Influence of acid dopants on the antibacterial activity of carrageenan/polyaniline composite films

Synthetic and petrochemical based polymeric antibacterial materials are typically used as surface coatings and have since led to pollution. To overcome this problem, a biopolymer, κ-carrageenan (κ-CGN) was introduced as a matrix of the antibacterial film incorporating polyaniline (PAni) as the antibacterial agent. PAni was synthesized by chemical oxidative method with different acid dopants which are hydrochloric acid (HCl), sulphuric acid (H 2 SO 4 ) and phosphoric acid (H 3 PO 4 ) followed by characterization of Fourier transform infrared spectrophotometry (FTIR), Ultraviolet-visible spectrophotometry (UV-Vis), electrical conductivity and thermogravimetric analysis (TGA). Among all the doped PAni, PAni–H 2 SO 4 showed the highest conductivity (28.65 ± 0.21 S/cm) and decomposition temperature, T d (536.74 °C) compared to PAni–HCl (8.67 ± 0.83 S/cm; T d : 478.45 °C) and PAni–H 3 PO 4 (8.29 ± 1.16 S/cm; T d : 508.76 °C). κ-CGN/PAni films were produced through ex-situ method and evaluated by FTIR, conductivity measurements, tensile tests and TGA. All κ-CGN/PAni films had successfully inhibited the growth of Staphylococcus aureus (Gram-positive bacteria) but not Pseudomonas aeruginosa (Gram-negative bacteria). The mechanism of the bacterial inhibition was suggested that the protonated PAni was electrostatically attracted to the anionic membrane of the bacteria and disrupted the membrane, leading to cell death. κ-CGN/PAni–HCl film had the best antibacterial performance against S. aureus with minimal doped PAni included in the film (10 % wt PAni; inhibition %: 35.82 %) compared to κ-CGN/PAni–H 2 SO 4 film (20 % wt PAni; inhibition %: 35.44 %) and κ-CGN/PAni–H 3 PO 4 film (30 % wt PAni; inhibition %: 37.65 %). κ-CGN/PAni–HCl film was the best composite that possesses the highest antibacterial performance as well as good mechanical properties (tensile strength: 1.51 MPa; elongation at break: 18.76 %) by utilizing only 10 % of PAni–HCl.