This study was conducted to investigate the feasibility of encapsulating dimethacrylate monomers within polyacrylonitrile (PAN) nanofibers via coaxial electrospinning an‎d to assess their performance in developing self-healing composites based on dimethacrylate resins. Conventional microencapsulation techniques used for methacrylate matrices are often associated with challenges, including inhomogeneous capsule distribution an‎d compromised mechanical properties of the matrix. The present research aimed to propose an alternative strategy utilizing nanofibers, which serve as a carrier for the healing agent an‎d also as a reinforcing component for the polymer matrix. These nanofibers were fabricated using the coaxial electrospinning technique. They were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared (FTIR) spectroscopy, contact angle measurements, an‎d tensile testing. The encapsulated healing agent was quantified using extraction methods an‎d Thermogravimetric Analysis (TGA). For comparison purposes, PAN nanofibers containing dimethacrylate monomers were also produced via single-nuzzle electrospinning. The flexural properties an‎d crack propagation behavior of the final composites were eva‎luated using three-point bending tests an‎d fracture toughness tests. The self-healing performance was assessed by measuring the recovery of the critical stress intensity factor (KIC) in the fracture toughness test. The findings of the study revealed that the core-to-shell viscosity ratio is a critical factor, with deviation from the optimal range (approximately 2) resulting in the formation of beaded fiber morphologies. The encapsulated monomer content within the fibers reached a maximum of 26.9%, an‎d the maximum monomer encapsulation efficiency in the nanofibers was measured at 36.85%, demonstrating the significant capacity of the coaxial electrospinning technique for encapsulation of the resin. The core-shell structure successfully preserved the tensile properties of the nanofibers compared to monolithic PAN fibers. In contrast, the dimethacrylate monomer-containing nanofibers produced via single-nuzzle electrospinning exhibited substantially lower tensile strength an‎d modulus compared to the core-shell nanofibers (by 60.22% an‎d 89.98%, respectively), indicating that the shell layer in the core-shell nanofibers is the key factor responsible for maintaining the mechanical integrity of the fibers. eva‎luation of the flexural properties of BisGMA/TEGDMA composites reinforced with different mass fractions (2.5 wt.%, 5 wt.%, an‎d 7.5 wt.%) of core-shell nanofibers showed an increase in flexural strength of 21.0%, 47.3%, an‎d 40.5%, respectively, compared to the neat resin. These results indicate that the encapsulation of BisGMA/TEGDMA monomers within the nanofibers significantly enhances the adhesion between the nanofibers an‎d the polymer matrix. The incorporation of core-shell nanofibers into the resin matrix resulted in a 29.4% increase in fracture toughness (KIC), indicating a significant improvement in the materialʹs resistance to crack propagation. However, composite specimens subjected to a secondary fracture toughness test exhibited no recovery of strength. The total encapsulated healing agent within the fibers was estimated to be 1.35 wt.% of the composite specimen. The primary cause for the lack of self-healing functionality was attributed to the insufficient release of the healing agent. The investigations conducted in this study revealed that in the nanofiber-based approach, the design of an appropriate test for eva‎luating self-healing efficacy is of critical importance. The assessment of self-healing must be conducted in a manner that enables the eva‎luation of the systemʹs efficiency in repairing initial damage. The ability to achieve healing after a sample has undergone complete fracture exceeds the restorative capacity of the fiber-based approach.

داريوش سمناني

سعيد نوري خراساني , محمد عطايي

حسين توانايي , لاله قاسمي مباركه , مهشيد خرازيهاي اصفهاني , روح اله باقرزاده