Tests Reveal Novel Ways to Improve Recyclability of Difficult-to-Recycle Plastics

Novel new findings have emerged from compatibility tests involving the ethylene vinyl alcohol (EVOH) barrier in high-density polyethylene (HDPE) containers in the recycling process. RecyClass, a cross-industry initiative to advance plastic packaging recyclability within Europe, will use these findings to update and enhance its Design for Recycling Guidelines for PE-HD Natural and Colored Containers.

HDPE container in grassy field

A compatibilizer layer was inserted to test how an embedded solution could improve recyclability of a structure usually considered difficult to recycle. The test was performed on natural, five-layer HDPE containers consisting of 6% EVOH and 3% PE-g-MAH (polyethylene-grafted maleic anhydride) tie layers (by weight), according to the Recyclability Evaluation Protocol for HDPE Containers. Apart from pretreatment, tests included extrusion at 220oC and use of pellets in the production of new HDPE containers with up to 25% recycled content.

The new findings indicate that recyclability is improved when EVOH is sandwiched in the packaging structure with PE-g-MAH tie layers. Laboratory test results show that the chemistry of these tie layers can enhance the compatibilization of EVOH and HDPE during extrusion by avoiding the typical yellowing effect as well as an increase of gels and specks in the pellets. However, this corresponds specifically to the PE-g-MAH tie layers and not to any other arbitrary tie layers. In case another type is used, the laboratory tests will have to be repeated, said RecyClass.

The 6% EVOH concentration and 3% PE-g-MAH tie layers (where MAH is >0.1%) is, therefore, reported in the design for recycling guidelines as compatible with the HDPE recycling stream and having no detrimental effects under testing conditions.

RecyClass noted, however, that an EVOH concentration above 1% with any other type of tie layer is reported as having no compatibility, as further testing will be required.

RecyClass welcomes industry submissions of additional products with other barrier combinations for evaluation to augment information on plastic packaging recyclability. Analysis of the impact of EVOH on the recyclability of a package is indispensable to advance design for recycling of plastic packaging, said RecyClass.

Image: Bits and Splits/Adobe Stock

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