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The Australian geosynthetics testing company ExcelPlas discusses the search for alternative stress cracking surfactants to the pollutant Igepal CO-630.
Geosynthetics testing company ExcelPlas in Highett, Victoria, Australia, has identified two alternative stress cracking surfactants for high-density polyethylene (HDPE) geomembranes. Igepal™ CO-630, the non-ionic surfactant used in high-density polyethylene (HDPE) stress cracking bath, is becoming harder to purchase with restricted supply in many countries because it can cause long-lasting harmful effects to aquatic life.
Background
The ASTM D5397 single-point, notched constant tensile load (SP-NCTL) test for assessing the stress crack resistance (SCR) of high-density polyethylene (HDPE) geomembranes specifies that the detergent (surfactant) to be used in the stress cracking baths is Igepal™ CO-630 (octylphenoxypolyethoxyethanol). However, the European Union (EU) and Canada classify Igepal CO-630 as a priority pollutant.
In recent years, the European Chemicals Agency (ECHA) has included octylphenoxypolyethoxyethanol group surfactants, including Igepal CO-630, in the Candidate List of substances of very high concern in the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) scheme. The REACH regulation addresses the production, import and use of chemical substances and their potential impacts on human health and the environment.
The issue with Igepal CO-630 is that if disposed in sewers and waterways it is harmful to fish where it can act as an endocrine hormone disrupter and a mutagen. As such, the EU no longer allows the sale of Igepal CO-630 due to such ecotoxicity issues.
The ECHA includes Igepal CO-630 in the substance group in the Authorisation List mandating the manufacturers of this detergent and user industries replace this detergent by the “sunset date,” which was Jan. 4, 2021, thereby affecting EU manufacturers such as Solvay, importers, and downstream users, as well as non-European manufacturers exporting their products into the EU.
Search for alternative stress cracking surfactants
Since the inclusion of Igepal CO-630 in the Candidate List of substances of very high concern, chemical companies, as well as geosynthetics research groups, have looked for an alternative detergent that is eco-friendly and effective.
Ideally, an Igepal CO-630 replacement should generate minimal process change to SP-NCTL SCR experiments and produce comparable stress crack times. Therefore, an alternative detergent should have physiochemical properties similar to Igepal CO-630, should be readily soluble, should be easy to remove, should have a similar critical micelle concentration (CMC), should be eco-friendly and should not degrade to toxic phenolic metabolites.
Ideally, an Igepal CO-630 replacement should generate minimal process change to SP-NCTL SCR experiments and produce comparable stress crack times. Therefore, an alternative detergent should have physiochemical properties similar to Igepal CO-630, should be readily soluble, should be easy to remove, should have a similar critical micelle concentration (CMC), should be eco-friendly and should not degrade to toxic phenolic metabolites.
Igepal CO-630 has been used for decades as the surfactant of choice in many studies on environmental stress cracking of polyethylene. It has been used widely to test the SCR of geomembranes and pipes. This liquid has two significant effects: a) It accelerates crazing by plasticizing the amorphous region of the bulk polymer; and b) it accelerates the fracture of the craze by plasticizing the crystalline region of the fibrils.
Alternative stress cracking surfactants
ExcelPlas researched alternative stress cracking surfactants for the SP-NCTL SCR test. It has found the following two detergents to be potential replacement options:
- Arkopal™ N-100 from Clariant Produkte (Deutschland) GmbH
- Dehyton™ PL from BASF based on lauramine oxide
Arkopal N-100 surfactant (nonylphenoxypolyethoxyethanol) has already been used in test stress cracking. For example, 2% Arkopal N-100 surfactant is used in the full-notch creep test at 176˚F (80˚C) specially designed for evaluating the slow crack growth resistance (SCR) of polyethylene used in pipe applications.
Similarly, Dehyton PL has also been used for the FNCT specially designed for evaluating the SCG resistance of polyethylene used in pipe applications. The test is carried out according to the international ISO 16770:2004 standard, using a square bar of material previously notched on all faces in a coplanar way. A constant stress is applied on the specimen at 176˚F (80˚C) in a solution of Dehyton PL.
Note, however, that both Arkopal N-100 and Dehyton PL require the SP-NCTL SCR test to be run at a higher temperature than the current 122˚F (50˚C). Temperatures of 149 and 158˚F (65 and 70 ˚C) with these surfactants show promise to potentially give comparable test times to that of Igepal CO-630 at 122˚F (50˚C).