The polyethylene terephthalate/carbon nanotube (PET/CNT) nanocomposites were prepared by melt mixing using a twin screw extruder. CNT content was varied up to 5 wt. %. Morphology as well as dynamic mechanical, calorimetric, and rheological properties of the PET/CNT nanocomposites was investigated. Morphological studies indicated that CNT bundles are regularly distributed within the polymer matrix creating a connected network structure which significantly affects the nanocomposite properties. Dynamic mechanical thermal analysis revealed increase in storage and loss modules of the investigated PET nanocomposites by increasing the content of CNTs. Differential scanning calorimetry results demonstrated increase in crystallinity of the investigated PET nanocomposites upon addition of the nanofiller. Rheological studies demonstrated that CNT addition up to 5 wt. % caused increment in complex viscosity and storage modulus. Rheological percolation threshold was observed to be 0.83 wt. % of CNT concentration, respectively.

This research is devoted to the fabrication of polyvinyl alcohol (PVOH) based n-type thermoelectric composites with innovative hybrid bismuth selenide-multiwalled carbon nanotube (Bi₂Se₃-MWCNT) fillers for application in flexible thermoelectric devices. Hybrid fillers were synthesized by direct deposition of Bi₂Se₃ on multiwalled carbon nanotubes using a physical vapor deposition method, thus ensuring direct electrical contact between the carbon nanotubes and Bi₂Se₃. The Seebeck coefficient of prepared PVOH/Bi₂Se₃-MWCNT composites was found to be comparable with that for the Bi₂Se₃ thin films, reaching −100 µV·K⁻¹ for the composite with 30 wt.% filler, and fluctuations of the resistance of these composites did not exceed 1% during 100 repetitive bending cycles down to 10 mm radius, indicating the good mechanical durability of these composites and proving their high potential for application in flexible thermoelectrics. In addition, other properties of the fabricated composites that are important for the use of polymer-based materials such as thermal stability, storage modulus and linear coefficient of thermal expansion were found to be improved in comparison with the neat PVOH.

The aim of the proposed paper is to synthesize graphite oxide (GO) and use it in combination with carbon nanotubes (CNT) for the preparation of polyurethane (PU) composites. We fabricated composites with CNT/GO content of 0.05, 0.1, 0.3 wt.% with the use of ultrasonic treatment and tested their thermo-mechanical properties. Thermo-mechanical analysis (TMA) and dynamic mechanical analysis (DMA) measurements for CNT/GO composites were compared with the unfilled PU. Thermo-mechanical characteristics of storage moduli and loss moduli for CNT/GO nanocomposite were improved in comparison to the unfilled PU. The introduction of CNT/GO to the PU matrix creates strong bonding with the matrix and leads to the decrease of the glass transition temperature, new solid-solid phase transitions of polymer in the glass state. Dilatometric curves testified the remarkable changes in the glass transition of the polymer after the introduction of CNT/GO hybrid filler. Thermal expansion coefficient was calculated from the curve slopes and expressed continuously increasing expansion rate for CNT/GO composite. The measured characteristics were directly dependent from the filler content in the composite and the operated temperature.

This work is devoted to the fabrication of p-type polyvinyl alcohol (PVA)-based flexible thermoelectric composites using multiwall carbon nanotubes-antimony telluride (MWCNT-Sb₂Te₃) hybrid filler, the study of the thermoelectrical and mechanical properties of these composites, and the application of these composites in two types (planar and radial) of thermoelectric generators (TEG) in combination with the previously reported PVA/MWCNT-Bi₂Se₃ flexible thermoelectric composites. While the power factors of PVA/MWCNT-Sb₂Te₃ and PVA/MWCNT-Bi₂Se₃ composites with 15 wt.% filler were found to be similar, the PVA/MWCNT-Sb₂Te₃ composite with 25 wt.% filler showed a ~2 times higher power factor in comparison with the PVA/MWCNT-Bi₂Se₃ composites with 30 wt.% filler, which is attributed to its reduced electrical resistivity. In addition, developed PVA/MWCNT-Sb₂Te₃ composites showed a superior mechanical, electrical, and thermoelectric stability during 100 consequent bending cycles down to a 3 mm radius, with insignificant fluctuations of the resistance within 0.01% of the initial resistance value of the not bent sample. Demonstrated for the first time, 2-leg TEGs composed from p-type PVA/MWCNT-Sb₂Te₃ and n-type PVA/MWCNT-Bi₂Se₃ composites showed a stable performance under different external loads and showed their potential for applications involving low temperature gradients and power requirements in the range of nW.