Root causes of post-consumer high-density polyethylene failing in new bottles

Abstract

High-density polyethylene (HDPE) is widely used in products such as bottles for cleaning products, in which Environmental Stress Cracking Resistance (ESCR) is required. This property is typically inferior in post-consumer recycled plastics (PCR), thus limiting their uptake in the rigid packaging industry. This study evaluated two PCR HDPE grades and the root causes of their low ESCR. Effects of sourcing the waste from detergent bottles (BPE) or milk bottles (UPE), Polypropylene (PP) contamination from bottle caps, and multiple recycling steps were all investigated. The findings revealed that ESCR is reduced by adding UPE, PP, and consecutive extrusion cycles. Unexpectedly, the presence of a high content of milk bottle grades in a given PCR hinders their uptake in detergent bottle production much more than the presence of PP caps, inferring that sorting based on bottle types instead of separating bottles and caps should be prioritized.