Root causes of post-consumer high-density polyethylene failing in new bottles
Amir Khaki, Christian Gerlach, Kim Ragaert, Rudinei Fiório
Abstract
• Low environmental stress cracking resistance (ESCR) in recycled HDPE hinders their use in rigid packaging. • Higher concentrations of HDPE from milk bottles in PCR notably impair their ESCR. • Prioritizing sorting based on bottle types over separating bottles and caps is recommended. • Comprehending the root causes of low ESCR in PCR is essential to devise strategies to improve this property. • Optimized sorting processes are the key to increasing PCR uptake in new products. 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.