Effect of lignin and hemicelluloses on the tensile strength of micro-veneers determined at finite span and zero span

Scots pine micro-veneers were subjected to hydrolysis with sulphuric acid or delignification with acidic sodium chlorite and a combination of both treatments. The tensile strength of untreated and treated veneers was determined at finite span (f-strength) and zero span (z-strength) under both dry (20 degrees C, 65% relative humidity) and water-saturated conditions. Acidic hydrolysis resulted in significant strength losses in both testing modes and both moisture conditions, with the greatest strength reduction found for f-strength tested dry. After delignification, only f-strength under wet conditions was substantially reduced; dry f-strength and both dry and wet z-strength hardly changed. A combined treatment of prehydrolysis and delignification resulted in disintegration of the veneers, which made strength determination impossible. It was concluded that, in addition to cellulose, the hemicelluloses determine the f-strength under dry conditions, while lignin confers wet strength but appears not to contribute to interfibre adhesion and f-strength under dry conditions.