Holz als Roh- und Werkstoff
European Journal of Wood and Wood Products
 Springer-Verlag 2004
10.1007/s00107-004-0506-x

KURZORIGINALIA BRIEF ORIGINALS

The effect of wood defects on chemical modification with acetic anhydride

A. N. PapadopoulosContact Information and G. A. Ntalos1

(1)  Technological Educational Institute of Karditsa, Department of Wood and Furniture Technology-Design, 43100 Karditsa, Greece

Contact Information A. N. Papadopoulos
Email: antonios1974@hotmail.com

Published online: 15 September 2004


Without Abstract

Introduction   Chemical modification of wood has been successfully employed to improve dimensional stability and decay resistance of both solid wood and wood based panels (Papadopoulos and Traboulay 2002; Papadopoulos and Hill 2003; Papadopoulos and Gkaraveli 2003). In all cases considered in the literature, chemical modification employed in small clear wood specimens. In many cases, samples with the same number of growth rings were preferentially chosen and carefully selected so that growth rings were parallel to the tangential face, to ensure rapid reagent penetration into the cell lumen (Papadopoulos and Hill 2003). However, deviations from normal structure are not common, since trees are living organisms and are subject to various influences throughout their life span. When wood is looked upon as a raw material, most abnormalities adversely affect its service value; these are commonly called defects (Panshin and DeZeeuw 1980). From the wood utilisation point of view, defects are also certain normal characteristics of all trees, namely knots and pith. Despite an exhaustive search of the literature, there was no studies published dealing with the modification of wood with defects. Consequently, the purpose of this paper was to look at the effect that some defects may have on chemical modification of wood. The defects studied here in were: false rings of pine wood (Pinus sylvestris), discontinuous rings of pine (Pinus nigra), compression wood of pine (Pinus sylvestris) and tension wood of beech (Fagus sylvatica).
Experimental   Chemical modification reactions were performed as described previously (Papadopoulos and Hill 2003).
Results and discussion   The weight percent gain (WPG) values of wood with defects and normal wood, modified with acetic anhydride at 100C for a 7 h period, are summarised in Table 1. Some interested points have come out from the Table. It can be seen that the presence of false and discontinuous rings did not affect the chemical modification reactions, bearing in mind that wood represents an exceedingly complex structure upon which to perform chemical reactions. Compression wood on the other hand, had a clearly adverse effect on chemical modification, since the WPG value was reduced by 61.7% compared to the normal wood. Two possible explanations can be offered for this behaviour. Firstly, it is known that chemical modification takes place upon the accessible hydroxyl groups of cellulose and hemicelluloses. Since the cellulose content of compression wood is less than that of normal wood (Panshin and DeZeeuw 1980; Siau 1984), less hydroxyl groups became available for the reaction to take place and this may affect the modification procedure. Secondly, it is known that the longitudinal permeability is reduced due to the reduced lumen size in the compression wood tracheids (Stamm 1964). It is also interesting to notice the high standard deviation values, which are almost four times higher than those of normal wood. In the case of tension wood, no definite observation can be made. The WPG values were lower than those of normal wood, but this can easily be attributed to the heterogeneous structure of the wood and to the fact that the differences between tension and normal wood are much less marked that those between compression wood and normal wood (Panshin and DeZeeuw 1980). Again, it is also interesting to notice the high standard deviation values, which are almost three times higher than those of normal wood.
Table 1  Weight percent gain (WPG) of wood with defects and normal wood modified with acetic anhydride (Standard deviation in parentheses)
Tabelle 1  Massenzuwachs von normalem Holz und Holz mit Fehlern nach Acetylierung mit Acetanhydrid (Standardabweichung in Klammern)

Wood history

WPG

(%)

Pine wood with false rings

19.8

(0.9)

Normal pine wood

21.3

(0.4)

Pine wood with discontinuous rings

19.2

(1.9)

Normal pine wood

18.7

(0.6)

Compression pine wood

14.1

(2.7)

Normal pine wood

22.8

(0.7)

Tension beech wood

12.9

(2.5)

Normal beech wood

15.2

(0.9)

An obvious limitation of the present study was the low number of replicates used and the fact that samples of only one tree were taken in each case. A higher number of replicates and repeatitive reactions should be performed using samples from different trees in order to make a more specific approach. Also a wider range of defects should be considered including wood with spiral grain, wood with indented rings and wood with abnormal colour, such as the red heartwood of beech and the brown heartwood of ash.


References

Panshin AJ, DeZeeuw C (1980) Textbook of wood technology, 4th edn. McGraw-Hill, New York
 
Papadopoulos AN, Hill CAS (2003) The sorption of water vapour by anhydride modified softwood. Wood Sci Technol 37:221–231
SpringerLinkChemPort
 
Papadopoulos AN, Traboulay E (2002) Dimensional stability of OSB made from acetylated fir strands. Holz Roh- Werkstoff 60(2): 84–87
 
Papadopoulos AN, Gkaraveli A (2003) Dimensional stabilization and strength of particleboard by chemical modification with propionic anhydride. Holz Roh- Werkstoff 61(2):142–144
 
Siau JF (1984) Transport processes in wood. Springer, Berlin Heidelberg New York
 
Stamm AJ (1964) Wood and cellulose science. The Ronald Press, New York