The development of wood composites was a direct result of wanting to minimise the negative properties and variability of solid timber. Many properties were improved, including the anisotropic nature of wood. The anisotropic nature of timber is the phenomenon of the timber moving or swelling by different rates in different directions. The manufacture of panel products prevent this.
The reaction with water and the swelling of panels is something that is governed by the resin component of the panel, with some resins being susceptible to degradation in a wet environment and others (such as MDI) being resistant. However, it is still the case that the wood component of the composite reacts to water and swells, with the potential for catastrophic failures.
In the area of solid wood, wood modification has been the subject of research for many years, with notable commercial ventures including Accoya, Lignia Wood Company and Thermowood, to name but three. Wood modification has been defined as a process that “involves the action of a chemical, biological or physical agent upon the material, resulting in a desired property enhancement during the service life of the modified wood.”
There are three major types of wood modification: chemical modification, thermal modification and polymer or resin impregnation. Each of these looks to alter the relationship between wood and moisture, and as a result restrict dimensional change, and reduce susceptibility to decay.
Of course, there is the potential to bring the two technologies, panel products and wood modification, together and create an advanced composite with enhanced properties, and indeed the joint venture between Accoya and Medite has brought the Tricoya product to the market which has given us an MDF that can be used in extreme conditions, or a true outdoor MDF.
With the first Tricoya plant under construction in Hull in the UK with a capacity of 30,000 tonnes of product per year and a second plant under consideration in Malaysia it is likely that we will see more of these advanced composites on the market in the coming years.
But is there potential for other modifications to be used in the composites world?
Thermal modification has been investigated as a post manufacture treatment for plywood and OSB. Matthew Aro led work that showed that thermal modification post treatments can improve the thickness swell and water absorption performance of plywood and OSB panels.
However, he did note that some mechanical properties decreased significantly at treatment temperatures exceeding 160°C.
Research has also been conducted on the thermal pre-treatment of OSB flakes prior to the manufacture of board. However, much of the work is inconclusive or has conflicting results (generally with the water sorption properties improving but the mechanical properties reducing).
Will we see more modified panels in the future? I am unsure. The investment that companies have to make to not only undertake the modification but potentially modify their production process is vast and it is doubtful as to whether these costs will be paid out for marginal gains on board properties.
It will take a game changing advance, as has been seen with Tricoya, to attract the size of investment that would be needed.
