**3.2 Treatment of ion exchange resins**

Ion-exchange resins (ion exchangers – ionites, IER) are polymers of spatial three-dimensional structure and are divided into cationites and anionites.

By chemical nature, ionites are high-molecular "weight" "crosslinked materials" (polymers such as phenol-formaldehyde resins or "copolymers" of styrene and divinylbenzene), having functional groups-carriers of ion-exchange catalytic properties.

Resins that exchange positive ions are called cation - exchanging (cationites), and those that exchange negatively charged ions are called anion-exchanging (anionites).

Due to the ability to reversibly exchange their ions for an equivalent amount of other ions in solution, ionites have found wide application in various fields of technology (in hydrometallurgy for the separation and purification of rare elements, in the processing of radioactive waste, in the chemical and pharmaceutical industries, to eliminate water hardness; as catalysts for organic reactions of various types: alkylation, esterification, condensation, cyanethylation, hydrolysis, etc.)

In particular, cationides with a particle size of 1.5 mm ÷ 300 μm (**Figure 5**) are widely used as a component of water purification filters, and the remains of this material can be used as a catalyst in petrochemistry, provided that at least 90% of the material has a particle size of less than 125 μm.

The study of the possibility of obtaining a cationide powder with a dimension less than 125 μm by disintegrator grinding is the topic and task of this part. To obtain such a material, it is proposed to use a disintegrator mill with a separation mode of operation. The results of separative milling is presented in **Figure 6a, b**.

**Figure 5.** *Ion exchange resin (IER): Initial granules (authors image).*

#### **3.3 Treatment of soft polyethylene**

High-density polyethylene (HDPE) is an example of thermoplastics.

Representing widespread polyethylene applications, HDPE offers excellent impact resistance, lightweight, low moisture absorption, and high tensile strength. HDPE is non-toxic with a high strength-to-density ratio. HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes, and plastic lumber.

Milling experiments to assess the grindability of HDPE (grade 277–73) were conducted in a semi-industrial disintegrator DSL-115. The parameter of grinding – the specific treatment energy *E*<sup>S</sup> – was used to estimate grindability.

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

#### **Figure 6.**

*Dependence of the particles size of the IER on the specific energy of treatment ES and the grinding scheme: (a) Direct multistep milling, (b) results of separative milling with a centrifugal separator (authors image).*

Initial HDPE granules with sizes from 1 to 10 mm were used as initial material for the following millings (**Figure 7** and **Table 2**).

The studied HDPE is difficulty to process with traditional disintegrator mills due to its plasticity, because most of the kinetic energy will be consumed in the deformation and heating of the material. However, still, there is a grinding method that allows obtaining a powder of the desired size and will turn out to be much less energy-consuming than melting.

Small particles of material are formed through low cyclic fatigue fracture, in which they peel off the surface in places of repeated plastic deformations formed during impact, therefore, this process requires a large number of impact cycles. Despite this, a fine fraction <355 μm of polyethylene can be obtained using separation grinding. It has been found that the size of the product can be adjusted within the required limits.

**Figure 7.** *HDPE particles: (a) initial; (b) disintegrator milled.*


#### **Table 2.**

*Granule size distribution of initial HDPE [9].*

The reprocessing technology of the HDPE in disintegrators consisted of two stages:


Considering that the reason for the formation of small particles of the material is low-cycle fatigue failure, and the fact that small particles peel off from large ones in the places of repeated plastic deformations formed upon impact, it was assumed

#### **Figure 8.**

*Modes for treatment of HDPE by disintegrator DSL-115: I – Direct multiple grinding; II – Direct multiple grinding of single-deformed material; III – Direct multiple grinding of repeatedly deformed material (authors image).*

#### **Figure 9.**

*Particles size and shape of HDPE after milling in DSL-115: Mode II (a – c) – Direct multiple milling at a single plastic deformation by rolls (a – 6.7 kWh/t, b – 33.5 kWh/t and c – 107.2 kWh / t; mode III (d – f) – Direct multiple milling after a multiple plastic deformation by rolls (e – Initial granules, f – Deformed by roll mill granules, g – Deformed and milled powder – 33.5 kWh/t) (authors image).*

#### **Figure 10.**

*Dependence of the average size of the HDPE particles on the specific energy of treatment ES and the grinding scheme: I, II, III – Modes of treatment (see Figure 8); ΔCE – The difference between the energy costs of different treatment modes (authors image).*

#### **Figure 11.**

*Dependence of fine fraction of crushed HDPE at different milling modes on the specific energy of treatment ES: (a) fraction 355 + 180 μm; (b) fraction <180 μm (authors image).*

that a preliminarily strongly plastically deformed material could exhibit the property of easier formation of small particles. It is proposed to preliminarily pass the raw material through the rollers. The testing scheme will look like this in **Figure 8**.

Particle size and shape are given in **Figure 9**. The dependence of the particle size of multiple direct milling on the specific energy of treatment *E*<sup>S</sup> is shown in **Figures 10** and **11**. Dependence of particle size at separative milling on the specific energy of treatment *E*<sup>S</sup> is given in **Table 3**.

The production of powders of a given fine fraction is a process with an energy consumption of the order of *E*<sup>S</sup> = 450 … 1350 kWh/t of specific energy of treatment and total energy *E* = 700 … 2200 kWh/t, depending on the separation mode.

A specific problem, arising at milling is the heating of the material during processing (on average 0.25 C° / kWh/t), which significantly reduces productivity. Possible options for solution of problem and increasing productivity may be:


**Table 3.**

*HDPE powder particles distribution at disintegrator milling DSL-115 with an inertial (IC) and centrifugal (CC) classifiers.*

	- a. air cooling (open-loop system of inertial or centrifugal separation, when air after separation of fine material does not return back to the working chamber) or
	- b. adding water or dry ice to the material or
	- c. pre-cooling of polyethylene in liquid nitrogen (perhaps the most effective option, which can notably increase the productivity of milling by an order of magnitude, since it will lead to embrittlement of a viscous particles).

**Figure 12.**

*Shear crushing of HDPE by the SD-25 with the gap of the cones: (a) 1 mm; (b) 0.5 mm (authors image).*
