The materials that come from post consumer, whether they are in HDPE or LDPE or PP or PET, to name only the most common, are produced, expressed in the form of packaging, which are collected from our homes as waste, in which a rough separation is made between other packaging such as paper, glass and metal.
The fraction of plastic waste is put into the bags creating a mix of plastics of various types, from PET bottles, to PP wrappers, to food trays in polylaminates, to HDPE detergent bottles, to caps, to polystyrene packaging. With them, we can also find inside them residues of the products they contained, from food to chemical ones such as detergents.
This complex of plastic products is sent to mechanical recycling, through which the types of plastic are separated by families of chemical products, which will then be ground, washed for can then be extruded and create new raw material.
However, mechanical recycling has limits in the separation of the incoming elements as it uses very high speed optical reading machines that read the density of materials, but that they can do little, for example, in products composed of coupled plastics, while still retaining a certain percentage of error, which could be reduced if the waste entered were more selected at source.
Furthermore, the washing of selected and ground plastics is not always managed effectively to further separate plastic fractions with different densities and to clean it from residues of products that the packaging contained.
The limits, therefore, can be organizational, technical or managerial, generating qualitative deficiencies on the final granule that is dedicated to the blowing or extrusion of products.
The main problems for a recycled HDPE by blow molding and extrusion are:
• Presence of a fraction of PP normally determined by the presence of caps on the packaging
• Small diameter impurities that could create holes in the blowing of bottles or surface irregularities in extruded products
• Difficulty in creating bright colors as the origin from colored packaging creates a certain opacity in subsequent colors
• Persistent odors in the final raw material especially due to the degradation of organic elements or the presence of surfactants in a porous material such as HDPE.
• Degradation of the plastic mixture in the extrusion phase due to the presence of plastics other than HDPE.
For some non-aesthetic applications the problems described above can be reduced by optimizing the production control phases of the waste and the final granule.
But in productions that require a bright color, the absence of odor and a high aesthetic quality of the product, such as the bottles of some types of packaging sectors, it is important to choose a post-consumer product that comes from a separate supply chain at the origin, in which the bottles must be in neutral HDPE, therefore without colors and that do not contain surfactant residues or organic waste.
The recycling of the single product creates a supply chain capable of generating a neutral granule, without odors, suitable for the highest uses in terms of structure, color, absence of odors, allowing the semi-transparency of the bottles.
This type of granule can be easily used, thanks to its brilliance and color fidelity, also in the extrusion of profiles, plates and tubes of colored RAL.
Automatic translation. We apologize for any inaccuracies. Original article in Italian