Development of biodegradable starch-based foams incorporated with grape stalks for food packaging

Carbohydrate Polymers 225 (2019) 115234

Contents lists available at ScienceDirect

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

Development of biodegradable starch-based foams incorporated with grape
stalks for food packaging

T

⁎

Juliana B. Engela, , Alan Ambrosib, Isabel C. Tessaroa
a

Laboratory of Membrane Separation Processes (LASEM) and Laboratory of Packaging Technology and Membrane Development (LATEM) - Department of Chemical
Engineering, Universidade Federal do Rio Grande do Sul (UFRGS), Ramiro Barcelos Street, 2777, ZC: 90035-007 Porto Alegre, RS, Brazil
b
Laboratory of Membrane Technology (LABSEM) - Department of Chemical Engineering and Food Engineering (EQA), Universidade Federal de Santa Catarina (UFSC),
Florianópolis, SC, Brazil

A R T I C LE I N FO

A B S T R A C T

Keywords:
Cassava starch
Grape stalks
Foam

Biodegradability
Applicability test

Biodegradable cassava starch-based foams incorporated with grape stalks were obtained by thermal expansion.
The morphology (SEM), chemical structure (FTIR), crystallinity (XRD), and biodegradability of the foams were
evaluated. An applicability test was performed in the storage of food. SEM images showed no residue agglomerations and cell structure generally observed in materials obtained by thermal expansion; FTIR analysis
verified interactions of foam components. XRD analysis showed native cassava starch characteristic peaks and
the loss of crystallinity after the expansion process, with the formation of an amorphous material. Foams were
completely biodegraded after 7 weeks, demonstrating that, for the experimental conditions used, the interactions
between the starch and the grape stalks did not generate recalcitrant compounds or structural alterations that
would impair foam degradation. Furthermore, the foams added with grape stalks presented good properties in
the applicability test, showing a promising application in the storage of foods with low moisture content.

1. Introduction
For more than half a century, the production of plastic materials has
presented continuous growth, currently estimated to be more than 300
million tons per year (PlasticsEurope, 2015). Most of plastics are used
for disposable applications, i.e., products that are discarded within a
year or less of their purchase (North & Halden, 2013), increasing the
critical pollution problem related to this kind of material. Although
almost all thermoplastics are recyclable, the separation of the materials
presents some limitations, since the process requires selection by resin
type (Marsh & Bugusu, 2007).
As packaging material, the expanded polystyrene (EPS) is one of the
most used plastics due to its versatility and cell structure that provides
low density, high impact resistance, and high thermal insulation.
However, due to the environmental problems associated to the discard
of this material (Bergel, da Luz, & Santana, 2017) and the long time for
complete degradation when incorrectly disposed in nature
(Henningsson, Hyde, Smith, & Campbell, 2004), consumers are gradually adhering to the idea of using biodegradable packaging (Bergel

et al., 2017). An alternative that can reduce carbon footprint, pollution
risks and greenhouse gas emissions caused by the use of conventional
polymers (North & Halden, 2013) is the use of biopolymers from agro-

⁎

industrial sources that are renewable, abundant and low cost (Davis &
Song, 2006).
Recent researches have shown that native cassava starch can be
used to obtain foams (Chiarathanakrit, Riyajan, & Kaewtatip, 2018;
Kaewtatip, Chiarathanakrit, & Riyajan, 2018; Machado, Benelli, &
Tessaro, 2017; Sanhawong, Banhalee, Boonsang, & Kaewpirom, 2017)
retaining its biodegradable character when converted to a thermoplastic material (Teixeira, 2007). Moreover, starch softens and expands
into a foam product similar to EPS (Mariotti, Alamprese, Pagani, &
Lucisano, 2006), and this process can be carried out in a molding machine similar to that utilized for EPS (Shey et al., 2007). However,
several limitations make the use of this material unfeasible for certain
applications, especially for food packaging, because of starch’s high
affinity for water (Van Der Maarel, Van Der Veen, Uitdehaag, Leemhuis,
& Dijkhuizen, 2002). In this context, residues from agro-industrial activities that are rich in lignocellulosic fibers can be added to the
polymer matrix to improve starch foams properties (Machado et al.,
2017; Mali, Debiagi, Grossmann, & Yamashita, 2010; Salgado, Schmidt,
Ortiz, Mauri, & Laurindo, 2008; Vercelheze et al., 2013). These materials can improve some properties due to their composition, mainly
based on cellulose, hemicellulose and lignin (Santos et al., 2012).
Sesame cake (Machado et al., 2017), plantain flour and wood fiber

Corresponding author.
E-mail addresses: (J.B. Engel), (I.C. Tessaro).

/>Received 22 May 2019; Received in revised form 21 August 2019; Accepted 21 August 2019
Available online 22 August 2019

0144-8617/ © 2019 Elsevier Ltd. All rights reserved.


Carbohydrate Polymers 225 (2019) 115234

J.B. Engel, et al.

(Vargas-Torres et al., 2017), sugarcane bagasse and asparagus peel fiber
(Cruz-Tirado et al., 2017), malt bagasse (Mello & Mali, 2014), kraft
fiber (Kaisangsri, Kerdchoechuen, & Laohakunjit, 2012), sunflower
protein and cellulose fiber (Salgado et al., 2008), fish scale waste
(Chiarathanakrit et al., 2018), plant proteins, kraft fiber, palm oil
(Kaisangsri, Kerdchoechuen, & Laohakunjit, 2014), and cellulose nanofiber (Ghanbari, Tabarsa, Ashori, Shakeri, & Mashkour, 2018) are
some examples of residues incorporated into the polymeric matrix to
produce starch-based foams. Although some of these studies have
identified that the foams produced have potential to be used as packing
for low water content foods, none focus on the applicability test nor the
biodegradability of the foams. A promising material to be added into
starch-based foams is the grape stalk, the lignocellulosic skeleton obtained at the beginning of the fruit processing, in the destemming stage
(Garcia-Perez, García-Alvarado, Carcel, & Mulet, 2010). The wine industry contributes substantially to the economy of Brazil and, considering the annual grape production, it is estimated that 37.5 million
kg of grape stalks are wasted every year in the country. Although this
material is not considered toxic, its high content of organic matter and
the high seasonal production can contribute to potential problems of
pollution (Spigno, Pizzorno, & De Faveri, 2008), which justifies the
importance of its use in applications such as biodegradable packaging.
The aim of this study was to evaluate the biodegradability and potential application of starch-based foams incorporated with Cabernet
Sauvignon grape stalks for packaging foods with low moisture content,
such as English cake. The morphology, chemical structure, and crystallinity of the foams were analyzed to support the results observed.

distilled water:1 g cassava starch and 3.19 g distilled water:1 g grape

stalks, according to previous results obtained from the grape stalks
water absorption capacity analysis) and added in the first homogenizing step.
The resulting mixture was equally distributed in a Teflon coated
metal mold (100 mm × 25 mm × 3 mm, length × width × thickness).
The mold was closed with a Teflon coated metal lid and set in a heated
hydraulic press (SL11/20E, Solab, Brazil). The thermal expansion
conditions were set at 70 bar and 180 °C for 7 min. After the foam
formation, the samples were stored for 7 days under controlled conditions (55% relative humidity, 25 °C) prior to characterization.

2. Materials and methods

2.2.5. Porosity
The porosity of the samples was evaluated relating the bulk density
(ρb), determined by the ratio of mass (g) to volume (cm3) of the samples, and the true density (ρt) using Eq. (2.1). The helium gas pycnometry technique (Accu Pyc II 1340, Micromeritics, USA) was used to
determine the true density.

2.2.3. Viscosity of the starch pastes
The viscosity of the cassava starch-based pastes with and without
the incorporation of grape stalks applied to develop the foams was
measured in duplicate using a viscometer (Fungilab, CQA Química) at
1 rpm. The results are expressed as the average ± standard deviation.
2.2.4. Morphology
The cross-section and surface morphology of the foams incorporated
with grape stalks were evaluated by Scanning Electron Microscopy
(SEM) (JSM-6060, JEOL, Japan) with an acceleration voltage of 12 kV.
The samples were dried at 40 °C for 24 h in an oven, fractured and
placed on aluminum stubs with carbon double-sided tape for visualization. Control samples (with no addition of grape stalks and the same
glycerol percentage) also had the cross-section morphology evaluated
by SEM, with an acceleration voltage of 5 kV.

2.1. Materials
Native cassava starch (Yoki, Brazil) containing 28.7 ± 0.4% amylose and 10.7 ± 0.1% moisture (previously determined), guar gum
(Exodus Cientifica, Brazil) to avoid sedimentation of solids, magnesium
stearate (Exodus Cientifica, Brazil) as releasing agent, glycerol
(Dinâmica, Brazil) as plasticizer, and Cabernet Sauvignon grape stalks
(11.19 ± 0.07% moisture, 7.3 ± 0.2% ash, 6.0 ± 0.1% protein,
0.60 ± 0.02% lipids, 23 ± 1% lignin, 14 ± 2% cellulose and
11.7 ± 0.1% hemicellulose, previously determined), kindly provided
by Salton Winery (Brazil), were used to prepare the foams.

ρ
Porosity (%) = ⎜⎛ 1 − b ⎟⎞ × 100
ρt ⎠
⎝

(2.1)

2.2.6. Chemical structure
In order to identify the interactions between the components used to
prepare the foams, native cassava starch, grape stalks and the produced
foams were analyzed by Fourier transform infrared spectroscopy
(FTIR). Foam samples were grinded with a mortar and pestle, dried in
an oven at 50 °C for 24 h, and stored in a desiccator containing calcium
chloride (30% relative humidity), for 7 days prior to the analysis. The
foam, native cassava starch and grape stalk samples were placed directly into the sample holder and compressed. The test were performed
using a spectrophotometer (Frontier FT-IR/NIR, Perkin Elmer, USA) in
the frequency range of 4000–400 cm−1 and diamond selenide test
point.

2.2. Methods

2.2.1. Grape stalks pretreatment
Cabernet Sauvignon grape stalks were collected during the destemming stage of the fruit processing in the winery, stored in plastic
bags, and kept under refrigeration for not more than 24 h until transportation to the laboratory. Then, the stalks were washed to remove dirt
and other impurities, placed in trays and dried in an oven (De Leo,
Brazil) at 40 °C for 24 h. After drying, stalks were milled with a knife
grinder (MF10 basic, IKA, Germany) and sieved in an 80 Mesh sieve
(Ø < 0.18 mm). The milled stalks were placed in bags and stored in a
freezer at −18 °C. Before using the stalk, it was re-dried at 40 °C for 1 h
to remove any residual moisture.

2.2.7. Crystallinity
X-ray diffraction (XRD) analysis was conducted to verify crystallinity type of raw materials (native cassava starch and grape stalks) and
their conversion to amorphous state after the thermal expansion
(thermoplastic starch-based foam). A diffractometer (X'Pert MPD,
Philips, the Netherlands) with Kα copper radiation (λ = 1.54184 Å),
40 kV voltage and 30 mA current was used. Assays were performed for
2θ between 5 and 75° with 0.05°/s ramping.

2.2.2. Cassava starch-based foams preparation
Based on the total mass, Cabernet Sauvignon grape stalks (7 wt%,
Ø < 0.18 mm), guar gum (0.4 wt%), magnesium stearate (0.4 wt%)
and distilled water (55 wt%) were mixed for 10 min with a mechanic
stirrer (713, Fisatom, Brazil). Then, cassava starch (32%wt) and glycerol (5%wt) were added to the mixture and homogenized for 10 min.
The amounts of glycerol, grape stalks and the granulometry of the residue added were determined by optimization of a central composite
experimental design developed in previous studies (data not shown).
The amount of water incorporated into the mixture was fixed (1 g

2.2.8. Biodegradability test
The biodegradability of the foams was analyzed with a modified
qualitative test according to the methodology proposed by MedinaJaramillo, Ochoa-Yepes, Bernal, and Famá (2017) and PiđerosHernandez, Medina-Jaramillo, López-Córdoba, and Goyanes (2017).

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J.B. Engel, et al.

Vegetable compost (soil) was poured into glass containers, and foams,
prepared with native cassava starch and grape stalks, and those only
with native cassava starch, were completely buried in the soil. The
containers were kept under aerobic conditions at room temperature,
and water was sprayed once a day in the soil to ensure moisture of the
system throughout the experiment. Samples of each formulation were
removed every 7 days and photographed; the degradation was monitored by visual inspection only.
2.2.9. Applicability test
Foams were tested in the storage of English cake (19.9 ± 1.7%
moisture) purchased in a local market. Moisture content, mass lost and
mechanical properties of thermoplastic cassava starch based-foams and
foams incorporated with grape stalks were evaluated. EPS trays were
also tested for comparison. The foams (10 cm × 8 cm) were prepared
and stored for 7 days in a climatic chamber (55% RH, 25 °C). The cake
samples were weighed (M214Ai, Bel Engineering, Italy) and placed on
the foams. Then the system (food + foam) was wrapped with PVC film.
The samples were kept at room temperature in order to reproduce sale
conditions of this product in commercial establishments. Temperature
and relative humidity of the environment were monitored daily.
The test lasted for 9 days (cake’s shelf life) and the analyses of
system mass loss, food moisture, packaging moisture, and mechanical
properties (flexural tests) were performed at the 3rd, 6th and 9th days of
the experiment. The mass loss analysis, performed in duplicate, was

determined in a scale (M214Ai, Bel Engineering, Italy) and the results
are presented as mean ± standard deviation of the mass loss percentage for each time of analysis. The moisture contents of the English
cake, foams, and EPS were determined in duplicate by thermogravimetric method. The samples were weighed and placed on aluminum
capsules, then submitted to oven drying at 105 °C for 24 h. After, the
samples were cooled in a desiccator and their masses measured. The
moisture content was determined by Eq. (2.2), where mi and mf are the
initial and final sample mass in grams, respectively. The results are
presented as the mean ± standard deviation.

Moisture content (%) =

mi − mf
× 100
mi

(2.2)

The flexural tests of the foams and the EPS at each analysis time
were performed according to ASTM D 790-03 (ASTM, 2003) using a
texture analyzer (TA.XT2i, Stable Micro Systems, United Kingdom)
with a 50 N load cell and a three-point bending method with span
setting of 4.5 cm. Foams (100 mm × 25 mm) were deformed until
break. The stress at break, strain at break and modulus of elasticity
were calculated with the data obtained. Six samples of each packaging
type were evaluated and the results are expressed as the mean of the
measurements.
2.2.10. Statistical analysis
Bulk density, true density, porosity, moisture content, mass loss and
mechanical properties, before and after the applicability test, were
evaluated by Tukey’s mean comparison test (p ≤ 0.05). These analyses

were performed using Statistica® v10 software (Statsoft Inc., US).

Fig. 1. Photography and SEM images of the foams. (a) Photography of foam
surface; SEM of the (b) surface and (c) cross section of thermoplastic cassava
starch-based foam incorporated with Cabernet Sauvignon grape stalks. (d) SEM
of the cross section of thermoplastic cassava starch-based foam (magnifications:
25×).

3. Results and discussion
3.1. Morphology

stalks. It can be observed that while the foam presents dense and
homogeneous external walls, with small closed cell structure, the interior shows a structure with large open cells, a characteristic sandwichtype structure of thermoplastic starch-based materials obtained by
thermal expansion (Soykeabkaew, Thanomsilp, & Suwantong, 2015).
This structure is formed because of the water content present in the
polymeric matrix that can significantly affect the foaming process. The
outer layer of the foams is denser because the polymer matrix dries
more rapidly and therefore cannot expand much close to the hot mold.

Fig. 1 shows the surface and cross section morphology of the thermoplastic cassava starch-based foam with (a, b and c) and without (d)
grape stalks. It is interesting to notice the homogeneity of the foam
surface (Fig. 1a and b) once it has not been detected particle agglomeration. This indicates a good dispersion of grape stalks in the polymer
matrix, which was induced by the small granulometry of the residue
used (Ø < 0.18 mm).
Fig. 1c shows the cross-section of the foam incorporated with grape
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3.2. Chemical structure

Water becomes gaseous during the preparation of starch foams and
creates bubbles when in temperatures higher than the boiling point,
enabling the expansion of the matrix and the formation of the foam
(Kaisangsri et al., 2014). The interior of the foam contains mainly larger
cells and more open structure due to the large amount of water expelled
to the outside of the mold in the form of vapor, causing the rupture of
the cells (Shogren, Lawton, Doane, & Tiefenbacher, 1998). Similar cell
structures have also been reported by other authors (Machado et al.,
2017; Matsuda, Verceheze, Carvalho, Yamashita, & Mali, 2013;
Shogren, Lawton, & Tiefenbacher, 2002; Vercelheze et al., 2012).
Comparing the structures of foams prepared with and without grape
stalks, Fig. 1c and d respectively, it can be inferred that the larger voids
present in the former are due to the extra amount of water incorporated
into that formulation. The big cells formed in the interior of the foam
became so large and absorbed the smaller cells (Rizvi, Park, & Guo,
2008), thus decreasing the amount of cells present in the foam and
causing the decrease in cell density (Bergel, Dias Osorio, da Luz, &
Santana, 2018). With higher water content in the batter, more steam is
produced, leading to a greater number and size of voids inside the foam
structure that affects the density (Andersen & Hodson, 1998). The
density of the foams is inversely proportional to the expansion ability of
the paste (Meng et al., 2019). The results observed in this study corroborate that stated by Andersen and Hodson (1998) in their study
about molding of starch items, once the foam prepared with cassava
starch and grape stalks presented lower density (0.18 g cm−3) due to its
high content of grape stalks (7 wt%) and high water content, attributed
to the high water absorption capacity (WAC) presented by the stalks

(3.19 g of water per gram of dry sample). Samples prepared only with
cassava starch were denser (0.21 g cm−3) and presented smaller voids
in the interior structure (Fig. 1d) probably due to the lower amount of
water present in the formulation (1 g distilled water:1 g cassava starch).
Furthermore, the viscosity of the polymeric matrix can affect the
foaming process and therefore, the morphology and the density of the
foams. Less viscous pastes cannot hold vapor bubbles as effectively as
more viscous pastes. Consequently, the lower the viscosity of the paste,
the greater the paste expansion, which generates foams with a thinner
outer layer and large inner cells (Pornsuksomboon, Holló, Szécsényi, &
Kaewtatip, 2016). The analysis of viscosity of the batters showed that
the matrix incorporated with grape stalks, and therefore with higher
water content, has a lower viscosity than the pure cassava starch matrix, 53,345 ± 1120 cP and 60,780 ± 1894 cP, respectively. These
results support the morphology of the foams (foams with grape stalks
presenting a thinner outer layer and inner layer with larger cells) and
the lower density of the foams added with grape stalks.
The morphology of the foam can also influence its gas permeability,
which is greatly affected by its porosity (Ishizaki, Komarneni, & Nanko,
2013). The porosity of the foams and the commercial EPS trays are
presented in Table 1. It is possible to observe a significant difference
between the porosity of samples; the foam incorporated with grape
stalks has higher porosity (87%), followed by the cassava starch foam
(84%) and the EPS trays (60%). These results agree with the SEM
images (Fig. 1c and d) because of the more open voids.

Fig. 2 shows the FTIR spectra of the foam and the main raw material
(native cassava starch and grape stalks) samples. The three spectra
present a peak from 3650 to 3000 cm−1, which can be attributed to: (i)
the presence of hydroxyl groups (eOH) from alcohols, phenols and
carboxylic acids in the grape stalks (Prozil, Mendes, Evtuguin, & Lopes,

2013); (ii) the presence of acetal (CeOeC) and hydroxyl (eOH) groups
from the constituent molecules of starch in the cassava starch (Avérous,
2004); and (iii) the occurrence of hydrogen bond-like interactions between the components of the expanded structure during processing of
the foam (Marengo, Vercelheze, & Mali, 2013), that may have occurred
due to stretching of vibrational complexes associated with free and
bound hydroxyl groups (Vercelheze et al., 2012). The peaks observed in
the range of 2900 cm−1 correspond to the CeH stretch (Matsuda et al.,
2013) and appear in the three spectra, with a higher intensity in the
foam spectrum.
The peak present at 1602 cm−1 in the grape stalks spectrum may be
due to the elongation of C]C bonds and can be attributed to aromatic
compounds, possibly lignin or tannins (Farinella, Matos, & Arruda,
2007; Fiol, Escudero, & Villaescusa, 2008). The Cabernet Sauvignon
grape stalks spectrum is very similar to that of the grape marc extract
(Garrido et al., 2019) and shows mainly the peaks indicating the presence of flavonoids and phenolic compounds, important components
present in the grapes and its residues. The low intensity peaks present at
1647 cm−1 and 1618 cm−1 in the native cassava starch and foam
spectra, respectively, are associated with the angular bending of the
−OH group in water molecules (Mano, 2000), indicating the formation
of interactions between water and components of the formulation
(Marengo et al., 2013). The most intense peaks present from 1200 to
900 cm−1 are attributed to vibrations in CeOeC bonds, characteristic
of starch and other polysaccharides (Wokadala, Emmambux, & Ray,
2014). The higher intensity of this peak in the foam spectrum is an
evidence of the occurrence of interactions between the components of
the formulation. Overall, the peaks observed in the starch-based foam
developed in this study are similar to those reported by other authors
(Bergel et al., 2018), and the major starch-related peaks are those found
between 3650 to 3000 cm−1 and between 1200 to 900 cm−1, associated with the three hydroxyl groups and the one CeOeC bond per
repeating unit of starch (Bergel et al., 2018).

3.3. Crystallinity
According to the water content and packaging configuration of the
amylopectin double helices (Imberty, Buléon, Tran, & Pérez, 1991),
starch may present three main crystallinity types (A, B and C), defined
by intensity of X-ray diffraction lines (Cereda et al., 2002). Native
cassava starch is generally classified in C-type, consisting of 90% of Atype and 10% of B-type (Schlemmer, 2007). According to the XRD
patterns presented in Fig. 3, cassava starch exhibited relatively broad
peaks at 2θ = 15; 17 and 22.7°. These peaks consist of a mixture of the
A-type (peaks at 2θ = 17 and 22.7°) and the B-type crystallinities (peak
at the 2θ = 15°) (Hoover, 2001). Similar results were observed by
Machado et al. (2017), Mello and Mali (2014) and Marengo et al.
(2013).
The grape stalks XRD pattern exhibits a low intensity, but broad
peak at 2θ = 21°, which may be related to cellulose residual crystallinity, one of the main components of grape stalks (Vercelheze et al.,
2012). This peak was found in cellulose samples in the study conducted
by Mulinari, Voorwald, Cioffi, da Silva, and Luz (2009). Due to the
gelatinization process that occurs during thermal processing of starch to
obtain foams (Marengo et al., 2013), the granular structure is totally or
partially destroyed, resulting in an amorphous matrix (Van Soest &
Vliegenthart, 1997). This amorphous pattern is evidenced by the diffractogram of the foam, in which the peaks previously present in the
cassava starch and in the grape stalks diffractograms are no longer

Table 1
Bulk density, true density and porosity of the cassava starch-based foams and of
the commercial EPS trays.
Foam sample
Starch + grape stalks
Starch
EPS

ρb (g cm−3)

ρt (g cm−3)
b

0.18 ± 0.02
0.21 ± 0.02a
0.031 ± 0.003c

Porosity (%)
a

1.447 ± 0.003
1.279 ± 0.002b
0.077 ± 0.002c

87 ± 1a
84 ± 1b
60 ± 5c

Different lowercase letters in the same column indicate significant difference
(p < 0.05) between means (Tukey’s test).
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J.B. Engel, et al.

Fig. 2. FTIR spectra of native cassava starch, Cabernet Sauvignon grape stalks and thermoplastic starch-based foam incorporated with grape stalks.

starch.
The effect of heat, as well as the enzymatic activity of the microorganisms present in the soil shorten and weaken the polymer chains of
the starch, causing the degradation process to start (Cerruti et al.,
2011). In addition, the moisture from the water that has been sprayed
daily on the system may have reacted with the hydroxyl groups of the
starch molecules, causing the chains to weaken and, therefore, accelerating the biodegradation process. Hydrogen bonds and molecular
interactions between starch molecules were possibly destroyed
(Jaramillo, Gutiérrez, Goyanes, Bernal, & Famá, 2016), leading to the
macroscopically observable result of polymer degradation (Albertson,
2000).
Biodegradability is also influenced by the morphology of starchbased foams. Xu, Dzenis, and Hanna (2005) reported that large cells in
the structure of the foams increased accessibility to microorganisms
attack, thus increasing the rate of degradation. Stoffel (2015) concluded
that starch-based trays that had interiors with larger voids showed a
higher surface area of enzyme-substrate contact, accelerating the enzymatic degradation of the material. Therefore, the SEM images presented in Fig. 1 can be taken into account in order to corroborate the
good results observed in the biodegradability test. It was possible to
observe that foams incorporated with grape stalks developed in this

observed. Because of the crystallinity loss, only a low intensity peak is
present at 2θ = 20° in the foam diffractogram, similar to that found in
the study conducted by Tavares, de Campos, Mitsuyuki, Luchesi, and
Marconcini (2019) and attributed to non-significant residual A-type
crystallinity.

3.4. Biodegradability test
Fig. 4 depicts the thermoplastic cassava starch-based foams biodegradation evolution. In the specific case of starch, biodegradation occurs mainly due to the hydrolysis of the polymer chain, under enzymatic action, with consequent breakage of the α-1,4 bonds of the
amylose and amylopectin chains (Oliveira, 2015).
The samples showed integrity in shape and size up to the third week
of analysis. It was possible to remove the samples easily from the soil

and to handle them without causing any damage. In the fourth week,
the sample with the incorporation of Cabernet Sauvignon grape stalks
lightly adhered to the screen used to facilitate the removal from the soil,
and showed cracks in its structure. In the fifth week, both samples
strongly adhered to the screen. From this moment on, it was possible to
note that the sample with residue incorporation showed faster degradation in comparison to the sample prepared only with cassava

Fig. 3. XRD patterns of native cassava starch, Cabernet Sauvignon grape stalks and thermoplastic starch-based foam incorporated with grape stalks.
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Fig. 4. Biodegradability test images of cassava starch-based foams, and cassava starch-based foams incorporated with grape stalks at different times of soil burial.

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samples reached similar levels of moisture, and no significant differences were observed when comparing the results obtained for the same
day of analysis. This indicates that the incorporation of grape stalks
does not prevent the increase of moisture during storage and that both
the environment and the characteristics of the product exert a greater
influence on this property. The loss of moisture observed for the cake
could have been caused in part by the absorption by the packaging and

partly by the lost to the environment through the PVC film, which has
permeability to water vapor, as also reported by Machado (2016) and
Stoffel (2015). This behavior can be associated to the high affinity that
starch has with water; in a ambient with high relative humidity, starch
absorbs water causing the material to collapse or disintegrate, losing
mechanical strength (Shogren et al., 1998). As a consequence, starchbased foams still have limited use, being appropriate only to be applied
as packaging for foods with low moisture content.
Table 2 also presents the results for the system mass loss, calculated
in relation to day 0. A gradual increase in percentage mass loss of the
systems applied in the storage of cake is observed. Only the system
composed by the thermoplastic cassava starch-based foam did not
present a significant increase in mass loss during the test period. Systems composed of starch-based foams applied on the storage of strawberries in the study developed by Stoffel (2015) showed similar mass
loss to that observed in the systems composed by the foams with incorporation of grape stalks applied in cake storage and higher to systems composed by foams prepared only with cassava starch.
The flexural properties of the foams, evaluated over the 9 days of
the applicability test, are presented in Table 2. Comparing the results
obtained for the foams prepared only with cassava starch, it is possible
to observe a significant decrease in stress at break between days 0 and
3. However, at the end of the experiment (day 9), the results resembled
those obtained at day 0 and the samples stress at break was not significantly different. The strain at break of the thermoplastic cassava
starch-based foams increased from day 0 to day 3 and no significant
differences were observed between days 3, 6 and 9. The increase in
flexibility, as evidenced by the increase in strain at break, was accompanied by a decrease in the stiffness of the samples, observed by the
decrease of the modulus of elasticity, probably due to the reduction of
internal hydrogen bonding between polymer chains and an increase in
molecular space (Gontard, Guilbert, & Cuq, 1993). The values obtained
for days 3, 6 and 9 showed no significant differences.
The reduction of stress at break observed for the foams incorporated
with grape stalks was accompanied by a significant increase in strain at
break and, similar to the thermoplastic cassava starch-based foams,
there were no significant differences for the strain at break at 3, 6 and 9

days of analysis. The reduction of mechanical strength and increased
flexibility of the samples may have occurred due to the presence of the
cake as well as to the foam formulation, which contained 5 wt% glycerol and high amounts of water, incorporated in the mixture because
of the grape stalks water absorption capacity.
Samples with and without the addition of grape stalks, as well as
EPS samples, showed significantly similar strain at break at 3, 6 and 9
days, although on day 0 the EPS sample showed higher strain at break
than the other samples. Similar to cassava starch-based foam samples,
the foams added with grape stalks became less rigid throughout the
experiment, as noticed by the significant decrease in the modulus of
elasticity. Comparable results were observed by Machado (2016) in
cake storage on cassava starch foams incorporated with residue from
the sesame processing. Only EPS samples presented increased stiffness,
although only significant differences were observed for the modulus of
elasticity between days 0 and 9. The EPS stress at break did not change
significantly during the analysis and the values were lower than those
obtained for samples prepared with cassava starch with and without
addition of grape stalks.

study had an interior with large cells and a more open structure
(Fig. 1c), morphology that may have influenced the more accelerated
biodegradation of these samples.
Moreover, the predominance of the amorphous pattern of the foam
structure, evidenced by the diffractogram presented in Fig. 3, also
contributed to the results observed in the biodegradability analysis,
since the degradation is initiated in the amorphous phase of the
polymer (Amass, Amass, & Tighe, 1998), once this phase is more susceptible to biodegrade than the crystalline region (Abraham et al.,
2012). Sanhawong et al. (2017) evaluated the biodegradation of cassava starch-based foams incorporated with cotton fiber and natural
rubber latex in a similar manner to the present study, and observed that
samples were completely degraded in 8 weeks, a similar result to that

found for thermoplastic cassava starch-based foams incorporated with
the grape stalks.
There was a pronounced change in the thermoplastic cassava starchbased foams color due to contact with the soil. It was not possible to
monitor sample mass loss during the biodegradation test, because
foams presented soil adhered to the surface, which configures a limitation of this analysis. Even so, it was possible to obtain good results
and, within 7 weeks, samples were totally degraded, as it can be seen in
Fig. 4. Thus, it can be concluded that foams prepared in this study can
be disposed in gardens and flowerbeds, which characterizes a solution
that in addition to helping reduce environmental problems, such as
pollution from plastic materials, can contribute to the reduction of costs
with waste processing, as was also reported by Sanhawong et al.
(2017).
3.5. Applicability test
The visual aspect of the foams applied on the storage of English cake
during 9 days is shown in Fig. 5. During the whole time of the experiment, the relative humidity and average temperature of the environment where the samples were maintained were 55% and 23 °C,
respectively. Both the cake and the packages samples showed no development of microorganisms. However, thermoplastic cassava starchbased foams with and without the addition of grape stalks presented
visible deformations at the end of the test. The deformations were located mainly in the regions where the cake was contacting the surface
of the foam. EPS packaging remained intact throughout the testing
period.
As shown in Table 2, when the foams faced the cake packaging test
(Packaging + cake column) a significant increase in the moisture content of the system foam + cake was observed between the first and 3rd
days of analysis, and the highest value was obtained for the sample with
cassava starch and grape stalks at 3 days of experiment (sample CS +
GSD3, Table 2). In 9 days, the foams prepared with cassava starch, both
with and without the addition of grape stalks (samples CS + GSD9 and
CSD9), presented no significant differences in the moisture content. The
EPS samples had the lowest moisture content (< 2.4%).
The cake moisture content decreased significantly over the analysis
and this behavior was observed in samples from all the tested packages.
At the end of the 9th day, cake samples stored in the different packaging

types showed no significant difference in moisture content (samples
CSD9, CS + GSD9 and EPSD9). Starch-based coated and uncoated
polylactic acid starch trays developed by Stoffel (2015) used in the
storage of strawberries had moisture contents higher than those observed in this work. However, it is noteworthy that the strawberries
have higher moisture content than the English cake.
The tests conducted on the packages without English cake, also
wrapped in PVC film in order to reproduce the same experiment conditions, showed that the moisture content of thermoplastic cassava
starch-based foams with and without the addition of grape stalks increased throughout the evaluated period, reaching 17%, higher than
those observed when the packages contained cake. Although they
presented significantly different moisture contents at day 0, these
7


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J.B. Engel, et al.

Fig. 5. Cassava starch, cassava starch with grape stalks and EPS foams applied on the storage of English cake during 9 days.

Table 2
Moisture content, system mass loss and flexural properties of cassava starch, cassava starch and grape stalks and EPS foams applied on the storage of English cake.
Moisture content (%)

System mass loss (%)

Flexural properties

Sample

Packaging + cake

Cake

Packaging

Packaging + cake

Stress at break (MPa)

Strain at break (%)

CSD0
CSD3
CSD6
CSD9
CS + GSD0
CS + GSD3
CS + GSD6
CS + GSD9
EPSD0
EPSD3
EPSD6
EPSD9

2.8 ± 0.2e
11.75 ± 0.04b
11.20 ± 0.04b
10.26 ± 0.07c
8.5 ± 0.1d
12.8 ± 0.2a

11.3 ± 0.2b
10.3 ± 0.1c
0.2 ± 0.2g
2.4 ± 0.5e
0.7 ± 0.1f,g
1.1 ± 0.3f

20 ± 2ª
10.0 ± 0.4b,c,d
9.2 ± 0.1b,c,d
7.97 ± 0.09d
20 ± 2ª
12.4 ± 0.2b,c
10.1 ± 0.1b,c,d
8.3 ± 0.1c,d
20 ± 2ª
12.9 ± 0.2b
9.8 ± 0.3b,c,d
8.1 ± 0.1d

2.8 ± 0.2f,g
10.8 ± 0.2b,c,d
13.4 ± 0.1ª,b
17.1 ± 0.7a
8.5 ± 0.1c,d,e
11.1 ± 0.2b,c,d
13.79 ± 0.08ª,b
17.05 ± 0.05a
0.2 ± 0.2g
12 ± 5ª,b,c

6 ± 2d,e,f
4.8 ± 0.8e,f,g

–
5 ± 1e,f
6 ± 1d,e
6.8 ± 0.6c,d,e
–
3.9 ± 0.3f
6.3 ± 0.7d,e
8.1 ± 0.8c
–
7.3 ± 0.3c,d
10.3 ± 0.3b
12.0 ± 0.2a

2.9 ± 0.6ª
1.3 ± 0.1e,f,g
2.1 ± 0.3b,c,d
2.6 ± 0.4ª,b
2.5 ± 0.4ª,b,c,d
1.5 ± 0.3e,f,g
1.6 ± 0.3d,e,f
1.7 ± 0.5c,d,e
0.57 ± 0.06h
1.00 ± 0.04f,g,h
0.87 ± 0.08g,h
0.96 ± 0.09f,g,h

1.6

3.9
3.5
3.7
1.6
3.8
3.2
3.3
6.4
3.9
3.4
3.6

±
±
±
±
±
±
±
±
±
±
±
±

0.3c
0.4b
0.7b
0.5b
0.2c

0.7b
0.6b
0.5b
0.8ª
0.3b
0.6b
0.9b

Modulus of elasticity (MPa)
202 ± 20ª
57 ± 8c,d
68 ± 19c,d
81 ± 12c
150 ± 15b
63 ± 20c,d
68 ± 20c,d
43 ± 13d,e
23 ± 2e
48 ± 5d,e
45 ± 10d,e
51 ± 13d

Different lowercase letters in the same column indicate significant difference (p < 0.05) between means (Tukey’s test).
CS – Cassava Starch foam; CS + GS – Cassava Starch and Grape Stalks foam; EPS – Expanded Polystyrene foam, followed by the day of analysis.
8


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J.B. Engel, et al.

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Thermoplastic cassava starch-based foams added with Cabernet
Sauvignon grape stalks were successfully developed by thermal expansion. Although further research is needed in order to improve foam’s
properties, especially regarding moisture resistance, it was possible to
observed that these structures are suitable for the packaging of foods
with low moisture content, especially as an alternative for the traditional EPS for short-term or single-use applications, because flexural
mechanical properties, at the end of the analysis, were similar to those
observed for foams developed with the petroleum based polymer.
Regarding biodegradability, the open cellular structure could have facilitated the microorganisms attack and made the biodegradation
faster. Besides, the amorphous pattern of the foams may also have
contributed to the rapid biodegradation, which is initialized in the
amorphous phase of the polymer.
Acknowledgements
The authors thank Salton winery (Brazil) for the Cabernet
Sauvignon grape stalks donation, the Thermodynamics and
Supercritical Technology Laboratory (LATESC) from Federal University
of Santa Catarina for the support on the porosity analysis, and the financial support received from CAPES (Coordination for the
Improvement of Higher Level Personnel, Brazil), CNPq (National
Council for Scientific and Technological Development, Brazil) and
FAPERGS (Research Support Foundation of the State of Rio Grande do
Sul, Brazil). In particular, thanks to the Programa Ciência sem
Fronteiras and CAPES CSF-PVE’s Project, process number:
88881.068177/2014-01.
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