feedstock: post consumer rigids
What are post-consumer rigids
Post-consumer rigids are estimated in the UK at approximately 1,000,000 tonnes a year, with the majority ending up in low value uses. These are generally collected from at MRF’s where they are separated as mixed plastic streams and consist of all types of objects including chairs, pipes, and children toys.
Mixed bales trade in the UK market for anywhere from a gate fee (negative value) of £80 to a sale price of £100. The prices depend on transportation distances and quality, with a £100 bale usually comprising hand-picked rigids producing a high purity polyolefin. Lower priced bales are likely to contain under 50% polyolefin, and therefore produce a lower value plastic.
As shown in the graph, different levels of bale produce a different return on investment via BOSS, as the assumption is the sink fraction will be lost to RDF and therefore maximising the polyolefin content is key.
BOSS output
PP rich stream – Based on an even split, BOSS will produce a 90% pure PP stream, with the other 10% being PE. Melt flow is typically around 20MFI.
PE rich stream – like the PP stream, this will be 90% PE and 10% PP. Settings can however be changed to produce a higher quality stream, with upto 99% achievable, with the other float stream being negatively affected. For more information see here. Melt flow is typically a fractional melt, ideal for extrusion applications.
Because of this, in the UK we recommend a high purity PP be created, with a lower quality PE as there is a ready market for consistent mixed PE rich PO at extrusion grade melt flows.
Sink fraction – this will be a mix of many polymers (ABS, PS, PVC the most common). While there is scope to further separate these through BOSS, or sink float systems, this requires density controlled solutions which are expensive to manage.
summary
An excellent use of BOSS, with low value plastic being turned into a high value feedstock.
