Dielectric and Small Angle Neutron Scattering Analysis of Molded and 3D Printed Polypropylene-Graphene Nanocomposites

Graphene is an important 2D material and has several beneficial characteristics [1-2]. 3D printing is a very useful technique for making polymeric materials of desired shapes. Dielectric characteristics are important physical properties of materials. Recently, we observed negative dielectric constant values in polyethylene – graphene nanocomposites [3]. It was observed that the composite became negative dielectric constant material when the concentration of graphene increased to 20%. In this research the variation in dielectric characteristics was studied for both molded and 3D printed polypropylene graphene nanocomposites. In this work polypropylene (PP) and graphene were mixed using plastic order (brabender) to have polypropylene with 0, 10 and 20% graphene. This average size of the graphene used is 5 micron length, 15 nm thickness and typical surface area is 60-80 m ²g ^-1. Graphene nano platelets – grade H5 were obtained from XG sciences, USA. Small angle neutron scattering (SANS) is a useful technique to understand the microstructure of the nanocomposites. Using SANS it was observed that fractal structures were observed in graphene containing molded and the 3D printed samples. As the graphene concentration increased the scattering increased. The scattering intensity for molded samples was greater than the scattering intensity for the 3D printed samples. Broadband dielectric relaxation spectroscopy (BDS) is a useful technique to study the polymer dynamics and conductivity in polymer composites. Using BDS it was observed that between at higher frequencies (10 3 -10 6 Hz) the dielectric constant for molded and 3D printed polypropylene is nearly the same (2.9 and 3.1) respectively. However the dielectric constant at higher frequencies for 90%PP-10%graphene molded samples is ~ 40.5±12.4 and for 3D printed samples it is ~12.1± 0.4. Similarly the dielectric constant for 80%PP-20%graphene at high frequencies for molded samples is ~102.4 ± 46.0 and for 3D printed samples it is ~52.3 ± 24.8 . Hence the dielectric constant at higher frequencies for molded samples is greater than that of 3D printed samples. Interestingly, negative dielectric constant was also observed at lower frequencies. It was observed that the dielectric constant for molded samples became more negative when compared to the 3D printed samples. other parameters such as dielectric loss, loss tangent, electric modulus were also measured and it was observed that their values were different for 3D printed samples from that of samples prepared by molding process. hence the dielectric properties can be tailored using 3D printing technique. This research could benefit using graphene in batteries.<br/><br/>References:<br/><br/>1 Wang, Y.; Huang, Y.; Song, Y.; Zhang, X.; Ma, Y.; Liang, J.; Chen, Y. Nano letters. 2008, 9(1), 220-224.<br/>2 Banhart, F.; Kotakoski, J.; Krasheninnikov, A.V. ACS nano. 2010 5(1), 26-41.<br/>3. Ramasamy, R.P., Aswal, V.K., Rafailovich, M.H. and Halada, G. Journal of Materials Science:Materials in Electronics,2020, 31(21), pp.18344-18359.