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Polyaniline-modified carbon nanofibers were prepared in the presence of five different dopant acids, namely toluene sulfonic acid (TSA), hydrochloric acid (HCl), sulfuric acid (H2SO4), phosphoric acid (H3PO4) and camphor sulfonic acid (CSA), by oxidative polymerization. A comparative study on the effect of various types of dopants on the properties of PANI/CNF composite was performed. The electrical, dielectric and thermal properties of PANI/CNF composites were studied in contrast to pure PANI. Unlike polyaniline, all polyaniline/carbon nanofiber combination resulted in enhanced electrical and dielectric properties. Higher conductivity and thermal dependence of DC conductivity were obtained for toluene sulfonic acid-doped composite. UV–Vis analysis of the composites showed that the appreciable increase in conductivity of TSA-doped PANI/CNF composite is due to the extensive electron transfer. Further, thermogravimetric analysis showed improved thermal stability compared to PANI. A significant improvement is observed for organic acid-doped composites which suggest the presence of strong interaction between π orbitals of CNF and the quinoid rings of PANI. Hence, the study indicated that the dopants had a remarkable effect on the properties of PANI/CNF composites. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Lightweight, flexible and foldable films of polyvinyl alcohol and polyaniline modified carbon nanofibers were prepared by solvent casting method. • The reported film exhibits high shielding efficiency in both S and X-band frequencies at a thickness of 0.11 mm thickness. • High specific EMI SE of -177 dB cm3/g was obtained for PANI/CNF/PVA composite which is more than the values reported for carbon-based composites. • The flexible composite films of carbon nanofibers exhibited a dielectric constant of 62 and very shallow skin depth of 0.05 at 10.97 GHz. • Easily foldable polymer composite film with excellent absorption dominated electromagnetic interference shielding can be an excellent EMI shielding material. Abstract Here we report the microwave characterization and electromagnetic interference (EMI) shielding property of polyvinyl alcohol (PVA) based thin and flexible composite films containing carbon nanofibers (CNF) and nanofibrillated cellulose (NFC). Microwave properties of the composites were analyzed in terms of permittivity, loss tangent, skin depth and absorption coefficient. High permittivity, absorption coefficient and low skin depth were obtained for carbon nanofiber-based composites owing to its good electrical conductivity. The shielding effectiveness (SE) of two composites was measured in the 2–4 GHz (S- band) and 8–12 GHz (X-band) frequency range. Abrupt increase of SE with increasing fiber concentration was observed for CNF based composite. An electromagnetic shielding effectiveness of about −31.5 dB in the S band and of -33.6 dB in the X band was achieved at 0.11 mm thickness. The SE due to absorption (SE A) and reflection (SE R) were increased with increase of PANI/CNF content. Additionally, CNF based composite film had a very low density of 0.11 g/cm3. Compared to metals and other carbonaceous materials, this composite film exhibited a high specific EMI shielding efficiency of −177 dB cm3/g. [ABSTRACT FROM AUTHOR]