Outline

  • Abstract
  • Keywords
  • 1. Introduction
  • 2. Theory
  • 2.1. the van Krevelen Diagram for Wood
  • 2.2. Average Carbon Oxidation State of Wood
  • 2.3. Stability of Organic Substance in Aerobic Environment
  • 2.4. Fungal Resistance Prediction for Thermally Modified Wood
  • 3. Results
  • 4. Discussion
  • 4.1. Sugar Reactions
  • 4.2. Elemental Composition Changes During the Thermal Modification
  • 4.3. Thermal Mass Loss Versus O/c Ratio As a Marker for Degree of Modification
  • 4.4. Influence of Oxidation Stability on Fungal Resistance
  • 4.5. Artefacts of the Fungal Test Procedure
  • 4.6. Other Possible Reasons for Fungal Resistance of Heat Treated Wood
  • 5. Conclusions
  • References

رئوس مطالب

  • چکیده
  • کلیدواژه ها
  • 1. مقدمه
  • 2. نظریه
  • 2.1 نمودار ون کرولن برای چوب
  • 2.2 متوسط حالت اکسیداسیون کربن چوب
  • 2.3 ثبات ماده آلی در محیط هوازی
  • 2.4 پیش بینی مقاومت در برابر قارچ برای چوب اصلاح شده حرارتی
  • 3. نتایج
  • 4. بحث
  • 4.1 واکنش های قند
  • 4.2 تغییرات ترکیب عناصر در خلال اصلاح حرارتی
  • 4.3 اتلاف جرم حرارتی در برابر نسبت O/C به عنوان شاخصی برای درجه اصلاح
  • 4.4 تاثیر پایداری اکسیداسیون بر مقاومت در برابر قارچ
  • 4.5 محصول فرآیند آزمون قارچ
  • 4.6 سایر دلایل ممکن برای مقاومت در برابر قارچ چوب تیمار شده با حرارت
  • 5. نتیجه گیری

Abstract

It has recently been reported that the oxygen to carbon-ratio (O/C) of thermally modified wood is a reliable indicator for the resistance against attack by Basidiomycete fungi. The present theoretical study is an attempt to clarify causality between the O/C-ratio of thermally modified wood and its fungal resistance, as measured by standardized laboratory test procedures. It is shown that different wood species, with varying degree of thermal modification, reveal a remarkable correlation in elemental composition when plotted in a van Krevelen state diagram, suggesting a common modification chemistry shared by these species. The overall chemical reaction types responsible for the composition changes appear to be mainly dehydration, with some decarboxylation. The latter reaction decreases the mean overall oxidation state of carbon atoms present in thermally modified wood, leading to an inherently improved resistance against oxidation of the material. A known general correlation, between the average oxidation state of organic matter and the Gibbs free energy of the oxidation half-reaction, was found quantitatively consistent with the observed trend in the fungal resistance of thermally modified wood with the O/C-ratio.

Keywords: - - - -

Conclusions

The quantitative theory in this work related the average carbon oxidation state to an inherent stability against oxidation and subsequently to the fungal resistance thermally modified wood. This theory does not intend to explain the complex fungal degradation mechanisms, but rather poses an semi-empirical thermodynamic limit on the relative degradation rates by fast degrading Poria placenta brown rot on heat-treated wood in comparison to untreated wood. The parameter-free theory was verified and found in reasonable agreement with published experimental fungal resistance results on a series of heat treated woods with known elemental composition. The elemental composition of several thermally modified wood species shows a universal correlation between the molar elemental ratios O/C and H/C. This correlation is partly understood on the basis of elimination reactions of small molecules, e.g. water and carbon dioxide. The elimination of volatiles, notably carbon dioxide, has a chemically reducing effect on wood, quantified by the average carbon oxidation state Z = 2(O/C) – H/C. Further research, assuring the relation between the composition of the volatile yield during heat-treatment of wood and its carbon oxidation state, is important for its potential to in-line process monitoring of the wood modification degree.

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