Tribological Performance Inspired by Nature: Plant Oils, Fungi and Algae

Mineral oil-based lubricants pose significant environmental risks due to poor biodegradability and toxicity, particularly when released into ecosystems. Sustainable lubrication therefore demands functional alternatives. This thesis investigates bio-based strategies inspired by natural systems, focusing on materials from plants, fungi and algae. First plant oils were evaluated as renewable biolubricants used without chemical modification. Tribological testing demonstrated reductions in both friction and wear. Mixtures of oils combined the advantages of individual components, providing a practical route for improving performance. A biomimetic approach was then applied to water-based lubrication using fungal polysaccharides. Extracts from mushrooms and aqueous β-glucan solutions reduced friction and wear, linked to polysaccharide concentration and particle size distribution. These findings establish fungal polysaccharides as promising candidates for bio-lubrication. Polysaccharides from plants and algae were subsequently explored as hydrogels. Both nonionic and ionic gelation mechanisms were investigated. Different metallic ions were added to assess their impact on hydrogel properties. Hydrogels exhibited tuneable viscoelastic properties and frictional behaviour, governed by the balance between network density, water mobility, and polymer-ion interactions. An existing model was applied to separate friction into deformational and interfacial components, allowing analysis of tribological behaviour through other material parameters. To address the limitations of Hertz-based contact models for soft solids, a novel theoretical framework was developed. The limit radius model introduces a finite limit radius, beyond which deformations vanish, providing improved predictions of contact mechanics. Validation against experimental data confirmed the suitability of a polynomial-type deformation profile. Together, these findings demonstrate that natural and nature-inspired materials offer functional pathways to sustainable lubrication and theoretical advances provide accurate interpretation of their tribological behaviour. Plant oils, fungal polysaccharides and polysaccharide hydrogels each present distinct advantages and limitations, advancing the development of environmentally compatible lubricants.