Bioinspired Ceramic Scaffold Reinforced Polytetrafluoroethylene Composite and Its Tribological Properties

The development of self-lubricating polytetrafluoroethylene-based composites with excellent wear resistance is urgently required for industrial lubrication applications, yet it remains a key challenge. Herein, inspired by the anti-wear mechanism of the rod/inter-rod microstructure of human tooth enamel, we present a biomimetic design strategy for creating aunidirectional porous ceramic scaffold reinforced polytetrafluoroethylene composite that achieves an elegant combination of tribological properties. The design and fabrication of the bioinspired composite were accomplished using finite element simulations and a directional freeze-casting technique modified with zirconium acetate. Simulation results indicated a significant enhancement in the load-bearing capacity of the bioinspired composite when the volume fraction of ceramic scaffold surpassed 20%. Accordingly, the bioinspired composite with a ceramic volume fraction of 25.6% was prepared and tested in this study. Vickers indentation tests, uniaxial compression tests, and reciprocating sliding wear tests were conducted to assess the mechanical and tribological properties of the bioinspired composite. Microscopic morphology and composition analysis techniques, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, were employed to investigate the wear mechanism of the bioinspired composite. The results demonstrated that the bioinspired composite had encouraging performance characterized by a self-lubricating capacity comparable to that of polytetrafluoroethylene and Igus material (a commercially available self-lubricating polytetrafluoroethylene-based composite), as well as significantly superior mechanical properties and wear resistance. Under the given friction condition, the bioinspired composite had a steady-state friction coefficient of 0.21, meeting the criteria for the application of self-lubricating polymer materials. Compared with the Igus material, the bioinspired composite showed an increase in the hardness, elastic modulus, and compressive strength by 1.8 times, 15.2%, and 2.8 times, respectively, and a reduction in the wear volume by 76.6%. Results of the morphology and composition characterizations showed that a substantial quantity of wear debris originating from counterpart surface adhered to the worn surface of the bioinspired composite, indicating an adhesive wear mechanism. Furthermore, tribochemical reaction was taken place for polytetrafluoroethylene on the friction interface, generating carboxylate end groups that enhanced the adhesion of polytetrafluoroethylene transfer film on the counterpart surface. Upon further analysis, it became evident that the exceptional tribological properties of the bioinspired composite were closely linked to its unidirectional porous ceramic scaffold-reinforced structure. This structure exhibited load-bearing characteristics similar to the Voigt model that defined the upper boundary of load-bearing capacity for composites. Consequently, it imparted excellent load-bearing capability to the composite, making the composite surface effectively resistant to deformation, damage, and wear. In addition, the bioinspired composite surface had good embeddability, retaining wear debris and mitigating three-body abrasive wear. As a result, the unidirectional porous ceramic scaffold, comprising only 25.6% of the total volume of the composite, significantly enhanced the material’s wear resistance, while the high polytetrafluoroethylene content facilitated effective interfacial lubrication during the friction and wear process.