Screening of Different Carbon Nanotubes in Melt-Mixed Polymer Composites with Different Polymer Matrices for Their Thermoelectrical Properties

Abstract

The aim of this study is to reveal the influences of carbon nanotube (CNT) and polymer type as well as CNT content on electrical conductivity, Seebeck coefficient (S), and the resulting power factor (PF) and figure of merit (ZT). Different commercially available and laboratory made CNTs were used to prepare melt-mixed composites on a small scale. CNTs typically lead to p-type composites with positive S-values. This was found for the two types of multi-walled CNTs (MWCNT) whereby higher Seebeck coefficient in the corresponding buckypapers resulted in higher values also in the composites. Nitrogen doped MWCNTs resulted in negative S-values in the buckypapers as well as in the polymer composites. When using single-walled CNTs (SWCNTs) with a positive S-value in the buckypapers, positive (polypropylene (PP), polycarbonate (PC), poly (vinylidene fluoride) (PVDF), and poly(butylene terephthalate) (PBT)) or negative (polyamide 66 (PA66), polyamide 6 (PA6), partially aromatic polyamide (PARA), acrylonitrile butadiene styrene (ABS)) S-values were obtained depending on the matrix polymer and SWCNT type. The study shows that the direct production of n-type melt-mixed polymer composites from p-type commercial SWCNTs with relatively high Seebeck coefficients is possible. The highest Seebeck coefficients obtained in this study were 66.4 µV/K (PBT/7 wt % SWCNT Tuball) and −57.1 µV/K (ABS/0.5 wt % SWCNT Tuball) for p- and n-type composites, respectively. The highest power factor and ZT of 0.28 µW/m·K2 and 3.1 × 10−4, respectively, were achieved in PBT with 4 wt % SWCNT Tuball.

Boron Doping of SWCNTs as a Way to Enhance the Thermoelectric Properties of Melt-Mixed Polypropylene/SWCNT Composites

“…The corresponding electrical conductivity and therefrom calculated PF were 145,000 S/m and 85 µW/(m•K 2 ) for pristine SWCNT films and 214,000 S/m and 226 µW/(m•K 2 ) for B-SWCNT films [23]. For pristine SWCNT and B-SWCNT powders, electrical conductivities of 1790 [18] and 1810 S/m and Seebeck coefficients of 39.6 ± 0.2 [18] and 42.2 ± 0.1 µV/K were measured. This results in PF values of 2.81 [18] or 3.23 µW/m•K 2 , respectively.…”

“…For pristine SWCNT and B-SWCNT powders, electrical conductivities of 1790 [18] and 1810 S/m and Seebeck coefficients of 39.6 ± 0.2 [18] and 42.2 ± 0.1 µV/K were measured. This results in PF values of 2.81 [18] or 3.23 µW/m•K 2 , respectively. The values obtained for the SWCNTs by the two measuring methods show significantly lower electrical conductivities and slightly higher values for the powder packages than for the thin films, which may derive from the different preparation methods and packing densities in both cases and the different equipment and measuring conditions used.…”

“…The same instrument was used to measure the electrical conductivity and Seebeck coefficient of the SWCNT powders. For this, an insert consisting of a PVDF tube (inner diameter 3.8 mm, length 16 mm) closed with copper plugs was used, which was filled with the SWCNT powder [18]. The final SWCNT package had a length of 6 mm.…”

“…Examples of this new kind of melt-mixed composites are polypropylene (PP) composites filled with single-walled carbon nanotubes (SWCNT) [6][7][8][9][10], polyetherimide/SWCNT nanocomposites [11], polycarbonate/multi-walled carbon nanotube (MWCNT) composites [12][13][14], polylactic acid (PLA)-based composites containing Bi 0.5 Sb 1.5 Te 3 and/or MWCNTs [15], PLA filled with MWCNT and/or expanded graphite [16], and poly(vinylidene fluoride) (PVDF)-based polymer composite foams with MWCNTs or GNPs [17]. In a recent paper, screening of different kinds of CNTs in different polymeric matrices was performed, showing that a variety of TE properties can be achieved when varying CNT and polymer type [18].…”

Nanocomposites with p- and n-Type Conductivity Controlled by Type and Content of Nanotubes in Thermosets for Thermoelectric Applications

“…Within CPCs, mainly thermoplastic matrices are currently considered, e.g., poly(vinylidene fluoride) (PVDF) [7], polypropylene (PP) [8][9][10][11][12][13][14] and polycarbonate [15][16][17]. Other polymers such as rubber, cellulose [18] or thermoset matrices (epoxy systems) have been studied less, or not at all.…”