Journal of Food Engineering 92 (2009) 448–453

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Journal of Food Engineering

journal homepage: www.elsevier .com/locate / j foodeng

Improved barrier and mechanical properties of novel hydroxypropylmethylcellulose edible films with chitosan/tripolyphosphate nanoparticles

Márcia R. de Moura a,d, Fauze A. Aouada a,d, Roberto J. Avena-Bustillos b, Tara H. McHugh b,John M. Krochta c, Luiz H.C. Mattoso d,*

a Chemistry Department, UFSCar, São Carlos, SP, Brazilb Agricultural Research Service, Western Regional Research Center, Albany, CA, United Statesc Department of Food Science and Technology, University of California, Davis, United Statesd National Nanotechnology Laboratory for Agriculture, EMBRAPA-CNPDIA, São Carlos, SP, Brazil

a r t i c l e i n f o

Article history:Received 20 June 2008Received in revised form 15 December 2008Accepted 18 December 2008Available online 30 December 2008

Keywords:Chitosan nanoparticlesSodium tripolyphosphateHydroxypropyl methylcelluloseEdible films

0260-8774/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.jfoodeng.2008.12.015

* Corresponding author. Tel.: +55 16 2107 2800; faE-mail address: mattoso@cnpdia.embrapa.br (L.H.C

a b s t r a c t

Chitosan/tripolyphosphate nanoparticles were prepared and incorporated in hydroxypropyl methylcellu-lose (HPMC) films. FT-IR and transmission electron microscopy (TEM) analyses of the nanoparticles,mechanical properties, water vapor permeability, thermal stability, scanning electron microscopy(SEM) of the films were analyzed. Incorporation of chitosan nanoparticles in the films improved theirmechanical and film barrier properties significantly. The chitosan nanoparticles tend to occupy the emptyspaces in the pores of the HPMC matrix, increasing the collapse of the pores and thereby improving filmtensile properties and water vapor permeability. The thermal stability of the films increased with addi-tion of nanoparticles. This study is the first to investigate the use of CS-TPP nanoparticles for the purposeof strengthening HPMC films.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

Nanotechnology research is entirely multidisciplinary and theresults of such research can be applied very quickly to improvecurrent products (Weitz et al., 2008; Clapper et al., 2008; Kow-alczyk and Holyst, 2008). Increasing consumer demands for high-quality and microbiologically safer foods, together with longerproduct shelf life, are continuously forcing researchers and theindustry to develop new food preservative strategies. To respondto this latter demand, the food industry makes use of several bio-degradable polymer-based edible films from food-grade proteins,polysaccharides, and lipids that could potentially serve as ediblepackaging materials (Olivas and Barbosa-Canovas, 2008; Sothorn-vit et al., 2007).

For the past 10 years, many research programs have focused ondeveloping more and more sophisticated edible films and coatings(Denavi et al., 2009; Sebti et al., 2007). Among them, polysaccha-ride polymers such as hydroxypropyl methylcellulose (HPMC)and chitosan (CS) have been particularly studied (Hernández-Muñoz et al., 2008; Pérez et al., 2008; Dogan and McHugh,2007). In the study by No et al. (2007) were discussed the applica-tions of chitosan for improvement of quality and shelf life of vari-

ll rights reserved.

x: +55 16 2107 2902.. Mattoso).

ous foods from agriculture, poultry, and seafood origin werefocused. However, the hydrophilic nature of such packaging mate-rials, which produces a loss of barrier properties or even a solubi-lization into foods with high-water activities, prevents theirindustrial applications (Bertuzzi et al., 2007). Villalobos et al.(2006) reported the syntheses of films with HPMC, sorbitan mon-ostearate, and sucrose palmitate. The water vapor permeability ofthese films was minimal with a hydrocolloid/surfactant ratio. Elsa-bee et al. (2008) reported the syntheses of films formulated withpolypropylene (PP) and CS/pectin. Chitosan forms complex com-pounds with pectin and this property was used to build up a stablemultilayered structure on the PP film surface, to produce a muchbetter antimicrobial film which can be used to fabricate excellentpackaging materials for post-harvest crop protection. Preparationmethods by ionically cross-linking cationic chitosan with specificpolyanions were particularly successful as, aside from its complex-ation with negatively charged polymers, CS has the ability to gelspontaneously on contact with multivalent polyanions due to theformation of inter- and intramolecular cross-linkage mediated bythese polyanions. Among some polyanions investigated, tripoly-phosphate (TPP) is the most popular because of its non-toxic prop-erty and quick gelling ability.

The CS-TPP nano system exhibits some attractive featureswhich render them promising carriers for the delivery of macro-molecules (Gan et al., 2005). The application of these nanoparticlesin edible films is very promising due to the food-grade properties

M.R. de Moura et al. / Journal of Food Engineering 92 (2009) 448–453 449

of both components. Hydroxypropyl methylcellulose films withCS-TPP nanoparticles could then be a potential material for foodpackaging applications to extent the shelf life of foods andproducts.

Research and development of bio-nanocomposite materials forfood applications, such as packaging and other food contact sur-faces is expected to grow in the next decade with the advent ofnew polymeric materials and composites with inorganic nanopar-ticles. The application of nanocomposites promises to expand theuse of edible and biodegradable films (Lagarón et al., 2005; SinhaRay and Bousmina,2005; Sorrentino et al., 2007). Some works (Ortset al., 2005; Okada and Usuki, 1995) has shown that, at relativelylow nanoparticle loadings, polymer composites are reinforced be-cause chains within these nanocomposites are restricted to con-fined domains between sheets of the films. For instance, thecombination of chain confinement, alignment of nanoparticles(i.e., nanostructure) and strong surface interaction, results inimprovements in mechanical properties, as well as in decreasesin gas and liquid permeability.

In this paper, chitosan/tripolyphosphate nanoparticles wereprepared and incorporated in hydroxypropyl methylcellulosefilms. FT-IR and transmission electron microscopy (TEM) analysesof the nanoparticles, mechanical properties, water vapor perme-ability, thermal stability, scanning electron microscopy (SEM) ofthe films were analyzed. The aim of the present study was to inves-tigate the effect of nanoparticles with chitosan on the HPMC filmsmechanical and water vapor permeability properties.

2. Materials and methods

2.1. Materials

Hydroxypropyl methylcellulose (Methocel E15) was obtainedfrom Dow Chemical Co. (Midland, MI, USA). Chitosan (MW71.3 kDa, degree of desacetylation 94%) was purchased from Poly-mar Ciência e Nutrição S/A (Fortaleza, Brazil). Sodium tripolyphos-phate was purchased from Sigma–Aldrich Chemical Co. (St. Louis,MO, USA).

2.2. Nanoparticles and film preparation

2.2.1. Preparation of chitosan-tripolyphosphate (CS-TPP)nanoparticles

The CS-TPP nanoparticles were obtained according to the pro-cedure first reported by Calvo et al. (1997), based on the ionicgelation of CS with TPP anions. Chitosan was dissolved in aceticacid solution at concentrations of 3.00 and 4.41 mg mL�1. Theconcentration of acetic acid in aqueous solution was, in all cases,1.5 times that of chitosan. Under magnetic stirring at room tem-perature, 28 mL sodium TPP aqueous solution with concentrationsof 1.2 and 2.1 mg mL�1 were added into 70 mL chitosan solution(Table 1). The preparations were mixed with a homogenizer(Polytron PT 3000 – Brinkmann) at 6000 rpm with continuousaddition of TPP solution rate of 1 mL min�1. The zone of opales-cent suspension was further examined as nanoparticles. Table 1shows the final concentrations of TPP and CS after different syn-theses processes.

Table 1Influence of chitosan and TPP concentration on the nanoparticle size.

CS concentration (mg mL�1) TPP concentration (mg mL�1) Particle size (nm)

2.14 0.3 852.14 0.6 1103.15 0.6 221

2.2.2. FT-IR analysisFT-IR spectra of CS, TPP and CS/TPP nanoparticles were taken

with a Paragon 1000 Perkin–Elmer Spectrum (Perkin–Elmer Lifeand Analytical Sciences, Inc., Waltham, MA USA) in the range from4000 to 400 cm�1. The FT-IR spectra were used to determine theexistence of TPP and CS in nanoparticles. The CS-TPP nanoparticleswere frozen by liquid nitrogen and lyophilized for 12 h, to obtaindried CS-TPP nanoparticles. Powdered samples were preparedusing KBr to form pellets.

2.2.3. Particle size distributionThe particle size distribution of solutions were measured in a

Horiba LA 900 laser light scattering particle size analyzer (HoribaInstruments Inc., Irvine, CA, USA) using laser diffraction to measureparticle size of suspensions. All analysis was performed bytriplicate.

2.2.4. Transmission electron microscopy (TEM)A Jeol 100 C (Jeol Ltd., Tokyo, Japan) transmission electron

microscope (TEM) was used to observe the morphology of thenanoparticles. CS-TPP nanoparticles solutions were sonicated for1 min to produce better particle dispersion and to prevent nano-particle agglomeration on the copper grid. One drop of the nano-particle solution was spread onto a carbon-coated copper gridwhich was then dried at room temperature for TEM analysis.

2.2.5. Preparation of solutions for film castingThe HPMC solution (control film) was obtained by dissolving

3.0 g of HPMC in 100 mL of distilled water under magnetic stirringfor 12 h. The HPMC: water ratio in all film-forming solutions was3:97 to study the effect of particle size and CS-TPP concentrationin the HPMC film matrix. The HPMC films with CS-TPP nanoparti-cles were obtained by addition of 3.0 g of HPMC in 100 mL of nano-particle solution (recently synthesized) under magnetic stirring for12 h. After the solutions were prepared, the flasks were kept closedduring 6 h to prevent microbubble formation in the films. The solu-tions were then poured in a glass plate (30 � 30 cm) covered withMylar (Polyester film, DuPont, Hopewell, Va., USA) for film castingpreparation. The solutions were cast at a wet thickness of 0.5 mmonto plates using casting bars and the plates were placed on a lev-eled surface at room temperature and let dry for 24 h. After drying,the films were removed and conditioned in sealed plastic bagsstored at room temperature.

2.3. Film characterization

2.3.1. Film thicknessFilm thickness was measured using a model 7326, digital

micrometer (Mitutoyo Manufacturing, Tokio, Japan) at 5 randompositions around the film. The mean values were used to calculatewater vapor permeability and mechanical properties.

2.3.2. Mechanical propertiesThe films were cut to have rectangular dimensions in accor-

dance to ASTM (1997). The films were conditioned at 30% RHand 23 �C for 48 h before measurements. A Model 1122 InstronUniversal Testing Machine (Instron Corp., Canton, MA, USA) wasused to determine the maximum tensile strength (TS), maximumpercentage elongation at break (%), and elastic modulus (orYoung’s modulus). Films were stretched using a speed of50 mm min�1. Tensile properties were calculated from the plot ofstress (tensile force/initial cross-sectional area) versus strain(extension as a fraction of the original length). The mechanicalproperties were analyzed as a function of CS and TPPconcentrations.

4000 3000 2000 1000 0

(C)

(B)

(A)

Tran

smitt

ance

Wavenumber (cm-1)

Fig. 2. Infrared spectra: (A) chitosan; (B) TPP; (C) CS-TPP nanoparticle.

450 M.R. de Moura et al. / Journal of Food Engineering 92 (2009) 448–453

2.3.3. Water vapor permeability (WVP)Water vapor permeability was determined by modification of

the ASTM E96-92 gravimetric method to determine the relativehumidity (RH) at the film underside according to McHugh et al.(1993). Five films were cast from each treatment, onto 15.5 cminternal diameter Teflon� plates. After drying, one sample withoutdefects was cut from each film. Distilled water (6 mL) was dis-pensed into flat-bottom Plexiglas� cups with wide rims. The filmwas sealed to the cup base with a ring using 4 screws symmetri-cally located around the cup circumference. The cups were placedin temperature-controlled cabinets at 25 �C, containing fans andheld at 0% RH using anhydrous calcium sulphate (W.A. HammondDrierite Co., Xenia, OH, USA). Weights were taken periodically aftersteady state was achieved and used to calculate the % RH at thefilm underside and the resulting WVP.

Water vapor permeability was calculated using the followingrelation:

WVP ¼ WVTRðp2 � p3Þ

y ð1Þ

where WVTR was obtained from the slope of the weight loss ratethrough the film surface and p2 was the water vapor partial pres-sure on the film underside calculated according to McHugh et al.(1993) while p3 was water vapor partial pressure at the film under-side and y was the average film thickness. Water vapor permeabilityof each film was measured as the mean and standard deviations of 5replications.

2.3.4. Thermal analysisThe thermal degradation of films was analyzed in a thermo-

gravimetric analyzer TGA-Q500 (TA Instruments, New Castle, DE,USA). The experiments were performed in the temperature range20–500 �C at a heating rate of 10 �C min�1. The nitrogen flow wasmaintained at 60 cm3 min�1. The analysis was performed intriplicate.

2.3.5. Scanning electron microscopy (SEM)A Hitachi S-4700 scanning electron microscope (Hitachi, Toron-

to, Ontario, Canada) was used to study the morphology of nanopar-ticles and films. The samples were deposited onto aluminumspecimen stubs using double-stick carbon tabs (Ted Pella Inc.,Redding, CA, USA) and coated with gold/palladium on an ion sput-ter coated (Denton Vacuum Inc., Moorestown, NJ, USA) for 45 s at20 mA. All samples were examined using an accelerating beam ata voltage of 1.5 kV. Magnifications of 40,000�; and 60,000� wereused.

Fig. 1. Molecular structure of chitosan (a) and TPP (b).

2.3.6. Statistical analysisAnalysis of variance (ANOVA) was applied using Minitab 14.2

(Minitab Inc., State College, PA, USA) to determine significance ofdifferences between means.

3. Results and discussion

3.1. FT-IR analysis

The molecular structures of chitosan and TPP are presented inFig. 1. The formation of nanoparticles is confirmed with theFT-IR spectrum showed in Fig. 2. In chitosan-TPP nanoparticles(C) the peak of 3430 cm�1 becomes wider, indicating that hydro-gen bonding is enhanced (Jia-hui et al., 1999). The peak at1530 cm�1 in the spectrum of the nanoparticles is indicative ofinteraction between NHþ3 groups of chitosan and phosphategroups of TPP. As can be seen from the IR spectrum of chitosannanoparticles, the peak indicating P@O stretching at 1219 cm�1

appear. The appearing of these peaks is an indication of nanopar-ticle formation.

3.2. Particle size distribution

Table 1 shows the influence of CS and TPP final concentrationson the size values of nanoparticles. A gradual increase in the parti-cle size was observed with increase in the CS and TPP concentra-tion. This trend may be explained by the fact that a higherweight CS is less soluble resulting in an increase in particle diam-eter or even aggregation. Nanoparticles with lowest particle size(85 nm) were obtained when the lowest CS and TPP concentrationwas used.

The effect of CS/TPP concentration on particle size was previ-ously studied. Calvo et al. (1997) reported that the particle sizeis dependent on both CS and TPP concentrations. Gan et al.(2005) further explored the difference between particles associ-ated with bovine serum albumin (BSA) protein and particle with-out BSA. BSA loading by the incorporation method significantlyincreased particle size in comparison to chitosan-TPP particles(without BSA); this fact occurs possibly due to the larger molec-ular weight and size of the protein molecule. All resulting filmswere transparent, flexible and homogeneous. Their surfaces weresmooth without pores and cracks. Flexible, transparent and sur-face smooth films were obtained after drying the film-formingsolutions containing chitosan and CS-TPP nanoparticles.

0

10

20

30

40

50

60

70

c

c

b

only HPMC without nanoparticle

221 nm110 nm85 nm

Tens

ile S

tren

gth

(MP

a)

HPMC films

a

Fig. 3. Effect of nanoparticles on tensile strength of HPMC films. Columns show themeans and error bars indicate the standard deviations. Different letters within acolumn indicated significant difference at P < 0.05.

Table 3Effect of particle size on WVP and % RH at film underside.

Particle size (nm) WVP (g mm K�1 Pa�1 h�1 m�2) RH at film underside (%)

(No nanoparticle) 0.794 ± 0.03c 78.2 ± 0.7NS

85 0.331 ± 0.06a 79.6 ± 0.3110 0.451 ± 0.05a 79.4 ± 0.5221 0.587 ± 0.05b 79.5 ± 0.9

a,b,cDifferent letters within a column indicated significant difference at P < 0.05.NS, Not significant differences between films.

M.R. de Moura et al. / Journal of Food Engineering 92 (2009) 448–453 451

3.3. Tensile properties of films

Fig. 3 shows the effect of CS/TPP nanoparticles on tensilestrength of HPMC films. There were significant differences in ten-sile strength, demonstrating that the incorporation of nanoparti-cles modified the resistance of the film. The tensile strength ofthe HPMC matrix without nanoparticle was 28.3 ± 1.0 MPa increas-ing to a maximum value of 62.6 ± 1.0 MPa when the particle sizewas reduced to a minimum value of 85 nm. Addition of nanoparti-cles resulted in a stiffer material confirming the reinforcing effectof the nanoparticle in the polymeric matrix, which is consistentwith previously results reported (Pereira de Abreu et al., 2007).This study reveals that the increased surface area of smaller sizeCS-TPP nanoparticles compared to their larger size counterparts in-creases the interaction of particles with the HPMC matrix. As thewater evaporates during film formation, the CS-TPP/HPMC com-posite network forms by the establishment of bonding. Hence,the increased surface area reinforces the structure. Second, the big-ger size particles may be disturbing the formation of HPMC filmduring drying, provoking the fragile structure in the film. Two-way ANOVA indicated that the addition of nanoparticle to HPMCfilms and its decrease of particle size increased tensile strengthof the films.

The percentage elongations also change when particle size wasdecreased as shown in Table 2. The increase of the elongation im-proved the tenacity of the films. The elastic modulus did not pres-ent significant variation with different sizes of particles, onlyincrease with addition of the nanoparticles. The elasticity of thefilms was preserved with addition of nanoparticles. In these ways,the addition of nanoparticles to HPMC films results in significantimprovements in film mechanical properties. Furthermore, theparticle size present has a tremendous influence on the final prop-

Table 2Effect of particle size on elastic modulus and % elongation of HPMC films.

Particle size (nm) Elastic modulus (MPa) Elongation (%)

(No nanoparticle) 900 ± 34a 8.1 ± 0.7b

85 1264 ± 65b 11.1 ± 1.0c

110 1190 ± 93b 5.2 ± 2.1a

221 1204 ± 64b 5.7 ± 1.0a

a,b,cDifferent letters within a column indicated significant difference at P < 0.05.

erties of the HPMC films, clearly demonstrating the reinforcing ef-fects of the nanoparticles on the films.

3.4. Water vapor permeability

Many studies in food science have been focused in studying thewater barrier properties of various edible films using proteins,polysaccharides and lipids (Hong and Krochta, 2004; Kim et al.,2003; Pérez-Gago and Krochta, 2001). The problem with compositefilms in the food industry is the relatively high-water vapor perme-ability of the edible films. Permeability in films is controlled by thediffusivity and solubility of water within the film matrix. Thususing nanoscience, new forms of tightly linked three dimensionalnetworks can be developed to prevent migration of water in foodproducts. Table 3 shows the values of water vapor permeabilityof HPMC film and nanoparticles edible films at different particlessizes. Validity of WVP comparisons is reliable when the same driv-ing force for water vapor diffusion for each film formulation is used(McHugh et al., 1993). The relative humidity at the film undersidewas not significant different (79.2 ± 0.6% RH) for the four differentfilms indicated in Table 3.

Two-way ANOVA showed that the presence of nanoparticlesin the films decreased the WVP of the HPMC films. Importantinformation is that a decrease on the particle size decreased theWVP values. This fact is very important in the nanotechnologyfield. WVP of HPMC film without nanoparticle was 0.794 g mmkPa�1 h�1 m�2. Incorporation of CS/TPP nanoparticles decreasedthe WVP of HPMC films to a considerable extent (Table 3). This de-crease could be due to the formation of hydrogen bonding betweenchitosan and the HPMC film matrix, thereby influencing water dif-fusion. The structure of films containing nanoparticles was morecompact influencing a decrease of water permeability of HPMCfilms. Nanoparticles with smaller size induced a greater decreasein WVP values. This fact occurs because small size nanoparticleshave more ability in occupying the empty spaces of the porousHPMC film matrix, what difficult the diffusion of water in the film.

In the work described by Lotti et al. (2008) was observed thatnanocomposites films (HDPE + organophilic treated clay) had a sig-nificant decrease of barrier properties (water and oxygen perme-ability) in comparison to the pure HDPE film. This trend wasattributed to the formation of water clusters (which increase thepenetrant volume) the main transport controlling mechanismcould be the diffusion through the polymer. The effectiveness ofthe reinforcing effect of nanosize microcrystalline cellulose(MCC) fillers in HPMC films was described by Dogan and McHugh(2007). In this study was shown that through the incorporation offillers such as MCC, edible film mechanical properties can be signif-icantly improved without reducing film barrier properties, espe-cially water vapor permeability (WVP). Rhim et al. (2006) studiedthe influence of the nanostructures on WVP values of the chitosanfilms. The WVP value of the chitosan film was 1.31 0.07 g mm K�1

Pa�1 h�1 m�2. Already, WVP of the nanocomposite films decreasedsignificantly (P < 0.05) by 25–30% depending on the nanoparti-cles. This is attributed to the presence of ordered dispersed nano-particle layers with large aspect ratios in the polymer matrix,

0 100 200 300 400 500 600

0

20

40

60

80

100

271 ºC (B)

232 ºC (A)

Temperature (ºC)

Mas

s Lo

ss (

%)

Fig. 4. TG scans of the HPMC film (A) and HPMC film with CS-TPP nanoparticle(110 nm) (B).

Fig. 5. Electron transmission microphotography of CS-TPP nanoparticle corre-sponds to the 3.00 mg L�1 CS and 1.2 mg L�1 TPP (85 nm) film solution.

452 M.R. de Moura et al. / Journal of Food Engineering 92 (2009) 448–453

what contributes to the water vapor traveling through the film tofollow a tortuous path through the polymer matrix surroundingthe nanoparticles, thereby increasing the effective path length fordiffusion.

3.5. Thermal degradation

Fig. 4 shows the TG scans of HPMC films and HPMC films con-tent CS-TPP nanoparticles. As the temperature is increased themass remains constant until about 232 �C for HPMC film and271 �C for HPMC film with 110 nm CS/TPP nanoparticles. Thesetemperatures correspond to the beginning of thermal degradation(TD). The thermal degradation temperature was very similar for allfilms containing nanoparticles (Table 4).

The additions of nanoparticles in HPMC films modified the ther-mal characteristic of the films. Two-way ANOVA showed that thepresence of nanoparticles in the films increased the thermal stabil-ity of the HPMC films. This fact is relevant for practical film casting.A pilot plant labcoater for edible film casting operates typically at100–132 �C to dry the film in 12 min (Du et al., 2008).

3.6. Film morphology

TEM micrograph of the CS-TPP nanoparticles prepared with a3.0 mg mL�1 of CS and 1.2 mg mL�1 of TPP solution shows distinc-tive spherical-shaped nanoparticles (Fig. 5). These nanoparticlesize values are smaller than those obtained by laser diffraction(85 nm), as expected, since TEM analyses were carried out in driednanoparticles samples, whereas the former used aqueous solutionand the nanoparticles were in swollen state. The morphology of thecomposite HPMC films containing nanoparticles (221 nm) wasanalyzed by scanning electron microscopy (SEM). Control film pre-pared from a solution containing only 3% w/v of HPMC in water(Fig. 6a), exhibited a high degree of porosity evenly distributed

Table 4Thermo-gravimetric parameters of HPMC films with nanoparticles.

Film Particle size (nm) TD (�C)

HPMC No nanoparticle 232HPMC + nanoparticle 85 279HPMC + nanoparticle 110 271HPMC + nanoparticle 221 276

throughout the film. Compaction of HPMC film was observed whenchitosan nanoparticles were added as shown in Fig. 6b. This com-pacting further decreased WVP and increased tensile properties offilms.Analysis of the morphology of films using SEM is extensivelydiscussed in literature. Xiong et al. (2008) showed that the struc-tures of films were smooth and compact and films had several dif-ferent holes, suggesting that the miscibility and compatibility in

Fig. 6. Scanning electron microphotographies of (a) HPMC films and (b) HPMC filmswith CS-TPP nanoparticles of 221 nm.

M.R. de Moura et al. / Journal of Food Engineering 92 (2009) 448–453 453

each film is different. These conclusions are taken from analyses ofSEM.

4. Conclusions

CS-TPP nanoparticles in HPMC films improved barrier andmechanical properties. From FT-IR analysis, it is proposed thatthe ionic gelation of CS with TPP anions resulting in nanoparticleformation. SEM images reveal that HPMC films become more com-pact and dense when chitosan nanoparticles were added. Therewere significant differences in tensile strength, demonstrating thatthe incorporation of nanoparticles modified the resistance of theHPMC film. The thermal degradation temperature was increasedin films containing nanoparticles from 232 �C to 271 �C. This factis important because the presence of nanoparticles in the HPMCfilms improved the thermo-stability of the films. The implicationof this finding to produce compression-molded sheets indicatesthat CS-TPP nanoparticles can be extruded into films for formationof edible or biodegradable films. These findings indicate that use ofnanotechnology can improve functionality to edible films for foodapplications.

Acknowledgements

The authors are grateful to CNPq (Processes MRM-141694/2005-0, FAA- 141695/2005-6 and PQ 307.935/2004-3), Emb-rapa-Brazil (Labex Program and MP1 Project). FINEP/LNNA(O1.06.0096.00) and USDA, ARS, WRRC for their financialssupports.

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