Relationship between chemistry and decay resistance of thermally modified Eucalyptus grandis wood in closed and open systems
Name: ANNA CLARA OLIVEIRA RUPF
Publication date: 30/07/2025
Examining board:
Name |
Role |
|---|---|
| DJEISON CESAR BATISTA | Presidente |
| MÁRCIO PEREIRA DA ROCHA | Examinador Externo |
| MAXIMILIAN WENTZEL | Examinador Externo |
Summary: Thermal modification is a sustainable alternative that improves the properties of juvenile wood, including dimensional stability and biological resistance. The main objective of this work was to evaluate the effect of thermal modification in closed and open systems on the chemical composition and decay resistance of juvenile Eucalyptus grandis wood. The wood was thermally modified in a pilot-scale reactor capable of operating in either closed or open systems. The treatments included untreated wood; thermally modified wood (TMW) in closed system at 150, 160, and 170°C; and TMW in open system at 170, 190, and 210°C. The thermal modification processes were assessed based on initial and final moisture content, process duration, and corrected mass loss (CML). The chemical composition of the wood was determined via wet chemical analyses (alpha-cellulose, hemicelluloses, total lignin, and extractives – total, acetone, and dichloromethane), crystallinity index by X-ray diffraction analysis, and FTIR spectroscopy. Decay resistance tests were carried out using the fungi Trametes versicolor (white rot) and Coniophora puteana (brown rot). A hygroscopicity test was conducted under climate-controlled conditions (20°C and 65% relative humidity) to evaluate the equilibrium moisture content and the moisture exclusion efficiency. Thermal modification in closed system resulted in higher CML, even at lower temperatures, due to the effects of high relative humidity and pressure. Significant changes were observed in the wood’s chemical components, except for the 170°C treatment in open system. For similar CML means, closed-system wood had higher contents of alpha-cellulose and extractives (total and in acetone). In comparison, the open-system wood had higher contents of hemicelluloses and dichloromethane extractives. All treatments reduced wood hygroscopicity, with the best results observed in the open system from 190°C onwards. Decay resistance against both fungi increased with temperature, with the best performance achieved in the open system at 210°C, classified as durability class 1 (“very durable”).
Keywords: Thermal modification; Wet chemistry; Crystallinity index; FTIR; Hygroscopicity; Coniophora puteana; Trametes versicolor.
