Comparison of the chemical and micromechanical properties of Larix spp. after eco-friendly heat treatments measured by in situ nanoindentation

Dong Xing,Jian Li,Siqun Wang

doi:10.1038/s41598-020-61314-6

Abstract

Heat treatment is a green, environmentally friendly and mild pyrolysis process that improves the dimensional stability and durability of wood. In this study, Larix spp. Samples were heated at 180 °C and 210 °C for 6 h with nitrogen, air or oil as heat-conducting media. The influence of high-temperature heat treatment on the microstructure, chemical components, and micromechanical properties was investigated. The mass loss rate increased with increasing temperature, and the degradation of wood components resulted in cracks in the cell walls. Samples treated with air showed more cracks in cell walls than were observed in the cells walls of wood treated with the other heat-conducting media. The hardness of the cell walls increased after all heat treatments. In addition, the results showed that heat treatment reduced creep behavior compared to that of untreated wood.

Highlights

Larix spp., an appealing source of wood products in China, are massively planted due to their excellent adaptability, rapid growth and long growth cycle
The mass loss rate showed the different amounts of hemicellulose degradation, oil uptake and the extent of heat treatment[21]
Slight mass loss rates of 1.68% and 4.63% were observed for N1 and N2, respectively, corresponding to vaporization of volatile extractives, degradation of hemicellulose and some amorphous cellulose and desorption of bound water in the wood samples[19,22,23]

Summary

Introduction

Larix spp., an appealing source of wood products in China, are massively planted due to their excellent adaptability, rapid growth and long growth cycle. A green process, alters the chemical composition of wood through pyrolysis of the hemicellulose and part of the amorphous cellulose, evaporation of extractives and condensation of byproducts[4,5]. This procedure caused a higher degree of cellulose crystallinity, lower hydrophilicity, improved color, and better dimensional stability and durability of wood[6,7]. Previous studies have shown that the elemental composition (C/O ratio or C content) is a useful marker for predicting the level or extent of heat treatment[9,10] These markers can be effectively used for the prediction of decay durability and mechanical properties of heat-treated wood. There are few publications regarding the influence of different heat media or atmospheres on the properties of heat-treated wood

Objectives

Results

Conclusion