Influence of Polyvinylpyrrolidone on Thermoelectric Properties of Melt-Mixed Polymer/Carbon Nanotube Composites

Abstract

For thermoelectric applications, both p- and n-type semi-conductive materials are combined. In melt-mixed composites based on thermoplastic polymers and carbon nanotubes, usually the p-type with a positive Seebeck coefficient (S) is present. One way to produce composites with a negative Seebeck coefficient is to add further additives. In the present study, for the first time, the combination of single-walled carbon nanotubes (SWCNTs) with polyvinylpyrrolidone (PVP) in melt-mixed composites is investigated. Polycarbonate (PC), poly(butylene terephthalate) (PBT), and poly(ether ether ketone) (PEEK) filled with SWCNTs and PVP were melt-mixed in small scales and thermoelectric properties of compression moulded plates were studied. It could be shown that a switch in the S-value from positive to negative values was only possible for PC composites. The addition of 5 wt% PVP shifted the S-value from 37.8 µV/K to −31.5 µV/K (2 wt% SWCNT). For PBT as a matrix, a decrease in the Seebeck coefficient from 59.4 µV/K to 8.0 µV/K (8 wt% PVP, 2 wt% SWCNT) could be found. In PEEK-based composites, the S-value increased slightly with the PVP content from 48.0 µV/K up to 54.3 µV/K (3 wt% PVP, 1 wt% SWCNT). In addition, the long-term stability of the composites was studied. Unfortunately, the achieved properties were not stable over a storage time of 6 or 18 months. Thus, in summary, PVP is not suitable for producing long-term stable, melt-mixed n-type SWCNT composites.

Comparative Thermoelectric Properties of Polypropylene Composites Melt-Processed Using Pyrograf® III Carbon Nanofibers

“…In comparison with other reports, the negative Seebeck coefficients are lower than the values around −23 µV K −1 reported in PP composites melt-mixed with 5 wt.% of nitrogen-doped MWCNTs [38]. More recently, promising S-values of −31.5 µV K −1 have been found for melt-mixed PP/2 wt.% SWCNT composites with the addition of 5 wt.% polyvinylpyrrolidone (PVP), though their n-type character was lost after 6 to 18 months of storage under ambient conditions [39]. In addition, a higher value of −56.6 µVK −1 was achieved in PP composites melt-extruded with 2 wt.% of single wall carbon nanotubes (SWCNTs) and 5 wt.% of copper oxide (CuO) after the addition of 10 wt.% of polyethylene glycol (PEG) during melt-extrusion [9].…”

Leading-Edge Polymer/Carbonaceous Nano-Reinforcement Nanocomposites—Opportunities for Space Sector

“…Another prominent method for polymer/carbon nanotube nanomaterials is the melt blending [67]. This technique involves a shear force forming viscous polymer melt with dispersed nanoparticles [68]. Important melt processed matrices with carbon nanotube include polyamide, nylon, polypropylene, and others [69].…”

Change of Conduction Mechanism in Polymer/Single Wall Carbon Nanotube Composites upon Introduction of Ionic Liquids and Their Investigation by Transient Absorption Spectroscopy: Implication for Thermoelectric Applications

“…In addition, it is possible to add n-type CNTs, such as nitrogen-doped ones, to polymers to obtain n-type composites . Another way shown before in the literature, is to combine CNTs with certain doping additives before they are incorporated in the polymer matrix by melt mixing. , The use of PEG, , PEI, as well as PVP was reported in the literature.…”

“… 37 Another way shown before in the literature, is to combine CNTs with certain doping additives before they are incorporated in the polymer matrix by melt mixing. 21 , 38 The use of PEG, 28 , 39 PEI, 40 as well as PVP 41 was reported in the literature.…”