Properties of Soda and Organosolv Lignins from Apple Tree Pruning

Apple tree pruning were fractionated by different reagents (soda and ethanol) in order to obtain lignin. Lignin was precipitated from the ethanol and soda black liquor in two ways: pH 5 and pH 2 in soda liquor, immediately and after 24 hours in acidified water in ethanol liquor. Characterization of apple tree pruning fibres (27.44% holocellulose, 27.32% alpha-cellulose and 26.15% lignin) was done and compared with chemical composition of other agricultural residues. Lignin samples isolated from the liquid fractions were submitted to FTIR, GPC and TGA in order to study their physicochemical properties. Antioxidant capacity and total polyphenolic content were determined and related to the physicochemical properties (depending on extraction and precipitation process) of the lignins. Alkaline lignins resulted more thermally stables and organosolv presented low molecular weight with low polydispersity more appropriate as antioxidant additive.