Tribological evaluation of date seed oil and castor oil blends with halloysite nanotube additives as environment friendly bio-lubricants

The biodegradable and eco-friendly nature of vegetable oils make them promising replacement for the depleting mineral oils as industrial lubricants. However, the poor tribological properties of vegetable oils remain a challenge in their industrial applications. In this study, environmentally friendly halloysite clay nanotube (HNT) additives have been incorporated (0.25, 0.5, 0.75, and 1 wt.%) in the pyrolysis date seed oil and castor oil blends for enhancement of tribological properties. HNTs are easily available, low priced, and non-toxic nanomaterials, making them potential green lubricant additives. The date seed oil was extracted employing a 20-L pyrolysis reactor and blended with castor oil in different ratios. The addition of HNTs into castor oil and date seed oil blends (bio-lubricant) increased the viscosities by up to 13.4% with 1 wt.% HNTs added. Wear scar diameter (WSD) was also reduced by 7.72, 8.08, 15.22, and 21.32% for formulated bio-lubricants containing 0.25, 0.5, 0.75, and 1 wt.% HNTs, respectively. Furthermore, coefficient of friction (COF) of bio-lubricants was reduced by 12.6, 16.4, 16.7, and 28.2% with 0.25, 0.5, 0.75, and 1 wt.% HNTs. SEM images further confirmed the level of abrasive wear was reduced and smooth surfaces were observed in bio-lubricants with HNT additives. The formulated bio-lubricants showed good stability with different concentrations of HNTs as tested for a period of up to 72 h. The environment friendly bio-lubricants formulated by utilizing date seeds waste source and non-toxic biocompatible HNTs with improved tribological properties will lead to develop advanced bio-lubricants for multiple energy conservation and environmental benefits.