Stress Cracking Detergent Price Increases Due to Restricted Supply Means Some Labs Running with 'Aged' Solutions
By GNA Reporter
Introduction
Stress cracking tests for HDPE geomembranes, such as ASTM D5397 and ASTM D-1693, play a crucial role in evaluating the durability and long-term performance of these lining materials.
One of the key components required for these tests is Igepal CA-630, a nonionic surfactant based on Polyoxyethylene nonyl phenol. However, recent restrictions on the supply of Igepal CA-630 in certain regions, due to its significant toxicity to aquatic life, have led to a substantial increase in its price.
Consequently, some geomembrane testing laboratories are forced to continue using their stress cracking bath solutions for extended periods, resulting in the aging and degradation of the surfactant.
Effects of Aging on Igepal CA-630
When Igepal CA-630 ages at the test temperature of 50°C, its structure undergoes changes, affecting the critical concentrations of micelles, also known as the CMC (critical micelle concentration).
This alteration in the CMC leads to different stress cracking resistance (SCR) times for the HDPE specimens being tested. As a consequence, the accuracy and reliability of stress cracking test results may be compromised when aged solutions of Igepal CA-630 are used.
Importance of Refreshing the Stress Cracking Solution
To ensure consistency and reliability in stress cracking test results, it is recommended to change or refresh the Igepal CA-630 stress cracking solution before significant aging and degradation of the surfactant occurs. By doing so, laboratories can maintain the integrity of the testing process and obtain accurate measurements of stress cracking resistance for HDPE specimens.
Monitoring the Condition of Igepal CA-630
Laboratories conducting stress cracking tests should employ methods to monitor the condition of Igepal CA-630 within the stress cracking solution. Two commonly used techniques are ATR-FTIR analysis and UV-visible spectrometry.
- ATR-FTIR Analysis: Periodic monitoring of the stress crack solution using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) analysis can help determine whether Igepal CA-630 has undergone significant degradation. ATR-FTIR analysis measures the changes in the molecular structure of the surfactant, providing valuable insights into its condition and integrity.
- UV-Visible Spectrometry: Another method to assess the condition of Igepal CA-630 is UV-visible spectrometry. This technique detects any discoloration or changes in the solution's appearance, which could indicate degradation or contamination of the surfactant.
Regular monitoring using UV-visible spectrometry allows laboratories to identify potential issues early on and take appropriate measures to maintain the quality of the stress cracking solution.
The figure below shows the IR scans of fresh Igepal CA-630 solution (blue) and extensively aged (red).
Conclusions
The restricted supply and subsequent price escalation of Igepal CA-630, a critical stress cracking detergent, have forced some geomembrane testing laboratories to continue using aged solutions for stress cracking tests. However, the aging and degradation of Igepal CA-630 can lead to altered stress cracking resistance times and compromise the accuracy of test results.
To ensure consistency and reliability, it is recommended that laboratories refresh the stress cracking solution before significant aging occurs. Regular monitoring of Igepal CA-630 using techniques such as ATR-FTIR analysis and UV-visible spectrometry can help maintain the integrity of the surfactant and ensure accurate stress cracking test outcomes. By prioritizing the quality of testing solutions, laboratories can uphold the standards necessary for evaluating the durability and performance of HDPE geomembranes.
Further Reading
