The change, over time, in density, longitudinal modulus of elasticity, shear modulus and chemical structure of Scots pine (Pinus sylvestris) under thermal treatment (110, 120 and 140 C) was evaluated. The determinations of the specific changes were carried out by means of impulse excitation, ultrasonic time-of-flight and near infrared spectroscopy.
The results show, that the stiffness and density decrease was linear with time, with no evidence of a slowing rate of degradation even at 140 C, after loss of more than half the
original wood stiffness and more than a quarter of the original mass. At all temperatures the ratio between the longitudinal modulus and shear modulus was unchanged by the treatment for individual samples and the stiffness change was proportional to mass loss irrespective of the temperature and time. Examination of the NIR spectra revealed modifications in the amorphous carbohydrates structure and small changes in the lignin structure.
Ridley-Ellis, D., Popescu, C., Keating, B. A., Popescu, M., & Hill, C. A. S. (2014). Stiffness changes during low temperature thermal treatment of Scots pine, assessed by acoustic NDT. In L. Nunes, D. Jones, C. A. S. Hill, & H. Militz (Eds.), Proceedings of the 7th European Conference on Wood Modification