Vol.2, No.6, 557-562 (2010) Natural Science
Copyright © 2010 SciRes. OPEN ACCESS
Poly (ethylene terephthalate) synthesis with catalysts
derived from chrysotile asbestos
Shigeki Habaue1*, Yusuke Takahashi2, Yu Hosogoe2, Hiroshi Yamashita2, Meisetsu Kajiwara3
1Faculty of Health and Nutrition, Shubun University, Ichinomiya, Japan; *Corresponding Author: habaue@shubun-ac.jp
2Department of Chemistry and Chemical Enginerring, Graduate School of Science and Engineering, Yamagata University, Yonezawa,
3School of Dentistry, Aichi-Gakuin University, Nagoya, Japan
Received 1 March 2010; revised 30 April 2010; accepted 13 May 2010.
The chrysotile asbestos was converted to the
forsterite-type compounds by calcination at 740
and 800 (F7-740 and F7-800), which were used
as a catalyst for the polycondensation of bis-
(hydroxyethyl) terephthalate affording poly (eth-
ylene terephthalate). The obtained forsterite-ty-
pe compounds did not show any catalytic activity.
However, the products obtained by simply treat-
ing them with acetic acid significantly pro- moted
the polymerization that produced a THF- insolu-
ble polymer. It was found that the polymer pre-
pared with the acetic acid-treated F7-740 at 160
for 2 h showed a 93% yield and the number av-
erage molecular weight of 6.4 × 103. The ob-
served catalytic activity was higher than that for
the acetic acid-treated magnesium oxide, as well
as the typical polycondensation catalysts, such
as magnesium acetate and antimony oxide.
Keywords: Chrysotile Asbestos Forsterite;
Polycondensation; Poly (Ethylene Terephthalate);
Poly(ethylene terephthalate) (PET) is a versatile thermo-
plastic resin and extensively used for various products in
the forms of fibers, films, etc. The PET is generally
produced by the esterification of terephthalic acid with
ethylene glycol followed by polycondensation, as well as
by transesterification using dimethyl terephthalate with
ethylene glycol or using bis(hydroxyethyl) terephthalate
(BHET) as the starting material. The latter system with
BHET is also important as one of the recycling proc-
esses of PET wastes, which is shown in Scheme 1.
During these polycondensation processes, antimony
compounds, such as the oxide and acetate, are typically
employed as the catalyst [1-4], and the replacing these
heavy metal catalysts with others that are safe, economic,
and highly catalytic has been desired [5-7]. For example,
it was recently reported that hydrotalcite, [Mg6Al2(OH)16]
(CO3)·4H2O, can be an efficient catalyst for the PET
synthesis [8,9].
The chrysotile asbestos, represented by the approxi-
mate composition of Mg3Si2O4(OH)4, is comprised of a
silica tetrahedral sheet [SiO4] joined into a brucite layer
of basic magnesium hydroxide [Mg(OH)2], and the cur-
vature of these layers affords a structure of tubular and
cylindrical rolls with nanometer-order diameters [10].
The chrysotile asbestos has been widely applied in ind-
ustry as a material having excellent physical and chemi-
cal properties, such as tensile strength, heat-resistance,
durability, etc. However, its use is prohibited or strictly
regulated at present, because of health hazards, that is,
asbestosis and carcinogenesis of respiratory systems.
Scheme 1. Polycondensation of BHET producing PET.
S. Habaue et al. / Natural Science 2 (2010) 557-562
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The fibrous and needle-like structure of the asbestos is
considered to be the main cause of these serious diseases.
A vast amount of chrysotile asbestos has already been
used, therefore, the development of potential disposal
methods for these waste materials and the unused raw
chrysotile is an essential and urgent subject. Especially,
their transformation into nontoxic and valuable materials
is of great significance.
Recently, we reported that chrysotile asbestos is ef-
fectively converted into polysiloxanes through selective
acid-leaching and silylation [11,12]. This result offers a
novel method for converting the hazardous chrysotile
asbestos wastes into valuable polymer materials. The
calcination of the chrysotile asbestos is another method
affording a harmless material, which mainly consists of
forsterite, Mg2SiO4, as shown in Scheme 2 [13-15]. Ac-
cordingly, effective utilization of this material can also
provide a certain way to solve this serious issue.
Scheme 2. Calcination process of chrysotile asbestos.
In this study, the forsterite-type compounds prepared
by the calcination of the chrysotile asbestos were evalu-
ated as the polycondensation catalyst for BHET, and it
was found that they show a significant catalytic activity
by treating with carboxylic acids. Therefore, this novel
catalyst system for the PET production from BHET can
simultaneously contribute to the effective recycling both
of the asbestos and PET wastes.
2.1. Materials
The class 7 chrysotile (F7) [mined in Furano, Hokkaido,
Japan (Nozawa Co.)] was used as the starting material,
and the calcination at 800 or 740 for 1 h was con-
ducted to produce a pale brownish, forsterite-type com-
pound, F7-800 or F7-740 (caution!: the asbestos must be
carefully treated, because the fibrils cause serious health
hazards). The silica (L-SiO2) with a fibrous structure
originating from the chrysotile was prepared by the
acid-leaching of the serpentine slag with sulfuric acid as
previously reported [11,12]. During this process, almost
all of the magnesium constituent was removed, that is,
the brucite layer was effectively leached. Its chemical
composition (%, fluorescent X-ray) was estimated to be
96.6, SiO2; 2.4, Al2O3; 0.2, Fe2O3; 0.1, CaO, and it has a
specific surface area of 178 m2/g. The monomer, BHET
(TCI), and the salts of magnesium and antimony, such as
MgO, Mg(OH)2, magnesium acetate [Mg(OAc)2] (Kanto),
MgSO4 (Wako), and Sb2O3 (Nihon Seiko), were used as
2.2. Treatment of Forsterite with Acid
A mixture of the forsterite-type compound (0.20 g,
F7-800 or F7-740) and acetic acid (7 equiv. based on Mg)
was stirred for 24 h under a N2 atmosphere at ambient
temperature. After evaporation of the acid, the product
was further vacuum-dried at 50for 12 h. The ob-
tained solid was used for the polycondensation reaction
as the catalyst without further purification.
2.3. Polymerization
A mixture of BHET (0.50 g) and a catalyst (1 wt%) was
reacted at 160for 2 h under reduced pressure (< 0.5
mmHg). After cooling to room temperature, the reaction
mixture was washed with methanol, then with tetrahy-
drofuran (THF). The insoluble fraction was isolated by
centrifugation and dried in vacuo.
2.4. Measurements
The chemical compositions were determined by X-ray
fluorescence using a Shimadzu EDX-800 spectrometer.
The specific surface area was measured by the BET
method. The powder X-ray diffraction (XRD) patterns
were obtained using monochromatic CuKa radiation
with a Rigaku RINT-2100-ultra diffractometer. The 1H
NMR spectra were measured by a Varian Unity Inova
(500 MHz) spectrometer. The infrared (IR) spectra were
recorded by a Horiba FT-720 spectrometer. The size ex-
clusion chromatography (SEC) analysis was performed
by a Jasco PU-2080-plus equipped with a Jasco UV-
2075-plus UV detector with Shodex AC8025 and TSK-
GEL columns connected in series (eluent = CHCl3, flow
rate = 1.0 mL/min). The polymers were dissolved in
CHCl3 by addition of a small amount of 1,1,1,3,3,3-
hexafluoroisopropanol (HFIP) and calibration was car-
ried out with standard polystyrenes.
3.1. Calcination of Chrysotile Asbestos
The XRD patterns of F7-800 and F7-740, prepared
by the calcination of the chrysotile asbestos at 800 and
740for 2 h under atmospheric pressure, are shown in
Figure 1. The peaks based on the chrysotile completely
disappeared during the calcination, and peaks due to the
formation of forsterite were observed for both products.
The compound calcined at the lower temperature, F7-
740, showed a broader peak pattern than that of F7-800,
suggesting that the calcination temperature affects the
S. Habaue et al. / Natural Science 2 (2010) 557-567
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Figure 1. X-ray powder diffraction patterns of
(a) chrysotile asbestos (serpentine slag), (b)
F7-800, and (c) F7-740 (: chrysotile, :
crystallinity of the products. The product, F7-740, sho-
uld have a lower crystallinity than F7-800.
The chemical composition, determined by a fluores-
cent X-ray analysis, and specific surface area of the sta-
rting material F7 and the calcined products, F7-800 and
F7-740, are listed in Table 1. The amounts MgO, SiO2,
Fe2O3, Al2O3, and CaO in the products (F7-800 and
F7-740) increased by the calcinations when compared to
those of F7. This is due to the dehydration as shown in
Scheme 2. The observed chemical compositions for the
calcined products are quite similar to each other, while
the BET surface area of F7-740, 25.1 m2/g, was higher
than that of F7-800. These results showed that the calci-
nation temperature should affect the crystallinity. In
other words, the product, F7-740, is rich in an amor-
phous phase.
3.2. Polycondensation of Bis(hydroxyethyl)
The polymerization of BHET at 160under vacuum
was carried out (Table 2). The polymerization without a
catalyst did not proceed (entry 1). The typical magne-
sium and antimony salts, such as MgO, Mg(OH)2,
Mg(OAc)2 and Sb2O3, except for MgSO4, as the catalyst
promoted the polymerization and produced the THF-in-
soluble polymers (entries 4-8). For example, Mg(OAc)2
afforded a polymer in a good yield with the number av-
erage molecular weight (Mn) of 6.2 × 103. However, the
forsterite-type compounds, F7-800 and F7-740, which
mainly contain the magnesium constituent, did not af-
ford any polymeric compounds (entries 2 and 3).
Table 1. Characterization of starting materials.
Chemical composition (%)a
Material MgO SiO2 Fe2O3 Al2O3 CaO
Surface area
aDetermined by fluorescent X-ray analysis. bDetermined by BET measurement.
Table 2. Polymerization of BHET with various catalysts at 160.
Entry Catalysta Yield (%)b Activity
(g-product·g-cat1·h1) Mn × 103c Mw × 103c
aBHET: 0.50 g, catalyst: 5 mg. bMeOH- and THF-insoluble part. cDetermined by SEC (polystyrene standards). dMgO: 2 mg.
eMg(OH)2: 3 mg. fMgSO4: 6 mg.
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F7-800 and F7-740 were then treated with acetic acid
(AcOH) at room temperature as stated in the experi-
mental section, and the obtained compounds were used
as the polycondensation catalyst. During this process,
the weight increases of 1.8 × 102 and 3.3 × 102 mg for
1.0 g of F7-800 and F7-740, respectively, were ob-
served. The IR spectra of these compounds are shown
in Figure 2, together with those of F7-740 and
Mg(OAc)2. The absorptions based on the magnesium
acetate around 1100-1300 cm 1 were clearly observed
for F7-800 and F7-740 when treated with AcOH. Ac-
cordingly, during this process, the formation of the
magnesium salt of AcOH should take place, whereas
the yields were poor, judging from the observed weight
On the other hand, MgO was also treated with AcOH
(12 equiv.) to give a reaction mixture, which showed a
weight increase of 3.0 × 103 mg for 1.0 g of MgO. The
leached silica, L-SiO2, prepared from the serpentine slag
[11,12], was calcined at 740for 1 h, and it was also
treated with 5 equiv. of AcOH. However, no weight in-
crease was observed. These results were quite different
from those observed for F7-800 and F7-740, supporting
the fact that the magnesium constituent in the forster-
ite-type compounds should react with AcOH.
The results of the polycondensation of BHET with the
catalyst (1 wt%), prepared from the forsterite-type com-
pounds by treating with various organic carboxylic acids, are
summarized in Table 3. The MgO derivative, obtained by
treating with AcOH, produced a polymer in 84% yield and
showed an catalytic activity of 42.0 g-product/g-cata- lyst·h
(Table 3, entry 1), whose values were almost comparable to
those of the polymerization using Mg(OAc)2 (Table 2, entry
6). The acid-treated L-SiO2, as well as the original L-SiO2,
produced no THF-insoluble fraction during the polymeriza-
tion (Table 3, entry 11 and Table 2, entry 9).
In marked contrast, the F7-800 and F7-740 derivatives,
treated with AcOH, resulted in good yields with the Mn
value of approximately 6.3 × 103 (Table 3, entries 2 and
3), although F7-800 and F7-740 without acid-treatment
showed no catalyst activity (Table 2, entries 2 and 3).
Especially, the AcOH-treated F7-740 showed the higher
Figure 2. IR spectra of (a) F7-740, (b)
F7-800 after treating with AcOH, (c)
F7-740 after treating with AcOH at room
temperature, and (d) Mg(OAc)2 (KBr).
Table 3. Polymerization of BHET with various acid-treated materials at 160a.
Entry Starting
material Acidb Yield (%)cActivity
(g-product·g-cat1·h1) Mn × 103d Mw × 103d
aBHET: 0.50 g, catalyst: 5 mg. bAbout 7 equiv. of acid was used. cMeOH- and THF-insoluble part. dDetermined by SEC (polysty-
rene standards). eReaction temp. = 220. fCatalyst: 3 mg. gF7-740 was treated with AcOH at 60. hF7-740 was treated with AcOH
at 100. iPropionic acid. jTrifluoroacetic acid. kL-SiO2 calcinated at 740was used.
S. Habaue et al. / Natural Science 2 (2010) 557-567
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yield of 93% and a catalytic activity of 46.5 g-product/
g-catalyst·h than those of the acid-treated MgO deriva-
tive, as well as those of Mg(OAc)2, although the weight
increase of F7-740 during the AcOH-treatment step was
much lower than that of MgO. These results suggest that
the activity of the catalyst sites in the F7-740, generated
during the acid-treatment process, should be signifi-
cantly high when compared to that of the acid-treated
MgO and Mg(OAc)2. Therefore, in addition to the for-
mation of the magnesium salt of AcOH in F7-740, some
structure of the forsterite, prepared from the chlysotile
asbestos, should play an important role in the polycon-
densation of BHET.
The polymerization of BHET with the AcOH-treated
F7-740 was performed at 220(Table 3, entry 4). Al-
though the observed polymer yield and catalytic activity
were similar to those of the polymerization at 160, the
obtained polymer showed an Mn value of 1.3 × 104,
which was estimated by SEC. Therefore, the polymeri-
zation at higher temperatures could be effective for this
catalyst system.
The 1H NMR spectrum of the THF-insoluble part ob-
tained using the AcOH-treated F7-740 (Table 3, entry 4)
was depicted in Figure 3. The polymer was soluble in
chloroform containing a small amount of HFIP, and the
peaks were assigned as shown in the figure. The small
peaks around 4.0 and 4.5 ppm were based on the me-
thylene protons of the terminal hydroxyethoxy groups
(Scheme 3). Accordingly, the Mn value calculated from
the integral ratio was 2.5 × 103, which is much lower
than that estimated by SEC, probably due to the rigid
aromatic main chain of the polymer and some aggrega-
Scheme 3. Structure of the obtained PET.
Figure 3. 1H NMR Spectrum of the obtained
polymer (Table 3, entry 4) (in CDCl3 contain-
ing HFIP).
The forsterite-type compound, F7-740, was treated
with heated AcOH for 24 h. During this process, the
weight increases of 6.1 × 102 and 9.3 × 102 mg/g-F7-740
for the reaction at 60 and 100, respectively, were ob-
served. Therefore, the reaction between the magnesium
in the compound and AcOH proceeded more effectively
than the reaction at room temperature. The obtained ma-
terials were employed as the catalyst (0.6 wt%) for the
polymerization of BHET at 160(Table 3, entries 5-7).
Under these reaction conditions, the acid-treated F7-740
at room temperature showed a catalytic activity of 56.7
g-product/g-catalyst·h, whereas the F7-740 derivatives,
treated with AcOH at higher temperatures, showed sig-
nificantly higher catalytic activities. For example, the
highest activity of 66.7 g-product/g-catalyst·h was ob-
served for the polymerization using the F7-740 deriva-
tive prepared at 100.
F7-740 was further ground and treated with AcOH at
100for 24 h. The weight increase was 1.1 × 103
mg/g-F7-740, which is higher than that observed for the
reaction of F7-740 without grinding. The polycondensa-
tion of BHET at 160 with this catalyst (0.6 wt%) was
conducted, and the THF-insoluble fraction was obtained
in a 72% yield with the catalytic activity of 60.0 g-
product/g-catalyst·h and the Mn of 5.4 × 103 as evaluated
by SEC. This result was almost comparable to that of the
polymerization using the acid-treated F7-740 without
Finally, the effect of the carboxylic acid on the cata-
lytic activity during the BHET polymerization at 160
(catalyst: 1 wt%) was examined (Table 3, entries 8-10).
The forsterite-type material, F7-740, was treated with
propionic acid (PA) at 100. After evaporation of the
unreacted acid, the weight increase was 9.4 × 102 mg/g-
F7-740, of which the molar yield is lower than that ob-
served for the reaction with AcOH at 100. The acidity
of the carboxylic acid should have an effect on the reac-
tion. The polymerization with this catalyst resulted in a
much lower yield and catalytic activity than those for the
polymerization using the AcOH-treated F7-740 catalyst.
F7-740 was also treated with trifluoracetic acid (TFA) at
room temperature or 60affording a reaction mixture
with the weight increase of 9.2 × 102 or 2.6 × 103 mg/g-
F7-740, respectively. The latter catalyst preparation re-
action at 60significantly proceeded, however, it sho-
wed a low catalytic activity of 21.5 g-product/g-cata-
lyst·h for the polymerization. Therefore, AcOH is cur-
rently the most effective carboxylic acid, that is, the
magnesium salt of AcOH generated in the forsterite-type
compound, F7-740, effectively promotes the polycon-
densation of BHET, although a detail structure of the
active site is not clear at present.
S. Habaue et al. / Natural Science 2 (2010) 557-562
Copyright © 2010 SciRes. OPEN ACCESS
The chrysotile asbestos was calcined affording the fors-
terite-type compounds. Although the polycondensation
of BHET with them did not proceed, the compounds,
just treated with acetic acid, showed a significant cata-
lytic activity, which was higher than that for the polym-
erization by the MgO derivative treated with acetic acid,
as well as typical polycondensation catalysts, such as
Mg(OAc)2 and Sb2O3. Some phases or amorphologies
having the composition of the forsterite derived from the
chrysotile asbestos by the calcination, in addition to the
magnesium salt generated by acid-treatment, should be
important for the catalytic activity during the polymeri-
zation. Accordingly, this novel catalyst system could
contribute to both the disposal of chrysotile asbestos
waste and the recycling of PET waste.
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