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The 11th European Conference on Wood Modification (ECWM11) was held in Florence, Italy, which gave the 155 participants from 30 different countries an opportunity to update and exchange knowledge on wood modification technologies.
After the first conference held in Ghent in 2003, the event has been held every two years, accounting for the rapid and constant evolution of the technologies used to alter the properties of wood and adapt it to different uses.

But why modify wood, which has been used by man since prehistoric times for its excellent mechanical properties, workability and aesthetic value?

The objective pursued through the various wood modification processes was originally to increase biological durability, so that wood from local tree species, which are readily available but also more susceptible to degradation by biological agents, would be just as durable as exotic woods. Although treatment with chemical preservatives with biocidal action remains the most widespread practice to improve the durability of wood, interest in preservation techniques without the use of biocides, such as wood modification techniques, has grown in recent decades. Modification processes, in addition to durability, alter other physical and mechanical properties of wood, which has stimulated research over the years to make the most of the potential of the various processes.

The conference, in which CATAS participated as a member of the organising committee, took place in the auditorium of Sant'Apollonia, on whose stage more than 90 speakers took turns during two intense days of work.
The significant participation of industry representatives, an indication of the vitality of the sector, shows that modified wood is a market reality and as such requires the attention of the standardisation bodies, whose shortcomings companies complain about.
To date, the methods used to determine the durability of modified wood are the same as those used for natural wood, which makes it easier to compare the performance of the different materials but overlooks the fact that modified wood may be susceptible to degradation under conditions and by species of organisms other than those that degrade natural wood. Therefore, the industry's request to the technical standardisation committees is to take note that modified wood is different from natural wood and must be treated as such.
Research is already moving in this direction by producing the first data to support standardisation activities.

The presentations, grouped into sessions according to topic, dealt with technical-scientific issues concerning the chemical and thermal modification of wood, but also gave space to the views and experiences of the industry in this sector, both in Italy and abroad.
 
CHEMICAL MODIFICATION
The chemical modification of wood is based on the use of molecules that react with reactive chemical groups of polymers that make up the wood cell wall or produce a bulking effect in the wood matrix. This leads to an improvement in hygroscopic properties, durability and a possible alteration of mechanical properties.
Chemical modification techniques, in addition to those that have resulted in products that are now well established on the market, such as Accoya obtained by acetylation and Kebony obtained by furfurylation of conifer wood, are now exploring the use of other bio-based compounds, such as thermosetting resins, tannins, vegetable oils, aqueous solutions of sorbitol and citric acid, and polylactic acid, with the aim of substituting natural products for synthetic ones while decreasing the environmental impact of the processes.
The results of these studies, many of which are at an early stage and therefore do not present an analysis of the economic impact on the industrial scale, seem to achieve the aim. The material obtained in these processes, which is aesthetically indistinguishable from wood, absorbs less water, providing greater dimensional stability and in many cases better fire resistance. The effect on elasto-mechanical properties varies depending on the process, hence the need to define the possible uses, which normally exclude structural use, but include outdoor and indoor flooring, façade cladding and other carpentry work.

THERMAL MODIFICATION
Industrial production of thermally modified wood started in the 1990s in Finland, France, Germany and the Netherlands. Today, there are more than a hundred manufacturers of thermally modified wood worldwide, most of which are located in Europe.
In Italy, several companies specialised in wood drying, among which Baschild, BIGonDRY, Incomac and WDE Maspell were represented at the conference, have directed part of their activity to the production of systems for the thermal treatment of wood and to the development, through collaboration with research institutes, of processes for the thermal treatment of wood. In fact, there are many brands of thermally treated wood on the market today that represent as many variants on the ThermoWood of Scandinavian origin, such as WDE Maspell's thermo-vacuum process, BIGonDRY's Styl+wood treatment, Slovenia's Silvapro, just to mention few of them.
Heat treatment is applicable to a variety of wood species, including those refractory to chemical treatment. Treatment in a low-oxygen environment at 160-240 ◦C partially degrades the wood, causing changes in the chemical composition and ultrastructure of the cell wall. Thermal degradation leads to a mass loss of wood that is proportional to the treatment temperature and its duration. Developed with the aim of improving the durability of wood for outdoor use, thermal treatment is now also applied to wood and wood-based products for indoor use, such as parquet flooring. For these uses, the properties sought are not so much durability as dimensional stability and the possibility of varying the colour shades of the product by modulating the process parameters. The properties of wood that are known to be negatively affected by thermal treatment include mechanical strength and ductility, which currently limits the use of thermally treated wood to flooring and façade cladding.
Another aspect that should be considered for indoor applications is the emission of volatile organic compounds (VOC), which is obviously an undesirable effect in indoor environments. Studies carried out to characterise the VOC emission profile over time show that thermally treated wood releases more VOCs than natural wood, with the exception of formaldehyde from thermally treated plywood, which is lower, drawing attention to the need for processes to be optimised so that thermally treated wood can meet the VOC limits set by current regulations.
Although all thermal modification processes follow the same basic principle, the product properties and characteristics vary greatly depending on the raw materials used or the technologies and process conditions applied. Quality schemes exist in several European countries that aim to increase the transparency of the thermally treated wood market, although to date it has not been possible to define parameters to characterise the entire range of products available on the market.

NEW TRENDS
In the past, the motivation behind research on wood modification technologies was to remedy wood's inherent “defects,” such as dimensional stability, UV resistance and fire resistance and resistance to biodeterioration.
However, the past decade has seen an extraordinary increase in projects and publications concerning the development of new functional wood-based materials.
This is because nowadays materials science focuses on the development of high-performance functional materials based on renewable resources, and wood, a quintessential renewable material, possesses a structure that can be extremely useful for the development of functional materials in combination with polymers, nanoparticles, metal-organic structures or metals.
Various scientific approaches have paved the way for interesting perspectives:

• wood is deconstructed and reconstituted to enhance the capillary properties of vessels, with interesting potential for practical water resource management applications.
• wood is delignified and impregnated with resins or nanoparticles with appropriate refractive index to achieve a transparent material, or even with modular transparency for optimal thermal management of the living space. “Optical wood” self-regulates solar radiation transmittance due to the low absorption in the solar spectrum and high absorption in the infrared of nanocellulose fibrils, functions as a UV screen, has good mechanical properties and low thermal conductivity.
• phase-change materials (PCMs) are incorporated into the wood matrix so that they absorb excess heat in the endoergonic melting process and release it in the exoergonic solidification process when the temperature drops - this is another example of an application for energy-efficient buildings.

The title of the last presentation was "Thermoplastics from wood: dream or reality?". Perhaps this is the final frontier: being able to obtain a material with thermoplastic properties from wood without the use of polymers or plasticisers of fossil origin.
The research and application of wood modification technologies take ecological as well as economic aspects into account, with a view to sustainability and renewability of resources.
Indeed, wood meets the requirements underlying any environmental policy.
The wood supply chain is an example of a circular economy, where wood is a renewable resource thanks to forest management practices; wood has a natural CO2 storage function, which can be prolonged through processes to improve the durability of wood in use and has potential as a functional material in energy-efficient buildings.
"Once upon a time there was a piece of wood" goes the opening line of Collodi's Pinocchio; the Blue-haired Fairy used her magic to animate a piece of wood; without going so far as to invoke magic, wood modification technologies prove that wood is a ductile and versatile material that lends itself to being transformed and adapted to many uses, even different from traditional ones.
 

For info:
Elena Conti
+39 0432 747219
conti@catas.com