Multifunctional additives for lubricating oil

Abstract

Lubricant additives play a critical role in delivering functionalities beyond those of base oils alone, including friction and wear control, corrosion inhibition, contaminant management and oxidation resistance. These functions are essential for maintaining engine durability, preserving lubricant performance and improving energy efficiency, thereby supporting long-term decarbonisation targets. However, conventional additive technologies rely heavily on metals, sulfur and phosphorus, which are increasingly restricted due to environmental concerns and incompatibility with modern after-treatment systems. This thesis addresses the need for more sustainable alternatives by exploring lubricant additive systems based on second-row elements, with particular emphasis on boron- and nitrogen-containing chemistries.

Two distinct additive strategies were investigated. In the first, dispersed covalent organic framework (COF) materials were evaluated in low-viscosity base oils. While certain COF structures exhibited limited effectiveness due to dispersion instability, alternative frameworks demonstrated clear potential to reduce friction and wear when appropriately stabilised, highlighting the importance of structural features and formulation compatibility. In the second approach, oil-soluble Schiff base–boron Lewis acid systems were examined as ashless multifunctional additives. These soluble formulations delivered notable anti-wear performance alongside effective corrosion protection, with boron-derived species contributing to tribofilm formation under boundary lubrication conditions.

Overall, this work broadens the design space for metal-, sulfur-and phosphorus-free lubricant additives and provides new insights into the development of environmentally responsible, next-generation lubrication technologies.

Thesis is embargoed until 31 December 2031.

Date of Award	Dec 2026
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Petronas, Malaysia
Supervisor	Gosia Swadzba-Kwasny (Supervisor) & Stuart James (Supervisor)