Estimating the Degree of Polymer Stretching during Electrospinning: An Experimental Imitation Method

It is commonly accepted that a polymer matrix inside electrospun nanofibers is in a stretched nonequilibrium state. This state develops as a result of significant elongation of the electrospun jet, at a high stretching rate. Due to high deformation level, the entangled polymer network in the jet experiences noticeable topological reorganization, meaning that the electrospinning is accompanied by both elastic and plastic deformations. Despite possible relaxation in the final state of polymer nanofibers due to some residual solvent, they remain noticeably stretched. Measurement or estimation of the resulting degree of stretching is still challenging. In this paper, an experimental method is proposed to estimate the degree of stretching, and electrospun nanofibers made of thermoplastic polyurethane (TPU) segmented block-copolymer are demonstrated. The rationale of this method is based on the similarity in the behavior of electrospun TPU nanofibers, and stretched cast TPU films; both demonstrate massive contraction upon heating. By comparing the degree of contraction of the nanofibers and the films, the level of polymer network stretching (both elastic and plastic) during electrospinning can be estimated. Depending on the strength of the applied electrostatic field, the degree of stretching of electrospun fibers is found to be noticeably increased in TPU. (Figure presented.).