Scanning UV microspectrophotometry as a tool to study the changes of lignin in hydrothermally modified wood

Abstract

Thermal modification (TM) of wood has occupied a relatively narrow but stable niche as an alternative for chemical wood protection. There are different technological solutions for TM and not all details of their effects on wood tissue have been understood. The one-stage hydrothermal modification (HTM) at elevated vapour pressure essentially changes the wood's composition and structure. In the present paper, the changes in three hardwood lignins (alder, aspen, and birch) were observed within the cell wall by means of cellular UV microspectrophotometry. The lignin absorbances in the compound middle lamella (CML) of unmodified wood are 1.7-to 2.0-fold higher than those in the fibre S2 layer. The woods were modified in the temperature range from 140 to 180°C, while in the lower temperature range (140°C/1 h), the UV absorbances are little affected. Essential changes occur in the range of 160-180°C and the UV data reflect these by absorbtion changes, while the absorbances at 278 nm rise with factors around 2 more in the S2 layer than in the CML. The absorbance increments are interpreted as polycondensation reactions with furfural and other degradation products of hemicelluloses with the lignin moiety of the cell wall.

Topochemical Correlation between Carbohydrates and Lignin in Eucommia ulmoides Cell Wall from Tissue to Cell Level

“…Although traditional microanalytical techniques, including ultraviolet microspectrophotometry, polarized light microscope, transmission electron microscope combined with immunocytochemistry, and fluorescence microscopy, have been comprehensively employed to investigate the distribution of lignin and carbohydrates (Vigneshwaran et al 2011;Donaldson and Knox 2012;Andersson et al 2015a;Zeng et al 2015), these measurements require chemical treatment or complicated embedding procedure that may inevitably cause changes in the cell structure and modify cell wall components. On the contrary, spectroscopic methods, such as infrared (IR) and Raman spectroscopies measurements can provide complementary information about the molecular vibrations and be performed on the samples without any preparatory steps.…”

Thermo-hydro treated (THT) birch plywood with improved service properties

“…Thermal modification is one of the most promising methods to modify wood materials (Sandberg, Haller and Navi 2013). In the thermo-hydro treatment (THT) process, not only are the chemical properties and structure of wood changed, but also the mechanical strength, water uptake and durability (Andersons et al 2010; Grinins et al 2013; Irbe et al 2014; Biziks et al 2015). Dimensional instability and biological durability are considered to be disadvantages of wood, when it is used as building and construction material.…”