Electrospun fibers consolidation

Highly consolidated electrospun fibers into a yarn.

Electrospinning uses a high voltage to produce fibers down to the nanometer dimension. The continuous fiber is usually deposited on a flat plate collector. Due to the presence of residual charges on the fibers, the formed non-woven membrane is relatively loosely packed. Stray fiber and loops may be seen on the surface of the membrane. In some cases, such characteristic is undesirable and a more compact form is needed for subsequent processing. Consolidation of the fibers may be achieved by fusing the fibers or through surface van der Waals forces.

A method of fusing fibers is to use heat with and without pressure. Concurrent application of pressure and heat may shorten the treatment duration and improve the connectivity between fiber intersections. Heating of electrospun membrane under pressure can be achieved easily using a hot press machine. It is important to note that the temperature to cause fusion at inter-fiber contact points will be lower under pressure. Na et al (2008) showed that with a hot-pressed temperature of 145 °C, polyvinylidene fluoride fibers have merged together to form a network of large pores.

For consolidation of fibers without fiber fusion, van der Waals forces may be used by bringing the fibers together. For non-water soluble polymers, the resultant electrospun fibers may be dipped in water and the surface tension of the water when the membrane can lifted out will bring the fibers together. Kozior et al (2019)suggested soaking and drying electrospun membrane in water or soap water as a pre-treatment prior to fuse deposition printing a supporting layer on it. In the construction of highly aligned electrospun fiber bundles, Teo and Ramakrishna 2005 used two knife-edge collectors placed in alignment with a gap in between for aligned fibers to bridge. However, there are numerous stray fibers that arched over the axial bundle. To consolidate the fibers, the bundle was dipped in water and lifted off such that the water surface tension causes the fibers to consolidate into a tight and well-aligned fiber bundle.