Reuse the pulper waste to create polymers suitable for molding

Paper mills use a mechanical process to recycle the waste paper that enters their factories.

The industrial process starts from the maceration in the tub of the cardboard and paper for daily use, through water and a rotary movement of equipment that have the purpose of separating the cellulose fibers from the unusable materials. From this process, simplifying, the pulper waste is formed.

These materials are mainly composed of aluminum and polyethylene found inside food packaging, such as Tetrapak or other similar packaging, which cannot be used in the paper mill production process.

The numbers that make up the waste of the pulper are really impressive because we consider that about 10% by weight of the produced paper generates this type of waste, with disposal costs for the very expensive paper mills.

Today there are technologies that allow to reuse the pulper waste from paper mills recovering the LDPE polymer that is inside, through the separation, trituration, washing and granulation process of the pulper waste .

However, the problems encountered in recycling this compound, PE + Aluminum, are important, both in terms of production and final product quality:

1. The pulper waste has a high humidity percentage, higher than 10% , which must be substantially reduced to avoid granulation and production loss problems.

2. Residual humidity inside the granule can create gas problems in the molding phase , with consequent reductions in the resistance of the product and aesthetic defects on the surfaces.

3. The residual presence of paper inside the compound to be processed entails additional work during the granulation filtering phases. In fact the micro-presence of paper in the production of the final granule would lead to the creation of micro-pores harmful to the final granule.

4. The presence of aluminum, even in the form of a flexible element, therefore not hindering during the molding phase, entails an aesthetic effect that must be tolerated since the colored surfaces will not be homogeneous.

There is no doubt that all these problems can be managed both from the technical point of view and from the point of view of the optical effect of the final product, which must be accepted as a peculiar characteristic of the product itself.

The resulting granule is usually an LDPE with a fluidity of around 1 to 2.16 kg / 190 ° with a percentage of LD over 90% and residues of aluminum and possibly paper.

Regarding the use of the granule deriving from the pulper reject, without prejudice to the solution of the preceding points, it is indicated for the molding of non-aesthetic products but where polymer quality is required in terms of flexibility and uniformity of composition.

We can mention the plastic pallets, vases and tubs, building accessories, non-drive-over gratings, etc.

The product is suitable for the creation of compounds with PP, PO and HD depending on the uses that the customer must do, thus creating a very flexible compound from the point of view of polymer recipes.

Obviously, since it normally has a regular DSC, it lends itself easily to the addition of mineral fillers, especially CACO3 , which help the recipe to give less flexibility, inherent in LDPE, if the customer requests it.

See more info about recycling

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