procedure for making nanofibilx

gapingthingsUrban and Civil

Nov 15, 2013 (4 years and 1 month ago)

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Procedures for making cellulose nanofibil
s


The cellulose hydrogel was kindly received from Forest Products
Laboratory, Madison, WI. It contains a cellulose fraction of ~1% by
weight, and was produced by TEMPO method. The hydrogel was first
transferred into a vial bottle (0.5 x 0.5 x 1 cm),
as shown

in figure (a),
and then plunged in a liquid nitrogen bath. A couple of minutes later,
the hydrog
el was completely frozen into ice

(see figure (b)).

It

was
then placed

inside a vacuum chamber
on top of a cryogenically
cooled thi
ck copper plate

(see figure
(c))
. The copper plate

was
employed as a cold head,
which

preserve
d

the open porous structure
of the ce
llulose, since the rough pump t
ook

away water in the sample
via sublimation
. The
freeze
-
dry procedure typically took about 12
hours
.
T
he dried hydrogel
w
as sponge
-
like and compressible as
shown in figure (d).


Low
-
tempera
ture ethanol can also be used for

freez
ing

hydrogel.
First of all
, ethanol was cooled

by liquid nitrogen to

around its
melting point temperature (159 K). The
n

hydrogel samples were
plunged

into the cold ethanol

bath
,
but should not be mixed with
ethanol.

After
approximately
10 minutes, hydrogel
samples slowly
became fro
z
en
. It was suggested that

(Korhonen et al.) the cooling by

liquid ethanol is more efficient in transferring heat than

usin
g

liquid
nitrogen, because it does not boil when the hydrogel is immersed in
it
. As a result, it helps
prevent Leidenfrost effect, that is
,

the
formation of an insulating gas layer,
and avoid
the ice crystals
pushing the fibrils into sheets.





Korhonen e
t al.,
ACS
N
ano

5
, 1967
-
1974 (2011).