Mixed plastic packaging waste refers to all plastic packaging waste sourced from the domestic waste stream and includes rigid and flexible plastic items of various polymer types and colours that are typically generated by households. It is reported that the share of plastic in the household waste ranges from 8% to 12% by weight. These materials, when collected, can be efficiently sorted in the material recovery facilities (MRF), but generating some rejects that are commonly send to final disposal or energy recovery.
The major challenge in the producing valuable recyclate from mixed plastic packaging waste is that most plastic types are inherently immiscible at the molecular level and have different process requirements. Likewise, when plastic is contaminated or of a limited quantity or with a varied composition, recycling becomes more difficult.
Therefore, in order to maximise recycling yields it is best practice to process separately collected mixed plastic packaging waste in individual material streams that can be transformed into valuable high-quality secondary raw materials and recycled products. This process consists of the following steps:
- sorting flexible plastic packaging waste from the rigid items (film sorting) by using film grabbers, air drum or ballistic separators followed by a manual quality assurance step;
- sorting plastic bottles and other rigid items by polymer and colour with optical sorting systems;
- reducing sorted film and residual rigid items (as separate flows) in flakes by using granulators;
- cleaning flaked plastic packaging using friction cleaning (dry or wet grinding systems);
- separating and washing flaked plastic packaging by polymer and colour by using optical sorting systems or density separation technologies;
- extruding flaked material into pellets.
Important prerequisites for the implementation of this best practice are the waste collection system in place for household post-consumer plastic packaging and the assurance of the good quality of the collected materials e.g. through effective household communications. Likewise, as in the best practice about maximising recycling yields for high quality output, it is important the sizing and the determination of the capacity of the processing plant.