Topochemistry of heat-treated and N-methylol melamine-modified wood of koto (Pterygota macrocarpa K. Schum.) and limba (Terminalia superba Engl. et. Diels)

Karl-Christian Mahnert,Stergios Adamopoulos,Holger Militz,Gerald Koch

doi:10.1515/hf-2012-0017

Karl-Christian Mahnert, Stergios Adamopoulos + Show 2 more

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https://doi.org/10.1515/hf-2012-0017

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Abstract

Abstract To broaden the knowledge about the chemical changes at the cell wall level of differently modified tropical hardwoods, heat-treated and N-methylol melamine (NMM)-treated samples of koto (Pterygota macrocarpa) and limba (Terminalia superba) were prepared. UV microspectrophotometry (UMSP) was applied at 278 and 240 nm as specific wavelengths to analyze chemical alterations of the samples caused by heat and NMM treatment, respectively. The absorbance of koto exceeded that of limba before and after treatment, potentially due to the higher extractive content of the former. Regardless of the wood species, the absorbance of the samples increased with increasing intensity of the NMM treatment. Additionally, the absorbance of lignin within the spectrum of 230–350 nm was altered due to the NMM treatment. The functionality of applying specific wavelengths for the analysis of different modification methods of wood was proven. However, the comparison with literature did not show differences in the absorbance, which could be assigned to the characteristics of tropical hardwoods.

Highlights

The term wood modification summarizes the physical and chemical processes applied to extend the service life of wood by decelerating biological degradation and improving the wood properties without biocide treatment
Thermal modification between 160°C and 260°C leads to an increased biological resistance (Tjeerdsma et al 2000) and dimensional stability (Burmester 1975) of wood, which are attributed to the thermal degradation of wood polymers, mainly hemicelluloses (Militz 2002)
The depolymerization and hydrolysis of hemicelluloses begins below 180°C (Garrote et al 2001; Rowell et al 2009)

Summary

Introduction

The term wood modification summarizes the physical and chemical processes applied to extend the service life of wood by decelerating biological degradation and improving the wood properties without biocide treatment. The NMM-modified wood samples (3 × 3 × 5 mm3, R × T × L) were prepared with a razor blade for cross-sectional microscopic observation. Representative 2D UV scans of untreated koto and limba at 278 nm (Figure 1) show the characteristic lignin distribution in the cell walls (Koch and Kleist 2001; Koch et al 2006; Scholz et al 2007; Carrillo et al 2008; Adamopoulos and Koch 2011).

Results

Conclusion