## 3 Results and Discussion
From the DTG curves, it can be noticed that neat TPU degrades in 2 steps: the first peak, occurring at 335 \({}^{\circ}\)C, is related to the scission of urethane bonds, while the second peak, at 390 \({}^{\circ}\)C, corresponds to the dehydration reaction of the material produced by the scission of polyol segments [41]. The introduction of MWCNTs can slightly shift these two degradation steps towards higher temperatures. In particular, the first peak was shifted to 336 \({}^{\circ}\)C and 338 \({}^{\circ}\)C, while the second one was shifted to 391 \({}^{\circ}\)C and to 393 \({}^{\circ}\)C, when the samples had MWCNT content values of 0.5 wt% and 1 wt%, respectively. In the M6D-filled composites, the first degradation step of the TPU matrix coincides with the decomposition of the paraffin inside the microcapsules at 350 \({}^{\circ}\)C. The last degradation step detectable in the M6D-filled samples is located at 395 \({}^{\circ}\)C, and it is probably attributable to the presence of the crosslinked organic shells of the capsules, which have superior thermal resistance with respect to the TPU matrix. If the breakage of the microcapsules could be prevented, the thermal  
Figure 3: High-magnification FESEM micrographs of 3D-printed (**a**) TPU, (**b**) TPU_1 MWCNT, (**c**) TPU_30M6D_1 MWCNT, and (**d**) TPU_40M6D_1 MWCNT samples. degradation resistance of the composites would be comparable to that of TPU. It can therefore be concluded that the introduction of MWCNTs, resulting in a slight positive shift of the degradation steps, did not significantly compromise the overall thermal stability of the material. On the other hand, in the M6D-filled composites, the coincidence of the paraffin decomposition temperature with the TPU first degradation step, coupled with the decomposition of the crosslinked organic shells of the capsules at high temperatures, underscores the complex thermal degradation behavior of the prepared multifunctional composites. Further efforts will be made in the future to prevent microcapsule breakage and thus render the degradation resistance of the nanocomposites comparable to that of neat TPU. DSC is the main technique for evaluating the efficiency of materials that should be utilized for thermal energy storage applications, as it can give a precise measurement of the latent heat involved in phase-change transformations. In Figure 5a,b, DSC curves of the 3D-printed neat TPU and relative composites collected during the first heating step and the cooling scan, respectively, are reported, while the most important results are summarized in Table 1. This table also contains some results obtained in ref. [34] for neat capsules and TPU filled only with M6D capsules is reported for comparison. Neat TPU does not present any crystallization or melting peaks in the temperature range from \(-100\)\({}^{\circ}\)C to \(200\)\({}^{\circ}\)C, and only an inflection point corresponding to the glass transition temperature (Tg) can be detected at \(-42\)\({}^{\circ}\)C. This very-low Tg value determines the rubbery behavior of this material at room temperature. Regarding the composite samples, the melting peak is located at around \(5\)\({}^{\circ}\)C in the heating stage, while the crystallization peak is at about \(-8\)\({}^{\circ}\)C in the cooling ramp. It can be noticed that both the melting and crystallization temperatures are only slightly affected by the introduction of M6D, and the limited Tm and Tc shifts can be attributed to the thermal inertia effect generated by the microcapsules [34; 37]. The melting and crystallization enthalpy values are proportional to the M6D content and do not seem to be influenced by the presence of MWCNTs. However, the thermal energy storage efficiency of the prepared composites is relatively high, with the relative melting and crystallization enthalpies being higher than 80% for all the tested compositions. These efficiency values are consistent with the results previously found for TPU/M6D blends [34; 37].