Cation exchange capacity tests on some lignocellulosic materials highlightsome aspects of the use of copper as wood preservative

The stoichiometric validity of copper(II) salts in the assessing the cation exchange capacity of lignocellulosic materials with respect to sodium salt s is determined on some materials like Populus euramericana, Pious pinea, f lax, hemp, cotton, and some of their derivatives. Copper exhibits the usual stoichiometry (bivalence) with saponified woods a nd Norman & Jenkins holocelluloses whereas it is present as bivalent and/or apparent monovalent ions in the other materials. The major groups responsi ble 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 c ontrary, influenced by the structure of lignin. In fact, when it forms este r bonds with polyoses it causes the rising of copper apparently working as monovalent species. Lacking these bonds, lignin does not provoke any chemic al interactions except for some isolated lignins. These data show that copp er interacts mainly with polyoses, secondly with lignin if bonded to polyos es whereas cellulose seems to be weakly involved in these interactions. To improve the assumption of copper from preservative formulations mild sap onification of woods is suggested since such treatment enhances the number of sites of exchange in polyoses.