Advances in Ma terials Physics and Che mist ry, 2012, 2, 181-184
doi:10.4236/ampc.2012.24B047 Published Online December 2012 (htt p://www.Sc
Copyright © 2012 SciRes. AMPC
Coacervation Microencapsulation of CaCO3 Particles with a
Fluoropolymer by Pressure-Induced Phase Separation of
Supercritical Carbon Dioxide Solutions
Kenji Mishi ma1*, Haruo Yokota1, Takafumi Kato1 , Tadashi Suetsugu2, Xiuq i n Wei2,
Keiichi Irie3, Ke nic hi Mishima3, Michihiro Fujiw ara3
1Department of Chemical Engi neering, Fukuoka Uni vers ity, Nanakuma Jonan-ku, Fukuoka, Ja pan
2Department of Electronics Engineering and Computer S cien ce, Fukuoka University, Nana kuma Jonan-ku, Fukuoka, Japan
3Department of N europharmacology, Fukuoka U niversity, Nanakuma Jonan-ku, Fukuoka, Japan
Received 2012
We report a method for the coacervation micro-encapsulation of several forms of CaCO3 microparticles with the fluoropolymer
poly(heptadecafluorodecyl acrylate) (poly (HDFDA)) by pressure-induced phase separation of a supercritical CO2 solution. A sus-
pension of CaCO3 in CO2 and dissolved poly(HDFDA) were mixed in supercritical CO2. After the system pressure was slowly de-
creased to atmospheric p ressure, the microcap sules were obt ained. Coacer vation was achieved by the precipi tation of pol y(HDFD A)
during the decrease in the pressure of CO2; the solubility of poly(HDFDA) in CO2 decreased with the pressure. The structure and
morphology of the microparticles were investigated by using a scanning electron microscope (SEM) and an electron probe micro-
analyzer (E PMA) eq uipped with a wavelength dispersive X-ray spectr os cope (WDX).
Keywords: Component; Supercritical Carbon Dioxide; Microencapsulation ; Coacervation; Fluoropolymer; Calcium Carb onate
1. Introduction
Polymer microcapsules containing inorganic materials are
attracting much attention as the field of supercritical CO2
(scCO2) technology. ScCO2 is the solvent of choice because it
is readily available, inexpensive, and environmentally benign.
Many investigators have attempted the formation of polymer
microcapsules using scCO2 [1-6]. Rapid expansion from
supercritical solutions (RESS) is a well-known process, and a
variety of polymer microcapsules have been produced with the
help of this process by many investigators [2,3,5-9]. However,
the RESS process is limited by the low polymer solubility in
CO2, caused by its low dielectric constant. Relatively few polymers
are soluble in CO2 without a cosolvent. RESS of fluoropolymers
such as perfluoropolyether, poly(1,1,2,2-tetrahydroperfluorodecyl
acrylate), and poly (heptadeca-fluorodecyl acrylate), which are
highly soluble in CO2 at temperatures near the ambient
temperatu re, prod uces coatin g materials [10-12] and submicron
to several micron -s ized par ticles and fibers [12, 13].
In this work, we try to form microcapsules of CaCO3 and
poly(heptadecafluorodecyl acrylate) (poly (HDFDA)) using
scCO2. In a previous work[9], we proposed a production me-
thod for the fluoropolymer microcapsules of talc particles by
pressure-in duced phase sep aration of scCO2. Figure 1 provides
a conceptual framework of our proposed process in comparison
with the conventional RESS process.
In RESS, a supercritical fluid solution is expanded across a
nozzle, leading to rapid supersaturation and the production of
small par ticles. After a susp ensio n o f CaCO3 in CO2 containing
a dissolved fluoropolymer is sprayed through the nozzle at
atmospheric pressure, microcapsules and small polymer particles
are obtained as shown in Figure 1(a). For the industrial applica-
tion s, we have to r estri ct the generat io n of polymer par ticl es no t
containing CaCO3 bec ause th ey degrad e the prod ucts. Therefore,
to prevent the nucleation and the precipitation of polymer particles
not containing CaCO3, the pressure is decreased slowly, and
microparticles are collected in the high-pressure cell as shown
in Figure 1 (b).
The objective of this work is to check the feasibility of the
pressure-induced phase separation of the scCO2 solution to the
formation of fluoropolymer microcapsules of several shapes of
parti cles of Ca CO3 and to stu dy the effe ct of se veral exp eriment al
conditions on particle morphology.
fluoropolymer+ CO2
+ CaCO3 at 20 M Pa
coacervation of
Figure 1. Principles of the formation of polymer microcapsules of
CaCo3 by (a) RESS and (b) pressure-induced phase separation of
scCO2 sol utions.
Copyright © 2012 SciRes. AMPC
2. Experimental Section
2.1. Materials
CaCO3 was obtained from Shiraish Calcium.Co., Ltd., and
carbon dioxide (CO2) (99.9% minimum purity) was purchased
from Fukuoka Sanso Co., Ltd. The fundamental idea and syn-
thesis of poly(HDFDA) was reported by DeSimone et al. [27],
and a similar approach based on their method is employed in
the present study. The fluoropolymer poly(HDFDA) was syn-
thesized in a high-pressure cell by the fre e-radical polymeriza-
tion of a homogeneous solution of the 3,3,4,4,5,5,6,6,7,7,8,
8,9,9,10,10,10-heptadecafluorodecyl acrylate (HDFDA) mono-
mer with an azobis(isobutyronitnile) (AIBN) initiator in CO2
for 48 h at 333 K and 20 MPa. AIBN and HDFDA were pur-
chased from Aldrich Co. Upon completion of polymerization,
the p olymer was p recip it ated from CO2 directly into a methanol
bath. Subsequently, the poly(HDFDA) was washed several
times and allowed to dry overnight.
2.2. Experimental Procedure
Known amounts of the fluoropolymer and CaCO3 were placed
in the high-pressure cell (25 cm 3) equipped w ith s a pphire w indows .
The cell was placed in a water ba th an d the s ystem te mperature
was maintained at the desired value within +0.1 K. CO2 was
pumped through a preheater to the high-pressure cell. The
mixture was stirred by a magnetic agitator for 30 min. The
system was slowly depressurized for approximately 30 min at
the expe r ime nta l tem pe rat ure . Follow i ng the dec r eas e in pr e ssur e ,
polymer microcapsules were obtained in the high- pressure cell.
The structure and morphology of the products were analyzed
using a scanning electron microscope (SEM, JEOL JSM6060)
and an electron probe microanalyzer (EPMA; Shimadzu, EPMA
1610) equipped with a wavelength dispersive X-ray spectrome-
ter (WDX). An EPMA equipped with WDX can identify ele-
ments through the use of a crystal monochromator to select
X-rays of a particular wavelength. For the SEM sample prepa-
ration , pol ymeric micropar ticles were mou nted on a small glas s
plate covered with a small piece of double-sided carbon con-
ductive tape. The samples were then sputter-coated with silver
palladium and imaged using the SEM and EPMA.
3. Results and Discussion
3.1. Evol ut ion of Microen capsul ati on
Prior to the experiment for microcapsule formation, the phase
behavior of the CO2 + poly(HDFDA) system at 20 MPa and
313 K was confirmed visually by using a high-pressure vessel
equipped with sapphire windows. Without the CaCO3, the mixtures
of CO2 and poly(HDFDA) form a single phase. Details of the
phase behavior of the CO2 + poly(HDFDA) system were
repor ted by Blasi g et al. [12] Similar phase b ehavi or s for CO2 +
poly(1,1-dihydroperfluorooctylacrylate) [14] and CO2 + poly
(1,1,2,2-tetrahydroperfluorodecyl acrylate) [13] systems were
SEM photographs of the CaCO3 and the fluoropolymer mi-
crocapsule containing CaCO3 that was produced by the pres-
sure-induced phase separation of scCO2 are shown in Figures
2(a) and (b).
Figure 2. SEM photographs of poly(HDFDA) microcapsules of (a)
spheres and (b) whiskers of CaCO3 particles formed by the pres-
sure-induced phase separation of scCO2 solutions. Pre-expansion
conditions: temperature, 313 K; pressure, 20 MPa; CO2, 97.9 wt%;
poly(HDFDA), 0.20 wt%; CaCO3, 2.1 wt%.
The system was slowly depressurized from 20 MPa to
atmospheric pressure for approximately 30 min at 313 K. The
spher ical p arti cles of CaCO3 and CaCO3 whiskers had a smooth
surface. Compared with the SEM photographs of the CaCO3,
the microcapsules of the fluoropolymer containing CaCO3 have
a similar configuration. The surface morphology of the
microcapsules reflects the configuration of CaCO3 in the
microcapsules because the coating thickness of CaCO3 is very
small. The primary particle diameter (PPD) and particles size
distribution (PSD) o f C a C O 3 and microcap sules wer e dete rmined
by a laser diffraction particle size analyzer (SALD-2000,
Shimadzu Co. Ltd.).
The PP D and PSD of spheri cal particles of CaCO3 are 7.6 μm
and 0.40, respectively. And the PPD and PSD of microcapsules
are 7.7μm and 0.403, respectively. The value of PPD and PSD
of the sph erical parti cles of CaCO3 and microcap sules is almost
same. We can not observe the change of particle size.
The CaCO3 whiskers were also coated by the fluoropolymer.
The surface morphology of the microcapsules reflects the
Copyright © 2012 SciRes. AMPC
configuration of CaCO3 whiskers in the microcapsules because
the coating thickness of CaCO3 is very small. But structure of
CaCO3 whiskers coated by the fluoropolymer were more bulky
than C aC O3 whiskers.
Further evidence for the formation of fluoropolymer
microcapsules of CaCO3 can be obtained using EPMA. The
peak corresponding to F caused by the fluoropolymer can be
observed for the microcapsules, it cannot be detected for
CaCO3 because CaCO3 does not possess F.
The surface distributions of F, O, and Ca were mapped in an
EPMA image. Although the distribution of F in the microcapsules
was fairl y sh arp, it was not detected on the CaCO3 surface. On
the other hand, the distribution of Ca and O on the CaCO3
surface was sharper and broader. However, the distribution of
Ca and O on the microcapsule surface was poorer than that on
the CaCO3 surface. It can be considered that CaCO3 was
completely encapsu lated by a thin fluoropolymer film.
It was difficult to check the coating performance for all the
collected microcapsules by using EPMA because in the
proposed process, an extremely large number of microcapsules
were produced. To evaluate the performance of the polymer
coating, we examined the stability of the microcapsules in pure
water. The CaCO3 particles or microcapsules were added to
pure water (particle concentration: 1 wt%), and the suspended
solution was shaken by a mechanical shaker. The stable conditions
of t he spheri cal particles of C aCO3 and microcap sules in water
were chec ked. Alth o ugh the CaC O3 was dispersed in pure water
for more than 5 min, all the microcapsules floated on water
because of the high water repellency of the fluoropolymer. The
density of CaCO3 and microcap sules is almost same (ab out 2.8
gcm-3), because microcapsules contain more than 90 %
CaCO3. Although the density of microcapsules is higher than
that of water, the microcapsules floated on the water. It is
inferred that bulk density of microcapsules is lower than that of
water. It is difficult to penetrate the water to the void between
the microcapsules, becau se of the repellency of fluoropolymer.
The CaCO3 was dispersed in water, because the CaCO3 has
hydrophilic surfaces. To check the stability of the microcap-
sules in pure water, a turbidity measurement was performed
using an ultraviolet/visible (UV/VIS) spectrometer at 600 nm
wavelength. The turbidity measurement was used to observe
the stability of small particle dispersions [29]. We could not
observe the dispersed particles through the stability analysis of
microcap sules in water becau se as in the case of pur e water, no
turbidity was observed. The stability analysis revealed that
most of the CaCO3 particles were coated with the fluoropoly-
mer and were p r es ent inside the produced microcapsules.
3.2. Formation M echanism of Microca psules
To identify the advantage of the formation mechanism of mi-
crocapsules by the pressure-induced phase separation of scCO2
as compared with RESS, the microcapsules were prepared by
RESS. Because RESS is one of the promising methods for the
formation of polymer microcapsules and/or composites by us-
ing scCO2, several investigators have reported the formatio n of
polymer microcapsules and/or composites by RESS [1,2]. The
particle formation mechanism by RESS was analyzed thermo-
dynamically [4]. In this work, we attempted the formation of
microcapsules by RESS under the following experimental con-
ditions. The pre-expansion pressure was 20 MPa, and the tem-
peratu re was 313 K. Th e feed concen trations of the CaCO3 and
the fluoropolymer were 2.1 wt% and 0.20 wt%, respectively.
The feed composition in the RESS experiment was the same as
that in the experiment on the formation of microcapsules by the
pressure-induced phase separation of scCO2. The mixtures of
scCO2, the fluoropolymer, and the CaCO3 were expanded
across the capillary nozzle (L = 500 mm, D = 1.2 mm) to at-
mospheric pressure. After the expansion, the microparticles
were precipitated. SEM photographs of the fluoropolymer mi-
crocapsules produced by RESS and containing CaCO3 were
obtained. Compared with the morphology of microcapsules
prepared by the pressure-induced phase separation of CO2 as
shown in Figure 2, the polymer particles prepared by RESS
were observed on the surfaces of the CaCO3 particles. The po-
lymer does not form a smooth surface at the CaCO3 particles
but is adhered as small particles at the s urface of the CaC O 3.
To examine the coating performance of RESS, the obtained
particl es were an al yzed by EP MA and b y per for ming a stab il it y
test in water. F, Ca, and O wer e d etected in the WDX spectrum
of the microcapsules. Furthermore, we examined the stability of
the microcap sules in pure water to evalu ate the performance o f
the polymer coating. The WDX spectrum and the stability test
revealed that most of the CaCO3 was microencapsulated with
the fluoropolymer. However, small polymer particles were
precipitated on the surface through the RESS process. The for-
mation mechanism of microcapsules and small polymer par-
ticles in the RESS process may be considered as follows. Dur-
ing rapid depressurization both the CaCO3 and the polymer
precipitate from the solutions. And the CaCO3 particles are
formed in the expanding jet. Some polymer coated on the Ca-
CO3 particles, and some fine polymer particles are generated
during the deposition. The evidence for the formation of fine
polymer particles by RESS can be obtained by performing the
RESS experiment without CaCO3. The mean particle diameter
Figure 3. Sta bility of micro capsules in pure water. (a) CaCO3 and
(b) poly(HDFDA) microcapsules formed by the pressure-induced
phase separation of scCO2 solutions. See Figure 2 for the
pre-expansion conditions.
Copyright © 2012 SciRes. AMPC
less than 1 μm. With regard to the RESS experiment for the
formation of fluoropolymer particles, similar particle morphol-
ogy was reported by Blasig et al.[12] and Mawson et al. [13]
These fine po lymer particles p recipitated on an d adhered to th e
CaCO3 surface by the supersaturation and homogeneous nuc-
leation of the fluoropolymer that was caused by rapid depressu-
rization. To prevent the formation of polymer particles, we
have to inhibit the supersaturation of the solute and the homo-
geneous nucleation caused by the rapid expansion of CO2.
However, it is impossible to prevent the supersaturation in
RESS. We can prevent the formation of polymer particles by
the pressure-induced phase separation of CO2. Because the
depressurizing rate is very slow compared with the convention-
al RESS process, it is possible to inhibit the large supersatura-
tion of the solute and the homogeneous nucleation of particles.
During the slow depressurization, the coacervation was
achieved. On the other hands, after the pressure in the
high-pressure cell containing no CaCO3 decreased, polymer
foams were obtained. With experimental setup, no pure fluoro-
polymer were formed. It is inferred that the CaCO3 suspended
in scCO2 act s as an accelerator for the precipit ation of polymer
particles and the occurrence of coacervation on the CaCO3
surface. Furthermore, it is very difficult for the microcapsules
to produce forms, because the microcapsules contain about
90 % CaCO3. In the conventional coacervation microencapsu-
lation technique, coacervation i s induced by a ph ase separatio n
caused due to a pH change and the addition of a nonsolvent or
electrolyte [16]. In contrast, in the present experiment, coacer-
vation was ind uced by a phase separatio n caused by a decreas e
in pressure.
4. Conclusions
The pressure-induced phase separation of scCO2 has been util-
ized to produce fluoropolymer microcapsules of several shape
particles of CaCO3. Prior to depressurization, the polymer and
CaCO3 were mixed i n scCO2. Fluo ropo lymer co acervation was
achieved during the slow decrease in the pressure. Following
the coacervation, we obtained the fluoropolymer microcapsules
of CaCO3. The products were analyzed by SEM and EPMA
equipped with WDX. The CaCO3 was complet el y coated with a
thin fluoropolymer film. Compared with the microcapsules
formed by RESS, the obtained microcapsules had a smooth
surface; fine polymer particles on the CaCO3 surface were not
[1] J. Jung and M. Perrut, “Particle design using supercritical fluids:
Literature and patent survey,” The Journal of Supercritical Flu-
ids, vol. 20, no. 3, pp .179-219, 2001. J. Clerk M axwell, A Trea-
tise on Electricity and Magnetism, 3rd ed., vol. 2. Oxford: Cla-
rendon, 1892, pp.68–73.
[2] S. D. Yeo and E. Kiran, “Formation of polymerparticles with
supercriticalfluids: A review,” The Journal of Supercritical Flu-
ids, vol. 34, no. 3, pp. 287-308, 2005.
[3] E. Reverchon and R. Adami, “Nanomaterials and supercritical-
fluids,” The Journal of Supercritical Fluids, vol. 37, no. 1, pp.
1-22, 2006.
[4] J.W.Tom, P.G. Debenedetti, R. Jerome, “ Precipitation of
Po ly(L-lactic acid) and Composite Poly(L-lactic acid)-Pyrene
Particles by Rapid Expansion of Supercritical Solutions.” J. Su-
percritical Fluids vol.7, 9,1994.
[5] K. Mishima, K. Matsuyama, D. Tanabe, S. Yamauchi, T. J.
Young, and K. P. Johnston, “Microencapsulation of proteins by
rapid expansion of supercritical solution with a nonsolvent,”
AIChE Journal, vol. 46, no. 4, pp. 857-865, 2000.
[6] K. Mi shima,” Biodegra dable part icle format ion for dru g and gene
delivery using supercritical fluid and dense gas, “Advanced Drug
Delivery Reviews, vol. 60, no. 3, pp. 411-432, 2008.
[7] K. Matsuyama, K. Mishima, K. Hayashi, and H. Matsuyama,
“Microencapsulation of TiO2 Nanoparticles with Polymer by
Rapid Expansion of Supercritical Solution,” Journal of Nano-
particle Research, vol. 5, no. 1-2, pp. 87-95, 2003.
[8] K. Matsuyama, K. Mishima, K. I. Hayashi, H. Ishikawa, H.
Mat suyama , and T. Harada, “Formation of microcapsules of me-
dicines by the rapid expansion of a supercritical solution with a
nonsolvent,” Journal of Applied Polymer Science, vol. 89, no. 3,
pp. 742-752, 2003.
[9] K. Matsuyama and K. Mishima, “Coacervation microencapsula-
tion of talc particles with a fluoropolymer by pressure-induced
phase separation of supercritical carbon dioxide solutions,” In-
dustrial and Engineering Chemistry Research, vol, 45, no. 18, pp.
6462-6168, 2006.
[10] DeSi mone, J. M. ; Guan, Z. ; Elsb ernd, C . S. Synth esis of Fluoro-
polymers in Supercritical Carbon Dioxide. Science 257,
[11] Chernyak, Y.; Henon, F.; Harris, R. B.; Gould, R. D.; Franklin, R.
K.; Edwards, J. R.; DeSimone, J. M.; Carbonell, R. G. Formation
of Perfluoropolyether Coatings by the Rapid Expansion of Su-
percritical Solutions (RESS) Process. Part 1: Experimental Re-
sults. Ind. Eng. Chem. Res. 2001, 40, 6118..
[12] Blasig, A.; Shi, C. M.; Enick, R. M.; Thies, M. C. Effect of
Concentration and Degree of Saturation on RESS of a
CO2-soluble Fluoropolymer. Ind. Eng. Chem. Res. 2002, 41,
[13] Mawson, S.; Johnston, K. P.; Combes, J. R.; DeSimone, J. M.
Formation of Poly(1,1,2,2-tetrahydroperfluorodecyl acrylate)
Submicron Fibers and Particles from Supercritical Carbon Dio-
xide Solutions. Macromolecules 1995, 28, 3182.
[14] Luna-Barcenas, G.; Mawson, S.; Takishima, S.; DeSimone, J. M.;
Sanchez, I. C.; Johnston, K. P. Phase Behavior of
Po ly( 1,1-dihydroperfluorooctylacrylate) in Supercritical Carbon
Dioxide. Fluid Phase Equilibria 1998, 146, 325.
[15] Calvo, L.; Holmes, J. D.; Yates, M. Z.; Johnston, K. P. Steric
Stabilization of Inorganic Suspensions in Carbon Dioxide. J.
Sup ercritical Fluids 2000, 16, 247.
[16] J. Lazko, Y. Popineau, J. Legrand, Soy Glycinin Microcapsules
by Simple Coacervation Method. Colloids and Surfaces B: Bio-
interfaces 2004, 37, 1.