**2. Bases of disintegrator milling**

#### **2.1 Theoretical aspects of impact milling and separation in disintegrator**

In traditional grinding using traditional jaw crushers, ball mills etc., the grindable material remains between the two grinding bodies (**Figure 1a**) and will be crush by pressure or shear stresses [6]. The generated stresses in the particle are equal to or less than the strength of the material.

At traditional grinding methods, will take place uniform size reduction. The selectivity of process is low. It means that by bring weak and strong particles in the active grinding zone both, the strong and weak pieces will be broken up.

In the disintegrator, grinding occurs when piece collides with the moving working blades. This collision is an unlimited hit with some speed. The speeds used in the disintegrator range from 30 to 200 m/s [7].

At the moment of impact of the moving piece on the grinding body, an intensive wave of compression stress begins to propagate in the piece from the area of contact with the working body. The piece remains as a whole, intact during the propagation of the compression wave, until it reaches the opposite side of the piece, where it is reflected as a stretching wave of the same intensity from which the destruction of the piece to particles occurs [8]. The stresses arising in the material in this case (**Figure 1b**) exceed its strength by an order of magnitude.

*Retreatment of Polymer Wastes by Disintegrator Milling DOI: http://dx.doi.org/10.5772/intechopen.99715*

Only by impact milling in the disintegrator, i.e. at a certain speed of impact, allows to implement a mode in which a less robust piece will collapse, and a more robust (or defect - free) one will remain intact, and selective size reduction occurs. The degree of selectivity of grinding depends on the materials properties (density, strength) and on the defectivity of the material crystallographic structure. It enables to grind selectively with disintegrator mills and is suitable for processing multicomponent materials and components, like polymer composites, blends and PCBs.
