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Cassava starch biodegradable lms: Inuence of glycerol and clay nanoparticlescontent on tensile and barrier properties and glass transition temperature

A.C. Souza a, R. Benze a, E.S. Ferro a, C. Ditcheld b, A.C.V. Coelho c, C.C. Tadini a,*a Department of Chemical Engineering, Escola Politcnica, University of So Paulo, P.O. Box 61548, 05424-970 So Paulo, Brazilb Department of Food Engineering, University of So Paulo, P.O. Box 23, 13635-900 Pirassununga, SP, Brazilc Department of Metallurgical and Materials Engineering, Escola Politcnica, University of So Paulo, P.O. Box 61548, 05424-970 So Paulo, Brazil

a r t i c l e i n f o

Article history:

Received 24 March 2011Received in revised form17 October 2011Accepted 27 October 2011

Keywords:

Cassava starchGlycerolClayTensile propertiesBarrier properties

a b s t r a c t

In this study, glycerol content and its incorporation method on tensile and barrier properties of biode-gradable lms (BF) based on cassava starch were analyzed. ANOVA showed that the glycerol incorpo-ration method did not inuence the results (P > 0.05), however the glycerol content inuencedsignicantly the tensile and barrier properties of the lms (P 0.05).

2011 Elsevier Ltd. All rights reserved.

1. Introduction

Over the last decades, the use of polymers as food packagingmaterials has increased considerably due to their advantages overother traditional materials such as glass or tinplate. A great advan-tage of plastics is the large variety of materials and compositionsavailable, so the most convenient packaging design can be adaptedto the very specic needs of each product (Lpez-Rubio et al., 2004).

However, it is widely accepted that the use of long-lastingpolymers for short-lived applications (packaging, catering,surgery, hygiene) is not entirely adequate (Avrous, 2004). A hugeamount of garbage is generated daily, in which food packagingplays a considerable part. This waste is composed of many differenttypes of material, some of which is not biodegradable and will

remain without decomposing for hundreds, sometimes thousandsof years. In this context, the development of biodegradable lms(BF) for packaging materials that can be used as a substitute forpetrochemical polymers is an interesting perspective, since itprovides an alternative to non-degradable products, and increasesincome in the agricultural sector (Souza, Ditcheld, & Tadini, 2010).

Starch has been considered as one of the most promisingcandidates for the future primarily because of an attractive

combination of its large availability and relatively low price(Chivrac, Angellier-Coussy, Guillard, Pollet, & Avrous, 2010).

Cassava starch has been extensively used to produce BF (Alves,Mali, Belia, & Grossmann, 2007; Chen & Lai, 2008; Chillo et al.,2008; Fam, Flores, Gerschenson, & Goyanes, 2006; Fam,Goyanes, & Gerschenson, 2007; Flores, Fam, Rojas, Goyanes, &Gerschenson, 2007; Henrique, Cereda, & Sarmento, 2008;Kechichian, Ditcheld, Veiga-Santos, & Tadini, 2010; Mali, Gross-mann, Garca, Martino, & Zaritsky, 2006; Mller, Yamashita, &Laurindo, 2008; Paes, Yakimets, & Mitchell, 2008; Parra, Tadini,Ponce, & Lugo, 2004; Shimazu, Mali, & Grossmann, 2007; Teixeira,da Rz, Carvalho, & Curvelo, 2007; The, Debeaufort, Voilley, & Luu,2009; Veiga-Santos, Oliveira, Cereda, Alves & Scamparini, 2005;Veiga-Santos, Suzuki, Cereda & Scamparini, 2005; Veiga-Santos,

Suzuki, Nery, Cereda, & Scamparini, 2008) and the results indi-cated that these carbohydrates are promising materials in thisregard (Mller et al., 2008). Films developed from starch aredescribed as isotropic, odorless, tasteless, colorless, non-toxic andbiologically degradable (Flores et al., 2007).

Unfortunately, there are some strong limitations for developingstarch based products, since they present poor tensile propertiesand high water vapor permeability when compared to conven-tional lms derived from crude oil (Souza et al., 2010) on account oftheir hydrophilic nature and their sensitivity to moisture content,a factor that is difcult to control (Wilhelm, Sierakowski, Souza, &Wypych, 2003).

* Corresponding author. Tel.: 55 11 30912258; fax: 55 11 30912255.E-mail address:[email protected](C.C. Tadini).

Contents lists available at SciVerse ScienceDirect

LWT - Food Science and Technology

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c om / l o c a t e / l w t

0023-6438/$e see front matter 2011 Elsevier Ltd. All rights reserved.

doi:10.1016/j.lwt.2011.10.018

LWT - Food Science and Technology 46 (2012) 110e117
mailto:[email protected]://www.sciencedirect.com/science/journal/00236438http://www.elsevier.com/locate/lwthttp://dx.doi.org/10.1016/j.lwt.2011.10.018http://dx.doi.org/10.1016/j.lwt.2011.10.018http://dx.doi.org/10.1016/j.lwt.2011.10.018http://dx.doi.org/10.1016/j.lwt.2011.10.018http://dx.doi.org/10.1016/j.lwt.2011.10.018http://dx.doi.org/10.1016/j.lwt.2011.10.018http://www.elsevier.com/locate/lwthttp://www.sciencedirect.com/science/journal/00236438mailto:[email protected]

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Usually, the second major component of a starch based lm isthe plasticizer, which is used to overcomelm brittleness causedbyhigh intermolecular forces. Plasticizing agents commonly used forthermoplastic starch production include water and glycerol (Alveset al., 2007; Fam et al., 2006; Fam et al., 2007; Jangehud &Chinnan, 1999; Mali et al., 2006; Parra et al., 2004), polyethyleneglycol (Parra et al., 2004) and other polyols, such as sorbitol,mannitol and sugars (Kechichian et al., 2010; Talja, Heln, Roos, &

Jouppila, 2008; Veiga-Santos et al., 2008).Some authors consider that the glycerol, a polyalcohol found

naturally in a combined form as glycerides in animal and vegetablefats and oils, is the best plasticizer for water soluble polymers(Bertuzzi, Castro Vidaurre, Armanda, & Gottifredi, 2007; Jangehud& Chinnan, 1999; Mller et al., 2008). The hydroxyl groupspresent in glycerol are responsible for inter and intramolecularinteractions (hydrogen bonds) in polymeric chains, providinglmswith a more exible structure and adjusting them to the packagingproduction process (Souza et al., 2010).

Sucrose, which is a non-toxic, edible and lowcost biodegradableraw material, has shown a higher plasticizing efciency whencompared to sorbitol and glycerol. However, evidence of sucrosecrystallization during storage was reported. Some authors have

demonstrated the possibility of substituting sucrose by invertedsugar that has a lower tendency to crystallize, increasing lm-forming suspension viscosity, makingit moredifcult forcrystals toform (Veiga-Santos et al., 2008).

In this way, the association of cassava starch with plasticizers asglycerol, sucrose, and inverted sugar can promote alterations in thelms, justifying the study of these additives to develop a potentialand ecological alternative to the synthetic packaging of several foodproducts (Parra et al., 2004).

To overcome high permeability caused by the plasticizer, otheradditives are used. In this area, the production of bionanocompositeshas proven to be a promising option, since polymer composites areincreasingly gaining importance as substitute materials due to theirsuperior tensile properties, making them especially suited for trans-

portation and packaging applications.Mineral clays are technologically important and are mainly

composed of hydrated aluminosilicate with neutral or negativecharged layers (Wilhelm et al., 2003). Clay is a potential ller; itselfa naturally abundant mineral that is toxin-free and can be used asone of the components for food, medical, cosmetic and healthcareproducts (Chen & Evans, 2005). Moreover, clay is environmentallyfriendly and inexpensive.

Clay/starch composites have been the most frequentlystudied, demonstrating a potential for improvement of tensilestrength, Youngs modulus, water resistance and decrease of thewater vapor permeability of starches from many differentsources (Avella et al., 2005; Chiou et al., 2007; Cyras, Manfredi,Ton-That, & Vsquez, 2008; Kampeerapappun, Aht-Ong, Pen-

trakoon, & Srikulkit, 2007; McGlashan & Halley, 2003; Tanget al., 2008). A decrease in water vapor permeability of up to 70%in relationship to pure starch lms (corn, wheat, potato, waxycorn and high amylose corn starch) has been reported (Tanget al., 2008). An increase in Youngs modulus of up to 500%has also been observed for potato starch/montmorillonitecomposites (Cyras et al., 2008).

In this paper, the inuence of glycerol and nanoclay particles ontensile (tensile strength and percent elongation at break), barrierproperties (water vapor permeability and oxygen permeabilitycoefcient) and glass transition temperature of BF based on cassavastarch was studied. In the rst phase, sucrose, inverted sugar,different glycerol contents and two methods of glycerol incorpo-ration were tested. In the second phase, the effects of different

contents of glycerol and clay nanoparticles were evaluated. X-ray

diffraction analyses were performed to evaluate the hypothesis ofglycerol and starch intercalation into the clay galleries.

2. Materials and methods

2.1. Materials

Native cassava starch, kindly supplied by Cargill Agrcola, Brazil(amylose: 19.7 g/100 g; amylopectin: 80.3 g/100 g; moisture:12.5 g/100 g) was used as the lm-forming component to providea continuous biodegradable lm matrix. Glycerol (Synth, Brazil),liquid inverted sugar from Copersucar, Brazil (inversion:65 g/100 g) and commercial sucrose from Guarani, Brazil (mois-ture: 0.2 g/100 g max.) were added to improve their exibility.Natural -Na montmorillonite clay (commercial product Argel T,used as received, without purication, Bentonit Unio, Brazil) wasused as ller. Distilled water and ethanol (Synth, Brazil) were usedas solvents for the lmogenic solutions.

2.2. Film preparation

In the rst phase, the lmogenic solution was prepared by dis-

solving 5.0 g of starch, 0.7 g of sucrose, 1.4 g of inverted sugar,glycerol at different contents ((0.0, 0.17, 0.34, 0.50 and 0.75) g), anddistilled water in order to complete 100 g of solution. Glycerolcontents were based on preliminary tests. The glycerol incorpora-tion was tested by two different methods.

In the rst method, the lmogenic solution was prepared bya simple mixture of all components (cassava starch, glycerol,sucrose, inverted sugar and distilled water) at ambient tempera-ture. Then, this solution was heated in a domestic microwave ovenuntil starch gelatinization which occurred at (692) C. Accordingto the casting technique, for each formulation, a specic content oflmogenic solution was poured onto cylindrical acrylic plates(154 cm2 of area) to obtain a constant thickness of (100 10)mm,followed by drying at (35 2) C for approximately 16 h, in an oven

with forced air circulation (Nova tica, series N480, Brazil).In the second method, glycerol and cassava starch were dried in

the oven at (170 2) C for 45 min and occasionally stirred,allowing diffusion of glycerol into the starch granule. After coolingat ambient temperature, sucrose, inverted sugar and distilled waterwere added and the lm preparation followed the same procedureas the rst method.

In the second phase of the work, the lmogenic solution wasprepared in three steps: rst, clay nanoparticles were suspended indistilledwaterfor1h,and,afterarestperiodof24h,theywereblendedwith a suspension of 5.0 g of starch, glycerol, and distilled water inordertocomplete100gofsolution.Thequantitiesofclaynanoparticlesand glycerol were varied from (0.0 to 0.1) g and from (0.75 to 1.25) g,respectively, yielding a total of 6 different formulations elaborated,

according toTable 1. After homogenization, this solutionwas heated ina domesticmicrowave oven untilstarchgelatinization, whichoccursat(69 2) C. After cooling, this solution was diluted with 14.25 g ofethanol, and, poured onto cylindrical platesand dried at (35 2) Cfor(18e24) h, in the same oven with forced air circulation.

After drying, all lms (produced in both phases) were stored ata controlled relative humidity of 75% for one week prior to testing.Since starch lms have a hydrophilic character, high moistureambient was chosen in order to evaluate lm performance ina typical tropical weather condition (Veiga-Santos et al., 2008).

2.3. Film characterization and tensile properties

The physical appearance of the lms was inspected visually and

by touch.

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The thickness (t) [mm] was measured using a at parallelsurface micrometer (MITUTOYO SulAmericana Ltda., model103-137, Brazil, precision 0.002 mm), at ve random positions.

Tensile strength (TS) [MPa] and percent elongation at break (E)[%] were evaluated by a tensile test performedon a texture analyzer(TA.XT2i e Stable Micro Systems, UK) using the A/TGT self-tightening roller grips xture, according to ASTM D882-09(2009). Filmstrips (130 mm 25 mm) were cut from each pre-conditioned sample and mounted between the grips of theequipment. Initial grip separation and test speed were setto 50 mmand 0.8 mm s1, respectively. Tensile strength (nominal) wascalculated dividing the maximum load by the original minimumcross-sectional area of the specimen (related to minimum thick-ness). Percent elongation at break (nominal) was calculated bydividing the extension at the specimen break point by its initialgage length and multiplying by 100. All specimens were evaluatedin triplicate.

2.4. Barrier properties

Water vapor transmission (WVT) was determined by a gravi-

metric method based on ASTM E96/E96M-05 (2005), using theDesiccant Method. This property was reported as water vaporpermeability (WVP) that is the rate of water vapor transmission(WVT)through a unit area ofat material of unit thickness inducedby unit vapor pressure difference between two surfaces, underspecied humidity condition of 75%. Each lm sample was sealedwith parafn over a circular opening of 44 cm2 at the permeationcell (PVA/4, REGMED, Brazil) that was stored, at room temperature,in a desiccator. To maintain 75% of relative humidity (RH) gradientacross the lm, silica gel was placed inside the cell and a sodiumchloride saturated solution (75% RH) was used in the desiccator.Two cells without silica gel were prepared and submitted to thesame conditions to account for weight changes occurring in thelm, since it is a hydrophilic material. The RH inside the cell wasalways lower than the outside, and water vapor transport wasdetermined from the weight gain of the permeation cell. Aftersteady state conditions were reached (about 2 h), ten weightmeasurements were made over 48 h. WVPwas calculated accordingEquation(1):

WVP w=q 24 t=A Dp (1)

wherein:WVPis the watervapor permeability [g mm m2 d1 kPa1]; w is

the weight gain (from the straight line) [g]; q is the time duringwhichwoccurred [h];tis the averagelm thickness [mm];Ais thetest area (cell top area) [m2] and Dpis the vapor pressure difference[kPa]. All specimens were evaluated in triplicate.

Oxygen transmission rate (OTR) [cm3 m2 d1] of the lms was

measured at 23

C and 75% RH on a 50 cm

2

circular

lms using an

oxygen permeation system (OXTRAN 2/21, MOCON, USA), inaccordance withASTM F1927-07 (2007). A starch based lm wassealed between two chambers (each one with two channels), thelower one supplied with O2at a controlled ow rate (20 mL min

1)to keep the pressure constant in that compartment, and the otherone was purged by a stream of nitrogen carrier gas (0.98 part ofnitrogen and 0.02 part of hydrogen), at controlled ow rate(10 mL min1). A colorimetric sensor determined the amount ofoxygen transmitted through the lm into the carrier gas. Theoxygen transmission rate was determined for all specimens induplicate. The permeance (PO2) of the lms was calculatedaccording to Equation(2):

PO2 OTR=p (2)

wherein:PO2 is the permeance of the lms [cm

3 m2 d1 Pa1]; OTR is theoxygen transmission rate [cm3 m2 d1]; and p is the partialpressure of oxygen, which is the mol fraction of oxygen multipliedby the total pressure (nominally, one atmosphere), in the test gasside of the diffusion cell. The partial pressure of O2on the carriergas side is considered zero.

The oxygen permeability coef

cient (P0

O2) was calculated asfollows:

P0O2 PO2t (3)

wherein:P0O2is the oxygen permeability coefcient [cm

3 m1 d1 Pa1];andtis the average thickness of the specimen [mm].

2.5. Glass transition temperature

Glass transition temperature (Tg) of BF was determined bydifferential scanning calorimetry, using a DSCTA 2010 controlled bya TA 4000 module (TA Instruments, New Castle, USA), witha quench cooling accessory, operated with nitrogen at

150 mL min1

. Temperature and melting enthalpy calibrations wereperformed with indium and bidistilled water and Milli-Q. Samplesof about (2e5) mg were weighed in a precision balance (Scientech,SA210, USA), conditioned in hermetic aluminum pans (20 mL), andsubmitted to a temperature program, under inert atmosphere(100 mL min1 of N2). In the rst scan, after cooling the sample at10 C min1 up to 60 C, it was submitted to heating at10 C min1 until 100 C. The second scan was between60 C and250 C, at the same cooling and heating rates. The glass transitiontemperature (Tg) [C] was calculated using the software UniversalAnalysis 2.6 (TA Instruments, New Castle, USA) as the inectionpoint of the base line, caused by the discontinuity of sample specicheat, in the second scan. All aluminum pans were weighed beforeand after tests to verify that no material was lost during the

experiment.

2.6. X-ray diffraction

X-ray diffraction (XRD) measurements were performed, usingqe2qreection geometry, on a PHILIPS X-PERT MPD diffractometerusing CuKa radiation (l 1.5406 ),operated at a generator voltageof 40 kV, a current of 40 mA, and goniometer speed of 0.02(2q) s1.

2.7. Statistical analyses

Analysis of variance (ANOVA) was applied on the results usingthe statistical program Statgraphics Centurion v.15.0 (StatPoint,Inc., USA) and the Tukey test was used to evaluate average differ-

ences (at a 95% of con

dence interval).

Table 1

Glycerol and clay nanoparticles contents used for production of biodegradable lmsbased on cassava starch at the second phase.

Coded values Real valuesa

Glycerol Claynanoparticles

Glycerol Claynanoparticles

A 1 1 0.75 0.00B 1 0 0.75 0.05

C 1 1 0.75 0.10D 1 1 1.25 0.00E 1 0 1.25 0.05F 1 1 1.25 0.10

a g/100 g oflmogenic solution.

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3. Results and discussion

Most formulations produced transparent, homogeneous andexible lms, and their surfaces were smooth, continuous andhomogeneous, without pores and cracks, or insoluble particles(Fig. 1).

3.1. Films preparation: selection of glycerol incorporation method

Tensile strength, elongation at break and water vapor perme-ability results obtained from lms produced in the rst phaseaccording to the different glycerol incorporation methods were

analyzed by ANOVA (data not shown) and the results indicatedthere were no signicant differences between the two methodstested (P> 0.05). Although the results were satisfactory, the lmsproduced by the second method did not present homogeneousappearance, especially those produced with lower glycerol content.Therefore, the rst method of glycerol incorporation was chosen,because it supplied lms with a better appearance and was alsoeasier to carry out.

3.2. Tensile properties

Tensile properties may vary with specimen thickness, methodofpreparation, speed of testing, type of grips used and manner ofmeasuring extension. Consequently, it is difcult to compare with

literature data.Tensile strength oflms produced at the rst phase, accordingto the rst method of glycerol incorporation, varied from

(1.85 0.34) MPa to (6.06 1.04) MPa. The use of glycerol, inde-pendent of its content, lowered the TSof the lms. The averagespecimen thickness was (85.59 13.57) mm and their valuesaccording to the glycerol content were very similar (Table 2).

The presence of glycerol changed the percent elongation atbreak of the lms: a decrease of this property was observed as theglycerol content increased from (0.17 to 0.75) g/100 g. This fact isprobably due to the antiplasticizing effect caused by the highplasticizer content, already reported by other authors (Shimazuet al., 2007), indicating stronger interactions between plasticizerand biopolymer that induce a loss of macromolecular mobility.Moreover, the use of sucrose and inverted sugar contributed to thiseffect because they also acted as plasticizing agents.Veiga-Santoset al. (2005)showed that sucrose addition in BF based on cassavastarch can increaseEuntil 2900% when compared to lms withoutsucrose. According to Teixeira et al. (2007), this particular behaviorcan be attributed tothe fact that sucrose has a higher number of OHgroups than other sugars and, therefore, is more hydrophilic and isa more efcient plasticizing agent.

In the second phase of the work, as can be observed inTable 3,an increase of clay and glycerol contents causeda decrease ofTS.Foreach content of clay nanoparticles, an increase of glycerol content

from 0.75 g to 1.25 g caused a signicant decrease ofTS(P 0.05).


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The regression analysis, using response surface methodology,was applied on results ofWVPandP0O2of the lms indicating thatboth components glycerol (G) and clay nanoparticles (C) inuencedsignicantly WVPand P0O2, however only for WVP, expressed byEquation (5), in real values, was obtained with good correlation(r2 77%). As can be observed in Fig. 2(b), biodegradable lmsproduced with lower contents of glycerol and higher contents ofclay nanoparticles presented lower WVP.

WVP 2:65 3:77 G 19:5 C 0:710:75 G 1:25 0:00 C 0:10

(5)

wherein WVPis the water vapor permeability [g mm m2 d1 kPa1];Gis the glycerol content [g/100 g oflmogenic solution]; andCis theclay nanoparticles content [g/100 g oflmogenic solution].

In order to compare these results with those of classic materials,cellophane water vapor permeability was obtained with assaysusing the same conditions of the tests performed with BF and theresult ((0.490.02) g mm m2 d1 kPa1) was 10 times lower thanfor the BF.

Comparable results ofWVPwere shown by commercial mate-rials produced by Cargill Dow (USA) under the Natureworks trademark and by Solvay (Belgium) under the CAPA trade mark(Avrous, 2004).

3.4. Glass transition temperature

Glass transition temperatures obtained from DSC experimentsare reported inTable 3. The results showed the same behavior forall samples of BF elaborated, independent of glycerol and claycontents. Two distinct glass transition temperatures, associatedwith twoheat capacity changes in the samples, were observed in allformulations produced, the rst varying from (35 to 39) C and thesecond one from (53 to 63) C. Similar values were observed inother polymeric materials. Polylactic acid (PLA), a biodegradablepolyester commonly used for trays, cups, bottles and lms, has

been industrially produced by Cargill Dow (USA) under theNatureworks trade mark, with a similar glass transition temper-ature: 58 C(Avrous, 2004).Tang et al. (2008)fabricated biode-gradable nanocomposites from corn starch and montmorillonitenanoclays by melt extrusion processing, with Tg varying from(50.71 2.76) C to (54.74 1.21) C, when watercontent of starch-clay nanocomposite decreased from (13.06 1.73) g/100 g to(9.750.21) g/100 g. Specimens fabricated by injection moldingusing pellets produced with wheat starch (74 g/100 g), glycerol(10 g/100 g) and water (16 g/100 g) presentedTgof 43 C (Avrous,Fauconnier, Moro, & Fringant, 2000).Arvanitoyannis, Psomiadou,and Nakayama (1996) observed a decrease on glass transitiontemperature of edible lms based on corn starch and plasticizedwith glycerol from (88.83.4) C to (33.01.2) C, when glycerolcontent increased from (5 to 15) g/100 g.

It has been reported that increasing glycerol content decreasesTgbecause the polymer matrix becomes less dense and the mobilityof polymer chains is facilitated with the addition of plasticizer (Maliet al., 2006). This fact was not observed in the present work, sincea signicant effect was not found (P> 0.05) at Tg in relation toglycerol content. This fact can be related to the same equilibriumwater content presented in all formulations elaborated,(14.11 0.12) g water/100 g oflm, since it is well known that watercontent of a material inuenced its glass transition temperature.

3.5. X-ray diffraction

Fig. 3 shows XRDpatterns of BF produced during the second

phase. Graph peaks represent inter-layer spacing values and,

therefore, they yield information about the crystalline structure ofthe analyzed material. It is generally thought that during theintercalation process, the polymer enters into clay spaces andforces apart the platelets, thus increasing the gallery spacing (Tanget al., 2008). The distance d001of pure clay (1.44 nm) is typical ofhydrated Na-montomorillonite and is lower than the distanceobserved in the peaks of BF ((1.76 0.01) nm), indicating theuptake of glycerol and/or starch into clay galleries. According toChen and Evans (2005), many polymers when taken up by mont-morillonite produce an expanded structure with d001 w 1.8 nm,therefore it is not clear if starch and glycerol have entered into theclay galleries or just glycerol.

Since the BF containing clay presented peaks, the clay was not

completely delaminated,indicating that starch did notenter into allclay inter-layer spacing, which is further supported by lower resultsfor TSwhen clay was used. Nevertheless, the reduction of watervapor and oxygen permeability values can also indicate a partialdelamination of the clay, which was not detected by XRD. Thestacks of clay lamellae (not delaminated) did not contributesignicantly to improve tensile properties and could initiate lmfracture, which could explain the lower values ofTS.

The adsorption and intercalation of glycerol into clays is knownand has been studied for many years (Hoffmann & Brindley, 1961).In fact, the glycerol used as plasticizer in the BF formulations, couldhave prevented the entry of starch molecules in the interlamellarspaces of clay and may have covered the entire inter-layer space.However, a non-volatile plasticizer is essential for processing useful

starch based materials; without it the mixture of starch and clay

Fig. 3. . X-ray diffraction patterns of biodegradable lms formulated with 0.50 g

(a) and 0.75 g (b) of glycerol at three levels of clay nanoparticles (0.00 g, 0.05 g and

0.10 g). Guide for 0.50 g: ; Guide for 0.75 g:

.


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powders cannot cohere after the evaporation of water (Chen &Evans, 2005).

4. Conclusions

Glycerol and sugars are plasticizers compatible with starch,improving lm exibility, facilitating its handling and preventing

cracks, but it was demonstrated in this study that their presencegreatly affected lm barrier properties. To overcome this problem,clay nanoparticles were used successfully, since permeabilityvalues decreased signicantly.

The results establish that lms based on plasticizedcassava starch reinforced with clay nanoparticles can beconsidered as an interesting biodegradable alternative pack-aging material. Nevertheless, further research is necessary toimprove their mechanical and barrier properties since adequatetensile strength and extensibility are generally required fora packaging lm to withstand external stress and maintain itsintegrity as well as barrier properties during applications in foodpackaging.

These issues should be focused in future studies. A direction of

the investigation will be the development of complementaryapproaches to give further insight into the molecular structure ofbiodegradablelms based on cassava starch.

Moreover, the elaboration of biodegradable lms by extrusion isthe main point to explore in a next future, representing an evolu-tion of this research, since a twin screw extruder, equipmentconventionally used in exible packaging industries, yields lmswith better mechanical and barrier properties due to the completedelamination of clay nanoparticles.

Finally, as a natural biopolymer, besides its biodegradablecharacter, starch would be a promising alternative for the devel-opment of new food packaging materials because of its attractivecombination of availability and price, supporting the continuity ofthis study.

Acknowledgment

This research was supported by FAPESP (The State of So PauloResearch Foundation) and CAPES (Brazilian Committee for Post-graduate Courses in Higher Education). Authors would like to thankProfa. Dra. Miriam Dupas Hubinger (Process Engineering Labora-tory, State University of Campinas, Brazil) for her help with DSCanalysis.

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