The Dimensional Stabilisation of Maritime Pine Sapwood (Pinus pinaster) by Chemical Reaction with Organosilicon Compounds

The dimensional stabilisation imparted to Maritime pine sapwood by chemical modification with hydrophobic organosilicon compounds was investigated. Modification was performed via esterification, using different chemically synthesised models bearing trimethylsilyl groups: 3-trimethylsilylpropanoic anhydride (I), 2-trimethylsilylmethylglutaric anhydride (II) and trimethylsilylethenone (III). Grafting was confirmed by infrared spectroscopy as well as 13C and 29Si NMR CP MAS analysis and was located into the wood cell walls. The dimensional stabilisation induced by I and II appeared to be stable during three oven-dry/water-soak cycles and, for a given number of hydroxyl blocked, to be superior to that imparted by acetylation. The graft from III, however, was found to hydrolyse progressively into an acetyl group via a metallotropic rearrangement. Further investigation on the hygroscopicity and swelling behaviour of modified wood from I and II indicated that dimensional stabilisation was attributable to a bulking effect rather than a change in substrate hygroscopicity. The bulky grafts from I and II were, in particular, thought to locally over-swell the wood cell wall, revealing regions with new water-accessible hydroxyl groups.