Aqualon | Construction | brochure | Methods of analysis for Natrosol

Methods of analysis for NATROSOL®

There are frequent occasions when, in addition to chemical analysis, an accurate determination of the viscosity of a NATROSOL® solution is needed. The apparent viscosity of a NATROSOL solution depends on a number of factors, and if reproducible results are to be obtained, a closely standardized method of solution preparation and viscosity determination must be followed. The preparation of the solution is critical, in that the NATROSOL must be completely dissolved in order to obtain a significant measurement. When weighing out the proper amount of NATROSOL for a viscosity determination, care must be taken to include a moisture correction. This correction compensates for the moisture in NATROSOL and places the viscosity measurement on a dry NATROSOL basis. The viscosity measurement test must be rigidly standardized because the viscosity reading obtained is dependent upon rate of shear, temperature, amount of agitation prior to measurement, and elapsed time between agitation and measurement. The method used in the Aqualon laboratories is therefore given here in detail.

Solution preparation on undried basis
Moisture correction

Weigh duplicate samples of 5 g to the nearest 0,001 g into previously dried and weighed moisture cans with covers (G1).
Place the samples in a gravity convection oven maintained at 105 ± 0,5°C and heat for 3 hours. Cool in a desiccator and weigh.
Return the sample to the oven for 45 minutes; cool and weigh as before. If the second dried weight is not within 0,005 g of the first dried weight, repeat the 45-minute oven periods until two subsequent weighings are in agreement. Then, using the lowest dried weight obtained (G2), calculate % moisture as follows:

G1 - G2
–––––––– x 100 = % moisture
G2

Solution preparation
Immediately after taking portions of the sample of NATROSOL for moisture determination, portions of the same undried NATROSOL should be taken for the viscosity solution preparation.

The moisture sample and solution sample weighings should be carried out practically together to ensure that the moisture content of the respective portions is the same at the time of weighings.

The standardized Aqualon method for determining viscosity of NATROSOL solutions specifies use of the Brookfield viscometer, type LVF. The solution volumes specified should not be less or there may not be sufficient solution to cover the appropriate Brookfield spindle.

Weigh the specified amounts to the nearest 0,005 g quickly into clean, ground-glass-stoppered weighing bottles, stoppering immediately to eliminate gain or loss of moisture content.
Carefully transfer the bulk of the sample of NATROSOL into a 350 ml screw-cap bottle by dumping sample avoiding any loss of dust in this transfer. Cover the mouth of the 350 ml bottle with cellophane, screw the cap on securely, and set aside until moisture is determined.
Reweigh the weighing bottle and stopper, and record this weight. Subtract this weight from the weight in step 4. This is the total weight of undried NATROSOL used for the viscosity solution (G3).
From the determined % moisture, calculate the water to be added for the respective viscosity solutions as follows:

For 1% viscosity solution

G3 x (99-% moisture) = Weight of water
For 2% viscosity solution

(98 - % moisture)
G3 x –––––––––––––––– = Weight of water
2
For 5% viscosity solution

(95 - % moisture)
G3 x –––––––––––––––– = Weight of water
5

Approximate weights for solutions
NATROSOL type	Sample weight, g	Solution concentration, %
L G, M MH, H, H4, HH	13,0 5,2 2,3	5 2 1

Add the calculated amount of distilled water to the respective 350 ml bottles containing the samples of NATROSOL.
Stir the contents with mechanical agitator to complete solution, being careful to avoid loss of solution. An anchor-shaped stirrer has been found to be satisfactory. After solution appears complete, stir 10 to 15 minutes at high speed.
When solution is complete, cover mouth of bottle with cellophane, screw cap on securely, and place in constant-temperature bath (25 ± 0,2°C) for 30 minutes, or for as long as necessary to adjust the solution temperature to 25 ± 0,5°C.

Viscosity procedure

While the solution is in the constant-temperature bath, select from Table 1 the Brookfield spindle-speed combination corresponding to the viscosity type of NATROSOL being tested. Attach the selected spindle to the instrument, which is then set for the corresponding speed. Determine viscosity of the NATROSOL solution between 30 and 60 minutes after removal from stirrer. If solution stands longer than 60 minutes, return it to stirrer for 10 minutes, place in bath for 30 minutes, and then determine viscosity.
Remove the bottle from the constant-temperature bath and shake it manually for 10 seconds avoiding entrance of air bubbles.
Immediately insert the appropriate Brookfield viscometer spindle into the solution, start the spindle rotating, and allow the spindle to rotate 3 minutes before taking the reading.
Stop the instrument, read the dial, and multiply the dial reading by the factor shown in column 4 of the table corresponding to the speed and spindle used. The result is the viscosity of the solution in mPa•s.

Table 1 Brookfield spindle speeds for viscosity determinations*
NATROSOL type	Spindle no.	Spindle speed, rpm	Factor	Maximum reading, mPa•s
L G M MH H or H4 HH High concentration of the above types	1 2 4 3 3 4 4 4	30 60 60 30 30 30 12 6	2 5 100 40 40 200 500 1 000	200 500 10 000 4 000 4 000 20 000 50 000 100 000
* The viscometer specified is the Brookfield Synchro-Letric Model LVF, 4 speeds, 4 spindles, covering the range 0 to 100 000 mPa•s, Brookfield Engineering Laboratories, Stoughton, Massachusetts. A no. 5 spindle is also available for this model, increasing the viscosity range from 0 to 200 000 mPa•s. Reference: Standard Methods of Testing Hydroxyethylcellulose, ASTM 2364 Ash content The sample is charred over a low Bunsen flame to remove the bulk of the volatile matter, cooled, moistened with sulfuric acid, the excess of acid evaporated, and the ashing completed in the normal way. The sulphate ash is calculated to percentage. Procedure Weigh a 2 to 3 g sample to the nearest 0,001 g into a previously ignited and tared platinum or porcelain dish of about 75 ml capacity. Ignite over a low Bunsen flame and allow to burn, with only occasional application of heat, until most of the carbonaceous material has burned off. Cool and moisten the entire residue with 1: 1 sulfuric acid. Evaporate the excess acid over a low Bunsen flame slowly so as to avoid spattering, and complete the ignition by placing in a muffle at 800 to 850°C for 30 minutes or until the ash is free of carbon. Cool, desiccate, and weigh. Calculation Grams of residue x 100 ––––––––––––––––––– = % ash as Na2 SO4 Grams of sample Duplicate results should agree within 0,05%. Back

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