**3.4 Treatment of blends of plastics**

Compounded plastics of the waste from electrical and electronic equipment (WEEE) subjected to recycling from dismantled personal computers (**Figure 13a**)

#### **Figure 13.**

*Compounded plastics from dismantled personal computers: (a) initial material; (b) precrushed by disintegrator DSL-158 with the specific energy of treatment ES = 1.4 kWh/t; (c) multistage milled by disintegrator DSA-2 with the specific energy of treatment ES = 20.6 kWh/t [9].*


#### **Table 4.**

*Physical and mechanical properties of the studied plastics of the WEEE at RT [9].*

are forming from processors (4 wt%), monitors (21 wt%) and keyboards (79 wt%). Physical and mechanical properties of the compounded plastics are given in **Table 4**.

Compounded plastics polycarbonate-acrylonitrile butadiene styrene (PC + ABS) and polyphenylene ether – polystyrene (PPE + PS) from monitor housings, forming 21 wt% of the monitors, were used as the compounded plastic waste.

The compounded plastics were cut into pieces and then preliminarily milled for the feed of DSA-158 (**Figure 13b**). The multistage milling (up to 16x) of the compounded plastics was performed in the DSA-2 disintegrator (**Figure 13c**). The final milling was performed in the semi-industrial disintegrator system DSL-115 with an inertial separator. The results of the preliminary and final milling of the compounded plastics from different parts of computers are given in **Table 5**. The photos of different precrushed and milled compounded plastics are given in **Figure 13b** and **c**.

Regarding the physical and mechanical properties of the plastics to be milled, the tensile strength and impact strength of the ABS plastics are lower than those of the compounded plastics PC + ABS (**Table 5**). After the fracture, the elongation of the PC + ABS plastics exceeds that of the ABS plastics for five times. These PC + ABS plastics were easy to cut with the guillotine shears for feeding the DSA-158 (100–150 mm). After the precrushing in the DSA-158, it was obvious that the material has a ductile fracture mechanism. The crushed material was appropriate for the feed of the DSA-2.

The multistage preliminary milling of the compounded material was performed by the DSA-2 disintegrator in the direct milling condition. The results of the preliminary crushing and milling of the compounded plastic PC + ABS in the disintegrator are shown in **Figure 14**.

As follows from **Table 5** and **Figure 14a**, the best results of size reduction were achieved after the two-stage preliminary milling in the DSA-158 when the mean


#### **Table 5.**

*Dependence of the milled compounded plastic powder particle medium size d50 on the disintegrator type and the specific energy of treatment ES.*

#### **Figure 14.**

*Dependence of the median particle size d50 of compound plastic PC + ABS on the specific energy of treatment ES after precrushing (a) and final multistage milling (b): 1 – PC + ABS monitor housings; 2 – ABS processors; 3 – ABS+HIPS keyboards after precrushing (a) and final multistage milling (b); 4 – PS + ABS+PPE monitor housings [9].*

particle size was about 11 mm, and after milling in the DSA-2 – particles size was about 5 mm. During the next stages of milling in DSA-2 (from stage 4 to 8), the size reduction is less effective (from 5 mm to 4 mm only). Thus, for fracturing the particles of the ductile material, the number of collisions must be more than ten.

After eight stages of preliminary milling in the DSA-2, the particle size was in the range of 4–6 mm (**Figure 13c**). The final direct milling in the DSL-115 disintegrator reduced the particle size by 40–50% (from 3.6–3.8 to 2.4–1.7 mm).


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

#### **Table 6.**

*The size, aspect and roundness of the milled PC + ABS powder fractions [9].*

As follows from **Table 6**, the shape parameters (roundness and aspect) of powder particles milled PC + ABC compounded plastics are slightly increasing when the size of particles is decreasing.

Different types of plastics have their own dynamics of size reduction with the same applied crushing energy. If this dynamics are considerably different, it is possible to separate different types of plastics during grinding from each other in one-step.

Different particle size reduction rates allow to separate soft/ductile and hard/ brittle plastics from each other in a single operation. When the viscous plastic pieces is crushed into relatively large pieces, at same time the brittle plastic pieces has time to reduce considerably in size and can be separated by a separation system (**Figures 15** and **16**).

**Figure 15.**

*Difference in particle size of the different types of plastics at the same crushing energy ES = 4.8 kWh/t: (a) sheets of material; (b) ductile (ABS); (c) brittle (PMMA) plastics (authors image).*
