Preparation and properties of aromatic polyester/TiO2 nanocomposites from polyethylene terephthalate

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DOI: http://dx.doi.org/10.1590/1980-5373-MR-2015-0203

Preparation and properties of aromatic polyester/TiO2

nanocomposites from polyethylene terephthalate

_Leonardo Moreira dos Santos_ _a_ _, Carlos Leonardo Pandolfo Carone_ _a_ _, Sandra Mara Oliveira Einloft_ _a,b_ _,_

_Rosane Angélica Ligabue_ _a,b*_

_aGraduation Program in Materials Engineering and Technology,_

_Pontifical Catholic University of Rio Grande do Sul – PUCRS,_
_6681 Ipiranga Avenue, CEP 90610-900, Porto Alegre, Rio Grande do Sul, Brazil_
_bSchool of Chemistry, Pontifical Catholic University of Rio Grande do Sul – PUCRS,_

_6681 Ipiranga Avenue, 90610-900, Porto Alegre, Rio Grande do Sul, Brazil_

Received: April 7, 2015; Revised: September 14, 2015; Accepted: November 26, 2015

The development of polyester based materials with enhanced properties as well as the use of
post- consumer plastics as raw material has been an increasing market demand. This work aims the
synthesis and characterization of aromatic polyesters/titanium dioxide nanocomposites from PET and
using TiO2 (0, 1, 3 and 5% w/w) as filler by _in situ_ polymerization. The results obtained by DSC, XRD
and FTIR analyzes evidenced an interaction between the OH groups on the TiO2 surface with the ester
groups of the polymer leading to decrease of the polymer crystallinity and of hydrophilicity. By SEM
images was possible to note a homogeneous distribution of the filler into polymer matrix with 1%w/w
TiO2 (average particle size of 199 nm), however for larger amounts of filler (3 and 5% TiO2) revealed
the aggregates formation. The results showed an improvement of thermal properties and hardness of
the nanocomposites containing TiO2 nanoparticles compared to pristine polyester.

Keywords: _Nanocomposites, Aromatic polyester, Titanium dioxide, Filler, in situ polymerization._

1. Introduction

Polyesters (PE) are a class of polymers with great
application in different market sectors, such as textile fibers 1,
engineering plastics 2, specialty resins and elastomers 3,4 .
Nowadays, the world production of polyester is one of the
largest among the most common polymers, expected to reach
about 40 million tonnes for 2015 5 .

On the other hand, the development of composites and
nanocomposites polymer/filler can produce new materials
with improved properties. The fillers or reinforcing materials
have micro or nano scale and are dispersed into the polymeric
matrix, having as main function to improve the barrier
properties to gases and liquids 6, physical-chemical 7, thermal
and mechanical properties 8, among others. The improvement
of these properties in nanocomposites materials is mainly
due to the increased interaction between the filler particles
and the polymer matrix, as a result of the higher surface
area when compared to the traditional composites 9 . It is
also known from the literature that the addition of fillers in
the polymer matrix can enhance the biodegradation of the
material allowing to find new application niches for these
composites 10 .

In preparing a nanocomposite, the interaction between
the polymer matrix and fillers depends on the nature and the
structure of the filler being used. Among the most studied
filler materials are the metal oxides, clays, aluminum silicates

with different kinds of forms (or habits), such as, layered,
spherical and nanotubes 11,12 .

Polyesters are widely used because of its excellent
processability, mainly when fillers are added 13 . The literature
has described several studies on the preparation of aliphatic
polyester nanocomposites with different inorganic fillers
(TiO2, Fe2O3, Al2O3) 14, but few studies have been reported
on the preparation of aromatic polyester nanocomposites
with TiO2 as filler. The addition of TiO2 nanoparticles (rutile
phase) in the polymeric matrix can improve properties such
as anti‑corrosion, anti-bactericidal, UV protection among
others 15 . A recent work described the preparation of a
non‑woven PET hybrid nanocomposite on which was made
the growth of TiO2 particles from the hydrolysis of TiCl416.

In our study, we chose to use inexpensive raw materials
to develop TiO2/aromatic polyester new nanocomposites.
The use of inexpensive raw materials such as plastics with
a large disposal volume, e.g. post-consumer polyethylene
terephthalate (PET) has great technological and commercial
interest 17,18 . The choice of titanium dioxide (TiO2, rutile phase)
as filler is due to this compound being widely used in the
industry, it has a low cost and their properties depend on
the crystal structure, size and particle morphology. And the
_in situ_ method has been shown suitable for preparation of
the nanocomposites of inorganic filler with polymer matrix
b i i l d i i h d d d

nanocomposites with good filler distribution in the polymer
matrix 13,16 .

In this context, the main goal of this work was to obtain
aromatic polyester (APE) nanocomposites from polyethylene
terephthalate (PET) and using different concentrations of
titanium dioxide (rutile phase) by _in situ_ polymerization
searching for the best relation polymer/filler that can improve
the nanocomposites properties (thermal stability, hardness
and wettability) when compared to the polymeric matrix
without filler.

2. Experimental

The synthesis reactions of polyester/TiO2 nanocomposites
via _in situ_ polymerization were carried out in a glass reactor
(500 mL), equipped with pneumatic stirring, thermocouple
column filled with glass rings, reflux condenser, with
temperature control at the top and inert gas inlet (N2).
The synthesis was divided in two steps: 1) the synthesis
of the prepolymer with the starting reactants; 2) the bulk
polymerization under reduced pressure aiming to increase
the molar weight of the polymer.

_2.1. In situ polymerization_

Into the reactor was added a mixture of dimethyl
terephthalate (DMT- Quimpetrol) and polyethylene
terephthalate (PET- M&G), in the molar ratio 9:1. After that,
a mixture of 1,4-butanediol (BD- Rudnik) and 1,6-hexanediol
(HD- Rudnik) in the molar ratio 1:1 was added and the
system temperature was increased to between 210-230°C
for 2 hours and after the system was kept at 230 o C under
reduced pressure for 2 hours to increase the molar weight of
the polymer. The dibutyl tin oxide (Miracema Nuodex) was
used as catalyst (0.1% w/w on total solids) and 2,6-di‑ _tert_ butyl- _p_ -cresol (Merck, 0.05% w/w on total solids) as an
antioxidant. The inorganic filler, TiO2 (Merck, 99% rutile
phase, average particle size=166±35nm) was added at the
beginning of the reaction in proportions of 1%, 3% and
5% relative to the total mass of solids (total weight of
reagents). The filler was used without any treatment and it
was dispersed in a hexanediol/butanediol mixture with the
aid of an Ultra-Turrax disperser (12,000 rpm for 60min).
To obtain the sample referred as pure polyester it was used
the same reaction conditions without the addition of TiO2.
In order to verify to possible role of TiO2 as a catalyst for the
reaction, also it was performed a reaction with the addition of
5% w/w of TiO2 and without addition of the catalyst. At the
end of the syntheses were obtained five samples named as:
pure APE (pure aromatic polyester), APE 1, 3 and 5% TiO2
(APE nanocomposites with different amount of TiO2), APE
W/C (APE nanocomposite with 5%w/w of TiO2 and without
catalyst for polymerization).

_2.2. Characterizations_

Fourier transform infrared spectroscopy/universal attenuated
total reflectance (FTIR/UATR, PerkinElmer FTIR spectrometer
model Spectrum100) in the wave number from 4000 to 650
cm -1 was used to evaluate the matrix/filler interaction of the
chemical bounding between the polymer and the filler. All

l l d i h f f d iff i l

scanning calorimetry (DSC, TA Instruments model Q20
equipment) was used to measure the melting temperature
( _Tm_ ), the crystallization temperature ( _Tc_ ) and the melting and
crystallization enthalpy (ΔH _m_ ; ΔH _c_ ). The DSC analyzes were
performed in a temperature range from -90°C to 220°C in
two cycles (heating rate of 10°C/min and a cooling rate of
5°C/min). It was weighed approximately 10mg of sample in
hermetic aluminum pan. The thermal stability of the materials
was analyzed by thermogravimetric analysis (TGA, TA
Instruments Model SDT Q600). Assays were performed in
a range of 25°C to 1000°C with a heating rate of 20°C/min,
under nitrogen atmosphere and using a platinum sample
holder. For the analysis it was used approximately 10mg of
sample. The hardness test was carried out on specimens with
dimensions 35x48x4 mm. For this test it was used a device
Woltest Sd 300, Shore A scale - Mainard “A” G112605.
The analyzes were carried out in quintuplicate according to
ASTM D2240. The XRD analyzes were performed on an
apparatus Bruker Siemens D5000, using radiation Kα of the
copper (λ= 1.542 Å), voltage 40KV, 30mA, scanning between
2 o -30° 2θ and scan speed of 0.02°/min. The contact angle
measurements were performed on the samples APE/TiO2
nanocomposites and pure APE (dimensions: 35x48x4 mm)
in quadruplicate. All analyzes were carried out using milli-Q
water in an equipment 15 + OCA and SCA202 software,
version 3.12.11. Scanning electron microscopy (SEM) mode
secondary electrons (SE), with a Philips model XL 30 with
energy dispersive spectrometry (EDS) was used for evaluation
of the surface morphology of the APE nanocomposites, as
well as, the dimensions of the fillers and dispersion thereof
in the polymer matrix. All the samples were fractured and
metallized with a thin layer of gold. The data of the particle
size and the clusters size were obtained by the digital program
“Image Tool” (version 2, GPL). The average molar weights
( _Mn_ and _Mw_ ) and polydispersity index (PI) of the pure APE
and nanocomposites were determined by gel permeation
chromatography (GPC). The samples were solubilized in
chloroform (PA, Vetec) at a concentration of 5.0 mg/mL
(stirring for 15 min and after filtered with a PTFE membrane
filter of 0.45 micrometers). The analyses were performed
using a liquid chromatographer equipped with an isocratic
pump-1515 (eluent: chloroform, flow: 1mL/min) and
refractive index detector (Waters Instruments-2414) with set
of Styragel columns and polystyrene calibration standards.

3. Results and Discussion

_3.1. Characterization of the APE/TiO2_
_nanocomposites_

In order to prove the composite formation and to evaluate
the matrix /filler interaction, the polyester matrix and the
obtained nanocomposites were analyzed by FTIR and DRX.

In Figure 1 is presented the infrared spectra of the
APE/TiO2 nanocomposites (in absorbance) and with a zoom
in the region in 1710 cm -1 characteristic of the vibration of
the carbonyl (C=O) of the ester group present in the polymer
backbone. When the filler content increases, the intensity
of this band decreases and its position is shifted toward
lower wavenumber as an effect of the interaction of the OH

h iO f i h h f l

matrix (Scheme 1). This behavior was also observed by
Sudirman et al _._ (2012) for nanocomposites formed between
aliphatic polyester resins and silica 19 and Ghanem et al.
(2014) for hyperbranched polyester/TiO2 nanocomposites 20 .

Figure 2 illustrates the X-ray diffraction patterns of TiO2,
pure APE and the synthesized APE/TiO2 nanocomposites.
The characteristic reflections of TiO2 (rutile phase) are
situated at 27.5 o 2θ ( _d=_ 3.24 Å); 36 o 2θ ( _d=_ 2.43 Å); 54.3 o 2θ

Scheme 1. Representation of the interaction filler-polymer.

Fig. 1. FTIR Spectra of the pure APE, APE/TiO2 nanocomposites
with 1%, 3%, 5% of TiO2 and zoom in the region around 1700 cm -1 .

Fig. 2. XRD patterns of TiO2, pure APE, APE W/C and the APE/TiO2

( _d=_ 1.68 Å), in agreement with the commercial TiO2 used to
obtain the nanocomposites and the assignments described in
literature 21,22 . The X-ray diffraction pattern of the pure APE
sample shows a broad region (15 o -27 o 2θ) characteristic of
semicrystalline polyester with one intense reflection at 24.5°
2θ ( _d=_ 3.57 Å) and two diffraction peaks (less intense) at 16°
2θ ( _d=_ 5.60 Å) and 16.5° 2θ ( _d=_ 5.39 Å) are evidenced in
agreement with the literature 23 . The X-ray diffraction patterns
of APE/TiO2 nanocomposites obtained with different filler
contents show the characteristic peaks of TiO2 and APE, that
evidences the filler/polymer interaction. However, intensity
and width of these reflections differ with the filler content.
In the region 15 o -27 o 2θ, characteristic peaks of pure APE
become narrower when the amount of the filler content
increases. This result indicates an effective interaction of
the filler with the polymer matrix 24 . The peak at 27.5 o 2θ,
characteristic of TiO2, is surprisingly less intense and broader
in the sample APE/TiO2 5% than in the sample APE/TiO2
3%. A similar trend was observed previously by Silva et al.
(2013) and was explained by sample heterogeneity 24 .

Regarding the XRD pattern of the sample named APE
W/C, which was synthesized without the addition of dibutyl
tin oxide, the characteristic peaks of pure APE are present
that indicates that the TiO2 filler can also act as a catalyst.

In Table 1 are presented the molar weights and polydispersity
index of the pure APE and the synthesized nanocomposites.
Molar weights differ with the filler content: the molar average
number ( _Mn_ ) and the molar average weight ( _Mw_ ) are lower
than pure APE in the case of 1% of TiO2; however these
values increase with higher filler content. It is believed that
the interactions between the particles of TiO2 and the growing
polymer chain limited the growth of the APE 24 . In the case
of 3 and 5% of TiO2, the filler is probably also acting as
a catalyst for esterification reaction, since titanium‑based
compounds are excellent catalysts for esterification and
transesterification reactions 23,25 . The polydispersity index (PI)
was around 2.0 that is a characteristic value of condensation
polymerization. The molar weights obtained for APE 5%w/w
TiO2 W/C (Table 1) show that filler also act as catalyst.

The Figure 3 shows the DSC curves of the pure APE
and the APE/TiO2 nanocomposites. As with the pure APE,
whatever the filler content two melting peaks (peak 1 and
peak 2 in Figure 3a) and only one crystallization peak
(Figure 3b) are observed.

Some studies evidenced the presence of double
crystallite regions produced by different morphologies 26,27 .
This behavior was observed in some flexibles semicrystalline
polymers such as polyethylene (PE) 28, polypropylene (PP) 28
or semi-rigid polymer such as poly(ether-ether-ketone)

Table 1. GPC analysis of the pure APE and APE/TiO2 nanocomposites
with 1, 3, 5% TiO2 and 5% TiO2 W/C.

TiO2 (%) _Mn_ (g/mol) _Mw_ (g/mol) PI

0 7495 12492 1.7
1 5883 10655 1.8
3 8802 17783 2.0
5 9965 17836 1.8
5 W/C 1734 2756 1 6

Fig. 3. DSC curves of pure APE and the APE/TiO2 nanocomposites: (a) melting peak; (b) crystallization peak.

Table 2. Thermal properties and contact angle of the pure APE and APE/TiO2 nanocomposites with 1, 3, 5% TiO2 and 5% TiO2 W/C.

_Tendset_

( o C)

TiO2

(%)

_Tm1_
(°C)

_Tm2_
( o C)

ΔHm _1_

(J/g)

ΔH _c_
(J/g)

Contact Angle

(°)

ΔHm _2_

(J/g)

_Tc_
(°C)

_Tonset_
( o C)

0 113 122 6 29 96 51 393 434 58
1 105 118 4 22 92 43 392 434 64
3 115 124 10 9 93 34 393 433 65
5 109 118 6 14 91 39 393 432 69
5 W/C 93 104 3 15 82 31 178 476 nd

nd not determine

Fig. 4. Thermogravimetric analysis of the pure APE, APE with 1, 3 and 5% TiO2 (a) initial region of degradation of APEs (b) and final
region of degradation of APEs (c).

(PEEK) 29, poly (ethylene terephthalate) (PET) 25, among
others and can be explained by the formation of different
morphologies associated with the crystallization process
of these polymers. These materials can present two or
more crystal modifications or, at least two groups with
various lamellar structures, or even different crystalline
morphologies 25 . These different structures can be formed
in the isothermal crystallization process at temperatures
much above the ambient (70°C-100°C) as observed for the
poly (alkylene succinate) (80°C-100°C) 26,27 . In our study, at
the end of the 2nd stage of synthesis (bulk polymerization),
the APE started to solidify at temperatures much above the
ambient (around 90 o C). Besides that, the APE was formed
by two linear aliphatic segments which could contribute to
the formation of different crystalline regions. One single
crystallization peak was observed and this behavior has
been seen after the cooling process from the melt polymer 23 .

Table 2 shows the values of  _Tm1_, _Tm2_ (melting temperatures
of the peak 1 and peak 2, respectively) ΔHm _1_, ΔHm _2_ (fusion
enthalpies of the peak 1 and peak 2, respectively) and the values 
of _Tc_ (crystallization temperature) and ΔH _c_ (crystallization
enthalpy) obtained from the DSC curves (Figure 3) of the
pure APE and APE/TiO2 nanocomposites synthesized.

From the data shown in Table 2 it could be seen that the
addition of different amounts of TiO2 did not significantly
modify the melting temperatures of the polymers. However,

h d i h l i h l f k 2

Fig. 5. Hardness of the APE/TiO2 nanocomposites and the pure APE.

indicating a decrease in the population of crystallites
associated with this peak. This result was also observed in
the work of Yoo and Im (1999) 26 .

The _Tc_ values for the nanocomposites showed a tendency to
decrease when compared to the pure polymer sample (Table 2).
On the other hand, there was a decrease in crystallization peak
area (Figure 3b) resulting in a decrease of the ΔH _c_, which
corroborates with the results of the polymers crystallinity
in the nanocomposites. This decrease in the crystallinity is

l f h fill l i i hi h i f

Fig. 6. Micrographs of the pure polymer (a); APE with 1% (c); 3% (e) and 5% TiO2 (g). EDS spectra of the pure polymer (b); APE with
1% (d); 3% (f) and 5% TiO ( h)

in the organization between the chains the same way as it
was observed by XRD.

The thermal degradation curves analyzed by TGA
(Figure 4a) show a single stage of degradation, both for
the pure polymer and for APE/TiO2 nanocomposites. It was
also not observed a change in the initial ( _Tonset_ ) and final
( _Tendset_ ) temperatures of the nanocomposites compared to
pure APE (Table 2). However slight variations in start and
end regions of degradation (Figures 4b and 4c, respectively)
were observed, indicating that there was an interaction of
TiO2 with the polymeric matrix, in agreement with reports
in the literature 30 . It was also observed an increase in the
residue content with the increase of filler added. For the APE
5%w/w TiO2 W/C was observed a _Tm_, _Tc_, ΔH _m_ and ΔH _c_ lower
and _Tonset_ much more lower compared the other samples due
the its low molar weight (Table 1).

Figure 5 presents the hardness results, where can be noted
an increasing trend of this property in the APE/TiO2 1 and
3% nanocomposites compared to the pure APE. However
for APE/TiO2 5% was not observed the increase compared
to APE/TiO2 3%.

In a study performed by Yinghong et al. (2003) with
unsaturated polyester/ TiO2 nanocomposites, was observed
a maximum impact resistance when 4% of the filler was
added and for higher percentage of TiO2, this property was
decreased 31 . This behavior was explained by the agglomeration
of fillers which cause stress points in the formed material 24,31,32 .

Figure 6 shows the micrographs of the pure APE and
the APE/TiO2 (1, 3, 5% w/w). With 1% of TiO2 in the APE
matrix, it can be seen a homogeneous distribution of the filler,
indicating a good compatibility with the polymeric matrix.
The diameter of the TiO2, inside the matrix, was around
199±58 nm. On the other hand, it was observed clusters
formation (in nanometer scale) in the materials with more
than 1% of the charge (Figure 6c and 6d). This fact was
evidenced by the larger average size in the nanocomposite,
263±96nm, since the untreated TiO2 used has an average
diameter of 164±33nm 24 . The same effect was verified by
Sudirman et al. (2012), when silica was added in unsaturated
polyester resin 19 and by Silva et al. (2013) with polyurethane
and TiO224.

The EDS spectra of nanocomposites (Figure 6d, 6f and 6h)
evidenced an increase in the Ti peak compared to the pure
polymer (Figure 6b) and confirm the incorporation of the
TiO2 filler in the APE matrix.

The measurement of the contact angle is a way to prove
the interaction between the polyester and the titanium dioxide,
since the filler modifies the surface of the material and the
wettability property (Figure 7). The filler addition promoted an
gradual increase in the value of the contact angle of the droplet
from 58 o (pure APE, Table 2) to 69° (APE/TiO2 5%, Table 2),
indicating a decrease tendency of the hydrophilicity of the
synthesized materials with larger amounts of the filler, when
compared with the pure APE.

Fig. 7. Images of the contact angle of milli-Q water on the surface of pure APE (a) and the APE/TiO2 nanocomposites with 1% (b), 3%

4. Conclusions

The nanocomposite APE/TiO2 (1% w/w) obtained by the
_in situ_ polymerization showed a homogeneous distribution
of the filler in the polymeric matrix (average particle sizes
of 199 nm) and an improvement of thermal properties and
hardness of the polyester matrix. However larger amounts of
filler (3 and 5% TiO2) revealed the aggregates formation in
the polymer matrix. The nanocomposites with the amount of
filler equal to or exceeding 3% presented molecular weight
higher than the pure APE, indicating that the filler also acts
as a catalyst for the polymerization reaction of the APE. The
increasing addition of TiO2 promoted a slight increase of the
contact angle and consequently a decrease tendency of the
hydrophilicity of the APE/TiO2 nanocomposites compared
to pure APE.

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Acknowledgements

The authors would like to thank FINEP and CAPES
for the financial support. SE and RL acknowledge CNPq
for DT grant and CAPES for PNPD post-doc fellowship.
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