ISO 307 Plastics - Polyamides - Determination of Viscosity Number

The standard "ISO 307 Plastics - Polyamides - Determination of viscosity number" published by the International Organization for Standardization (ISO) describes a method for the determination of the viscosity number of dilute solutions of polyamides in specified solvents. The method is applicable to the polyamides designated PA 16396, PA 1, PA 1, PA 46, PA 6, PA 66, PA 69, PA 610, PA 612T/11, PA 12I/6T, PA 66T/6I/6, PA 6T/6I, PA 66I/6T/6 and PA MXD6 as defined in the standard "ISO 6-66 Plastics - Polyamide (PA) molding and extrusion materials - Part 6: Designation system and basis of specifications" and to copolyamides, polyamide compounds and other polyamides dissolved in one of the specified solvents under the specified conditions.

This method does not apply to polyamides produced by anionic polymerization of lactams or produced with crosslinking agents. Such polyamides are normally insoluble in the solvents specified. The viscosity number is determined according to the general procedure specified in ISO 1628-1 Plastics - Determination of the viscosity of polymers in dilute solution using capillary viscometers - Part 1: General principles", taking into account the special conditions specified in this document.

For the purposes of this standard, the viscosity number, polymer value, and terms given in ISO 1628-1 are calculated by the formula given in the standard for flow times long enough to avoid the need for kinetic energy correction. The formula is valid for suspended level Ubbelohde type viscometers that comply with the requirements of ISO 3105. An Ubbelohde type viscometer or suspended level viscometer is a measuring instrument that uses a capillary-based method for measuring viscosity. For a particular viscometer used, and when the densities of the solvent and solution are essentially equal, the viscosity ratio is given by the ratio of the solution concentration to the flow time. As specified in ISO 3105, a correction for kinetic correction should be applied for flow times below 1 seconds and 2 seconds for type 200 and type 60 Ubbelohde viscometers, respectively. The flow time of a liquid is related to its viscosity by the formula given in the standard.

In principle, the flow times of a solution of a solvent and a polyamide with a concentration of 0,005 g/ml in the solvent are measured at a temperature of 25 degrees, using the same viscometer for both measurements. The viscosity number is calculated from these measurements and the known concentration of the solution.

Only reagents of recognized analytical quality and only distilled water or water of equivalent purity should be used in the tests.

Major equipment used in testing includes:

Vacuum drying cabinet with pressure less than 100 kPa.
Scales accurate to 0,1 mg.
Volumetric flask with a capacity of 50 ml or 100 ml, compliant with the requirements of ISO 1042 standard, equipped with a ground glass stopper.
100 ml weighing bottle (fitted with ground glass stopper).
0,2 ml pipette (can be read down to 0,01 ml).
Shaker or magnetic stirrer.
Sintered glass filter with a pore size of 40 μm to 100 μm (class P 100) or a stainless steel sieve with an opening of approximately 0,075 mm2.
Suspended level Ubbelohde type viscometer conforming to the requirements of ISO 3105. The basic dimensions of the viscometer are shown in the figure given in the standard. For use with formic acid solution, the internal diameter of the capillary shall be 0,58 mm plus/minus 2 percent. For use with sulfuric acid solution or m-cresol, the internal diameter of the capillary shall be 1,03 mm plus/minus 2 percent. Other types of viscometers listed in ISO 3105 may be used provided that they are shown to be equivalent to the results of the Ubbelohde viscometers specified above. In cases of disagreement, the recommended viscometer shall be used. ISO 1628-1 shall be followed in the selection of other types of viscometers. This standard recommends Ubbelohde viscometers according to ISO 3105.
The thermometer, which is a liquid-glass, total immersion thermometer, reads to within 0,05 degrees in the range to be used and is in a known state of calibration. Other thermometric devices of at least equal accuracy may be used.
Thermostatic bath that can be kept and controlled at 25,00 degrees plus/minus 0,05 degrees.
A time device with an accuracy of up to 0,1 seconds, such as a stopwatch.
Centrifugal.

When preparing test samples, polyamide test samples for determination of viscosity number must be soluble in the specified solvents, excluding any additives present such as reinforcements or fillers. The sample must contain less than 0,28 percent moisture. If it contains more than 0,28 percent moisture, the sample must be dried. Generally, drying for 70 to 4 hours at 6 degrees in a vacuum is sufficient. The dissolution time of some samples may be too long for adequate production control. In these cases, the material may be ground to shorten the dissolution time, provided that the results are shown to be equivalent.

For samples containing less than 98 percent polyamide by mass, i.e., for samples containing more than 2 percent additive, the amount of additive must either be determined by a specially developed method or taken from the recipe. The determination method must be stated in the report.

The water content of the sample should be determined according to the ISO 15512 standard, and the ash content should be determined according to the ISO 3451-4 standard.

The correct amount of polyamide sample to be weighed is calculated using the formula given in the standard.

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