BS EN ISO 305:2019 pdf – Plastics – Determination of thermal stability of poly(vinyl chloride), related chlorine- containing homopolymers and copolymers and their compounds – Discoloration method.
1 Scope This document specifies two methods for the determination of the thermal stability of products and compounds based on vinyl chloride homopolymers and copolymers (referred to simply as PVC in the following text) by the extent of the discoloration that occurs when they are exposed, in the form of sheet, to elevated temperatures. The two methods are: — Method A: Oil-bath method; — Method B: Oven method. These methods are particularly applicable to the determination of the resistance of PVC to degradation by heat, as assessed by the change in colour after different times of heating under standardized conditions. The results are comparative only, and can be unsatisfactory when coloured PVC materials are tested. The stability times given by the two methods might not be similar and cannot be used for direct- comparison purposes. 2 Normative references There are no normative references in this document. 3? Terms? and? definitions No terms and definitions are listed in this document. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https://www.iso.org/obp — IEC Electropedia: available at http://www.electropedia.org/ 4 Principle 4.1 Method A: Oil-bath method Method A is a simple method, which requires little expenditure on apparatus and permits materials to be tested almost in the absence of air. A series of test specimens is heated at an elevated temperature for different lengths of time in a temperature-controlled oil bath. The test specimens are placed between an aluminium block and an aluminium cylinder to promote heat transfer and restrict air access.
4.2 Method B: Oven method Method B requires a forced-air oven, in which the air flow is adjusted to provide a sufficiently uniform temperature throughout the entire test area. This method is not applicable to materials that will cross- contaminate during oven exposure. A series of test specimens is heated at an elevated temperature for different lengths of time in a forced-air-circulation oven. The test specimens are supported by new, clean aluminium foil laid on removable racks. 5 Preparation and number of test specimens 5.1 The test specimens shall consist of — discs of diameter 14 mm 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 5. If the stability of the compound is very high, remove the test specimens every 10 min to 15 min instead of every 5 min during the first stage of heating, before the appearance of discoloration. 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 If the 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 unplasticized 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.
7 Method A: Oil-bath method 7.1 Apparatus 7.1.1 Thermostatically controlled oil bath, capable of maintaining the temperature within ±0,5 °C in the range 120 °C to 200 °C, fitted with a suitable stirrer and a suitable device for holding a convenient number of test tubes immersed to a depth of 60 mm to 70 mm.