BS EN ISO 305 pdf download Plastics – Determination of thermal stability of poly(vinyl chloride), related chlorine- containing homopolymers and copolymers and their compounds – Discoloration method
Method B: Oven method
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shall be applied to the temperature measurement.
220.127.116.11The air flow in the oven shall be adjusted to provide a temperature which is sufficiently uniformthroughout the test area of the oven that specimens of uniform colour are produced (see 8.1.2, secondparagraph). This will usually require an air flow of 0,3 m3/min.
8.1.,1.4 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 rackwith 8 to 10 specimens from the same sample distributed over the test area and exposing them untilan early stage of discoloration is reached. The formulation shall be such as to cause a sharp change incolour within 45 min to 60 min under the test conditions.A non-uniform temperature distribution, asindicated by differences in the colours of the exposed specimens, shall be corrected before proceedingwith the test.
18.104.22.168The inside of the oven shall be free of contamination and surface deposits. Use stainless-steeloven 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).lf an oven equipped with a rotating specimen-holder is employed, the specimens shall be supported sothat no appreciable elongation or necking down of the test specimens occurs during the test, since thiswould alter the specimen dimensions, and especially the thickness. In this case, the uniformity of theoven 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.
8.2.1 Prepare, for each exposure time envisaged, a specimen support (8.1.2) of sufficient size to holdone 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 theminimum time necessary.The oven air-circulation fan shail 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 ofexposure, 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 specimenand the test temperature.
9Expression 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.
ln cases of dispute, when greater precision is required, it is recommended that test specimens becompared by means of an agreed colour scale or by means of a photometer.
The precision of this test method is not known because interlaboratory data are not available. Thismethod may not be suitable for use in specifications or in case of disputed results until these dataare 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);
) 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.
The test report shall be accompanied by a piece of an untreated test specimen and the complete seriesof treated test specimens fastened on a card ( it is essential that this be stored in the dark).