Wednesday, 10th february 2021 | Technical information
Marco Arezio - Consulente materie plastiche - Odors in Plastic: Check the Supply Chain to Avoid Complaints

If it is known that in the waste coming from separate collection and therefore from post-consumption, the presence of odors can consistently persist, once transformed into granules, the expectations on the production of raw material from post industrial waste or from post industrial + post consumer compounds, from the point of view of odors, are definitely higher.

So high, that you expects not to have to face the problem of delivering to the customer plastic granules suitable for producing items that until a few years ago were made with virgin raw material, which contain an unpleasant odor gradient.

The qualitative ambitions of these customers who buy the recycled plastic raw material remain high (as if they were still buying a virgin raw material), so as to be able to boast of green productions , but at the same time not having to risk losing their final customers due to an issue linked to unpleasant odors.

A couple of requests that are really difficult to sustain, where the producer of recycled plastic raw material must find certain solutions to control its production chain, with the aim of avoiding to purchase scrap and manage processes that could increase the problem.

But what tools do we have today to be able to create a control strategy that warns us when an incoming plastic waste can cause odors in the final granule, with the consequent possible dispute of the customer who buys it, or what tools do we have to understand if the extrusion of the raw material creates degradation processes that could generate odors?

First we can say that the tool for odor control in all stages of production exists, it gives us a chemical photograph of our processes and shows us where there may be the error that will cause the dispute.

This laboratory machine, the size of a desktop printer, is a gas chromatograph combined with an ion mobility spectrometer which, through a quick analysis and without preparation of the particular samples, it tells us what is, chemically, the origin of the fragrances that the human nose intercepts but which does not know how to separate them and understand their origin.

If you think it will only be useful to give a scent license to the plastic granule you produce, you are only one third of the way, as the help that this type analysis can give the company not only the final control of the raw material, but also identify the critical stages of production in order to prevent odors from forming.

The areas of use of the technology can be summarized here:

Purchase of plastic waste for production

Whether they are post consumer or post industrial, a company that produces recycled granules has several suppliers of plastic waste and, not all of them work in the same way: washing with different efficacy, waste selection with different systems and methods, risks of contamination of waste with other plastics and many other similar situations.

So it is necessary to build a qualitative database of suppliers, as regards the odors of waste, so that you can, chemically, have a photograph of what it is waste it can contain and how this waste could behave in its transformation into plastic granule.

The chemical analysis of the incoming flows makes us understand which supplier, by raw material, we can use to create our granule recipes, without generating unpleasant odor problems in the production phase.

The flow analyzes create a database through which you can attribute a specific waste of a particular supplier to a specific recipe.

If the chemical photograph of a flow of plastic waste contemplates the presence of a series of chemical compounds in a certain quantity, we can know with certainty which odorous imprint the our final granule.

Granulation of plastic waste

In this phase it may happen that, without a chemical photograph of the input entering the extruder, the waste can be used for the production of granules, without we can intercept a particular odor disturbance, thus trusting to produce a good quality granule, perhaps comforted by the fact that the laboratory analyzes that are normally done, such as density, DSC, ashes and fluidity, tell us that the material can be eligible.

But during production there may be very small fractions, in terms of quantity, of materials unrelated to the main raw material, which can degrade creating important odor signals that could have the material contested.

The chemical photograph gives us indications that are expressed in values so small that the chemical compounds entering the extruder and those that can be generated during processing, are precisely intercepted and analytically defined.

So even the control of the extrusion phase of recycled plastics gives us a precise, non-empirical picture of odors, on which we can work for a possible adjustment of the recipes .

Quality control in sales and after sales

How can you define a smell of a recycled polymer? Seen by the manufacturer in one way, seen by a buyer perhaps in another. This difference in evaluation creates the greatest number of disputes and commercial embarrassments which, at times, ends with a surrender of the producer for lack of certain proof.

This yield almost always turns into economic damage to be recognized to the customer by the polymer manufacturer but, in most of the times, there is also a commercial uncertainty between customer and supplier managed in a completely empirical way through the nose test.

The customer has his men who smell the smell of the granule they receive and give an evaluation, while the supplier provides his team. In both cases, the human nose, however sophisticated, can interpret the smell in a different way.

To resolve the uncertainty, possible disputes and possible loss of trust on the part of the customer, providing them with a chemical photograph of what you are selling is the best way to demonstrate that the product is made up of chemical elements that can generate odor gradients within the limits that the customer has previously accepted, not through a questionable nose but through chemistry.

In fact, customer and supplier can create, in a certain and analytical way, an agreement that limits certain chemical substances that generate odors to values accepted by both parties.

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

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