Production of thermoplastic starch and poly (butylene adipate-co-terephthalate) films assisted by solid-state shear pulverization

Carbohydrate Polymers 258 (2021) 117732

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Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol

Production of thermoplastic starch and poly (butylene
adipate-co-terephthalate) films assisted by solid-state shear pulverization
H.S.M. Lopes a, *, G.H.M. Oliveira a, S.I. Talabi a, b, A.A. Lucas a
a
b

Federal University of Sao Carlos, Graduate Program in Materials Science and Engineering, CEP 13565-905, Sao Carlos, SP, Brazil
University of Ilorin, Materials and Metallurgical Engineering Department (MME), PMB 1515, Ilorin, Nigeria

A R T I C L E I N F O

A B S T R A C T

Keywords:
TPS
PBAT
Films
Biodegradable
Blends
SSSP

A novel processing technique involving Solid-State Shear Pulverization (SSSP) was used to produce thermoplastic
starch (TPS) and Poly (Butylene Adipate-co-Terephthalate) (PBAT) films to improve processability and produce
well-dispersed blends. Four different compositions (50− 80 wt% TPS content) were processed using two different

production routes. In one instance, the compositions were pre-treated by SSSP before melt extrusion (SSSPE).
Secondly, starch was initially plasticized and thereafter blended with PBAT by melt extrusion (EXT) method. Flat
films were produced using both routes and processability, visual and tactical aspects, mechanical and optical
properties, crystallinity, and water absorption behavior were evaluated. High starch content films (70 and 80 wt
%) prepared based on SSSP incorporation showed easier processability, and better visual aspect and mechanical
integrity than EXT ones. However, EXT films with 50 and 60 wt% of starch presented higher elongation at break
and lower water absorption due to finer dispersion of TPS and better starch plasticization.

1. Introduction
Government policies with focus on reducing non-biodegradable
plastics have been implemented over the last years. Nevertheless, the
high cost of biopolymers is one of the main obstacles to a wide com­
mercial application. Starch is one of the most promising biopolymers to
produce biodegradable materials, especially for packaging and food
applications, due to its low cost, abundance and renewable sources
(Av´
erous & Halley, 2009; Fakhouri et al., 2013; Halley & Av´
erous,
2014). It is mainly composed of two macromolecules, namely, linear
amylose and branched amylopectin, and their quantity affects its crys­
tallinity and mechanical properties (Averous, 2004; Hoover, 2001;
Jenkins & Donald, 1995). Depending on the area of utilization, starch
can be processed by many techniques to obtain different properties
(Fakhouri et al., 2013; Halley & Av´erous, 2014).
In its native structure, starch does not flow or melt, and plasticization
under high temperature and shear conditions is required to transform it
to a thermoplastic material (Moad, 2011; Olivato et al., 2017; Yu &
Christie, 2005). The procedure disrupts starch granules in the presence
of water and a plasticizer additive. After plasticization, thermoplastic
starch (TPS) has a metastable amorphous structure that causes its

recrystallization over time via a process called retrogradation. During
this process, amylose and amylopectin recrystallize, leading to proper­
ties change, which limits its application to a large extent (Fu, Wang, Li,
Zhou, & Adhikari, 2013; Hoover, 2001; Wang, Li, Copeland, Niu, &
Wang, 2015). Due to additional limitations such as low mechanical
properties and high-water absorption, starch is commonly blended with
synthetic polymers for the development of commercially attractive films
with good visual aspects and improved mechanical properties (Raquez,
Nabar, Narayan, & Dubois, 2008; Brandelero, Yamashita & Grossmann,
2010; Olivato, Grossmann, Bilck, Yamashita, & Oliveira, 2013; Silva,
2013).
Blending thermoplastic starch, a hydrophilic polymer, with nonpolar synthetic polymers, like polyesters, produces immiscible blends.
Hence, the employed processing route and quantity of the blend com­
ponents are important parameters that can affect the developed material
properties (Paul & Bucknall, 2000; Utracki, 1990). A novel technique
called Solid-State Shear Pulverization (SSSP) has been employed to
produce finely dispersed immiscible blends in the solid-state. Previous
works used this technology to produce polymer blends that have unique
physical characteristics and better mechanical properties compared to
other processing routes (Furgiuele, Lebovitz, Khait, & Torkelson, 2000;

* Corresponding author.
E-mail addresses: (H.S.M. Lopes), (G.H.M. Oliveira), (S.I. Talabi),
(A.A. Lucas).
/>Received 5 October 2020; Received in revised form 12 January 2021; Accepted 27 January 2021
Available online 30 January 2021
0144-8617/© 2021 Elsevier Ltd. This article is made available under the Elsevier license ( />

H.S.M. Lopes et al.

Carbohydrate Polymers 258 (2021) 117732

Table 1
Processing parameters.
Processing routes
SSSPE
EXT
Film production

Stages

Processing techniques

i
ii
i
ii

SSSP
Melting extrusion
Melting extrusion
Melting extrusion
Film extrusion

Zones temperature (◦ C)
1

2

3

4

5

27
145
142
130
100

27
145
142
132

27
150
147
137

27
140
137
132

27
130
130

127

Furgiuele, Lebovitz, Khait, & Torkelson, 2000; Furgiuele, Khait, &
Torkelson, 1998; Khait, Carr, & Mack, 2001). It involved processing the
material using a twin-screw co rotational extruder at temperatures
below its melting/softening point under high shear and compression
forces, which causes particle size reduction and intense mixing. This
technique can facilitate the mixing of PBAT with starch before its
plasticization.
Some researchers have manufactured polymer blends by incorpo­
rating SSSP technique in the preparation and processing routes. Walker,
Tao, and Torkelson (2007), attributed improved mechanical properties
of HDPE/starch blends to intense fragmentation of starch granules
caused by incorporating SSSP technique in the material production. The
stabilization of dispersed phase in PS/PMMA and PS/HDPE blends has
been observed (Lebovitz, Khait, & Torkelson, 2002; Lebovitz, Khait, &
Torkelson, 2002). The improved morphology and in-situ compatibili­
zation of these blends were attributed to the utilization of pulverization
technique, which resulted in a fine filler dispersion in the immiscible
blends. Regarding these blends, similar results were obtained with the
incorporation of SSSP technique during processing (Lebovitz, Khait, &
Torkelson, 2003; Tao, Kim, & Torkelson, 2006). In this instance, the
attained properties were attributed to intense and repeated fragmenta­
tion, which led to higher compatibility of the blend components.
Based on such previous studies, this work investigated the incorpo­
ration of SSSP in the processing of TPS/PBAT blends for film production.
The proposed processing routes involving this innovative technique was
used to produce finely dispersed biodegradable PBAT blends/films with
high thermoplastic starch content (≥50 wt%) using conventional
equipment. Processing parameters like ease of manipulation, feeding

and granulation were observed as an indication of better processability
during preparation. Based on the surveyed literature, this is the first
report involving SSSP incorporation in the manufacturing of these
materials.

150

150

Screw rotation (rpm)
200
120
120
80
50

Table 2
Samples designations.
Samples designation

Composition

50SSSPE
60SSSPE
70SSSPE
80SSSPE
50EXT
60EXT
70EXT
80EXT

50 wt.% TPS
60 wt.% TPS
70 wt.% TPS
80 wt.% TPS
50 wt.% TPS
60 wt.% TPS
70 wt.% TPS
80 wt.% TPS

Processing route
+50
+40
+30
+20
+50
+40
+30
+20

wt.% PBAT
wt.% PBAT
wt.% PBAT
wt.% PBAT
wt.% PBAT
wt.% PBAT
wt.% PBAT
wt.% PBAT

SSSPE

SSSPE
SSSPE
SSSPE
EXT
EXT
EXT
EXT

homogeneous formulation. The resulting mix was then oven-dried for 12
h at 90 ◦ C (Olivato et al., 2017).
2.2.2. Preparation of TPS/PBAT films
Two different processing techniques were used to prepare the TPS/
PBAT blends. A batch was prepared using both SSSP and melting
extrusion techniques (designated as SSSPE), while another batch was
prepared using only the latter method (designated as EXT). The pro­
duction was done in a Baker & Perkins co-rotational twin-screw
extruder, with a screw diameter of 19 mm and L/D of 25.
Samples prepared using the SSSPE route followed this procedure: (i)
pulverization of starch/plasticizers mix in the presence of PBAT (SSSP);
(ii) melting extrusion to plasticize starch and homogenize the blend
components. Samples prepared using EXT route followed this sequence:
(i) starch/glycerol/water mix was plasticized through conventional
melting extrusion to obtain TPS; (ii) TPS and PBAT were subsequently
blended using the same technique.
Thereafter, flat films were produced from the blends in a singlescrew extruder AX Pl´
asticos equipment with a screw diameter of 40
mm and L/D of 25. Due to the unique behaviour of each formulation
during processing, in terms of feeding, flow and pulling, the film
thickness varied between 0.110 to 0.450 mm. The film thickness was
measured by a micrometre.

The temperature profiles and screw rotation used during each pro­
cessing stage are provided in Table 1.
Furthermore, the samples were designated as shown in Table 2.

2. Materials and methods
2.1. Materials
Cassava starch (23 % amylose content) was purchased from Fecu­
laria Pantanal® (Mato Grosso do Sul, Brazil). Its molecular weight was
estimated using intrinsic viscosity method, described by Millard, Dint­
zis, Willett, and Klavons (1997) and found to be 422 × 106 g mol− 1. The
detail about the experimental procedure used for this measurement can
be found in a supplementary information file. Poly (butylene
adipate-co-terephthalate) (PBAT) was purchased from BASF® (Sao
Paulo, Brazil), under the commercial name Ecoflex F Blend C1200.
Glycerol P.A. was obtained from Neon® Commercial Ltda (Sao Paulo,
Brazil) and Sodium Chloride, Citric and Stearic Acid from Synth® (Sao
Paulo, Brazil).

2.2.3. Water absorption
Water absorption measurement was done following ASTM E104-02
standard (American Society for Testing and Materials, 2012). All the
film samples were oven-dried at 60 ◦ C until their mass stabilized and
were then kept in a desiccator containing saturated sodium chloride
solution (NaCl, 75 % relative humidity) at 23 ◦ C ± 1 ◦ C. After that, each
sample was weighed at different intervals for a total period of 200 h and
the weight gain was plotted as a function of time. Each formulation was
assayed in duplicate.
2.2.4. Mechanical properties
Mechanical properties were determined with Instron 5569 equip­
ment according to ASTM D882-00 standard (American Society for

Testing and Materials, 2010). An initial grip separation of 125 mm and
12.5 mm/min crosshead speed at 23 ◦ C were used for the test. The
specimens, 50 mm wide and 175 mm long, were maintained under two

2.2. Methods
2.2.1. Cassava starch modification
The cassava starch was oven-dried for 12 h at 60 ◦ C before me­
chanically mixing it with glycerol and water solution (plasticizers),
following the composition 250:100 g 1000g− 1 of starch, to obtain a
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Carbohydrate Polymers 258 (2021) 117732

Fig. 1. Visual aspect of the films. Fig. 1(a) EXT films (i-iv) and Fig. 1(b) SSSPE films (i-iv).

different conditions before measurements. Some samples set were kept
in a desiccator containing saturated sodium chloride solution, at a
relative humidity (RH) of 75 % and 23 ◦ C (designated as high RH) and
the other groups were kept in a ventilated oven at 60 ◦ C for 12 h
(designated as low RH). The analysis provided information about tensile
strength at yield, percentage of elongation at break and Young’s
modulus under the various storage conditions. The measurements were
performed in ten replicates.

Ia = amorphous area.
2.2.6. Scanning Electron Microscopy (SEM)
The morphology of selected film samples was observed under a FEI

Magellan 400R scanning electron microscope, operated at 5 kV. The
samples were cryogenically fractured and covered with a thin gold layer
before the examination.
2.2.7. Polarized light microscopy (POM)
The films were also observed under polarized light using a Leica
DMRXP optical microscope at room temperature, 180 days after
production.

2.2.5. X-ray diffraction (XRD)
For the measurements, 1 cm2 film samples were kept in a desiccator
containing saturated sodium chloride solution at 75 % relative humidity
and 23 ◦ C. The examination was done 20 and 50 days after production.
The XRD patterns were obtained using a Rigaku Geiger-Flex diffrac­
tometer, with voltage and current of 40 kV and 30 mA, respectively,
from 5 to 50◦ at 2◦ /min scan speed. Crystallinity index was subsequently
calculated based on the crystalline and amorphous peaks areas using Eq.
(1) (Canevarolo, 2004).
Ic
Xc =
× 100%
Ic + Ia

3. Results and discussion
3.1. Processing of thermoplastic starch and blends
The incorporation of solid-state shear pulverization during produc­
tion resulted in easier manipulation of the materials in terms of feeding,
mixing and granulation compared to when only melting extrusion
method was employed. This observation was made relative to the pro­
cessing conditions and equipment used in this work. Due to high water
absorption of TPS, the samples’ surfaces become sticky and brittle,

which made manipulation and granulation more difficult during EXT
steps such as feeding and granulation. This brittle and sticky behaviour

(1)

Where:
Xc = crystallinity index;
Ic = crystalline area;
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Carbohydrate Polymers 258 (2021) 117732

Fig. 2. SEM images of the films: (a) EXT films prepared with 50, 60, 70 and 80 wt.% TPS, respectively (i-iv), and (b) SSSPE films prepared with 50, 60, 70 and 80 wt.
% TPS, respectively (i-iv).

led to a decrease in the films’ mechanical integrity. However, this
challenge was reduced with the adoption of SSSPE since the starch has
already been mixed with PBAT before plasticization. Similar drawbacks
relating to sticky surfaces and brittleness are found in the literature and
are mostly attributed to TPS water absorption characteristic, crystal­
linity and low plasticization degree during processing (Fakhouri et al.,
2013; Thunwall, Kuthanova, Boldizar, & Rigdahl, 2008; Thuwall, Bol­
dizar, & Rigdahl, 2006).

presence of this structure hinders interfacial adhesion, which negatively
affects their mechanical properties. More so, as the starch content in­
creases, the surface of the film became less rough and more brittle,

howbeit with a similar distribution level of the second phase. These
observations agree well with literature findings regarding similar blends
(Fourati, Tarr´es, Mutj´
e, & Boufi, 2018; Garcia et al., 2018; Li, Luo, Lin, &
Zhou, 2013).
3.4. Mechanical properties

3.2. Visual and tactile aspects

The mechanical properties of the TPS/PBAT films were investigated
after subjecting them to different relative humidity conditions. Firstly,
the elongation at break and tensile strength at yield were found to
decrease with an increase in TPS content due to its brittle nature. This
result agrees with an earlier observation regarding surface characteristic
revealed through SEM examination of the samples. For low starch con­
tent (50 and 60 wt%), the EXT method produces finely dispersed blends
with significantly higher tensile strength, elongation at break and
Young’s modulus, especially for those subjected to a high RH condition.
For example, at low RH, EXT films with 50 wt% of starch have about 150
% elongation at break and the SSSPE ones have approximately 10 %,
while at high RH, it was about 320 % and 35 %, respectively. More so, at
high RH, EXT and SSSPE samples containing 60 wt% starch have elon­
gation at break values of 250 % and 25 %, respectively. The attained
result can be attributed to the higher plasticization of the TPS phase and
better interfacial adhesion, which were promoted by adopting the
former procedure. Nevertheless, at a low RH condition, these films (60
wt% starch), have similar values, irrespective of the employed pro­
cessing routes.
The sample containing high starch content (80 wt%) exhibited
similar mechanical properties despite the difference in the production

procedure. Hence, it can be inferred that SSSPE provides a good alter­
native for the preparation of TPS/PBAT blend containing a high quantity
of TPS.
Generally, there is a clear difference in the mechanical properties of
films conditioned under high and low relative humidity environment
(Fig. 3). Low RH conditioned films presented significant higher Young’s

Samples of the produced films are shown in Fig. 1. EXT films with
high starch content (70 and 80 % of the total film mass) are brittle and
have high adhesivity. The adhesiveness and brittleness of these films
increased with increasing TPS content due to glycerol exudation from
the starch. However, films produced using the SSSPE route did not
exhibit this behaviour.
Furthermore, low starch content films (50 and 60 % of total mass)
prepared by SSSPE presented high adhesiveness and poor mechanical
integrity, compared to the ones produced by EXT method. Generally,
SSSPE films have more flexibility, ease of handling and mechanical
integrity, especially for films with high TPS content, compared to the
EXT ones.
3.3. Microstructure of the TPS/PBAT films
Morphological differences were observed as a function of the films’
compositions (Fig. 2). Films with low TPS content (50 wt%) have higher
rough surfaces (Fig. 2ai and bi), irrespective of the adopted production
route. This observation suggests that the sample matrix is less brittle.
Residual granular structure attributed to incomplete plasticization of
starch granules was observed in all the films at high TPS content.
However, this structure was conspicuous in samples prepared by SSSPE
method. Films with 50 and 60 wt% of starch content processed by EXT
route presented well-dispersed, homogeneous surfaces with less pres­
ence of the starch residual granular structure, which indicates higher

plasticization compared to those produced by SSSPE method. The
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Carbohydrate Polymers 258 (2021) 117732

Fig. 3. Elongation at break (a and b), tensile strength at yield (c and d) and Young’s modulus (e and f) of TPS/PBAT films under low (left column) and high (right
column) relative humidity conditions.

modulus and lower elongation at break, except for the 50 wt% starch
content films produced by EXT method. This behaviour can be attrib­
uted to plasticization and increased chain mobility of starch by water
molecules (Mali, Sakanaka, Yamashita, & Grossmann, 2005; Brandelero
et al., 2010; Li et al., 2013). The results agree well with literature
´z, Luzia, de Carvalho, & da Silva Curvelo, 2005;
findings (Teixeira, Ro
Brandelero, Yamashita & Grossmann, 2010; Fakhouri et al., 2013;
´lez-Seligra, Guz,
Fakhouri, Martelli, Caon, Velasco, & Mei, 2015; Gonza

´, 2017; Moraes et al., 2017).
Yepes, Goyanes, & Fama
3.5. Water absorption
The water absorption property of the films was directly proportional
to the starch content and exposure time (Fig. 4). This behaviour was due
to starch hydrophilic nature associated with a high quantity of hydroxyl
groups that are present within its chemical structure and the use of
5

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Carbohydrate Polymers 258 (2021) 117732

Fig. 4. Water absorption of the TPS/PBAT films: 50 (a), 60 (b), 70 (c) and 80 (d) wt% TPS, produced by EXT (squares) and SSSPE (circles) routes.

glycerol as plasticizer (Pelissari, Grossmann, Yamashita, & Pineda,
2009; Silva et al., 2015; Van Soest & Knooren, 1996). SSSPE and EXT
samples exhibit a similar pattern of water absorption, although the films
produced by the former procedure show a slightly higher water intake
ability, especially for the formulation containing 50 wt% TPS. The EXT
films containing 50 wt% TPS have the lowest level of water absorption
due to a finer dispersion of TPS phase (see Fig. 2), which allows them to
have a more compact structure in agreement with Li et al. (2013)
observation. Regarding high starch content blends (70 and 80 wt%), the
weight gain was almost the same after 200 h, irrespective of the
employed preparation techniques. Generally, the results suggest that the
blends morphology (at low starch content) and composition play a role
on the water absorption characteristic of the samples.

be higher in SSSPE films (Fig. 5b and c). This peak is due to residual
cassava starch granules with double-helical crystal lattices from native
amylopectin. The increased intensity of this peak in SSSPE films suggests
lower plasticization of the samples. Additionally, retrogradation could
be occurring since chain mobility could promote recrystallization of
amylopectin molecules after 20 days in high-moisture storage (Van Soest
& Knooren, 1997; Van Soest, Hulleman, De Wit, & Vliegenthart, 1996).
As observed by (Raquez et al., 2008), TPS/PBAT blends may not be

completely plasticized after processing and this can be revealed by XRD
measurement. A slight increase in the intensity of the B-type crystalline
phase after 50 days of storage, further confirms retrogradation. This
observation applied to all the samples, irrespective of the adopted pro­
cessing route. The increase in chain mobility by water molecules and/or
the plasticizer content contributed to the faster retrogradation of the
films. Furthermore, the presence of this phase can reduce the blends/­
films mechanical properties such as their elongation at break (Van Soest
& Knooren, 1997). Consequently, the result agrees with an earlier
observation regarding the detrimental effect of starch residual granular
structure.
The intensity of the peaks at 13.0◦ and 19.8◦ assigned to V-types
structures of TPS crystallinity becomes higher as the samples’ starch
content increases. The presence of this crystalline phase can be attrib­
uted to fast amylose recrystallization in single-helical crystal lattice (Li
et al., 2013; Raquez et al., 2008; Van Soest et al., 1996). The orientation

3.6. Phase composition of the TPS/PBAT films
The XRD patterns and crystallinity index (Xc) of PBAT and the TPS/
PBAT films prepared by SSSPE and EXT methods are shown in Fig. 5.
PBAT film presented peaks at 17.2◦ , 20.6◦ , 23.0◦ and 24.7◦ , as seen in
Fig. 5(a). The calculated crystallinity level and the polymer diffracto­
gram peaks agree with literature findings (John, Mani, & Bhattacharya,
2002; Raquez et al., 2008; Silva, 2013; Silva et al., 2015).
Compared to films produced by EXT method, the intensity of the
peak at 17.0◦ (belonging to the B-type crystalline phase) was observed to
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Carbohydrate Polymers 258 (2021) 117732

Fig. 5. XRD diffraction patterns and crystallinity index (Xc) of PBAT film (a) and TPS/PBAT films processed by EXT and SSSPE after 20 days (b) and 50 days (c).

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Carbohydrate Polymers 258 (2021) 117732

Fig. 6. POM images of the films and native starch granules: (a) EXT films prepared with 50, 60, 70 and 80 wt.% TPS, respectively (i-iv); (b) SSSPE films prepared
with 50, 60, 70 and 80 wt.% TPS, respectively (i-iv), and (c) native starch granules.

of V-types structures is processing-induced in the presence of water
molecules, generating several V- type structures (Van Soest & Knooren,
1997; Van Soest et al., 1996).
The calculated crystallinity index value of each film was presented
(Fig. 5). The observed changes in the Xc values could be related to
structural rearrangement during ageing as proposed by (Van Soest &
Knooren, 1997).
Irrespective of the processing route, TPS/PBAT blends presented
similar characteristics and retrogradation pattern. However, a higher
amount of B-type crystalline phase, which could be due to residual
granular structure, was observed in SSSPE films.

4. Conclusions
The incorporation of SSSP technology provides benefits such as
better processability and easier manipulation of TPS, which resulted in

the production of films with improved visual aspects and good me­
chanical integrity by conventional equipment. However, low starch
content blends prepared by SSSPE have relatively lower mechanical
properties and water absorption due to low starch plasticization
compared to when EXT route was employed. Also, the low starch con­
tent films produced by EXT method have finely dispersed composition as
a result of better plasticization. Irrespective of the processing and
preparation procedure, the samples containing high amount of starch
showed no significant difference in mechanical properties. Furthermore,
these blends have similar morphology, crystallinity level and water
absorption. Generally, the results suggest that SSSPE can be a promising
technique to produce high-TPS/PBAT blends using typical equipment
and procedures. Consequently, there is need for future studies to pro­
mote better starch plasticization when SSSP is incorporated in the
preparation of TPS/PBAT blends. This can be achieved by optimizing
production conditions and processing parameters such as the equipment
screw design and temperature or incorporating methods that can pro­
mote starch plasticization.

3.7. Optical property of the TPS/PBAT films
Fig. 6 shows the presence of granular birefringent structures in the
films. As observed earlier, the presence of residual starch granules
negatively affects the samples mechanical properties. The effect was
more pronounced in films with high starch content and more residual
granular structure, irrespective of the difference in their preparation
procedure. Regarding the low starch content films, this structure was
obvious in films produced by SSSPE method. This was expected since the
micrography of EXT films revealed less presence of residual granular
structure. Generally, the results obtained by mechanical properties,
water absorption, SEM and XRD examination followed a similar pattern.

However, it is still not clear how mixing of starch with larger
quantities of PBAT (blends containing 50 and 60 wt% of starch) by
SSSPE technique hinders starch plasticization during melting extrusion.
Consequently, future efforts would be focused on improving starch
plasticization when SSSPE method is used for the preparation of TPS/
PBAT blends for films production.

CRediT authorship contribution statement
H.S.M. Lopes: Conceptualization, Data curation, Investigation,
Methodology, Writing - original draft. G.H.M. Oliveira: Conceptuali­
zation, Data curation, Investigation, Methodology, Writing - review &
editing. S.I. Talabi: Conceptualization, Writing - review & editing. A.A.
Lucas: Supervision.

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Carbohydrate Polymers 258 (2021) 117732

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o de Aperfeiỗoaư
This study was financed in part by the Coordenaỗa
mento de Pessoal de Nớvel Superior - Brasil (Capes) – Finance Code 001.
The authors would like to thank Nidustec/Tecbio and LCE/UFSCar for
financial and technical support.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
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