Sustainable enhanced microwave synthesis of polypyrrole and polypyrrole/chitosan composites: Structural characterisation and antimicrobial performance

Polypyrrole (PPy) is a widely studied conducting polymer (CP) due to its low-cost synthesis, environmental stability, intrinsic electrical conductivity, bioactivity and inherent antibacterial activity. Strong antibacterial performance typically requires polymerisation under highly acidic conditions (pH ≤ 2) to obtain the doped conductive form. To enhance processability, support large-scale production, and tune the properties, the biopolymers such as chitosan (Ch) can be incorporated to form composites. In this study, PPy and PPy/Ch composites were synthesised using both the classical chemical synthesis (CS) and an eco-friendly enhanced microwave (MW) method. Two oxidising agents were evaluated: the standard ammonium persulfate ((NH 4 ) 2 S 2 O 8 ) and, for the first time in a scalable approach, potassium iodate (KIO 3 ). Pristine PPy synthesised with (NH 4 ) 2 S 2 O 8 displayed a cauliflower-like granular morphology, while KIO 3 -based samples exhibited denser surfaces with well-defined spherical particles. MW-processed PPy/Ch composites showed more compact structures with uniformly dispersed globular PPy domains and demonstrated higher conductivity than CS-synthesised samples. FTIR spectra confirmed successful incorporation of PPy within the composite matrix. All PPy/Ch composites showed enhanced antibacterial activity against both bacteria and bacteriophage Phi X 174 compared with pure Ch. PPy/Ch composites were consistently more active against Gram-negative Escherichia coli than Gram-positive Staphylococcus aureus . The antiviral results indicate that PPy and PPy/Ch behave similarly at 0.5 wt%, independent of synthesis method, while the MW-derived PPy/Ch formulation is noticeably less potent, showing the weakest activity at 1 wt%. Overall, the results indicate that the rapid, scalable MW method enables controlled PPy formation and tuning of composite properties for targeted applications.