Dispersion of the Thermodynamically Immiscible Polypropylene and Ethylene—Propylene Triple Synthetic Rubber Polymer Blends Using Supercritical SEDS Process: Effect of Operating Parameters

Abstract

In this paper, we present the results of dispersion of thermodynamically immiscible polypropylene (PP) and ethylene-propylene triple synthetic rubber (EPTSR) polymer blends using the Solution-Enhanced Dispersion by Supercritical Fluid (SEDS) technique at operation conditions in the pressure range of (8 to 25) MPa and at temperatures t = 40 °C and 60 °C. The kinetics of crystallization and phase transformation in polymer blends obtained by conventional method (melt blending) and by mixing in the SEDS process have been studied using the DSC technique. The effects of the SEDS operation process on the physical—chemical (melting temperature, heat of fusion) and mechanical (microparticle size) characteristics of the SEDS-produced polymer blends were studied.

1. Introduction

The use and various technological applications of composite materials based on polymer blends is of great practical importance, since it allows to significantly expand the range of properties of polymeric materials [1,2,3,4]. Materials based on polymer blends with superior and tailored properties allow can replace basic structural materials such as reinforced concrete, metal (steel or aluminum, for example), wood, etc. Polymeric blends are widely used for technological applications due to the variety of polymers modified with reinforced fillers, the inexhaustible variability of the compositions of composites based on them, and the methods of their modification. However, most polymer blends are thermodynamically immiscible [5,6], and only a few polymer pairs form single-phase mixtures. Approximately 90% of all binary polymer blends have mutual solubility limits of no more than a few percent [7,8]. When polymer compositions are produced using conventional techniques, such as the melt blending method, a single-phase mixture can be obtained with a probability of no more than 0.05 [8].

In works [9,10], as in the present work, a mixture of PP with ethylene–propylene–diene rubber (EPDR) was used. In general, the studies on the modification of polymers with elastomers were carried out at relatively low concentrations up to about 15–20 wt%, which is associated with the heterogeneity of the resulting system. With an increase in the elastomer concentration, the filler separates from the polymer matrix, which leads to a deterioration in physical and mechanical properties [11].

Sub- and supercritical fluids are widely used in the processing of polymeric materials to tackle the problems of dispersion of polymeric materials [12,13,14,15,16,17,18,19]. There are many dispersion methods using supercritical fluid media such as RESS, SAS, GAS, SEDS, ASES, PGSS, etc. [20,21,22,23,24,25,26,27,28,29,30]. These methods make it possible to obtain homogeneous microparticles with specific physicochemical properties and sizes that are highly sensitive to the process conditions. The most promising method in the problems of mixing polymers is the SEDS method. This method is based on intensive mixing of a supercritical fluid medium with a solution of a dispersible material in an organic solvent, which leads to the desired intensification of mass transfer.

The present study is a continuation of the series publications by the authors [31,32,33] on the production of composite materials using supercritical fluid (SCF) technologies. In [31], dispersion of polymer blends of ethylene-vinyl acetate copolymers (EVAC-113 and EVAC-118), as well as PEVD-153 and EVAC-118, was carried out in order to dissolve it using the SEDS technique. In work [33], the dispersion of polymer blends of EVAC and polycarbonate was carried out. It has been established that when melt blending (conventional technology), the crystalline phase is a two-phase system of two types of crystallites formed by individual polymers (two melting peaks on the DSC diagram are present). However, when mixed by the method of supercritical fluid antisolvent (SEDS method), a mixture with increased compatibility is obtained, which exhibits only one melting peak on the DSC diagram with an increased specific heat of fusion caused by an increase in the degree of crystallinity. As a result, it was concluded that when mixing these polymers, the conventional method is not the only possible and best-suited one, and the use of the supercritical fluid antisolvent method makes it possible to obtain a new composite material with improved properties (see below). Thus, the aim of the present study is the mixing of thermodynamically immiscible PP and EPTSR polymers using a dispersion process based on the supercritical fluid anti-solvent method (SEDS technique).

2. Materials and Methods

The following polymers were used in the present study: polypropylene (PP-01030) and synthetic rubber ethylene-propylene triple (EPTSR-50). Supplier PAO “Nizhnekamskneftekhim” (Russia). Some of the physical properties of the polymers are presented in

Table 1. Physical properties of polymers used in the present study.

Polymers	Melting Temperature ${\mathit{t}}_{\mathbf{fus}}\mathbf{,}$ °C	Heat of Fusion $\mathbf{\left(}{\mathbf{\Delta }}_{\mathbf{fus}}\mathit{H}\mathbf{\right)}\mathbf{,} \mathbf{kJ}\mathbf{/}\mathbf{kg}$
PP-01030	160–168	92.3
EPTSR-50 1	Tg −50	-

¹ EPTSR-50 is amorphous material, i.e., there is no crystalline phase; T_g is the glass transition temperature.

.

Carbon dioxide with a purity of 99.9% was purchased from Tekhgazservis (Russia). Toluene (organic solvent) with a purity of 99.8% (CAS#108-88-3) was supplied by the company “Baza No. 1 of Chemical Reagents” (Russia).

Experimental Method

A schematic diagram of an experimental apparatus for the dispersion of polymer blends using the SEDS method is shown in Figure 1. A detailed description of the method, the apparatus, and the experimental procedures, can be found in our recent publication [33]. Only a brief review and essential information will be given here. The experimental apparatus consists of a system for creating, regulating, and measuring pressure; a system for measuring and controlling temperature; systems for supplying a solution of a polymer blend in an organic solvent and an antisolvent; a deposition cell (precipitation vessel); and a particle collection system.

The precipitation cell (10) is a hollow cylinder with a volume of 1000 mL. Measurements and regulations of pressure in the cell are carried out by a reference pressure gauge and a back pressure regulator (11), respectively. The polymer + organic solvent solution under study and SC-CO2 are simultaneously supplied into the cell through a coaxial nozzle (9) using plunger pumps (3,4). The coaxial design of the nozzle provides the supply of CO2 and the solution through the outer and inner holes, respectively. The flows are preheated to the desired temperature in heaters (5.6). The obtained polymer particles are captured in the lower part of the cell (10) using a metal mesh filter. The organic solvent is precipitated in the separator (12), and the carbon dioxide passes on and is released into the atmosphere.

The polymer blend obtained as a result of dispersion was analyzed by scanning electron microscopy (SEM, see below, Figure 2, Figure 3, Figure 4 and Figure 5) using an AURIGA Cross Beam instrument (Germany) with an INCA X-MAX energy dispersive spectrometer.

Polymer compositions obtained by melt blending were prepared in a mixing chamber “Measuring Mixer 350E” of Brabender mixing equipment “Plasti—Corder^® Lab-Station” (Germany). The compositions of PP and EPTSR were mixed for 3 min at a temperature of 255 °C. The rotor speed rate was 60 rpm. After being removed from the mixing chamber, the samples were passed through cold rollers and kept at room temperature for a day to relieve internal stresses. The study of the crystallization kinetics and phase transformation in mixtures of copolymers was conducted using a differential scanning calorimeter (DSC) DSC-200 TA (USA) with Pyris software (see details in [34]). The heating and cooling rates were 10 °C/min.

3. Results and Discussion

The selection of optimal thermodynamic parameters of the process of dispersion of polymer blends by the method of supercritical fluid anti-solvent is required for the study of the thermodynamic characteristics of the binary system of organic solvent+CO₂. In this work, toluene was used as the organic solvent, which is a good solvent for PP and EPTSR (see

Table 2. Solubility parameters of polymers and solvents.

Solvent/Polymer	Solubility Parameter/ (cal/cm3)1/2
Polypropylene	8.20
EPTSR	8.00
Toluene	8.97
Chloroform	9.30

). According to the theory of polymer solutions [35], the mutual solubility of the solvent (toluene or chloroform) and solute (PP and EPTSR) strongly depends on the ratio between the solubility parameter of the solvent and the solute. The closer the value of the solubility parameter of the solute to the solvent, the higher the mutual solubility of the solvent (toluene) and solute (PP and EPTSR). Table 2 provides the values of the solubility parameter of the polymers (PP and EPTSR) and potential solvents (toluene and chloroform) that are supposed to be dissolved [36]. As one can see from Table 2, toluene is the most suitable solvent for polymers (PP and EPTSR).

From the data presented in Table 2, it follows that the solubility of PP in toluene should be higher than in chloroform. The solubility of EPTSR in toluene and chloroform is almost the same. The results of the phase equilibrium (VLE, PTxy diagram) study of the CO₂–toluene binary mixture were reported in our previous publication [33] together with the reported data [37,38,39,40,41,42]. According to the VLE results, the binary CO₂–toluene mixture belongs to type I-II phase behavior, therefore, a single-phase supercritical fluid state corresponding to the SEDS dispersion method, which is supposed to be implemented at a temperature of around t = 40 °C, takes place at pressures above 8.0 MPa. Therefore, based on this result, the preferred optimal operating parameters for the implementation of the process of SEDS dispersion of PP/EPTSR polymer blends were selected (see

Table 3. Operating pressures for the process of dispersing polymer mixtures by the SEDS method at temperature of t = 40 °C (polymer’s mixture concentration in the solvent is 4 wt%, nozzle diameter is 200 μm).

No.	Polymers	P, MPa
1	PP-01030 (100%)	8
2	EPTSR-50 (100%)	8
3	PP-01030 (75%)/ EPTSR-50 (25%)	8
4	PP-01030 (75%)/ EPTSR-50 (25%)	15
5	PP-01030 (75%)/ EPTSR-50 (25%)	25
6	PP-01030 (75%)/ EPTSR-50 (25%)	15
7	PP-01030 (50%)/ EPTSR-50 (50%)	8
8	PP-01030 (25%)/ EPTSR-50 (75%)	8

).

Figure 2, Figure 3, Figure 4 and Figure 5 show SEM images (phase morphology) of the polymer blend of PP-01030 (75%)/EPTSR-50 (25%) microparticles produced at a temperature of 40 °C and 60 °C various pressures between 8 and 25 MPa.

Figure 2. SEM image (phase morphology, left) of the polymer blend microparticles with a composition of PP-01030 (75%)/EPTSR-50 (25%) and photo (right) produced by SEDS at a temperature of t = 40 °C and pressure P = 8 MPa (see Table 3, operating condition No. 3).

Figure 2. SEM image (phase morphology, left) of the polymer blend microparticles with a composition of PP-01030 (75%)/EPTSR-50 (25%) and photo (right) produced by SEDS at a temperature of t = 40 °C and pressure P = 8 MPa (see Table 3, operating condition No. 3).

Figure 3. SEM image (phase morphology, left) of the polymer blend microparticles with a composition of PP-01030 (75%)/EPTSR-50 (25%) and photo (right) produced by SEDS at a temperature of t = 40 °C and pressure P = 15 MPa (see Table 3, operating condition No. 4).

Figure 3. SEM image (phase morphology, left) of the polymer blend microparticles with a composition of PP-01030 (75%)/EPTSR-50 (25%) and photo (right) produced by SEDS at a temperature of t = 40 °C and pressure P = 15 MPa (see Table 3, operating condition No. 4).

Figure 4. SEM image (phase morphology, left) of the polymer blend microparticles with a composition of PP-01030 (75%)/EPTSR-50 (25%) and photo (right) produced by SEDS at a temperature of t = 40 °C and pressure P = 25 MPa (see Table 3, operating condition No. 5).

Figure 4. SEM image (phase morphology, left) of the polymer blend microparticles with a composition of PP-01030 (75%)/EPTSR-50 (25%) and photo (right) produced by SEDS at a temperature of t = 40 °C and pressure P = 25 MPa (see Table 3, operating condition No. 5).

Figure 5. SEM image (phase morphology, left) of the polymer blend microparticles with a composition of PP-01030 (75%)/EPTSR-50 (25%) and photo (right) produced by SEDS at a temperature of t = 60 °C and pressure P = 15 MPa (see Table 3, operating condition No. 6).

Figure 5. SEM image (phase morphology, left) of the polymer blend microparticles with a composition of PP-01030 (75%)/EPTSR-50 (25%) and photo (right) produced by SEDS at a temperature of t = 60 °C and pressure P = 15 MPa (see Table 3, operating condition No. 6).

The produced microparticles of the polymer blend with the composition of PP-01030 (75%)/EPTSR-50 (25%) have a rectangular shape with the sizes of 0.37 to 1.5 µm, depending on the operating parameters of the SEDS dispersion process.

Figure 6 shows the pressure dependence of the average particle size of the polymer blend PP-01030 (75%)/EPTSR-50 (25%) produced by SEDS dispersion process. As one can see from Figure 6, within the studied pressure range, increasing the pressure leads to increasing the average particle size. The polymer blend samples obtained by SEDS and melt blending technique were analyzed using a differential scanning calorimeter (DSC). Before studying the processes of melting and crystallization of EPTSR and PP mixtures obtained both by melt blending and the SEDS process, the melting and crystallization diagrams of the initial mixture pure components (EPTSR and PP) were analyzed.

As can be noted from Figure 7, the melting-crystallization-melting diagram (DSC scan curve, thermograms) of the initial PP polymer exhibits an intense peak at a temperature of 164.41 °C, with a heat of fusion of ${\Delta }_{\mathrm{fus}}H$ = 95.4 kJ/kg. Upon cooling, an abrupt behavior of the DSC scan curve (crystallization peak) is observed at a temperature of 116.76 °C, which corresponds to the process of PP-01030 crystallization. Upon repeated heating, the melting-crystallization-melting diagram does not change significantly, only the melting point slightly shifts to a high temperature of 166.9 °C, and the heat of fusion was ${\Delta }_{\mathrm{fus}}H$ = 94.33 kJ/kg.

The melting diagram of PP obtained by the SEDS method (condition No. 1, Table 3) is shown in Figure 8. We found the presence of only one melting peak at a temperature of 164.79 °C with a heat of fusion of ${\Delta }_{\mathrm{fus}}H$ = 99.08 kJ/kg. Upon cooling, a crystallization peak was observed with a heat of fusion of 92.79 kJ/kg at a temperature of 114.98 °C. Upon repeated heating, one melting peak was also observed at a temperature of $t_{\mathrm{fus}}$ = 161.23 °C; however, the heat of fusion decreased to 82.86 kJ/kg, which indicates a decrease in the degree of PP crystallinity.

When considering the melting-crystallization-melting diagram of the initial EPTSR polymer sample (Figure 9), two regions can be observed with a small heat releases of 1.88 kJ/kg and 0.008 kJ/kg at temperatures of 77.420 °C and 120.9 °C which may be associated with the melting of single crystalline that formed after cooling of the original EPTSR sample.

The melting-crystallization-melting diagram (DSC thermograms) of the initial EPTSR polymer sample obtained by the SEDS method (conditions No. 2, Table 3) is depicted in Figure 10. As one can see from Figure 10, one small melting peak at a temperature of 129.02 °C with a heat of fusion of 0.49 kJ/kg, which is associated with the formation of crystal structures similar to polyethylene crystallites, can be seen. This is confirmed by the melting point of the peak corresponding to low-pressure polyethylene. In this case, we observed the same melting curve behavior, with the only difference being that the melting point is 0.37 kJ/kg at a temperature of 123.23°C. It can also be noted that the DSC thermograms of the melting curves of PP and EPTSR, both initial and obtained by the SEDS method, do not change significantly. This means that the initial pure PP and EPTSR samples preparation method in this case does not affect the structure of the polymers.

The next goal of the present work was the study of the melting-crystallization-melting curves of PP/EPTSR blends produced both by melt blending and by using the SEDS methods. For this purpose, we used the polymer blends with a concentration of 25, 50, and 75 mass% of EPTSR-50. Figure 11 shows the DSC diagram of a polymer blend 25% PP + 75% EPTSR obtained by the melt blending technique. As one can see from Figure 11, we found two peaks at a temperature of 39.96°C with a small heat of fusion of 0.07 kJ/kg, related with the EPTSR phase, and at a temperature of 163.95°C with a heat of fusion of 17.5 kJ/kg, corresponding to the PP phase. However, the heat of fusion for PP component of the polymer blend is lower than the additive value of 23.07 kJ/kg. During the crystallization of the polymer blend (cooling run), two peaks can also be observed at a temperature of 112.16°C, corresponding to the PP phase, and at a temperature of 47.15°C, related to the EPTSR phase with a total heat of crystallization of 18.33 kJ/kg, which is higher than for the initial (pure) polymer. However, upon reheating the polymer’s mixture, we observed only one peak at a temperature of 163.00 °C with a heat of fusion of 16.68 kJ/kg, which is related to the PP component only.

The melting diagram of the same polymer blend (25% PP–75% EPTSR) produced by the SEDS method (conditions No. 8, Table 3) is depicted in Figure 12. As evident, two peaks can be observed: (1) a very small peak at a temperature of 71.65 ° C with a heat of fusion of 0.19 kJ/kg related to the EPTSR phase and (2) at a temperature of 162.82 °C with a heat of fusion of 22.76 kJ/kg, corresponding to the PP phase. The heat of fusion characteristic of the second peak is the additive 23.07 kJ/kg. During the crystallization (cooling run) of the polymer blend, two peaks are observed at a temperature of 107.38 °C, corresponding to the PP phase, and at a temperature of 48.72 °C, which is related to the EPTSR phase with a total heat of fusion 15.21 kJ/kg. Upon reheating the sample, only one peak was observed at a temperature of 163.61 °C with a heat of fusion of 16.93 kJ/kg, which is less than the additive one and belongs to PP phase.

Brief conclusion: Thus, it can be concluded that when blending the polymers using the SEDS method, better conditions are realized for the mixture than in the case of the melt blending technique, under which complete crystallization of the PP phase is possible, which is confirmed by the additivity of the melting heat. This is additionally confirmed by the fact that during heat treatment, the mixture acquires properties similar to those obtained by the melt blending method.

The study of the melting-crystallization-melting curve of a polymer blend of 50% PP-50% EPTSR produced by the melt blending technique (Figure 13) showed the presence of one melting peak at a temperature of 163.48 °C with a heat of fusion of 24.74 kJ/kg, corresponding to the PP phase. Moreover, the heat of fusion is significantly lower than the additive value of 46.15 kJ/kg. During the crystallization of the polymer blend, one peak is observed at a temperature of 115.6 °C, with a heat of fusion 30.19 kJ/kg, which is also related to the PP phase. At the reheating run, one peak is also observed at a temperature of 161.91 °C with a heat of fusion of 24.30 kJ/kg, which is equal to the initial value and also corresponding to the PP phase.

In the melting diagram of the same polymer blend (Figure 14) produced by the SEDS method (at condition of No. 7, Table 3), one melting peak was observed at a temperature of $t_{\mathrm{fus}}$ = 162.68 °C with a heat of fusion ${\Delta }_{\mathrm{fus}}H$ = 50.95 kJ/kg, corresponding to the PP phase. Moreover, the value of the heat of fusion ${\Delta }_{\mathrm{fus}}H$ is higher than the additive value of 46.15 kJ /kg. During the crystallization (cooling run) of the polymer blend, one peak was observed at a temperature of 114.13 °C with a heat of crystallization of 47.88 kJ/kg, which also corresponds to the PP phase. Upon reheating, just one peak is also observed at a melting temperature of $t_{\mathrm{fus}}$ = 159.74 °C with a heat of fusion of ${\Delta }_{\mathrm{fus}}H$ = 38.97 kJ/kg, which is lower than the additive value of 46.15 kJ/kg and also related to the PP phase.

Brief conclusion: Thus, for this polymer blend (50% PP–50% EPTSR) produced by the SEDS method, a more ordered structure is realized, which is confirmed by an increase in the specific heat of fusion and, therefore, an increase in the degree of crystallinity.

The study of the DSC scan curve of the third polymer blend with a composition of 75% PP–25% EPTSR showed that when mixed by melt blending technique (Figure 15), one peak is observed at a temperature of $t_{\mathrm{fus}}$ = 163.58 °C with a heat of fusion of ${\Delta }_{\mathrm{fus}}H$ = 60.51 kJ/kg corresponding to the PP phase, which is lower than the additive value of ${\Delta }_{\mathrm{fus}}{H}_{\mathrm{add}}$ = 66.22 kJ/kg. During the crystallization of the polymer blend (cooling run), one peak is observed at a temperature of 115.91 °C, with a heat of crystallization of 72.93 kJ/kg, which also corresponds to the PP phase. Upon reheating, one peak is again observed at a temperature of 161.05 °C with a heat of fusion 57.91 kJ/kg corresponding to the PP phase, which is also lower than the additive value.

The analysis of the DSC scan curve of a polymer blend with a concentration of 75% PP + 25% EPTSR (Figure 16) produced by the SEDS method (at condition No. 3, Table 3) showed the presence of one peak at a temperature of 163.47 °C with a heat of fusion 86.25 kJ/kg related to the PP phase, with the heat of fusion being significantly higher than the additive value of 66.22 kJ/kg. During the crystallization of the same polymer blend, one peak is observed at a temperature of 115.42 °C, with a heat of crystallization of 78.08 kJ/kg corresponding to the PP phase, which is lower than the initial heat of fusion. Upon reheating, one peak is again observed at a temperature of 161.11 °C with a heat of fusion 67.61 kJ/kg related to the PP phase, and the heat of fusion is almost equal to the additive value.

The details of the present results of melting-crystallization-melting diagrams (DSC scan curves) studies of PP-EPTSR polymer blends are summarized in

Table 4. Summary of the DSC scan curve results for PP +EPTSR polymer blends at operating condition of (t = 40 °C and P = 8 MPa).

Polymer Blend Composition	Melt Blending Method		Blending in the SC CO2 (SEDS Method)
	${\mathit{t}}_{\mathbf{fus}}\mathbf{,}$ °C	Total ${\mathbf{\Delta }}_{\mathbf{fus}}\mathit{H}\mathbf{,} \mathbf{kJ}\mathbf{/}\mathbf{kg}$	${\mathit{t}}_{\mathbf{fus}}\mathbf{,}$ °C	Total ${\mathbf{\Delta }}_{\mathbf{fus}}\mathit{H}\mathbf{,} \mathbf{kJ}\mathbf{/}\mathbf{kg}$
Pure PP (100%)	164.41	95.40	164.79 (one peak)	99.08
Pure EPTSR (100%)	77.42	1.88	129.02 (one peak)	0.49
PP (25%)/EPTSR (75%)	39.96 163.95 (two peaks)	17.60	71.65 162.82 (two peaks)	22.95
PP (50%)/EPTSR (50%)	163.48 (one peak)	24.74	162.68 (one peak)	50.95
PP (75%)/EPTSR (25%)	163.58 (one peak)	60.51	163.47 (one peak)	86.25

and Figure 17.

As a result, it can be stated that for a polymer blend with a sufficient content of a crystallizable polymer (PP), as well as for pure PP obtained by mixing in supercritical carbon dioxide by the SEDS method, conditions are realized that facilitate the crystallization process. The increase in the specific heat of fusion, and thus, in the degree of crystallinity, confirms that.

Thus, the phase transition temperatures of polymers during melting and crystallization runs are different to simple pure substances, for which they coincide (see above). Moreover, the melting process always occurs at a temperature above the crystallization temperature. As is well-known, to start the crystallization process, it is necessary to create a certain degree of supercooling of the polymer melt, i.e., the temperature should be below the melting temperature. In this case, the greater the temperature difference (supercooling), the higher the rate of nucleation and, accordingly, the rate of crystallization, which always occurs when using the SEDS process.

Another goal of the present work is the study of the influence of the operating parameters of the dispersion process by the SEDS method on the value of the specific heat of fusion of the studied polymer blends. Relevant data are presented in

Table 5. Influence of operating conditions of the process of dispersion (PP 75%+ EPTSR 25%) polymer blend by the SEDS method on the heat of fusion.

SEDS Process Parameters		Heat of Fusion (SEDS Method), ${\mathbf{\Delta }}_{\mathbf{fus}}\mathit{H}\mathbf{,} \mathbf{kJ}\mathbf{/}\mathbf{kg}$	Heat of Fusion (Melt Blending) ${\mathbf{\Delta }}_{\mathbf{fus}}\mathit{H}\mathbf{,} \mathbf{kJ}\mathbf{/}\mathbf{kg}$
t, oC	P, MPa
40	8	86.25	60.51
	15	75.25	60.51
	25	59.64	60.51
60	15	85.99	60.51

and depicted in Figure 18.

Based on the DSC thermograms (melting curves) studies, it can be concluded that for all polymer blends, the heat of fusion ${\Delta }_{\mathrm{fus}}H$ obtained by mixing using the SEDS method is much higher than the heat of fusion in the case of melt the blending method. For example, for the polymer blend of PP 75%/EPTSR 25% with the SEDS operating parameters of 8 MPa and 40 °C, and 15 MPa and 40 °C, the specific heat of fusion exceeds the additive values by more than 1.5 times.

We experimentally studied the effect of particle sizes on the heat of fusion ${\Delta }_{\mathrm{fus}}H$ of samples of a mixture of PP 75%+ EPTSR 25% (see Figure 19 below). Experimentally, it was observed that the heat of fusion ${\Delta }_{\mathrm{fus}}H$ of the polymer blend (PP 75% + EPTSR 25%) significantly changed when the particle size changed. With a smaller particle size of the polymer, a more perfect crystal structure (fewer defects) is formed. As the particle size increased, the crystal structure became less perfect due to an increase in the number of defects in the crystal phase. The heat of fusion ${\Delta }_{\mathrm{fus}}H$ of samples dispersed by the SEDS method was higher than the heat of fusion of the mixture obtained by the conventional method, which is equal to 60.51 kJ/kg. Reducing the particle size to 0.545 µm lead to an increase in the heat of fusion to 86.26 kJ/kg (see Figure 19).

4. Conclusions

The dispersion of polymer blends of polypropylene and ethylene-propylene triple synthetic rubber was performed in the pressure range of 8.0 to 25 MPa at temperatures of t = 40 °C and 60 °C using both the SEDS and melt blending methods. Based on the results of the melting-crystallization-melting diagrams (DSC scan curves) of the samples produced in the dispersion process, it can be concluded that for all of polymer blends with concentrations of 25, 50, and 75 wt% of PP, the heat of fusion obtained by mixing using the SEDS method is much higher than that obtained by melt blending. It can also be stated that mixing using the SEDS method leads to an increase in the degree of crystallinity and, therefore, to an improvement in the structure of the polymer matrix. The DSC thermograms of the melting curves of pure PP and EPTSR, both initial and obtained by the SEDS method, did not change significantly. However, when mixing PP and EPTSR polymers using the SEDS method, better conditions were realized for the mixture than mixing in a melt, under which complete crystallization of the PP phase is possible. For the polymer blend of (50% PP/50% EPTSR) produced by the SEDS method, a more ordered structure was realized, increasing the specific heat of fusion and, therefore, the degree of crystallinity. The pressure dependence of the average particle size of the polymer blend PP-01030/EPTSR-50 produced by the SEDS dispersion process showed that increasing the pressure leads to an increase in the average particle size.