Effect of oxidizing thermal modification on the chemical properties and thermal conductivity of Norway spruce (Picea abies L.) wood

ABSTRACT

This research work aims to investigate the effects of thermal modification and wood cutting direction (transverse, radial and tangential) on the content of extractives, lignin, cellulose, and hemicelluloses, and on the thermal conductivity of Norway spruce (Picea abies L.) wood. Samples were thermally modified for 3, 6, and 9 h at temperatures of 160°C, 180°C, and 200°C in the oxidizing atmosphere with natural convection. The extractives, lignin, cellulose, and holocellulose contents were determined by wet chemistry methods, the structural changes were evaluated by using Fourier-transform infrared spectroscopy (FTIR). The highest relative content of extractives was determined at the temperature of 200°C and a thermal modification duration of 9 h. The lignin content decreased at the temperature of 160°C and increased at higher temperatures due to the formation of pseudo-lignin. The cellulose content increased, and hemicellulose content decreased with the increased temperature and thermal modification duration. FTIR analyses revealed changes mainly at the temperature of 200°C, primarily a decrease in the intensities of the characteristic absorption bands of lignin due to degradation reactions. Markedly, density and thermal conductivity decreased mostly due to depolymerization of hemicelluloses. Regarding the thermal conductivity, a slightly higher decrease in transversal and tangential sections was determined.

KEYWORDS:

• Norway spruce
• thermal modification
• chemical composition
• infrared spectroscopy
• thermal conductivity
• cutting orientation

Disclosure statement

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

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by Slovak Scientific Grant Agency VEGA [1/0378/18, 1/0717/19, 1/0397/20] and Slovak Research and Development Agency [APVV-20-0159]. This publication is also the result of the project implementation: Progressive research of performance properties of wood-based materials and products (LignoPro), ITMS 313011T720 supported by the Operational Programme Integrated Infrastructure (OPII) funded by the ERDF [1/0378/18, 1/0717/19, 1/0397/20].