Cation Exchange Capacity Tests on Some Lignocellulosic Materials Highlight Some Aspects of the Use of Copper as Wood Preservative

Abstract

Summary The stoichiometric validity of copper(II) salts in the assessing the cation exchange capacity of lignocellulosic materials with respect to sodium salts is determined on some materials like Populus euramericana, Pinus pinea, flax, hemp, cotton, and some of their derivatives. Copper exhibits the usual stoichiometry (bivalence) with saponified woods and Norman & Jenkins holocelluloses whereas it is present as bivalent and/or apparent monovalent ions in the other materials. The major groups responsible for cation exchange are the carboxyls of polyoses while hydroxyls seem inert at this reaction. Cation exchange of wood and raw fibers is, on the contrary, influenced by the structure of lignin. In fact, when it forms ester bonds with polyoses it causes the rising of copper apparently working as monovalent species. Lacking these bonds, lignin does not provoke any chemical interactions except for some isolated lignins. These data show that copper interacts mainly with polyoses, secondly with lignin if bonded to polyoses whereas cellulose seems to be weakly involved in these interactions. To improve the assumption of copper from preservative formulations mild saponification of woods is suggested since such treatment enhances the number of sites of exchange in polyoses.