**3. Results and discussion**

#### **3.1. SrTiO3 Nanoparticles**

Previous research showed that the particle size affects electrical, mechanical, and thermal properties of similar composites [20]. As aforementioned, to improve the dispersion of the particles in the polymeric matrix, the particle size was reduced using the high energy ball mill. Furthermore, reducing the size of the particles can create impurities upon ball milling and to confirm that the crystalline structure of the strontium titanate remained without changes, the powder was analyzed by x-ray diffraction. **Figure 2** displays the resulting diffractogram that matched with the expected STO pattern; the presence of impurities was not detected.

As aforementioned, from the diffractograms, Scherrer equation allowed estimating the particle size of the STO powder at different milling times. The equation takes into consideration the width of the largest XRD peak in the diffractogram [21, 22], which in our case (**Figure 2**) lies at θ = 32.5°. The Miller indexes were identified by comparison with a prior publication by Trepakov et al. [23].

**Figure 3** presents the milling time effect on the particle size. Two stages can be observed in the reduction (by fragmentation) of the particle size. The first stage occurs between 0 to 5 h of milling and presents a rapid reduction in the particle size from 46 to 18 nm. The rapid reduction in the particle size may be attributed to the fragmentation of large agglomerates into individual aggregates and therefore, the fracture of aggregates into individual primary particles and small aggregates [24]. In the second stage (5–20 h) of milling, the change in size was negligible. This was attributed to the increasing agglomeration of the fractured particles that impedes further fragmentation and, hence, size reduction; further, formation of surface cracks between the small aggregates or at the surface of individual particles could also have occurred [24].

As indicated previously, the relevance of adjusting the particle size lies on its effect on the electrical and mechanical properties of the nanocomposites. According to the literature, the nanoparticles agglomeration could adversely affect the electrical and mechanical properties of the nanocomposites [21, 22]. As the particle size decreases, the dispersion of the nanoparticles increases in the polymeric matrix and, therefore, improves the electrical and mechanical properties.

*2.3.3. Thermal analysis*

78 Ferroelectrics and Their Applications

the thermal analyzer.

*2.3.4. Mechanical characterization*

**3. Results and discussion**

 **Nanoparticles**

**3.1. SrTiO3**

22 mm gauge length, a 5 mm width, and a 5 mm radius fillet.

A Mettler Toledo TGA/SDTA thermogravimetric / differential thermal analyzer (operated at a 5°C/min. Temperature ramp from 25 to 500°C) allowed determining the degradation temperature (Tdeg) of the composites in a nitrogen atmosphere. The samples were placed on a weight scale, which detects the mass loss of the samples as a function of temperature. To determine the said Tdeg, the first derivate was applied to the heating rate curve obtained from

**Figure 1.** Calframo™ stirrer clamp utilized in the measurement of the dielectric properties.

The samples' ultimate tensile strength was measured at room temperature (25°C) using a low force Instron® model 5944 universal testing machine. The deformation velocity was set at 1 mm/min. Also, the dimensions of the samples followed the ASTM D-1708, which specifies a

Previous research showed that the particle size affects electrical, mechanical, and thermal properties of similar composites [20]. As aforementioned, to improve the dispersion of the particles in the polymeric matrix, the particle size was reduced using the high energy ball mill. Scanning electron microscopy (SEM) images in **Figure 4** allow observing the dispersion of the nanoparticles in the polymer matrix. At low magnification, the presence of STO aggregates

**Figure 2.** X-ray diffraction pattern of STO after 10 h of milling and powder diffraction line pattern.

**Figure 3.** Particle size of STO nanoparticles at different milling times.

As aforementioned, chitosan was dissolved in a water/acetic acid solution, enhancing the interaction between cellulose and water molecules in the solution. Such molecular interactions can be: (a) water molecules linked to cellulose hydroxyl (–OH) groups, or (b) water molecules confined between the polymer chains due to intermolecular hydrogen bonds. These interactions heightened the water content in the nanocomposites and, hence, raised the cur-

On the Mechanical and Dielectric Properties of Biocomposites Containing Strontium Titanate Particles

http://dx.doi.org/10.5772/intechopen.76858

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**Figure 5.** Calculated dielectric constant of the nanocomposites as a function of frequency.

Moreover, higher amounts of STO nanoparticles increased the dielectric constant of the material [11]. The main characteristic of these ferroelectric nanoparticles consists of their ability to raise the material's stored energy. However, these ferroelectric nanoparticles are difficult to disperse in a polymeric matrix due to their high internal energy. It has also been reported that particle size reduction, by expanding the polymer-particles interface, enhanced the electrical

Furthermore, the literature demonstrates how frequency alters the dipoles orientation of the STO nanoparticles [4–7]. When those nanoparticles are aligned with the applied electrical field, the dielectric material becomes polarized. However, the dipoles cannot remain aligned to the electrical field at higher frequencies [11]. In as much as the dielectric constant dwindles at those high frequencies, the polarization mechanism cannot contribute effectively to the dielectric properties. This represents a limitation because for higher frequencies applications

After analyzing the dielectric constant of the composites, we gaged the current density, i.e., charge transported through the cross-sectional area (**Figure 6**). Thus, we discovered that the current density raised for higher amounts of cellulose in the composites, as well as for voltages from 5 to 60 V. As explained previously, the water content of in the nanocomposites swells with the addition of cellulose, resulting in higher current densities through the dielectric material. Moreover, the STO nanoparticles addition improves the capacitor's ability to store more energy by lowering the current flow through the dielectric material. As shown in **Figure 6**, the current density for the composites with STO nanoparticles increased

rent flow through the capacitor [11, 26].

properties of nanocomposites [11, 14].

this will cause decrease in the dielectric properties.

**Figure 4.** Secondary electron images obtained from the biocomposite with 20 wt% STO particles: (a) low magnification; (b) high magnification.

is apparent on the polymer surface. However, a significant dispersion of STO aggregates becomes visible on the polymer surface at high magnification.
