Use of an Acylated Chitosan Schiff Base as an Ecofriendly Multifunctional Biolubricant Additive

Two acylated chitosan Schiff base samples <i>ACSB-1</i> and -<i>2</i> were synthesized via a two-step reaction pathway. First the chitosan Schiff base (<i>CSB</i>) was prepared utilizing 3,5-di-<i>tert</i>-butyl-4-hydroxybenzaldehyde. In the second step, esterification with lauroyl chloride catalyzed by 4-(dimethylamino)­pyridine (DMAP) in <i>N</i>,<i>N</i>-dimethylacetamide (DMAc) solvent affords the final product acylated chitosan Schiff base (<i>ACSB-1</i> and -<i>2</i>). The products were identified and characterized by Fourier transform infrared (FT-IR) spectroscopy, CHN analysis, thermogravimetry (TG), X-ray diffraction (XRD), etc. The synthesized compounds were evaluated as multifunctional additives for antioxidant and lubricity properties in <i>N</i>-butyl palmitate/stearate. A rotating pressure vessel oxidation test (ASTM D2272) was used for evaluating antioxidant property. The thermo-oxidative stability of the <i>N</i>-butyl palmitate/stearate oil was increased 1.5 times by using this additive in 3000 ppm concentration of <i>ACSB-2</i> at 150 °C. Lubricity property was evaluated by using the four ball test (ASTM D4172A) which was performed at 75 °C temperature, frequency of 1200 rpm, and 198 N load for 60 min. The lubricating efficiency of the synthesized sample was estimated by measuring the average wear scar diameter (WSD) of the spherical specimen. The WSD is also found to be decreased significantly by adding these compounds as additives in <i>N</i>-butyl palmitate/stearate. Both samples passed the copper strip corrosion test (ASTM D130) too