Updates on Lamination of Nanofiber - Modern Trends in Chemistry and Chemical Engineering - page 78

simple to create a strong bond between these layers, which guarantees no delamination
or failure in multilayer structures; the challenge is to preserve the original properties
of the nanofiber web and fabrics to produce a laminate with the required appearance,
handle, thermal comfort, and protection. In other words, the application of adhesive
should have minimum affect on the fabric flexibility or on the nanofiber web structure.
In order to achieve to this aim, it is necessary that: (a) the least amount of a highly ef-
fective adhesive applied, (b) the adhesive correctly cover the widest possible surface
area of layers for better linkage between them, and (c) the adhesive penetrate to a
certain extent of the nanofiber web/fabric [12]. Therefore, we selected PPSN, which
is a hot-melt adhesive in web form. As mentioned above, the perfect use of web form
adhesive can be lead to produce multilayer fabrics which are porous, flexible, and per-
meable to both air and water vapor. On the other hand, since the melting point of PPSN
is low, hot-melt laminating can perform at lower temperatures. Hence, the probability
of shrinkage that may happen on layers in effect of heat becomes smaller. Of course
in this study, we utilized cotton fabrics and PAN nanofiber web for laminating, which
intrinsically are resistant to shrinkage even at higher temperatures (above laminat-
ing temperature). By this description, laminating process performed at five different
temperatures to consider the effect of laminating temperature on the nanofiber web/
multilayer fabric properties.
Figure 4.3(A-E) shows a SEM image of multilayer fabric cross-section after lami-
nating at different temperatures. It is obvious that these images do not deliver any
information about nanofi ber web morphology in multilayer structure, so it becomes
impossible to consider the effect of laminating temperature on nanofi ber web. There-
fore, in a novel way, we decided to prepare a secondary multilayer by substitution of
one of the fabrics (ref. Fig. 4.2) with Tefl on sheet. By this replacement, the surface of
nanofi ber web will become accessible after laminating; because Tefl on is a non-stick
material and easily separates from adhesive.
Figure 4.3(a-e) presents optical microscope images of nanofi ber web and ad-
hesive after laminating at different temperatures. It is apparent that the adhesive
gradually fl attened on nanofi ber web (Fig. 4.3(a-c)) when laminating temperature
increased to melting point of adhesive (140ºC). This behavior is attributed to incre-
ment in plasticity of adhesive because of temperature rise and the pressure applied
from the iron weight. But, by selection of melting point as laminating temperature,
the adhesive completely melted and began to penetrate into the nanofi ber web struc-
ture instead of spread on it (Fig. 4.3(d)). This penetration, in some regions, was con-
tinued to some extent that the adhesive was even passed across the web layer. The
dark crisscross lines in Fig. 4.3(d) obviously show where this excessive penetration
is occurred. The adhesive penetration could intensify by increasing of laminating
temperature above melting point; because the fl uidity of melted adhesive increases
by temperature rise. Figure 4.3(e) clearly shows the amount of adhesive diffusion
in the web which was laminated at 150ºC. At this case, the whole diffusion of adhe-
sive lead to create a transparent fi lm and to appear the fabric structure under optical
microscope.