Post-draw PAN-PMMA Nanofiber Reinforced and Toughened Bis-GMA Dental Restorative Composite

Objectives: The polyacrylonitrile (PAN)-poly(methyl methacrylate) (PMMA) core-shell nanofiber reinforced dental composites have been investigated for their excellent interface adhesive, and this kind of novel dental composite has the potential for clinical uses such as denture base resin and crown-bridge material. The first objective of this work was to determine the improving effect of tensile properties by post-drawing PAN-PMMA nanofibers membrane. The second objective was to examine the flexural strength (Fs), flexural modulus (Ey) and work of fracture (WOF) of Bis-GMA/TEGDMA composites reinforced with PAN-PMMA nanofibers.

Methods: PAN(core)-PMMA(shell) nanofiber was made by an electrospinning setup with a high-speed rotating rod-like collector. The post-draw process was carried out at 120 degrees C for 5 min, and all the nanofiber membranes were elongated to the desired elongation ratio (30%, 60% or 100%). Tensile properties and flexural properties of both nanofiber membranes and nanofiber reinforced Bis-GMA/TEGDMA composites were investigated. A scanning electron microscope (SEM) was used to observe the fiber morphology and the fracture surface of the composite. A dynamic mechanical thermal analyzer (DMTA) was employed to determine the dynamic mechanical properties such as tandelta and E'.

Results: The post-drawing treatment significantly improved the tensile properties and fiber parallelism of nanofiber membranes. The addition of PAN-PMMA nanofibers into Bis-GMA/TEGDMA clearly showed the reinforcement effect; the flexural strength (Fs), flexural modulus (Ey) and work of fracture (WOF) kept rising with the nanofiber mass fraction changing from 0%, 0.6%, 0.8%, 1.0% to 1.2%. The flexural properties of composites reinforced with post-drawn nanofiber were further increased in comparison with those of untreated nanofiber reinforced ones. Also, the SEM observations of the fracture surface of the composites demonstrated good interfacial adhesion between fibers and resin.

Significance: The post-drawing treatment was confirmed as a useful method for significantly increasing the tensile strength (673.4%) and tensile modulus (875.3%) of nanofiber membranes. In addition, the composites reinforced with post-drawn PAN-PMMA nanofibers exhibited higher Fs (13.6%), Ey (5.3%) and WOF (30.4%) than those reinforced with as-electrospun PAN-PMMA nanofibers. When 1.2% mass fraction of post-drawn nanofibers were added to Bis-GMA/TEGDMA resin, the Fs, Ey and WOF increased by 51.6%, 64.3% and 152.0%, respectively, compared with neat resin.