Rapid semi-quantitative determination of aspen lignin in lignocellulosic products

In the present study different methods for the determination of aspen lignin were investigated. In experiments, dried samples of extractive-free aspen wood and grinded bleached-chemo-thermo-mechanical-pulp (BCTMP) of aspen were used. For isolating lignin from aspen wood and BCTMP, Klason method was used. For the quantification of lignin content, a series of aspen wood powder/microcrystalline cellulose binder were mixed and analysed with FTIR-ATR and UV-VIS. To compare with colour reactions, an average content 21% of lignin was assigned to experimental content in 100% aspen wood powder. FTIR-ATR absorbance maximum between 1234-1237 cm(-1) and UV-VIS pseudo-absorbance of measured samples maximum at 280 nm were taken as measurement points for the calibration of lignin content. Nearly linear dependence was established with both methods. Weisner and Maule colour tests were used for staining to detect lignin in samples. Suspensions, containing samples with staining solution, were prepared and photographed. Best positive Weisner reaction with violet colour, both with aspen wood and BCTMP samples, were established with the 1 : 1 phloroglucinol/HCl staining solution. Carefully mixed suspension of 0.1 g samples and 5 min reaction time were applied. In Maule reaction, intensive red colour appeared to samples after 10 min treatment with 1% KMnO4. Samples were washed with distilled water and treated with 3% aqueous HCl until the colour changed from black to beige/yellow. Then samples were treated with concentrated NH3 center dot H2O for 2 min to achieve the most intensive colour. A simple semiquantitative method for detection of lignin in BCTMP was worked out.