Structure and functional properties of cellulose acetate films incorporated with glycerol

Carbohydrate Polymers 209 (2019) 190–197

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

Structure and functional properties of cellulose acetate films incorporated
with glycerol

T



Sheyla Moreira Gonỗalvesa, , Daiane Cardial dos Santosb, Joyce Fagundes Gomes Mottac,
Regiane Ribeiro dos Santosa, Davy William Hidalgo Cháveza, Nathália Ramos de Meloa,c
a

Departamento de Ciência e Tecnologia de Alimentos, Rodovia BR 465 - Km 7, UFRRJ, Seropédica, CEP:23891-360, RJ, Brazil
Departamento de Engenharia Metalúrgica e Materiais, Av. dos Trabalhadores 420 - Vila Sta. Cecília, UFF, Volta Redonda, CEP: 27255-125, RJ, Brazil
c
Departamento de Engenharia de Agronegócios, Av. dos Trabalhadores 420 - Vila Sta. Cecília, UFF, Volta Redonda, CEP: 27255-125, RJ, Brazil
b

A R T I C LE I N FO

A B S T R A C T

Keywords:
Food packaging
Physicochemical properties

Plasticizer
Mechanical properties

Tests were performed with cellulose acetate films (CA) incorporating 5, 10, 20, 30, and 50% (w/v) of glycerol
with the purpose of evaluating the possible changes caused by the plasticizer on the functional properties of the
packaging. The glass transition temperature (Tg) and relative crystallinity (RC) were are obtained by DSC and
XRD, respectively. The results showed that, the presence of glycerol in the films caused increased thickness,
water vapor transmission rate (WVTR), and optical properties for most treatments. Moreover, morphological
changes were evidenced in scanning electron microscopy (SEM). A reduction of tensile strength (TS) and Young's
modulus (YM) was observed only in the concentration of 50% of glycerol. Therefore, the results suggest that
there was an interaction between glycerol and cellulose acetate, demonstrating that the film has potential for use
as food packaging.

1. Introduction
Consumer demand for quality, practical, and convenient food that is
associated with growing global environmental awareness has been
motivating the food industry to seek technologies for food production,
storage, and conservation. Thus, the natural polymers have gradually
gained industrial importance (Canevaloro, 2006; Mano & Mendes,
2004). The environmental issue regarding the disposal of food packaging developed with non-biodegradable (petroleum-based) polymers
can be solved by partially replacing these materials with biodegradable
polymers from renewable sources. In this context, industries have been
looking for polymers such as cellulose acetate obtained by chemical
modification of cellulose. For this reason, cellulose derivatives have
attracted the attention of researchers worldwide, due to their biodegradability, easy availability, respect for the environment, flexibility,
ease of processing, and important physico-mechanical properties
(Andrade-Molina, Shirai, Grossmann, & Yamashita, 2013; Thakur,
Thakur, & Gupta, 2013; Thakur, Gupta, & Thakur, 2014).
The increasing search for the development of food packaging with
particular properties has motivated research to evaluate and demonstrate the possibility of plasticizer applications with the purpose of altering the polymeric characteristics that are desired, such as greater

⁎

malleability and improvement of the physical and mechanical properties. Plasticizers are generally low volatility fluids used to increase
flexibility and extensibility of films by reducing the intermolecular
forces between polymer chains. These tend to reduce the energy level
required to give the chain mobility by reducing the glass transition
temperature of the polymer. Among the plasticizers, glycerol is one of
the most used in biopolymers, since it behaves or has the qualities, such
as hydrosoluble, polar, non-volatile, low molecular weight, and a hydroxyl group in each carbon (Moore, Martellia, Gandolfoa, Sobralb, &
Laurindo, 2006; Azeredo, 2012). Extensive research has evaluated the
possible changes caused by the addition of glycerol in films of different
polymer bases and observed that among the alterations, reduction of
tensile strength, increase in elongation at rupture, and thickness, are
more evident (Liu, Adhikari, Guo, & Adhikari, 2013; Srinivasa, Ramesh,
& Tharanathan, 2007).
The use of polymer films commercially applicable as food packaging
depends mainly on their functional properties as a barrier to water
gases and vapors, mechanical and rheological properties, lipid and
water solubility, and optical properties. For this, both the chemical
composition of the polymers and the interaction between the polymer
matrix and the additive used must be considered. Therefore, the characterization and collection of data on the main properties of the

Corresponding author.
E-mail address: (S.M. Gonỗalves).

/>Received 5 May 2018; Received in revised form 3 January 2019; Accepted 10 January 2019
Available online 11 January 2019
0144-8617/ © 2019 Elsevier Ltd. All rights reserved.

Carbohydrate Polymers 209 (2019) 190197

S.M. Gonỗalves et al.

2.6. Water vapor transmission rate (WVTR)

polymeric materials are of fundamental importance for the choice of
the most appropriate polymer base for a given function and/or use. The
characterization predicts the polymer behavior in different conditions
of use, as well as its useful life (Atarès, Jésus, Talens, & Chiralt, 2010;
Gyawali & Ibrahim, 2014).
This study therefore set out to assess the influence of the incorporation of different concentrations of glycerol in cellulose acetate
films on visual, physical, thermal (DSC), and mechanical properties and
evaluate the chemical interactions through the analysis of Fourier
Transformation Infrared Spectroscopy (FTIR), X-ray diffractometer
(XRD) and morphological changes by SEM.

WVTR was performed according to the gravimetric method (ASTM
E96-95) with modifications according to the method described by
Ghasemlou et al. (Ghasemlou, Khodaiyan, Oromiehie, & Yarmand,
2011). Anhydrous calcium chloride (CaCl2) was used inside capsules,
and they were packed in a desiccator containing saturated sodium
chloride (NaCl) solution to promote controlled humidity (75% ± 2) and
placed at room temperature (25 ± 2 °C).
The permeability of the films was determined by linear regression of
the constant mass transfer region between the weight gain (g) and the
time (t) that is correlated with the exposed area, allowing for determination of the WVTR (Eq. (1)).

2. Experimental

WVTR =

2.1. Materials

G
t. A

(1)

Where,
WVTR: Water vapor transmission rate expressed in g. m–2.day−1;
G/t: Angular coefficient of the line expressed in g.day−1;
A: Permeation area of the sample expressed in m2.

The cellulose acetate (CA) resin was purchased from Sigma-Aldrich,
Brazil, with a degree of substitution of 1.48°, Acetone PA was purchased
from Cap-Lab, São Paulo, Brazil. Glycerol 99.5% was purchased from
Vetec, Rio de Janeiro, Brazil.
2.2. Preparation of films

2.7. Mechanical properties

The films were elaborated using the casting method, according to
Melo (2003) with modifications. The cellulose acetate was solubilized
in acetone (1:10 w/v) and held for 12 h to form the gel. Glycerol was
added to the formed filmogenic solution in different concentrations (5,
10, 20, 30, and 50%) (w/v).
The filmogenic solution prepared from each formulation was poured
into glass plate and spread with the help of a glass rod having the

predetermined height, using a calibrated spacer. The solvent was evaporated under controlled temperature conditions (25 ± 2 °C) for
10 min. Afterwards, the films were detached from the glass plates,
packed in a vacuum, and stored for further analysis. The control film
was made with 0% glycerol.

The mechanical properties of tensile strength (TS), elongation at
break (EB), and Young´s modulus (YM) of films were determined using
the TA.XTplus Texturometer (Stable Micro Systems, Surrey, England),
operating according to the standard ASTM D method 882-82. Samples
with dimensions of 10 × 2.5 cm were fixed to the claws with initial
separation of 25 mm in the texturometer operated with 30 kg cell, force
of 0.049 N, and speed of 1 mm/s.
The tensile strength was controlled by the program Exponent
Texture TEE32 (Stable Micro Systems) through the relation of the
maximum force (N) and the sample area (mm). The modulus of elasticity (Young´s modulus) was calculated from the linear region of the
stress versus strain curve. The elongation at break was given by the
deformation at the moment the sample was ruptured by the initial
length of the sample, according to Eq. (2).

2.3. Thickness

R=
The films thickness (μm) was obtained with the aid of a digital
micrometer (Datamed). Measurements were taken at ten points for each
film.

L
× 100
Ci

(2)

Where,
R: elongation at rupture expressed in %;
L: Distance at moment of rupture expressed in mm;
Ci: Initial sample length in mm.

2.4. Fourier transform infrared attenuated total reflection (FTIR-ATR)
spectroscopy

2.8. Scanning electron microscopy (SEM)
The structural chemical analysis of the films was performed using
FTIR-ATR, (FT/IR-4700, Jasco Corporation) under attenuated total reflection (ATR) mode, according to Moura et al. (Moura, Mattoso, &
Zucolotto, 2012) and Ramos et al. (2013) with modifications. The
spectra were obtained in the wavelength range of 500–4000 cm−1,
4 cm−−1 resolution, and with 32 scans.

The surface analysis of the films were performed using the Scanning
Electron Microscope (Carl Zeiss, model EVO MA 10). Samples of
1.5 × 0.7 cm were fixed on a specific support (stub). Being a material of
low conductivity, samples were coated with gold (Au) (metallizer
EMITEC K550X) with current of 25 mA/2 min. The SEM observation
was performed in low vacuum with 3000 and 6000 Kv of acceleration
voltage, 480 filament current, and scans with magnifications of 5000
and 500×. The samples were evaluated on the surface and cross-sectional level (fracture region).

2.5. Visual aspect of the films
The films were evaluated for color and transparency, and a sample
(2 × 4 cm) was placed on the inner side of a colorimeter/spectrophotometer cell (Minouta CM-5-ID) to obtain the luminosity degree L*
and chromaticity a* and b*. The opacity was determined according to

ASTM D1746 (ASTM, 2003) at 560 nm wavelength, being evaluated
according to the amount of light the films were able to absorb. The
greater the amount of light absorbed indicates greater opacity of the
material (Fabra, Talens, & Chiralt, 2009). The color and opacity were
determined by the average of three readings for each film.

2.9. X-ray diffraction (XRD)
The XRD standards were obtained in a Bruker D2 Phaser diffractometer (Bruker, Germany), operated at 30 kV and 10 mA. The
diffractograms were collected in the range of 2 to 29° and ω-2θ. The
relative crystallinity (RC) was calculated according to Eq. (3) (Candido,
Godoy, & Gonỗalves, 2017):
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Carbohydrate Polymers 209 (2019) 190197

S.M. Gonỗalves et al.

RC =

(TA-AA)
ì 100
TA

structure containing CH and OH groups, so its incorporation into cellulose acetate may have caused an increase in the interactions between
both compounds in the regions of the bands that represent these attributes. Hydrogen bonds between OH groups of CA and glycerol may
occur, since an OH group of the plasticizer is available for possible
interactions. However, glycerol has two more OH groups that will not
be available for interactions. Therefore, the OH prominent band may
also be related to the higher amount of OH present in the film resulting

from the addition of glycerol.

(3)

Where,
RC: Relative crystallinity in %;
TA: Total area
AA: Area of amorphous region
2.10. Differential scanning calorimetry (DSC)
Samples of 3.5 mg of the preconditioned films at 75% relative humidity were analyzed in a Q200 DSC (TA Instruments, United States).
The thermograms were recorded with heating of 20–250 °C at a heating
rate of 10 °C/min, followed by cooling from 250-20 °C at a heating rate
of 20 °C/min. The glass transition temperatures (Tg) were determined
from the second heating of 20–250 °C at a heating rate of 10 °C/min. in
order to discard the influence of thermal history.

3.2. Visual aspect of the films
The average values of color and transparency of the films are shown
in Table 1, being the films with greater amount of light absorbed
considered opaque (Fabra et al., 2009). The comparisons that evaluate
the possible influence of the different concentrations of glycerol on the
luminosity parameter (L*) of the cellulose acetate film show that there
was a significant difference (p < 0.05) only for the concentration of
50% in relation to the control film. For the opacity, the films with 30
and 50% of glycerol had the highest opacity. Chia mucilage films
containing a high concentration of glycerol (75% w/w) also showed
highest opacity (Dick et al., 2015).
Villalobos et al. (Villalobos, Chanona, Hernández, Gutiérrez, &
Chiralt, 2005) reported that the opacity of the polymer films is closely
linked to the internal structure formed during drying, and this structure, in turn, is strongly influenced by the nature of the initial solution.

Therefore, higher opacity may be related to the presence of non-miscible dispersion, due to differences in refraction of the phases, as well as
particle size and concentration. However, in this work, glycerol and
cellulose acetate, both of hydrophilic nature as demonstrated by the
FTIR analysis (Fig. 1), present a possible chemical interaction between
their chains. Thus, of miscible dispersion formed by CA and glycerol
justify the maintenance of opacity by the films, even after incorporation
of up to 20% glycerol. Although, according to SEM images (Fig. 2), the
surfaces of the films with 30 and 50% glycerol were characterized by
pore-like structures of different sizes, which may have influenced the
opacity results.
Closer inspection of Table 1 shows that the addition of glycerol to
the cellulose acetate films caused an increase in the red coloration (a*),
while only 20 and 30% of glycerol caused an increase in the yellow

2.11. Statistical analysis
A one-way ANOVA and Tukey multi comparative test were performed to detect the differences between samples with a significant
level of 5%. Additionally, multivariate analyses were applied, such as
Principal Component Analysis (PCA), for the study of correlations and
similarities between variables and/or treatments. All statistical analyses
were carried out using software R version 3.2.4 (R Foundation for
Statistical Computing, Viena, Áustria) and FactoMineR version 1.32.
3. Results and discussion
3.1. Fourier transform infrared attenuated total reflection (FTIR-ATR)
spectroscopy
The spectra of the pure CA films and CA films incorporating 5, 10,
20, 30 and 50% glycerol analyzed by FTIR are show in Fig. 1. The CA is
an ester, therefore, the presence of the bands at 1741 cm−1 (steric
carbonyl elongation) and the band 3478 cm−1 (cellulosic OH elongation) characterize the film (Meireles, 2007). It was observed that the
addition of glycerol caused an increase in the bands 2936 cm−1 (CH
elongation), 3478 cm−1 (OH elongation), 1232 cm−1 and 1045 cm-1

(steric carbonyl elongation). Glycerol is an alcohol with a chemical

Fig. 1. FTIR spectra of CA film (CA0%) and CA films incorporating with glycerol (CA5%, CA10%, CA20%, CA30% or CA50% w/v).
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Carbohydrate Polymers 209 (2019) 190197

S.M. Gonỗalves et al.

Table 1
Average values of the visual appearance of the CA films (CA0%) and CA films incorporating with glycerol (CA5%, CA10%, CA20%, CA30%, or CA50% w/v), for the
parameters the luminosity (L*), chromaticity (a* and b*), and opacity.

*

Treatments

L*

CA0% Glycerol
CA5% Glycerol
CA10% Glycerol
CA20% Glycerol
CA30% Glycerol
CA50% Glycerol

96.75
97.41
97.95

97.67
97.09
98.06

a*
±
±
±
±
±
±

1.46
0.41
0.68
0.47
1.14
0.45

b
ab
ab
ab
ab
a

0.01
0.08
0.11
0.74

0.72
0.19

b*
±
±
±
±
±
±

0.01
0.09
0.09
0.09
0.16
0.09

c
bc
bc
a
a
b

0.22
0.11
0.16
1.41
1.27

0.31

Opacity
±
±
±
±
±
±

0.12 b
0.08 b
0.16 b
0.3 a
0.36 a
0.41 b

92.85
93.48
94.81
94.13
92.69
95.07

±
±
±
±
±
±

0.86
1.02
1.71
1.26
2.82
1.11

ab
ab
ab
ab
b
a

Average followed by the same letters do not differ from each other (p > 0.05) by the Tukey test at the 5% level of significance.

the effect of glycerol and sorbitol on the barrier properties of starchbased films. The researchers observed increased permeability to water
vapor as the concentration of plasticizers increased from 15 to 45%
(Sanyang, Sapuan, Jawaid, Ishak, & Sahari, 2015). However, incorporation of glycerol in chitosan-based films caused a 5.5% reduction
in WVTR (Priyadarshi, Sauraj Kumar, & Negi, 2018).

color (b*). Previous studies showed that an addition of 70% (v/v)
glycerol to chia seed mucilage film caused an increase of the a* and b*
parameters (Dick et al., 2015). However, in the present work, the films
presented reduction of the red color for 50% addition of the plasticizer.
It is noteworthy that the film produced without the addition of glycerol
already presented reddish and yellowish coloration, having the red
coloration presenting a tendency to grayscale.
It must be remembered that, among the optical properties of importance for food packaging, color and opacity stand out. According to

consumer habits, packaging with a strong color, high brightness, or low
opacity represent both a type of information and an emotional link
between the consumer and the product, a tool widely explored by
marketing (Yoshida & Antunes, 2009; Zanela et al., 2015). According to
the values obtained in the present research, CA films are sufficiently
bright and transparent, which makes them suitable for use as food
packaging.

3.5. Mechanical analysis
All treatments with glycerol presented a difference (p < 0.05) in
relation to the control film. The incorporation of glycerol to the acetate
film caused an increase in the tensile strength (46.56 N–51.28 N) up to
the concentration of 30%, (Table 3), noting the highest average values
were at the 10 and 20% of glycerol concentrations. The literature reports that the presence of plasticizer leads to the disarrangement of the
polymer network, giving greater flexibility to the material and consequent reduction of the tensile strength (Liu et al., 2013; Moore et al.,
2006). However, when the final amount of plasticizer in the polymeric
material is low or high, there may be few or excessive interactions,
respectively, between the polymer network and the plasticizer modifying the flexibility of the films (Reis et al., 2015).
It is noted that up to 30% glycerol concentration, the films were
more resistant when compared to the control film. However, it is worth
noting that in comparison with the resistance values presented by the
films with 10 and 20% of glycerol, the film with 30% already presented
a reduction of the values for the parameter evaluated. Nevertheless,
with the concentration of 50% of glycerol, the films acquired high
flexibility and presented less resistance to the traction. This demonstrates that the concentrations of 5, 10, 20, and 30% of glycerol may not
have been sufficient to plasticize the films, although morphologically
the surfaces and fracture regions of 30 and 50% of glycerol films exhibit
some similarity.
For the Young's modulus, the incorporation of glycerol to the cellulose acetate film provided increased stiffness for most films, and the
highest values were observed for films with 10 and 20% glycerol. For

tensile strength, it is noted that at the concentration of 30% glycerol,
there was a reduction of the stiffness of the material when compared to
the film with 20% of the plasticizer. Consequently, the film containing
50% of glycerol already presented a lower stiffness, presenting a difference (p < 0.05) from the control film, which confirms that plastification may have been achieved only in the presence of 50% glycerol.
The elongation at break (EB) reflects the degree of flexibility and
extensibility of the films, i.e., it reflects how much the material will be
able to stretch before rupture. For this parameter, it was observed in
Table 3 that there was no difference (p > 0.05) caused by the incorporation of different concentrations of glycerol in the cellulose
acetate film. The mechanical behavior of polymeric packaging depends,
especially, on its development, which depends among other factors, on
polymer-additive interactions, as related by Laohakunjit et al.
(Laohakunjit & Noomhorm, 2004). The researchers showed that
20–30% glycerol increased EB in starch films, while 35% of plasticizer
caused EB reduction.

3.3. Thickness
It was verified that the addition of glycerol contributed to increasing
the thickness of the cellulose acetate films, presenting a difference
(p < 0.05) for all plasticizer concentrations (Table 2). These results
reflect those of Farias et al. (Farias, Fakhouri, Carvalho, & Ascheri,
2012) and Shimazu et al. (Shimazu, Mali, & Grossmann, 2007), who
also verified the increase in the thickness of cassava starch films as a
function of the incorporation of different glycerol concentrations. In
this way, the presence of the plasticizer may have provoked a certain
disarrangement and breakage of the intra and intermolecular interactions of the polymeric material that caused the chains to move away,
which was manifested as an increase in the thickness of the films.
3.4. Water vapor transmission rate (WVTR)
The addition of glycerol to the cellulose acetate film at concentrations of 10 and 30% caused an increase in WVTR as compared to the
control film (Table 2). Jost et al. (Jost, Kobsik, Schmid, & Noller, 2014)
also observed that alginate films incorporating glycerol had their rate of

oxygen permeability and water increased. However, in this work, the
concentrations of 20 and 50% of glycerol caused a reduction in the
water vapor permeability. This must have occurred due to the antiplasticizing effect caused by the incorporated glycerol, which even
decreased the intermolecular bonds in the chain and may still create
possibilities for other bonds. Shimazu et al. (Shimazu et al., 2007)
evaluated the antiplasticizing effect of glycerol on the moisture sorption
properties of cassava starch films. The authors reported that, depending
on the concentration of the plasticizer, it may cause a contrary effect,
instead of increasing the hydrophilicity of the material. Therefore, the
interactions between the additives and the polymer matrix may have
provided less polar characteristics, which may have been caused due to
the low concentration of hydrogen-like bonds in the polymeric network
added.
The barrier properties of the polymeric materials can be influenced
by the type and concentration of plasticizer. Studies were conducted on
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Carbohydrate Polymers 209 (2019) 190197

S.M. Gonỗalves et al.

Fig. 2. SEM of the surface (left column with 500 and 5000x) and fracture region (right column with 500 and 5000x) of the CA films (CA0% (A and B)) and CA films
with glycerol (CA5% (C and D); CA10% (E and F); CA20% (G and H); CA30% (I and J) and CA50% (L and M)).

3.6. Scanning electron microscopy (SEM)

(Fig. 2B). From the addition of glycerol, the surface images (Fig. 2C, E,
and G) for films with 5, 10, and 20% of glycerol, respectively, are already presented small and uniform depressions. Moreover, the films
incorporating 30 and 50% of glycerol (Fig. 2I and L), respectively,

SEM images (Fig. 2) for the control film (0% glycerol) are smooth
and homogeneous for the surface (Fig. 2A) and fracture regions

194


Carbohydrate Polymers 209 (2019) 190197

S.M. Gonỗalves et al.

the presence of glycerol caused a slight increase of RC in this region,
being the highest values for the films with 30 and 50% of glycerol. The
presence of glycerol may have caused a slight rearrangement of the
chains, via hydrogen bonds between plasticizer and CA that increased
crystallinity.

Table 2
Average values of the thickness and water vapor transmission rate (WVTR) of
the CA films (CA0%) and CA films with glycerol (CA5%, CA10%, CA20%,
CA30%, or CA50% w/v).
Treatments

Thickness (μm)

WVTR (g.m-2. day−1)

CA0% Glycerol
CA5% Glycerol
CA10% Glycerol

CA20% Glycerol
CA30% Glycerol
CA50% Glycerol

41.3 ± 4.64 b
52,43 ± 337 a
50.17 ± 6.28 ab
56.07 ± 3.52 a
55.47 ± 1.66 a
54.07 ± 1.53 a

258.09
270.18
316.64
257.83
308.26
238.16

±
±
±
±
±
±

5.9 bc
28.69
31.34
20.86
37.17

17 c

3.8. Differential scanning calorimetry (DSC)

abc
a

Fig. 4 shows DSC curves for CA (CA0%) films and CA films with
different concentrations of glycerol (CA 5, 10, 20, 30, and 50%). The
curves representing the first heating (Cycle 1) have endothermic peaks
at 148.16, 117.57, 109.37, 147.27, 146.20, and 132.59 °C for the
CA0%, CA5%, CA10%, CA20%, CA30%, and CA50% films, respectively
(Cycle 1). According to De Freitas et al. (De Freitas, Senna, & Botaro,
2017), such endothermic events between 77.5 and 91.1 °C are related to
the water adsorption capacity of each polymer material, which depends
on the degree of CA substitution. The authors also report the occurrence
of endothermic peak at 123.5 °C for cellulose. Thus, as with acetyl, the
plasticizers also have the ability to modify the arrangement of the CA
chains, thereby altering their water adsorption capacity.
The glass transition temperature of the films was observed in Cycle
1 and confirmed in Cycle 2 (second heating) (Fig. 4). The CA0%, CA5%,
CA10%, CA20%, CA30%, and CA50% films had Tg at 229.02, 223.74,
224.10, 218.73, 211.09, and 207.34 °C, respectively (Cycle 2). The literature reports that the Tg of CA with a replacement grade of 1.48° is
concentrated around 223.45 °C (De Freitas et al., 2017), close to that
found for the CA0% film (229.02 °C) (Fig. 4). However, for the other
films, the presence of the glycerol in different concentrations must have
caused a reduction of the intermolecular forces of the polymer chains,
causing a reduction of the Tg of the CA films.

bc

ab

*

Average followed by the same letters do not differ from each other (p > 0.05)
by the Tukey test at the 5% level of significance.

Table 3
Mechanical properties of CA films.
Treatments

Tensile Strength
(N)

CA0% Glycerol
CA5% Glycerol
CA10% Glycerol
CA20% Glycerol
CA30% Glycerol
CA50% Glycerol

46.56
51.16
56.28
57.57
51.28
39.04

±
±

±
±
±
±

2.08
2.69
2.31
1.69
7.03
0.63

b
ab
a
a
ab
c

Young's Modulus
(MPa)
5±
5.51
6.42
6.62
5.78
3.87

0.28 c
± 0.61

± 0.24
± 0.21
± 0.56
± 0.68

bc
ab
a
abc
d

Elongation at break
(%)
6.8 ± 0.63 a
8.99 ± 1.48 a
8.18 ± 1.7 a
7.83 ± 0.71 a
8.49 ± 2.46 a
6.86 ± 1.23 a

Average ± standard deviation. Average in columns followed by the same letters do not differ from each other (p > 0.05) by the Tukey test.

already show surface containing micropores of different diameters and
depth. It is observed that these pores present similarity in number and
diameter in both films containing 30 and 50% of glycerol, while it was
also noted that there was a slight increase in relation to the amount of
pores for the film with 50% of the plasticizer.
As can be seen in Fig. 2 the fracture images of the films with glycerol
(D, F, H, J and M), present small pores start to appear. Hence, the
presence of glycerol possibly modified the polymer network, which

caused internal morphological changes reflected with the appearance of
micropores.
According to the results presented in the mechanical evaluation
(Table 3), the film incorporating 30% glycerol presented numerical
reduction of the values for tensile strength (but in relation to the control
film is still higher), while the films with 5, 10, and 20% of glycerol
showed higher resistance. For the tensile strength analysis, the concentration of 50% glycerol presented a difference (p < 0.05) in relation to the other concentrations. This evidences a film with lower resistance, which may have been influenced by the porous structure.
Therefore, the presence of these micropores on the surface and fracture
region may be a reflection of the lack of interfacial interaction between
the cellulose acetate and glycerol, making the material more vulnerable
to forces in the mechanical test, resulting in a decrease in tensile
strength.

3.9. Principal component analysis (PCA) and Pearson’s correlation
The first two components explained approximately 70% of total
variability of the experimental data (Fig. 5) (PC1 = 44.5% and
PC2 = 25.5%), and this value was adequate. Opacity (Abs), L*, and
Thickness (Fig. 5) showed greater influence on the differentiation of the
treatments (variables with reddish colors presents high influence). Abs
and L* (Table 4) had a positive correlation (r = 0.958), as well as the
variables a* and b* (r = 0.987) and between TS and YM (r = 0.997). As
mentioned previously, according to Table 1, the variables a* and b*
behave in a similar manner against different concentrations of glycerol.
Likewise, the same was observed in Table 3, which corroborates the
similarity of the mechanical analyses (TS and YM) in the presence of
different concentrations of glycerol on the CA film. The control and
50% glycerol films were the most differentiated (Fig. 5b). The 50%
Glycerol treatment showed higher values for opacity, L*, and thickness
(Tables 1 and 2). This shows that the addition of glycerol caused
changes in certain properties of the CA film.

4. Conclusion
According to the results of this study, the cellulose acetate films
incorporated with different glycerol concentrations underwent changes
in the polymer matrix and were reflected by the majority of the evaluated parameters. This confirms that the chemical structure of the additives and the polymer matrix is of fundamental importance in defining the functional properties of the polymer films.
The films incorporating glycerol proved to be thicker, opaque, luminous, yellowish and reddish, semi-crystalline, and with higher water
vapor transmission rate for most treatments, in addition to presenting
morphological change and alteration of the mechanical properties.
Such alterations can be confirmed by the FTIR spectra that demonstrated possible chemical interaction between the polymer matrix and
the additive. Therefore, given the properties shown, most of the films
incorporated with glycerol are particularly suitable for packaging foods

3.7. X-ray diffraction (XRD)
XRD revealed (Fig. 3) materials with low crystallinity that had little
distinction between different treatments. The diffractograms present
small peaks in the region of 2θ = 8.8° and 23°. According to Wan Daud
et al. (Wan Daud & Djuned, 2015), the region corresponding to 2θ = 8°
indicates possible disturbances caused by acetylation of cellulose for CA
production. The presence of acetyl may cause disruption in the cellulose
chains and consequent breakage of its microfibrillar structure. Chen,
Xu, Wang, Cao, and Sun, (2016) reported that the crystalline diffractions of CA occur at approximately 2θ = 8, 10, and 13°.
The values of relative crystallinity (RC) (Fig. 3) for the control film
(CA0%), CA5%, CA10%, CA20%, CA30%, and CA50% were 10.5%,
10.8%, 11.4%, 11.8%, 18.3%, and 18.2%, respectively. It is noted that
195


Carbohydrate Polymers 209 (2019) 190197

S.M. Gonỗalves et al.

Fig. 3. XRD diffractograms of cellulose acetate film (CA0%) and CA films incorporating with glycerol (CA5%, CA10%, CA20%, CA30%, or CA50% w/v).

Fig. 4. DSC thermograms of CA film (CA0%) and CA films with glycerol (CA5%, CA10%, CA20%, CA30% and CA50%).

Fig. 5. Bi-plot distribution (PCA- PC1 and PC2); (a) PCA response variables and (b) score plot of for treatments.
196


Carbohydrate Polymers 209 (2019) 190197

S.M. Gonỗalves et al.

Table 4
Pearsons correlation for dependent variables.
Variables

Thickness

L*

a*

b*

Abs

Young's modulus

Tensile strength

Elongation at break

WVTR

Thickness
L*
a*
b*
Abs
Young modulus
Tensile strength
Elongation at break
WVTR

1
0.547
0.709
0.596
0.307
0.215
0.210
0.463
0.321

1
−0.001
−0.109
0.958
−0.013
0.002

0.008
−0.146

1
0.987
−0.183
0.450
0.407
0.246
0.309

1
−0.258
0.451
0.404
0.153
0.306

1
−0.122
−0.108
−0.231
−0.293

1
0.997
0.586
0.570

1

0.616
0.616

1
0.674

1

Values in bold are different from 0 with a significance level alpha = 0.05.

that require greater protection against mechanical forces, greater
moisture exchanges, and protection against light. Soon, such films
could be used to pack fresh produce, such as vegetables. The application of every package depends on the desirable conditions for each
food. Therefore, it is concluded that the ideal amount of plasticizer and
the resulting film ideal for possible applications will depend on the food
to be packaged.

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Acknowledgements
The authors express their sincere appreciation to the Dr. Carlos
Wanderlei Piler de Carvalho (Embrapa-Rio de Janeiro), to the Federal
University Rural Rio de Janeiro (UFRRJ), Federal Fluminense
University (UFF), Coordination of Improvement of Higher Level
Personnel - Brazil (CAPES) - Finance Code 001, National Council of
Scientific and Technological Development - Brazil (CNPq), and Carlos
Chagas Filho Foundation for Research Support of the State of Rio de
Janeiro - Brazil (FAPERJ) - Process E-26/112.582/2012.
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