Wood Science and Technology

, Volume 20, Issue 1, pp 71–81 | Cite as

Polyflavonoid tannins — a main cause of soft-rot failure in CCA-treated timber

  • A. Pizzi
  • W. E. Conradie
  • A. Jansen
Article

Summary

Polyflavonoid tannins are proven to be fast-reacting with CCA solutions and hence, to be strong competitors of the structural wood constituents for fixation of CCA preservatives. The consequence of this effect is that even relatively small amounts of tannin cause severe undertreatment of the structural wood constituents which in turn badly affects the long term durability of CCA treated timber. The effect is compounded by heavy disproportionation between tannins and structural wood constituents of Cu, Cr and As. This leads to the well-known high susceptibility to soft-rot attack in eucalyptus species and in vineyard posts even experienced with some susceptible softwoods. Relationships found by other authors between soft-rot incidence and lignin content in CCA-treated timber are proven here to be only part of the total failure mechanism. The total mechanisms of resistance and failure are due to the balance of distribution of reactions among the various proportions of highly reactive tannins and more abundant but less reactive lignin and carbohydrates present in any wood. As a consequence of the clarification of these mechanisms the liability of different woods to soft-rot attack can then be accurately determined. Solutions to the problem are presented and discussed.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. American Wood Preservers Association 1971: Specification for waterborne preservatives. AWPA standard P5-71Google Scholar
  2. American Society for Testing and Materials 1971: specification for chromated copper arsenate. ASTM standard D1625-68Google Scholar
  3. Butcher, J. A.; Nilsson, T. 1982: Influence of variable lignin content amongst hardwoods on soft-rot susceptibility and performance of CCA preservatives. International Research Group on Wood Preservation Document IRG/WP/1151, Stockholm, SwedenGoogle Scholar
  4. Butcher, J. A. 1983: Private communicationsGoogle Scholar
  5. Garbutt, D. 1985: Institute for Commercial Forestry Research, Pietermaritzburg, South Africa. Personal communication.Google Scholar
  6. Hedley, M. E. 1983: Inadequacies in preservative retention and formulation as contributory causes of premature failure of CCA-treated vineyard posts. Presented at Tanalith 83 Conference, Auckland, New ZealandGoogle Scholar
  7. Jansen, A.; Conradie, W. E.; Pizzi, A. 1984: The penetration characteristics of CCA preservatives in wood. Part 1: radial/tangential, processes and species effects Holz Roh-Werkstoff (accepted for publication)Google Scholar
  8. Jenkin, D. J. 1984: Adhesives from Pinus radiata bark extractives. J. Adhesion 16: 299–310Google Scholar
  9. Kubel, A.; Pizzi, A. 1981: Protection of wood surfaces with metallic oxides, Holzforsch. Holzverwert. 33: 11–14Google Scholar
  10. Leightley, L. E. 1983: Wood preservation requirements in Queensland, Australia. Symposium on wood preservation, Pretoria, South AfricaGoogle Scholar
  11. Nilsson, T. 1982: Comments on soft-rot attack in timbers treated with CCA preservatives: A document for discussion. International Research Group on Wood Preservation document IRG/WP/1167, Stockholm, SwedenGoogle Scholar
  12. Peek, R. D.; Willeitner, H. 1981: Beschleunigte Fixierung chromathaltiger Holzschutzmittel durch Heißdampfbehandlung. 1. Mitteilung: Einfluß verschiedener Wärmebehandlungen auf die Auswaschung von Schutzsalzen, Holz Roh-Werkstoff 39: 495–502Google Scholar
  13. Pizzi, A. 1979: Wood waterproofing and lignin cross-linking by means of chromium trioxide/guaiacyl units complexes. Holzforsch. Holzverwert. 31: 128–131Google Scholar
  14. Pizzi, A. 1981: The chemistry and kinetic behaviour of Cu-Cr-As/B wood preservatives. I. Fixation of chromium on wood. J. Polym. Sci., Chem. Ed. 19: 3093–3121Google Scholar
  15. Pizzi, A. 1983: The chemistry and kinetic behaviour of Cu-Cr-As/B wood preservatives. IV. Fixation of CCA to wood. J Polym. Sci. Chem. Ed. 20: 739–764Google Scholar
  16. Pizzi, A. 1983: A new approach to the formulation and application of CCA preservatives, Wood Sci. Technol. 17: 303–319Google Scholar
  17. Pizzi, A.; Conradie, W. E. 1984: Unpublished dataGoogle Scholar
  18. Richardson, B. A. 1978: Wood preservation. Lancaster: The Construction Press,Google Scholar
  19. Slabbert, N. P. 1972: Metal complexes of black wattle tannins and related model polyphenols. Ph.D. thesis, Rhodes University, Grahamstown, South AfricaGoogle Scholar
  20. South African Bureau of Standards specification SABS 673-1976: Mixtures of copper-chromearsenic compounds for timber preservationGoogle Scholar
  21. Swann, D. A.; Stuart, K. R.; Russel, D. C.; Chiang, C. L. 1976: New Zealand patent 179933, 11. Febr. 1976Google Scholar
  22. Vogel, M. C.; Pizzi, A.; Conradie, W. E. 1983: Comparative leaching tests of Cu, Cr and As from timber treated with CCA types I and II (C and B). CSIR Special Report HOUT 308, Pretoria, South AfricaGoogle Scholar

Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • A. Pizzi
    • 1
  • W. E. Conradie
    • 1
  • A. Jansen
    • 1
  1. 1.PretoriaSouth Africa

Personalised recommendations