Characterization of MWCNT and SWCNT functionalized by acid treatments and the effect of functionalized carbon nanotubes on electrical properties of PMMA-MWCNT and PMMA-SWCNT nanocomposites

Acid functionalization of multi-walled carbon nanotubes (MWCNT) and single-walled carbon nanotubes (SWCNT) were conducted with combination of mixtures of acids including sulfuric acid (H2SO4), nitric acid (HNO3) and hydrochloric acid (HCl). It was observed that moderate acid concentration combined with moderate reaction time, efficiently surface modified the carbon nanotubes (CNT) with adequate introduction of defects and attachment of necessary functional groups. Acid-treated CNT was evaluated for its compositional, morphological, and thermal properties evidencing that individual usage of H2SO4 did not damage the CNT, whereas combination of H2SO4/HNO3/HCl produced mild damages to the CNT. Energy dispersive X-ray spectroscopy (EDX) showed that oxygen percentage in functionalized CNT increased to 7.36–8.19% as against zero percentage in pristine CNT. Presence of hydroxyl, carboxyl, and carbonyl groups was evidenced in Fourier transform infrared (FTIR) spectroscopy for CNT treated with all acid treatments. Thermogravimetric studies (TGA) displayed that H2SO4-functionalized CNT displayed a greater structural stability of CNT despite higher attachment of functional groups as compared with conventional acid mixture method involving H2SO4 and HNO3. It was also observed from TGA that weight residue percentage of pristine MWCNT was 89% and pristine SWCNT was 94% and with functionalization residue percentage significantly decreased, indicating that CNT were more prone to thermal degradation after functionalization. Nanocomposite films were fabricated using functionalized CNT as filler and polymethyl methacrylate (PMMA) as matrix. Electrical properties of the nanocomposite films were evaluated. On comparing the electrical properties of the nanocomposites, composites containing H2SO4-functionalized CNT displayed higher electrical properties as it was supported by stable CNT structure along with attachment of oxygen containing functional groups. It was observed that maximum value of electrical conductivity of PMMA-MWCNT and PMMA-SWCNT nanocomposites was enhanced to the order of 10–3 S/cm and 10–2 S/cm respectively, from 10–6 S/cm for pure PMMA at 1 MHz. This enhancement is an increase in conductivity of the order of 103 times for PMMA-MWCNT and 104 times for PMMA-SWCNT nanocomposites. © 2023, King Abdulaziz City for Science and Technology.