Water absorption and mechanical properties of starch foam ... · Water absorption and mechanical properties of starch foam ... using a model XL-30 ... performed using a modified procedure

Braz. J. Food Technol., v. 12, n. 1, p. 34-42, jan./mar. 2009

Autor Correspondente | Corresponding Author

Recebido | Received: 20/04/2007Aprovado | Approved: 22/08/2008

Summary

Starch foam trays were developed as an alternative to the single-use expanded polystyrene (EPS) trays used for food products. The foam trays were prepared by heating a mixture composed of cassava starch, cellulose fibres and calcium carbonate inside a metallic mould. Starch-based foam trays are brittle and sensitive to moisture and thus further treatments are necessary to improve their mechanical properties and water resistance. To minimize water absorption, the foam trays were impregnated with starch acetate dissolved in chloroform at concentrations of 1:3 (g.mL–1), 1:5 (g.mL–1) and 1:10 (g.mL–1). The impregnation was carried out at atmospheric pressure and also by applying a vacuum pulse. The use of vacuum pulses decreased the water absorption of the impregnated foam trays by about 66%. On the other hand, there was no significant improvement in the mechanical properties of the impregnated trays. This work demonstrates that impregnation of porous samples with starch acetate is an alternative to decrease their water absorption.

Key words: Starch foam trays; Starch acetate; Impregnation; Biopolymer.

Resumo

Bandejas à base de amido expandido foram desenvolvidas como uma alternativa às badejas de poliestireno expandido (EPS), normalmente utilizadas para acondicionar alimentos. Bandejas à base de amido expandido foram preparadas através do aquecimento de uma mistura de amido, fibras de celulose e carbonato de cálcio no interior de um molde metálico. Bandejas à base de amido são quebradiças e sensíveis à umidade. Para reduzir a absorção de água, as bandejas foram impregnadas com acetato de amido dissolvido em clorofórmio em concentrações de 1:3 (g.mL–1), 1:5 (g.mL–1) e 1:10 (g.mL–1), com aplicação de um pulso de vácuo e totalmente à pressão atmosférica. O uso de um pulso de vácuo reduziu a absorção de água das amostras impregnadas em até 66%. Por outro lado, não houve melhora significativa nas propriedades mecânicas das amostras impregnadas. Este trabalho demonstra que a impregnação de materiais porosos com acetato de amido pode ser uma alternativa para a redução da absorção de água.

Palavras-chave: Bandejas de amido; Acetato de amido; Impregnação; Biopolímero.

Water absorption and mechanical properties of starch foam trays impregnated with starch acetateAbsorção de água e propriedades mecânicas de bandejas de

amido expandido impregnadas com acetato de amido

Autores | Authors

Vivian Consuelo Reolon SCHIMIDTUniversidade Federal de

Santa Catarina (UFSC) Campus Universitário TrindadeDepartamento de Engenharia

Química e Alimentose-mail: [email protected]

João Borges LAURINDOUniversidade Federal de

Santa Catarina (UFSC) Campus Universitário TrindadeDepartamento de Engenharia

Química e AlimentosCaixa Postal: 476CEP: 88040-090

Florianópolis/SC - Brasile-mail: [email protected]

DOI: 10.4260/BJFT2009260700005

Braz. J. Food Technol., v. 12, n. 1, p. 34-42, jan./mar. 2009 35

Water absorption and mechanical properties of starch foam trays impregnated with starch acetate

SCHIMIDT, V. C. R. and LAURINDO, J. B.

www.ital.sp.gov.br/bj

pressing process, the steam generated escaped from the sides of the hot plate, expanding the mixture. The mould was then maintained under a pressure of 0.36 MPa for a further 3 min. This heating time was necessary to reduce the moisture of the foam trays to 2-4%. The foam (expanded starch) trays were cooled to room tempera-ture.

The density of the foam trays was determined from the mass/volume ratio. The samples (4 × 4 cm) were weighed on a balance with a precision of 0.001 g (Gehaka, BG 400, Brazil). The sample thickness was measured using a digital external micrometer (Mitutoyo Co., Japan) at four different points of the sample and the other dimen-sions were measured with a caliper. The density was expressed in g of dry matter/volume (g.cm–3).

2.1 Preparation of the starch acetate and impregnation of the trays

The starch acetate was prepared by the process described in US Patent nº 5,710,269 (FEUER, 1998), replacing the catalytic agent MSA (methane sulphonic acid) by concentrated sulphuric acid (LAROTONDA et al., 2004). The highest possible degree of substitution (DS) is 3, since there are three hydroxyl groups (OH) available for substitution on each anhydroglucose unit (LEPENIOTIS and FEUER, 1997; MILADINOV and HANNA, 2001). The best mechanical properties and water resistance for use in food packing and for biodegradation have been reported for DS values between 1.2 and 1.7 (NARAYAN et al., 1999). The starch acetate used in this work had a DS =1.48.

The starch acetate used to impregnate the foam trays was prepared and diluted in chloroform at ratios of 1:3, 1:5 and 1:10 (g starch acetate: cm3 of chloroform). Foam tray samples with dimensions of 25 × 100 mm and 100 × 100 mm were impregnated by immersion in the starch acetate solutions. Foam tray samples were impregnated at atmospheric pressure and by the appli-cation of vacuum pulses in a desiccator containing the samples and the starch acetate solution. Impregnation at atmospheric pressure was performed by immersing the foam tray samples in the solutions for 5, 10 or 30 min. The procedures were all performed at room temperature. In the second case, pressures of 40 mmHg were applied to the desiccator containing the samples and solution for 3 min, followed by a period of 5, 10 or 30 min at atmospheric pressure. The vacuum was applied to remove most of the air present in the system and in the porous spaces of the samples, which facilitates the subsequent penetration of the solution (FITO, 1994). After impregnation, the samples were maintained at 100 °C for 3 h in a ventilated oven, to evaporate off the chloroform. The conditions used for sample impregnation are given in Table 1.

Introduction1

Foam trays were produced by heating starch-water mixtures (with or without the addition of fibres) under pres-sure in closed moulds (TIEFENBACHER, 1993; LAWTON et al., 1998; SHOGREN et al., 1998; GLENN et al., 2001; LAWTON et al., 2004; SOYKEABKAEN et al., 2004). However, starch-based materials are brittle and sensi-tive to moisture, thus further treatments are necessary to obtain the strength, flexibility and water resistance neces-sary for their commercial use (FANG and HANNA, 2000; SHOGREN et al., 2002).

An improvement in the properties of starch/water composite foams has been achieved by casting them with polyesters by adding polyvinyl alcohol (PVOH) to the starch-water mixture before the heat treatment (LAWTON et al., 1998; SHOGREN et al., 1998), or by impregnating them with a solution of starch acetate in chloroform ( LAROTONDA et al., 2005; MATSUI, et al., 2004). The water affinity of starch materials can be reduced chemically by substituting the starch hydroxyl groups by a hydrophobic group (SAGAR and MERRIL, 1995; THIEBAUD et al., 1997; PAVLATH and ROBERTSON, 1999; DEMIRGOZ et al., 2000; KIATKAMJORNWONG et al., 2001). Starch acetate with a high degree of substitution (DS) is one of the most important starch esters for use in engineering materials (MULLEN and PACSU, 1942; WHISTLER and HILBERT, 1944; WOLFF et al., 1951). Xu and Hanna (2005) and Larotonda et al. (2005) reported that starch hydrophobicity increased with the degree of substitution (DS), increasing its suitability as packaging material.

The objective of this work was to investigate the effect of impregnating starch-based foam trays with starch acetate, on the mechanical properties and water absorp-tion of the resulting material.

Material and methods2

Foam trays were produced from a mixture of cassava starch, cellulose fibres and calcium carbonate. Unmodified cassava starch was purchased from Yoki Alimentos S.A., Brazil. Calcium carbonate was purchased from a local retail store in Florianópolis, Brazil. Cellu-lose pulp fibres with 1.2 mm softwood short fibers were obtained from Klabin S.A., Brazil. The mixture was prepared in the proportions of 50% cassava starch, 39% calcium carbonate and 11% cellulose fibres by weight. The compounds were weighed and blended with water for 8 min, using a mechanical stirrer (Fisaton, mod 713D, Brazil). A thermopressing process was carried out in a mould using a hydraulic machine, where the temperature was set at 200-205 °C by two PID controllers. The size of the mould cavity was 159 mm in length, 109 mm in width and 1.12 mm in depth. The mixture was placed in the centre of the mould and covered by a lid. During the





texture analyser (SMS, Surrey, UK) with the 25 N load cell was used to determine the mechanical properties of the foam tray samples. The tensile strength and elonga-tion at break were determined from the tension tests. In the tension tests, foam tray samples with dimensions of 25 × 100 mm were fixed to the machine, and the tests performed at 2 mm/s.

The force at break and relative deformation were determined from the puncture tests. The puncture tests were performed using a spherical probe (21 mm diameter), previously fixed in an annular space with a diameter of 80 mm, as sketched in Figure 1. The spherical steel probe was built specially for these mechanical tests, to avoid sharp edges that could influence the material break. During the tests, the probe was moved through the sample, from top to bottom, with a speed of 1 mm/s, until 30 mm below the sample level. The load applied was 0.5 N and the tests were performed with 10 repetions for each sample. For this test, the relative deformations at break were represented by Equation 1.

∆d = LD

(1)

where ∆L = the probe vertical shift, from the moment it touched the sample to the break point; D = diameter of sample under test and d = relative deformation of the samples at break.

2.5 Water sorption isotherms

The foam tray samples were previously dried and conditioned in recipients with different relative humidities (RH = 7 to 90%), obtained using saturated salt solutions at constant temperature (25 °C). The samples were

2.2 Scanning electron microscopy (SEM)

Micrographs of the foam tray samples were obtained using a model XL-30 (Philips, Holland) scanning electron microscope. Before obtaining the micrographs, the foam tray samples were coated with a thin gold layer using a model SCD 005 (BAL-TEC, Switzerland). All samples were examined using an accelerating voltage of 20 kV.

2.3 Tray water absorption

A comparative water absorption study was performed using a modified procedure based on the ABNT NBR NM ISO 535 Standard (1999), which was derived from the Cobb method. It consisted of a gravimetrical analysis in which a sample (with a known dimension of 25 × 50 mm) was weighed before and after immersion in distilled water for 1 min. The water adhered to the sample surface was removed with absorbent paper.

2.4 Measurement of the mechanical properties

The mechanical properties of the foam trays were determined using the tensile strength test in accordance with the ASTM D828-97 standard test method. Before the mechanical tests, the foam tray samples were conditioned for 5 days at ambient temperature (about 25 °C) and a rela-tive humidity of 75% (obtained using a saturated solution of sodium chloride). The conditioning is important because the water absorbed by the materials acts as a plasticizing agent, modifying the material properties (SHOGEN et al., 1998; SOYKEABKAEW et al., 2004). The model TA.XT2i

Table 1. The conditions used for sample impregnation.Sample codes

Starch acetate/

chloroform (g.mL–1)

Impregnation time

(min)

*Pressure condition

A = non - impregnated sample

- - -

AP, 1:3,05 min 1:3 5 APAP, 1:3,10 min 1:3 10 APAP, 1:3,30 min 1:3 30 APVP, 1:3,10 min 1:3 10 VP AP, 1:5,05 min 1:5 5 APAP, 1:5,10 min 1:5 10 APAP, 1:5,30 min 1:5 30 APVP, 1:5,10 min 1:5 10 VPAP, 1:10,05 min 1:10 5 APAP, 1:10,10 min 1:10 10 APAP, 1:10,30 min 1:10 30 APVP, 1:10,10 min 1:10 10 VP* Pressure condition: AP = atmospheric pressure; and VP = vacuum pulses, followed by a period at atmospheric pressure.

Figure 1. Spherical probe and base used to fix the sample during the puncture tests.

Spherical probe

Sample securing screw





Figure 3 shows the results for the specific mass (from triplicates) of the foam trays, before and after impregna-tion. Foam trays impregnated with the 1:3 (g.mL–1) starch acetate solution (most concentrated solution) presented the greatest specific mass when compared to those impregnated with the 1:5 and 1:10 (g.mL–1) concentra-tions. Increases of 24, 15 and 16% were observed in the specific mass for samples from VP, 1:3,10 min; VP, 1:5,10 min and VP, 1:10,10 min, respectively. The specific mass of samples from experiments AP, 1:10,05 min; AP, 1:10,10 min and AP, 1:10,30 min increased by 4.0, 5.0 and 5.5%, respectively, while those from AP, 1:5,05 min; AP, 1:5,10 min and AP, 1:5,30 min showed increases of 6.5, 7.0 and 10.0%, respectively. Finally, the specific mass of samples from AP, 1:3,05 min; AP, 1:3,10 min and AP, 1:3,30 min increased by 10, 13 and 18%, respectively. These values can be explained by the application of vacuum, which removed the air entrapped inside the mate-rial, facilitating penetration of the starch acetate solution (FITO, 1994; LAROTONDA et al., 2005).

Figure 4 shows the water absorption values obtained for foam trays impregnated with the different starch acetate solutions (1:3, 1:5 and 1:10 g.mL–1) for the different immersion times (5, 10 and 30 min). In most cases, the sample water absorption decreased to about 70% of the value found for non-impregnated samples. The non-impregnated samples absorbed about 80 g.cm–2 more water than any of the impregnated samples. For samples impregnated under the conditions VP, 1:3,10 min and AP, 1:3,30 min, the water uptake decreased to about

frequently weighed to constant weight and the equilibrium moistures determined. The water sorption isotherms were fitted using the GAB model (Guggenhein, Anderson, de Boer), Equation 2.

=− − +

o w

w w w

X k C aX(1 k a ) (1 k a C k a )

(2)

where X = sample equilibrium moisture content on a dry weight basis; Xo= monomolecular layer equilibrium mois-ture content on a dry weight basis; aw = water activity (RH/100); C = Guggenheim constant, related to the first molecular layer heat sorption; k = constant related to the multilayer heat sorption.

Results and discussion3

Figure 2 shows the micrographs of a regular starch foam tray obtained by thermopressing. Figures 2a, b represent the surface and cross section, respectively, of a foam tray sample. In both figures, interlacement of the compounds (starch, calcium carbonate and fibres) and voids formed by steam escaping can be visualized.

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b

Figure 2. Micrographs of the foam trays: a) Surface; b) Cross-section.

350 400 450 500 550 600

AP, 1:10,05 min

AP, 1:10,10 min

AP, 1:10,30 min

AP, 1:5,05 min

AP, 1:5,10 min

AP, 1:5,30 min

AP, 1:3,05 min

AP, 1:3,10 min

AP, 1:3,30 min

VP, 1:3,10 min

VP, 1:5,10 min

VP, 1:10,10 min

Impr

egna

tion

cond

ition

Specific mass (kg.m 3)

16%

14%

24%

18%

10%

10%

7%

6.5%

5.5%

4%

5%

13%

Before impregnation After impregnation

Figure 3. Influence of impregnation on tray specific mass.





of 1:5 and 1:10 (g.mL–1), for 5 and 10 min). The impreg-nation decreased water absorption by the material by about 75%. The water uptake by commercial Kraft paper (75 g.m–2) impregnated with starch acetate/chloroform solution, decreased by 56.4% for the samples impreg-nated using vacuum pulses and 11.4% for the samples impregnated under atmospheric pressure (LAROTONDA et al., 2003).

Shogren et al. (2002) studied the preparation of starch foam trays with the addition of hydrophobic compounds to improve the water absorption resist-ance. Trays produced with the addition of paraffin wax, vegetable oil, silicone oil, resin, aryl acid ester, citric acid, butane-tetra-carboxylic acid, succinic acid and ethylene glycol resin failed to reduce the water absorption. Only monoester citrate presented a significant decrease in water absorption.

The values obtained for tensile strength and elon-gation at break of the impregnated and original foam trays are shown in Figures 5a and b. The results obtained with the impregnated foam trays were compared with non-impregnated samples and with commercial EPS (expanded polystyrene) trays. Impregnation had a small influence on the mechanical properties mentioned above. Similar results were reported by Matsui et al. (2004) for composites formed from cassava bagasse and Kraft paper, impregnated with starch acetate/chloroform solu-tions (concentrations of 1:5 and 1:10 (g.mL–1) for 5 and 10 min). These authors reported that impregnation did not influence the tensile strength and elongation at break of the samples. Larotonda et al. (2003) reported that impregnation of Kraft paper with starch acetate/chloro-form solutions (concentrations of 1:5 g.mL–1) increased the material tensile strength 1.5 times.

40%, compared to the non-impregnated samples. This can be explained by the filling up of the porous spaces in the material by starch acetate solution and by the coating on the material surface. Figure 8 shows the more homogeneous starch acetate film formed at the material surface for VP, 1:3,10 min. Moreover, since starch acetate is hydrophobic (LAROTONDA et al., 2005), the impreg-nated material became less hygroscopic, contributing to a reduction in water uptake. Similar results were reported by Larotonda et al. (2003) and Matsui et al. (2004).

Matsui et al. (2004) reported data obtained with cassava bagasse-Kraft paper composites impregnated with starch acetate/chloroform solutions (concentrations

a b

0.0

0.5

1.0

1.5

2.0

2.5

Elon

gatio

n at

bre

ak (%

)

0

1

2

3

4

5

6

Tens

ile s

treng

th (M

Pa)

AP,

1:5

,10

min

non

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EPS

AP,

1:3

,05

min

VP, 1

:10,

10 m

in

VP, 1

:5,1

0 m

in

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:3,1

0 m

in

AP,

1:10

,30m

in

AP,

1:1

0,10

min

AP,

1:1

0,05

min

AP,

1:5

,30

min

AP,

1:5

,05

min

AP,

1:3

,30

min

AP,

1:3

,10

min

AP,

1:5

,10

min

non

impr

egna

ted

EPS

AP,

1:3

,05

min

VP, 1

:10,

10 m

in

VP, 1

:5,1

0 m

in

VP, 1

:3,1

0 m

in

AP,

1:10

,30m

in

AP,

1:1

0,10

min

AP,

1:1

0,05

min

AP,

1:5

,30

min

AP,

1:5

,05

min

AP,

1:3

,30

min

AP,

1:3

,10

min

Figure 5. Foam trays impregnated with a starch acetate/chloroform solution: a) Tensile strength; and b) Elongation at break.

Figure 4. Influence of impregnation on tray water absorption.

60 80 100 120 140 160 180 200 220 240

non impregnated

AP, 1:10,05 min

AP, 1:5,05 min

AP, 1:3,05 min

AP, 1:10,10 min

AP, 1:5,10 min

AP, 1:3,10 min

AP, 1:10,30 min

AP, 1:5,30 min

AP, 1:3,30 min

VP, 1:10,10 min

VP, 1:5,10 min

VP, 1:3,10 min

Impr

egna

tion

cond

ition

Water absorption (g.cm 2)

34%

64%

66%

40%

63%

70%

72%

69%

67%

73%

72%

72%

100%





starch acetate film inside the structure, but details of the fibres and calcium carbonate distribution can be seen, as well as the voids formed by the arrangement of the materials formed during the heating process.

The environmental aspects of using chloroform as the solvent must be carefully evaluated. For industrial use, it is important to evaluate the residual concentration of this solvent in the foam trays and also find ways to recover the chloroform evaporated during the vacuum pulses (impregnation) and foam tray drying procedures.

The puncture tests results for the impregnated and non-impregnated foam trays are presented in Figures 6a and b. In general, the samples impregnated with the more concentrated solutions (1:3 and 1:5 g.mL–1) presented relatively less deformation than samples impregnated with the lower concentration (1:10 g.mL–1). This behaviour can be explained by the greater starch acetate impregnation obtained with the more concentrated solutions.

Moisture sorption isotherms of the impregnated and non-impregnated foam trays are shown in Figure 7. The GAB model fitted the experimental sorption data for the impregnated and non-impregnated samples well. The values for the GAB constants are shown in Table 2. The moisture content of the monomolecular layer was higher for non-impregnated samples. A plausible explanation for this result is the coating of both the sample surface and part of its porous space by starch acetate, which is hydro-phobic (LAROTONDA et al., 2005). Figure 8 shows the SEM micrographs of the surface of an impregnated foam tray, and some aspects of the thin acetate film that coat the sample surface can be observed. The film presented a dense structure, interspersed with cracks, due to the brittle characteristic of starch acetate (LAROTONDA et al., 2004, 2005). Similar film coatings were reported by Matsui et al. (2004) and Larotonda et al. (2005).

Figure 9 shows micrographs of cross-sections of the impregnated foam trays. It is impossible to identify the

a b

0.030

0.045

0.060

0.075

0.090

0.105

0.120

0.135

Rel

ativ

e d

efor

mat

ion

0

10

20

30

40

5060

70

80

90

100

Forc

e at

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)

AP,

1:1

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min

AP,

1:5

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min

AP,

1:3

,30

min

AP,

1:1

0,10

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AP,

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AP,

1:3

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AP,

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AP,

1:5

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AP,

1:3

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VP, 1

:10,

10 m

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0,10

min

VP,

1:5

,10

min

VP,

1:3

,10

min

non

imp

reg

nate

d

EP

S

Figure 6. Foam trays impregnated with a starch acetate/chloroform solution: a) Force at break, N; and b) Relative deformation at break, d.

Table 2. Values for the GAB constants.Constants Non-impregnated

sample Impregnated

sample (1:10 g.mL–1)

K 0.9613 0.9989Xo 0.0269 0.0168C 17.981 11.574R2 (Adjusted) GAB 0.9941 0.9645

0.00

0.10

0.20

0.30

0.40

0.00 0.20 0.40 0.60 0.80 1.00

Water activity

Equi

libriu

m m

oist

ure

(gw

/gss

)

GAB Impregnated sample

Impregnated sample

GAB Non-impregnated sample

Non-impregnated sample

Figure 7. Sorption isotherms for the impregnated and non-impregnated foam trays.





Figure 8. SEM micrographs of foam tray surfaces: a) VP, 1:3,10 min; b) AP, 1:3,10 min; c) AP, 1:5,10 min; and d) non-impregnated sample.

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Figure 9. SEM micrographs of foam tray cross-sections: a) VP, 1:3,10 min; b) AP, 1:3,10 min; c) AP, 1:5,10 min; and d) non-impregnated sample.

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sheets. Polymer Degradation and Stability, Kidlington, Oxford, v. 73, n. 2, p. 363-375, 2001.

LAROTONDA, F. D. S.; MATSUI, K. N.; PAES S. S.; LAURINDO, J. B. Impregnation of Kraft paper with Cassava-Starch acetate: analysis of the tensile strength, water absorption and water vapor permeability. Starch/Stärke, Weinheim, v. 55, n. 11, p. 504-510, 2003.

LAROTONDA, F. D. S.; MATSUI, K. N.; SOLDI, V.; LAURINDO, J. B. Biodegradable films made from raw and acetylated cassava starch. Brazilian Archives of Biology and Technology, Curitiba, v. 47, n. 3, p. 477-484, 2004.

LAROTONDA, F. D. S.; MATSUI, K. N.; SOBRAL, P. J. A.; LAURINDO, J. B. Hygroscopy and water vapor permeability of kraft paper impregnated with starch acetate. Journal of Food Engineering, Kidlington, Oxford, v. 71, n. 4, p. 394-402, 2005.

LAWTON, J. W.; SHOGREN, R. L.; TIEFENBACHER, K. F. Structure and morphology of baked starch foams. Polymers, Kidlington, Oxford, v. 39, n. 25, p. 6649-6655, 1998.

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MATSUI, K. N.; LARONTONDA, F. D. S.; PAES, S. S.; LUIZ, D. B.; PIRES, A. T. N.; LAURINDO, J. B. Cassava bagasse-kraft paper composites: analysis of influence of impregnation with starch acetate on tensile strength and water absorption properties. Carbohydrate Polymers, Kidlington, Oxford, v. 55, n. 3, p. 237-243, 2004.

MILADINOV, V. D.; HANNA, M. A. Temperatures and ethanol effects on the properties of extruded modified starch. Industrial Crops and Products, Amsterdam, v. 13, n. 1, p. 21-28, 2001.

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NARAYAN, R.; BLOEMBERG, S.; LATHIA, A. Method of preparing biodegradable modified-starch moldable products and films. US Patent 5.869.647, 9 February 1999.

PAVLATH, A. E.; ROBERTSON, G. H. Biodegradable polymers vs. recycling: what are the possibilities. Critical Reviews in Analytical Chemistry, Philadelphia, v. 29, n. 3, p. 231-241, 1999.

SAGAR, A. D.; MERRIL, E. W. Properties of fatty-acid esters of starch. Journal of Applied Polymer Science, Hoboken, v. 58, n. 9, p. 1647-1656, 1995.

SHOGREN, R. L.; LAWTON, J. W.; DOANE, W. M.; TIEFENBACHER, K. F. Structure and morphology of baked starch foams. Polymers, Kidlington, Oxford, v. 39, n. 25, p. 6649-6655, 1998.

SHOGREN, R. L.; LAWTON, J. W.; TIEFENBACHER, K. F. Baked starch foams: starch modifications and additives improve

Conclusions4

The impregnation of starch foam trays with starch acetate solutions did not significantly influence their mechanical properties, but decreased their water absorp-tion, increasing the potential use of this material for food packaging. Moreover, starch acetate impregnation is a feasible procedure to reduce the water sensitivity of packaging for hygroscopic materials and represents an option for industrial starch use.

For industrial use, it is important to evaluate the residual chloroform concentration in the foam trays and how to recover the chloroform evaporated during the vacuum pulse (impregnation) and foam tray drying proce-dures. Furthermore, the use of the trays presented in this work should be evaluated with respect to the legislation for food packaging in Brazil.

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