These days, nanofiber layers are used not only for filtration and separation purposes, but also in the clothing industry. Nanofiber
membranes are highly suitable for this purpose because of their high porosity, which is 25 % higher than the porosity of common
porous PTFE membranes, and which provides much better water vapour permeability than other membranes available on the
market.
In Figure 1 you can see how such a nanofiber membrane for
clothing works. Drops of water (snow, rain) fall on the top surface
material. The top material tries to stop these drops from getting
under this textile. This top material is often impregnated or has some
chemical finish to achieve this, but at the same time it must be able to
let water vapor through. This top material with its good properties
has also got its limits and that’s why a nanofiber membrane is added.
The different materials (woven or knitted textile and nanofiber
membrane) are laminated together to form 2-layer, 2.5-layer
or 3-layer laminates. The membranes are made of polymers,
the most common ones being PTFE (Polytetrafluoroethylene),
PES (Polyethersulfone) or PUR (Polyurethane). The membrane
thickness is in the range of micrometer units [1-3].
Figure 2: The Nanospider machine for the production of
nanofibers by electrospinning [4].
A Nano spider machine was used to produce the nanofiber
membrane (Figure 2) [4]. Polyurethane polymer was chosen
because it is easy to use on a Nano spider machine, but also for
its elasticity as it gives the final laminate sensibility that is very
desirable in some kinds of closing. The produced nanomembrane
is made hydrophobic using Fluorocarbon type C6 monomer in low
vacuum plasma to achieve a higher hydrostatic resistance. The
hydrostatic resistance can be more than 20,000mm depending on
the top material laminated to the membrane. After hydrophilization
the nanomembrane is laminated together with other textile
materials. Many long-term tests have shown that a 3-layer laminate
is the only solution for nanofiber layers as these layers are very
susceptible to friction and for that reason must be well protected
on both their sides by other textile materials laminated onto them.
Figure 3 shows such a 3-layer laminate.
Table 1 shows the results for 2-layer and 3-layer laminates with
a nanofiber membrane and also a 3-layer laminate from the Goretex
company (with the same areal weight).
Table 1: 2-layer and 3-layer laminates with a nanofiber membrane
and also a 3-layer laminate from the Gore-tex company (with the
same areal weight).
Top layer: 100% PES, 80gsm, ripstop weave
Membrane: 100% PU, 3gsm
Lining: 100% PES, 66 gsm, weft-knit fabric
Gore-tex: Active
The results show, that the nanofiber layer laminate has a much
higher water vapor permeability than the laminate with a Gore-tex
membrane while at the same time both laminates have a similar
hydrostatic resistance. The nanofiber membrane shows a slightly
higher air permeability, but the value is insignificant with respect to
the material’s function. All laminates are 100% windproof.