BS EN ISO 305:2019 pdf download – Plastics – Determination of thermal stability of poly(vinyl chloride), related chlorine- containing homopolymers and copolymers and their compounds – Discoloration method
8 Method B: Oven method
8.1 Apparatus
8.1.1 Forced-air-circulation oven, having the following additional features: The temperature of the oven shall be controlled by a thermostat capable of maintaining it to within ±0,5 °C of the temperature selected. The oven shall be equipped with a calibrated thermometer and the proper system correction shall be applied to the temperature measurement. The air flow in the oven shall be adjusted to provide a temperature which is sufficiently uniform throughout the test area of the oven that specimens of uniform colour are produced (see 8.1.2, second paragraph). This will usually require an air flow of 0,3 m 3 /min. Prior to the test, the uniformity of the temperature within the oven shall be verified. Temperature uniformity is usually verified by placing thermocouples near each corner and at the centre; checks are made at 5 min intervals. It may also be done by inserting, at the test temperature, a rack with 8 to 10 specimens from the same sample distributed over the test area and exposing them until an early stage of discoloration is reached. The formulation shall be such as to cause a sharp change in colour within 45 min to 60 min under the test conditions. A non-uniform temperature distribution, as indicated by differences in the colours of the exposed specimens, shall be corrected before proceeding with the test. The inside of the oven shall be free of contamination and surface deposits. Use stainless-steel oven liners to reduce corrosion due to extended exposure to decomposition gases.
8.1.2 Specimen supports, made of new, clean aluminium foil laid on a removable oven rack (grille). If an oven equipped with a rotating specimen-holder is employed, the specimens shall be supported so that no appreciable elongation or necking down of the test specimens occurs during the test, since this would alter the specimen dimensions, and especially the thickness. In this case, the uniformity of the oven temperature shall be checked with the specimen holders mounted on the rotating device.
8.1.3 Timing device, for example a stopwatch, with an accuracy of 0,5 min or better. 8.2 Procedure 8.2.1 Prepare, for each exposure time envisaged, a specimen support (8.1.2) of sufficient size to hold one specimen of each of the different compositions under test. 8.2.2 Place one specimen of each composition on each of the specimen supports. 8.2.3 Place all the supports on the rack.
8.2.4 Place the rack in the oven (8.1.1) at the test temperature, keeping the oven door open for the minimum time necessary. The oven air-circulation fan shall be off while the door is open.
8.2.5 Start the timing device (see 8.1.3).
8.2.6 Remove one support together with its specimens, at selected intervals over the period of exposure, preferably continuing exposure until blackening occurs. Number the specimens consecutively.
8.2.7 Fasten the test specimens on a card with a note of the exposure time in minutes of each specimen and the test temperature.
9 Expression of results
Note the times, in minutes, from the start of the test to
— the first observed change in colour and
— the end of the test.
In cases of dispute, when greater precision is required, it is recommended that test specimens be compared by means of an agreed colour scale or by means of a photometer.
10 Precision
The precision of this test method is not known because interlaboratory data are not available. This method may not be suitable for use in specifications or in case of disputed results until these data are available.
11 Test report
The test report shall include the following information:
a) a reference to this document, i.e. ISO 305:2019;
b) the method used (A or B);
c) all details necessary for the complete identification of the sample, including the composition of the compound and the method of preparation of the test specimens (for example thermal treatment);
d) the test temperature;
e) the times, in minutes, from the start of the test to
— the first observed change in colour and
— the end of the test;
f) the date of the test.BS EN ISO 305 pdf download.