- The strategic role of fragmentation in the plastic recycling supply chain
- Crushing and grinding: operational differences and impact on ground product quality
- Shredders, mills, blades and rotors: designing the controlled cutting of post-consumer polymers
- Granulometry control: size distribution, shape of the flakes and behaviour of the ground product
- Dust, blade wear and fine fraction management in the grinding process
- Flakes, process fluidity and stability of washing, drying and dosing in extrusion
- Flake size, productivity and energy: the industrial balance between cost and quality of recycled material
- From ground to melted: effects of fragmentation on rheology, degassing and final quality of the regenerated granule
How the design of shredders and mills, particle size control, fines management and energy optimisation determine the stability of washing, drying and extrusion
Essay. Post-Consumer Plastics Recycling. Chapter 8: Grinding and particle size distribution in plastics recycling
Fragmentation is one of the most crucial steps in the plastic recycling chain, not only because it reduces the size of the waste, but because it defines its processability in the subsequent stages. It is a process that does not simply “cut” the material: it turns it into an industrial element with a controlled geometry, a surface suitable for washing, and a predictable behaviour within feeding, extrusion or compounding systems.
Bottles, caps, trays, compacted films, technical components, bumpers, bins, RAEE parts: it is only through fragmentation that these objects acquire a form compatible with industrial recycling processes. Without this geometrical transformation, polymers could not be managed in a continuous, mechanised way.
Fragmentation is the stage in which the thickness, shape, mechanical inertia and size distribution of the material that will subsequently be washed (when washing is placed downstream), dried, metered and extruded are defined. In many plants, it represents the first contact of the material with an intentional mechanical force, aimed not at cleaning, sorting or separating, but at physically transforming the waste into a processable material. This step is crucial because it determines the material’s “industrial personality”: a grind that is too fine leads to dust formation and loss; one that is too coarse causes instability in dosing, difficulties in preheating and energy inefficiencies; a heterogeneous one compromises the rheological consistency of the flow in extrusion.
Fragmentation almost always takes place in two main stages:
- a primary shredding, carried out by slow- or medium-speed rotor shredders, which reduce the material into coarse pieces and handle bulky items
- a secondary grinding, carried out by high-speed knife mills, which produce grinds with a more controlled particle size distribution destined for subsequent thermal processing
The distinction between shredding and grinding is not only technical but conceptual: shredding is a phase of “controlled demolition”, in which the material is brought to a manageable size; grinding is a phase of “geometrical refinement”, in which the material is prepared for extrusion.
The former works on resistance, torque and the ability to “digest” difficult materials; the latter works on precision, shape and repeatability......© Reproduction Prohibited
