Supercritical impregnation of polymers - ZyXEL NSA210

402 I. Kikic, F. Vecchione / Current Opinion in Solid State and Materials Science 7 (2003) 399–405
only be dyed in SCCO 2 when a small amount of water is
dissolved in the SCCO 2 and in the silk.
Cotton was dyed poorly under all conditions. Aminated
cotton was dyed better than cotton but not as well
as silk and wool. Fixation on aminated cotton was 87%.
It was concluded that dichlorotriazine dye can react in
moist SCCO 2 with amino groups of protein textile (e.g.
silk and wool) but not with hydroxyl groups of cellulosic
textiles (e.g. cotton) [15].
3.3. Organic metallic complexes impregnation
Synthesis of metallopolymer nanocomposites has attracted
much attention recently. Owing to their small
size, metal particles exhibit some unusual structural,
magnetic, catalytic and biological properties untypical
for large particles.
The process consists in the diffusion of an organometallic
compound from the supercritical solution into
the polymer matrix followed by its reduction/decomposition,
achieved by application of heat, chemical reagents
or radiations.
The method of impregnation from solution in SCCO 2
has several advantages:
1. The matrix tends to prevent an agglomeration of
metal particles.
2. SCCO 2 shows high penetrability into polymers.
3. It is possible to control the solvent power and the impregnation
rate and, therefore, to control the composition
and morphology of the obtained composite.
4. The final product does not require special drying.
5. Low surface tension allows impregnation even of
such barrier polymers as Teflon or obtaining of a
continuous metal layer on their surface [16].
Platinum (Pt) nanoparticles in poly(4-methyl pentene)
and poly(tetrafluoroethylene), silver (Ag) nanoparticles
on the surface of polyimide film, Ag nanoparticles in
poly(ethylether ketone) and poly(styleneme-divinyl benzene)
were investigated [17].
Preparation of noble metal (Pt, Pd) particle-dispersed
polyimide films as precursors of metal-doped carbon
molecular sieve membranes (CMS) was performed by
Yoda et al. [17] using impregnation of an acetyl-acetonate
complex dissolved in supercritical CO 2 .
Carbon molecular sieve membranes are known as
good gas separation membranes even at high temperature.
The gas separation properties of CMS membranes
can be controlled by doping metal particles having an
affinity to the relevant gas. Therefore, the hydrogen
separation performance of CMS is expected to be improved
by noble metals having an affinity to hydrogen.
Significant increase of the Pt content will depend on
the decomposition of polyimide catalyzed by Pt particles
during thermal treatment, and on the temperature. Since
the solubility of the Pt(II)(acac) 2 or Pd(II)(acac) 2 is independent
of the temperature, the increase of the metal
content should be ascribable to polyimide films, probably
to thermal relaxation of the polymer network. Both
Pt(II)(acac) 2 and Pd(II)(acac) 2 have similar solubility in
SCCO 2 . The high dispersion of Pd particles could be
related to lower decomposition temperature (>453 K in
air) than Pt(II)(acac) 2 (its melting point is 523 K) and to
chemical interactions with carboxyl structures of polyimide.
Nazem et al. [18] investigated the preparation of reflective
poly(etherether) ketone (PEEK) thin silvercoated
films via supercritical fluid impregnation with
CO 2 as the carrier and subsequent thermal reduction
of (1,5-cyclooctadiene-1,1,1,5,5,5-hexafluoroacetylacetonato)silver(I)
dimer, [Ag-(COD)HFA] 2 . No chemical
reducing agent was needed to effect silver reduction.
The resulting films were (a) reflective, (b) maintained
their flexible nature and (c) had a surface electrical resistance
higher than 10–11 X cm 1 , in spite of their
metallic appearance.
The reflectivity of the surface depends on the impregnation
and cure conditions. At constant CO 2 pressure
(15 MPa) and impregnation time (120 min) at 20%
additive, silver atomic concentration increased from
7.5% to 18.5% as the impregnation temperature increased
from 80 to 110 °C. At 10 wt.% additive and
constant temperature and pressure (110 °C and 15 MPa)
in another set of preliminary experiments, the amount of
silver increased from 9.6% to 15.5% in going from 60 to
120 min impregnation time. At constant impregnation
conditions (e.g. 110 °C, 15 MPa, 120 min) the amount of
silver on the surface decreased as the weight percent of
additive changed from 20% to 10% and 5%, as might
have been expected (e.g. 18.5%, 15.5%, 3.9%).
At constant CO 2 pressure, the reflectivity of the surface
increased increasing the impregnation temperature
and the impregnation time.
Thermal cure parameters at fixed impregnation conditions
suggested that lower cure temperatures require
longer cure times in order to obtain high reflectivity. Ten
nanometer diameter silver particles appeared in the film
bulk near the surface. Different sized silver clusters on
the surface could be grown by controlling the impregnation
and cure conditions. The silver on the surface
strongly adhered to the polymer surface [18].
New chelate complexes of copper diiminate (Cu(II)–
HFDI) and iron diiminate (Fe(III)–HFDI) were synthesized
by Said-Galiyev et al. [16]. The polymers
impregnated via supercritical CO 2 were polyarylate
(PAR) films with thicknesses of 12and 39 mm. The
equilibrium degree of polyarylate swelling in SCCO 2 at
45 °C and 8 MPa is 10%; this establishes the impregnation
operating conditions. In the case of Cu(II)–HFDI
the impregnation can be as large as 11–51% while the
content of pure copper in film is as large as 1.3–6.3 wt.%;