Flexible films of a conductive polymer nanocomposite-based castor oil polyurethane (PUR), filled with different concentrations of carbon black (CB) nanoparticles or multiwall carbon nanotubes (MWCNTs), were obtained by a casting method. The piezoresistive, electrical, and dielectric properties of the PUR/MWCNT and PUR/CB composites were compared. The dc electrical conductivity of both PUR/MWCNT and PUR/CB nanocomposites exhibited strong dependences on the concentration of conducting nanofillers. Their percolation thresholds were 1.56 and 1.5 mass%, respectively. Above the threshold percolation level, the electrical conductivity value increased from 1.65 × 10⁻¹² for the matrix PUR to 2.3 × 10⁻³ and 1.24 × 10⁻⁵ S/m for PUR/MWCNT and PUR/CB samples, respectively. Due to the better CB dispersion in the PUR matrix, the PUR/CB nanocomposite exhibited a lower percolation threshold value, corroborated by scanning electron microscopy images. The real part of the alternating conductivity of the nanocomposites was in accordance with Jonscher’s law, indicating that conduction occurred by hopping between states in the conducting nanofillers. The piezoresistive properties were investigated under tensile cycles. The nanocomposites exhibited piezoresistive responses and, thus, could be used as piezoresistive sensors.

In this study, multiwalled carbon nanotubes (MWCNTs) were incorporated into vulcanized natural rubber (VNR) matrixes to create nanocomposites with improved mechanical, thermal, and electrical properties. The interfacial interaction of the MWCNTs with the VNR matrix was quantitatively evaluated based on the crosslink density value calculated using the Flory–Rehner methodology. Various rheometric parameters were influenced by the addition of the MWCNTs, including minimum torque (M_L), maximum torque (M_H), and scorch time (t_S1). The MWCNTs significantly enhanced the vulcanization of the composites based on the VNR matrix. This study highlights the impact of MWCNTs on crosslink density, improving mechanical properties and reducing swelling in the VNR matrix. We discovered that the MWCNTs and the VNR matrix interact strongly, which improved the mechanical properties of the matrix. The MWCNTs improved the hardness, tensile strength, and abrasion resistance of the VNR/MWCNT nanocomposites. Based on dynamic mechanical analysis, MWCNT incorporation improved stiffness as indicated by a change in storage modulus and glass transition temperatures. The addition of MWCNTs to the VNR/MWCNT nanocomposites significantly improved their electrical properties, reaching a percolation threshold where conductive pathways were formed, enhancing their overall conductivity. Overall, this study demonstrates the versatility and functionality of VNR/MWCNT nanocomposites for a variety of applications, including sensors, electromagnetic shielding, and antistatic blankets.

A flexible piezoresistive material based on vulcanized natural rubber (VNR) and multiwalled carbon nanotubes (MWCNTs) was developed and systematically investigated for strain sensing applications. The nanocomposites were prepared by melting and vulcanizing MWCNT, while keeping the rubber composition constant to isolate the effect of the conductive nanofiller. By scanning electron microscopy, morphological analyses indicated that MWCNTs were dispersed throughout the rubber matrix, with localized agglomerations becoming more evident at higher loadings. In mechanical tests, MWCNT incorporation increases the tensile strength of VNR, increasing the stress at break from 8.84 MPa for neat VNR to approximately 10.5 MPa at low MWCNT loadings. According to the electrical characterization, VNR-MWCNT nanocomposite exhibits a strong insulator–conductor transition, with the electrical percolation threshold occurring between 2 and 4 phr. The dc electrical conductivity increased sharply from values on the order of 10⁻¹⁴ S·m⁻¹ for neat VNR to approximately 10⁻³ S·m⁻¹ for nanocomposites containing 7 phr of MWCNT. Impedance spectroscopy revealed frequency-independent conductivity plateaus above the percolation threshold, indicating continuous conductive pathways, while dielectric analysis revealed strong interfacial polarization effects at the MWCNT–VNR interfaces. The piezoresistive response of samples containing MWCNT exhibited a stable, reversible, and nearly linear response under cyclic tensile deformation (10% strain). VNR/MWCNT nanocomposites demonstrate mechanical compliance and tunable electrical sensitivity, making them promising candidates for flexible and low-cost piezoresistive sensors.

The purpose of this study is to evaluate the morphological and electrical properties of a composite made from vulcanized natural rubber (VNR) reinforced with PZT particles and leather residue (LR). The materials were processed using a simple open-roll mixing method, keeping constant proportions of natural rubber and leather residue, while varying the PZT content at 25 and 50 phr. Scanning electron microscopy revealed homogeneous dispersion of both the LR and PZT particles within the VNR matrix, with no visible agglomerations, confirming the effectiveness of the mixing process. Electrical impedance analyses indicated that all composites exhibited frequency-dependent conductivity, a characteristic of disordered solid materials. Samples containing higher PZT concentrations showed increased conductivity at low frequencies, mainly due to dipole movement within the ceramic phase. Dielectric permittivity and capacitance also decreased with increasing frequency, while the composite with 50 phr of PZT presented the highest dielectric constant and energy storage capacity. Mechanical tests demonstrated that the inclusion of LR enhanced tensile strength and reduced elongation at break, acting as a fibrous reinforcement. The addition of PZT particles increased stiffness, resulting in slightly more brittle behavior. The VNR-LR/PZT three-phase composite with 50 phr PZT achieved the best balance between the mechanical strength and electrical performance. Overall, the results confirm that the developed composite exhibits promising multifunctional behavior suitable for piezoelectric sensing and energy-harvesting applications. Furthermore, the reuse of leather waste provides an environmentally responsible alternative, converting an industrial residue into a functional, high-value material with both technological and ecological benefits.

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