BS ISO 21436:2020 pdf free.Pulps一Determination of lignin content一Acid hydrolysis method.
BS ISO 21436 If the analysis is being made to evaluate a lot of a consignment of pulp, the sample shall be taken in accordance with ISO 7213. If the analysis is made on another type of sample, report the origin of the sample, and if possible the sampling procedure.Obtain a representative sample of pulp equivalent to about 10 g moisture-free pulp. Air dry the pulp
and disintegrate in a household blender, or grind in a Wiley mill to pass a No. 20 (0,85 mm) screen.Groundwood and high yield pulps containing a significant amount of resins shall be extracted with acetone (6.3) according to ISO 14453 before testing.NOTE Resins, if not extracted from the pulp prior to analysis, would remain insoluble in acid and be weighed as lignin.
NOTE Acetone is considered an effective solvent for extracting resin from pulp. Dichloromethane and ethanol/ benzene (1:2), as specified in other methods, are not recommended due to health hazards. In particular, benzene is a confirmed carcinogen.Determine the moisture content of the pulp according to ISO 638 by drying a 2-3 g specimen in an oven at 105土3 °C to constant weight. If the pulp shall be pre-extracted, the moisture content shall be determined on the extracted pulp.Measure the absorbance of the filtrate at 205 nm in the 1,0 cm pathlength cuvette of the spectrophotometer (5.2). Use 4 % sulfuric acid (hydrolysis procedure A] or 3 % sulfuric acid (hydrolysis procedure B), as a blank. If necessary, dilute the filtrate with 4 % sulfuric acid (hydrolysis procedure A) or 3 % sulfuric acid (hydrolysis procedure B), such that its absorbance is in the range of 0,2-0,7 AU.NOTE Degradation products from carbohydrates can contribute to the measured acid-soluble lignin[6]. However, this contribution is generally small and can be neglected.NOTE In the round robin study (Annex A), labs using the autoclave (hydrolysis procedure A) reported levels of acid-soluble lignin that were on average 0,2 % higher than those obtained when using the water bath (hydrolysis procedure B]. This could indicate that furfural compounds are not completely removed when using the autoclave, due to the fact that the beaker is covered with aluminium foil during the secondary hydrolysis.
However, since these differences are relatively small, they are unlikely to have a significant impact on the total lignin results.BS ISO 21436 pdf download.