The effects of transition metal sulfates on cellulose crystallinity during accelerated ageing of silver fir wood

Abstract

During the hydrolytic degradation of cellulose caused by acidic transition metal sulphates, new low molecular products such as monosaccharides and their degradation products are usually formed which can increase the cellulose sensitivity to oxidation. This work was aimed at elucidation of the chemical and structural changes of cellulose in silver fir (Abies alba Mill.) wood treated with iron, copper and zinc salts to achieve a detailed understanding of cellulose deterioration during accelerated ageing. Cellulose samples were isolated from the wood by the Kurschner-Hoffer method and the Seifert method. Changes in cellulose structure were evaluated by wide-angle X-ray scattering (WAXS) measurements, Fourier transform infrared spectroscopy (FTIR), and high performance liquid chromatography. The presence of metal cations (Cu2+, Zn2+, Fe3+) caused a significant loss in the content of cellulose for treated and aged wood samples. Wet-thermal accelerated ageing led to a decrease (~ 20%) in the content of monosaccharides. The Seifert cellulose samples had a higher crystallinity than the Kurschner-Hoffer samples. A strong correlation was found between crystallinity indices obtained from the FTIR and WAXS measurements. Two cluster groups of cellulose samples, segregated from each other, were identified within each cellulose type in a multivariate cellulose trait analysis.