BS ISO 1409:2020 pdf download – Plastics/rubber — Polymer dispersions and rubber latices (natural and synthetic) — Determination of surface tension
8.1 Method A
8.1.1 Preparation of apparatus Clean the dish or vessel (6.3) carefully, since any contamination may lead to variable results. Clean the ring of the tensiometer (6.1) by washing in water (5.1) and then heating in the oxidizing section of a Bunsen or ethanol flame (6.5). Take extreme care to avoid touching or distorting the tensiometer ring when handling it. Ensure that the ring remains parallel to the surface of the liquid during the determination. Failure to observe these precautions will lead to inaccurate results.
8.1.2 Calibration Carefully calibrate the tensiometer scale against a standard mass or a reference liquid such as distilled water (5.1) or toluene (5.2) in accordance with the manufacturer’s instructions, so that the scale reads in mN/m. Calibration is generally carried out against a standard mass. It should be noted that the calculation of the results (see Clause 9) requires different correction factors depending on the method of calibration.
8.1.3 Preparation of the test sample
184.108.40.206 If the total solids content of the test sample of latex or polymer dispersion is not known, determine it in accordance with ISO 124. If the mass fraction of total solids is greater than 40 %, dilute the test sample to a mass fraction of total solids of 40 % ± 1 % with water (5.1). If it is suspected that the viscosity of the diluted test sample is still greater than 200 mPa·s, determine it by the appropriate method given in ISO 1652, ISO 2555 or ISO 3219. If necessary, dilute the test sample further until the viscosity is less than 200 mPa·s, noting the final total solids content.
NOTE Dilution to a mass fraction of 40 % has a negligible effect on the surface tension of polymer dispersions and rubber latices. In some cases, the surface tension at a higher total solids content can be required, in which case this can be measured by the method as specified with little loss of accuracy, provided that the viscosity is less than 200 mPa⋅s. If the density of the diluted test sample of latex or polymer dispersion is not known, determine it in accordance with ISO 705.
220.127.116.11 Using the thermostatic bath (6.4), adjust the temperature of the diluted test sample to 23 °C ± 1 °C (or 27 °C ± 1 °C in tropical countries).
18.104.22.168 Take approximately 25 cm 3 of the diluted test sample, using a pipette with its tip well below the surface of the liquid, and transfer it to the dish or vessel (6.3). Remove any air bubbles from the surface of the sample by wiping with a piece of hard filter paper. Measure the surface tension immediately to avoid errors due to the formation of surface skin.
8.1.4 Determination With the tensiometer protected from air currents, place the dish or vessel containing the diluted test sample on the adjustable platform of the instrument beneath the ring of the tensiometer. Adjust the instrument, following the manufacturer’s guidelines, so that the beam is in the balance position when the ring is dry and the scale reading is zero. Raise the platform until the liquid makes contact with the ring and then immerse the ring to a depth of approximately 5 mm. Slowly lower the platform by means of the platform-adjusting screw, and simultaneously increase the torsion in the wire, proportioning these two adjustments so that the beam remains exactly in its balance position. As the film adhering to the ring approaches its breaking point, proceed very slowly with adjustments. For determinations with an automatic tensiometer, regulate the penetration depth of the ring to approximately 5 mm below the surface of the liquid and adjust the rate of movement of the dish or vessel to 10 mm/min. Record the maximum scale reading just prior to the point at which the ring separates from the dispersion or latex (this is of particular importance with undiluted latices or polymer dispersions of high viscosity). Immediately raise the dish again before the film breaks, re-submerging the ring.
Repeat the determination three times for a total of four determinations. Should the film break, clean the ring as described in 8.1.1 and repeat the determination. Discount the first reading and record the average of the next three readings, which should agree to within ±0,5 mN/m of the median value.
8.2 Method B
8.2.1 Preparation of apparatus Clean the dish or vessel (6.3) carefully.
The surface of the plate (6.2) should be roughened enough to obtain a perfect wetting and with no bright spots on the plate. Rinse the plate thoroughly by washing in water (5.1), then heating in the oxidizing section of a gas burner or Bunsen (6.5) until the plate is clean. Hang the plate on the instrument after cooling to room temperature. Make sure that the lower edge of the plate is exactly straight by checking whether the light gap between the edge of the plate and the surface of the liquid is parallel and not wedge-shaped. Ensure that the plate remains parallel to the surface of the liquid during the determination.BS ISO 1409 pdf download.