The Dimensional Stabilisation of Corsican Pine Sapwood by Reaction with Carboxylic Acid Anhydrides. The Effect of Chain Length

Abstract

The dimensional stabilisation imparted to Corsican pine sapwood by chemical modification with carboxylic acid anhydrides of varying chain length was investigated. Dimensional stabilisation was determined by the water soak/oven dry method through a total of ten cycles in order to determine the stability of the ester bond to hydrolysis at neutral pH. These tests indicated that the dimensional stabilisation was attributable solely to a bulking effect. The loss of material due to hydrolysis was minimal, with modified wood blocks exhibiting lower weight loss following water soaking than unmodified blocks. Considerable variation in dimensional stabilisation (as determined by volumetric swelling coefficient and anti-shrink efficiency) was found throughout the water soak tests. A contribution to this variability was found to be due to changes in the water saturated volume caused by variations in the ambient air temperature, h was found that weight percent gain provided an excellent measure of dimensional stabilisation irrespective of the chain length of the anhydride involved. Increases in volume due to modification were found to be larger than theoretically expected. IntroductionVarious chemical modifications have been investigated for improving the dimensional stability, and decay resistance of wood (Rowell 1983;Kumar 1994). Of all the methods investigated, modification using acetic anhydride has received by far the most attention, and will in all likelihood form the basis for a commercial process in the near future (Sheen 1992). However, in spite of intensive investigations into acetylation, there is little evidence in the literature of the effect of higher homologues upon the dimensional stabilisation of wood. Despite an exhaustive search of the literature, we are aware of only two publications dealing with higher homologues (Rugevista and Embreksha 1988;Goldstein et al. 1961). There has been no comprehensive study of the effect of chain length of a single modifying agent upon the dimensional stabilisation of wood although Goldstein et al. did study the effect of chain length upon reaction rate. The effect of carbon chain length of a series of linear chain anhydrides upon dimensional stabilisation of wood samples has been investigated and the results are presented in this paper. Since variation in chain length would affect hydrophobicity of the substrate, it is possible to determine whether dimensional stabilisation arises purely from a bulking effect or is in part due to denial of access

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