Thermoelectric properties of polypropylene carbon nanofiber melt-mixed composites: exploring the role of polymer on their Seebeck coefficient

• Published in: Polymer journal 2021-10, Vol.53 (10), p.1145-1152
• Main Authors: Paleo, Antonio José, Krause, Beate, Cerqueira, Maria Fátima, Melle-Franco, Manuel, Pötschke, Petra, Rocha, Ana María
• Format: Article
• Language: English
• Subjects: 639/301/923/1028; 639/925/357; Biomaterials; Bioorganic Chemistry; Carbon fibers; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Conducting polymers; Electrical resistivity; Extrusion; Nanofibers; Nanostructure; Original Article; Polymer matrix composites; Polymer Sciences; Polymers; Polypropylene; Power factor; Seebeck effect; Surfaces and Interfaces; Thermoelectricity; Thin Films
• ISSN: 0032-3896; 1349-0540
• DOI: 10.1038/s41428-021-00518-7

The effect of polypropylene (PP) on the Seebeck coefficient (S) of carbon nanofibers (CNFs) in melt-extruded PP composites filled with up to 5 wt. % of CNFs was analyzed in this study. The as-received CNFs present an electrical conductivity of ~320 S m −1 and an interesting phenomenon of showing negative S-values of −5.5 μVK −1 , with 10 −2  µW/mK 2 as the power factor (PF). In contrast, the PP/CNF composites with 5 wt. % of CNFs showed lower conductivities of ~50 S m −1 , less negative S-values of −3.8 μVK −1 , and a PF of 7 × 10 −4  µW/mK 2 . In particular, the change in the Seebeck coefficient of the PP/CNF composites is explained by a slight electron donation from the outer layers of the CNFs to the PP molecules, which could reduce the S-values of the as-received CNFs. Our study indicates that even insulating polymers such as PP may have a quantifiable effect on the intrinsic Seebeck coefficient of carbon-based nanostructures, and this fact should also be taken into consideration to tailor conductive polymer composites with the desired thermoelectric (TE) properties. The higher negative Seebeck coefficients (S) at 30 °C of as-received carbon nanofibers (CNFs) with respect to their polypropylene carbon nanofiber (PP/CNF) melt-mixed composites are explained by a slight electron donation from the outer graphitic shells of the CNFs to the PP molecules. Our study denotes that, contrary to expectations, insulating polymers may play a non-negligible role on the final S-values of conductive polymer composites composed of carbon-based nanostructures.