Formaldehyde is by far the primary aldehyde used. The name amino-plastic is traditional, but is a misnomer these are thermosetting, irreversibly hardening resins. Two main classes of these resins exist urea-formaldehyde (UF) resins and melamine-formaldehyde (MF) resins. Today, for wood adhesives, pure MF resins are not used anymore because of cost, and only melamine-urea-formaldehyde (MUF) adhesives are used. The main use of these resins is in composite products such as particle board, plywood, medium density fibreboard (MDF), oriented strand board (OSB), glu-lam/flngerjointing and furniture. 

Producers of medium density fibreboard for the building industry opt for powder coatings instead of vinyl and laminate films because of waste savings, the environmental advantage of eliminating VOC-containing lamination adhesives and the possibility of using only a one-step process and not a multi-step one like lamination [116]. 

The most common resin for lignocellulosic composites is urea formaldehyde. About 90% of all lignocellulosic composite panel products are bonded with UF [12]. UF is inexpensive, reacts quickly when the composite is hot-pressed, and is easy to use. UF is water-resistant, but not waterproof. As such, its use is limited to interior applications unless special treatments or coatings are applied. UF resins are typically used in the manufacture of products where dimensional uniformity and surface smoothness are of primary concern, for example, particleboard and medium density fibreboard (MDF). Products manufactured with UF resins are designed for interior applications. They can be formulated to cure anywhere from room temperature to 150 °C press times and temperatures can be moderated accordingly. UF resins (often referred to as urea resins) are more economical than PF resins and are the most widely used adhesive for composite wood products. The inherently light colour of UF resins make them quite suitable for the manufacture of decorative products. 

Wood by itself as well as its composite products, such as particleboard, plywood, and medium density fibreboard (MDF) are widely used in indoor products (structural panels. 

The production of high density fibreboard (HDF), medium-density fibreboard (MDF), particleboard (PB) and other wood composite materials uses huge amounts... 

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