Microscale and Macroscale Deformation Behavior of Electrospun Polymeric Nanofiber Membranes Using In Situ SEM during Mechanical Testing

Abstract

Electrospun nanofiber membranes show high potential in various application fields (e.g., filtration, catalysis, and sensing). Nevertheless, knowledge of the mechanical behavior, and more specifically, the deformation of nanofiber membranes is still limited today which can complicate the appliance of nanofiber membranes in applications where they are mechanically loaded. In this paper, we, therefore, analyzed the mechanical behavior of polymeric nanofiber membranes with different fiber orientations (random and aligned) extensively. Polyamide 6 was used as a representative reference polymer for proof-of-concept. Mechanical tests show that all membranes have a coherent deformation behavior at the macroscale up to the point of fracture. Large variations in stiffness, ultimate strength, and ultimate strain were observed between membranes with different fiber orientations (Random: E-mod: 370 ± 34 MP; UTS: 38.5 ± 6.0 MPa; εmax: 30.0 ± 2.8%; Parallel aligned: E-mod: 753 ± 11 MPa; UTS: 55.4 ± 0.8 MPa; εmax: 12.0 ± 0.1%; Perpendicular aligned: E-mod: 24.1 ± 3.7 MPa; UTS:/; εmax: >40%). This shows the versatility and tunability of the mechanical behavior of these nanofiber membranes. At the microscale, the fibrous structure results in deformation mechanisms that resist failure formation and progression when the membrane is mechanically loaded. This results in a high fracture resistance, even for pre-damaged membranes. Realignment of the fibers along the loading direction causes crack tip blunting, locally reinforcing the membrane.

A Finite Element Method for Determining the Mechanical Properties of Electrospun Nanofibrous Mats

“…The complexity and high porosity of nanofiber mats pose additional challenges in identifying the mechanical properties of individual fibers within the mats. Various researchers [ 14 , 15 ] have developed methods to approximate the thickness of nanofiber mats by identifying their porosity and measuring the mass of specimens in comparison to known polymer densities. When nanofibers are randomly oriented, the determination of the force acting on individual fibers is complicated; however, it becomes feasible to determine the mechanical properties of a mat when the fibers are aligned, allowing for the direct observation of the forces at play.…”