Thermal Modification of Spruce and Maple Wood for Special Wood Products

Anna Danihelová; Zuzana Vidholdová; Tomáš Gergeľ; Lucia Spišiaková Kružlicová; Michal Pástor

doi:10.3390/polym14142813

Thermal Modification of Spruce and Maple Wood for Special Wood Products

Polymers (Basel). 2022 Jul 10;14(14):2813. doi: 10.3390/polym14142813.

Authors

Anna Danihelová¹, Zuzana Vidholdová², Tomáš Gergeľ³, Lucia Spišiaková Kružlicová⁴, Michal Pástor³

Affiliations

¹ Department of Fire Protection, Faculty of Wood Sciences and Technology, Technical University in Zvolen, T. G. Masaryka 24, 960 01 Zvolen, Slovakia.
² Department of Wood Technology, Faculty of Wood Sciences and Technology, Technical University in Zvolen, TU in Zvolen, Masaryka 24, 960 53 Zvolen, Slovakia.
³ National Forest Centre, Forest Research Institute, T. G. Masaryka 22, 960 01 Zvolen, Slovakia.
⁴ Department of Furniture Design and Interior, Faculty of Wood Sciences and Technology, Technical University in Zvolen, TU in Zvolen, Masaryka 24, 960 53 Zvolen, Slovakia.

Abstract

This article presents a proposal of thermal modification of Norway spruce and sycamore maple for special wood products, mainly for musical instruments. Selected physical and acoustical characteristics (PACHs), including the density (ρ), dynamic modulus of elasticity along the wood grain (E_L), specific modulus (E_sp), speed of sound along the wood grain (c_L), resonant frequency (f_r) and acoustic constant (A), logarithmic decrement (ϑ), loss coefficient (η), acoustic conversion efficiency (ACE), sound quality factor (Q), and the timbre of sound, were evaluated. These two wood species were chosen regarding their use in the production or repair of musical instruments. For the thermal modification, a similar process to the ThermoWood process was chosen. Thermal modification was performed at the temperatures 135 °C, 160 °C and 185 °C. The resonant dynamic method was used to obtain the PACHs. Fast Fourier transform (FFT) was used to analyze the sound produced. The changes in the observed wood properties depended on the treatment temperature. Based on our results of all properties, the different temperature modified wood could find uses in the making of musical instruments or where the specific values of these wood characteristics are required. The mild thermal modification resulted in a decrease in mass, density, and increased speed of sound and dynamic modulus of elasticity at all temperatures of modification. The thermally modified wood showed higher sound radiation and lower loss coefficients than unmodified wood. The modification also influenced the timbre of sound of both wood species.

Keywords: musical instruments; physical and acoustical characteristics; spruce and maple wood; thermal modification; timbre of sound.

Grants and funding

This scientific work was supported by grant APVV-17-0583 “Construction and decorative materials based on recycled and modified wood”, as well as by grant APVV-20-0326 “Research possibilities of the utilisation of black walnut (Juglans nigra L.) and chestnut (Castanea sativa Mill.) from a production-ecological aspect in agroforestry systems in Slovakia” and APVV-21-0032 “Certification of log quality based on internal wood defects”. This publication is one of the results of the project implementation of Centrum excelentnosti lesnícko-drevárskeho komplexu LignoSilva (Centre of Excellence of Forest-based Industry, ITMS: 313011S735) supported by the Research and Development Operational Programme funded by the ERDF.