Mechanical recycling is currently by far the most used process. 80% of plastics collected for recycling are mechanically recycled.
Currently, mechanical recycling works relatively well for PET bottles, but for other polymers or mixed plastics it faces some limitations, at least for premium quality recyclates. After a few recycling loops the polymer properties have declined so much that it will become very difficult to re-use the recyclates.
There is also a need for a better understanding of the colorant behaviors after multiple recycling loops.
It is extremely important to ensure that the pigments and polymer soluble dyes used for the coloration of the collected resins will not decompose or generate any toxic substances during the compounding process.
Some pigment chemistries are more stable than others in terms of heat stability or migration behavior. However, it will require intensive work to select a safer range of pigments to be used to color plastic articles intended to be recycled. Because an organic pigment is often not only one single molecule; depending on the production process there might be other substances which could have a negative influence on the toxicological profile.
This is where a pigment producer with long experience and expertise in product safety and records can support the industry, brand owners, packaging processors and masterbatch producers. Clariant is already focusing attention in this direction.
A further challenge is the base color of the recyclate coming from the recyclers. It can be any kind of grey from a light, a dark or a brownish one. The re-coloration of these recycled polymers becomes an issue for the masterbatch producer. There are strong quality variations between the different recyclers. To ensure a faster and constant color matching Clariant Pigments, together with a software provider, is developing a calibration set that will allow easy corrections for the base tone of the resin. This will be a major improvement to enhance the usage of post-consumer recyclates (PCRs).
Chemical recycling can be seen as a complementary technology, which will extend the offer of recycled resins in a quality that can meet the requirements of the packaging industry.
There are different types of chemical recycling, but they are all currently at an emerging stage.
A solvent based process is a mix between chemical and physical recycling. It involves a solvent that will specifically dissolve a certain type of polymer. Practice shows that some residues remain in the polymer, and even the colors haven’t fully been extracted. The recyclate looks greyish. Further research work is needed. Especially one aspect that should be investigated is to find out which type of pigment chemistry will better be removed from the polymer. This is a long-term project.
Another type of chemical recycling is “depolymerization” which breaks the molecular bonds into the initial monomers. There are different technologies to achieve this: using enzymes or catalysts.
Pyrolysis or gasification are further methods to decompose a polymer and generate fuels that can be used to then produce new plastics.
For the colorant and masterbatch or compounding industry, chemical recycling would be the ideal way since the recycled resin will look very much like a virgin polymer and can thus be colored just like a virgin resin.
Although still a small market, bio-degradable polymers enjoy increasing attention from brand owners and packaging companies.
Not every pigment can be used to color bio-degradable polymers, because they must comply with very strict standards in terms of impurities.
Clariant Pigments has set up a range of 26 organic pigments from its Graphtol® and PV Fast™ product line fulfilling the requirements of the European Norm EN 13432. They cover the whole color spectrum and therefore provide valuable support to masterbatch producers and designers in extending color horizons for biodegradable plastics.
Steps in the right direction
Developments like these in the field of colorants contribute to advancing a closed loop for plastic packaging. As the necessary focus on re-use and recycling gains momentum, color will not pose a challenge to the technologies, to the efficient, viable recovery of plastic waste, and creation of high-quality PCR, but instead work in harmony towards the goal of achieving a Circular Economy for Plastics.
By Philippe Lazerme
Head of Marketing Segment Plastics at Business Unit Pigment