GB/T 7979-2020Pulp—Determination of dichloromethane soluble matter (English PDF)

1 Scope

This Standard specifies the method for determining the content of dichloromethane extracts in pulp.

This Standard is applicable to all kinds of pulps except waste pulp. When the sampling volume is 10g, the limit of detection for this method is 0.05%.

2 Normative References

The following documents are essential to the application of this document. For the dated documents, only the versions with the dates indicated are applicable to this document; for the undated documents, only the latest version (including all the amendments) is applicable to this document.

GB/T 462 Paper, Board and Pulp - Determination of Moisture in the Analysis Specimen

GB/T 740 Pulps - Sampling for Testing

3 Principle

In the Soxhlet extractor, the pulp sample is extracted by dichloromethane. After at least 24 cycles of extraction, the solvent is evaporated, and the extraction residue is dried at (105±2) °C, and then weighed. The ratio of the mass of the dichloromethane extract to the absolute dry mass of the sample is the dichloromethane extract content in the sample. and the bulk pulp sample shall be torn into fragmented specimens. Place the sample in a wide-mouth bottle with a ground mouth; cap the bottle; and equilibrate it in the bottle for 24h for later use.

7 Test Procedures

7.1 Use a balance (5.4) to weigh about 10g (or 5g, accurate to 0.0001g) specimen for parallel determination. If it is a bulk pulp specimen, wrap the specimen tightly by filter paper extracted by dichloromethane in advance; and tie it by cotton thread extracted by dichloromethane in advance. At the same time, determine the water content according to the provisions of GB/T 462.

7.2 Firstly, put a small group of absorbent cotton that has been pre-extracted by dichloromethane at the outlet of the Soxhlet extractor (5.1); and then put the specimen into the Soxhlet extractor; and connect the flat-bottomed flask that has been dried in the electric heating blast drying oven (5.5), and has been cooled to the constant weight to the extractor; and then add dichloromethane equivalent to 1.5 times the volume of the Soxhlet extractor to the flat-bottomed flask; connect to the condenser; and turn on the cooling circulating water bath (5.3) and start the extraction.

7.3 Adjust the temperature of the constant temperature water bath (5.2) and control the extraction cycle of dichloromethane for 8 times per hour. When the sampling volume is 5g, use a 150mL flat-bottomed flask to extract for at least 6h, so that the total number of extractions is at least 48. When the sampling volume is 10g, use a 250mL flat-bottomed flask to extract at least 3h, so that the total number of extractions is at least 24. If the return flowrate is too slow, the extraction time shall be extended appropriately. After the extraction, the extracting solution shall be clear and free of fibers.

7.4 After the end of extraction, lift the condenser; use a clean glass rod or medicine spoon to take out the specimen; then reconnect the condenser to the extractor; and recover a part of the solvent until there is only a small amount of dichloromethane at the bottom of the bottle. Then the flat-bottomed flask is placed on a water bath to evaporate the solvent to dryness. Put the flat-bottomed flask into an electric heating blast drying box for drying. The drying time shall not exceed 16h. After cooling in a desiccator for 45min, weigh it and repeat the drying until the weight is constant.

8 Calculation of Results

The extract content of the dichloromethane shall be calculated as per Formula (1); and the results shall be expressed by a percentage. […]