ID22

Development of a New Quality Control Test Method to Assess the Stress Crack Resistance of HDPE with Recycled Content

Michael Pluimer - University of Minnesota Duluth, United States of America

Sara Stone - University of Minnesota Duluth, United States of America

Content

Currently, the majority of test methods for determining the stress crack resistance (SCR) in recycled polyethylene (PE) blends ignore crucial information regarding the stress cracking mechanism for these materials. Specifically, most test methods for assessing the SCR of PE materials involve notching the specimens and therefore only address crack propagation, ignoring the initiation of the cracks. Because the prevalence of contaminants and impurities is more likely in recycled materials than for virgin materials, it is especially important to assess crack initiation as well as propagation. The UCLS test (ASTM F3181) is currently the only ASTM-standardized test method for assessing the SCR of recycled PE blends that does not involve notching the test specimens, therefore giving an accurate depiction of both crack initiation and crack propagation in the polymer. The UCLS test is conducted on un-notched specimens in water at elevated temperatures and can be used to predict the service life of pipes manufactured with recycled materials when conducted in accordance with AASHTO R 93, Standard Practice for Service Life Determination of Corrugated HDPE Pipes Manufactured with Recycled Content.

 
While the UCLS test is an excellent predictor of the service life of HDPE materials containing recycled content, one of its drawbacks is that the failure times can be quite long, making it more useful for a quality assurance test than a quality control test. As such, there is a need for a test method that can more quickly assess the SCR of recycled material blends so that pipe manufacturers can more efficiently develop and qualify various materials. This research will develop a new accelerated test method for assessing the SCR of recycled PE blends correlating with the UCLS test but have considerably shorter failure times, making it more useful for a quality control test. The research investigates the strain hardening test (at both room and elevated temperatures) as well as a new dynamic accelerated fracture test, with both tests being conducted on un-notched specimens similar to those used in the UCLS test. The research will also include an assessment of the variability of material performance within a given lot.

The research is currently underway and will establish a correlation between the dynamic accelerated fracture test, the strain hardening tests, and the UCLS test to affirm the validity of these new tests for these applications and to provide additional quality control testing methods to allow pipe manufacturers to more efficiently develop and qualify blends of recycled materials.

Acknowledgement

We would like to thank the University of Minnesota- Duluth for funding this research.

References

ASTM F3181, ISO 18488:2015

Keywords (mandatory 3-5 keywords)

Recycled polyethylene, UCLS, Strain hardening, Stress Crack Resistance