Surface properties of thermally treated European beech wood studied by PeakForce Tapping atomic force microscopy and Fourier-transform infrared spectroscopy

Abstract

<jats:title>Abstract</jats:title><jats:p>Natural constituents of wood cell-wall layers are affected in various ways by thermal treatment. This study investigated the effect of high-temperature treatment on the properties of cell-wall layers. The properties were studied using PeakForce quantitative nanomechanical mapping and Fourier-transform infrared spectroscopy (FTIR). European beech wood was thermally treated at 200 °C for 1, 3, and 5 h in an oxidizing atmosphere. Modulus of elasticity, adhesion force, and roughness of the secondary S<jats:sub>2</jats:sub> layer and the compound middle lamella (CML) were determined using atomic force microscopy (AFM). Results showed that both the S<jats:sub>2</jats:sub> layer and CML were affected by thermal treatment. Stiffening of the S<jats:sub>2</jats:sub> layer was caused by increased crystallinity of the cellulose-dominated component, having peaked after 1 h of treatment. The degradation thereafter resulted in a decrease of the S<jats:sub>2</jats:sub> as well as the CML stiffness. An increase of CML roughness after 3 h of treatment was associated with the effect of thermal degradation on CML integrity. The analysis suggested that the reduction in syringyl lignin is potentially associated with an increase in adhesion of cell-wall layers.</jats:p>

The Effect of CO2 Laser Engraving on the Surface Structure and Properties of Spruce Wood

“…At higher raster densities, a shift in the band´s maximum towards lower wavenumbers (from 1728 to 1712 cm −1 ) was also recorded, possibly caused by carbonyl group conjugation with other double bonds in alkenes, supported by thermo-oxidation reactions [39]. These facts point to the changes in several functional groups in lignin and in hemicelluloses [40,41]. The growth of the absorbance value of the band (belonging to the non-conjugated C=O groups) indicates increasing amounts of carbonyl and carboxyl groups in lignin and in polysaccharides, formed in oxidation processes [39], which is optically reflected in wood surface darkening [42].…”

Effects of Thermal Aging on the Adhesion Forces of Biopolymers of Wood Cell Walls

“… 17 − 21 Some studies used adhesion forces from force–displacement curves to characterize the wood fine structure nanomechanically 17 , 22 , 23 and to detect whether adhesion forces on wood surfaces changed with UV light or heat. 24 − 27 However, the interpretation of the adhesion force measurements is limited, at best. This gap is mainly due to the structural and chemical heterogeneity of natural wood surfaces, the lack of reliable repositioning techniques, and the small sample sizes, which prevents drawing statistically significant conclusions.…”

“…Wood is a cellular structure composed of biopolymers: cellulose, hemicelluloses, lignin, and small portions of other substances, such as extractives. Several studies used atomic force microscopy (AFM) to visualize the ultrastructure of the cell wall on transverse cross sections. − Some studies used adhesion forces from force–displacement curves to characterize the wood fine structure nanomechanically ,, and to detect whether adhesion forces on wood surfaces changed with UV light or heat. − However, the interpretation of the adhesion force measurements is limited, at best. This gap is mainly due to the structural and chemical heterogeneity of natural wood surfaces, the lack of reliable repositioning techniques, and the small sample sizes, which prevents drawing statistically significant conclusions.…”