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.
5 Preparation and number of Lest specimens
5.1 The test specimens shall consist of
— discs of diameter 14mm and thickness approximately 1 mm, for method A;
— squares of side 15 mm and thickness approximately 1 mm, for method B.
They shall be punched out From the sheets to be tested.
5.2 The number of test specimens required is the expected time of the test in minutes divided by S. II the stability of the compound is very high, remove the test specimens every 10 mm to 15 mm instead of every S ruin during the first stage of heating, before the appearance oldkcoloratlon, Thus, the number of test specimens used can be less than that specified above.
5.3 If the material to be tested is an extrusion or moulding material in granule, powder or pellet form, this shall be sheeted on a roll-mill under the conditions specified In the material specification, or as agreed upon between the interested parties (ISO 293 may be helpful in this respect).
5.4 lithe material to be tested is in the form of a paste (plastisol), it shall be gelled to give a well fused sheet; the test specimens shall be punched out from the sheet thus obtained,
If the surface finish of specimens (particularly those made from unpiasticized materials) prepared by milling does not ensure sufficient contact with the aluminium block and cylinder, press-polishing of the specimens Is recommended as an optional additional step.
Warming of the milled unplasticized sheets permits test specimens to be cut without shattering.
6 Test temperature
The test temperature shall be that stated in the material specification or as agreed upon bctween the interested parties; in the latter case, the temperature shall be chosen so that the test duration is in the range of 60 mm to 120 mm. If there is no specification or agreement, a temperature of 180 °C shalt be used.
8.1.1.3 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 of0,3 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 thermucouples near each corner and at the centre; checks are made at S mm 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 mm to 60 mm 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.
8.1.1.5 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 thwkness. 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 nun or better.
8.2 Procedure
8.2.1 Prepare. for each exposure time envisaged, a specimen support (8.12) 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 8.12).
8.2.6 Remove one support together with its specimens, at selected intervals over the period of exposure, preferably continuing exposure until bbckening occurs. Number the specimens consecutively.
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
