The enhancement of recycled polymers also passes through the solution of the problem of odors

In a circular economy perspective, the recycled polymers that come from post-consumption, therefore from the domestic separate collection, must be valorized, also managing to solve the problem of odors.

The need to make greater use of recycled polymers that come from post-consumption has now become a primary issue for the recycling of plastics.

As reported in the article published on the plastic and circular economy portal  two fundamental conditions must occur:

• Remodeling of the aesthetic expectations of finished products made of recycled plastic

• Reduction or cancellation of the smells that products made with post-consumer input bring with them after production.

In the first case it is important to be able to produce more products with recycled plastics , especially those made today with virgin plastics only for aesthetic reasons that could be defined as negligible, thus increasing the consumption of plastic waste.

In the second case, the problem of odor still strongly affects the purchase of recycled granules, especially in those countries where the problem of environmental protection is less felt.

If we want to give an example, a bottle of detergent produced with a recycled HDPE , after production, maintains a quota of smell (perfume?) Of detergent that comes from the processing of the bottles of the separate collection, in which the fragrances of the liquids previously contained also remain after washing.

As you can see, it is not a disabling problem for those who will have to refill the recycled bottle with perfumed liquids, but it is and has always been a topic discussed by polymer buyers.

Although things from this point of view are slowly changing, where there are major complications are those products made with PP or PP / PE or LDPE whose raw material has contained food residues, detergents, cosmetics or where the regeneration process has critical issues .

The factors that contribute most to the creation of odors are represented by:

•  Food residues, which create microbiological processes
•  Cosmetic residues that present difficulties in cleaning during washing
•  Surfactants that are incorporated into plastics
•  Contaminations in the washing water of plastic waste
•  Contaminations caused by the degradation of polymers during the production of granules.

To date, a full and definitive solution to the problem, to be applied in the large-scale production of recycled polymers, does not seem to exist yet, in fact, various paths are being followed to try to mitigate and, in the future, resolve the presence of these odors.

Coverage of odors

There are numerous products on the market, in the form of masterbach, which are used in the extrusion or injection phase of the products, containing various fragrances that help to mitigate a pungent odor like some polymer productions can be. The fragrances are numerous: vanilla, pine, strawberry, orange, lemon, lavender and many others.

Mechanical processes

There are plants for the production of recycled granules which, during the processing of plastic waste and the production of the granule itself, substantially reduce the sources that generate unpleasant odors. These systems are based on a triple combination of filtration, degassing and suction of volatile parts in order to improve the problem.

Scientific research

At the same time, research is making progress to try to identify, in a scientific and unequivocal way, the source of the odors of the compounds coming from the separate collection.

The German Fraunhofer Institute for Process and Engineering and Packaging ( IVV ) is studying how to improve the recycling processes of post-consumer waste. The work focuses, with an olfactometric and analytical approach, on the study and cataloging of the smells present in post-consumer plastics, evaluating their intensity and origin, identifying the materials that produce them through a chemical analysis.

The data collected from these scientific catalogings will help researchers find suitable processes for solving problems caused by microbiological decay, aging of the plastic, chemical results of thermal processes and residues from mechanical processing of plastic that cause unpleasant odors.

Analytical control of odors in the laboratory

Today, however, we have the possibility, through a laboratory instrumentation, which combines the activity of a gas chromatograph (GC) and an ion mobility spectrometer (IMS) to have a precise picture on the intensity and nature of the odors that come from the waste from recycle either from the flake or granule produced by post consumer plastics. 

This tool helps us to identify the annoying components from the odorous point of view in the incoming waste, but also on the raw material produced or on the final products made with recycled plastic, so as to establish corrective actions or, with the customer, an analytical range and not questionable, the level of odors in the products and accepted by the parties.

Automatic translation. We apologize for any inaccuracies. Original article in Italian.