# Epoxy/Glass Fiber Nanostructured p- and n-Type Thermoelectric Enabled Model Composite Interphases
## 4 Discussion
### Thermal Stability of the Produced Coated GF Tows  
Thermogravimetric analysis was used in order to characterize the thermal stability of the SWCNTs coated GFs in comparison to the reference GFs. As depicted in Figure 5, a minor mass loss in the order of almost 0.05% was observed for the reference GFs as well as for the n-type SWCNTs coated GFs above 100 \({}^{\circ}\)C and up to 241.5 \({}^{\circ}\)C and 213.2 \({}^{\circ}\)C, respectively. The p-type SWCNTs coated GFs depicted a similar behavior at that temperature range losing, however a slightly higher amount of its mass, namely 0.28% up to 175.3 \({}^{\circ}\)C. This mass loss is attributed to the evaporation of residual moisture for all the samples and is observed to be increased in the p-type SWCNTs coated GFs due to the increased amount of carboxy moieties. At higher temperatures, between about 241.5 \({}^{\circ}\)C and 539.2 \({}^{\circ}\)C the reference GFs lost 0.7% of their mass due to the combustion of the silane type sizing [38; 39; 40]. Then, the mass of the E-glass fibers remained almost constant without considerable weight loss up to 1000 \({}^{\circ}\)C.  
The thermal degradation of the p-type and the n-type molecular doped SWCNTs is a multistage process due to the existence of the various functional groups that are absorbed on their surface or are interacting with it. The functional chemical groups as moieties that SWCNTs contain are in general decomposed during the second temperature range that spans from roughly 200 \({}^{\circ}\)C to 500 \({}^{\circ}\)C. In more detail, the p-type SWCNTs exhibited the typical decomposition behavior of pristine SWCNTs that are  
Figure 8: (**a**) Interfacial shear strength values for the p-type and the n-type TE model composites compared to the reference one, (**b**) fractography images for the respective three examined categories. inherently p-doped by a small amount of adsorbed oxygen containing groups. The oxygen-based moieties promote the electron withdrawing process from the CNT electron-rich back-bone, effectively introducing holes as main charge carriers (p-doping). The p-type SWCNTs coated GFs lost ca. 1% of their mass up to 373 \({}^{\circ}\)C that can be attributed to smaller in size oxygen containing functional groups like hydroxy and ether moieties. Another 1.35% mass loss was observed up to 531 \({}^{\circ}\)C that can be due to larger oxygen containing moieties like carboxyl and ester moieties [41]. The initial mass loss of SDBS molecules is owing to burning with the presence of oxygen (330-450 \({}^{\circ}\)C) and the burning of the SDBS continued to occur above 800 \({}^{\circ}\)C [42]. Overall, due to the fact that the SDBS concentration is lower (2 mg/mL) in the n-type SWCNTs coatings, this may also explain the loose of less weight compared to the p-type SWCNTs coatings (5 mg/mL). The observed loss amount is in agreement with the percentage of SDBS and CNTs that were used for the preparation of the inks. Additionally, any amorphous carbon that might be present into the SWCNTs coating would also be combusted at this temperature range. A further 0.7% mass loss occurred up to 756 \({}^{\circ}\)C that can be attributed to the combustion of the SWCNTs. Then, the mass of the underlying GFs remained almost stable up to 1000 \({}^{\circ}\)C with only a further 0.18% mass loss that can be attributed to some possible remaining percentage of catalyst particles from the production process of the CNTs [43]. A slightly different behavior was presented by the n-type SWCNTs coated GFs. The decomposition of the nitrogen containing moieties that are included in the PEI molecules, which are entangled in between the CNT network, was responsible for the 0.53% mass loss from 213 \({}^{\circ}\)C up to 368 \({}^{\circ}\)C. A further 1% mass loss was observed up to 626 \({}^{\circ}\)C that is attributed the total decomposition of the SWCNTs.