BS ISO 21436:2020 Pulps — Determination of lignin content — Acid hydrolysis method.
7 Sampling
lithe analysis is being made to evaluate a lot of a consignment of pulp, the sample shall he 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 (63) 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, bcnzenc 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 ± 3 °C to constant weight. lithe pulp shall be pre-extracted, the moisture content shall be determined on the extracted pulp.
8 Test Specimens
Weigh (5.6) a test specimen, equivalent to 300 mg to 1,0 g of oven-dried mass of pulp to the nearest 0,1 mg (see NOTE) and transfer to a 200 ml beaker. Make sure that the test specimens taken are representative of the sample received.
The mass of the test specimen is such as to provide a minimum of 20 mg of lignin in the residue remaining after acid hydrolysis, for accurate weighing. The following can be used as a guide to the amount of pulp that should be selected for analysis, based on the lignin content:
— >10 % lignin: 300 mg pulp
— 5-10 % lignin: 500 mg pulp
— <5 % lignin: 1,0 g pulp
NOTE The amount of pulp selected for analysis also depends on whether hydrolysis procedure A or
hydrolysis procedure B is used.
9 Procedure
Run the entire procedure in duplicate.
9.1 Hydrolysis
9.1.1 General
Two hydrolysis procedures are described in this Standard. In procedure AIZH9I, the primary hydrolysis is performed at 30 °C for 1 h, followed by secondary hydrolysis in an autoclave at 120 °C for 1 h. In procedure BL1DII1.II, the primary hydrolysis is performed at 15 – 20 °C for 2 h, followed by secondary hydrolysis in a water bath at 100 °C for 4 h.
NOTE Boiling under reflux is not allowed if acid-soluble lignin is to he determined in the solution (TAPPI T222, Section 9.4, NOTE 6). This is due to the possible contribution of furfural compounds to the acid- soluble lignin, if not removed in this step (Rcf.2, p. 192).BS ISO 21436 pdf download.