The chemical modification of Scots pine with succinic anhydride or octenyl succinic anhydride. I. Dimensional stabilisation

The effect of chemical modification on the dimensional stability of Scots pine (Pinus sylvestris) sapwood using succinic anhydride (SA), or 2-octen-l-yl succinic anhydride (OSA) has been studied. Calculation of the theoretical volume increase due to modification, based on the density of the reagents was found to yield theoretical volume increases less than those measured, indicating that there are contributions to the volume increase from the space occupied by the reagent and a free-space or void volume. The ratio of void volume to reagent volume increased at low weight percent gains (wpg), however above 20 % wpg OSA treated wood exhibited a linear relationship between void and reagent volume, whilst with SA treated wood the ratio decreased continuously as wpg increased. Cyclic water-soak/oven-dry tests showed that with OSA treated wood, the volumetric swelling coefficient (S %) in cycle one was larger than that of unmodified wood, but less in subsequent cycles. This behaviour is attributed to a rearrangement of the eight carbon side chain of the OSA within the cell wall during the first soak cycle when the wood is in the swollen stale. In the case of SA treated wood, the S % value is lower in cycle one, compared with subsequent cycles, but always less than unmodified wood. This change between cycles one and two may be due to loss of non-bonded but swelling reagent from the cell wall in the first water soak. Evidence from weight loss data suggests that the ester bond in SA treated wood is unstable to hydrolysis, but that in OSA treated wood the ester bond is protected by the alkenyl chain. Both SA and OSA treated wood is less stable dimensionally than linear anhydride modified wood when plotted on a wpg basis, but when the same data is plotted in terms of the number of OH groups substituted, OSA is found to have superior properties when compared with linear chain anhydrides.