**1. Introduction**

Biopolymers have attained significant market potential due to their numerous applications in diverse fields such as "bio-ceramic, bio-sensing, bio-encapsulation, and bio-inorganic nanoparticles" [1]. The main motivation for studying these biopolymers rises from their unique characteristics: bio-compatibility, low environmental impact, and nontoxicity (for human use) [2, 3]. Since these materials are biodegradable, they can be recycled, which translates into waste reduction and smaller recycling cost. An additional appealing feature is the low fabrication cost of these biopolymers when compared to petroleum-based ones.

Hosokawa et al. fabricated composites made of chitosan and cellulose to study their mechanical properties [9]. To fabricate the composites, chitosan was dissolved in a water/acetic acid while cellulose fibers were diluted in an aqueous solution. Then, a small amount of chitosan was added into the cellulose solution containing glycerol. The ensuing solution was mechanically stirred and degassed before the drying process. Their results suggest that the tensile strength decreased as the swelling degree increased in the composites. The authors attributed this to the crosslinking between the carbonyl groups (C═O) and the carbonyl groups (C–OH)

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

Another pertinent study was conducted by Ibrahim et al., who fabricated polyester-oil palm ash composites [10]. The specimens were prepared at different volume fraction of oil palm ash (0, 10, 20 and 30%) in unsaturated polyester matrix. All samples were mechanically characterized with a universal testing machine with a 10 kN load capacity, operated at a 5 mm/min strain rate. The measured tensile strength of the composites decreased from 26.8 to 13 MPa with the tensile modulus rising from 375 to 499 MPa as the content of nanofillers increased from 0 to 30%. The smaller tensile strength was attributed to the interaction of the nanofiller with the polymer matrix. Conversely, the fillers imparted greater stiffness to the composite. In addition, when the authors analyzed the composites' thermal properties, they discovered that the particles enhanced the thermal stability of the composites from 293.55°C without oil

Aware of such trend and in an effort to propose an alternative material suitable for capacitors, in the present research we engineered a composite with a chitosan-cellulose matrix,

nanoparticles helped tune the dielectric constant, the current density, and the electrical conductivity. The control of the capacitance dependency on the frequency would allow devices to vary their capacitance depending on the application in which they would be deployed. Hence, this work brings about a novel perspective on the tunable properties of the chitosan-

The present research encompassed two stages. In the first one, the composites were synthesized to produce enough material for the second stage. Upon this stage, the composites underwent both mechanical and electrical characterization. This experimental section was completed in the facilities of the Nanotechnology Center hosted by the University of Puerto

All samples were fabricated using poly (D-glucosamine) deacetylated chitosan ((C<sup>6</sup>

75% deacetylation, Sigma Aldrich), cellulose powder (cotton linens, Sigma Aldrich) and stron-

), 99 + %, Fisher). A chitosan solution was dissolved in acetic

flexibility, which is adjustable with the relative amount of cellulose, while the SrTiO<sup>3</sup>

based composite for flexible electronics and bio-compatible properties.

) nanoparticles. The polymeric matrix provides

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

75

(STO)

H11O<sup>4</sup>

N)n,

in the cellulose structure with the amine groups of the chitosan.

palm ash to 401.72°C with 30% oil palm ash.

reinforced with strontium titanate (SrTiO3

**2. Experimental procedure**

**2.1. Materials selection**

tium titanium oxide ((SrTiO3

Rico – Mayagüez, from August 2013 to August 2015.

Researchers have been using these biopolymers as matrices for composites containing ferroelectric particles, i.e., BaTiO3 , SrTiO3 , CaTiO3 , and PbTiO3 . In particular, they have been seeking for an alternative for processable high permittivity materials with high dielectric constant, moderate dielectric strength, low dielectric loss, high electrical resistivity, among other properties [4, 5]. These electrical characteristics made these composites particularly suitable for capacitors, transistors, and actuators.

For instance, Neagu et al. studied dielectric properties of bio-composites made of chitosan with different percentages of BaTiO<sup>3</sup> particles: 0, 1 and 10% [6]. Among the different fabrication methods available to produce the polymeric films, the authors selected the dry phase inversion casting process. This research demonstrated that higher BaTiO3 concentrations in the polymeric matrix raised the dielectric constant while lowering the dielectric loss. This led to a simple approach to create flexible electronic devices made of polymeric and ferroelectric constituents.

Moreover, Elimat evaluated the electrical properties of composites made of epoxy with various zinc oxide (ZnO) concentrations and reinforced with 1.0 wt% of conductive carbon black nanoparticles to dissipate any potential electrostatic charges [7]. The results revealed an increase in higher dielectric constant values as the temperature and the ZnO concentration heightened. However, that dielectric constant diminished for higher frequencies, namely from 0.1 to 1 MHz; this was attributed to the dipoles' lack of time to align with the electrical field. In addition, the authors demonstrated that higher concentrations of ZnO nanoparticles increased the electrical conductivity of the composites. Such higher electrical conductivity is due to the increase of the charge carriers' density in the polymeric matrix.

Petrov et al. studied the electrical properties of chitosan and hydroxyapatite (HA) biocomposites. In their study, they implemented an innovative approach via a corona discharge treatment to increase the charge surface of the polymeric matrix. The researchers tested the dielectric permittivity of the composites using dielectric spectroscopy and by employing a parallel plate capacitor for the electrical measurements. Their results evinced no difference in dielectric permittivity between the composites made of 6 and 10 g/L of chitosan solution. However, a notable difference was observed in the dielectric permittivity as a function of temperature and frequency. Although higher temperatures increased the dielectric permittivity of the composites, such permittivity decreased at higher frequencies [8].

Hosokawa et al. fabricated composites made of chitosan and cellulose to study their mechanical properties [9]. To fabricate the composites, chitosan was dissolved in a water/acetic acid while cellulose fibers were diluted in an aqueous solution. Then, a small amount of chitosan was added into the cellulose solution containing glycerol. The ensuing solution was mechanically stirred and degassed before the drying process. Their results suggest that the tensile strength decreased as the swelling degree increased in the composites. The authors attributed this to the crosslinking between the carbonyl groups (C═O) and the carbonyl groups (C–OH) in the cellulose structure with the amine groups of the chitosan.

Another pertinent study was conducted by Ibrahim et al., who fabricated polyester-oil palm ash composites [10]. The specimens were prepared at different volume fraction of oil palm ash (0, 10, 20 and 30%) in unsaturated polyester matrix. All samples were mechanically characterized with a universal testing machine with a 10 kN load capacity, operated at a 5 mm/min strain rate. The measured tensile strength of the composites decreased from 26.8 to 13 MPa with the tensile modulus rising from 375 to 499 MPa as the content of nanofillers increased from 0 to 30%. The smaller tensile strength was attributed to the interaction of the nanofiller with the polymer matrix. Conversely, the fillers imparted greater stiffness to the composite. In addition, when the authors analyzed the composites' thermal properties, they discovered that the particles enhanced the thermal stability of the composites from 293.55°C without oil palm ash to 401.72°C with 30% oil palm ash.

Aware of such trend and in an effort to propose an alternative material suitable for capacitors, in the present research we engineered a composite with a chitosan-cellulose matrix, reinforced with strontium titanate (SrTiO3 ) nanoparticles. The polymeric matrix provides flexibility, which is adjustable with the relative amount of cellulose, while the SrTiO<sup>3</sup> (STO) nanoparticles helped tune the dielectric constant, the current density, and the electrical conductivity. The control of the capacitance dependency on the frequency would allow devices to vary their capacitance depending on the application in which they would be deployed. Hence, this work brings about a novel perspective on the tunable properties of the chitosanbased composite for flexible electronics and bio-compatible properties.
