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SCAN-P 48:83
pH value of an aqueous suspension
slurry form, the pH value is determined after dilution to a concentration of 100 g per kilogram of suspension. This SCAN-test Method specifies a method for determining the pH value of an aqueous suspension of a filler or pigment used in the production of paper. The Reagents
Method is applicable to all kinds of fillers and pigments, Distilled or deionised water, freshly boiled and The sampling procedure is not covered by this Buffer solutions, of known pH values close to 4 Reference
Note − Suitable buffer solutions are commercially Fillers and pigments − Dry matter content available. They can also be prepared in the laboratory as follows: Definition
Buffer solution, pH 4,01: In a 1000 ml volumetric For the purpose of this Method, the following definition to the mark. There is normally no need to dry the The pH − the value determined on the slurry salt. The solution is stable for 2 months. when the dry filler or pigment is dispersed at about Buffer solution, pH 9,18: In a 1000 ml volumetric flask, dissolve 3,80 Principle
decahydrate (borax), Na2B4O7 ⋅ 10 H2O, in distilled water from which carbon dioxide has been expelled A slurry of 10 g of pigment in 90 ml of water is by boiling. Dilute to the mark. The solution is prepared. The pH of the slurry is measured at room stable for 6 weeks. The solution will absorb carbon temperature. For fillers or pigments delivered in the dioxide when in contact with ambient air. Therefore, keep the solution in a stoppered bottle SCAN-P 48:83
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and do not leave the bottle open more than is Note − The solid particles in the suspension affect the performance of the glass electrode and may cause large errors. Therefore stirring of the suspension should be stopped in good time before Apparatus
the measurement. The 30 min period stated above pH measuring device, consisting of a glass electrode, a reference electrode and a suitable potentiometer, calibrated against buffer solutions of Express the pH to the nearest 0,1 unit as the mean of the duplicate determinations. The individual results should not differ by more than 0,2 units; if they do, repeat the determination on two additional suspensions. Preparation of sample
The test report should include reference to this Keep samples in water-vapour-tight vessels, such as glass or plastic jars with a tightly fitting lid. Determine the dry matter content in accordance with SCAN-P 39. Before taking a portion for analysis, make sure that (b) identification of the material tested; (c) the result; (d) any departure from the procedure described in this SCAN-test Method or any other circumstances that Procedure
Carry out the procedure in duplicate. Weigh a portion of the sample containing (10,0 ± 0,5) g of dry filler or Additional information
pigment into a 250 ml beaker. Add 90 ml of distilled water (5.1) and a magnetic rod. Many pigments contain small amounts of water-soluble If the sample is a slurry, weigh a sample of about salts. Suspensions made from such pigments have a low 20 g and calculate the volume of water required to obtain buffer capacity and their pH value is therefore poorly a slurry containing (10,0 ± 0,5) g of solid material per defined. This may lead to poor reproducibility since the 90 ml of water. Prepare the dilute slurry in a beaker. measured pH value can depend on the time allowed for Place the beaker on the stirring device (6.1) and start stirring and settling. If the time allotted is shorter than the stirrer. Adjust it to produce a vortex and let it run for here specified, for example in routine control, the 30 min. Stop the stirring and allow the suspension to Calibrate the pH meter (6.2) with the two buffer solutions (5.2). Rinse the electrodes several times with pure water. Immerse the electrodes in the supernatant liquid above the filler or pigment and measure the pH value after 2 min. SCAN-test Methods are issued and recommended by
KCL, PFI and STFI-Packforsk for the pulp, paper and
board industries in Finland, Norway and Sweden.
Distribution: Secretariat, Scandinavian Pulp, Paper
and Board Testing Committee, Box 5604,
SE-114 86 Stockholm, Sweden.

Source: http://www.pfi.no/Documents/Scan_test_methods/P/P_48-83.pdf