IMPREGNATION OF PET FILMS AND PHB GRANULES WITH CURCUMIN IN SUPERCRITICAL CO2

Brazilian Journal




of Chemical

ISSN 0104-6632
Engineering
Printed in Brazil
www.abeq.org.br/bjche


Vol. 23, No. 02, pp. 227 - 234, April - June, 2006



IMPREGNATION OF PET FILMS AND PHB
GRANULES WITH CURCUMIN IN
SUPERCRITICAL CO2

L. C. S. Herek1, R. C. Oliveira1, A. F. Rubira2 and N. Pinheiro1*

1Universidade Estadual de Maringá, Depto. de Engenharia Química, Bloco D-90,
Av. Colombo 5790, Zona 07, CEP: 87020-900 Maringá - PR, Brazil
E-mail: nanci@deq.uem.br
2Universidade Estadual de Maringá - Depto. de Química,
Av. Colombo 5790, Zona 07, CEP: 87020-900 Maringá - PR, Brazil.

(Received: October 20, 2004 ; Accepted: February 8, 2006)

Abstract - The process of dyeing poly(ethylene terephthalate) - PET films at 50, 60 and 65ºC and
poly(hydroxybutyrate) – PHB granules at 60, 70 and 80ºC using supercritical carbon dioxide (scCO2) as
solvent and ethanol as cosolvent was studied by DSC, TGA analysis and measurements of shrinkage to
determine the morphological modifications caused by the scCO2 treatment of these materials. A comparison
of the effects of annealing both polymers in scCO2 provided evidence that PHB had plasticization activity due
to its crystallinity and that PET favored the dyeing process at high pressure when its temperature was raised to
close to the Tg value. DSC and TGA measurements were obtained for all the samples. The DSC results
showed that there was no significant structural change and the TGA data showed that thermal stability was
not affected in the samples analyzed.
Keywords: Supercritical CO2; PET films.


INTRODUCTION
Giorgi, et al., 2000). According to Stinson and

Obendorf (1996), PET absorbs only 0.4% of the water
Researchers have directed their attention to the
and does not swell in water. This lack of interaction
process of dyeing polymeric materials with
between PET and the aqueous dye bath requires the
supercritical fluids, popularly known as the green
use of either high-temperature or a high-pressure
process. The conventional process of dyeing PET
system in a dyeing with disperse dyes or natural
fiber produces wastewater contaminated by many
pigments. Santos et al. (2000; 2001) studied the
kinds of dispersing agents, surfactants and unused
effects of modifying agents and dyeing conditions of
dye. The technique of dyeing with supercritical fluids,
dispersed dyes and azo dyes on PET films and fibers.
an alternative that does not contaminate the
These researchers reported on the process of
environment, has been under development since the
incorporating dye in unmodified and N,N-
early 1990s. Poly(ethylene terephthalate) ? PET is the
dimethylacrylamide ? modified PET fibers with
most important polyester with a variety of
scCO2. However, the sorption of natural pigments by
applications, from textile fibers to bottles for
PET films with scCO2 at elevated pressures
carbonated beverages and for photographic film
(>10MPa) and temperatures (>50°C) are not very well
packaging and automobile components. Studies have
understood and further research is still necessary.
recently been published on the dyeing of polymers,
Poly(hydroxybutyrate) ? PHB, which is a
especially polyesters (Beltrame et al., 1998; De
bacterially produced thermoplastic polyester with

*To whom correspondence should be addressed

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L. C. S. Herek, R. C. Oliveira, A. F. Rubira and N. Pinheiro

considerable potential for use in situations where
in curry powder. With the growing demand for
biodegradability or biocompatibility are required ?
natural colors, the use of turmeric is likely to
offers an attractive alternative to the disposal of
increase.
plastics in the environment (Agnelli et al., 1999;

Simielle, 1993). PHB is a semicrystalline material

with a highly crystalline content and a fairly high
MATERIAL AND METHODS
melting temperature of around 177ºC, at which the

polymer degrades quickly (Iriondo et al., 1995). Its
Raw Materials
chemical resistance is somewhat limited as it is

attacked by acids and alkalis and dissolved in
The PHB granules used were obtained from PHB
chlorinated solvents. Some of the undesirable
Industrial S/A (Brazil). The average molecular
properties can be modified by copolymerization of
weights, as determined by gel permeation
hydroxybutyrate (HB) with hydroxyvalerate (HV)
chromatography in chloroform at room temperature,
units. Increasing the HV content reduces the melting
were MW ? 200,000. The particle size distribution of
temperature and crystallinity, making the polymer
the PHB granules was determined using sieves of the
more processable (Avella and Martuscelli, 1988;
Tyler series (35 and 48 mesh) or their corresponding
Kumagai and Doi, 1992; Pearce et al., 1992; Abe et
metric units (0.417 and 0.297mm) and an agitator
al., 1994; Godbole et al., 2003).
(Belter, Piracicaba, Brazil). The physical
Supercritical carbon dioxide (scCO2) has been
characteristics were the following: (i) appearance:
shown to have very high solubility in many
yellow/white solid; (ii) odor: mild; (iii) melting
polymers, similar to those of organic solvents show a
point: ? 170ºC and (iv) solubility in water: negligible.
swelling action. Moreover, it is able to induce a
The commercial samples of PET films (thickness
decrease in the glass transition temperature (Tg) of
of 100?m) were kindly supplied by COCAMAR,
polymers such as poly(methyl methacrylate) and its
Maringá, Brazil and the PET samples were cleaned
blends with poly(vinylidene fluoride) (Chiou et al.,
prior to use with analysis grade ethyl alcohol
1985). These properties of scCO
®
2 support its use as a
(Nuclear) .
temporary plasticizer in order to facilitate the uptake
Pure standard curcumin, indexed under no. 75300,
of additives (Berens et al., 1992), flavoring agents
E-100 (Takahashi & Nazário, 1987), was acquired
and dyes in several polymers. Distribution or
from Sigma-Aldrich Chemical Representações Ltda
partitioning of a solute between scCO2 and the
(São Paulo, Brazil). Demethoxycurcumin and
polymer as a stationary phase occurs in
bisdemethoxycurcumin, homologues of curcumin, are
cosolvent?modified supercritical chromatography.
sold together and have the same colorizing capacity
The addition of small quantities of cosolvent to the
(Sanagi and Ahmad, 1993).
scCO2 mobile phase in SCF usually improves the
CO
applicability of SFC in more polar analytes.
2 liquefied at a high pressure (White
Martins)® served with solvent. Analysis grade N,N-
However, adsorption of cosolvent in the polymeric
dimethylformamide (Induslab, Arapongas, Brazil)
stationary phase will significantly affect the retention
of a solute and thus the thermodynamic properties
was also used to extract the pigment from the film
measured by SFC (Kazarian et al., 1998).
after dyeing. The solvent (modifier) was analysis
In this paper, the impregnation of PET films and
grade ethanol (Induslab, Arapongas, Brazil).
PHB granules with curcumin under different
In Figure 1 the PET, PHB and three curcuminoid
conditions of temperature, pressure and time was
structures are shown.
studied by using supercritical carbon dioxide with

ethanol as cosolvent. Factorial designs were used to
Factorial Design
assess the effects of these variables on the

impregnation of PET and PHB and DSC and TGA
The factorial design was developed and the
techniques were used to analyze occasional changes
parameters of the supercritical CO ?
2 aided dye
in the structure and properties of the PET and PHB.
sorption on (i) the PHB granules were pressure (P) at
Curcumin obtained from rhizomes of Curcuma
five levels (14, 18, 22, 26 and 30MPa) and
longa is one of the main pigments produced in Brazil
temperature (T) at three levels (60, 70 and 80ºC) and
(Manzan et al., 2003). Besides the yellow pigment
on (ii) the PET films were pressure (P) at three levels
for food, this plant is widely used as a seasoning.
(16, 21 and 26MPa), time (t) at two levels (2 and 8
Mature rhizomes are ground to give an aromatic
hours) and temperature (T) at three levels (50, 60 and
yellow powder, employed as the coloring ingredient
65ºC).

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Impregnation of PET Films and PHB Granules 229



Poly(3-hydroxybutyrate)



Figure 1: Structures of the Poly(3-hydroxybutyrate), Poly(ethylene terephathalate) and of the three
curcuminoids (1. curcumin; 2. demethoxycurcumin; 3. bisdemethoxycurcumin).

Procedures
PET films were precisely weighed, washed with

ethanol and water and then dried; (ii) 15 samples of
The experiments were performed in a module of
PHB granules of 35 and 48 mesh sizes and 1 mL of
supercritical sorption in a static process using
ethanol as cosolvent were used.
commercial CO2, which was compressed until the
In each experiment, the sample placed inside the
required pressure was obtained with a high?pressure
sorption cell had an amount of dye that was 2% of
compressor. The infusion cell was immersed in a
the weight in relation to the mass of the PET film or
heat bath, maintained at the required temperature.
PHB granules. The amount of dye greatly exceeded
The PET film?dye and PHB granule?dye?cosolvent
the average pigment solubility in supercritical CO2.
systems were placed inside the sorption cell with
The system was heated to the desired temperature
scCO
and then it was pressurized, maintaining the static
2, as shown in Figure 2.
A factorial design was used for the purpose of
system. After being submitted to the procedures of
analyzing the effect of each variable under study on
dyeing in scCO2, the concentrations of pigment
the process of the dye incorporation as well as the
absorbed by PHB and PET were measured
effects of interaction between them (i) 18 samples of
spectrophotometrically.




Figure 2: Scheme of supercritical impregnation equipment scheme



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L. C. S. Herek, R. C. Oliveira, A. F. Rubira and N. Pinheiro

Measurements
polymer is annealed by plasticization with CO2,

thereby allowing polymer chains to reorient to
The amount of curcumin absorbed on (i) the PHB
more thermodynamically favorable positions,
granules with ethanol was measured at 60ºC in two
forming crystallites (Lambert & Paulaitis, 1991;
steps of 45 min each, using 5 mL in each step, under
Santos et al., 2000). At 80ºC equilibrium was
constant stirring and on (ii) PET films the dye was
obtained at 22MPa, while at 60ºC and 70ºC,
extracted in 5mL of N,N dimethylformamide at 85ºC,
equilibrium was not reached. Comparing the
under stirring for about 1 hour. The samples were read
experimental data in Figure 3, a retrograde
by spectroscopy UV-VIS (spectrophotometer
condensation can be observed because there was a
Shimadzu UV1203) at 425 nm.
considerable increase in impregnation at 70ºC. On
Differential scanning calorimetry (DSC)
the other hand, the impregnation of PHB with
measurements were obtained to determine melting
curcumin was increased by use of a cosolvent
temperature of PHB before and after impregnation.
(ethanol) at 60, 70 and 80ºC.
The thermogravimetric (TGA) analyses were
A statistical analysis was conducted using
performed to verify the thermal stability of the
impregnation of PHB as the response variable. The
polymer. The DSC and TGA measurements were
results showed that pressure (P) and temperature (T)
obtained using Shimadzu equipment, model 50.
exerted significant effects on impregnation

(p=0.0031, p=0.0025, respectively). Impregnation

was not affected by the interaction between P and T.
RESULTS AND DISCUSSION
The decomposition temperature at a 10% level

determined by thermogravimetric (TGA) analysis for
The amount of curcumin incorporated into PHB
pure PHB and PHB dyed in scCO2 at 70ºC and
at three different temperatures as a function of
22MPa are 277 and 270ºC, respectively (Figure 4).
pressure is shown in Figure 3. As can be observed,
This is evidence that the dyeing process does not
the increase in pressure at all temperatures, resulted
alter the thermal stability of the polymer.
in an increase in the impregnation of PHB with
Analysis of the DSC data on pure PHB (Figure 5-
curcumin as well as the mass transfer rate, except at
A) and on PHB dyed in scCO2 at 70ºC and 22MPa
70oC and 14 and 26MPa. The decrease in
(Figure 5-B) and at 80ºC and 14MPa (Figure 5-C)
impregnation and absorption at these pressures can
showed the main melting temperature peak of the
probably be attributed to changes in the isolated
samples was at around 174ºC with a second melting
ordered chain to short?range changes in PHB
peak due to the thinner lamellae at around 150ºC. As
crystallinity. These results are in accordance with the
was shown, the melting temperature of PHB does not
data on other systems in which a semicrystalline
depend on dyeing conditions.



Figure 3: Amount of curcumin incorporated into PHB at three
different temperatures as a function of pressure.

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Impregnation of PET Films and PHB Granules 231



Figure 4: TGA curves of pure (A) and dyed (B) PHB.

Figure 5: DSC curves of pure PHB (A) and PHB dyed in scCO2 at 70ºC
and 22MPa (B) and at 80ºC and 14MPa (C).

The data on impregnation of PET films with
impregnation as temperature increased was also
curcumin are shown in Figure 6. These data are in
verified at pressures of 16 and 21MPa and at a
the form of histograms in order to give an idea of the
temperature of 65ºC. The solubility of the curcumin in
behavior of the process in relation to the
CO2 was higher at a temperature of 50ºC than at
modifications under experimental conditions. The
temperatures of 60 and 65ºC when the pressure was
®
results obtained by use of the SAS software show
around 20MPa. It was observed that by increasing the
that pressure is a significant parameter for the
pressure to over 20MPa, impregnation increased with
impregnation of PET films (p=0.0285) and that
temperature. Sicardi et al. (2000) and Santos et al.
temperature is not significant (p=0.2025).
(2001) found that by increasing the pressure, there
The results indicate an increase in impregnation
was a small increase in the diffusion coefficient, and
with time, justifying the large quantity of impregnated
these results were explained by the CO2 plasticizing
dye at equilibrium (8 hours). An increase in
effect. On the other hand, at a temperature of 65ºC the

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L. C. S. Herek, R. C. Oliveira, A. F. Rubira and N. Pinheiro

system approximated the transition glass temperature
significant modifications of the structure of the
of PET, at which the molecules are more mobile,
material. The fusion heat of PET for the samples
improving the effect of diffusion and slightly
(16MPa, 65ºC without dye) and (26MPa, 65ºC with
increasing the quantity of impregnated pigment as the
dye) was calculated and the values obtained were
system reached equilibrium. Thus, it should be
43.8 J/g and 44.3J/g, respectively; the insignificant
emphasized that the amount of pigment that can be
difference between the values shows that the
incorporated into a PET film is limited by high
presence of dye in the system does not modify it.
pressure and by transition glass temperature.
The same behavior was found by Santos et al. (2000)
In Figure 7 it can be seen that there were no
when working with PET films.



Figure 6: Amount of curcumin impregnating PET films as
a function of temperature and pressure, using scCO2.




Figure 7: DSC curves of PET samples: (A) pure PET film and undyed (C-D)
and dyed (E-F) PET films submitted to CO2 at a temperature of 65ºC
and pressures of 16, 21 and 26MPa.



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Impregnation of PET Films and PHB Granules 233

CONCLUSIONS
Chiou, J.S., Barlow, J.W. and Paul, D.R.,

Plasticization of Glassy Polymers by CO2, J.
The melting temperature of PHB did not depend
Appl. Polym. Sci., vol. 30, p. 2633 (1985).
on dyeing conditions and the thermal stability of the
Giorgi, M.R. de., Cadoni, E., Maricca, D. and Piras,
polymer was not affected during the dyeing process.
A., Dyeing Polyester Fibers with Disperse Dyes
The dyeing process did not produce waste effluents
in Supercritical CO2, Dyes and Pigments, vol. 45,
and the CO2 could be reused after being compressed.
p. 75 (2000).
Thus, the process with supercritical CO2 is an
Godbole, S., Gote, S., Latkar, M. and Chkrabarti, T.,
interesting alternative to the process of dyeing
Preparation and Characterization of
polymeric because neither pre nor postreatment is
Biodegradable Poly?3?hydroxybutyrate?starch
necessary. Carbon dioxide acted as a
Blend Films, Bioresource Techn., vol. 86, p. 33
low?molecular?weight plasticizing agent, which
(2003).
enhanced the mobility of the monomer inside the
Iriondo, P., Iruin, J.J. and Fernandez-Berridi, M.J.,
swollen substrate but did not change the
Thermal and Infrared Spectroscopic
compatibility of the polymers with the dye. Thus, it
Investigations of a Miscible Blend Composed of
should be emphasized that the amount of pigment
Poly(vinyl phenol) and Poly(hydroxybutyrate),
that could be incorporated into a polymer was
Polymer, vol. 36, no. 16, p. 3235 (1995).
limited by high pressure and transition glass
Kazarian, S.G., Vincent, M.F., West, B.L. and
temperature.
Eckert, C.A., Partitioning of Solutes and Co-

solvents between Supercritical CO2 and Polymer

Phases, J. Superc. Fluids, vol. 13, p. 107 (1998).
ACKNOWLEDGEMENT
Kumagai, Y. and Doi, Y., Enzymatic Degradation of

Poly(3-hydroxybutyrate) Blend. Poly Degrad.
The authors are grateful to PHB-Industrial S/A
Stab., vol. 35, p. 87 (1992).
(Brazil) and COCAMAR (Brazil), which supplied
Lambert, S.M. and Paulaitis, M.E., Crystallization of
the PHB granules and PET films.
Poly(ethylene terephthalate) Induced by Carbon

Dioxide Sorption at Elevated Pressures. J. Superc.

Fluids, vol. 4, p. 15 (1991).
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