Using an Ionic Liquid to Reduce the Electrical Percolation Threshold in Biobased Thermoplastic Polyurethane/Graphene Nanocomposites

Abstract

Biobased thermoplastic polyurethane (bTPU)/unmodified graphene (GR) nanocomposites (NCs) were obtained by melt-mixing in a lab-scaled conventional twin-screw extruder. Alternatively, GR was also modified with an ionic liquid (GR-IL) using a simple preparation method with the aim of improving the dispersion level. XRD diffractograms indicated a minor presence of well-ordered structures in both bTPU/GR and bTPU/GR-IL NCs, which also showed, as observed by TEM, nonuniform dispersion. Electrical conductivity measurements pointed to an improved dispersion level when GR was modified with the IL, because the bTPU/GR-IL NCs showed a significantly lower electrical percolation threshold (1.99 wt%) than the bTPU/GR NCs (3.21 wt%), as well as higher conductivity values. Young’s modulus increased upon the addition of the GR (by 65% with 4 wt%), as did the yield strength, while the ductile nature of the bTPU matrix maintained in all the compositions, with elongation at break values above 200%. This positive effect on the mechanical properties caused by the addition of GR maintained or slightly increased when GR-IL was used, pointing to the success of this method of modifying the nanofiller to obtain bTPU/GR NCs.

Extrusion of Polymer Nanocomposites with Graphene and Graphene Derivative Nanofillers: An Overview of Recent Developments

“…In this case, the dispersion of IL-modified graphene resulted in a better dispersion of the nanophase. The obtained nanocomposites showed higher mechanical and electrical properties [78] (see Figure 2) and better processability [21]. Low concentrations of GO are used in PMMA matrices in presence of 1 wt.% TiO 2 processed by using twin-screw extrusion [79] with potential dental applications.…”

“…Other widely used thermoplastics include polystyrene (PS), thermoplastic polyurethane (TPU) or poly (methylmethacrylate) (PMMA) matrices [21,78,79]. Ionic liquids have been utilized to modify the surface of the nanophase aiming at better dispersibility in the polymeric matrix.…”

“…Increase of Young's Modulus (a) and conductivity (b) of thermoplastic polyurethane (TPU) −based nanocomposites with the addition of graphene[78].…”

A review concerning the main factors that interfere in the electrical percolation threshold content of polymeric antistatic packaging with carbon fillers as antistatic agent

“…[16] Besides, the addition of such materials may diminish the water vapor permeability of the polymer by increasing the tortuosity path for the diffusion of water molecules, conferring better protection for electronic components sensitive to moisture. [17] Among the carbon materials used as antistatic agents, it is possible to mention CNTs, [18] carbon black (CB), [19] glassy carbon (GC), [20] graphene, [21] and graphite/graphene nanoplatelets (GNP). [22] The particles of antistatic agents have different shapes.…”

Carbon-Based Polymer Nanocomposites for High-Performance Applications

“…Nonetheless, the properties of this type of nanocomposites are frequently limited by the heterogeneous graphene dispersion within the PU matrix. To solve this issue, an ionic liquid can be used as a dispersing agent [30]. The resulting nanocomposites exhibited a lower electrical percolation threshold, about 2 wt %, than the counterparts with pristine graphene, together with higher conductivity values.…”