The photodegradation of wood during solar irradiation

Part I: Effects on the structural integrity of thin wood strips

Der photolytische Abbau von Holz unter Sonnenlichstrahlung

Teil 1: Einflüsse auf das Gesamtgefüge von dünnen Holzstäben

Abstract

The photodegradation of wood is essentially a surface phenomenon, and although in practical terms it has no effect on strength properties, it does have serious consequences for the surface technologist. A principal concern is photodegradation of the timber surface underlying clear and lightly-pigmented finishes—a problem which can lead to early failure of the coating and to expensive remedial measures. Recent thinking is directed towards the development of pretreatments which could stabilise the timber surface against photodegradation. However, in the absence of detailed investigations on the wood-degrading capabilities of different regions of the solar spectrum such developments have so far been restricted. In this paper, thin strips of Scots pine and lime were irradiated behind filters which transmitted selected regions of the ultraviolet and visible spectrum. Tensile tests on irradiated strips show that ultraviolet light is highly active in degrading wood, but indicate that the visible part of the spectrum also contributes significantly to loss of strength. Throughout the exposure period, samples were taken for SEM observation. The loss of strip strength is associated with a light-induced depolymerisation of lignin and cell wall constituents, and to the subsequent breakdown of the wood microstructure.

Zusammenfassung

Die Photolyse von Holz ist hauptsächlich ein Oberflächenphänomen und sie hat, obwohl ohne direkten Einfluß auf die Festigkeit, wichtige Auswirkungen auf die Oberflächen-Technologie. Ein wichtiger Gesichtspunkt ist hierbei die Photolyse von Holzoberflächen unter transparentem, schwach pigmentiertem Finish, ein Problem, das zu frühzeitigem Versagen der Beschichtung und teuren Instandsetzungsarbeiten fürhren kann. Neuere Bemühungen richten sich auf die Entwicklung von Vorbehandlungen zur Stabilisierung der Holzoberfläche gegen Photolyse. Derartige Bestrebungen wurden bislang dadurch erschwert, als detaillierte Untersuchungen über diejenigen Anteile des Sonnenlichts, die den photolytischen Abbau des Holzes bewirken, nicht vorlagen. In der vorliegenden Arbeit wurden dünne Stäbe aus Kiefer und Linde durch Filter bestrahlt, welche bestimmte Anteile aus dem ultravioletten und sichtbaren Bereich abtrennten. Zugbelastungsprüfungen mit bestrahlten Proben zeigen, daß ultraviolettes Licht in hohem Maße abbauend wirkt, daß aber auch der sichtbare Lichtanteil erheblich zum Festigkeitsverlust beiträgt. Während der gesamten Expositionsdauer wurden die proben durch REM beobachtet. Der Festigkeitsverlust der Proben war stets mit einer durch die Lichteinstrahlung bedingten Depolymerisierung des Lignins, des Zellwandbestandteile und dem anschließenden Zusammenbruch der Mikrostruktur verbunden.

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References

  1. Ashton, H.E. 1967: Claer finishes for exterior wood. J. Paint Technol. 39 (507):212–224

    CAS  Google Scholar 

  2. Borgin, K. 1970: The use of the scanning electron microscope for the study of weathered wood. J. Microscopy 92 (1):47–55

    Google Scholar 

  3. Borgin, K.; Parameswaran, N.; Liese, W. 1975: The effect of ageing on the ultrastructure of wood. Wood Sci. Technol. 9 (2):87–98

    Article  Google Scholar 

  4. Boxall, J. 1977: Painting weathered timber. Building Research Establishment Information Sheet IS 20/77

  5. Browne, F. L.; Simonson, H. C. 1957.: The penetration of light into wood. Forest. Prod. J. 7 (10):303–314

    Google Scholar 

  6. Davis, A.; Gordon, D. 1974: Rapid assessment of weathering stability from exposure of polymer films. II, the effectiveness of different regions of the solar spectrum in degrading ABS polymer. J. Appl. Polym. Sci. 18: 1173–1179

    Article  CAS  Google Scholar 

  7. Davis, A.; Deane, G. H. W.; Gordon, D.; Howell, G. V.; Ledbury, K. J. 1976: A world-wide program for the continuous monitoring of solar UV radiation using poly (phenylene oxide) film and a consideration of the results. J. Appl. Polym. Sci. 20:1165–1174

    Article  CAS  Google Scholar 

  8. Desai, R. L. 1968: Photodegradation of cellulosic materials—a review of the literature. Pulp & Paper Mag. Canada: 53–61

  9. Desai, R. L.; Shields, J. A. 1969: Photochemical degradation of cellulose material. Makromolekulare Chem. 122: 134–144

    Article  CAS  Google Scholar 

  10. Feist, W. C.; Mraz, E. A. 1978.: Comparison of outdoor and accelerated weathering of unprotected softwoods. Forest. Prod. J. 28 (3):38–43

    Google Scholar 

  11. Ifju, G. 1964: Tensile strength behaviour as a function of cellulose in wood. Forest. Prod. J. 14(8): 366–372

    Google Scholar 

  12. Kalnins, M. A. 1966: Surface characteristics of wood as they affect durability of finishes, Part II Photochemical degradation of wood. US Forest Service Research Paper FPL 57

  13. Kleinert, Th. N. 1970: Physikalisch-chemische Holzveränderungen im Freien. Holzforsch. Holzverwert. 22(2):21–24

    CAS  Google Scholar 

  14. Kringstad, K. 1969: Degradation of wood and high-yield pulps by light. TAPPI 52 (6):1070–1074

    CAS  Google Scholar 

  15. Lindström, T.; Söremark, C.; Westman, L. 1977: The influence on paper strength of dissolved and colloidial substances in the white water. Svensk Papperstidn. 11:341–345

    Google Scholar 

  16. Marian, J. E.; Wissing, A. 1960: The chemical and mechanical deterioration of wood in contact with iron. Part I, mechanical deterioration. Svensk Papperstidn. 63 (3):47–57

    CAS  Google Scholar 

  17. Miniutti, V. P. 1964: Microscale changes in cell structure at softwood surfaces during weathering. For. Prod. J. 14 (12):571–576

    Google Scholar 

  18. Miniutti, V. P. 1967: Microscopic observations of ultraviolet irradiated and weathered softwood surfaces and clear coatings. US Forest Service Research Paper FPL 74

  19. Moon, P. 1940: The solar constant. J. Franklin Inst. 30 (1379):584–617

    Google Scholar 

  20. Phillips, G. O.; Arthur, J. C. 1964: Chemical effects of light on cotton cellulose and related compounds. Part II, photodegradation of cotton cellulose. Textile Res. J. 34:572–580

    Article  CAS  Google Scholar 

  21. Raczkowski, J. 1980: Seasonal effects on the atmospheric corrosion of spruce microsections. Holz Roh- Werkstoff 38:231–234

    Google Scholar 

  22. Sell, J. 1968: Investigations on the infestation of untreated and surface treated wood by blue-stain fungi. Holz Roh- Werkstoff 26:215–222

    Google Scholar 

  23. Sell, J. 1975: Grundsätzliche Anforderungen an Oberflächenbehandlungen für Holz im Außenbau (Literaturübersicht). Holz Roh-Werkstoff 33:336–340

    Google Scholar 

  24. Smith, D. N. R. 1971: A possible method for the rapid evaluation of wood preservatives. Mitt. Dt. Ges. Holzforsch. 57:18–22

    Google Scholar 

  25. Wiesner, J. 1864: The decomposition of wood in the atmosphere. Sitzungsber. K. Akad. Wissenschaften Wien 49:61–94

    Google Scholar 

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The authors wish to thank Dr. F. J. Clark of the National Physical Laboratory for providing transmission data on the filters, and Dr. J. Gascoigne of the Cross and Bevan Laboratories for the determinations of cellulose viscosity. They are grateful to Dr. A. Davis of the Explosives Research and Development Establishment for helpful discussions

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Derbyshire, H., Miller, E.R. The photodegradation of wood during solar irradiation. Holz als Roh-und Werkstoff 39, 341–350 (1981). https://doi.org/10.1007/BF02608404

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Keywords

  • Lignin
  • Strength Loss
  • Middle Lamella
  • Scanning Electron Microscope Investigation
  • Tangential Surface