Nobody knows for certain whether wood or stone was the first material to be used by primitive mankind, but there is absolutely no doubt that wood will have been used from very early as a material for constructing hunting weapons, hand tools, shelters and so on.

Depending on the tree from which the wood comes, wood can offer some remarkable properties, such as a combination of stiffness and strength with low density. Some woods are relatively elastic, while others exhibit greater hardness and density. However, unlike the vast majority of engineering materials, wood is a renewable resource; the supply is not limited, because more can be grown and harvested.

There is a long history of innovation in the use of wood, from the development of plywood, chipboard, blockboard, hardboard and MDF (medium-density fibreboard), to what is known as Bendywood.

Steam was used even by the Ancient Egyptians to soften wood in order to bend it into shape, but the process is not the most convenient to use. Bendywood, on the other hand, is treated in the factory and delivered to the customer wrapped in polythene to keep it moist. It can then be bent without further heating to produce tightly radiused curves (around 10 times the plank's thickness), three-dimensional shapes, and twisted forms.

High-quality timber is required for producing Bendywood, as knots, defects and variations in grain cause the Bendywood production process to fail. Planks of selected timber are steamed in such a way as to heat the timber and the moisture therein, without any net loss of moisture. After steaming, the hot timber is placed in a press that compresses it longitudinally, and with no expansion permitted in the other two directions.

The plank can then either be removed, whereupon it springs back to almost its original length, or it can be left to cool in the press, in which case there is less spring-back and, importantly, the flexibility of the Bendywood is greater. By compressing the cell walls on a microscopic scale, there is scope for cells on the outside of curves to expand again -- in a similar way to a concertina or a flexible drinking straw.

Thinner planks tend to remain flexible, whereas thicker sections loose much of their flexibility when they dry out. This is why the Bendywood is delivered wrapped in polythene and, if kept cool, it will remain flexible for six months. When Bendywood dries it shrinks along the grain, unlike conventional wood that shrinks across the grain. This has to be taken into account when the material is being used, though the shrinkage is not easily predictable.

Bendywood is available from Candidus Prugger in Italy, in beech, ash, oak and maple, and most applications are architectural -- such as for handrails -- and in furniture making. Nevertheless, as the material properties become better understood, there is no reason why engineering products could not benefit from the combination of finished material properties and simpler formability.

Although wood has always been popular as a structural material for constructing frameworks, with habitable buildings be one example, steel and aluminium are today preferred for both mass-produced products such as shelving, and one-off designs including machinery frameworks and guarding. In particular, modular aluminium frameworks have found favour in recent years due to the ease with which structures can be assembled and subsequently modified, especially in comparison with steel structures that need welding and then finishing to avoid corrosion.

However, an alternative material has recently been introduced by a company that is best known for its aluminium framework systems, MK Profile Systems. This company is now offering profiles made from extruded TPF (thermoplastic fibrin), an innovative new material that consists of 85percent wood fibre and 15percent polypropylene -- which means that it is totally recyclable, according to MK (Fig.1).

But environmental impact is not the only advantage offered by this new technology; the profiles have a lower cost than aluminium profiles of the same size.

The dimensions for the new profiles are based on the popular MK40 series aluminium profiles, which are used for many industrial and non-industrial applications, having a standard profile of 40x40mm cross-section. This series has the widest range of compatible accessories, most of which can also be used with the TPF extrusions, such as slot nuts, angles, plates and other connecting elements.

Of course, the wood profiles can also be combined with a standard aluminium frame to give a localised change in material where necessary. The TPF profiles benefit from being considerably lighter than their aluminium counterparts, and are non-metallic, so they can be used in areas where metal parts are discouraged -- such as in the vicinity of electronic measurement systems, magnetic devices, metal detection and protective packaging.

Although the TPF profiles are compatible with most of the components designed for the aluminium series 40 extrusions, a range of new accessories has been developed for the TPF profiles, with shelving being one application targeted (Fig.2), though many other users could benefit, especially if there is a desire to avoid the plain anodised or black finish in which aluminium profiles have been traditionally supplied.

While wood flour has been used as a filler to modify the properties of (often relatively expensive) polymers for many years, the use of wood fibres is a newer development.
Although the processing costs are higher, the advantage is that the fibres can act as a reinforcer rather than a filler, thereby enhancing the material properties.

A good deal of research is now underway into wood-plastic composites (WPCs) by organisations such as the Forest Products Laboratory in the USA, though the proportion of wood fibre is more usually in the range 30--60percent. In the future it is almost certain that we will see more products being launched that take advantage of the potential benefits offered by this new use of what is probably the original engineering material.