Carbon isotope behaviour in wood and cellulose during artificial aging

Modern wood was subjected to an artificial decay process to investigate its behaviour with respect to the stable carbon isotope composition of wood and the corresponding cellulose. Four different woods were used, namely: oak (Quercus robur), beech (Fagus sylvatica), pine (Pinus sylvestris), sequoia (Sequoiadendron giganteum) and pure spruce cellulose. The process of decay was simulated by heating samples in water at 180 degrees C from minutes to months. During the decay period, the carbon content of wood increased to almost 70% while the cellulose content decreased gradually to zero. The degradation proceeds according to a two stage process: an initial Very fast break down is followed by a rather slow degradation. After a strong discrimination against (13)C during the initial phase, the (13)C/(12)C ratio increases again, mostly up to its initial value. The carbon isotope trend for cellulose shows a similar pattern though it is less pronounced. Maximum discrimination was 1 parts per thousand relative to the untreated wood. delta(13)C values of cellulose decreased by up to 0.3 parts per thousand. The (13)C depletion is presumably a consequence of the preferential decomposition of cellulose as compared to lignin. Data on fossil trees are compared with the results obtained from this treatment of aging. The (13)C decrease is in line with observations from these fossil woods, but the ensuing (13)C enrichment is at most weakly to be seen. (C) 1999 Elsevier Science B.V. All rights reserved.