Sources of Delectric Loss in Polypropylene Based Nanocomposites

As data-rate communication speeds continue to increase to hundreds of GHz, low-loss polymer nanocomposites have emerged as a promising material for producing interconnects and waveguides capable of operating at these high frequency speeds with minimal loss in signal transmission. A major roadblock to increasing data-rate communications is a lack of low-loss interconnects, similar to metallic waveguides at the microwave regime, at these submillimeter-wave frequencies. Current coaxial cables are capable of operating speeds of 15 Gbps, but require high power consumption due to their high signal loss. Polymer nanocomposites, materials consisting of metal oxide nanoparticles in a polymer matrix, offer unique advantages over current waveguides. Higher permittivities than the pure polymer can be obtained while maintaining low loss of the polymer matrix. Furthermore, the dielectric properties can be tuned, depending on the choice of materials and the loading fraction of inorganic nanoparticles while retaining the processibility of polymers. In this work, each constituent’s role and its contribution to the overall dielectric loss of the nanocomposite across two frequency ranges, 100 Hz – 300 kHz and 140 – 220 GHz, will be discussed. We have achieved an effective permittivity of 6.84 with loss tangent of 0.0049 at 220 GHz in a 21.5vol% TiO2/polypropylene nanocomposite. The role of polypropylene-graft-maleic anhydride as a compatibilizer, and its effects on nanoparticle distribution and as a source of dielectric loss will be presented. Furthermore, the effects of TiO2 nanoparticle size on the effective permittivity and loss in polypropylene is investigated. Introducing complex permittivity into Lichtenecker’s model, we are able to separate the loss contributions from either the polymer matrix or the TiO2 nanoparticles to the measured loss in the nanocomposites. Finally, future areas of study and routes for reducing loss in polymer nanocomposites are introduced.