Compatibility of the EVOH barrier in HDPE containers with the recycling process was tested by an independent laboratory. A compatibiliser layer was originally put into the structure to test how an embedded solution could improve the recyclability of a structure usually considered difficult to recycle.
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New findings for functional barriers in HDPE containers
The test was performed on natural, five-layer HDPE containers consisting of six per cent EVOH and three per cent PE-g-MAH tie layers (by weight) and carried out as per the Recyclability Evaluation Protocol for HDPE containers. Apart from pre-treatment, tests include extrusion at 220°C and use of pellets in the production of new HDPE containers with a recycled content of up to 25 per cent.
These novel findings show that when EVOH is sandwiched in the packaging structure with PE-g-MAH1 tie layers, recyclability is improved. The results of laboratory tests show that the chemistry of these tie layers can enhance the compatibilisation of EVOH and HDPE during extrusion by avoiding typical yellowing effects, as well as an increase of gels and specks in the pellets. However, this corresponds specifically to the PE-g-MAH1 tie layers and not to any other arbitrary tie layers. In case another type is used, the laboratory tests will have to be repeated.
Consequently, these findings will be used to update and enhance the RecyClass Design for Recycling Guidelines for PE-HD Natural and Colored Containers, which are one of the pillars serving as a database for the recyclability evaluation within the RecyClass Tool.
The respective concentrations of EVOH and PE-g-MAH1 tie layers (where MAH is > 0.1%), is therefore reported in the design for recycling guidelines as compatible with the HDPE recycling stream as no detrimental effects were reported in the testing conditions.
However, EVOH concentration above one per cent with any other types of tie layers is reported as having no compatibility as further testing will be required.
RecyClass welcomes the industry to submit additional products with other barrier combinations for evaluation in order to improve the best available information on plastics packaging recyclability. Analysis of the impact of the EVOH on the recyclability of a package is indispensable to advance design for recycling.