Advantages and disadvantages in the use of fillers in regenerated polypropylenes

Polypropylene from the processing of rigid and semi-rigid post-consumer waste carries with it a more or less marginal presence of other plastics, especially polyethylene, which are not completely intercepted during the separation phase of the packaging. In addition, depending on the source of the input, we can also find mineral fillers that can be composed of talc, calcium carbonate, glass fibers and other types of charges of minor use.

The basis of the recipe, which comes from the selected heterogeneous waste that will form the granule in post-consumption PP, can be modified by adding the granule with mineral fillers to vary the behavior of the polypropylene and consequently the product.

Talc is one of the most used mineral fillers in the modification of regenerated polypropylene recipes as it improves stiffness and dimensional stability, heat resistance and flow behavior.

However, there are some disadvantages to be weighed when deciding to add a polypropylene with a talc charge, in fact we have to record a decrease in resistance to impact at low temperatures, a reduction in weldability and the formation of opaque surfaces.

Calcium carbonate acts like talc but has some undisputed advantages: better dispersion capacity, better flow of the melt, greater stability to UV rays, less wear over time of the manufactured product and less cycle time during the molding phase. percentage of charges added.

Glass fibers can be mixed in the recipe in the form of flakes or cut fibers and are distinguished in short and long fibers.

Using short ones we will increase the stiffness and toughness of the product, while using the long ones they increase the resistance of the product and the sliding resistance.

However, it should be kept in mind that the very long fibers increase the anisotropic behavior due to the orientation of the fibers, with danger of distortion, opaque surfaces and greater wear of the product. To obviate the problem of distortion, a certain percentage of glass fiber spheres can be added in mixture, which contribute to increase the compressive strength and the stiffness, effectively counteracting the phenomenon of distortion.

The advantage of using glass fibers in regenerated polypropylenes is also the tendency to contribute to the reduction of the smell typical of this product family.

Other fibers, less used, are mica, which has the advantage of achieving the same rigidity of a 30% glass fiber-reinforced polypropylene with a use of 40% of mica at a lower price.

In addition, wood flour improves acoustic insulation, calcium silicates improve electrical and thermal properties, while zinc oxide protects against microorganisms and increases resistance to U.V.