ISO 291:2008 pdf download – Plastics — Standard atmospheres for conditioning and testing
7 Standard and ambient temperatures If humidity has no influence or only a negligible influence on the properties being examined, the relative humidity does not have to be controlled. The corresponding environments are designated “temperature 23” and “temperature 27”, respectively. Similarly, if neither temperature nor humidity has any noticeable influence on the properties being examined, neither the temperature nor the relative humidity has to be controlled. In this case, the atmospheric condition is termed the “ambient temperature”. 8 Procedure 8.1 Conditioning The period of conditioning shall be as stated in the relevant specifications for the material. When the conditioning periods are not stated in the applicable standard, the following shall be adopted: a) unless otherwise specified, a minimum of 88 h for atmospheres 23/50 and 27/65; b) unless otherwise specified, a minimum of 4 h for temperatures of 18 °C to 28 °C. NOTE 1 The length of time necessary for a plastics material to come to humidity equilibrium is in general much longer than the length of time necessary for it to come to temperature equilibrium. NOTE 2 Samples conditioned in accordance with a) may not reach humidity equilibrium. A sufficient equilibrium is reached after conditioning longer than the time t 70 as defined in ISO 62. t 70 depends on the square of the thickness. More information about the time needed to reach equilibrium can be found in Annex A. NOTE 3 For particular tests and for plastics or test specimens that are known to reach temperature and humidity equilibrium either very rapidly or very slowly, a shorter or longer time may be specified for the conditioning period in the appropriate International Standard (see Annex A). 8.2 Testing Unless otherwise specified, specimens shall be tested in the same atmosphere or at the same temperature in which they have been conditioned. In all cases, the test shall be carried out immediately after the removal of the specimens from the conditioning enclosure.