The Washing of Post-Consumer Plastic Waste is Done in Three

Post-consumer plastic waste is, in quantitative terms, one of the major items that make up the basket of waste that our company produces.

If until a few years ago intensive mechanical recycling was not applied but only noble plastics were tried to be separated and extracted, today environmental awareness and the need to reduce the transfer of waste to landfills has imposed an increasingly massive use of post-consumer recycled polymers for the creation of new finished products, making the supply chain as circular as possible.

It was not a sudden turning point, it took time to subvert the cultural preconception that a product made with recycled polymers was second class compared to one made with virgin raw material.

When public opinion cleared the use of recycled raw materials as a necessary and irreplaceable element of our life, the demand grew exponentially.

There is no doubt that, from an industrial point of view, the treatment of post-consumer plastic waste for the creation of a raw material, which takes on a new aesthetic and structural nobility in products, today needs a decidedly more professional and qualitative approach to recycling than in the past.

In fact, in the post-consumer plastic waste work cycle, which includes the collection, selection, grinding, separation, washing and granulation, it is interesting to focus on the washing phase to better understand some aspects.

The concept of washing must include three basic steps that cannot be avoided, if you want to create a raw material suitable for the production of a good plastic granule . The three steps of the washing activity can be summarized here:

• Washing of waste through a machine with forced washing, which allows, through the action of water and the centrifugal rotation of the plastic containment basket, a detachment of polluting parts, such as organic food residues, sand, earth or other, which otherwise would not occur in a traditional tank with water.

• Use of a settling tank in which the materials, that have come out of the forced washing phase, follow a studied path, in terms of speed of movement and length, in which the plastic waste is separated by specific weight. In fact, materials with a lighter specific weight such as HDPE, LDPE, PS and PP, which make up the families with the greatest presence in post-consumer waste, remain afloat, while those with the highest specific weight such as loaded materials , PVC and other elements sink.

• The last essential system to complete a good washing cycle of post-consumer plastic materials is the centrifuge. In fact, once the waste has been energetically washed and separated from plastics with different specific weight, it is absolutely necessary, before the production of the final raw material, to reduce the moisture concentration. By passing the waste itself into the centrifuge it is possible to reduce high humidity percentages that cause many problems, such as the degradation of the polymer, the creation of aesthetic defects on the finished product and a substantial reduction in mechanical performance.

The washing phase, in the post-consumer material recycling activities, has often seen the assertion of a wrong theory, definable as "rinsing", where the process involved the '' immersion of the plastic ground in tanks with low water quality, a high rate of flotation of the waste and an inadequate tank length.

All this was reflected in a decisive economic saving, an increase in the hourly production of the department but with a low or very low quality of the future polymer.

If, in partial defense of this approach, we can recall that in the past the polymers derived from post-consumer waste were used only for low quality products, we must however remember that today, a higher quality is expected from this family of polymers as the user base has increased.

A low quality level of the process during the washing, separation and drying phases, inevitably brings with it the problem of the odors of post-consumer plastics.

If we talked previously about negative aspects related to the mechanics and aesthetics of the products, saving time and technology in the 3 phases that make up washing, increases considerable unpleasant odor in finished products made with polymers that have undergone a poor washing process.

The presence of pungent and persistent odors in finished products not only leads to a reduction in sales in quantitative terms, but also leads to the depreciation of the article itself, with a reduction in the company's contribution margins.

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