Miscibility study of thermoplastic starch/polylactic acid blends: Thermal and superficial properties

Carbohydrate Polymers 293 (2022) 119744

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

Miscibility study of thermoplastic starch/polylactic acid blends: Thermal
and superficial properties
Abril Fonseca-García a, b, Brayan Hern´
andez Osorio c, Rocio Yaneli Aguirre-Loredo a, b,
d
Heidy Lorena Calambas , Carolina Caicedo e, *
a

Centro de Investigaci´
on en Química Aplicada (CIQA), Blvd. Enrique Reyna Hermosillo 140, Saltillo, Coahuila 25294, Mexico
CONACYT-CIQA, Blvd. Enrique Reyna Hermosillo 140, Saltillo, Coahuila 25294, Mexico
Semillero de Investigaci´
on en Química Aplicada (SEQUIA), Facultad de Ciencias B´
asicas, Universidad Santiago de Cali, Pampa linda, Santiago de Cali 760035,
Colombia
d
Grupo de Investigaci´
on en Desarrollo de Materiales y Productos, Centro Nacional de Asistencia T´ecnica a la Industria (ASTIN), SENA, Cali 760003, Colombia
e
Grupo de Investigaci´
on en Química y Biotecnología (QUIBIO), Facultad de Ciencias B´
asicas, Universidad Santiago de Cali, Pampalinda, Santiago de Cali 760035,
Colombia
b

c

A R T I C L E I N F O

A B S T R A C T

Keywords:
Achira starch
PLA
Pluronic® F127
Polymeric blend films
Emulsion

In this work, the miscibility of blends of thermoplastic Achira Starch (AS) and polylactic acid (PLA) was eval­
uated, assisted by Pluronic® F127 an amphiphilic triblock copolymer that acts as a surfactant and promotes the
reduction of surface tension among AS and PLA in solution by emulsion stabilization. Different formulations of
AS/PLA blends were obtained at 75:25, 50:50, and 25:75 containing 0 %, 4 %, and 8 % of Pluronic® F127, and
glycerol was used as a plasticizer. Solvent casting was the method used to obtain blended polymeric films, which
were characterized by Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Xray diffraction (XRD), Thermogravimetric Analysis (TGA), differential scanning calorimetry (DSC) and wetta­
bility by contact angle measurements. The results demonstrate that miscibility of PLA in AS or vice versa was
achieved. The stability of emulsion and posterior drying of the different formulations allows the production of
films for packaging, pharmaceutical, or biomedical applications.

1. Introduction
Synthetic polymers are produced from petroleum derivatives, and
because of their characteristics, they have been used in many industrial
areas. In the food area, packaging materials play a fundamental role, not
only for the protection of food and the maintenance of its quality, but it
can also define the purchasing preference of consumers. The world
production of packaging has experienced exponential growth with 368

million tons remaining in 2020 due to the health crisis caused by Covid
19 (Manufacturers, 2021). Current synthetic packaging materials have
favorable characteristics such as low cost, rapid transformation, good
optical properties, and excellent mechanical and barrier performance
(Ceron M, 2013), which is why they are used in more significant pro­
portions than other materials such as paper, cardboard, glass, and
aluminum. However, despite these advantages, they have become a
severe environmental problem due to their slow degradation, which can

take longer than 50 years (Mohanan et al., 2020). Due to the enormous
amount of pollution that is generated by its widespread use, various
solutions have been sought to reduce or replace its consumption. Among
the options are management strategies for recycling and generating new
biodegradable and compostable materials that are sustainable (Villada
Castillo, 2014). The use of biodegradable polymers such as chitosan,
starch, collagen, zein, polyvinyl alcohol, polylactic acid, cellulose, and
its derivatives have been extensively explored since they can be a viable
option for the generation of novel, biodegradable, compostable, and
sustainable packaging materials that can be used with food. One of these
biopolymers is starch, which is an excellent alternative due to its low
cost and diverse sources of production. The search for new sources of
starch has become increasingly important, taking advantage of uncon­
ventional raw materials that can be a sustainable option and preferably
that do not compete with the human population's food. Achira (Canna
edulis sp.) is a root with high starch content, which it is native to South

* Corresponding author.
E-mail addresses: (A. Fonseca-García), (B.H. Osorio), (R.Y. AguirreLoredo), (H.L. Calambas), (C. Caicedo).
/>Received 28 March 2022; Received in revised form 1 June 2022; Accepted 15 June 2022
Available online 20 June 2022

0144-8617/© 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( />

A. Fonseca-García et al.

Carbohydrate Polymers 293 (2022) 119744

America, widely known in countries such as Colombia, Bolivia and Peru
as well as in the Asian continent in countries like China, Thailand, and
Vietnam (Estrada Rivera, 2020). In the year 2000, the production of
achira in Colombia was estimated at 14000 tons, with the departments
of Huila and Cundinamarca being the main producers (Rodríguez Borray
et al., 2003). In Peru, the consumption of achira root occurs mainly in
isolated and marginalized rural areas. Due to its low cost, it is a viable
alternative for starch extraction. It has been observed that starches with
different physicochemical, thermal, structural, and viscosity properties
can be obtained from achira's distinct varieties or ecotypes (Cisneros
et al., 2009), even when the content of amylose and amylopectin is the
same (Caceres et al., 2021). Its gel-forming ability can rival that of corn
starch (Caceres et al., 2021). In recent years, achira starch has been
evaluated as an additive in the restaurant industry (Caceres et al., 2021),
´mezas encapsulating material for active antimicrobial compounds (Go
Aldapa et al., 2019), as a source to isolate nanofibers (Andrade-Mahecha
et al., 2015), and in the generation of biodegradable materials (Andrade´mez-Aldapa et al., 2020).
Mahecha et al., 2012; Caicedo et al., 2019; Go
In the last two decades, blends of plasticized starch (starch/plasti­
cizer, TPS) and polylactic acid (PLA) have drawn attention because of
their favorable cost and benefits, among which are chemical and phys­
ical properties such as chemical stability, mechanical and thermal
resistance, water vapor and oxygen permeability, brightness, and
biodegradability (Prieto, 2018; Tyuftin & Kerry, 2021). However,

preparation of blends of this type is complicated because of their in­
compatibility, since starch is hydrophilic, while PLA is a hydrophobic
polymer, and this limitation has been demonstrated experimentally and
theoretical by phase separation of TPS and PLA (P. Müller et al., 2016).
Other approaches have been reported to promote compatibility between
starch and PLA, including the use of plasticizers such as glycerol to
render the starch more thermoplastic, which can promote better
compatibility between TPS and PLA blends. However, mechanical
properties such elongation at break and impact resistance were not
improved relative to the pure components (Cai et al., 2011; Martin &
Av´erous, 2001). In addition, co-plasticizer such as glycerol-sorbitol and
glycerol-formamide can promote migration from the TPS phase to PLA
during melt blending (Esmaeili et al., 2019; Wang et al., 2008). Com­
patibilizing agents such as citric acid (Wang et al., 2007), maleic an­
hydride (Przybytek et al., 2018), polyethylene glycol (PEG), and oil
polyols (VOP) (Hu et al., 2020) have been used to promote the depo­
lymerization of starch and disruption of the granules (Caicedo et al.,
2019; Caicedo & Pulgarin, 2021; Wang et al., 2007). Blends of TPS/PLA
can be prepared by extrusion or blow molding processes, and samples of
TPS/PLA/citric acid processed in this manner produced highly
deformable materials with improved toughness and reduced water
vapor and oxygen permeability (Abdillahi et al., 2013; Chabrat et al.,
2012). Naturals oils also have been employed as plasticizers, these
include castor oil (Xiong et al., 2013), epoxidized castor oil (Przybytek
et al., 2018), epoxidized thistle oil (Turco et al., 2019), epoxidized
sesame oil (Ortega-Toro et al., 2021) and maleinized linseed oil (Ferri
et al., 2018). Maleinized hemp oil (Lerma-Canto et al., 2021) has been
employed as a plasticizer in TPS/PLA blends, and these combinations
had a positive effect, since the blends could be processed by injection
molding and blow molding. In addition to plasticizing starch, plastici­

zation of PLA by citrate and adipate esters has also studied. Adipate
esters were incorporated at low concentrations due to their low molec­
ular weights and linear structures, and films produced with these ma­
terials by blown extrusion optimal characteristics (Shirai et al., 2013;
Shirai et al., 2016). In addition to thermal and mechanical analyses,
morphological results allow evaluation of immiscibility by observing
relationships within the domain dimension (Müller et al., 2012). Sila­
nization of the starch used in blends where the concentration of PLA was
dominant led to improved compatibility based on morphological ana­
lyses, and the Tg values decreased while the crystallinity increased. The
mechanical properties of these blends were comparable to those pre­
pared using PLA (Jariyasakoolroj & Chirachanchai, 2014). Chemical

modifications to starch, such as etherification, provide an opportunity to
alter its hydrophilicity and increase its compatibility with PLA, and are
more effective than other treatments of starches, which contain a high
content of amylose (Wokadala et al., 2014). Lactur grafting in starch,
using PLA-g-starch as a compatibilizing agent in PLA/TPS blown films,
resulted in improved droplet sizes, flowability, extensibility and a better
distribution of TPS dispersed in the PLA matrix (Noivoil & Yoksan,
2020). Palai et al. reported in situ chemical grafting using glycidyl
methacrylate (GMA) react with the carboxyl or hydroxyl groups of PLA
(Palai et al., 2019). Protection of hydroxyl groups with acetyl groups
decreased the polarity and enhanced the intermolecular mobility of the
starch (Jim´
enez-Regalado et al., 2021). In this regard, PLA-acetylated
starch blends with varied acetylation grades have been developed and
their mechanical properties were evaluated (Noivoil & Yoksan, 2021).
Increasing the degree of acetylation did not produce favorable results.
Therefore, the challenge remains to find an effective, profitable and

environmentally friendly procedure to expand the use of PLA by
improving its toughness and ductile properties through an optimal
formulation that achieves a homogeneous blend with TPS (Ferri et al.,
2018). Chemical crosslinking, interfacial transition and the formation of
amphiphilic bridges are some of the approaches being used to increase
of the interfacial adhesion in a TPS/PLA phase (Koh et al., 2018; Mar­
tinez Villadiego et al., 2021). Therefore, to address these issues,
amphoteric surfactants are proposed as an alternative for use as coupling
agents among TPS and PLA. However, the surfactants are active in
aqueous environment, and the TPS/PLA blend only have studied by
processes as molten state, injection or blow molding, and extrusion.
Therefore, the approaching toward to understand the miscibility of the
blend TPS-PLA by a preparation of this blend by a method such as sol­
vent casting where in the beginning of the process polymers are in liquid
phase and to promote the miscibility among them due to the presence of
a surfactant as Pluronic® F127, it is an attractive work to develop, which
it can gain more information about the miscibility of this biodegradable
polymers. Commercially available poloxamers, such as the Pluronics®
are known for their properties as nonionic amphoteric surfactants that
can generate thermoreversible aqueous gels. The Pluronic® F127 is
composed of polyethylene oxide (PEO) and polypropylene oxide (PPO)
units, and its arrangement in the poloxamer provides it with amphi­
philicity, and a variation in the proportion of PEO and PPO in the
composition allows it to be classified and characterized by its distinctive
hydrophilic-hydrophobic balance (Zarrintaj et al., 2018). In aqueous
solutions Pluronic® at concentrations above the critical micelle con­
centration (CMC), these copolymers self-assemble into micelles with a
hydrophobic PPO core surrounded by hydrophilic PEO segments, which
generates interesting self-assembly and thermogelling properties (Fon­
seca-García et al., 2021; Russo & Villa, 2019). They possess favorable

solubilization properties and low toxicity; therefore, the Pluronics®
have properties that are useful for applications in drug administration or
controlled release systems (Feitosa et al., 2019; Shaker et al., 2020).
The hypothesis proposed in this work is that the miscibility of
biodegradable polymers such as TPS and PLA is low because of limited
chemical affinity between the polymers; however, the incorporation of
Pluronic® F127 to TPS/PLA aqueous blends promotes their miscibility
to allow production of materials for a variety of applications in the
pharmaceutical industry, biodegradable packaging, or material design.
The goal of this work was the preparation and stabilization of different
formulations of TPS/PLA blends by solvent casting techniques, and to
evaluate their structural, thermal, morphological, and surface proper­
ties. We expect that the results will add to our knowledge regarding the
structural interactions between TPS and PLA.
2. Material and methods
2.1. Materials
Achira starch (AS) was supplied by Surtialmidones S.A.S (Huila,
2


A. Fonseca-García et al.

Carbohydrate Polymers 293 (2022) 119744

Colombia) with a density of 1.59 g/mL and 29.1 % of amylose content
calculated by ISO 6647. The polylactic acid (PLA) Ingeo 2003-D was
obtained from Nature Works Company (Lancaster, PA, EE. UU.) with a
density of 1.24 g/cm3. MFI (210 ◦ C/2.16 kg) of 6.0 g/10 min. Pluronic®
F127 (P2443, 70 % ethylene oxide), glycerol (density of 1.28 g/mL and
purity 99.5 %), and ethyl acetate (purity of 99.8 %) were purchased

from Sigma-Aldrich.

electron microscope (SEM) was employed. A voltage of 10 kV was
applied. The samples were covered with a gold layer. The surface films
were analyzed at 500× and 2000× magnification.
2.3.2. Fourier Transformed Infrared Spectroscopy (FT-IR)
FT-IR analysis of dry films at room temperature was carried out by
ATR mode using a spectrophotometer Spectrum by PerkinElmer (Wal­
tham, MA, USA).

2.2. Methods

2.3.3. X-ray diffraction analysis
The atomic arrangement of films was observed by X-ray diffraction
(XDR) using a Malvern-Panalytical equipment (Empyrean model, Wor­
cestershire, United Kingdom) at 45 kV, 40 mA and Cu Kα = 1.541 Å. The
measurements were done by Bragg–Brentano configuration of powder
diffraction.

2.2.1. Film preparation
Solvent casting was the method used in the preparation of polymeric
blend films. And, the preparation of the blends was done from Table 1,
´mez-Aldapa (Go
´mezwhich was elaborated according to reports by Go
Aldapa et al., 2019). The precursor solutions of achira starch (AS) and
PLA were prepared independently. The PLA solutions at 5 % w/v were
prepared by solubilization of PLA in ethyl acetate by reflux at 100 ◦ C for
1 h. AS solutions at 5 % w/v were prepared by solubilizing starch,
glycerol and according to the case F127 in distilled water, the glycerol
was added in relation of 25 % w/w respect to starch. However, the

incorporation of Pluronic® F127 was added according to glycerol re­
placements as shown in Table 1. The starch dispersion reached the
gelatinization at 85 ◦ C by 5 min, later, were kept at 77 ◦ C and the PLA
solution was incorporated slowly the bubbles were removed of the fil­
mogenic solutions by vacuum pump, and, the solutions were dumped
circular molds with a diameter of 5.5 cm. Finally, the film polymeric
blends were dried in a Binder convection oven at 60 ◦ C by 5 h.

2.3.4. Thermal properties
Thermal stability of films was determined by thermogravimetric
analysis (TGA) using a TGA/DSC 2 STAR System instrument (Mettler
Toledo, Columbus, OH, USA). The sample was heated from 25 ◦ C to
600 ◦ C at a heating rate of 20 ◦ C/min under a nitrogen purge at a flow
rate of 60 mL/min. Weight loss was shown as a function of temperature.
Differential Scanning Calorimetry (DSC) was used with TA Q-2000
equipment (TA Instruments, New Castle, DE, USA), to identify the
thermal transitions of films at a heating rate of 10 ◦ C/min in a tem­
perature range from 25 ◦ C to 200 ◦ C with a nitrogen purge.
The crystallinity grade was determined by calculations based on
ΔH0m for 100 % crystalline PLA being equal to 93 J/g (Fischer et al.,
1973). The degree of crystallinity (Xc) of the blends could be calculated
from the melting enthalpy in the secondary heating curves (ΔHm) ac­
cording to the Eq. (1):
/
]
[
(1)
%Xc = ΔHm − ΔHc ωPLA ⋅ΔHm 0 × 100

2.3. Physicochemical characterization of the films

2.3.1. Morphology by Scanning Electron Microscopy
The surface morphology of polymeric blends was analyzed at low
magnification using a canon EOS Rebel T5 camera at 1:1 scale, and, at
higher magnification a JEOL, JCM 50,000 (Tokyo, Japan) scanning

where ωPLA is the mass fraction of PLA in the blends and ΔHc is cold
crystallization enthalpy.

Table 1
Proportions of achira starch (AS), poly(lactic acid) (PLA), plasticizer, and
poloxamer used for the preparation of the polymer blends.

2.3.5. Wettability by contact angle
The wettability of AS-PLA-pluronic® F127 polymeric blend films was
evaluated by sessile drop contact angle method using distilled water
drops of 20 μL. The test was measured at room temperature using a
goniometer Ram´
e-Hart Model 250 (New Jersey, USA) and performed by
triplicate.

Film

Achira starch (AS)
(g)

PLA
(g)

Pluronic® F127
(g)

Glycerol
(g)

AS100-PLA00
AS100-PLA04
AS100-PLA08
AS75-PLA250
AS75-PLA254
AS75-PLA258
AS50-PLA500
AS50-PLA504
AS50-PLA508
AS25-PLA750
AS25-PLA754
AS25-PLA758
AS0-PLA1000
AS0-PLA1004
AS0-PLA1008

5

0

0

1.25

5

0

0.25

1

5

0

0.5

0.75

3.75

1.25

0

1.25

3.75

1.25

0.25

1

3.75

1.25

0.5

0.75

2.5

2.5

0

1.25

2.5

2.5

0.25

1

2.5

2.5

0.5

0.75

1.25

3.75

0

1.25

1.25

3.75

0.25

1

1.25

3.75

0.5

0.75

3. Results and discussion

0

5

0

1.25

3.1. Morphology

0

5

0.25

1

0

5

0.5

0.75

In Fig. 1, images of AS-PLA-Pluronic® F127 blended films at a scale
of 1:1 can be observed, as well as SEM micrographs of these blends for
both sides, top and bottom, and transverse sections. A visual inspection

2.3.6. Mechanical properties
The mechanical properties of tensile stress and elongation at fracture

were performed on an INSTRON EMIC 23–50 universal machine (S˜
ao
Jos´e dos Pinhais, Paran´
a, Brazil). The films were cut into thin strips
measuring 100 mm long and 25 mm wide. Five replicates were evalu­
ated for each formulation, previously conditioned at 23 ◦ C, 50 % relative
humidity for 48 h. The determinations were carried out at a speed of 10
mm⋅min− 1 until the sample ruptured.
2.3.7. Statistical analysis
Analysis of variance (ANOVA) was performed by Tukey's test (sig­
nificance level: 0.05) to compare mean differences of the film formu­
lations. All statistical analyses were performed with IBM SPSS Statistics
for Windows version 25 (New York, United States).

3


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Carbohydrate Polymers 293 (2022) 119744

Fig. 1. Images of AS-PLA blend films: (a) AS100-PLA0-0, (b) AS100-PLA0-8, (c) AS75-PLA25-0, (d) AS75-PLA25-8, (e) AS50-PLA50-0, (f) AS50-PLA50-8, (g) AS25PLA75-0, (h) AS25-PLA75-8, (i) AS0-PLA100-0 and (j) AS0-PLA100-8. Micrographs by SEM of AS/PLA blend films, the chemical composition correspond to the image
of above, 1: is f1 correspond to contact with the environment or top side, opaque surface, 2: Transversal section of film, and, 3: is f2 side in touch with the mold or
bottom side.

of the films by images at a scale of 1:1 shows that AS100-PLA-0 is a
translucent film, and that AS100-PLA-8 is a translucent, slightly opaque
film, compared to AS100-PLA-0. This result demonstrates the good
miscibility between AS and Pluronic® F127. AS0-PLA100-0 is a white
film, and no visible color changes are evident in AS0-PLA100-8 films

with respect to AS0-PLA100-0. In the blended films AS75-PLA25-0,

AS50-PLA50-0, and AS25-PLA75-0, the miscibility of AS and PLA is
complicated, and segregation of PLA is visually observed. However, the
incorporation of poloxamer promotes miscibility, since the blended
films AS25-PLA75-8, AS50-PLA50-8, and AS25-PLA75-8 exhibit
conformation and homogeneity, suggesting that the incorporation of
Pluronic® F127 at 8 % w/w in these blends promoted miscibility in the
4


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Carbohydrate Polymers 293 (2022) 119744

films.
The SEM micrographs were obtained on three sections of the films:
the top side of the films, which engages in contact with the environment
(named f1), the transverse section of the film, and the bottom of the film,
the side in contact with the mold (named f2). In general, the SEM images
of the blended films showed that for both sides f1 and f2, the confor­
mation of the films are different on a micrometer scale, although for the
AS100-PLA0-0, AS100-PLA0-8. And, AS25-PLA75-0 films, where both
film sides f1 and f2 have the same conformational behavior, the
topography is smooth, with no hills or valleys, and are without
scratches. The AS100-PLA0-0 and AS25-PLA75-0 films are transversely
compact, and in the AS25-PLA75-0 film, it is possible to identify
segregation of PLA particles. The polymeric blends AS75-PLA25-8 and
AS50-PLA50-8 contained spherical particles in the matrix, which may be
due to PLA in solution with AS, and Pluronic® F127 is stabilized as an

emulsion, where in these formulations a continuous phase emulsion
corresponds to water (AS), and the disperse phase emulsion corresponds
to ethyl acetate (PLA). Since poloxamer (a triblock polymer) acts as a
surfactant and forms micelles that help to stabilize the emulsion by
reducing the surface tension, even when the casting process with PLA is
stable, as shown in Fig. 1 for AS75-PLA25-8 and AS50-PLA50-8 blends.
However, the AS50-PLA50-8 film contains a greater number of spherical
particles due to the PLA content being higher than it is in the AS75PLA25-8 film, and both blends generate compact films with particles
along the matrix. However, with AS25-PLA75-0 and AS25-PLA75-8, the
blends are stabilized in an inverse emulsion. In these cases, the contin­
uous phase emulsion corresponds to ethyl acetate (PLA), and the
dispersed phase emulsion corresponds to water (AS). The addition of
poloxamer leads to a reduction in the surface tension, and interactions
between ethyl acetate (PLA) and water (AS) are made possible, thereby
promoting miscibility. Micrographs of AS25-PLA75-0 and AS25-PLA758 blends are shown in Fig. 1, and crushed spherical particles are
observed with AS25-PLA75-8. These spherical particles may be associ­
ated with AS blends, as the AS is at a low concentration with respect to
PLA; also, particles are observed in the transverse section of the AS25PLA75-0 film. This result can be explained by the segregation of AS
that is immiscible in PLA, while in the AS25-PLA75-8 film they are
observed only in the f2 side. Finally, differences in the AS0-PLA1000 and AS0-PLA100-8 blended films are a result of the use of Pluronic®
F127. In the case of AS0-PLA100-0 films, a visible porosity at a micro­
meter scale is observed along the film on sides f1 and f2, and on the
transverse sections of the film; while in the case of AS0-PLA100-8
blended films, the porosity is lower than that observed in the AS0PLA100-0 film.

PLA100-0) films, respectively, with different concentrations of Plur­
onic® F127 (0 %, 4 % and 8 % w/w, respectively). In the AS100-PLA00 film, the absorption band at 3280 cm− 1 is attributed to -OH groups and
is indicative of starch. This band corresponds to stretching vibrations of
the -OH groups of amylose, amylopectin, glycerol, and absorbed water
(Collazo-Bigliardi, Ortega-Toro, & Chiralt, 2019). Another broadband

with less intensity was observed at 1648 cm− 1, which is attributed to the
vibrational bending mode of water molecules, which absorbs strongly
along with the hydroxyl groups in the amorphous regions of the starch.
Other relevant bands are located at 2930 cm− 1 and 1344 cm− 1, which
are due to the C–H and –CH2 groups located at carbon 6 of the starch
glucose units (Caicedo et al., 2019; Caicedo & Pulgarin, 2021; FonsecaGarcía et al., 2021). Finally, the band at 1005 cm− 1 corresponds to
C–O–H bending, this band is very important due to changes in starch
structure such as retrogradation (Warren et al., 2016). In the AS0PLA100-0 sample, characteristic bands for PLA were identified. These
include a band at 1750 cm− 1, which corresponds to stretching of the
– O) an important band to describe PLA (Yang et al.,
carbonyl group (C–
2008), a band at 1453 cm− 1 that is due to bending vibrations of the CH3
group, and bands at 1380 cm− 1 and 1359 cm− 1 which are attributed to
symmetrical and asymmetrical strains of the –CH group. A typical ab­
sorption for the asymmetric stretching of the C–O bond in the ester
group (–COOR) appears at 1183 cm− 1 (Yang et al., 2008). The bands at
867 and 754 cm− 1 are related to the stretching vibration of the C–C
bond and correspond to the amorphous phases and crystalline PLA,
respectively, thus indicating a semi-crystalline PLA (Palai et al., 2019;
Takkalkar et al., 2019; Turco et al., 2019). Other bands at 2998 cm− 1
and 2948 cm− 1 are related to asymmetric and symmetric stretching vi­
brations of the CH group, and the bands at 1127 cm− 1, 1084 cm− 1 and
1033 cm− 1 correspond to stretching vibrations of the asymmetric
C–O–C bond. The bands at 953 and 924 cm− 1 are characteristic of
vibrations of a helical structure with an oscillation of the CH3 group. And
finally, the -OH band centered at 3298 cm− 1 is attributed to the acid
groups of PLA. Regarding the incorporated poloxamer Pluronic F127,
characteristic bands are observed in the region from 1129 to 1082 cm− 1,
which indicate stretching of the C–O bond of the C–OH group in TPS
mixtures, and the bands at 1001 and 1041 cm− 1 are attributed to

stretching of the C–O bond of the C–O–C group (Fonseca-García et al.,
2021; Shaker et al., 2020; Zarrintaj et al., 2018). After identifying the
characteristic functional groups of each polymer, interactions within the
polymer mixtures were evaluated in response to an increase in the
content of starch and poloxamer in the PLA base matrix. According to
the spectra presented in Fig. 2, the polymers predominate on one side of
the film, leaving the PLA in the lower part of the mold (f2) and the starch
on the surface (f1). When starch is added in low amounts (AS25-PLA75),
with a poloxamer content of 4 % or 8 %, suitable material compatibility
is observed, with a similar arrangement of the polymers on both sides of
the film, which could indicate a homogeneous material in the matrix.
Fig. 3 presents a diagram of the possible interactions that originate
during the formation of polymeric materials. Regarding the increase in
the concentration of the poloxamer, no significant change was observed
in the spectrum of starch plasticized with glycerol; only a slight increase
in the intensity of the bands was observed, especially those for OH and
C–OH groups, which results in competition by interactions between
glycerol and poloxamer. However, the plasticizer may interact through
hydrogen bonds with greater probability due to a greater chemical af­
finity with AS, and the fact that the molecule is smaller and therefore
easier to mobilize (Müller et al., 2016). Thus, the poloxamer may be
limited in its ability to generate new interactions by leaving available
the functional groups that increase the intensity of the bands with an
increase in surfactant. In the PLA films without starch (AS0-PLA100)
(Figs. 2, 1-B), the incorporation of poloxamer caused a decrease in the
band corresponding to –OH groups because the vibration of these
groups is restricted when they interact with hydrogen bonds. This same
effect was observed at wavelengths of 1638 cm− 1 and 1380 cm− 1. These
changes imply that the hydrogen groups present interact through dipole-

3.2. Fourier Transformed Infrared Spectroscopy (FT-IR)
This technique provides a spectrum of bands that are related to
various functional groups, making it possible to identify the materials.
According to the SEM, only one of the polymers could be present in a
more significant proportion on each side of the film; therefore, FTIR
analyses were performed on each side of the sample. Fig. 2 shows the IR
spectra obtained using ATR of PLA films that contain different pro­
portions of Achira Starch (AS) and poloxamer (0 %, 4 % and 8 % w/w,
respectively). The spectra obtained are presented in two columns (A)
and (B) and four numbered rows. According to the signals reported in
the different spectra, it was observed that the polymers were ordered
during the drying process, so that a polymer was obtained from one side
of the film and another from the opposite side. Column A shows the
spectra corresponding to the different compositions of the films that
have a predominance of bands associated with AS (TPS) and that
remained in the upper part of the material, that is, the f1 side. In
contrast, column B shows the spectra obtained from the side of the film
that is in contact with the mold (f2) and has a more significant rela­
tionship with the characteristic bands of PLA. Images A1 and B1 show
the control spectra for Achira Starch (AS100-PLA0-0) and PLA (AS05


A. Fonseca-García et al.

Carbohydrate Polymers 293 (2022) 119744

A)

B)

AS100-PLA0-0

AS100-PLA0-4

AS0-PLA100-0

Transmittance (%)

1)

Transmittance (%)

Pluronic

AS0-PLA100-4

AS0-PLA100-8

AS100-PLA0-8

2)

1000

Transmittance (%)

Wavenumber (cm-1)

3600

500

AS75-PLA25-0 f1

AS75-PLA25-4 f1

3000

2400

1800

Wavenumber (cm-1)

1200

Transmittance (%)

4000 3500 3000 2500 2000 1500

600

AS75-PLA25-0 f2

AS75-PLA25-4 f2
AS75-PLA25-8 f2

AS75-PLA25-8 f1

2400

1800

Wavenumber (cm-1)

1200

3600

600

AS50-PLA50-0 f1

AS50-PLA50-4 f1

3000

2400

1800

Wavenumber (cm-1)

1200

Transmittance (%)

3)

3000

Transmittance (%)

3600

AS50-PLA50-0 f2

AS50-PLA50-0 f2

AS50-PLA50-0 f2

AS50-PLA50-8 f1

2400

1800

Wavenumber (cm-1)

1200

600

3600

3000

2400

1800

Wavenumber (cm-1)

1200

AS25-PLA75-0 f1

AS25-PLA75-4 f1

AS25-PLA75-4 f2

AS25-PLA75-8 f2

AS25-PLA75-8 f1

3600

3000

2400

1800

Wavenumber (cm-1)

1200

600

600

A25-PLA75-0 f2

Transmittance (%)

4)

3000

Transmittance (%)

3600

600

3600

3000

2400

1800

Wavenumber (cm-1)

1200

600

Fig. 2. FTIR-ATR spectra of AS-PLA polymeric blend films in different proportions (25–75, 50–50, 75–25 w/w) with the addition of Pluronic® F127 (0 %, 4 %, and 8

% w/v), f1 and f2 are on each side of the material.

6


A. Fonseca-García et al.

Carbohydrate Polymers 293 (2022) 119744

Starch – Glycerol

Pluronic® F127 – PLA

Pluronic® F127 –
Starch

Fig. 3. Proposed structure of the possible interactions between the components of the AS-PLA-Pluronic blend.

induced dipole interactions between the PLA and the poloxamer chains
(Takkalkar et al., 2019). When the starch content in the polymer blend is
equal to or higher than 50 % (w/w), the material maintains a structural
matrix similar to that present in the AS25-PLA75 sample; however, a
decrease in the size of the characteristic bands begins to be observed for
PLA on the shiny side (f2) of the material. At the same time, addition of
the poloxamer had a significant effect on the accommodation of said
polymers, since increasing their presence in the formulation with the
same concentration of biopolymers led to a spectrum that identified the
same functional groups with similar sizes on each side of the material.
The poloxamer promoted miscibility of these polymers, where the more
starch in the mixture, the more poloxamer, up to 8 % for equal pro­

portions of both Achira Starch and PLA (AS50-PLA50-8, Figs. 2, 3-B). In
Table 2 is shown a summary of relevant bands in the FTIR spectra of AS,
PLA and mixture of AS-PLA- Pluronic® F127. According to Table 2 the
characteristic band of AS is the band at 1005 cm− 1 corresponds to
C–O–H bending and this band is representative of AS in the mixture
with PLA and Pluronic® F127. While to PLA the bands that represent it
– O stretching
are at 1750 cm− 1 and 1183 cm− 1, which correspond to C–
and C–O–C stretching, respectively. Due to the important bands to AS
and PLA are summarized in Table 2, it is possible to understand the
interaction among AS with PLA along with the different formulations,
and both sides of films.

pristine films and with Pluronic® F127 at 8 % w/v, and AS75-PLA25
films with Pluronic® F127 concentrations at 0 %, 4 %, and 8 % w/v.
In the diffraction patterns for Pluronic® F127 powder there are two
characteristic peaks of this poloxamer at 19.4◦ and 23.35◦ (2θ), these
peak previously were reported (Fonseca-García et al., 2021). Also, for
both starch films, AS100-PLA0-0 and AS100-PLA0-8, no diffraction
peaks were observed, thus, the poloxamer did not influence the atomic
ordering in Achira Starch. However, for PLA, the poloxamer prevented
atomic ordering due to AS0-PLA100-0 as evidenced by three peaks at
17◦ , 19.5◦ , and 22.8◦ (2θ). These peaks are associated with the planes
200/110, 203, and 210, respectively. These planes are characteristics of
a pseudoorthorhombic α structure in PLA (Brizzolara et al., 1996;
Hoogsteen et al., 1990; Sasaki & Asakura, 2003; Zhang et al., 2008). In
the AS0PLA100-8 diffractogram, a small peak at 17◦ was identified,
which is associated with plane 200/100 in the crystalline structure in
phase α of PLA. In both the AS0-PLA100-0 and AS0-PLA100-8 films, the
α structure is formed due to PLA that was treated at 100 ◦ C, a temper­

ature that commonly produces an α structure for PLA. Relative to the ASPLA-Pluronic® F127 blends, the AS75-PLA25-0 diffractogram showed a
peak at 16.80◦ , and in the AS75-PLA25-4 diffraction pattern there are
peaks at 16.80◦ and 19.30◦ . Finally, the AS75-PLA25-8 diffraction
pattern contains peaks at 17.42◦ , 19.80◦ and 23.95◦ . The AS/PLA/
Pluronic® F127 blends showed an atomic ordering in the formulation
AS75-PLA25-8 and AS25-PLA75-8, which can be associated with PLA in
the phase α. It is important to mention that the crystalline structure
increases as the amount of Pluronic® F127 increases in the blends. Also,
in AS75-PLA25-8 and AS25-PLA75-8, the peaks are shifted slightly to
higher angles, which suggest that the crystalline domain is compacted.
However, PLA in blends with AS/Pluronic® except to AS50-PLA50-8
behaves in opposite ways to PLA with Pluronic® F127, since in that

3.3. X-ray diffraction (XRD) analysis
Table 2 shows a summary of diffraction patterns of the AS and PLA
pristine films and with Pluronic® as well as the AS75-PLA25 films with
Pluronic® F127 concentrations at 0 %, 4 %, and 8 % w/v. Also, the Fig. 4
shows the diffraction patterns for Pluronic® F127 powder, AS and PLA
7


A. Fonseca-García et al.

Carbohydrate Polymers 293 (2022) 119744

Table 2
Summary of relevant bands in the FTIR spectra and peaks identified from X-ray diffraction of AS, PLA, Pluronic® F127 and AS-PLA- Pluronic® F127 blends.
Film

Important wavenumber (cm− 1)

Assignment

XRD peak (2θ)

Crystalline
phase

AS100PLA0-0
AS100PLA0-4
AS100PLA0-8
AS75PLA25-0
AS75PLA25-4
AS75PLA25-8
AS50PLA50-0
AS50PLA50-4
AS50PLA50-8
AS25PLA75-0
AS25PLA75-4
AS25PLA75-8
AS0PLA1000
AS0PLA1004
AS0PLA1008

f1and f2:1005

C–O–H bending

Amorphous

f1and f2:1005

C–O–H bending

One wide peak from
15◦ to 25◦
–

f1and f2:1005

C–O–H bending

f1: 1750s and
1005
f1: 1750s and
1005
f1: 1750s and
1005
f1: 1005

f2: 1750, 1183s
and 1005s
f2: 1750, 1183 and
1005s
f2: 1750, 1183 and
1005s
f2: 1750 and 1005

–O stretching and
f1: C–

C–O–H bending, resp.
–O stretching and
f1: C–
C–O–H bending, resp.
–O stretching and
f1: C–
C–O–H bending, resp.
f1: C–O–H bending

f1: 1750s and
f2:1750 and 1005
1005
f1: 1750s and
f2: 1750 and 1005
1005
f1: 1750s and
f2: 1750 and 1005
1005s
f1: 1750 and
f2: 1750 and 1005
1005
f1: 1750 and
f2: 1750 and 1005
1005
f1and f2: 1750 and 1183, resp.

–O stretching, C–O–C stretching,
f2:C–
and C–O–H bending, resp.
–O stretching, C–O–C stretching,

f2:C–
and C–O–H bending, resp.
–O stretching, C–O–C stretching,
f2:C–
and C–O–H bending, resp.
–O stretching and C–O–H bending,
f2: C–
resp.
–O stretching and
–O stretching and C–O–H bending,
f1: C–
f2: C–
C–O–H bending, resp.
resp.
–O stretching and
–O stretching and C–O–H bending,
f1: C–
f2: C–
C–O–H bending, resp.
resp.
–O stretching and
–O stretching and C–O–H bending,
f1: C–
f2: C–
C–O–H bending, resp.
resp.
–O stretching and
–O stretching and C–O–H bending,
f1: C–
f2: C–

C–O–H bending, resp.
resp.
–O stretching and
–O stretching and C–O–H bending,
f1: C–
f2: C–
C–O–H bending, resp.
resp.
–O stretching and C–O–C stretching, resp.
C–

f1and f2: 1750 and 1183, resp.
f1and f2: 1750 and 1183, resp.

No identified

One wide peak from
15◦ to 25◦
16.84◦

Amorphous

16.84 , 19.31 and
22.75
17.42◦ , 19.79◦ and
23.93◦
One wide peak from
15◦ to 25◦
–

α compacted

◦

◦

Amorphous

α compacted
Amorphous
No identified

One wide peak from
15◦ to 25◦
17.44◦

Amorphous

–

No identified

Amorphous

17.27, 19.71 and
23.36◦
17.11◦ , 19.42◦ , and
22.79◦

α compacted

–O stretching and C–O–C stretching, resp.
C–

–

No identified

–O stretching and C–O–C stretching, resp.
C–

16.97◦

Amorphous

◦

α

Abbreviations: f1: The film side that is in contact with environment, f2: the film side that is in contact with the mold, s: small or tiny; resp.: respectively and α:
pseudoorthorhombic α structure.

Fig. 4. X-ray diffraction patterns of (a) Pluronic® F127, AS and PLA pristine films and, AS and PLA films with Pluronic® F127 8 % w/v and (b) F127, and AS/PLA
blends at a relation of 75 % of starch and 25 % PLA with different Pluronic® F127 concentrations, 0 %, 4 % and 8 % w/v.

this case the polymer did not show diffraction peaks, but in the pristine
condition PLA exhibited typical diffraction peaks of α structure. In ASPLA-Pluronic® F127 blends, the crystallization of PLA at concentration
low or high can be promoted due to the chemical affinity with the
Pluronic® F127. However, when the formulation contains a same con­
centration of AS and PLA the poloxamer promotes the microspheres

formation of PLA but, with amorphous structure due to at this

concentration the poloxamer interacts superficially and intrinsically
with PLA causing disorganization in the PLA polymer network. While at
low and high concentration of PLA with respect to AS, the crystalline
structure of the PLA in the blend is of α phase.

8


A. Fonseca-García et al.

Carbohydrate Polymers 293 (2022) 119744

3.4. Thermal properties

degradation temperature range of the same polymer, indicating a null
absorption of moisture due to its low polarity. In general, the first de­
rivative of the TGA curve for blends shown as DTG (see Fig. 5A and B, Y2
axis) exhibits two bands for the maximum degradation temperature
(Td): the first (Td1) which is related to starch appears at 299.9 ◦ C, and the
second (Td2) is related to PLA at 367.7 ◦ C. This behavior is typical of
degradation when there is low miscibility due to the hydrophilic and
hydrophobic nature of the polymers (Wang et al., 2008). The incorpo­
ration of surfactant produced an increase in the values of Td1 up to 8 ◦ C,
as did the increase in the concentration of PLA on AS, this increased the
Td1 by ~2 ◦ C. In the case of the PLA degradation band, no significant
changes are observed for Td2. In contrast to other studies (Yokesahachart
& Yoksan, 2011), the incorporation of poloxamer led to an improvement
in the thermal stability of the mixtures in the process temperature range

(>100 ◦ C and <300 ◦ C), and the degradation temperatures did not show
an adverse effect; on the contrary, the maximum addition of PLA and
poloxamer (AS25-PLA75-8) produced an increase in the Td1 of 37 ◦ C.
The differential scanning calorimetry thermograms are presented in
Fig. 5c and d, and the temperatures for the first and second order
thermal transitions are indicated in Table 3. The Tg in plasticized starch
shows a widening and shifting of the band at higher temperatures
(90.9 ◦ C) due to interactions with glycerol, compared to pure starch
(59.5 ◦ C) (Mikus et al., 2014). With the addition of 8 % surfactant, a Tg
at 101.1 ◦ C was observed, this allowed the disruption of the granules,

Fig. 5a and b show thermogravimetric analysis (TGA) curves for the
pure samples and the AS/PLA blends in the presence of the poloxamer,
respectively. The first mass loss effected (at ≤100 ◦ C) is related to the
release of water that has weak interactions with the starch matrix, fol­
lowed by losses at >100 ◦ C for bound water (or structural, strong in­
teractions) up to 180 ◦ C. Table 3 lists the differences in the values of the
first loss at 10 % mass (T10) as very significant between the AS samples
when increasing both the content of PLA and poloxamer. The T10 for
pure starch occurs at 93.4 ◦ C. When comparing these data with those
obtained for the AS control samples (AS100-PLA0-0) and AS100-PLA08, an increase in this temperature was observed that relates to the
presence of glycerol and Pluronic®. This effect is produced by a limi­
tation in the interactions of environmental water molecules (moisture)
through hydrogen bonds with starch, and with glycerol and poloxamer,
which function as plasticizers (Mikus et al., 2014). Likewise, an increase
in the T10 (>40 ◦ C) was observed, which leads to an improvement in the
thermal stability when incorporating PLA; this produces moderate in­
teractions between the components (it follows a mixing rule behavior).
The presence of the poloxamer led to an improvement in the thermal
stability with increases >60 ◦ C with respect to the homologue of the

blend without surfactant. In the case of pure PLA, the value for T10 is
342.9 ◦ C, and according to the TGA graphs, it is located within the

100

100

80

Pluronic
Starch
AS100-PLA0-0
AS100-PLA0-8
PLA
AS0-PLA100-0
AS0-PLA100-8

60
40

TG (%)

0

0
-20
-5

-40

100

200

300

400

0

DTG (u.a)

0

-20
-5

-40

500

Temperature (°C)

a)

100

200

300

400

500

Temperature (°C)

b)

1.4

2.0
Starch

1.2

Heat flow relative (Normalizaded) (W/g)

Heat flow relative (Normalizaded) (W/g)

40
20

20

AS100-PLA0-0

1.0
0.8

AS100-PLA0-8

0.6
PLA

0.4

AS0-PLA100-0

0.2
0

AS0-PLA100-8

-0.2
Pluronic

-0.4
-0.6
50

c)

AS75-PLA25-0
AS75-PLA25-4
AS75-PLA25-8
AS50-PLA50-0
AS50-PLA50-4
AS50-PLA50-8
AS25-PLA75-0

AS25-PLA75-4
AS25-PLA75-8

60

DTG (u.a.)

TG (%)

80

75

100

125

150

AS75-PLA25-0
AS75-PLA25-4

1.5

AS75-PLA25-8

1.0

AS50-PLA50-0
AS50-PLA50-4

0.5

AS50-PLA50-8

0

AS25-PLA75-0
AS25-PLA75-4

-0.5
AS25-PLA75-8

50

175

Temperature (°C)

d)

75

100

125

150

175

Temperature (°C)

Fig. 5. TG and DTG thermograms of a) neat biopolymers (Starch and PLA) and b) blends (AS/PLA). DSC thermograms of c) neat biopolymers (Starch and PLA) and d)
blends (AS/PLA).
9


A. Fonseca-García et al.

Carbohydrate Polymers 293 (2022) 119744

Table 3
Thermal analysis parameter summary for neat biopolymers (Starch and PLA) and blends with different content of Pluronic (0 %, 4 % and 8 %).
Film sample

T10 (◦ C)

Td1 (◦ C)

Td2 (◦ C)

Tg (◦ C)

Tc (◦ C)

Tm (◦ C)

ΔHc

ΔHm

%Xc

Starch
PLA
Pluronic® F127
AS100-PLA0-0
AS100-PLA0-8
AS75-PLA25-0
AS75-PLA25-4
AS75-PLA25-8
AS50-PLA50-0
AS50-PLA50-4
AS50-PLA50-8
AS25-PLA75-0
AS25-PLA75-4
AS25-PLA75-8
AS0-PLA100-0
AS0-PLA100-8

93.4
342.9
367.0
232.7
216.0
135.2
183.9
195.8
175.8

287.4
231.2
221.7
285.2
283.3
340.0
314.7

299.9
–
390.5
300.4
303.9
304.5
306.6
307.1
307.1
307.8
309.5
315.1
313.5
337.7
–
–

–
367.7
–
–
–

362.7
366.8
369.9
368.1
366.4
368.2
365.2
368.9
366.7
367.1
366.5

59.5
61.0
–
90.9
101.1
88.6
82.9
56.5
94.6
68.5
71.8
71.1
67.3
64.5
66.2
50.1

–

112.9
–
–
–
–
–
–
–
–
–
–
–
–
–
85.5

–
148.8–156.5
55.9
–
161.6
153.8
153.9
157.3
148.2
154.5
151.9
153.5
151.9
151.9

154.0–158.3
145.9–149.8

–
23.01
–
–
–
–
–
–
–
–
–
–
–
–
–
18.21

–
30.71
–
–
–
5.27
7.05
6.97
7.40
15.29

27.16
37.39
14.77
15.66
32.84
24.41

–
7.16
–
–
–
19.62
26.24
25.93
13.76
28.44
50.52
46.37
18.32
19.42
30.54
5.76

completing the plasticization, which is seen with the fusion at 161.6 ◦ C.
In the AS-PLA blends, the Tg decreases (up to 32.1 ◦ C) with increasing
poloxamer, this change is radical when the starch content increases. This
can be explained by interactions between starch and PLA chains that
cause a nucleation effect. This result is consistent with those obtained by
others, who discuss a decrease in the ordering of the polymers in the

mixture, and migration of the plasticizer toward the PLA phase that
generates an increase in the free volume (Ortega-Toro et al., 2021; Park
et al., 2000). In this case, the type of interactions that occur upon
incorporation of an amphiphilic macromolecule allows the structure
greater freedom of movement, on the other hand, to the functionalizing
agents that induce chemical bonds (crosslinks) (Ortega-Toro et al.,
2021). For each proportion of AS/PLA containing 8 % surfactant, an
excess is observed that appears in the characteristic Tm band of the
poloxamer at 55 ◦ C. The PLA exhibited a glass transition temperature
(Tg) at approximately 61.0 ◦ C. The other two transitions observed refer
to the crystallization temperature located at 112 ◦ C and two bands that
represent the melting temperature of the α and β conversion crystals at
148 and 156 ◦ C (Keridou et al., 2020). The melting temperatures remain
close to the second transition band of PLA, ranging between 148 ◦ C and
156 ◦ C (see Table 3) (Takkalkar et al., 2019). This transition is modified
as shown by a partial overlap after film formation with controlled
release of the solvent. A thermodynamic equilibrium for preparation of
the samples with PLA favors an increase in crystallinity and was esti­
mated from the enthalpies of fusion and crystallization of PLA (%Xc =
30.54). It should be noted that a correspondence with the XRD pattern
was observed for this same compound. The crystallinity data identified
the behavior in the degree of ordering of the polymers in the different
emulsions. In this case, the AS75PLA25 blend presents structures
defined as-PLA spherulites dispersed in the starch matrix (see Fig. 1,
micrographs), these are more defined with the presence of poloxamer,
which reduces the surface tension to produce a homogeneous dispersion.
This behavior was similar in the AS50PLA50 blend; however, a higher
concentration of poloxamer allowed greater ordering, although in
separate phases. In contrast, the AS25-PLA75 mixture showed a decrease
in the melting enthalpy values when poloxamer was incorporated,

indicating greater miscibility between the amorphous region of the PLA
with the surfactant, and in turn with the starch.

Furthermore, the formulations AS25-PLA75-8 and AS-AS100-8 were
super hydrophilic in nature with 0◦ on both faces, f1 and f2, and AS50PLA50-0 exhibited super hydrophilicity only on the f1 side. The blends
AS100-PLA-0, AS100-PLA-4, AS100-PLA-8, AS25-PLA75-4 and AS0PLA100-0 produced a similar contact angle with no >8◦ of difference
and were <63◦ for both sides, f1 and f2. For the AS0-PLA100-4, AS75PLA25-0, AS75-PLA25-4, AS75-PLA25-8, AS50-PLA50-0, AS0-PLA50-4,
AS0-PLA50-8, and AS25-PLA75-0 blends, the hydrophobicity was
different on both sides. In the case of pristine films of AS and PLA
without poloxamer, the wettability of both polymers was similar. The
contact angle for AS films obtained by solvent casting was reported to
cover a wide range and was dependent on the plasticizer content, starch
origin, etc.; although in general, starch films possess hydrophilic sur­
faces with contact angles <90◦ (Bangyekan et al., 2006; Fechner et al.,
˙
2005; Shahbazi et al., 2017; Zołek-Tryznowska
& Holica, 2020), while
PLA has contact angles of 70◦ to 80◦ (Kiss et al., 2002; Li et al., 2004;
Rapacz-Kmita et al., 2017). Therefore, the incorporation of poloxamer to
pristine AS and PLA (Kiss et al., 2002) and their blends enhances the
hydrophilic behavior on the top and bottom surfaces. For example, when
poloxamer is incorporated into AS100-PLA0 at 4 % and 8 %, the hy­
drophilicity increases to 50 %, while AS0-PLA100-0 with poloxamer at
4 % has a wettability similar to that for f1. However, on the f2 side, the
hydrophilic nature changes and is increased 274 %, and the incorpora­
tion of poloxamer at 8 % demonstrated a marked improvement in hy­
drophilicity due to the superhydrophilicity behavior, which is associated
with an excess of poloxamer and, this triblock polymer is segregated to
the top and bottom surfaces of the film, similar to that observed with
AS25-PLA75-8. In these films it is interesting to evaluate the reason for

the super hydrophilicity, since in the case of AS05-PLA50-0 f2, the super
hydrophilicity is complicated and associated with segregation of the
poloxamer according to the SEM images. It is possible that in the side
film, f1, the capillarity promotes wettability, and it is important to
consider than on the f1 side, a higher proportion of AS is obtained. This
result is supported by the FTIR results. In the blended films AS75-PLA250, AS75-PLA25-4, and AS75-PLA25-8, the stabilization of AS, PLA and
poloxamer along the matrix is similar for the three blends because the
wettability is similar for all. While in the AS50-PLA50-0, AS50-PLA50-4,
and AS50-PLA50-8 films the wettability was different for every formu­
lation. In the same formulation but on different sides the wettability is
unique, contrary to AS75-PLA25-8, where the wettability is absolute.
For the AS50-PLA50-8 film, the wettability was lower than that obtained
with AS50-PLA50-4 films. These results can be related to an equilibrium
between AS and PLA promoted by the poloxamer, that is to say 4 % of
poloxamer is not sufficient to maintain miscibility, while with 8 %
poloxamer, the emulsion is stable and the final film has better misci­
bility. Finally, in AS25-PLA75-0, AS25-PLA75-4, and AS25-PLA75-8
films, the proportion of PLA is higher than in AS, thus, these blends

3.5. Wettability by contact angle
Fig. 6 shows the bar graphs obtained for the wettability analysis of
the blended polymeric films using the sessile drop method. This char­
acterization was performed on both sides of the film, f1 and f2, due to
the segregation of poloxamer in both sides of the films. The results
suggest that all the blended and pristine polymer films are hydrophilic in
nature on both sides, f1 and f2, since the contact angles were <90◦ .
10


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Carbohydrate Polymers 293 (2022) 119744

Fig. 6. Average contact angle values for AS/PLA-Pluronic® F127 blends film of both sides, f1 y f2.

exhibit a PLA-like behavior, although with 8 % poloxamer the excess of
this polymer present segregates to the top and bottom surfaces.

not be evaluated due to their high brittleness and rigidity. In general, the
tensile strength results for the control film (AS100-PLA0-0) were the
highest; however, the incorporation and gradual increase of the sur­
factant (at 4 % and 8 %) decreased the strength and flexibility of the
material. With the increase of PLA, specifically in the formulation AS75PLA25 with 4 % poloxamer (AS75-PLA25-4), a significant improvement
in the tension that the material can resist compared to the film without
PLA at the same concentration of poloxamer was observed (AS100PLA0-4). On the contrary, when the ratio of starch-chitosan biopolymers

3.6. Mechanical properties
Table 4 shows the mechanical properties of tensile stress, Young's
modulus, and the percentage of deformation of the composite starchchitosan films at different proportions depending on the poloxamer
content. It was observed that the films with PLA contents ≥75 % could
11


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Carbohydrate Polymers 293 (2022) 119744

predominating on one side of the film, and on the other side for AS.
However, a small amount of PLA was located on the side with AS, and
vice versa. The XRD studies suggest that the stability of PLA and its

nature is conserved in blended films, where the AS is dispersed in the
matrix, due to the Pluronic® F127 which promotes reduction of the
superficial tension in PLA and AS solutions. PLA interacts weakly with
Pluronic® F127, causing the formation of microspheres PLA. In general,
the surfactant increases the thermal stability of the samples in the pro­
cess temperature range. Crystalline domains with increasing fusion
enthalpy values are observed in the presence of Pluronic® F127 when a
polar chemical environment predominates (for equal or lower concen­
trations of PLA), these tend to induce the formation of spherulites with
micrometer to nanometer diameters that become well dispersed in the
polar matrix. Alternatively, the presence of Pluronic® F127 in blends
with higher PLA content exhibited a plasticizing behavior due to the
effective interactions between the amorphous regions of PLA and the
low polarity regions (hydrophobic segment) of the copolymer. Thermal
analyses demonstrated improved miscibility with the incorporation of
the amphiphilic copolymer that induces nucleation in PLA, and there­
fore the growth of crystals with spherulitic morphology at concentra­
tions less than or equal to those used with TPS. The wettability of AS/
PLA/Pluronic® blends is high, in particular to blend with 8 % of Plur­
onic® F127. Finally, the mechanical properties of blends are poorer than
the pristine precursor polymers, these results indicated that the AS/
PLA/Pluronic® F127 blends by solvent casting need to continue being
analyzed.

Table 4
Tensile properties in the TPS, PLA and blends with different content of Pluronic
(0 %, 4 % and 8 %).
Film sample

Tensile strength

(MPa)

Young modulus
(MPa)

Deformation
(%)

AS100-PLA00
AS100-PLA04
AS100-PLA08
AS75-PLA250
AS75-PLA254
AS75-PLA258
AS50-PLA500
AS50-PLA504
AS50-PLA508
AS25-PLA750
AS25-PLA754
AS25-PLA758
AS0-PLA1000

4.25 ± 0.36a

0.43 ± 0.03a

37.53 ± 1.15a*

2.88 ± 0.32a*

0.47 ± 0.02a

28.35 ± 1.38a*

2.34 ± 0.31a*

0.48 ± 0.03a

25.90 ± 1.10a*

1.92 ± 0.03b

0.56 ± 0.02b

8.11 ± 1.00b

3.06 ± 0.26b*

0.53 ± 0.02b

16.28 ± 1.14b*

2.14 ± 0.26b

0.41 ± 0.01b

20.70 ± 0.66b*

0.57 ± 0.09c

0.13 ± 0.01c

6.57 ± 0.96c

1.26 ± 0.12c

0.28 ± 0.04c

8.99 ± 0.83c

1.85 ± 0.15c*

1.06 ± 0.09c*

5.82 ± 0.23c

–

–

–

–

–

–

–

–

–

–

–

–

(a, b, c) Different letters in the same starch-chitosan ratio formulation for each
mechanical property indicate significant differences (p < 0.05). * Mean of five
replicates ± standard deviation. (–) Films too fragile that it was not possible to
evaluate them.

Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.

is the same (50:50), its tensile strength values are drastically reduced by
>50 %, even when the percentage of poloxamer remains the same (4 %).
The presence of the surfactant had a positive effect on the tensile stress
in most of the films, especially at a concentration of 4 %, since when it is
increased to 8 %, the performance of the materials seems to decline.
Regarding the modulus of elasticity, with the presence of both PLA and
the poloxamer, Young modulus were higher than those of the control
sample based on pure starch (AS100-PLA0-0), which is an indication of
the generation of materials with higher stiffness (Caicedo et al., 2019;
Caicedo & Pulgarin, 2021; Fonseca-García et al., 2021). This is the case

of the AS50-PLA50-8 sample, which presented the highest Young's
modulus (1.06 MPa, while the control was 0.43 MPa). The other films
may have a particular elastic character; however, the maximum tensile
strength shows strength results that indicate materials with high
brittleness.
On the other hand, the plastic behavior of the mixtures was not
satisfactory; they presented a low deformation compared to the control
(Turco et al., 2019; Yokesahachart & Yoksan, 2011). The AS75-PLA25
blend in the presence of 4 % Pluronic stood out with the best mechan­
ical behavior concerning resistance vs. elongation. This evidences the
existence of more excellent intermolecular interactions in the polymeric
matrix, which were promoted by the poloxamer, which manages to
make the mixtures of both biopolymers compatible, generating more
resistant materials.

Data availability
Data will be made available on request.
Acknowledgements
The author Abril Fonseca-Garcia and Rocio Aguirre-Loredo thanks to
CONACYT for the support by Investigadoras por M´exico. Carolina Cai­
cedo, Brayan Hernandez and Heidy L. Calambas appreciate to USC and
SENA the support for physicochemical characterization.
Formatting of funding sources
´n General de Inves­
This research was funded by the Direccio
tigaciones (DGI) of Universidad Santiago de Cali under call no. 01-2022.
Financial support from DGI of Universidad Santiago de Cali under
project No. 939-621120-2148.
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