Structure-property relationships in bifunctional benzoxazines and their basalt-fiber-reinforced composites: curing behavior, thermal stability, antimicrobial activity, and corrosion protection

This study synthesized bifunctional benzoxazine monomers via Mannich condensation of 4-tert-butylcatechol (C) with five structurally varied amines to tailor curing studies and multifunctional performance. Molecular structures of benzoxazines were confirmed through spectral techniques, while thermal behavior was evaluated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Among the benzoxazines, C-ap exhibited the lowest curing temperature (181 °C). In this DSC curing kinetic study, the activation energy value E a = 124.71 kJ mol -1 for C-ap and 174.59 kJ mol − 1 for C-at (Kissinger) and 118.54 kJ mol − 1 for C-ap and 173.86 kJ mol − 1 for C-at (Ozawa) at different heating rates. C-aa possessed good antimicrobial property against Escherichia coli and Staphylococcus aureus , with inhibition zones of 20 and 15 mm, respectively. Minimum inhibitory concentration (MIC) analysis showed that C-aa exhibit inhibition against both E. coli and S. aureus . In TGA analysis, poly (C-ap) exhibited the highest char yield of 58% than rest of the polybenzoxazines. In addition, basalt-fiber-reinforced with poly (C-at) exhibited improved thermal performance. Among the polybenzoxazines, poly (C-ap) showed the highest water contact value of 148°. All poly (C-bz) demonstrated outstanding corrosion protection, achieving a corrosion inhibition efficiency of 99%, which was further rationalized by density functional theory (DFT) calculations.