Degradation of Chemical Components of Thermally Modified Robinia pseudoacacia L. Wood and Its Effect on the Change in Mechanical Properties

Abstract

Currently, emphasis is placed on using environmentally friendly materials both from a structural point of view and the application of protective means. For this reason, it is advisable to deal with the thermal modification of wood, which does not require the application of protective substances, to increase its service life. The main reason for the thermal modification of black locust is that although black locust grows abundantly in our country, it has no industrial use. It is mainly used outdoors, where thermal modification could increase its resistance. This article deals with the thermal modification of black locust wood (Robinia pseudoacacia L.) and the impact of this modification on the chemical components of the wood with an overlap in the change in mechanical properties compared to untreated wood. Static (LOP, MOR, and MOE) and dynamic (IBS) bending properties were evaluated as representative mechanical properties. At the same time, the impact of thermal modification on the representation of chemical components of wood (cellulose, lignin, hemicellulose) was also tested. As a result of the heat treatment, the mechanical properties gradually decreased as the temperature increased. The highest decrease in mechanical values found at 210 °C was 43.7% for LOP and 45.1% for MOR. Thermal modification caused a decrease in the content of wood polysaccharides (the decrease in hemicelluloses content was 33.2% and the drop in cellulose was about 29.9% in samples treated at 210 °C), but the relative amount of lignin in the wood subjected to increased temperature was higher due to autocondensation, and mainly because of polysaccharide loss. Based on the correlations between chemical and mechanical changes caused by thermal modification, it is possible to observe the effects of reducing the proportions of chemical components and changes in their characteristic properties (DP, TCI) on the reduction in mechanical properties. The results of this research serve to better understand the behavior of black locust wood during thermal modification, which can primarily be used to increase its application use.

Synthesis and Characterization of Poly(hydroxy)urethane from Polyols for Beech (Fagus sylvatica) Wood Impregnation

“…Thermal modification of the internal structure of wood has been proven to improve the dimensional stability and durability of wood, with a diminution of its mechanical properties (Ayrilmis et al 2011;Hill et al 2021). The strength loss of wood due to thermal treatment might be brought about by the degradation of hemicelluloses and modification of lignin structures (Sikora et al 2022). Chemical treatments brought about comparable effects, except that the mechanical properties of wood could be retained through in-site polymerization (Iaych 2010).…”