PRACTICALITY OF SINGLE-STREAM RECYCLING OF HIGH-DENSITY POLYETHYLENE (HDPE) IN THE UNITED STATES

Abstract

Increasing plastic recycling rates, leading to more products being made from recycled rather than virgin plastic material, is one possible solution to reducing emissions and preventing plastic pollution from entering the environment. While research into new chemical methods of recycling plastic is ongoing, mechanical recycling is still the most prevalent and economically viable recycling approach in current use. While still a better option than landfilling plastics, mechanical recycling has disadvantages, such as high processing costs and lower material quality compared to virgin plastic. Methods such as mixing virgin material with recycled plastics, using various additives, and downcycling recycled plastics are currently used to mitigate the resulting quality gap. This work investigates the viability of recycling single-stream post-consumer HDPE using a low-complexity process without augmentation using virgin material. It assesses the material properties of the resulting recyclate and determines whether it meets the requirements of HDPE manufacturers established via a producer survey. The material properties of both unsorted and sorted classes of post-consumer recycled HDPE streams were determined using industry-standard Melt Flow Index (MFI) and Differential Scanning Calorimetry (DSC) test methods operating on both flaked and extruded material from each HDPE class. Flaked material was used to create a baseline for the material properties of each class and then compared to the extruded material to analyze if material degradation, such as thermal degradation, occurred during processing. MFI and DSC testing generally showed no significant degradation after extrusion, including within the unsorted HDPE class. In parallel, a companion survey of plastics producers based primarily in the Midwest region of the United States was carried out to understand the attitudes, practices and material requirements of manufacturers relating to their current and projected future use of recycled HDPE. The primary reported concerns regarding using recycled HDPE in production were the quality and predictability of recycled materials, the impact of additives on material properties, and recyclate price. Improving recycling technology will likely improve quality and predictability and lead to lower-priced recyclate in the long term. Nevertheless, the negative impact of additives and colorants on the HDPE recyclate will remain for some production categories if mechanical recycling continues in its current form, indicating that further advancement is needed in alternative recycling methods in addition to mechanical recycling. In summary, this work found that the material properties of unsorted, single-stream, post-consumer, recycled HDPE processed in a low-complexity fashion without virgin plastic augmentation maintained key material properties and that the resulting recyclate was a viable substitute for virgin HDPE material. Further, the results from the industry survey of producers established that HDPE processed in this way can meet the current and likely future material property needs of plastics producers where some requirements, such as color contamination, are relaxed. The low complexity of processing indicates that such recyclate has the potential to meet producer HDPE raw material cost targets. However, further work is required to establish whether such low-complexity processing can scale while preserving cost and to determine how the resulting recyclate can meet the requirements of color-sensitive HDPE market segments.