Chitosan Starch Composite Film Preparation 1

Industrial Crops and Products 21 (2005) 185–192

Chitosan–starch composite film: preparationand characterization�

Y.X. Xu a, K.M. Kim b, M.A. Hannaa,∗, D. Nagc

a Department of Food Science and Technology, Industrial Agricultural Products Center, University of Nebraska,208 L.W. Chase Hall, Lincoln, NE 68583-0730, USA

b Industrial Agricultural Products Center, University of Nebraska, 208 L.W. Chase Hall, Lincoln, NE 68583-0730, USAc Department of Chemistry, University of Nebraska, 824 Hamilton Hall, Lincoln, NE 68588-0304, USA

Received 27 October 2003; accepted 17 March 2004

Abstract

Chitosan film has potential applications in agriculture, food, and pharmacy. However, films made only from chitosan lackwater resistance and have poor mechanical properties. Forming miscible, biodegradable composite film from chitosan with otherhydrophilic biopolymers is an alternative. The objective of this study was to prepare chitosan/starch composite films by combiningchitosan (deacetylated degree, 90%) solution and two thermally gelatinized cornstarches (waxy starch and regular starch with 25%amylose). The film’s tensile strength (TS), elongation-at-break (E), and water vapor transmission rate (WVTR) were investigated.The possible interactions between the two major components were evaluated by X-ray diffraction and Fourier-transform infraredspectroscopy (FTIR). Regardless of starch type, both the TS andE of the composite films first increased and then decreased withstarch addition. Composite film made with regular starch showed higher TS andE than those with waxy starch. The additionof starch decreased WVTRs of the composite films. The introduction of gelatinized starch suppressed the crystalline peaks ofchitosan film. The amino group band of chitosan molecule in the FTIR spectrum shifted from 1578 cm−1 in the chitosan film to1584 cm−1 in composite films. These results indicated that there was a molecular miscibility between these two components.© 2004 Elsevier B.V. All rights reserved.

Keywords: Chitosan–starch films; Mechanical properties; Water resistance; Miscibility

� Journal Series No. 13966, Agricultural Research Division,Institute of Agriculture and Natural Resources, University ofNebraska-Lincoln. This study was conducted at the Industrial Agri-cultural Products Center, University of Nebraska, Lincoln, NE,USA.

∗ Corresponding author. Tel.:+1-402-4721634;fax: +1-402-4726338.

E-mail address: [email protected] (M.A. Hanna).

1. Introduction

In recent years, increasing interest in edible filmshas developed mainly due to concern over the dis-posal of conventional synthetic plastic materialsderived from petroleum. Degradation of plastics re-quires a long time and most of them end up over-burdening on landfill. Conversely, edible films fromrenewable agriculture products not only are degradedreadily after their disposal, but also can extend

0926-6690/$ – see front matter © 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.indcrop.2004.03.002

186 Y.X. Xu et al. / Industrial Crops and Products 21 (2005) 185–192

the food shelf-life, thus improving the quality offood.

Among various available edible film materials, con-siderable attention has been given to chitosan becauseof its unique properties. First of all, abundant commer-cial supplies are available. Chitosan is derived fromchitin, which is the second most abundant polysaccha-ride on earth next to cellulose and is available fromwaste products in the shellfish industry (Wong et al.,1992). Chitosan possesses repeating units of 1,4 linked2-deoxy-2-aminoglucose. The amino group NH2 canbe protonated to NH3+ and readily form electrostaticinteractions with anionic groups in an acid environ-ment. This property has been applied on edible films.Systematic investigations have been reported on theeffects of factors such as plasticizers concentrations,storage time (Butler et al., 1996), acid types and con-centrations (Caner et al., 1998), molecular weights ofchitosan (Park et al., 2002), and the degree of deacety-lation of chitosan(Wiles et al., 2000) on the mehan-ical properties and barrier characteristics of chitosanfilms. Although chitosan films are highly imperme-able to oxygen, they have relatively poor water vaporbarrier characteristics (Butler et al., 1996). Plasticizershave negative effects on barrier properties and posi-tive effects on mechanical properties. The functionalproperties of chitosan films are improved when chi-tosan is combined with other film-forming materials.Hoagland and Parris (1996)prepared chitosan-pectinlaminated films by interacting the cationic groups onchitosan with the anionic groups on pectin.Hosokawaet al. (1990)reported that when biodegradable filmswere made from chitosan and homogenized celluloseoxidized with ozone the number of carbonyl and car-boxyl groups on the cellulose interacting with theamino groups on the chitosan increased. The water re-sistance of chitosan film was ameliorated by the incor-poration of hydrophobic materials such as fatty acidsto enhance the film’s hydrophobicity (Wong et al.,1992).

Starch has been used to produce biodegradable filmsto partially or entirely replace plastic polymers be-cause of its low cost and renewability. However, wideapplication of starch film is limited by its water sol-ubility and brittleness (Wu and Zhang, 2001). In or-der to overcome these shortcomings,Jagannath et al.(2003) blended starch with different proteins to de-crease the water vapor permeability of the films and

to increase their tensile strength (TS). The objectiveof this study was to prepare composite films from chi-tosan and starch and to evaluate their mechanical prop-erties, water resistance, and compatibility.

2. Materials and methods

2.1. Film preparation

Chitosan solutions (2%, w/v) were prepared by dis-persing 10 g of chitosan (deacetylated degree of 90%;Vanson, Redmond, WA) in 500 ml of lactic acid solu-tion (1%, v/v). After the chitosan was dissolved com-pletely, the solutions were filtered with cheesecloth byvacuum aspiration. Starch solutions with concentra-tions of 1, 2, 3 and 4% (w/v) were prepared by dispers-ing 25% amylose cornstarch or waxy starch (Ameri-can Maize Products Co., Hammond, IN) in distilledwater and heating the mixtures on hotplates with stir-ring until it gelatinized, and then cooling to 25◦C.A series of chitosan/starch composite films were pre-pared by mixing 100 ml of 2% chitosan solution with100 ml of 1, 2, 3, 4% starch solutions. Glycerin wasadded as 25% (w/w) of the total solid weight in solu-tion. The blend compositions are given inTable 1. Themixtures were cast onto flat, level Teflon-coated glassplates. After drying the films at room temperature forat least 72 h, they were peeled from the plates. Driedfilms were conditioned at 50% RH and 25◦C for 48 hprior to testing.

2.2. Thickness

Film thickness was measured to the nearest 2.54�m(0.1 ml) with a hand-held micrometer (B.C. Ames

Table 1Compositions of chitosan/starch blends

Starch tochitosanratio (g)

Compositions

Chitosan solution(2%, w/v) (ml)

Starch solution(w/v) (ml)

Glycerin(g)

0 200 0 1.000.5:1 100 100 of 1% 0.751:1 100 100 of 2% 1.001.5:1 100 100 of 3% 1.252:1 100 100 of 4% 1.50

Y.X. Xu et al. / Industrial Crops and Products 21 (2005) 185–192 187

Co., Waltham, MA). Five thickness measurementswere taken along the length of each specimen andthe mean was used in calculating the film tensilestrength.

2.3. Mechanical properties

Mechanical properties of TS andE were measuredwith an Instron Universal Testing Machine (Model5566, Instron Corp., Canton, MA) following the guide-lines of ASTM Standard Method D 882-91 (1995a).The initial grip separation was set at 50 mm and thecrosshead speed was set at 500 mm/min. TS was ex-pressed in MPa and calculated by dividing the maxi-mum load (N) by the initial cross-sectional area (m2)of the specimen.E was calculated as the ratio of thefinal length at the point of sample rupture to the ini-tial length of a specimen (50 mm) and expressed as apercentage. TS andE tests were replicated five timesfor each type of film.

2.4. Water vapor transmission rate (WVTR)

Five film specimens were tested for each typeof film. WVTR (g/m2 h) was determined gravi-metrically using a modification ofASTM MethodE 96-95 (1995b)described byGennadios et al. (1994,1996). Film specimens were mounted on polymethyl-methacrylate cups contaning 16 ml of distilled water.The cups were placed in an environmental chamberat 25◦C and 50% RH. A fan in the chamber wasused to move the air at a velocity of approximately200 m/min over the surface of the films to removethe permeating water vapor. The weights of the cupswere recorded every hour for a total of 6 h. Linearregression was used to estimate the slope of this linein g/h.

2.5. X-ray diffraction

X-ray patterns of chitosan, starch powders, andchitosan/starch composite films were analyzed usingan X-ray diffractometer (Rigaku D/Max-B, Tokyo,Japan) with Cu K� radiation at a voltage of 40 kVand 30 mA. The samples were scanned between2θ = 3–40◦ with a scanning speed of 2◦ min−1. Priorto testing, the samples were dried and stored in adesiccator.

2.6. Fourier transform infrared (FTIR)

FTIR spectra of the films were recorded using anattenuated total reflection (ATR) method in IR spec-tometer (Nicolet Avatar 360, Madison, WI). The thinfilms were applied directly onto the ZnSe ATR cell.For each spectrum, 128 consecutive scans at 4 cm−1

resolutions were averaged.

3. Results and discussions

3.1. Mechanical properties

3.1.1. Tensile strength (TS)The TS values of the chitosan/starch composite

films with the different starch ratios are shown inFig. 1a. It was found that, no matter which type starchwas present, the TS values of the composite films firstincreased with the addition of starch, passing througha maximum at 40.25 MPa for those with regular starchand 33.69 MPa for those with waxy starch. Both max-imums occurred at the starch to chitsan ratio of 1:1.The TS then decreased with further increase in thestarch to chitosan ratio up to 2:1. The increasing TSvalues of the composite films, with the starch to chi-tosan ratio increasing from 0 to 1:1, are attributableto the formation of inter-molecular hydrogen bondsbetween NH3+ of the chitosan backbone and OH−of the starch. The amino groups (NH2) of the chi-tosan were protonated to NH3

+ in the lactic acidsolvent, whereas the ordered crystalline structuresof the starch molecules were destroyed with gela-tinization, resulting in the OH groups being exposedto readily form hydrogen bonds with NH3+ of thechitosan. The number of hydroxyl groups increasedwith increasing starch ratio in the film-formingsolution.

Based on the data set, the starch to chitosan ratioof 1:1 was the critical value for the TS value of thecomposite films and indicated the greatest integrity ofthe two main film-forming components. At the higherstarch to chitosan ratios, the TS of the composite filmsdecreased abruptly. The decrease in TS with increasingstarch ratio may occur because starch intra-molecularhydrogen bonds rather than inter-molecular hydrogenbonds are formed, resulting in a phase separation be-tween the two main components.


Ten

sile

str

engt

h (M

Pa)

5

10

15

20

25

30

35

40

45

Elo

ngat

ion

(%)

10

20

30

40

50

60

70

Ratio g starch : chitosan

0.0 0.5 1.0 1.5 2.0

40

45

50

55

60

Wat

er v

apor

tran

smis

sion

rat

e (g

/m2.

h)

(a)

(b)

(c)

Fig. 1. Effects of starch ratios on (a) tensile strengths (TS), (b) elongation-at-breaks (E), and (c) water vapor transmission rates (WVTR)of the composite films (solid symbol denotes regular cornstarch (∼25% amylose) and open symbol denotes waxy cornstarch (∼100%amylopectin)).


Furthermore, the regular starch composite filmsshowed higher TS than the waxy starch films becauseof differences in the compositions of the two starches.Regular starch contains about 25% amylose, whereaswaxy starch contains almost 100% amylopectin. Am-lyose consists of�-1,4-glucopyranose, which is along linear polymer that can readily align closely orassociate with similar linear chitosan molecules toform the inter-molecular hydrogen bonds. Conversely,steric hindrance in the highly branched amylopectin,comprised of both�-1,4 and �-1,6-glucopyranose,decreases the possibility of forming hydrogen bonds(FTNS, 1997).

3.1.2. Elongation-at-break (E)The E values of the composite films were affected

by the starch to chitosan ratios (Fig. 1b). The averageE values of the composite films behaved similar to theTS values, increasing from 33.3% for chitosan film toa maximum of 61.1% for the regular starch film, and58.9% for the waxy starch film. The maximum oc-curred at the starch to chitosan ratio of 1.5:1. However,when the ratio was increased further to 2:1, theE val-ues suddenly decreased to 27.9% for the regular starchand 44.7% for the waxy starch film. Starch films aretypically very brittle. The addition of too much starchlowered the flexibility of the film.

3.2. Water vapor transmission rate (WVTR)

The WVTR values of the composite films as a func-tion of starch ratio in the film-forming solutions areshown inFig. 1c. The WVTR maximum occurred atthe starch to chitosan ratio of 0.5:1, and then decreasedwith the addition of starch. When the ratio was 2:1,the WVTR was 46.45 g/m2 h for the regular starchcomposite film and 47.83 g/m2 h for the waxy starchfilm. Pure chitosan film had a WVTR of 52.73 g/m2 h.Low WVTR widens the application of the compositepackaging film, especially in a highly humid environ-ment. A tough film, resulting from the interactions be-tween chitosan and starch molecules, prevented watermolecules from diffusing through the films, thus re-ducing the WVTR values.

The composite films with regular starch had alower WVTR than those with waxy starch. The dif-ferent compositions of these two starches along withthe different interaction intensity between starch and

chitosan were responsible for the differences. In spiteof having an interaction between the two main com-ponents, the intensity of non-thermal mixing waslower than that obtained by intensive thermal mixing(Jagannath et al., 2003). The cross-linking causedby thermal mixing transformed the hydrophilic–hydrophilic blend into a more hydrophobic one, thusresulting in a five- to six-fold decrease in the WVTRof the film.

The preceding discussions focused on the changesin the mechanical properties and water resistance ofchitosan/starch composite films. The addition of starchis assumed to cause hydrogen bond formation betweenthe two main components. In the following sections,we identify whether interactions existed between chi-tosan and starch molecules by X-ray diffraction andFTIR spectroscopy.

3.3. X-ray diffraction

X-ray diffractograms of chitosan/starch compositefilms are shown inFig. 2a and b. As observed, the chi-tosan powder was in a crystalline state because twomain diffraction peaks (2θ = 11.6 and 20.25◦) wereobserved in its X-ray diffraction pattern. This agreeswith the finding ofNunthanid et al. (2001). After mak-ing the films, two crystalline peaks still existed, butthe intensities were less. Moreover, native cornstarchhas a typical A-type crystalline structure (Kim et al.,2003). The dried regular starch films and waxy starchfilm, after gelatinization, had different structures. Thecrystalline structure still existed in the regular starchfilm, whereas an amorphous state was observed in thewaxy starch film.

When these two film-forming components weremixed at a starch to chitosan ratio of 0.5:1, two chi-tosan peaks still were observed for the low ratio,indicating that chitosan structure was not influencedby the addition of a small amount of starch. How-ever, the crystalline peaks of the chitosan were sup-pressed when the starch ratio in the composite filmwas increased. In its place, a new broad amorphouspeak, with greater intensity was observed, demon-strating an interaction between these two components(Yin et al., 1999). Interestingly, one chitosan peakreappeared in the chitosan/regular starch compositefilm when the ratio of starch to chitosan was 2:1.Reappearance of this peak suggests that there was a


Fig. 2. X-ray patterns for (a) chitosan/regular starch composite films and (b) chitosan/waxy starch composite films.

phase separation between the two main componentsof the composite films. This was consistent with theresults of the TS andE values as both decreasednoticeably at the highest starch ratio due to phaseseparation.

3.4. FTIR spectroscopy

FTIR spectroscopy was used to examine the interac-tions between chitosan and starch. The infrared spec-tra of chitosan, starch, and chitosan/starch compositefilm are presented inFig. 3. The chitosan spectrumwas similar to previous reports (Nunthanid et al., 2001;Ritthidej et al., 2002). The broad band at 3351 cm−1

was the OH stretching, which overlaps the NH stretch-ing in the same region. The band at 1578 cm−1 was theNH bending (amide II). A small peak near 1655 cm−1

was due to the C=O stretching (amide I), and a peak at1741 cm−1 suggested the presence of a carbonyl groupin the film. In the spectrum for starch film, the broad

band at 3413 cm−1 was the OH stretching. The peak at2929 cm−1 corresponded to the C–H stretching, whilethe bands at 1648 cm−1 and 1458 cm−1 were assignedto theδ(O–H) bendings of water and CH2, respectively(Mano et al., 2003). The bands from 763 to 1136 cm−1

corresponded to the C–O bond stretching.When two or more substances are mixed, physi-

cal blends versus chemical interactions are reflectedby changes in characteristic spectra peaks (Guanet al., 1998; Yin et al., 1999). In the typical spec-trum of chitosan/starch composite film, the aminopeak of chitosan shifted from 1578 to 1584 cm−1

with the addition of starch. This result indicatedthat interactions were present between the hydroxylgroups of starch and the amino groups of chitosan(Meenakshi et al., 2002). This is consistent with ourother results. In our case, the peak of the hydroxylgroups could not be used to evaluate the interactionsbecause of the effects of content of glycerin andwater.


Wavenumbers (cm -1)

050010001500200025003000350040004500

Tra

nsm

itta

nce

(%

)

33512923

1741

1655 1578

34132929

1648 14581136

763

3314

2923

1584

chitosan

starch

chi tosan-starch

Fig. 3. Attenuated total reflection (ATR) spectra of chitosan film, starch film, and typical chitosan/regular starch composite film with theratio of starch to chitosan of 1:1.

4. Conclusion

Chitosan/starch composite films were made fromblends of either regular or waxy corn starch andchitosan. The composite films had increasing tensilestrengths and elongation-at-breaks, and decreasingwater vapor transmission rates with increasing starchto chitosan ratios. X-ray diffraction and FTIR spec-troscopy were used to evaluate the interaction betweenstarch and chitosan molecules. For the X-ray diffrac-tion pattern, the crystalline structure of chitosan wasdepressed with the addition of the gelatinized starchand a broad amorphous peak appeared. The aminogroup peak in IR spectrum of chitosan moleculeshifted from 1578 to 1584 cm−1 with the incorpora-tion of starch. These results suggested that these twofilm-forming components were compatible and aninteraction existed between them.

Acknowledgements

The authors thank Sara Basiaga, Chemistry Depart-ment, University of Nebraska for her assistance withthe FTIR measurements. We also thank Mr. BrianJones of the Physics Department for the use of X-raydiffractometer.

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Chitosan Starch Composite Film Preparation 1