Environmental stress cracking of polymers: Case studies from industry (ABS and LDPE)

Abstract

Two industrial examples are described which demonstrate how environmental stress cracking (ESC) can give rise to unexplained, apparently random and catastrophic in-service part failures. In the two case studies, the companies could not identify the cause of failure through normal quality control procedures. Mild environmental stress cracking (ESC) was suspected and this project aimed to investigate and replicate the failures in a laboratory setting. The first case study involved ABS (acrylonitrile butadiene styrene) consumer parts which were exposed to an ester-based lubricant/glue during assembly. Samples were exposed to this product and aged at a range of temperatures (18–80 °C and at elevated humidity) for 6 months. The second case study involved medical grade LDPE (Low-density polyethylene) tubing for use in medical ventilators which was exposed to isopropanol as an assembly aid. The aim was to investigate whether adding an elastomer poly(ethylene–vinyl acetate), or if using an alternative solvent (methyl ethyl ketone) would reduce the likelihood of failure. In both case studies it was found that the failures were due to mild ESC. In the ABS parts it was due to the combination of the polymer, lubricant and residual stress from injection moulding. In the medical tubing, the failures were also determined to be as a result of ESC. It was found that blending the LDPE with an elastomer and using an alternative solvent reduced the likelihood of failure.