How do additive packages, resins, HPOIT and OIT testing, and other components and quality control measures to geomembranes affect material durability and performance? Solmax engineer Mathieu Cornellier led a webinar on these topics earlier this month. The company has posted the presentation on its YouTube Channel.
Cornellier focuses on polyethylene (PE) geomembranes, including high-density (HDPE) and linear low density (LLDPE). He addresses questions such as how to define, or think about, a geomembrane’s “end of life”; how geomembranes age; and how additive packages are developed to enhance characteristics of a geosynthetics for UV resistance, chemical compatibility, etc.
“The longer it keeps its mechanical properties, the better the product and the better the long-term performance you’re going to get,” he says. “That’s why we put in anti-oxidants.”
The anti-oxidants discussed, including notes on the characteristics they impart, include hindered phenols, phosphites, and hindered amine light stabilizers (HALS). He describes oxidative induction time (OIT) and high-pressure OIT (HP-OIT) testing processes. And, importantly, he talks about how particular values (like an OIT) do not provide all the information you will need to truly understand additives packages, geomembrane service lives, and other key factors to design and performance.
ADDITIVE PACKAGES & GEOMEMBRANE AGING
Cornellier separates geomembrane aging into three phases:
- Phase A: Anti-oxidant depletion phase – In this phase, anti-oxidants patch free radicals, a process by which they lost their electrons and become less effective. During this phase, the polymer is not yet being attacked by the free radicals—because additive packages are doing their work—so a geomembrane essentially retains its mechanical properties.
- Phase B: Induction time – The anti-oxidants have depleted, but the chain-reaction of deterioration across the geomembrane’s polymer has not yet occurred. This phase is in general significantly shorter than Phase A.
- Phase C: The reaction has begun and a geomembrane’s polymer is being affected by free radicals. When the mechanical properties are reduced to 50% of their original value, the geomembrane has reached the end of its useful life.
“An anti-oxidant will react differently with a different resin,” Cornellier says. He stresses this isn’t about polyethylene versus polypropylene or another formulation.
“Even two HDPE from two different suppliers will react differently with an anti-oxidant,” he says.
This underscores not only why geomembranes are extensively tested but how highly engineered they are to provide long-term performance in critical containment applications.
See other geomembrane videos on the Solmax YouTube Channel.
Learn more about Solmax geosynthetics, HDPE geomembrane additives, and other engineering issues at www.solmax.com.