Changes of Meranti, Padauk, and Merbau Wood Lignin during the ThermoWood Process.

Danica Kačíková,Ivan Kubovský,Milan Gaff,František Kačík

doi:10.3390/polym13070993

Danica Kačíková, Ivan Kubovský + Show 2 more

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https://doi.org/10.3390/polym13070993

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Abstract

Thermal modification is an environmentally friendly process in which technological properties of wood are modified using thermal energy without adding chemicals, the result of which is a value-added product. Wood samples of three tropical wood species (meranti, padauk, and merbau) were thermally treated according to the ThermoWood process at various temperatures (160, 180, 210 °C) and changes in isolated lignin were evaluated by nitrobenzene oxidation (NBO), Fourier-transform infrared spectroscopy (FTIR), and size exclusion chromatography (SEC). New data on the lignins of the investigated wood species were obtained, e.g., syringyl to guaiacyl ratio values (S/G) were 1.21, 1.70, and 3.09, and molecular weights were approx. 8600, 4300, and 8300 g·mol−1 for meranti, padauk, and merbau, respectively. Higher temperatures cause a decrease of methoxyls and an increase in C=O groups. Simultaneous degradation and condensation reactions in lignin occur during thermal treatment, the latter prevailing at higher temperatures.

Highlights

As a renewable composite material, wood is an ideal building material that is easy to work with and offers advantages such as a high strength-to-weight ratio and lower processing energy
This yield drop can be due to preferential lignin degradation reactions, and it corresponds with the decline of lignin molecular weight determined by size exclusion chromatography (Table 4)
Padauk, and merbau wood samples were thermally treated according to the ThermoWood process at different temperatures (160, 180, 210 ◦ C), lignin was extracted by dioxane and its changes were evaluated by chemical, chromatographic, and spectroscopic analyses

Summary

Introduction

As a renewable composite material, wood is an ideal building material that is easy to work with and offers advantages such as a high strength-to-weight ratio and lower processing energy. Apart from that, it is susceptible to fungal degradation and to weathering [1,2,3] These shortcomings can be minimized by making hydrophilic wood hydrophobic, and thermal treatment is a widely used modification method for this purpose. Tropical woods have high commercial value on the market and wood industry due to their good appearance and excellent physical, mechanical, and machinability properties. Thermal treatment appears to be an environmentally friendly and economical technology to improve the properties and colour of wood products. The thermal modification of wood at temperatures from 180 to 260 ◦ C leads to hemicellulose and lignin degradation. This process changes the chemical composition of the wood and reduces its hygroscopicity. Thermally modified wood tends to be more dimensionally stable than unmodified wood of the same species [8,9,10,11]

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