*Review* **Influence of the Polarity of the Plasticizer on the Mechanical Stability of the Filler Network by Simultaneous Mechanical and Dielectric Analysis**

**Sahbi Aloui 1,\* , Horst Deckmann 1 , Jürgen Trimbach 2 and Jorge Lacayo-Pineda 3**

**Abstract:** Four styrene butadiene rubber (SBR) compounds were prepared to investigate the influence of the plasticizer polarity on the mechanical stability of the filler network using simultaneous mechanical and dielectric analysis. One compound was prepared without plasticizer and serves as a reference. The other three compounds were expanded with different plasticizers that have different polarities. Compared with an SBR sample without plasticizer, the conductivity of mechanically unloaded oilextended SBR samples decreases by an order of magnitude. The polarity of the plasticizer shows hardly any influence because the plasticizers only affect the distribution of the filler clusters. Under static load, the dielectric properties seem to be oil-dependent. However, this behavior also results from the new distribution of the filler clusters caused by the mechanical damage and supported by the polarity grade of the plasticizer used. The Cole–Cole equation affirms these observations. The Cole–Cole relaxation time τ and thus, the position of maximal dielectric loss increases as the polarity of the plasticizer used is also increased. This, in turn, decreases the broadness parameter α implying a broader response function.

**Keywords:** plasticizer; polarity; carbon black network; simultaneous mechanical and dielectric analysis; mechanical stability

## **1. Introduction**

Plasticizers are a widely used additive in rubber compounds [1–4]. They are particularly important and, as the third-highest ingredient in terms of content level, come in right after rubber and fillers. As processing aids, the plasticizers are added in different concentrations in order to impart rubber products with the desired elastic properties in the operating temperature range [5–10].

As a fluid component, the plasticizer migrates in the rubber matrix and its macromolecules are integrated into the polymer chains through intermolecular interactions. Consequently, the intermolecular forces of the polymer chains and the number of free valences in the three-dimensional structure are reduced. The internal space between the polymer chains is thus larger, and the free volume that allows the polymer chains to flow above their glass transition temperature increases [11–15]. This new conformation of the polymer chains, in turn, increases their mobility and enhances the filler distribution in the rubber mixture [16–21]. Above a certain percolation threshold, a filler network is formed that reinforces the rubber compounds and provides the necessary mechanical stability [16,17]. This applies to both the carbon-based fillers such as carbon black and silica [18–21]. Indeed, the plasticizer type strongly affects the mechanical properties of rubber products due to a shift in the glass transition temperature. Consequently, the strain, the mechanical stress, the modulus of elasticity and the damping behavior change [22–24].

**Citation:** Aloui, S.; Deckmann, H.; Trimbach, J.; Lacayo-Pineda, J. Influence of the Polarity of the Plasticizer on the Mechanical Stability of the Filler Network by Simultaneous Mechanical and Dielectric Analysis. *Polymers* **2022**, *14*, 2126. https://doi.org/10.3390/ polym14102126

Academic Editors: Radek Stoˇcek, Gert Heinrich and Reinhold Kipscholl

Received: 7 April 2022 Accepted: 27 April 2022 Published: 23 May 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Furthermore, the dielectric properties of rubber samples filled with electrically conductive filler depend on the structure of its filler network [25–32]. This applies to filler networks made of electrically conductive fillers such as carbon-based carbon black or hybrid filler networks, provided that at least one electrically conductive filler is present [25–28]. The nonconductive component is mainly used because of its excellent mechanical reinforcement, as is the case with silica used in dynamic systems such as car tires [29–32]. Aloui et al. have shown that mechanically induced changes in the structure of the electrically conductive filler network have a direct impact on dielectric mechanisms such as charge transport and polarization [33,34]. These, in turn, have consequences for the dielectric constant and the dielectric conductivity of rubber samples [35–39].

The direct relationship between mechanical and dielectric properties makes simultaneous mechanical and dielectric analysis of rubber samples filled with electrically conductive filler an outstanding technique for opening up new horizons in evaluating the microstructure dynamics of rubber materials under mechanical load and hence reproducing authentic situations from operation modes [40–43]. In addition to quality measurements on test samples, examinations on installed end products can also be guaranteed if sensors are installed to record the current material properties during use and to monitor them in the subsequent step. Mainly the dielectric properties are used as a response to the mechanical load [44].

In this study, the influence of the polarity of the plasticizer on the mechanical behavior of carbon black filled SBR under static loading is investigated. It is about the dynamics of the reinforcing filler network under mechanical loading and how this behavior can be described with simple material models. This study serves to understand the usage process and opens up the possibility of describing dynamic systems such as tires or seals during application. The electrical response is used as the display variable.

In this study, the influence of the plasticizer on the dielectric response of carbon black filled SBR under static load is examined, particularly with respect to the polarity of the plasticizer. The simultaneous dynamic-mechanical and dielectric analyzer DiPLEXOR® 500 N from NETZSCH-Gerätebau in Ahlden, Germany is used for this purpose.

#### **2. Excursus: Dielectric Relaxation in Elastomers**

Dielectric relaxation describes the build-up of the electric polarization of a dielectric medium after application of an external electric field. The characterization of the dielectric relaxation is based on the measurement of the variation of the permittivity as a function of frequency. The permittivity stems from dipole orientation and transport of free charge carriers under the action of an electric field. The measuring method uses capacitance measurements as a function of frequency for a sample placed between two electrodes. An extensive explanation of the phenomenon and the measurement technology can be found in [45].

The permittivity *ε* ∗ is a complex function with the real part *ε* 0 and the imaginary part *ε* 00 , also known as dielectric loss. As is typical for elastomers, not all dipoles have the same relaxation time, but different relaxation times, which exhibit a distribution with a relaxation peak. In order to describe these types of relaxation correctly, there are various empirical models derived from the Debye equation. In the case of symmetrical frequency response, the Cole–Cole approach is mainly used for amorphous dielectrics [46]. According to the Cole–Cole equation,

$$
\varepsilon^\*(\omega) = \varepsilon\_{\text{inf}} + \frac{\Delta \varepsilon}{1 + \left(i\omega\tau\right)^a} \text{ with } 0 < a \le 1 \tag{1}
$$

where *ε*inf is the infinite frequency dielectric permittivity, ∆*ε* is the relaxation strength, *α* is the broadness parameter and *τ* is the Cole–Cole relaxation time. *ω* = 2*π f*el is the angular frequency and *f*el is the electrical frequency. The expressions of *ε* 0 and *ε* 00 take the following form:

$$\varepsilon'(\omega) = \varepsilon\_{\text{inf}} + \Delta \varepsilon \frac{1 + (\omega \tau)^a \cos\left[a\frac{\pi}{2}\right]}{1 + 2(\omega \tau)^a \cos\left[a\frac{\pi}{2}\right] + (\omega \tau)^{2a}} \tag{2}$$

And

And

the following form:

$$\varepsilon''(\omega) = \frac{\sigma\_{dc}}{\omega \varepsilon\_0} + \Delta \varepsilon \cdot \frac{\left(\omega \tau\right)^{\alpha} \sin\left[a\frac{\pi}{2}\right]}{1 + 2\left(\omega \tau\right)^{\alpha} \cos\left[a\frac{\pi}{2}\right] + \left(\omega \tau\right)^{2\alpha}}\tag{3}$$

1 ሺሻఈ cos ቂ

1 2ሺሻఈ cos ቂ

2ቃ

2ቃ ሺሻଶఈ (2)

where *σdc* is the direct current conductivity or DC conductivity [33,34]. where ௗ is the direct current conductivity or DC conductivity [33,34].

*Polymers* **2022**, *14*, x FOR PEER REVIEW 3 of 16

ሺሻ ൌ ୧୬ Δ ∙

ᇱ

#### **3. Materials 3. Materials**

Four carbon black filled SBR based compounds were prepared at Hansen and Rosenthal KG in Hamburg, Germany. The carbon black N 330 was used at a filler concentration of 60 phr. For a reference sample, no plasticizer was added. The three other samples each contain 20 phr of one plasticizer grade, which differ by polarity. Of course, the good miscibility of the plasticizers in the rubber matrix must be taken into account. Therefore, the following plasticizers are used: The plasticizers used are a paraffinic base oil (SN400), mild extraction solvate (MES) and distillate aromatic extract (DAE). Figure 1 shows the structural formula of the plasticizers with different polarities used [47]. Four carbon black filled SBR based compounds were prepared at Hansen and Rosenthal KG in Hamburg, Germany. The carbon black N 330 was used at a filler concentration of 60 phr. For a reference sample, no plasticizer was added. The three other samples each contain 20 phr of one plasticizer grade, which differ by polarity. Of course, the good miscibility of the plasticizers in the rubber matrix must be taken into account. Therefore, the following plasticizers are used: The plasticizers used are a paraffinic base oil (SN400), mild extraction solvate (MES) and distillate aromatic extract (DAE). Figure 1 shows the structural formula of the plasticizers with different polarities used [47].

angular frequency and ୣ୪ is the electrical frequency. The expressions of ᇱ and ᇱᇱ take

**Figure 1.** Structural formula of plasticizers SN400, MES and DAE. **Figure 1.** Structural formula of plasticizers SN400, MES and DAE.

Plasticizers SN400, MES and DAE have an aniline point in accordance with DIN ISO 2977 at 101 °C, 84 °C and 43 °C [47]. The aniline point is the temperature at which a homogeneous mixture of equal volumes of aniline and plasticizer separates into 2 phases during the cooling process. The degree of miscibility of aniline with the plasticizer estimates the aromatic content in the plasticizer. The lower the aniline point, the more polar the plasticizer. Plasticizers SN400, MES and DAE have an aniline point in accordance with DIN ISO 2977 at 101 ◦C, 84 ◦C and 43 ◦C [47]. The aniline point is the temperature at which a homogeneous mixture of equal volumes of aniline and plasticizer separates into 2 phases during the cooling process. The degree of miscibility of aniline with the plasticizer estimates the aromatic content in the plasticizer. The lower the aniline point, the more polar the plasticizer.

The solubility parameter *δ* is an indicator of the miscibility quality of the various plasticizers within the SBR matrix. SN400, MES and DAE have a solubility parameter *δ* of 16 MPa1/2, 16.7 Mpa1/2 and 18.5 Mpa1/2. With a value of 17.2 Mpa1/2, the solubility parameter *δ* for SBR is in the same range as for the plasticizers, implying a good compatibility [47].

The aniline point and the solubility parameter are shown in Figure 2.

compatibility [47].

The aniline point and the solubility parameter are shown in Figure 2.

The solubility parameter is an indicator of the miscibility quality of the various plasticizers within the SBR matrix. SN400, MES and DAE have a solubility parameter of 16 MPa1/2, 16.7 Mpa1/2 and 18.5 Mpa1/2. With a value of 17.2 Mpa1/2, the solubility parameter for SBR is in the same range as for the plasticizers, implying a good

**Figure 2.** Aniline point and solubility parameter of the plasticizers. **Figure 2.** Aniline point and solubility parameter of the plasticizers.

The compound formulation is shown in Table 1. The compound formulation is shown in Table 1.

**Table 1.** Compound formulation in phr.

Sulphur 1.5 1.5 1.5 1.5 The antioxidants 2,2,4‐Trimethyl‐1,2‐dihydrochinolin (TMQ) and N‐(1.3‐Dimethylbutyl)‐N′‐ phenyl‐p‐phenylenediamine (6PPD) were added at a concentration of 1 phr. The samples were The antioxidants 2,2,4-Trimethyl-1,2-dihydrochinolin (TMQ) and N-(1.3-Dimethylbutyl)-N0 -phenyl-pphenylenediamine (6PPD) were added at a concentration of 1 phr. The samples were sulfur-vulcanized. In addition to sulfur, the vulcanization accelerators N-cyclohexyl-2-benzothiazolesulfenamide (CBS) and Dimethyldiphenylthiuram disulfide (DDTD) were used.

#### sulfur‐vulcanized. In addition to sulfur, the vulcanization accelerators N‐cyclohexyl‐2‐ benzothiazolesulfenamide (CBS) and Dimethyldiphenylthiuram disulfide (DDTD) were used. **4. Methods**

#### *4.1. Dielectric Analysis*

**4. Methods** *4.1. Dielectric Analysis* Purely dielectric measurements were carried out at room temperature using the broadband dielectric spectrometer BDS from Novocontrol in Montabaur, Germany. The mechanical load was infinitesimally small, and it only served to maintain contact between the SBR samples and the electrodes. The coin-shape samples had a diameter of 30 mm and a thickness of 0.1 to 0.3 mm. The applied sinusoidal alternating voltage had an amplitude of 3V. The electrical frequency ranged between 1 Hz and 1 MHz.

#### *4.2. Simultaneous Mechanical and Dielectric Analysis*

Simultaneous mechanical and dielectric analysis were performed on the DiPLEXOR 500 N of NETZSCH-Gerätebau in Ahlden, Germany. The DiPLEXOR 500 N is the result of coupling the EPLEXOR 500 N dynamic-mechanical analyzer with the broadband dielectric spectrometer BDS from Novocontrol in Montabaur, Germany. Coin-shaped samples with a diameter of 10 mm and thickness of around 2 mm were used. The measurements were carried out at room temperature applying a static force of 10 N and a sinusoidal alternating voltage with an amplitude of 1 V. The electrical frequency ranged between 1 Hz and 1 MHz.

Three measurements were performed to confirm the validity of the results. However, only one measurement is shown to represent the overall result.

#### **5.

The physical mechanisms behind the dielectric response of carbon black filled elastomers are based on the electrical frequency of the electrical alternating field applied. In the frequency range between 1 Hz and 1 MHz, the free charge carriers can be transported along the electric field lines. This conduction mechanism, described by the dielectric conductivity *σ* ∗ , is initially frequency-independent and reaches a constant plateau value, known as direct current conductivity or DC conductivity, abbreviated *σdc*. This is the result of phase-equal change in the electric field and the sample polarization. From a material-dependent frequency threshold, *σ* ∗ becomes frequency-dependent because the change in electric field and the change in sample polarization become time-delayed. This dielectric dispersion is caused by additional relaxation processes which come into play. This part is known as AC conductivity.

Furthermore, the present dipoles in the SBR materials are oriented along the electric field lines. Orientation polarization arises. Depending on the sample thickness, the applied electric field can also lead to accumulation of dipoles at the interfaces, also known as interface polarization. Both polarization mechanisms are described by the permittivity *ε* ∗ .

#### *5.1. Dielectric Analysis*

Purely dielectric measurements on the SBR samples are performed at room temperature without mechanical load. This serves first to determine the contribution of the different components to the dielectric response without the influence of static load. The measurements are performed on SBR samples with a thickness of 0.1 to 0.3 mm. Figure 3 shows the frequency-dependent change in the real part of the conductivity *σ* 0 of the SBR samples with and without plasticizers. *Polymers* **2022**, *14*, x FOR PEER REVIEW 6 of 16

**Figure 3.** Frequency‐dependent change of the real part of the conductivity ᇱ of SBR samples with different plasticizers at 25 °C. **Figure 3.** Frequency-dependent change of the real part of the conductivity *σ* 0 of SBR samples with different plasticizers at 25 ◦C.

covered by the free charge carriers along the electric field lines become longer.

For the SBR samples with 20 phr MES, ௗ is 5.8 × 10−5 S/cm.

*5.2. Simultaneous Mechanical and Dielectric Analysis*

the SBR samples with and without plasticizers.

Figure 3 indicates that the real part of the conductivity ᇱ of the SBR sample without plasticizer hardly shows any changes within the frequency range of the measurements. A direct current conductivity ௗ of 4.8 × 10−4 S/cm is recorded. It is to note that this high

The oil‐extended SBR samples show at least two disparities compared with the SBR sample without plasticizer. First, the real part of the conductivity ᇱ is from an electrical frequency of 100 kHz frequency‐dependent, regardless of the polarity of the plasticizer used. ᇱ increases with increasing frequency. Second, the direct current conductivity ௗ becomes smaller. It is 7 × 10−5 S/cm for the SBR samples with 20 phr SN400 and DAE.

In this context, it is worthy to note that the polarity of the plasticizer has no big influence on the conductivity. The addition of plasticizer has only influenced the distribution of the filler clusters within the rubber matrix. As a result, the distances

Dielectric measurements on the SBR samples are carried out at room temperature under a static force of 10 N. The latter corresponds to a mechanical stress of 0.127 MPa. Figure 4 shows the frequency‐dependent change in the real part of the conductivity ᇱ of

At a filler concentration of 60 phr, the mechanical percolation threshold is exceeded, resulting in a network of interconnected filler clusters. The contribution of polymer chains to the conductivity of SBR samples is approximately ten orders of magnitude less.

Figure 3 indicates that the real part of the conductivity *σ* 0 of the SBR sample without plasticizer hardly shows any changes within the frequency range of the measurements. A direct current conductivity *σdc* of 4.8 × 10−4 S/cm is recorded. It is to note that this high conductivity in carbon black filled rubber is clearly related to the carbon black network. At a filler concentration of 60 phr, the mechanical percolation threshold is exceeded, resulting in a network of interconnected filler clusters. The contribution of polymer chains to the conductivity of SBR samples is approximately ten orders of magnitude less.

The oil-extended SBR samples show at least two disparities compared with the SBR sample without plasticizer. First, the real part of the conductivity *σ* 0 is from an electrical frequency of 100 kHz frequency-dependent, regardless of the polarity of the plasticizer used. *σ* 0 increases with increasing frequency. Second, the direct current conductivity *σdc* becomes smaller. It is 7 × 10−5 S/cm for the SBR samples with 20 phr SN400 and DAE. For the SBR samples with 20 phr MES, *σdc* is 5.8 × 10−5 S/cm.

In this context, it is worthy to note that the polarity of the plasticizer has no big influence on the conductivity. The addition of plasticizer has only influenced the distribution of the filler clusters within the rubber matrix. As a result, the distances covered by the free charge carriers along the electric field lines become longer.

#### *5.2. Simultaneous Mechanical and Dielectric Analysis*

Dielectric measurements on the SBR samples are carried out at room temperature under a static force of 10 N. The latter corresponds to a mechanical stress of 0.127 MPa. Figure 4 shows the frequency-dependent change in the real part of the conductivity *σ* 0 of the SBR samples with and without plasticizers. *Polymers* **2022**, *14*, x FOR PEER REVIEW 7 of 16

**Figure 4.** Frequency‐dependent change in the real part of the conductivity ᇱ of SBR samples with different plasticizers at 24 °C under a static force of 10 N. **Figure 4.** Frequency-dependent change in the real part of the conductivity *σ* 0 of SBR samples with different plasticizers at 24 ◦C under a static force of 10 N.

Figure 4 shows a completely different picture than Figure 3. This has to do with the different geometries of the test specimens and the applied contact forces. The simultaneous mechanical and dielectric analyses were performed on 2‐mm‐thick SBR samples with a contact force of 10 N. The purely dielectric measurements were performed on SBR samples with a thickness of 0.1 to 0.3 mm and a contact force in the mN range. It is therefore not possible to readily perform a direct comparison of the absolute measured Figure 4 shows a completely different picture than Figure 3. This has to do with the different geometries of the test specimens and the applied contact forces. The simultaneous mechanical and dielectric analyses were performed on 2-mm-thick SBR samples with a contact force of 10 N. The purely dielectric measurements were performed on SBR samples with a thickness of 0.1 to 0.3 mm and a contact force in the mN range. It is therefore not possible to readily perform a direct comparison of the absolute measured values.

The real part of the conductivity ᇱ becomes frequency‐dependent for all SBR samples independently of the plasticizer content. The characteristic frequency between

For the SBR sample without plasticizer, the application of a static force of 10 N reduces ௗ from 4.8 × 10−4 S/cm to 1.4 × 10−4 S/cm. This is due to the mechanical damage that reduces the density of the conduction paths within the carbon black network, and

For the SBR samples with plasticizer, the polarity of the plasticizer used strongly influences the conductivity. ௗ is 10−4 S/cm for the SBR sample with 20 phr SN400, 7.7 × 10−5 S/cm for the SBR sample with 20 phr MES and 2.7 × 10−5 S/cm for the SBR sample with 20 phr DAE. It is obvious that increasing the polarity of the plasticizer used decreases ௗ. The AC conductivity, abbreviated , is the frequency‐dependent part of ᇱ at which the change in the electric field and the change in sample polarization are time‐ delayed. The curve shape of for the different SBR samples also suggests that the polarity of the plasticizer used has a huge influence on the relaxation processes caused by

However, as mentioned in the previous section, the polarity has no influence on the conductivity. It strongly affects the distribution of the filler clusters within the rubber

The difference in DC conductivity ௗ between the mechanically undamaged (without mechanical load) and damaged (static force of 10 N) SBR samples is illustrated

values.

plasticizer.

thus the SBR samples.

this dielectric dispersion.

matrix.

in Figure 5.

The real part of the conductivity *σ* 0 becomes frequency-dependent for all SBR samples independently of the plasticizer content. The characteristic frequency between the DC and AC conductivity shifts towards lower frequencies with the addition of the plasticizer.

For the SBR sample without plasticizer, the application of a static force of 10 N reduces *σdc* from 4.8 × 10−4 S/cm to 1.4 × 10−4 S/cm. This is due to the mechanical damage that reduces the density of the conduction paths within the carbon black network, and thus the SBR samples.

For the SBR samples with plasticizer, the polarity of the plasticizer used strongly influences the conductivity. *σdc* is 10−4 S/cm for the SBR sample with 20 phr SN400, 7.7 × 10−5 S/cm for the SBR sample with 20 phr MES and 2.7 × 10−5 S/cm for the SBR sample with 20 phr DAE. It is obvious that increasing the polarity of the plasticizer used decreases *σdc*.

The AC conductivity, abbreviated *σac*, is the frequency-dependent part of *σ* 0 at which the change in the electric field and the change in sample polarization are time-delayed. The curve shape of *σac* for the different SBR samples also suggests that the polarity of the plasticizer used has a huge influence on the relaxation processes caused by this dielectric dispersion.

However, as mentioned in the previous section, the polarity has no influence on the conductivity. It strongly affects the distribution of the filler clusters within the rubber matrix. *Polymers* **2022**, *14*, x FOR PEER REVIEW 8 of 16

> The difference in DC conductivity *σdc* between the mechanically undamaged (without mechanical load) and damaged (static force of 10 N) SBR samples is illustrated in Figure 5.

**Figure 5.** Difference in DC conductivity ௗ between the mechanically not damaged (without static **Figure 5.** Difference in DC conductivity *σdc* between the mechanically not damaged (without static load) and damaged (static force of 10 N) SBR samples.

Figure 5 shows that ௗ of the undamaged SBR samples is only affected by the presence of plasticizer, and not by the polarity of the plasticizer used. In contrast, ௗ of the mechanically loaded and hence damaged SBR samples seems to be indirectly influenced by the polarity of the plasticizer used. In fact, the use of plasticizer influences Figure 5 shows that *σdc* of the undamaged SBR samples is only affected by the presence of plasticizer, and not by the polarity of the plasticizer used. In contrast, *σdc* of the mechanically loaded and hence damaged SBR samples seems to be indirectly influenced by the polarity of the plasticizer used. In fact, the use of plasticizer influences the inner structure of the SBR samples by generating new dispersion states following the mechanical load.

the inner structure of the SBR samples by generating new dispersion states following the mechanical load. In order to examine the impact of the plasticizer and its polarity on the dispersive part of the conductivity , it is more convenient to consider the global dielectric response of the SBR samples, expressed in terms of permittivity. In addition to conductivity, relaxation processes are taken into account. Figures 6 and 7 show the change In order to examine the impact of the plasticizer and its polarity on the dispersive part of the conductivity *σac*, it is more convenient to consider the global dielectric response of the SBR samples, expressed in terms of permittivity. In addition to conductivity, relaxation processes are taken into account. Figures 6 and 7 show the change in the real and imaginary part of the permittivity, *ε* 0 and *ε* 00 of SBR samples with different plasticizers at 24 ◦C under a static force of 10 N.

in the real and imaginary part of the permittivity, ᇱ and ᇱᇱ of SBR samples with

different plasticizers at 24 °C under a static force of 10 N.

load) and damaged (static force of 10 N) SBR samples.

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**Figure 6.** Frequency‐dependent change in the real part of the permittivity ᇱ of SBR samples with different plasticizers at 24 °C under a static force of 10 N. **Figure 6.** Frequency-dependent change in the real part of the permittivity *ε* 0 of SBR samples with different plasticizers at 24 ◦C under a static force of 10 N. **Figure 6.** Frequency‐dependent change in the real part of the permittivity ᇱ of SBR samples with different plasticizers at 24 °C under a static force of 10 N.

**Figure 7.** Frequency‐dependent change in the imaginary part of the permittivity ᇱᇱ of SBR samples **Figure 7.** Frequency‐dependent change in the imaginary part of the permittivity ᇱᇱ of SBR samples with different plasticizers at 24 °C under a static force of 10 N. **Figure 7.** Frequency-dependent change in the imaginary part of the permittivity *ε* 00 of SBR samples with different plasticizers at 24 ◦C under a static force of 10 N.

#### *5.3. Cole–Cole Relaxation Model 5.3. Cole–Cole Relaxation Model*

*5.3. Cole–Cole Relaxation Model* To determine the dielectric relaxation in the SBR samples, the real and imaginary part of the permittivity ᇱ and ᇱᇱ are simultaneously fitted with the Equations (2) and (3) according to the Cole–Cole approach. With these basic equations, an own fitting program was developed, which simultaneously fits the real and imaginary part of the permittivity. To determine the dielectric relaxation in the SBR samples, the real and imaginary part of the permittivity ᇱ and ᇱᇱ are simultaneously fitted with the Equations (2) and (3) according to the Cole–Cole approach. With these basic equations, an own fitting program was developed, which simultaneously fits the real and imaginary part of the permittivity. To determine the dielectric relaxation in the SBR samples, the real and imaginary part of the permittivity *ε* 0 and *ε* 00 are simultaneously fitted with the Equations (2) and (3) according to the Cole–Cole approach. With these basic equations, an own fitting program was developed, which simultaneously fits the real and imaginary part of the permittivity. Figure 8 displays the behavior of *ε* 0 and *ε* 00 at 24 ◦C under a static force of 10 N. The SBR sample filled with 20 phr MES is shown as representative for all other SBR samples.

with different plasticizers at 24 °C under a static force of 10 N.

Figure 8 displays the behavior of ᇱ and ᇱᇱ at 24 °C under a static force of 10 N. The SBR sample filled with 20 phr MES is shown as representative for all other SBR samples.

Figure 8 displays the behavior of ᇱ and ᇱᇱ at 24 °C under a static force of 10 N. The SBR sample filled with 20 phr MES is shown as representative for all other SBR samples.

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**Figure 8.** Simultaneous Cole–Cole fitting of real and imaginary part of the permittivity ᇱ and ᇱᇱ of SBR sample filled with 20 phr MES at 24 °C under a static force of 10 N. **Figure 8.** Simultaneous Cole–Cole fitting of real and imaginary part of the permittivity *ε* 0 and *ε* 00 of SBR sample filled with 20 phr MES at 24 ◦C under a static force of 10 N. **Figure 8.** Simultaneous Cole–Cole fitting of real and imaginary part of the permittivity ᇱ and ᇱᇱ of SBR sample filled with 20 phr MES at 24 °C under a static force of 10 N.

Figure 8 suggests a good fitting quality for the measurement data of the SBR sample filled with 20 phr MES at 24 °C under a static force of 10 N. The fitting parameters are displayed on the inset. Hereinafter, the individual fitting parameters related to all SBR samples are presented. Figure 9 first shows the Cole–Cole relaxation time . Figure 8 suggests a good fitting quality for the measurement data of the SBR sample filled with 20 phr MES at 24 ◦C under a static force of 10 N. The fitting parameters are displayed on the inset. Hereinafter, the individual fitting parameters related to all SBR samples are presented. Figure 9 first shows the Cole–Cole relaxation time *τ*. Figure 8 suggests a good fitting quality for the measurement data of the SBR sample filled with 20 phr MES at 24 °C under a static force of 10 N. The fitting parameters are displayed on the inset. Hereinafter, the individual fitting parameters related to all SBR samples are presented. Figure 9 first shows the Cole–Cole relaxation time .

**No oil SN400 MES DAE Figure 9.** Cole–Cole relaxation time of the SBR samples determined by means of simultaneous **Figure 9.** Cole–Cole relaxation time *τ* of the SBR samples determined by means of simultaneous mechanical and dielectric measurements at 24 ◦C under a static force of 10 N.

**Figure 9.** Cole–Cole relaxation time of the SBR samples determined by means of simultaneous

mechanical and dielectric measurements at 24 °C under a static force of 10 N. The Cole–Cole relaxation time *τ* gives the position of maximal dielectric loss. Figure 9 shows that *τ* increases as the polarity of the plasticizer used increases. *τ* is related to a characteristic electrical frequency of maximal loss *f*el according to *τ* = 1/(2*π f*el). Increasing *τ* means a decrease in the characteristic electrical frequency of maximal loss *f*el. This

mechanical and dielectric measurements at 24 °C under a static force of 10 N.

resembles the results shown in Figure 4, in which the frequency limit between DC and AC conductivity shifts to lower frequencies with higher polarity. DC and AC conductivity shifts to lower frequencies with higher polarity. In the following, Figure 10 illustrates the broadness parameter of the SBR

The Cole–Cole relaxation time gives the position of maximal dielectric loss. Figure 9 shows that increases as the polarity of the plasticizer used increases. is related to a characteristic electrical frequency of maximal loss ୣ୪ according to ൌ 1⁄ሺ2ୣ୪ሻ . Increasing means a decrease in the characteristic electrical frequency of maximal loss ୣ୪. This resembles the results shown in Figure 4, in which the frequency limit between

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In the following, Figure 10 illustrates the broadness parameter *α* of the SBR samples determined by means of simultaneous mechanical and dielectric measurements at 24 ◦C under a static force of 10 N. samples determined by means of simultaneous mechanical and dielectric measurements at 24 °C under a static force of 10 N.

mechanical and dielectric measurements at 24 °C under a static force of 10 N.

**Figure 10.** Broadness parameter of the SBR samples determined by means of simultaneous **Figure 10.** Broadness parameter *α* of the SBR samples determined by means of simultaneous mechanical and dielectric measurements at 24 ◦C under a static force of 10 N.

In contrast to the Debye model where the broadness parameter equals one, Figure 10 shows that all values for SBR samples are less than one. This indicates a symmetrically broad loss peak. Furthermore, decreases as the polarity of the plasticizer used is increased, implying a broader response function. This behavior is caused by the interaction of the dipoles with each other, inducing a dispersion of the relaxation time . In physical terms, the dipoles participating in the relaxation phenomenon do not have the same relaxation time. Most probably this behavior is promoted by the polarity of the In contrast to the Debye model where the broadness parameter *α* equals one, Figure 10 shows that all *α* values for SBR samples are less than one. This indicates a symmetrically broad loss peak. Furthermore, *α* decreases as the polarity of the plasticizer used is increased, implying a broader response function. This behavior is caused by the interaction of the dipoles with each other, inducing a dispersion of the relaxation time *τ*. In physical terms, the dipoles participating in the relaxation phenomenon do not have the same relaxation time. Most probably this behavior is promoted by the polarity of the plasticizer, since the more polar the plasticizer, the more dipoles are available.

plasticizer, since the more polar the plasticizer, the more dipoles are available. Figure 11 depicts the infinite‐frequency dielectric permittivity ୧୬ of the SBR samples determined by means of simultaneous mechanical and dielectric measurements Figure 11 depicts the infinite-frequency dielectric permittivity *ε*inf of the SBR samples determined by means of simultaneous mechanical and dielectric measurements at 24 ◦C under a static force of 10 N. *ε*inf = lim*ω*→∞ *ε* 0 (*ω*) is also known as the high frequency permittivity.

at 24 °C under a static force of 10 N. ୧୬ ൌ limఠ→ஶ ᇱ ሺሻ is also known as the high frequency permittivity. Figure 11 shows that *ε*inf seems to depend on the presence of plasticizer within the SBR samples rather than the type of plasticizer. The doubling of the high frequency permittivity *ε*inf for the oil-extended SBR samples as compared to the SBR sample without plasticizer can be attributed to the increase in dead ends caused by the mechanical damage of the filler network and the presence of additional polar molecules. Locally, more polar regions arise and permittivity increases.

The last parameter according to the Cole–Cole Equation (1) is the relaxation strength ∆ε and it is shown in Figure 12.

The relaxation strength ∆*ε* shown in Equation (1) is the difference between the static dielectric permittivity *ε*S = lim *ω*→0 *ε* 0 (*ω*), also known as low frequency permittivity, and *ε*inf. ∆*ε* = *ε*S − *ε*inf gives the contribution of the orientation polarization to the dielectric function and evaluates the mean molecular dipole moment on the conditions that the present dipoles do not interact with each other and shielding effects are insignificant [19]. Since this is not the case for the SBR samples, no reliable conclusions can be drawn in this regard.

*Polymers* **2022**, *14*, x FOR PEER REVIEW 12 of 16

**20**

**inf (-)**

**25**

**Figure 11.** Infinite‐frequency dielectric permittivity ୧୬ of the SBR samples determined by means **Figure 11.** Infinite-frequency dielectric permittivity *ε*inf of the SBR samples determined by means of simultaneous mechanical and dielectric measurements at 24 ◦C under a static force of 10 N. ∆ε and it is shown in Figure 12.

of simultaneous mechanical and dielectric measurements at 24 °C under a static force of 10 N.

**2500 Figure 12.** Relaxation strength ∆ of the SBR samples determined by means of simultaneous **Figure 12.** Relaxation strength ∆*ε* of the SBR samples determined by means of simultaneous mechanical and dielectric measurements at 24 ◦C under a static force of 10 N.

## **(-)**mechanical and dielectric measurements at 24 °C under a static force of 10 N. **6. Summary and Conclusions**

Four SBR compounds were prepared to investigate the influence of plasticizer polarity on the mechanical stability of the filler network using simultaneous mechanical and dielectric analysis.

**Figure 12.** Relaxation strength ∆ of the SBR samples determined by means of simultaneous mechanical and dielectric measurements at 24 °C under a static force of 10 N. **No oil SN400 MES DAE 2000** The SBR compound without plasticizer serves as a reference. In a mechanically unloaded state, a constant conductivity of 4.8 × 10−4 S/cm was measured, showing no influence exerted by the electrical frequency. Under a static force of 10 N, which corresponds to a mechanical load of 0.127 MPa, the conductivity becomes frequency-dependent. The direct current conductivity *σdc* decreases from 4.8 × 10−4 S/cm to 1.4 × 10−4 S/cm due to the generated mechanical damage that reduces the density of the conduction paths within the carbon black network, and thus the SBR samples.

The other three compounds are expanded with oils that have different polarities.

The picture looks different for the three oil-expanded SBR samples. From an electrical frequency of 100 kHz, the real part of the conductivity *σ* 0 shows a dispersive part and increases as the frequency increases, regardless of the polarity of the plasticizer used. In addition, *σdc* is lower by almost an order of magnitude. It is 7 × 10−5 S/cm for the SBR samples with 20 phr SN400 and DAE. For the SBR samples with 20 phr MES, *σdc* is 5.8 × 10−5 S/cm.

The polarity of the plasticizers used does not directly contribute to the conductivity of the SBR samples. It solely influences the distribution of the filler particles within the matrix by increasing the distances covered by the free charge carriers along the electric field lines.

Under mechanical stress, the conductivity of all SBR samples becomes frequencydependent, independent of the plasticizer content and type. Furthermore, applying a static force of 10 N reduces *σdc* from 4.8 × 10−4 S/cm to 1.4 × 10−4 S/cm for the SBR sample without plasticizer. This also applies to the SBR sample with 20 phr DAE. *σdc* decreases from 7 × 10−5 S/cm to 2.7 × 10−5 S/cm. For the SBR samples with 20 phr SN400 and MES, a small increase in *σdc* is observed. *σdc* is 10−4 S/cm for the SBR sample with 20 phr SN400 and 7.7 × 10−5 S/cm for the SBR sample with 20 phr MES. These experimental findings can be explained by the new internal structure, which is characterized not only by damage to the filler clusters, but also by a new distribution of the filler clusters within the matrix. It is also worth noting that *σdc* for the oil-expanded SBR samples decreases as polarity of the plasticizer increases.

The dielectric relaxation was analyzed to describe the behavior of the SBR samples under mechanical stress. The real and imaginary part of the permittivity, *ε* 0 and *ε* 00 , were simultaneously fitted according to the Cole–Cole approach. The Cole–Cole relaxation time τ and thus also the position of maximal dielectric loss both increase as the polarity of the plasticizer used increases. This, in turn, decreases the broadness parameter α, implying a broader response function. The high frequency permittivity *ε*inf depends on the presence of plasticizer within the SBR samples rather than the type of plasticizer. *ε*inf for the oilexpanded SBR samples is double that of the SBR sample without plasticizer. This can be attributed to the increase in dead ends, implying more polar regions in the SBR matrix. Finally, no clear trend can be seen for the relaxation strength ∆*ε*. No reliable conclusions can be drawn in this regard.

This study is primarily application-oriented. These investigations are intended to describe and evaluate the influence of mechanical stress on a rubber compound in use as simply as possible. Rubber mixtures are mechanically loaded with the dynamic-mechanical analyzer in order to transfer the real operating conditions from the field to the laboratory and then to characterize the material behavior based on the dielectric properties.

In future work, the mechanical loads will be increased in order to reach the non-linear range of the rubber compounds in order to create conditions that are as realistic as possible. The study of rubber compounds with hybrid filler systems is also planned in order to characterize end products such as tires while driving, since the tire treads usually have a carbon black/silica filler system.

**Author Contributions:** Conceptualization, S.A., H.D., J.T. and J.L.-P.; methodology, S.A., H.D., J.T. and J.L.-P.; investigation, S.A., J.T. and J.L.-P.; writing—original draft preparation, S.A.; writing—review and editing, S.A., H.D., J.T. and J.L.-P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Acknowledgments:** The DiPLEXOR 500 N dynamic-mechanical and dielectric analyzer was developed within the ZIM project KF2473302DF0 in cooperation with M. Wilhelm from the Karlsruhe Institute of Technology.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **References**


6.1 European Union

The member states of the European Union (EU) are subject to the Waste Framework Directive (WFD) or the Directive 2008/98/EC of the European Parliament concerning general requirements for waste management. Established in 1975, this directive has been substantially amended with the latest revision provided in 2008. HHW is covered in article 20 of this directive, and as with previous directives, it is excluded from the definition of hazardous waste, while it is mixed with other types of household waste. The exclusion also applies when HHW has been separated from mixed household waste and remains until it has been collected properly. Under this legislation, there is no guidance to the management of HHW or legal obligation to the house owners [1, 16].

Directives exist for specific categories of hazardous waste. These documents provide some direction for member states on collection and disposal of the waste and encourage the education of householders on the importance of separating HHW from mixed municipal waste and of the collection and recycling programs that are available to them. The categories include waste from electrical and electronic equipment (WEEE), batteries and accumulators, and waste oils.

Waste oils are covered under the WFD directly in article 21. About 3 million tons of waste oil need to be managed annually in the EU that can severely damage soil and water. The directive prohibits any type of disposal that may adversely affect the environment and human health, discourages mixing of different types of waste oils, and encourages separate collection. The directives for 'batteries and accumulators' and WEEE call for accessible and free collection points and requires producers and distributors to take back waste batteries, accumulators and electrical and electronic equipment (EEE). However, while the disposal of industrial and automotive batteries and accumulators in landfills and incinerators are prohibited, no such legislation is put forth for household batteries. On the other hand, disposal of WEEE is prohibited until proper treatment has been carried out [17].


**1. Introduction**

Today, several challenges are besieging the environment, and as such, an equal measure to address such challenges must be in place to counter environmental and ecological degradation [1]. For example, in maintaining a clean and safe environment, waste reduction and recovery of valuable products [2] and/or their repurposing is a must [3]. Nutrient-rich agro-waste is usually produced from agro-processing industries [4]. Similarly, one of the major wastes is agro-based wastewater containing many carbon-based compounds [5], which in turn affects the receiving water bodies when released untreated [5]. Agricultural residues are also considered one of the most prominent substrates in energy and

**Citation:** Pandit, S.; Savla, N.; Sonawane, J.M.; Sani, A.M.; Gupta, P.K.; Mathuriya, A.S.; Rai, A.K.; Jadhav, D.A.; Jung, S.P.; Prasad, R. Agricultural Waste and Wastewater as Feedstock for Bioelectricity Generation Using Microbial Fuel Cells: Recent Advances. *Fermentation* **2021**, *7*, 169. https://doi.org/10.3390/ fermentation7030169

Academic Editors: Giuseppa Di Bella and Alessia Tropea

Received: 25 June 2021 Accepted: 19 August 2021 Published: 28 August 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

carbon source content. Their sugars are obtained either via treatment with dilute acids or enzymes [6].

An example of an important agricultural residue is wheat straw containing about 34–40% cellulose organic carbon content, hemicellulose containing about 21–26% of organic carbon, and lignin-containing about 11–23% of organic carbon. All of these can undergo hydrolysis yielding wheat straw hydrolysate, generating a substantial amount of electricity in a microbial fuel cell (MFC) [7]. Similarly, raw corn stover is another important agricultural waste that contributes immensely to the production of electricity when a single-chamber MFC is used. However, the treatment thereof was effective, but the power output was much lower compared to MFC in which glucose is used as a substrate [8].

Agricultural waste, even in agro-industrial wastewater, is produced during agriculture produce pre-harvesting, harvesting, and processing activities. Agricultural processing activities and industrial food processing operations contribute to agro/food-waste and wastewater generation. Agricultural waste can easily undergo biodegradation as it contains a high level of organic matter and many other different macro-and micro-nutrients suitable for microbial growth. Many agro-industrial wastewaters also contain a high concentration of organic pollutants, including a large amount of waste effluent produced from livestock and agro-products processing [9]. However, these agricultural residues and wastewater can be considered new alternative sources of renewable energy that can be converted into biofuels, biogas, bioelectricity, bio-bricks, fertilizer, and biochar [9] suitable technology such as MFCs, among others.


**4.2. Gastroepiploic artery**

Excellent long-term angiographic results have been reported with GEA [131], but its progres‐ sive loss of caliber with mobilization and its greater tendency for vasospasm compared with other arterial conduits both in in vitro testing [13] and in clinical practice [7] has limited its widespread use.

Spasm of the GEA is a well-described clinical phenomenon [7] Some studies have suggested that the GEA and the IMA have similar response to NE, phenylephrine, and 5-HT [132,133], and that the IMA is more reactive to the TXA2 mimetic, U46619. On the other hand, Dignan and associates [15] have found that the GEA has a stronger contractility than the IMA and more reactive to K+ , NE, and 5-HT. He and Yang [13,134] compared the contractility of the GEA, the IMA, and the IEA and found that among arterial grafts the GEA has the highest contractility. Variation of techniques used in the studies may account for diverse results from different groups. Therefore, the above mentioned vasoconstrictors may be the spasmogenic agents for the GEA [15]. Additionally, relaxation of the GEA to SNP [15] or to endotheliumdependent vasodilators [134,135] appears to be similar to the IMA.

Several vasodiators have been studied to counteract GEA spasm [81,136]. It has been demon‐ strated that papaverine, when given externally on the perivascular fat of the GEA, prevents GEA spasm for up to 2 hr [136]. In contrast, intraluminally applied papaverine does not show graft protection against NE-induced spasm. In addition, nifedipine prevents NE-induced spasm only when given intraluminally. Same study has also shown that verapamil is the most potent and versatile vasodilator with effective graft protection of up to 2 hr whether applied externally or internally and is the preferred agent for protecting against GEA spasm [136]. During intraoperative preparation of the GEA graft, GTN and papaverine to a lesser extent, used as topical vasodilators, appear to be more efficient in external application to increase the free flow of the GEA [81]. GV solution has been suggested to be suitable to treat spasm of GEA [137] GTN has a more rapid onset and verapamil has a longer action than papaverine [11]. That should prevent spasm of conduit in the early postoperative hours [137].


**1. Introduction**

Taking the social significance of digital media1 [1] and the opportunities it offers in disseminating various content as a starting point, it is necessary to emphasise its role in spreading fake news and disinformation alike. This type of content is not a new phenomenon and not solely a product of digital media either: "The problem of information credibility is nothing new" [2] (p. 70). As Obadă [3] (p. 148) states: "Fake news is not a new phenomenon [4,5] because the partisan press has always peddled biased opinions and stories lacking factual basis" [2,5] (p. 70); "New technologies, from the telegraph in the 19th century to contemporary social media algorithms, have led to the proliferation of fake news" [2,4] (p. 70). However, it is evident that various forms of digital media, in a technical sense, have great potential to spread and multiply information, although they are not the sole carrier.The exponential growth of content that has a primary intention of deception or manipulation represents one of the threatening features of the contemporary digital environment2. To what extent this content is widespread is obvious from the reference to the past decade as being "fake news" [6] (p. 977). Having recognised disinformation as a serious threat to democratic processes, security, and the welfare of citizens, the European Union adopted an Action Plan Against Disinformation in December 2018, with the aim of increasing awareness, social resistance, private sector mobilisation, and the ability of EU institutions to find, analyse, and discover disinformation [7,8] (p. 7).

The production and distribution of fake news, disinformation, and content with a solely commercial function significantly endangers the approach to credible information, which further problematises both the inability to recognise and deconstruct such contents from the perspective of digital media users. With regard to the latter, in relation to fake news

**Citation:** Trnini´c, D.; Kuprešanin Vukeli´c, A.; Bokan, J. Perception of "Fake News" and Potentially Manipulative Content in Digital Media—A Generational Approach. *Societies* **2022**, *12*, 3. https://doi.org/ 10.3390/soc12010003

Academic Editors: Eugène Loos, Loredana Ivan and Gregor Wolbring

Received: 25 October 2021 Accepted: 13 December 2021 Published: 24 December 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

and potentially manipulative content, it is necessary to examine the level of competence in the domain of information and digital literacy, especially the skills that imply a critical approach and an ability to deconstruct media content. Namely, this research considers members of the young and the middle-aged generations in order to compare their respective competences at recognising fake news, photographs and video footage, disinformation, and potentially manipulative content. Furthermore, their respective competences at verifying these contents and the levels of their responsibility in relation to the listed contents in the digital sphere. In this paper, a distinction is made between media literacy and other factors that constitute the concept of literacy in the 21st century. In this respect, this is different from IT literacy, information literacy, and digital literacy in that it is a complex notion with numerous definitions, but the authors opt for the definition describing it as an ability to access, analyse, evaluate, and create a message in various communication forms [9]. The idea of access to media content refers to technical competences—those denoting analysis and evaluation to critical thinking competences—whereas the idea of creating media content implies practical competences [10]. The notion of information literacy is observed as the effective usage of information within the context given [11], while IT literacy could be seen as "an ability to use and understand new information technologies and a wide range of their possible applications" [12]. In this regard, digital literacy refers to the application of information literacy in a digital form [11].

The significance of this research is reflected in a generational approach to ubiquitous and increasingly viral ethically problematic content and in comparing and qualitatively analysing the differences in competences between a generation that was raised using digital technologies, on the one hand, and a generation that has come into contact, both professionally and privately, with digital technologies subsequently and in a gradual manner on the other. The leading assumption of the paper is that growing up in a digital environment and intense use of digital media do not necessarily imply that one possesses the competences to recognise and verify fake news and potentially manipulative content. We ask the following research questions: in what way do members of different generations (young and middle-aged generations) perceive the phenomenon of "fake news" and similar content in digital media? Can they recognise them, and what do they do to verify them? What relation do they establish towards them? What are their proposals for building resistance to them? The answers to these questions will imply the achievement of our research goals.

In addition, it is assumed that those who have not experienced living in a digital environment could have developed digital and media competences, given that they belong to the middle-aged generation and that they possess lifelong experience concerning the use of various other media. The auxiliary hypotheses that the paper is based upon are as follows: (1) both young and middle-aged generation members in Bosnia and Herzegovina do not possess adequately developed media and digital literacy competences to recognise and verify "fake news" and potentially manipulative content in digital media, and (2) neither of the aforementioned generations have fully established a resistance mechanism to "fake news" and potentially manipulative content in digital media. The principal goal of the research is to examine how members of different generations (young and middleaged generations) perceive the phenomenon of "fake news" and potentially manipulative content in digital media. In this respect, the additional goals of the research are to examine whether members of the aforementioned generations are able to recognise "fake news" and potentially manipulative content, how they verify them, what kind of relationship they have developed towards them, and what their proposals are for building resistance to such content.

According to our findings, no research was conducted in Bosnia and Herzegovina in regard to a generational approach to fake news, but as a result of the current interest in this issue, there has been other research related to its various aspects. Consequently, some of the comprehensive research in the field, encompassing 450 digital media entities, offers an insight into the patterns of creation and dissemination of disinformation and

points to the level of their presence in the aforementioned media. Namely, the results of the research show that "media reports featuring incorrect or deceptive contents are widely released in Bosnia and Herzegovina and the region of former Yugoslavia, most often in the form of 'fake news'—inaccurate pieces of information released on purpose—that makes up almost one third of all disinformation analysed in this research" [8] (p. 7), with anonymous portals being identified as main sources and carriers of disinformation in the online area [13]. Based on the results of the conducted research, authors Lejla Turˇcilo and Belma Buljubaši´c highlight the issue of "fake news" in Bosnia and Herzegovina, pointing out that hyper-production of "fake news" in Bosnia and Herzegovnia is the result of "media enslaving, whose employees have agreed to or have been forced to serve political and economic tycoons and their particular interests" [14] (p. 49).

The extreme presence and exposure of citizens of Bosnia and Herzegovina to "fake news", disinformation, and potentially manipulative content, whose hyper-production has been determined not only by technical but also social—that is, political and economic factors—in the first place contributes to the justification of this research. Within the context of a generation approach, the research encompasses age groups that exclusively and primarily use digital media for gaining information, along with traditional information channels. In the end, the research makes a contribution to the field in terms of the lack of empirical studies concerning the manner in which different generations perceive fake news and potentially manipulative content.

#### **2. Fake News and Potentially Manipulative Content**

There is a lack of research into the role of age regarding the consumption of 'fake news' on social media [2], but we know that the hyper-production of fake news and potentially manipulative content is followed by a multitude of definitions and classifications that attempt at clearly dividing fake news from content that is similar in its nature but different in terms of their function, intention, format, and structure. In that sense, one of the important features is either the presence or the lack of an intention to deceive audiences. It is possible to observe fake news and potentially manipulative content as various forms of media manipulation, and this particular research is interested, apart from fake news, in the following phenomena: disinformation, satire, clickbait, conspiracy theory, and photomanipulation. With regard to the latter list, the idea of manipulation is best reflected in the phenomena of "fake news", clickbait, and photomanipulation. The rest of the aforementioned contents are potentially manipulative, which depends on the context and perception of the user of such content, but these phenomena cannot be generally considered as featuring any intention of manipulation.

At the core of numerous definitions of fake news lies a statement that it contains information that does not correlate with facts and that it is directed towards disinforming the public in a conscious manner [15] (p. 48), which implies that the major features of fake news are untruthfulness/incorrectness and intended deception. For this reason, Jaster and Lanuis attribute the lack of truth and lack of truthfulness to the notion of fake news and, using this as a starting point, they claim that fake news is "wrong or deceptive (lack of truth) and that it is released with the intention of deceiving or, eventually, discrediting or neglecting the truth (lack of truthfulness)" [16] (p. 208). In her efforts to draw a line between fake news and the contents similar to it, Milica Kulji´c defines the former as "incorrect information containing unprovable, mostly completely fabricated data or claims, as well as quotations, released with a view to deceiving audiences" [17] (p. 13).

As a prevalent form of media manipulation, and one quite similar to fake news, there is the notion of disinformation, "which is based on facts, but which misrepresents them—that is, which contains a 'mixture' of facts and false information or semi-truths" [15] (p. 52). In relation to fake news, disinformation is a wider notion, with the key difference being reflected in the fact that the latter is not necessarily intentional, meaning that there is no intention of deceiving audiences. Matthew R. X. Dentith claims that in the case of disinformation, "one does not necessarily deal with completely fabricated information, but

that it may contain some elements of truthfulness, yet not the entire context, that it may be completely false, or that it may lack one piece of information so that the picture would be complete, and the media release truthful in its entirety" [18] (p. 66).

Unlike fake news and disinformation, satire does not represent a form of media manipulation. Yet, if there is no reference to the fact that it is a case of satirical contents based on fabricated news, it is possible to perceive such contents as true to reality. This sort of danger is exactly what Bhawna Narwal points to, stating the following: "This type of news is intended for entertainment and parody—the purpose is not to harm anybody but it can be misinterpreted as facts. Lots of websites and social media offer critical commentary on society, celebrities and politicians to amuse readers, but these stories have the potential to fool" [6] (p. 977). In relation to fake news, which is based on incorrect information whose purpose is to deceive the public, satirical news is "based on information that is exaggerated, overturned, and accentuated in order to point to deceptions", implying elements of humour at all times [17] (p. 13).

Clickbait represents one of the most widespread forms of manipulation in digital media, but it is not its exclusive feature. According to the results of a research work entitled Dezinformacije u onlajn sferi: sluˇcaj BiH (Disinformation in the online sphere: the case of Bosnia and Herzegovina), clickbait appears as the second most common type of media manipulation [8] (p. 21). In reality, it appeared as a technique for drawing attention much earlier in the form of sensationalist and intriguing titles in tabloids. With regard to digital media, it does not relate solely to titles construed in a sensationalist manner, but, in general terms, to contents whose primary function is drawing attention and generating "clickability" on a massive scale. "The review of the literature on the subject allows us to point out two main notions or definitions: a restrictive one that reduces clickbait to the strategies used in the formulation of news headlines, and a more general and inclusive one that encompasses different formulas to attract readers' attention and increase traffic to a webpage" [19] (p. 97).

Next is the conspiracy theory notion, which refers to "a media release that makes claims concerning some organised and harmful actions of an entity, but that offers no proof for such claims (...) conspiracy theories emerge at the moment when the very assumption of possible harmful action is presented as a fact, without any actual investigation into the subject matter and presentation of any piece of evidence to support the claim" [15] (p. 52).

Multimedia, as one of the features of digital media that makes it superior to traditional mass media, implies a possibility of the visualisation of media contents as well, which is largely realised, apart from various illustrations and video footage, by means of photography. The latter, as a valuable asset within the context of gaining information, represents, at the same time, a means of manipulation that can significantly contribute to the credibility of fake news and potentially manipulative content, without verifying their authenticity3 [20,21]. "The manipulation of images has become an increasingly common occurrence with the advent of digital photos, powerful image manipulation software, and knowledge of techniques" [18] (p. 144). Where the subject matter of our research is concerned, the most significant definition of "fake news" is the one that features it as information that is not consistent with facts and that is intended for the conscious and deliberate manipulation of the public [16] (p. 48), since it successfully divides "fake news" from other potentially manipulative content.

#### *2.1. Recognition and Verification of "Fake News" and Potentially Manipulative Content*

The recognition and verification of "fake news" and potentially manipulative content represent significant competences in the contemporary digital environment. In this sense, digital media users have at their disposal tools whose usage, in addition to possessing certain knowledge and skills, makes an important contribution to identifying contents primarily intended for deception and manipulation.

The hyper-production of "fake news" and potentially manipulative content is mostly evident on Facebook, but the activity has been lately gaining strength on Twitter [22] as

well—the social media company that provides the most popular service for mainstream media reporting. Tools such as Bot Sentinel, Botcheck.me, Botometer, and Hoaxy are intended to detect and monitor trollbots and false accounts, and they have been developed for Twitter exclusively [23]. The Objective Analysis Effective Solutions—Fighting Disinformation network database features the tools of "Dirt Protocol" and "Emergent.Info", which offer a high level of interactivity to users4 [24].

In addition, the same database offers tools for verifying the credibility of photographs as well, along with metadata on photographs, video contents, and texts5 [24]. With regard to the aforementioned, the tools for verifying newspaper contents and for differentiating between the notions of "fake news", satire, conspiracy theories, and the like are the following: Disinformation Index, Factcheck.org, Factchecking, FakerFact, Fakey, Lead Stories FactChecker, KnowNews, and Polygraph (BBG).

Although the existing technical tools are indisputably useful, it is necessary, within the context of responsible and adequate media usage and the recognition and verification of "fake news" and potentially manipulative content, that users should continually develop their media literacy competences6 [25,26], the complexity of which implies special training courses for media users—in other words, media literacy. For that reason, the key factor is education in the field of media, which implies "gaining knowledge about every single form of media, whether printed, electronic, or digital. Under no circumstances is this type of education to be confused with media-assisted learning, which is within the domain of media didactics" [27,28] (p. 25).

#### *2.2. Influence of "Fake News" on Media Users' Emotions*

The key to the success of fake news is that it relies, for the most part, on media users' emotions, along with other elements of cognitive partiality, in opposition to critical thinking. One of the disturbing features with regard to fake news consumption is the fact that users are actually under the impression that other people are more influenced by fake news than they are [29,30]. "Given that fake news is seen as potentially harmful [29,31], a small but growing number of studies have documented the effect of fake news on TPP, generally indicating that TPP persists in the context of fake news" [29,30,32] (p. 6).

Sivri´c [33] points out that social media, so far, has been observed as mere places to have fun, but it has lately gained much more impact. By using social media, people, often unconsciously, become a part of social spheres circulating fake news and disinformation "for various reasons, such as satire, humour, and fun" [33] (p. 10). In their paper, Martel, Gertler Rand, and Pennycook [34] refer to the claims of scholars who advocate the thesis that a negative, anxious, and sad state of mind increases the overall quality of searching for information, skepticism towards fake news, and doubt and the amount of critical thinking about opposed standpoints, whereas positive moods increase users' level of gullibility and decrease their ability to detect deception [35–38]. The factor that makes a difference between fake and credible news is that articles featuring the former show "higher levels of anger and disgust and substantially lower levels of 'joy' in their article body than real news stories" [39] (p. 18).

As for the contents of fake news, it could be filled with images and narratives of violence which, according to Katarina Kacer [40], can urge us to develop emotions, such as compassion, pity, and empathy for victims and fascination for such scenes, but contents like these often open an opportunity for the radicalisation of viewers, for developing some mental unease by disturbing one's mental balance, as well as for becoming numb and indifferent to suffering. Kacer [40] says that this depends, in the first place, on the level of cognitive involvement, where the intensity of the latter is disproportionate to the influence of the message.


*3.1. Temporal Modulation of Statistically Steady Pu*ff *Dynamics*

Figure 2a shows the typical intermittent behaviour of statistically steady pipe flow at *Re* = 2400. Here, the vorticity is viewed from a reference frame co-moving at the constant bulk speed *us* = *ubt*. This case was run for 6000 convective time units ( *D us* ) or an equivalent to more than 100 periods beforehand in order to relax from its initial conditions and to let the flow develop its typical patchy and intermittent character: Turbulence is spatially localised and surrounded by laminar regions of relative calm. The time scale of laminar–turbulent interactions is on the order of 100 *D us* , as can be seen in Figure 5a, where we plot the temporal evolution of the turbulent (volume) fraction (*Ft* = *V*turb *V*pipe ) in the computational pipe domain (*V*pipe). It changes considerably every two or three hundred time units, reflecting the interactions visible in the corresponding space–time diagram. We computed *Ft* based on the streamwise vorticity plotted in Figure 2a and the threshold to separate laminar regions (deep blue in Figure 2) from turbulent ones was set to ω2 *z* = 4 × 10−2 in order to match the average turbulent fraction reported by Avila and Hof [12] at *Re* = 2400 (approximately 50%, as in Figure 5b).

We started all pulsatile IC SSPF runs from the same initial flow field and set the initial time to *t T* = 0.25 to match the instantaneous bulk velocity of the pulsation (see Equation (1)) to the one of the steady flow. This ensured a smooth evolution from the initial condition and further allowed us to track the exact same realisations of localised flow structures in space and time as *A* was increased. The resulting spatiotemporal dynamics are shown in Figure 2b–d,f in a frame co-moving at the instantaneous bulk speed

$$\mathbf{x}^\*(t) = \int\_{t\_0}^t \boldsymbol{\mu}\_b \mathbf{d}t. \tag{9}$$

Already at *A* = 0.2, the time scale of the flow modulation (*T* ≈ 60 *D us* ) dominates the dynamics (Figure 2b). In general, as the amplitude of the pulsation increases, the turbulent fraction in the flow decreases, as seen in Figure 5b. Many structures in the initial flow field decay quickly and do not survive the first acceleration (AC) phase. At *A* = 0.2, only two puffs survive after *t* = 5*T*, and the dynamics appear to reach an equilibrium state that repeats cyclically. The two surviving puffs grow in intensity and in length during the early deceleration (DC) phase of the flow, and they split into two in the late stages of DC before the minimum flow rate is reached. Out of these two, only the upstream puff survives the entire AC phase and reaches the peak flow rate, where this cycle starts over. Indeed, it is well known that for SSPF, only the upstream puff survives in puff interactions [26]. Overall, it appears that for *A* = 0.2, the flow is clearly self-sustained (above the critical point) and that a successful splitting event may occur at later times. However, the length of the computational domain (100*D*) may not be sufficient to accommodate three puffs without strong interactions due to the periodic boundary conditions. Similar results were obtained for *A* = 0.4 and 0.5 and are shown in Figure 2c,d; the question of whether, in these cases, the puffs will ultimately decay or successfully split would require substantially longer runs than those performed here and is not further pursued. Figure 6 shows typical localised structures at four equispaced points of the cycle for *A* = 0.5, illustrating the cyclically occurring splitting attempts. In agreement with Xu et al. [15], Xu and Avila [16], these figures show that the surviving puffs (Figure 6d,c) are very similar to the puffs in the steady case (Figure 1c) even at this relatively large pulsation amplitude. For *A* = 0.6, no turbulent structure survived the first pulsation period, and the flow fully relaminarised. We checked amplitudes up to *A* = 1.4 (see Figure 5b). In general, with increasing amplitude, the downstream puff separates farther away from the upstream puff during AC before it dies at almost the end of AC.

**Figure 6.** Instantaneous representation of localised turbulent structures in a pulsatile pipe flow (*Re* = 2400, *Wo* = 8, *A* = 0.5). Grey surfaces represent low-speed streaks (*u z* = −0.4*us*) and blue/red surfaces represent positive/negative axial vorticity (ω*z* = ±8 *us D* ). (**a**) Death of downstream puff. (**b**) Splitting event. (**c**) Growing puff. (**d**) Isolated puff. The exact location and time for each snapshot are as indicated in Figure 2d. The direction of the mean bulk flow (*us*) is always from left to right.


**2.6 Signalling pathways blocked by polyphenols**

 In addition to the antioxidant effects above mentioned, these bioactive compounds can induce two phases during ROS activation. Phase I starts when polyphenols inhibit cytochrome P450 (CYPs) including CYP1A1 and CYP1B1, and the increase and excretion of polar metabolites and prevention of the formation of DNA adducts remark phase II [35, 44]. But, pro-oxidant activities mediated by polyphenols and phenolic compounds increase the ROS production. Lin et al. reported that resveratrol induced apoptosis in HeLa cell line [15]. The extract of *Cudrania tricuspidata* stem (CTS) on cell viability was investigated in HPV-positive cervical cancer cells. CTS induced apoptosis by downregulating the E6 and E7 viral oncogenes. Also, the mRNA expression levels of extrinsic pathway molecules such as Fas, death receptor 5 (DR5) and TNF-related apoptosis-inducing ligand (TRAIL) were increased by CTS. CTS induced apoptosis by activating the extrinsic pathway in SiHa cervical cancer cells. Chlorogenic acid has been reported to have anticancer, antioxidant and antidiabetic effects. Also, galangin increased ROS, which induced the activation of cell death via various mechanisms including apoptosis or arrest of cell cycle [15, 20, 25]. Bruges reported that pyrogallol induced mitochondrial apoptotic response. Mitochondrial pathway probably begins with the activation of BH3-only proteins. This protein causes the production of BAK1 and BAX, which promote a membrane permeabilisation. Last, in cytoplasm increasing cytochrome C level, this allows apoptosome formation and caspase-9 activations. In extrinsic apoptosis pathway, binding of the cell death ligands and cell death receptors activates caspase-8 and caspase-3 (**Figure 1**) [35, 45]. Similarly, *Terminalia sericea* enabled caspases-7 and -8 and poly (ADP-ribose) polymerase (PARP) in HeLa cancer cell line [31]. Also, pyrogallol induces superoxide anion, and this generates activation of caspase-3 and phosphatidylserine [45]. Silva et al. mentioned that the hexane partition derived from the crude extract presented cytotoxic effect in SiHa cells and initiates cell responses, such as DNA damage (H2AX activity), apoptosis via intrinsic pathway (cleavage of caspase-9, caspase-3, poly (ADP-ribose) polymerase (PARP) and mitochondrial

#### **Figure 1.**

*Effect of biocompounds in cellular processes. In the figure, it is observed that at low concentrations, biocompounds (left) can exert an antioxidant effect, whereby it acts by reducing reactive oxygen species. However, at high concentrations (right), biocompounds have pro-oxidant effects, which can affect both normal and carcinogenic cells and result in alteration of key pathways for homeostasis of the cell, causing cell cycle arrest and stop cell proliferation, damage to DNA and apoptosis, among others, cellular process.*

 membrane depolarization) and decreased p21 expression by ubiquitin proteasome pathway [42]. Fusi et al. reported that the antioxidant activity of resveratrol, catechin, curcumin, etc. increases sirtuin 1 (SIRT1) expression and monophosphateactivated protein kinase (AMPK) activation in HeLa cell line [27, 44]. Prior reports indicated AMPK is an enzyme that inhibits anabolic process and increases catabolic activity. Perhaps, the relationship between SIRT1 and AMPK may protect against oxidative stress [27, 44]. On the other hand, pro-oxidant activities induced by polyphenols generate ROS and produce [1] cell cycle arrest, and [2] induction of apoptosis and DNA fragmentation. In HeLa cells, autophagy-signalling pathways are modulated by polyphenols, i.e. resveratrol, curcumin and genistein, and act on epidermal growth factor kinase B (EFGR)/AMPK, and this inhibits the mammalian target of rapamycin (mTORC1) via TSC1/2. Also, these three polyphenols inhibit nuclear factor kappa-light-enhancer of activated B cells (NF-κB), and these compounds plus quercetin stop phosphatidilinositide 3-kinases/protein kinase B (PI3K/Akt), and last, rottlerin breaks PKC5 [35, 44]. Last, safflower polysaccharide (SPS) is a major active component of *Carthamus tinctorius*. SPS inhibited proliferation and increased apoptosis of HeLa cells through downregulation of the phosphatidylinositol-3-kinase/ AKT pathway [46].