Multi-walled carbon nanotube/polyurethane electrothermal films

Multi-walled carbon nanotubes (MWNTs) were prepared by pyrolysis of cheap natural gas over Ni/La2O3-MgO catalyst at 740 °C. The purified MWNTs were easily dispersed by ball milling method and aqueous dispersion with 10 wt% MWNT concentration was obtained. MWNT aqueous dispersion was mixed with waterborne polyurethane to prepare MWNT-polyurethane composite films containing 20–60 wt% MWNTs on PET substrate by a rod-coating method. The electrical resistivity of composite films decreased from 0.38 Ω·cm of the film with 20 wt% MWNTs to 0.032 Ω·cm of the film with 60 wt% MWNTs owing to gradual formation of a more efficient MWNT conductive network. The time-dependent temperature curves indicated that the steady-state temperature of MWNT-polyurethane composite films as electric heating elements was positively correlated with MWNT content and applied voltage. For the composite film (4 cm × 4 cm heating area) with 40 wt% MWNTs, the steady-state temperature was 41.4 °C, 54.5 °C and 70.2 °C, respectively, at 5 V, 7.5 V and 10 V, while that of the composite film with 50 wt% MWNTs can reach 48.6 °C, 69.7 °C and 95.5 °C, respectively, under 5 V, 7.5 V and 10 V. Furthermore, aqueous dispersion with 14 wt% MWNTs could also be easily and well dispersed. The composite film with 50 wt% MWNTs prepared by 14 wt% of MWNT dispersion showed higher steady-state temperature of 53.6 °C, 82.5 °C and 120.2 °C, respectively, at 5 V, 7.5 V and 10 V.