Q: I am contacting you in regard to the requirements for oxidative induction time (OIT) (standard [STD] and high pressure [HP]) in the GRI-GM13 specification for both ultraviolet light and oven aging. Do you need to conduct both OIT tests or just one or the other?
A: I would strongly recommend reading the EuroGeo 4 keynote paper “Long-Term Performance and Lifetime Prediction of Geosynthetics” by Hsuan et al. from 2008 in Edinburgh, United Kingdom.
To properly understand and assess the long-term behavior of geosynthetic materials, it is necessary to investigate the various types of possible degradation mechanisms. Degradation of geosynthetics depends on the polymer type, formulation and quality of the components. For example, polyolefins are vulnerable to oxidation. The oxidation reactions of polyolefins are rather well known. The sequential steps of the oxidation chain reaction include initiation, propagation, chain branching and finally the termination reactions. Furthermore, the influence of temperature, pressure and ultraviolet light on the service life are critical.
The OIT value indicates the amount of, but not the type, remaining in the test specimen of antioxidant. Many researchers use this method to monitor the depletion of antioxidants because of its simplicity. However, for different antioxidant formulations (types and amount), direct comparisons can be misleading. There are two OIT tests, standard OIT (STD-OIT) and high pressure OIT (HP-OIT), which are carried out using a differential scanning calorimeter (DSC) with standard and high-pressure cells, respectively. The STD-OIT is performed according to ASTM D3895. The test specimen is subjected to 5-psi (35-kPa) gauge pressure of oxygen at 392˚F (200˚C). The HP-OIT test is performed under 51-psi (350-kPa) gauge pressure of 302˚F (150˚C) condition according to ASTM D5885. The determination of the OIT value is typically based on the STD-OIT test for GRI-GM13. The main application of the HP-OIT is for antioxidants that have low efficiency temperature range, such as hindered amine light stabilizers (HALS). Therefore, the answer to your question is complex and you need to guess (assume) how your high-density polyethylene (HDPE) geomembrane was formulated. There is no sense in running the expensive HP-OIT test if the HDPE geomembrane doesn’t have any HALS in it.
Hsuan, Y. G., Schroeder, H. F., Rowe, K., Muller, W., Greenwood, J., Cazzuffi, D., and Koerner, R. M. (2008). “Long-term performance and lifetime prediction of geosynthetics.” Proc., EuroGeo 4, the 4th European Geosynthetics Conference, IGS UK, Edinburgh, United Kingdom, 5–24.