Wood heat treatment has increased significantly in the last few years and is still growing as an industrial process to improve some wood properties. The first studies on heat treatment investigated mainly equilibrium moisture, dimensional stability, durability and mechanical properties. Mass loss, wettability, wood color, and chemical transformations have been subsequently extensively studied, while recent works focus on quality control, modeling, and study the reasons for the improvements. This review explains the recent interest on the heat treatment of wood and synthesizes the major publications on this subject on wood properties, chemical changes, wood uses, and quality control.

https://bioresources.cnr.ncsu.edu/BioRes_04/BioRes_04_1_0370_Esteves_P_Wood_Mod_Heat_Treatment_Rev_367.pdf

Wood modification by heat treatment: a review.

Characterisation of thermally modified hard- and softwoods by 13C CPMAS NMR

Investigation of wood wettability changes during heat treatment on the basis of chemical analysis

Investigations of the reasons for fungal durability of heat-treated beech wood

Thermal treatments of beech wood with different temperature loads on the wood cause characteristic changes in the chemical composition. The determination of specific changes was carried out by means of suitable methods, both wet chemical and instrumental analyses. It could be confirmed that in addition to the degradation of polyoses, lignin, known as the thermally most stable compound, shows significant thermal alterations too.

Chemical changes during the production of thermo-treated beech wood

Norway spruce (Picea abies) was heated for 2–8 h in the temperature range 180–225 °C, under a steam atmosphere. The chemical analyses of the treated feedstock samples indicated that during heating (total mass loss 1.5–12.5% of the initial DS) carbohydrates (hemicelluloses and cellulose) were clearly more amenable to various degradation reactions than lignin. In addition, major water-soluble products released from the feedstock material during the treatments were classified into several compound groups and changes in the relative mass portion of these groups were monitored by GC during a separate experiment.

Thermochemical behavior of Norway spruce ( Picea abies ) at 180–225 °C

Scots pine ( Pinus sylvestris ) and silver birch ( Betula pendula ) were heated for 4-8 h in a steam atmosphere at low temperatures (200-230°). The birch feedstock decomposed slightly more extensively (6.4-10.2 and 13.5-15.2% of the initial DS at 200° and 225°, respectively) than the pine feedstock (5.7-7.0 and 11.1-15.2% at 205° and 230°, respectively). The results indicated that the differences in mass loss between these feedstocks were due to mainly the fact that carbohydrates (cellulose and hemicelluloses) were more amenable to various degradation reactions than lignin in intact wood. The degradation reactions were also monitored in both cases by determining changes in the elemental composition of the heat-treated products.

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Thermal Behavior of Scots Pine ( Pinus Sylvestris ) and Silver Birch ( Betula Pendula ) at 200-230°

A multivariate chemometric method for monitoring the mass loss of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) by IR spectroscopic determination of chemical changes occurring during the heat treatment (160 - 260 °C, 2 - 8 h) of these wood materials was developed. The method was based on the handling of FTIR data on treated and untreated wood powder samples by the partial least squares (PLS) method. In addition, unknown samples (treated and untreated pine and spruce) were classified into separate groups by the principal component analysis (PCA) method. The chemical changes occurring in the wood samples during heating were also briefly discussed.

Risto A. Kotilainen

Papers

Thermochemical behavior of Norway spruce ( Picea abies ) at 180–225 °C

Thermal Behavior of Scots Pine ( Pinus Sylvestris ) and Silver Birch ( Betula Pendula ) at 200-230°

FTIR Monitoring of Chemical Changes in Softwood During Heating