Oxidation of Wood Components During Chromated Copper Arsenate (CCA-C) Fixation

Abstract

Pre-extracted radial sections of southern yellow pine sapwood were treated with CCA-C and analyzed by x-ray photoelectron spectroscopy (xps). The ratio of CI (carbon bonded only to carbon and/or hydrogen) to C2 (carbon bonded to one oxygen with a single bond) was used to determine the progress of oxidation of wood components during CCA fixation. This ratio increased after treating times of 10 minutes and 60 minutes and decreased after 180 minutes soaking suggesting that oxidation of C2 predominates on initial contact with CCA solution but oxidation of CI (lignin) becomes more important with extended exposure to the treating solution. Oxidation of C2 to C3 (carbon bonded to two oxygens or a carbonyl group) was demonstrated by in situ trapping of C3 with ethylene glycol as it was formed. Further oxidation of C3 to C4 (carboxylic carbon) was not observed in the xps spectra, consistent with the findings of others. The hypothesis that rapid decarboxylation results in loss of C4 as evolved CO₂ is supported by the observation that the C4 component of untreated wood was reduced by more than 90% after 10 minutes of CCA soaking followed by high temperature fixation and by the observation of CO₂ evolution during early stages of accelerated fixation. The Cr(2p) spectra of Cr^VI and Cr^III were established at 580.2 and 577.8 eV respectively. Accelerated fixation of CCA-C treated specimens resulted in a very high degree of reduction of Cr^VI to Cr^III. XPS Cu (2p3/2) peaks were established at 935.1 for CCA-C, 935.3 for Cu(OH)₂, and 933.7 for CuO. Cu (2p3/2) peaks in CCA-treated wood were shown at 932.9 with no satellite peaks for the 10-60 minutes soaking in CCA series, and at 933.9 and 936.4 with satellite at 941-948 for the 3 hours soaking time. The latter are attributed to complexed copper oxide and hydroxide forms of Cu^II. Peaks attributed to Cu^II hydroxides were shown to diminish in leached samples.