Recycling of plastics

Method and system for separating plastics, in particular different plastic materials intended for recycling.

Title of the patent Silicon nanostructures as luminescent markers for the recycling of plastic
Thematic area Chemistry and biotechnology
Ownership Alma Mater Studiorum - Università Di Bologna
Inventors Paola Ceroni, Francesco Romano
Protection International
Licensing status Available for licensing agreement
Keywords Nanostructure, silicon, plastic, luminescence, recycling, marker, separation
Filed on Oct 26, 2018


Plastics constitute a widespread material as well as the awareness that they can be a threat to the planet's ecosystem. This is why strategies to reduce the presence of plastic focus, rely on recycling. However, many polymeric materials today are not recycled because a low-cost and efficient automated separation system has not yet been developed.

In fact, the current differentiation systems use human personnel or automated systems based on various types of detectors (optical, X-ray, tribological). Mechanized systems are the most promising, and among these, those that use an optical recognition system are receiving particular interest for the simplicity of the instrumentation required and the reproducibility of the results. But these systems have limitations in the differentiation of complex mixtures or polymers with different compositions.

One of the biggest challenges in the field of recycling of plastics is the differentiation of multi-waste materials into mono-materials with a high degree of purity.

The invention consists of a method for separating different plastic materials, destined for recycling, by inserting luminescent markers (silicon nanocrystals) in them. These markers are invisible to the human eye.

The plastic materials, in which these markers have been inserted, can be uniquely recognized by an optical detector.


The invention applies to the plastic recycling sector, as well as to anti-counterfeiting systems.

Among the advantages of this system:

  • uses an inexpensive, biodegradable, abundant, non-toxic material;
  • long luminescence life times allow the use of time-gated detection technology;
  • it offers the possibility of separating black plastic, currently the most complex to separate.