RESEARCH ARTICLE Open Access Effect Of Carboxymethyl .
COREMetadata, citation and similar papers at core.ac.ukProvided by Springer - Publisher ConnectorTongdeesoontorn et al. Chemistry Central Journal 2011, /6RESEARCH ARTICLEOpen AccessEffect of carboxymethyl cellulose concentrationon physical properties of biodegradable cassavastarch-based filmsWirongrong Tongdeesoontorn1, Lisa J Mauer2, Sasitorn Wongruong3, Pensiri Sriburi4, Pornchai Rachtanapun5,6*AbstractBackground: Cassava starch, the economically important agricultural commodity in Thailand, can readily be castinto films. However, the cassava starch film is brittle and weak, leading to inadequate mechanical properties. Theproperties of starch film can be improved by adding plasticizers and blending with the other biopolymers.Results: Cassava starch (5%w/v) based films plasticized with glycerol (30 g/100 g starch) were characterized withrespect to the effect of carboxymethyl cellulose (CMC) concentrations (0, 10, 20, 30 and 40%w/w total solid) andrelative humidity (34 and 54%RH) on the mechanical properties of the films. Additionally, intermolecularinteractions were determined by Fourier transform infrared spectroscopy (FT-IR), melting temperature by differentialscanning calorimetry (DSC), and morphology by scanning electron microscopy (SEM). Water solubility of the filmswas also determined. Increasing concentration of CMC increased tensile strength, reduced elongation at break, anddecreased water solubility of the blended films. FT-IR spectra indicated intermolecular interactions between cassavastarch and CMC in blended films by shifting of carboxyl (C O) and OH groups. DSC thermograms and SEMmicrographs confirmed homogeneity of cassava starch-CMC films.Conclusion: The addition of CMC to the cassava starch films increased tensile strength and reduced elongation atbreak of the blended films. This was ascribed to the good interaction between cassava starch and CMC. Cassavastarch-CMC composite films have the potential to replace conventional packaging, and the films developed in thiswork are suggested to be suitable for low moisture food and pharmaceutical products.BackgroundThe development of biopolymer-based edible filmscould replace the use of some petrochemicals in thefood packaging industry and reduce the negative environmental impact associated with packages from nonrenewable and non-recyclable resources. Edible films aregenerally produced from renewable natural and abundant biodegradable polymeric materials such as polysaccharides, proteins, lipids, or the combination of thesecomponents. Some edible films and coatings have beenwidely used for fresh fruits, vegetables, confectioneries,frozen foods, and meat products [1]. However, manyedible films have limitations in mechanical or barrierproperties or are prohibitively expensive. Starch films* Correspondence: p.rachta@chiangmai.ac.th5Division of Packaging Technology, Faculty of Agro-Industry, Chiang MaiUniversity, Chiang Mai 50100, ThailandFull list of author information is available at the end of the article 2011 Rachtanapun et aloften have good barrier properties to oxygen, carbondioxide, and lipids and can protect products from lipidoxidation [2]. Films from polysaccharides are also stronger and more extensible than proteinaceous films [3].Cassava (Manihot esculenta crantz) or tapioca is oneof the economically important crops in Thailand and isthe cheapest raw material for starch production. Structurally, cassava starch consists of 17% amylose content,and this is responsible for its strong film-forming characteristics [4]. Cassava starch can readily be cast intofilms. However, the cassava starch film is brittle andweak, leading to inadequate mechanical properties.Overcoming the brittleness of the film can be accomplished by adding plasticizers [5]. Common plasticizersused in the production of starch films are water,glycerol, sorbitol, and other low-molecular weight polyhydroxy compounds [6]. Glycerol and sorbitol arewidely used as plasticizers because of their stability and
Tongdeesoontorn et al. Chemistry Central Journal 2011, /6edibility. The addition of plasticizers makes the brittlefilms more flexible, but also less strong [5] and resultsin higher moisture permeability [7]. This problem mustbe addressed to improve the functional properties ofcassava starch films. Blending [8] or laminating [9] withother polysaccharide materials could improve cassavastarch film mechanical functionality. Carboxymethyl cellulose (CMC), xanthan, guar, and arabic gum, which arewater-soluble heteropolysaccharides with high molecularweights, are often used together with starches to providedesirable texture, control moisture and water mobility,and improve overall product quality and/or stability[10]. CMC is an anionic linear polysaccharide derivedfrom cellulose. It is an important industrial polymerwith a wide range of applications in flocculation, drugreduction, detergents, textiles, papers, foods, and drugs[11]. CMC is used primarily because it has high viscosity, is non-toxic, and is non-allergenic. The numeroushydroxyl and carboxylic groups in CMC enable waterbinding and moisture sorption properties. CMC hydrogel has a high water content, good biodegradability, anda wide range of applications due to its low cost [12].Because of its polymeric structure and high molecularweight, it can be used as a filler in biocomposite films[13]. CMC is able to improve the mechanical and barrier properties of pea starch-based films [14].Some edible films based on mixtures of multiple polysaccharides such as starch-methylcellulose [15], pullulan-starch [16], chitosan-starch and chitosan-pullulan[17], CMC-rice starch [10], and CMC-pea starch [14]have been investigated. These publications demonstratedthat homogeneous structures containing a single-phaseof polymeric complexes have been obtained. Dependingon the interactions between components, these formulascan improve the mechanical and moisture barrier properties of the edible films in some cases. In a previousstudy [18], water vapor permeability and moisture sorption isotherms of cassava starch based films blendedwith CMC were studied. The addition of CMC to cassava starch films had no effect on the WVPs of all filmstested (WVP ranged from 0.05 to 0.10 and 0.2 to 0.3 gmm/day m2 mmHg at 33% and 54% RH, respectively),but moisture sorption of cassava starch based filmsincreased with increasing CMC contents. It was suggested that the cassava starch based films with and without CMC had potential for use as biodegradable andedible packaging due to the moderate WVP. However,the mechanical properties of biodegradable films arealso important for their applications. There is no dataavailable about the physical properties of cassava starchfilms blended with CMC, thus the objective of thisstudy was to determine the effect of CMC concentrationon mechanical and physical properties of cassava starchbased films.Page 2 of 8Results and discussionThe influence of CMC concentrations on properties ofcassava starch based films was analyzed in terms ofFT-IR spectra, mechanical properties of the films, watersolubility, DSC thermograms, and film morphology asreported below. All the cassava starch films with andwithout CMC appeared smooth, clear, and transparent.Film thickness ranged from 120-160 μm.The FT-IR spectrum of a cassava starch film (withoutCMC) is shown in Figure 1a. A broad absorption bandat 3268 is evident, due to the stretching frequency ofthe -OH group, and a band at 2920 cm-1 attributable toC-H stretching vibration [11]. The presence of a strongabsorption band at 1648 cm-1 confirms the presence ofwater. The bands around 1413 and 1337 cm -1 areassigned to -CH2 bending in plane and C-OH bendingvibration, respectively. The band at 1149 cm-1 is due toC-O-C antisymmetric bridge stretching [19].The FT-IR spectrum of a CMC film is shown inFigure 1f. The broad absorption band at 3260 cm-1 isdue to the stretching frequency of the -COO group [20]which overlaps with the -OH stretching region at 34803440 cm -1 . The band at 2876 cm -1 is due to the C-HFigure 1 FT-IR spectra of cassava starch film with and withoutCMC. (a) cassava starch film (control); (b) cassava starch-10% CMCfilm; (c) cassava starch-20% CMC film; (d) cassava starch-30% CMCfilm; (e) cassava starch-40% CMC film; and (f) CMC film.
Tongdeesoontorn et al. Chemistry Central Journal 2011, /6stretching vibration. The bands around 1412 and 1319cm-1 are assigned to -CH2 scissoring and -OH bendingvibration, respectively. The band at 1060 cm-1 is due toCH-O-CH 2 stretching [11]. Spectra of CMC filmsshowed peaks around 1592 cm-1 , attributable to antisymmetric vibration of COO- groups [21,22].Adding a range of CMC concentrations to cassavastarch films resulted in similar characteristics in theFT-IR spectra (Figures 1b, c, d and 1e). Blending CMCwith cassava starch caused minimal shifting butincreased absorption in the COO - band around 1592cm-1 in cassava starch films containing 10, 20, 30 and40% CMC, respectively. This indicated that the antisymmetric and symmetric vibrations of C O and C-Obonds were enhanced, probably due to the disruption ofintermolecular H-bonds between carboxylic groupscaused by added starch [23]. The symmetric COO stretching was found at 1411 cm-1 in all film samples.The water absorption band of cassava starch at 1648cm -1 disappeared upon addition of CMC. The broadband located around 3270 cm -1 appeared in all filmsand was caused by O-H stretching and intermolecular/intramolecular hydrogen bonds [23,24]. The O-H bandof CMC and cassava starch occurred at 3267 and 3261,respectively. By blending cassava starch with CMC, theO-H band of films shifted to 3265-3272 cm-1. The bandof C-OH bending of cassava starch film that appeared at1337 cm -1 was shifted to 1322-1333 cm -1 with CMCaddition. Xu et al. [25] reported that the ester bondswere mostly formed between the hydroxyl groups inamylopectin branches of starch and carboxylic acidgroups of CMC, forming a stable cross-linked structure.This is likely what occurred in the composite cassavastarch CMC films studied here. These results were correlated with FT-IR spectra of rice flour-CMC blendedfilm [10], chitosan-cassava starch-gelatin films [26], andcorn starch-CMC-nanoclay biocomposite films [13].The effects of CMC concentration and % relativehumidity (RH) on tensile strength and elongation at breakof cassava starch based films are shown in Figure 2. It wasobvious that the tensile strength and elongation at breakwere strongly influenced by the concentration of CMC inboth 34 and 54% RH conditions.The tensile strength and elongation at break of cassavastarch based films were inversely related. At 34% RH,cassava starch based films containing CMC had significantly higher tensile strength but lower elongation atbreak than control films (cassava starch film withoutCMC). As the concentration of CMC increased, the tensile strengths of films significantly increased but theelongations at break significantly decreased. Theseresults were consistent with corn starch films [27] andpea starch films [14] which had improved tensilestrength as the concentration of added CMC increased.Page 3 of 8Figure 2 Effect of CMC concentrations on mechanicalproperties of the films. (a) tensile strength and (b) elongation atbreak of cassava based films at 34 and 54% RH.The increasing tensile strength of the cassava starchfilms with increasing concentrations of CMC is likelyattributable to the formation of intermolecular interaction between the hydroxyl group of starch and carboxylgroup of CMC [10]. During the processing and dryingof the composite films, the original hydrogen bondsformed between starch molecules could be replaced bynew hydrogen bonds formed between the hydroxylgroups in starch molecules and the hydroxyl andcarboxyl groups in CMC [13]. Intermolecular interactionbetween starch and CMC resulted in more compactmolecule structure of starch-CMC mixture, and tensilestrength was therefore increased [10]. This finding corroborates the FT-IR results reported above. Theseresults are similar to reports of the tensile strength ofchitosan-starch films [25], rice starch-CMC film [10],and corn starch-CMC-nanoclay films [13]. At 54% RH,the tensile strength of all films decreased but % elongation increased when compared with the films at 34%RH. Gennadios et al. [28] reported that films with
Tongdeesoontorn et al. Chemistry Central Journal 2011, /6higher elongation values usually require a lower load tocause film breakage. These results could be related tostructural modification of the starch network by waterwhich causes a greater flexibility in polymer structure.At 54% RH, increasing CMC concentration in the cassava starch films improved the tensile strength butreduced the elongation at break. This result agreed witheffect of humidity on tensile strength and % elongationof blended chitosan-methylcellulose films [29].Solubility in water is an important property of starchbased films. Potential applications may require waterinsolubility to enhance product integrity, moisture barrier properties, and shelf-life. However, in other casesthe water solubility of films before product consumptionmight be useful, such as for the encapsulation of foodingredients or additives [30].The water solubility of cassava starch film blendsdepended on the CMC concentration (Figure 3). Thewater solubility of the control cassava starch film wasabout 73%, and film solubility decreased with theincrease of CMC concentration. This result was similarto the water solubility of rice starch-CMC films [10],corn starch-CMC films [27] and corn starch-CMCnanoclay films [13]. The decreased solubility indicatedthat intermolecular interaction occurred between starchand CMC in the cassava starch-CMC films [10]. Thehydroxyl group and carboxyl group of CMC can formstrong hydrogen bonds [27,13] and ester bonds [10],respectively, with the hydroxyl groups on starch, thusimproving the interactions between molecules, improving the cohesiveness of the biopolymer matrix, anddecreasing the water solubility [13]. The intermolecularinteraction level depended on the amount of CMC andstarch [10]. Besides the intermolecular interaction thatPage 4 of 8occurred between starch and CMC, the decrease inwater solubility as a function of CMC concentrationcould be due to the reduction of the starch concentration itself (as shown in Table 1) in the blended films.The melting temperature (Tm) and total heat of fusion(ΔHf) of cassava starch films with and without CMC arepresented in Table 2. DSC thermograms of cassava starchfilm, the blended films, and CMC film are shown inFigure 4. Thermograms of the films blended with CMC(Figure 4b) exhibited a single sharp endothermic peak,which indicated homogeneity of the films. This endothermic peak has been associated with the melting of crystalline starch domains reorganized during retrogradation [13].This result agreed with DSC thermograms of pea starchCMC films [14] and corn starch-CMC-nanoclay films [13].The melting temperature (Tm) of cassava starch filmsblended with CMC were lower than the T m of cassavastarch films but higher than the Tm of CMC films (exceptfor the film with 40% CMC). The Tm of film blends shifteddue to the interaction of the two biopolymers [31]. Thearea under the endothermic peak expressed the total heatof fusion of the films [32,33], which increased withincreasing CMC concentrations in cassava starch films.The increased heat of fusion should be the effect of highercrystallization because of the high degree of crystallinity ofCMC [34]. The total heat of fusion of blended films waslower than for CMC alone, likely because the interactionbetween cassava starch and CMC molecules interruptedthe rearrangement of polymer chains [33]. Gimeno et al.[34] found that a higher interaction of hydrocolloids andstarch retained more water molecules, causing a highermobility during heating, increasing the kinetic energy, anddecreasing the enthalpy value (ΔH). These results weresimilar to DSC thermograms of HDPE/PP blends [32] andchitosan-MC films with vanillin [33].Scanning electron micrographs of cassava starch filmswith and without CMC were observed (Figure 5). All samples presented smooth and compact surface structures.Micrographs of cryogenic fracture surfaces of cassavastarch film, cassava starch film with 30% CMC, and CMCfilm obtained by SEM are shown in Figures 5a, b and 5c,respectively. They showed a dense and smooth crossTable 1 Composition of CMC/cassava starch in 100 mlfilm va starchFigure 3 Effect of CMC concentration on cassava starch-CMCblended film solubility at 25 C.Composition (g/100 ml water)
Tongdeesoontorn et al. Chemistry Central Journal 2011, /6Table 2 Melting temperature and heat of fusion ofcassava starch film without and with CMCFilm samplesCassava starch: CMC (100:0)Cassava starch: CMC (90:10)Cassava starch: CMC (80:20)Tm starch-CMC Heat of fusion (ΔHf) offilm ( C)starch-CMC film (J/g)165.46a135.34aa, b91.98ba, b92.07bb147.20144.53Cassava starch: CMC (70:30)Cassava starch: CMC (60:40)128.2696.62c160.10a, c173.26cCassava starch: CMC (0:100)102.46c212.98dDifferent letters in the same column indicate significant differences betweenthe means obtained in Duncan’s test (p 0.05).section that indicated homogeneous structure. This resultwas similar to the surface and cross-section morphologiesof cassava starch-gum films [35] and pullulan/alginate/CMC film [23].ConclusionsThe effects of CMC concentrations and relative humidityon physical properties of cassava starch based films werestudied. The addition of CMC to the cassava starch filmsincreased tensile strength and reduced elongation atbreak of the blended films. This was ascribed to the goodinteraction between cassava starch and CMC. FT-IRPage 5 of 8spectra indicated intermolecular interactions betweencassava starch-CMC film blends by shifting of carboxyl(C O) and OH groups. The thermogram of film blendsalso confirmed chemical interaction of cassava starchCMC as ΔH decreases. The homogeneity of cassavastarch-CMC films was represented as a single meltingpeak, and SEM micrographs visibly confirmed the homogeneous structure of cassava starch-CMC films. All filmsstored at 54% RH gave higher elongation but lower tensile strength than films at 34% RH. Increasing CMC concentrations in the cassava starch film decreased watersolubility of the blended films. Films containing 30%CMC had better physical properties (high tensilestrength, moderate elongation and low water solubility)than the other films. Thus, it seems that the CMC-starchbiocomposite films show better physical properties thancassava starch films alone, and cassava starch-CMC composite films have the potential to be used as edible andbiodegradable films for low and intermediate moistureproducts.ExperimentalMaterialsCassava starch (Bangkok Inter Food Co., LTD., Thailand)and glycerol (EM Science, Germany) were employed toFigure 4 DSC thermograms of cassava starch film, blended film and CMC film. (a) cassava starch film (control); (b) cassava starch-30% CMCfilm; and (c) CMC film.
Tongdeesoontorn et al. Chemistry Central Journal 2011, /6Page 6 of 8produce the films. CMC was donated from Akzo Nobel(Netherlands).Cassava starch-CMC film preparationSolutions used to prepare films (5% w solid/v) were prepared by dispersing cassava starch and CMC at differentconcentrations in distilled water (Table 1). Glycerol (30%w/w solid) was added as the plasticizer. The film solutionswere heated to 80 C with constant stirring to obtain starchgelatinization. Then the
the mechanical properties of biodegradable films are also important for their applications. There is no data available about the physical properties of cassava starch films blended with CMC, thus the objective of this study was to determine the effect of CMC concentration on mechanical and physical properties of cassava starch based films.
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