Colour as a quality indicator for industrially manufactured ThermoWood®

ABSTRACT

Since its market entry in 2001, ThermoWood® has become the most established form of thermal modification globally. Whilst its properties have been widely reported, there is still a need for a readily-applied quality control method to ensure treatments meet the criteria outlined by the International ThermoWood Association. One such method for quality control has focussed on the use of colour measurements. In the largest study of its kind, colour measurement data have been evaluated for Norway spruce and Scots pine subjected to the Thermo-D ThermoWood® process at twelve industrial plants between 2007 and 2018. This showed that the colour measurement according to the CIELAB* colour space on newly planed surfaces of thermally modified timber (TMT) may be used for quality control of the ThermoWood® Thermo-D process with regard to process intensity, i.e. the combined effect of temperature (212 ± 3°C) and time. In order to obtain more robust control, only the L* parameter (lightness) should be used as a quality indicator, as both a* and b* parameters for the TMT showed little variation from those of the unmodified wood and too high a scatter in values.

KEYWORDS:

• Thermal modification
• wood
• ThermoWood
• quality control
• colour

Acknowledgements

Assistance from the International ThermoWood Association and its members for allowing the creation of the long-term data-set used within this study is gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Support from CT WOOD – a centre of excellence at Luleå University of Technology supported by the Swedish Wood Industry – is also acknowledged, along with additional support through the project “Advanced research supporting the forestry and wood-processing sector’s adaptation to global change and the 4th industrial revolution”, OP RDE [grant number CZ.02.1.01/0.0/0.0/16_019/0000803].