Wet Relaxation of Electrospun Nanofiber Mats

Abstract

Electrospinning can be used to produce nanofiber mats. One of the often used polymers for electrospinning is polyacrylonitrile (PAN), especially for the production of carbon nanofibers, but also for a diverse number of other applications. For some of these applications—e.g., creation of nano-filters—the dimensional stability of the nanofiber mats is crucial. While relaxation processes—especially dry, wet and washing relaxation—are well-known and often investigated for knitted fabrics, the dimensional stability of nanofiber mats has not yet been investigated. Here we report on the wet relaxation of PAN nanofiber mats, which are dependent on spinning and solution parameters such as: voltage, electrode distance, nanofiber mat thickness, and solid content in the solution. Our results show that wet relaxation has a significant effect on the samples, resulting in a dimensional change that has to be taken into account for nanofiber mats in wet applications. While the first and second soaking in pure water resulted in an increase of the nanofiber mat area up to approximately 5%, the dried sample, after the second soaking, conversely showed an area reduced by a maximum of 5%. For soaking in soap water, small areal decreases between approximately 1–4% were measured.

Stabilization of Electrospun Nanofiber Mats Used for Filters by 3D Printing

“…Detailed observation of the printing process if the nozzle is slightly too high suggests that the problem of missing adhesion for too large distances between nanofiber mat and printing nozzle may be based on electrostatic repulsion between the 3D printing polymer and the nanofiber mat. In a previous experiment, the electrostatic charging could be significantly reduced by soaking the nanofiber mat into water with a surfactant that was typically negatively charged [49]. Thus, 3D printing was also tested on a nanofiber mat that was soaked in soap water and dried in the air.…”

“…On the other hand, soaking and drying the sample in pure water or soap water before printing on it supports relaxation [49]. In this way, fixing it in a slightly stretched position was simpler than in case of not watered samples, in order to ensure that no elongation of the specimen was possible due to thermal and mechanical impact during printing.…”

“…This suggests either using a chemical method to bond the nanofibers inside the mats better [25] or to fix the whole nanofiber mats on the 3D printed polymer by printing an open grid on the nanofiber mats after the first printing step. Due to the strong relaxation of nanofiber mats during evaporation of residual solvent [49], the opposite procedure of electrospinning on 3D printed layers does not seem to be suitable, but can be expected to result in breaking of the nanofiber mats, which may also happen during electrospinning on the commonly used polypropylene nonwoven.…”

Polyvinyl Butyral (PVB) Nanofiber/Nanoparticle-Covered Yarns for Antibacterial Textile Surfaces

“…Apart from their many advantages, the weak mechanical properties of nanofibers restrict their use in a wider variety of applications. Grothe et al [17] found that the dimensional stability of nanofibers changes in wet applications. Attempts have been made to improve the mechanical weakness of nanofibers, including polymer blending [18], inorganic blending [19], the use of epoxy composites [20], thermal lamination [21], dip-coating [22], and ultrasonic welding [23].…”

Analyzing the thermal and hygral behavior of wool and its impact on fabric dimensional stability for wool processing and garment manufacturing

“…5 Recent decades have seen much attention paid to the effect of the textile manufacturing process and domestic garment laundering on fabric dimensional stability. [6][7][8][9][10][11][12][13][14][15][16][17] During these processes, fabric dimensional properties are largely affected by moisture content and temperature. Attention has also been extended from wool [6][7][8] to other textile materials, such as cotton, [9][10][11] linen, 12 silk 13 and polyester.…”