Rust conversion of archeological cannonball from Fort Cornwallis using oil palm frond lignin

The utilization of rust converters is one of the strategies invented to prevent further rusting of the archeological iron. This study reports oil palm fronds (OPF) lignin as a new green substitute in industrial applications such as rust converters due to its antioxidant properties. First, the lignin samples isolated from soda and organosolv pulping were evaluated using complementary analyses such as FTIR, 13C NMR, and TGA. The analyses revealed that soda is lignin-rich in antioxidant properties compared to organosolv lignin. A rust sample from an archeological cannonball was evaluated using complementary analyses such as FTIR, XRD, and SEM/EDX. The analyses showed that lepidocrocite was the main component of the rust in the archeological cannonball. The FTIR study on the performance of OPF on rust treatment via the effects of concentration, pH, and reaction time were evaluated. Soda lignin showed the best rust converter from the FTIR spectra at 7 wt% concentration with 92.73%. The treated rust at a 7 wt% concentration of soda lignin was then further analyzed using XRD and SEM/EDX analysis, which showed that the treated rust has nearly changed to an amorphous form. Potentiodynamic polarization measurement revealed that 7 wt% soda lignin-modified archeological cannonball rust sample immersed in 3.5 wt% NaCl solution was able to attain a corrosion inhibition efficiency of 86.9%.