Synthesis and characterization of a new acrylamide- based antioxidant for improving thermal and oxidative stability of fuel systems

A new antioxidant made from acrylamide, called (E)- N -(3-hydroxypyridin-2-yl)-3-(2-nitrophenyl)acrylamide (HPNP-AM), was created through a chemical reaction and its structure was confirmed using techniques like Fourier Transform Infrared spectroscopy (FT-IR), ¹H and ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy, and elemental analysis. The antioxidant capacity of HPNP-AM was comprehensively assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH˙) radical scavenging assay, which is widely accepted for evaluating the free radical neutralization potential of antioxidant agents. HPNP-AM showed a strong antioxidant effect, with an IC₅₀ value of 35.70 ± 0.03 µg/mL, which is much better than the reference antioxidant BHA at 71.62 ± 0.14 µg/mL. These results show that HPNP-AM is very effective at fighting free radicals and could be a useful additive for improving the stability of biodiesel and diesel fuel mixtures. The compound was tested as an additive in a biodiesel–diesel mixture (B30D70) to evaluate its influence on oxidative and thermal stability. Differential Scanning Calorimetry (DSC) analysis demonstrated that the HPNP-AM enriched blend exhibited the lowest crystallization onset temperature (–10.78°C), indicating improved cold flow performance at low temperatures. Thermogravimetric Analysis (TGA) showed an increased decomposition onset temperature (162.56°C), confirming enhanced thermal resistance. Furthermore, FT-IR spectroscopy revealed the incorporation of amide and phenolic functional groups within the fuel matrix, suggesting effective radical-scavenging and molecular stabilization. These findings highlight the utility of HPNP-AM as a promising multifunctional additive for improving the oxidative stability and heat resistance of biodiesel–diesel fuel blends.