Have you heard of MDF? Some people aren’t sure what it is or how to use it.

Medium-density fibreboard (MDF) is an engineered wood product made by breaking down hardwood or softwood residuals into wood fibers, often in a defibrator, combining it with wax and a resin binder, and forming panels by applying high temperature and pressure. MDF is generally denser than plywood. It is made up of separated fibres, but can be used as a building material similar in application to plywood. It is stronger and much denser than particle board.

There are several misconceptions about MDF boards and are often confused with plywood and fibreboards. An MDF board is an acronym for medium density fibreboard. It is mostly considered to be a wood substitute and is taking over the industry as a useful material for decorative products as well as home furniture.

If you aren’t familiar with MDF wood, we’ll take you through what it is, the concerns with MDF wood, How are MDF boards made.

Material

MDF was created by breaking down both hardwood and softwood into wood fibres, MDF is typically made up of 82% wood fibre, 9% urea-formaldehyde resin glue, 8% water and 1% paraffin wax. and the density is typically between 500 kg/m³(31 lb/ft³) and 1,000 kg/m³ (62 lb/ft³). The range of density and classification as light, standard, or high density board is a misnomer and confusing. The density of the board, when evaluated in relation to the density of the fibre that goes into making the panel, is important. A thick MDF panel at a density of 700–720 kg/m³ may be considered as high density in the case of softwood fibre panels, whereas a panel of the same density made of hard wood fibres is not regarded as so.

Fiber production

The raw materials that make a piece of MDF must go through a certain process before they are suitable. A large magnet is used to remove any magnetic impurities, and the materials are separated by size. The materials are then compressed to remove water and then fed into a refiner, which shreds them into small pieces. Resin is then added to help the fibers bond. This mixture is put into a very large dryer that is heated by gas or oil. This dry combination is run through a drum compressor equipped with computerized controls to guarantee proper density and strength. The resulting pieces are then cut to the correct size with an industrial saw while they are still warm.

Fibres are processed as individual, but intact, fibres and vessels, manufactured through a dry process. The chips are then compacted into small plugs using a screw feeder, heated for 30–120 seconds to soften the lignin in the wood, then fed into a defibrator. A typical defibrator comprises two counter-rotating discs with grooves in their faces. Chips are fed into the centre and are fed outwards between the discs by centrifugal force. The decreasing size of the grooves gradually separates the fibres, aided by the softened lignin between them.

From the defibrator, the pulp enters a ‘blowline’, a distinctive part of the MDF process. This is an expanding circular pipeline, initially 40 mm in diameter, increasing to 1500 mm. Wax is injected in the first stage, which coats the fibres and is distributed evenly by the turbulent movement of the fibres. A urea-formaldehyde resin is then injected as the main bonding agent. The wax improves moisture resistance and the resin initially helps reduce clumping. The material dries quickly in the final heated expansion chamber of the blowline and expands into a fine, fluffy and lightweight fibre. This fibre may be used immediately, or stored.

Sheet forming

Dry fibre gets sucked into the top of a ‘pendistor’, which evenly distributes fibre into a uniform mat below it, usually of 230–610 mm thickness. The mat is pre-compressed and either sent straight to a continuous hot press or cut into large sheets for a multi-opening hot press. The hot press activates the bonding resin and sets the strength and density profile. The pressing cycle operates in stages, with the mat thickness being first compressed to around 1.5× the finished board thickness, then compressed further in stages and held for a short period. This gives a board profile with zones of increased density, thus mechanical strength, near the two faces of the board and a less dense core.

After pressing, MDF is cooled in a star dryer or cooling carousel, trimmed and sanded. In certain applications, boards are also laminated for extra strength.

MDF production Process