Effect of self-healing microcapsules on the tribological properties of UHMWPE composites

[Objective] The water-lubricated tail bearing is a critical component of a ship's propulsion System. Its stability and reliability significantly affect the safety of ship Operations. Under low-speed, heavy-load conditions, forming a stable hydrodynamic lubrication water film becomes challenging, often resulting in poor lubrication. This can cause micro-defects on the composite material's surface. To address this, microcapsules containing diisoeyanate are incorporated into the composite material, enabling it to autonomously repair such micro-defects. This study explores how the mass fraction of self-healing microcapsules affects the self-repairing ability, mechanical properties, and tribological Performance while also analyzing the underlying mechanisms.[Methods] Self-healing microcapsules containing active IPDI self-healing agents were prepared using a combination of Pickering emulsion and in situ polymerization methods. Composite materials infused with these microcapsules were then fabricated using hot pressing. The mechanical properties of the composites were analyzed using differential scanning calorimetry, dynamic mechanical analysis, and mechanical Performance tests. Scratch tests were employed to assess the self-repairing capabilities of the composites, while an Rtec tribometer was used to evaluate their tribological properties. The worn surfaces were examined using a scanning electron microscope and laser confocal microscopy.[Results]The addition of self-healing microcapsules negatively impacted the mechanical properties of the composite materials as the microcapsule mass fraction increased. Specifically, the crystallinity of the composites containing 5%, 10%, and 15% microcapsules decreased to 9.87%, 12.37%, and 14.50%, respectively, compared to UHMWPE-1. The storage modulus decreased by 28.33%, 31.8%, and 38. 61% while bending strength decreased by 13.56%, 18.29%, and 26.58%. When the microcapsule mass fraction exceeded 10%, the decline in mechanical properties accelerated. This was attributed to poor microcapsule dispersion of microcapsules within the matrix material content, which reduced rigidity and elasticity. Regarding self-repairing Performance, the self-healing efficiencies of UHMWPE-I5, UHMWPE-I10, and UHMWPE-115 composites reached 16%, 33%, and 78%, respectively. However, the tribological properties degraded under low-speed, heavy-load working conditions (Condition 2). Compared to UHMWPE-1, the average friction coefficients of UHMWPE-15, UHMWPE-I10, and UHMWPE-115 increased by 22. 68%, 49.03%, and 101.72%, while wear volumes grew by 66.88%, 67. 57%, and 73.42%. Additionally, higher microcapsule content led to more pronounced adhesive wear on the composite surface. Similarly to the mechanical properties, the decline in tribological properties intensified when the microcapsule mass fraction exceeded 10%.[Conclusions] This study analyzed the impact of self-healing microcapsules on composite material Performance, focusing on mechanical properties, tribological behavior, and self-repairing ability. As the microcapsule mass fraction increased, the self-repairing Performance improved significantly but at the expense of reduced mechanical and tribological properties. The optimal microcapsule mass fraction was identified as 10%, striking a balance between maintaining mechanical and tribological integrity and achieving effective self-repairing capabilities. These findings lay a solid experimental foundation for optimizing self-healing water-lubricated composite materials. © 2025 Tsinghua University. All rights reserved.