Improving HDPE milk bottle recycling

According to Wrap – the UK based organisation that encourages recycling and sustainable packaging – the amount of recycled HDPE plastic that can be used to make new milk bottles is limited because the recycled material currently has a green hue to it.

A Wrap funded project, authored by Systems Labelling, has identified some ‘quick wins’ that combined would enable the production of milk bottles with at least 30% rHDPE to be acceptable from a colour perspective. This has the potential to enable around 50% rHDPE to be achieved.

This supports the achievement of Milk Roadmap targets for higher recycled content in new milk bottles and helps achieve environmental benefits by reducing the use of virgin plastic. This uses resources more efficiently, reduces waste to landfill, saves energy and reduces greenhouse gas emissions.

Tinted caps

The most significant quick win for caps is the use of ‘tinted caps’ with a range of lighter colour tones. This can be achieved by reducing the level of pigment and in some cases using a different colour within the masterbatch used to colour the caps.

A broad range of colours is achievable whilst maintaining clear identification of the milk variant (skimmed, semi-?skimmed, whole) by colour.

Investigations have indicated that there would be no technical or cost barriers to implementing tinted caps and Wrap is encouraging retailers and the dairy supply chain to consider implementing this.

Wrap recommend that retailers and the dairy supply chain agree a standard colour for skimmed, semi and whole milk products, and ensure that each dairy can work with the modified cap colours prior to implementation.

Labels

Over laminated paper labels of the specification tested were found to leach colour and sediment into the wash process and cross contaminate the HDPE flake. The level of label removal for this specification of label was found to be comparatively low.

However the project did find that synthetic (polypropylene, PP) labels of a certain specification had a much higher removal rate and did not leach colour so switching to this type of label would reduce the colour contamination in the rHDPE.

This may incur around a 3% to 5% increase in material costs, but the same equipment can be used to apply the label so no additional capital costs would need to be incurred.

The recycling process

There are a number of suggested improvements that food grade rHDPE reprocessors can make to reduce the overall colour hue of rHDPE.

These include tighter monitoring to check that the wash process is operating at optimum settings (temperature and dosage of cleaning agents), as well as optimising the final colour sort process, where possible.

Source: Wrap