At the moment about 1.5 million Tonnes of plastic are being recycled yearly, 75% of which is polyethylene, both low density (LDPE) and high density (HDPE). Recycling of plastic film so far one is of the weakest points in all-recycling schemes. The reason for this failure is that post-consumer plastic film waste is usually a mixture of diverse plastics, specially polyethylene (LDPE, HDPE) and polypropylene (PP), all together comprising 95% of the total film. Although cleaning and separation of the polyolefins (LDPE, HDPE and PP) from the rest is easy using flotation or hydro-cycloning methods, individualisation of LDPE, HDPE and PP is difficult, since their respective densities are very similar while their variable shape do not allow the use of automated, sensor-based methods (such as use of near-infrared detection).
RECFINMIX proposes the Research and Development of a novel separation principle of LDPE, HDPE and PP films, based on the their differences in cristallinity. When heated, the plastic film contracts. Since LDPE has an amorphous area with a higher degree of freedom, it contracts at lower temperatures than both HDPE and PP. Thus, while at an operating temperature of around 100C, shredded LDPE film pieces will curl, equivalent pieces of HDPE and PP will not be altered at least until 120C, remaining therefore in lamellar structure. The change in dynamic shape suffered by the LDPE is enough for an accurate separation using centrifuges, obtaining highly marketable purified LDPE.
Fields of science
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Funding SchemeCooperative - SMEs-Co-operative research contracts