Antioxidative properties of hydrogenated cardanol for cotton biodiesel by PDSC and UV/VIS

Biodiesel is a non-toxic biodegradable fuel that consists of alkyl esters produced from renewable sources, vegetal oils and animal fats, and low molecular mass alcohols, and it is a potential substitute for petroleum-derived diesel. Depending on the raw materials used, the amount of unsaturated fatty acids can vary in the biodiesel composition. Those substances are widely susceptible to oxidation processes, yielding polymeric compounds, which are harmful to the engines. Based on such difficulty, this work aims to evaluate the antioxidant activity of cashew nut shell liquid (cardanol), as additive for cotton biodiesel. The oxidative stability was investigated by the pressure differential scanning calorimetry (PDSC) and UV/Vis spectrophotometer techniques. The evaluated samples were: as-synthesized biodiesel - Bio T-0, additivated and heated biodiesel - Bio A (800 ppm L-1 of hydrogenated cardanol, 150A degrees C for 1 h), and a heated biodiesel - Bio B (150A degrees C, 1 h). The oxidative induction time (OIT) analyses were carried out employing the constant volume operation mode (203 psi oxygen) at isothermal temperatures of 80, 85, 90, 100A degrees C. The high pressure OIT (HPOIT) were: 7.6, 15.7, 22.7, 64.6, 124.0 min for Bio T-0; 41.5, 77.0, 98.6, 106.6, 171.9 min for Bio A and 1.7, 8.2, 14.8, 28.3, 56.3 min for Bio B. The activation energy (E) values for oxidative processes were 150.0 +/- 1.6 (Bio T-0), 583.8 +/- 1.5 (Bio A) and 140.6 +/- 0.1 kJ mol(-1)(Bio B). For all samples, the intensities of the band around 230 nm were proportional to the inverse of E, indicating small formation of hyper conjugated compounds. As observed, cardanol has improved approximately four times the cotton biodiesel oxidative stability, even after the heating process.