Dielectric properties and electromagnetic interference shielding effectiveness of graphene-based biodegradable nanocomposites

• Electrical permittivity and conductivity of PLA and PBAT and therefore their EMI SE enhanced markedly with GNP embedding.
• Variations of complex permittivity of PLA and PBAT with GNP loading were successfully modelled by Sihvola's mixing rule.
• For both PLA and PBAT, electrical percolation occurred at GNP loading of between 6 and 9 wt% (3.5 and 5.3 vol%).
• PLA nanocomposites with 9 – 15 wt% GNPs had higher dielectric loss values compared to PBAT nanocomposites.
• PLA/GNP nanocomposites exhibited significantly higher potential for EMI absorption than PBAT/GNP nanocomposites.

Graphene nanoplatelets (GNPs) were dispersed in poly lactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) via melt-mixing. Effect of GNP incorporation on electromagnetic properties and electromagnetic interference shielding effectiveness (SE) of PLA and PBAT was investigated and the two systems were systematically compared. Furthermore, applicability of Sihvola's mixing rule of complex electrical permittivity to these nanocomposites was studied. GNP addition significantly enhanced permittivity of both polymers. Dielectric constants of PLA and PBAT nanocomposites had comparable values. However, above 6 wt% GNPs, PLA nanocomposites showed significantly higher dielectric loss than PBAT nanocomposites, even though pure PLA had lower dielectric loss than pure PBAT. This was attributed to the dispersion state of GNPs in the two matrices, detected in morphological studies. SE of both polymers increased with GNP addition due to enhancement of their dielectric properties. The difference in dielectric loss of the two systems was revealed in their ability to attenuate the radiation by absorption. At 15 wt% GNPs, 1 mm-thick PLA/GNP nanocomposite had an effective absorbance of 70%. This value was only 43% for PBAT/GNP nanocomposite. Variations of polymers' permittivities with GNPs were successfully modelled by Sihvola's rule. While both systems returned close values for model's fitting parameters, it better fitted PBAT/GNP nanocomposites.

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