ASTM D5870 - Standard Practice for Calculating Property Retention Index of Plastics
ASTM D5870 standard is a standard practice intended to establish procedures for calculating Property Retention Index (PRI) of thermoplastic and thermosetting plastics after exposure to deteriorative conditions such as thermal aging, accelerated natural or artificial weathering, or chemical exposures. The primary objective of this index is to provide information on the relative performance of material durability for design engineers.
The PRI is dependent on the tested material, the evaluated property, and the exposure conditions used. It should be noted that the PRI obtained for a specific property will likely not be the same as the PRI for a different property of the same material, even if the same exposure test is used. It is up to the user to determine which exposure test conditions are most relevant for the specific material and service condition used.
It is important to note that this standard does not aim to establish a fixed procedure for conducting the exposure test. Instead, it proposes a set of specific procedures used to calculate the retention index of a characteristic property of the material after its exposure. Material sampling procedures for testing are also not described in this standard; these procedures are defined in the material's own standards and specifications.
Under this standard, various pieces of information must be taken into account, including a complete description of the tested material, methods of preparing the material and individual test specimens, and the procedure used to condition the specimens before and after exposure. Furthermore, results may vary depending on the exposed side of the test specimen in certain tests. Therefore, it is imperative to ensure that all exposed specimens have the same orientation in the test apparatus used to hold the specimens during exposure.