Investigations on chemical changes of surface contact-charred Norway spruce (Picea abies L.) using ATR-FTIR spectroscopy and pH value measurements

Surface charring of wood has been used for many centuries to make wood more durable against biological pests (e.g. wood decaying fungi). The exact reasons for the increased durability of surface charred wood however remain more or less unclear. To obtain more information on possible reasons for the increased durability of surface charred wood, the chemical changes of surface contact-charred Norway spruce ( Picea abies L.) got investigated by ATR-FTIR spectroscopy and pH value measurements. Temperatures of 300°C, 350°C and 400°C were used to carbonize the surface of specimens for a duration of ≈ 3 min. Measurements were conducted not only on the surface of the specimens but also on areas underneath the surface by removing material in steps. By that a “depth profile” of chemical changes could be created. Overall, the results of the applied methods seem to confirm the literature regarding the occurrence of different temperature zones in areas below the surface where different chemical changes occur. Concerning possible reasons for the increase of durability of charred wood the formation of phenolic compounds during pyrolysis could be determined. Those might play a key role inhibiting the infestation by wood decaying fungi.