BS ISO 21436:2020 pdf download – Pulps — Determination of lignin content — Acid hydrolysis method

BS ISO 21436:2020 pdf download – Pulps — Determination of lignin content — Acid hydrolysis method 9.1.2 Hydrolysis procedure A Hydrolysis procedure A is based on the use of 300 mg of pulp. This procedure is more commonly used in laboratories equipped with an autoclave, and is similar to that described in other methods [7]-[9] in situations in which analysis of carbohydrates is required, in addition to analysis of lignin. For larger pulp specimens, the acid concentrations for both primary and secondary hydrolysis must remain the same as those used for 300 mg of pulp; thus the volume of solutions must be adjusted accordingly. Add 3,0 ml of 72 % sulfuric acid (6.2) to the test specimen in the beaker. Add the acid gradually in small increments while stirring and macerating the material with a glass rod. To avoid losses, ensure that no material is sticking to the glass rod when it is removed. NOTE Some pulps do not absorb the acid and therefore do not disperse readily. In such cases, after addition of acid, place the beaker under vacuum, in a vacuum desiccator for at least 15 minutes to facilitate wetting and absorption. Place the beaker in a water bath adjusted to 30 ± 1,0 °C for 1 h. Stir occasionally. Add 84,0 ml of water. Mix, cover the beaker with aluminium foil and place it in an autoclave at (120 ± 3) °C for 1 h. Allow the insoluble lignin to settle and for the beaker and contents to cool to approximately 80 °C. NOTE In some cases, the lignin requires an overnight or a longer period to settle, especially if it is finely dispersed. 9.1.3 Hydrolysis procedure B Hydrolysis procedure B is based on the use of 1,0 g of pulp, and is similar to that described in other methods [10][11] . This procedure is also used in some laboratories. NOTE Hydrolysis procedure B is not used when carbohydrate analysis is also required. For smaller pulp specimens, the acid concentrations for both primary and secondary hydrolysis must remain the same as those used for 1,0 g of pulp; thus the solution volumes shall be adjusted accordingly. Place the beaker with the test specimen in a water bath (5.2) at 20 ± 1 °C and add gradually 20,0 ml of 72 % sulfuric acid (6.2), maintaining a reaction temperature of 20 ± 1 °C Stir thoroughly with a...