The conditions for buying and selling recycled plastics have changed after China's stop, which is why tests on recycled polymers are so important

The world of quality controls on recycled polymers has lived through two historical periods: the before and after compared to the blockade of imports of waste by China. Let’s see why.

Until 2017, waste plastic materials , especially those more difficult to treat or those that cannot be recycled with mechanical waste treatment plants, found a simple outlet on the Chinese market , without therefore having to worry about investing in research and development on recycling of this type of products.

The consequence of the influx of these materials into the Chinese market was the lower presence on the world markets of raw materials of low or very low quality , as the western recyclers kept the noble or very noble recycled materials at their factories, to create direct trade .

These qualitative plastic waste were resold in the form of bales, ground or granules in order to produce good quality recycled products.

At the time when China started to reject the plastic “garbage” that arrived at their ports, world recyclers were faced with a serious problem regarding their disposal on alternative markets.

At first they found alternative routes to countries near China, such as Thailand, Vietnam, the Philippines, Laos, Cambodia and others, but within a short time the local governments, submerged by waste, adopted a Chinese pushback system.

Africa has also been interested in this phenomenon of international waste disposal, but also on this continent, opposition to this traffic is increasing.

With the increase in the presence of poor plastic waste in the countries of production, the average quality of the basic products which contemplated the basket of plastics deriving from separate collection began to deteriorate .

There were phenomena of mix of technically unworkable materials , which clearly worsened the quality of the recycled raw materials, creating a phenomenon of greater attention and necessary technical checks on the lots purchased or sold.

The explosion of on-line transactions on recycled polymers and on waste by specialized portals made a new approach to the purchase and sale of plastic products necessary.

Before the purchase, some minimal analyzes were indispensable for the definition of the quality of the proposed product to avoid careless purchases.

The three basic tests are the Melt Index, the DSC and the Density , which can be requested both for the incoming sample and on the delivered load, to check the quality correspondence between the two tests and tie the payment to the test result made by an independent laboratory.

The Arezio Marco company takes care of these online services , through an independent laboratory, to facilitate transactions between interested parties.

Among the three basic tests, necessary to identify a recycled polymer, we find the proof of the fluidity of the material that is done on a sample that can be represented by a granule, but can also be carried out on a ground product.

The value of the Melt Flow Index (MFI) is a value necessary to identify the fluidity of the material inside a cylinder, under the effect of a weight, at a certain temperature and for a precise interval of time.

Since there is a clear relationship between the fluidity and viscosity of the polymers put into the machine, it can be generally stated that the more fluid a polymer is, the less viscous it is, and vice versa.

The value of the MFI is important for understanding the fluid dynamic behavior of the material in the extrusion, blowing or molding phases and, also, for being able to combine other types of materials in the field of polymeric compounds.

The MFI test can also give some other collateral indications by observing the spaghetti coming out of the machine, in fact if the outgoing spaghetti become progressively heavier, it can be deduced that the material is degrading under the effect of temperature.

If, on the other hand, the spaghetti become lighter and more rough, this may indicate that the material is in the cross-linking phase which reduces its flow.

The calculation of the MFI can be done according to the gravimetric or volumetric method .

In the case of the test according to the gravimetric principle , the polymer is loaded into a cylinder heated to a stable temperature, then exerting a constant force which pushes the molten polymer through a calibrated nozzle. The mass that passes through this nozzle, for a set time, determines the value of the MFI.

The heating temperature of the cylinder and the weight to be exerted on the polymer depend on the type of plastic to be tested.

In the case of the test according to the volumetric principle , the system is also equipped with an accessory that can establish how many cm3 of material will pass through the calibrated nozzle in a given time interval.

The value of the MFI will also indicate the volume of matter that will be passed through the nozzle, based on the weight and time established in the test, indicating an estimate of the average molecular weight.