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Properties of Novel Hydroxypropyl Methylcellulose Films Containing Chitosan Nanoparticles M.R. DE MOURA, R.J. AVENA-BUSTILLOS, T.H. MCHUGH, J.M. KROCHTA, AND L.H.C. MATTOSO
ABSTRACT: In this study, chitosan nanoparticles were prepared and incorporated in hydroxypropyl methylcellulose (HPMC) films under different conditions. Mechanical properties, water vapor and oxygen permeability, water solubility, and scanning and transmission electron microscopy (SEM and TEM) results were analyzed. Incorporation of chitosan nanoparticles in the films improved their mechanical properties significantly, while also improving film barrier properties significantly. The chitosan poly(methacrylic acid) (CS-PMAA) nanoparticles tend to occupy the empty spaces in the pores of the HPMC matrix, inducing the collapse of the pores and thereby improving film tensile and barrier properties. This study is the first to investigate the use of nanoparticles for the purpose of strengthening HPMC films. Keywords: chitosan nanoparticles, hydroxypropyl methylcellulose, packaging, tensile strength, water vapor permeability
MS 20080216 Submitted 3/25/2008, Accepted 6/12/2008. Author de Moura is with Chemistry Dept. of UFSCar, S˜ao Carlos/SP, Brazil. Authors AvenaBustillos and McHugh are with Agricultural Research Service, Western Regional Research Center, Albany, CA, U.S.A. Author Krochta is with Dept. of Food Science and Technology, Univ. of California, Davis, CA, U.S.A. Authors de Moura and Mattoso are with Natl. Nanotechnology Lab. for Agriculture, EMBRAPA-CNPDIA, S˜ao Carlos/SP, Brazil. Direct inquiries to author Mattoso (E-mail:
[email protected]). R Institute of Food Technologists doi: 10.1111/j.1750-3841.2008.00872.x
C 2008
Further reproduction without permission is prohibited
and others 2007). However, cellulose films are poor water vapor barriers because of the inherent hydrophilic nature of polysaccharides. In addition, they possess poor mechanical properties (Moller and others 2004). The aim of the present study was to study the effect of addition of nanoparticles made using chitosan on the mechanical and water vapor and oxygen permeability properties of HPMC films. Different sizes and concentrations of nanoparticles were investigated to optimize the performance of the composites obtained.
Materials and Methods Materials HPMC (Methocel E15) was obtained from Dow Chemical Co. (Midland, Mich., U.S.A.). Chitosan (CS) (MW 71.3 kDa, degree of desacetylation 94%) was purchased from Polymar Ciˆencia e Nutric¸a˜ o S/A, Brazil. Potassium persulfate (K 2 S 2 O 8 ) and methacrylic acid (MAA) were purchased from Aldrich Co. (St. Louis, Mo., U.S.A.). All chemicals were used as received.
Film preparation Preparation of CS-PMAA nanoparticles. CS-poly(methacrylic acid) (CS-PMAA) nanoparticles were obtained by polymerization of MAA in a CS solution by a 2-step process, described in detail in the literature (Moura and others 2008), which is summarized here. In the 1st step, chitosan was dissolved in methacrylic acid aqueous solution (0.5 in v%) for 12 h under magnetic stirring. Three CS concentrations were used (0.2, 0.5, and 0.8 in wt%), which led to different nanoparticles sizes. In the 2nd step, 0.2 mmol of K 2 S 2 O 8 was added to the solution of CS and MAA with continued stirring, until the solution became clear. The polymerization was then carried out at 70 ◦ C under magnetic stirring for 1 h leading to the formation of CS-PMAA nanoparticles, which were then cooled in an ice bath. Particle size analysis. A Partica LA-900 laser scattering particle size distribution analyzer (Horiba Instruments Inc., Irvine, Calif., U.S.A.) was used to obtain the particle size distribution in the Vol. 73, Nr. 7, 2008—JOURNAL OF FOOD SCIENCE
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Introduction
he performance of polymeric packaging is greatly influenced by the chemical structure, molecular weight, crystallinity, and processing conditions of the polymers used. The physical characteristics required in packaging depend on what item will be packaged as well as on the environment in which the package will be stored. The use of protective coating and suitable packaging by the food industry has become a topic of great interest because of its potential for increasing the shelf life of many food products (Ahvenainen 2003; Sorrentino and others 2007). A current challenge for composite films to be used in the package industry is their relatively high water vapor permeability and poor mechanical behavior. Water vapor permeability in films is controlled by the diffusivity and solubility of water within the film matrix (Morillon and others 2002; Yakimets and others 2007). By using nanoscience, new forms of nanocomposites dispersed with nanoparticles can be developed to minimize migration of water through the polymeric package as well as to improve mechanical properties (Schuetz and Caruso 2002; Hong and Krochta 2004). For instance, it has been shown that the addition of nanosized clay particles to polyamides can lead to improved mechanical and barrier properties (Okada and Usuki 1995; Orts and others 2005). Chitosan (CS) is of particular interest in the packaging field because it is biodegradable, bioabsorbable, and bactericidal (Coma and others 2002; No and others 2007). Cellulose derivatives such as hydroxypropyl methylcellulose (HPMC) are promising materials for edible coatings or films for packaging. HPMC is a water-soluble polymer used in the food industry as a gelling and stabilizing agent (Burdock 2007; Turowski
Properties of novel hydroxypropyl methylcellulose films . . . Tensile tests. Films used for tensile tests were conditioned at about 30% RH at 24 ◦ C for 48 h before the measurements. These films (thickness of approximately 0.03 mm) were then cut to have a rectangular dimension in accordance with ASTM D638-02A type 1 (ASTM 2002): midsection 15 mm wide, 100 mm long, flaring to 25 × 35 mm square sections on each end. An Instron Universal Testing Machine (Model 1122, Instron Corp., Canton, Mass., U.S.A.) was used to determine the maximum TS (tensile strength), maximum percentage elongation at break (%), and elastic modulus E (or Young’s modulus). The edges of the films were clamped with pneumatic grips and films were stretched using a speed of 50 mm/min. Testing conditions were 30% ± 2% RH and 24 ± 2 ◦ C. Tensile properties were calculated from the plot of stress (tensile force/initial cross-sectional area) compared with strain (extension as a fraction of the original length) (Perez-Gago and Krochta 2001). The elastics modulus was obtained by the ratio of stress to strain at the initial linear portion of the curve and the elongation to break was calculated by dividing the extension at rupture of the films by the initial length of the specimen (100 mm) and multiplying by 100. The mechanical properties were analyzed as a function of particle size and CS-PMAA content. Water vapor permeability (WVP). Measurement of the WVP was determined according to the modified ASTM E96-92 gravimetric method (McHugh and others 1993). Four films were cast from each treatment (4 replicates) onto 15.5-cm internal diameter R Teflon plates. After drying, 1 sample without defects was cut from each film. Distilled water (6 mL) was dispensed into flat-bottom R Plexiglas cups with wide rims. The rim of each cup was coated with silicon sealant (High Vacuum Grease, Dow Corning, Midland, Mich., U.S.A.). The film was sealed to the cup base with a ring using 4 screws symmetrically located around the cup circumference. The cups were placed in climate-controlled cabinets containing fans and held at 0% RH using anhydrous calcium sulphate (W.A. Hammond Drieritr Co., Xenia, Ohio, U.S.A.). Weights were taken periodically after steady state was achieved and used to calculate the % RH at the film underside and the resulting WVP. Film characterization The relative humidity at the film underside was calculated using Scanning electron microscopy (SEM). A Hitachi S-4700 mi- Eq. 2 to 4: croscope (Hitachi High-Tech Corp., Tokyo, Japan) was used to study the morphology of the films. The samples were deposited onto aluWater vapor transmission rate (WVTR) minum specimen stubs using double-stick carbon tabs (Ted Pella (2) = weight loss per time/film area Inc., Redding, Calif., U.S.A.) and coated with gold/palladium on an ion sputter coated (Denton Vacuum Inc., Moorestown, N.J., U.S.A.) for 45 s at 20 mA. All samples were examined using an accelerating mwP D In[(P − p2 )/(P − p1 )] (3) WVTR = beam at a voltage of 1.5 kV. Magnifications of 10000×, 20000×, and RT z 60000× were used. Film solubility in water. To determine the water solubility of the films, a modification of the procedure proposed by Gontard P2 × 100 (4) RHunderside = and others (1992) was used. Approximately 150 mg of film sample P1 ◦ was weighed and dried in a drying oven (100 ± 2 C; 24 h) to obtain the initial dry matter weight of the films. The dried films were where mw is the molecular weight of water (18 g/g/mol), P is total immersed into 50 mL of deionized water containing 0.02% (w/v) pressure (1 atm), D is diffusivity of water vapor through air at 298 K 2 sodium azide (to prevent microbial growth) and gently stirred (20 ± (0.102 m /s), p 1 is saturation pressure vapor at 298 K (0.0313 atm), ◦ 2 C, 24 h). At the end of 24 h, the unsolubilized film was separated p 2 is water vapor partial pressure underside of the film, R is gas con−6 3 −1 −1 −1 by successive centrifugation at 5000 rpm and taken out of the wa- stant (82.1 × 10 m atm g mol K ), and z is the height of the ter and dried (100 ± 2 ◦ C; 24 h) to determine the weight of the dry mean stagnant air gap. Water vapor permeability (WVP) was calculated using the followmatter that was not solubilized in water. The weight of dry matter solubilized was calculated using Eq. 1 and reported as the water sol- ing equation: solutions using a refractive index of 1.52 and dissolving about 2 mL nanosolutions in 100 mL deionized water. Transmission electron microscopy (TEM). A Jeol 100C (Jeol Ltd., Tokyo, Japan) transmission electron microscope (TEM) was used to observe the morphology of the nanoparticles. CS-PMAA nanoparticles solutions were sonicated for 1 min to produce better particle dispersion and to prevent nanoparticle agglomeration on the copper grid. One drop of the nanoparticle solution was spread onto a carbon-coated copper grid, which was then dried at room temperature for TEM analysis. Film preparation by casting. The HPMC solution (control film) was obtained dissolving 3 g of HPMC in 100 mL of distilled water under magnetic stirring for 12 h. A 3% (w/v) HPMC solution was used in all film formulations. To study the effect of particle size and CS-PMAA concentration in HPMC film matrix, different concentrations of CS-PMAA solutions were mixed with the 3% HPMC solution to get the different film compositions. The HPMC films based on CS-PMAA nanoparticles and CS-MAA were obtained by addition of 3 g of HPMC in 100 mL of nanoparticle containing solution or chitosan containing solution (both freshly synthesized) at the content necessary to achieve the desired component proportions under magnetic stirring for 12 h. In CS-MAA solution, no nanoparticles are present, and the MAA was added to decrease the pH of the solution, as well as to provide a control composition to be more fairly compared to the presence of the CS-PMAA nanoparticles in the HPMC films. After the solutions were prepared, the flasks were allowed to rest for 6 h to degas to prevent microbubble formation within the films. The solutions were then poured on a glass plate (30 × 30 cm) covered with Mylar (Polyester film, DuPont, Hopewell, Va., U.S.A.) for film preparation by casting. The mixes were cast at a wet thickness of 0.5 mm onto plates using casting bars and the plates were placed on a leveled surface at room temperature and allowed to dry for 24 h. After drying, the films were removed from the Mylar and conditioned (for 3 d) in plastic bags at room conditions: 23 ± 1 ◦ C and 30% ± 2% RH.
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ubility percentage of the films: water solubility (%) = N32
WVP =
WVTR y ( p2 − p3 )
(5)
wt. of initial dry matter − wt. of dry matter not solubilized (1) where y is mean film thickness and p 3 is water vapor partial pressure at the upper side of the film. wt. of initial dry matter JOURNAL OF FOOD SCIENCE—Vol. 73, Nr. 7, 2008
Properties of novel hydroxypropyl methylcellulose films . . . Oxygen permeability (O 2 P) of films. An Ox-Tran 2/20 ML modular system (Modern Controls Inc., Minneapolis, Minn., U.S.A.) was utilized to measure oxygen transmission rates through the films according to standard method D3985 (ASTM 1995). Oxygen transmission rates were determined at 23 ◦ C and 55 ± 1% RH. Each film was placed on a stainless steel mask with an open testing area of 5 cm2 . Masked films were placed into the test cell and exposed to 98% N 2 + 2% H 2 flow on one side and pure oxygen flow on the other. The system was programmed to have a 10-h waiting period to allow the films to achieve equilibrium. Oxygen permeability was calculated by dividing O 2 transmission rate by the difference in O 2 partial pressure between both sides of the film (1 atm) and multiplying by the average film thickness measured at 5 random places. Four replicates of each film were evaluated. Units for O 2 P were cm3 μm m−2 d−1 kPa−1 . Statistical analysis of data. Data were analyzed by 2-sample t-Student tests, 2-way analysis of variance (ANOVA), and 1-way ANOVA with Tukey’s multiple comparison tests at 95% confidence level using Minitab version 14.12.0 statistical software (Minitab Inc., State College, Penn., U.S.A.).
ing a laser scattering particle size analyzer resulting in mean particle sizes of 110, 82, and 59 nm, respectively, to CS-PMAA prepared with 0.2, 0.5, and 0.8 (in wt%) of chitosan. These hydrated mean particle size values were used in the plots and discussion of the present study, as is commonly done in the literature (Wu and others 2005). The values of nanoparticle size measured by TEM are not trustworthy values in that they are dependent on the sample drying conditions, the setting time, and the amount of sample.
Film morphology
The morphology of the composite HPMC films containing nanoparticles was analyzed by SEM. Our control film prepared from a solution containing only 3 (in wt%) HPMC in water (Figure 2A) exhibits a high degree of porosity evenly distributed throughout the film. On the other hand, the SEM micrograph of the CS-PMAA nanoparticles prepared with a 0.2 in wt% CS solution (Figure 2B) shows clearly spherical shaped nanoparticles homogeneously distributed with particle sizes of approximately 100 nm. Compaction of HPMC films was observed when chitosan nanoparticles were added to films as shown in Figure 2C. In the microResults and Discussion graph of the films with greatest magnification (20000×), shown in Figure 2D, this compaction is well observed. The effects of the presParticle size of films and solutions ence and size of nanoparticles on the properties of the films are anThe sizes of nanoparticles prepared by polymerization of alyzed in the next section. methacrylic acid in the presence of chitosan solution were estimated taking into account at least 15 values of individual nanoparticle sizes as measured using TEM micrographs. The average sizes Film solubility of nanoparticles (shown in Figure 1) as measured by TEM were 78, Solubility in water is an important property of HPMC-based 38, and 50 nm, respectively, for CS-PMAA nanoparticles prepared films. Potential applications may require water insolubility to enwith 0.2, 0.5, and 0.8 (in wt%) of CS. These nanoparticle sizes, as hance product integrity and water resistance. Table 1 shows the wameasured by TEM, were analyzed in dried state, and therefore dif- ter solubility of films with and without nanoparticles. Differences fer from those in solution where the nanoparticles are present in a in the solubility may be due to the differences in the particle size swollen state. For the latter case, particle sizes were measured us- incorporated in the HPMC films. HPMC films with only chitosan
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Figure 1 --- TEM microphotographs of chitosan nanoparticles prepared with (A) 0.2; (B) 0.5; and (C) 0.8 (in wt%) CS-PMAA at pH 4.
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Properties of novel hydroxypropyl methylcellulose films . . . Figure 2 --- SEM micrograph of (A) control film (plain HPMC); (B) CS-PMAA nanoparticles prepared from a 0.2 (in wt%) CS solution; (C) HPMC film with 6.3% CS-PMAA nanoparticles prepared with 0.2% CS at 10000× magnification, and (D) the same as in (C) at 20000× magnification.
70
% CS in HPMC films
Solubility (%)
60
6.3 (no nanoparticle)A 14.3 (no nanoparticle)A 20.7 (no nanoparticle)A 6.3 (110 nm nanoparticles)B 14.3 (82 nm nanoparticles)B 20.7 (59 nm nanoparticles)B
100 ± 1.1c 100 ± 1.2c 99.7 ± 1.0c 94.5 ± 1.3a 96.4 ± 1.1b 97.3 ± 1.0c
50
A MAA: B
Methacrylic acid was added only to help the solubilization of chitosan. CS-PMAA: this refers to the CS nanoparticles whose preparation was described in this article. C Different letters within a column indicated significant difference at P < 0.05.
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(no nanoparticle) have high solubility because the chitosan is very soluble in water and acid. Two-way ANOVA indicated that addition of nanoparticles significantly (P < 0.05) decreased the solubility of the HPMC films. It was found that film solubility significantly decreased with increasing particle sizes in the films. In previous studies, Moura and others (2008) observed that particle size increased with increase in pH of the aqueous solution. This fact contributed to a decrease in film solubility when nanoparticles were added.
Mechanical properties The suitable use of packaging is also strongly dependent on its favorable mechanical and barrier properties. Tensile strength, elongation, and elastic modulus are parameters that are related with mechanical properties of films and their chemical structures (Dufresne and Vignon 1998). Figure 3 shows a typical tensile load– percent strain curves for films. The nanoparticle-HPMC films presented high stress values when nanoparticles with large particle sizes are included in HPMC film. The films with particle size of 59 nm (20.7%) presented lower mechanical resistance than those containing larger nanoparticles. Films containing no nanoparticles exhibited the lowest stress values. N34
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Stress (MPa)
Table 1 --- Solubility values of different films made from solution casting.
6.3 (110 nm)
40 30 20
14.3 (82 nm)
20.7 (59 nm)
10 0
CS/MAA
0
2
4
6
8
10
12
14
16
18
Strain (%) Figure 3 --- Typical load–percent strain curves for compression-molded sheets of HPMC films with 6.3% (110 nm), 14.3% (82 nm), or 20.7% (59 nm) CS-PMAA added.
Table 2 shows the effects of nanoparticle size on tensile strength of CS-PMAA/HPMC films. When particles with 59 nm are included in the HPMC films, the tensile strength of the film increased significantly from 28.3 ± 1.0 (HPMC film without nanoparticles) to 58.0 ± 1.8 MPa. This increase in TS increased further with greater CSPMAA nanoparticle concentrations. For films containing nanoparticles of the size 82 nm, TS increased from 28.3 ± 1.0 to 58.4 ± 2.0 MPa when added to films at a 14.3% concentration. When the nanoparticle CS-PMAA concentration was increased from 0% to 6.3% for films containing 110 nm nanoparticles, TS increased to 66.9 ± 2.1 MPa. The nanoparticles fill in gaps in the films acting as reinforcing agents. In the literature, the same reinforcing effect has been observed in different matrixes. For example, Angellier and others (2005) observed this effect in waxy maize starch nanocrystal
Properties of novel hydroxypropyl methylcellulose films . . . films with 110 nm increased elongation of HPMC films. This increase of the elongation provokes improvements in the tenacity of the films. This finding is positive because it demonstrates that the films did not lose their original elasticity when CS-PMAA nanoparticles were added inside the HPMC films. In these ways, the addition of nanoparticles to HPMC films results in significant improvements in film mechanical properties. Furthermore, the particle size present has a tremendous influence on the final properties of the HPMC films, clearly demonstrating the reinforcing effects of the nanoparticles on the films.
Water vapor permeability
In addition to film mechanical properties, film water vapor permeability properties are very important for a variety of food applications. Effects of CS-PMAA concentrations, as well as nanoparticle size, on WVP of films were studied (Figure 4). The WVP of the control HPMC film (0/100) was 0.79 ± cm3 μm m−2 d−1 kPa−1 . The WVP decreased significantly when nanoparticles were included in the HPMC matrix films. For example, WVP decreased to 0.64 ± 0.04, 0.59 ± 0.06, and 0.47 ± 0.07 for HPMC films with 20.7% (59 nm), 14.3% (82 nm), and 6.3% (110 nm) CS-PMAA nanoparticles, respectively. Dogan and McHugh (2007) reported a decrease in the diffusion coefficient of water with the addition of cellulose fibrils in HPMC films, as the diffusion of water in the films depends on the available pathways for water molecules. This effect, in addition to the previously shown reduction in film water solubility with the addition of nanoparticles, is most likely the cause of the decreases in WVP that were observed in this study. No significant changes in WVP were observed with varying concentrations of CS-PMAA in the 59 and 82 nm nanoparticlecontaining films (Figure 4A and 4B). We hypothesize that this is because neither the diffusion coefficient nor the solubility changed significantly when the CS-PMAA concentration was varied. On the other hand, WVP data for films containing 110 nm nanoparTable 2 --- Tensile strength for hydroxypropyl methyl cellu- ticles (Figure 4C) showed significant decreases when CS-PMAA lose films with different concentrations and particle sizes concentration was increased. This effect is thought to be a reof chitosan CS-PMAAcontent nanoparticles and films with sult of further decreases in the solubility and diffusion coeffionly chitosan (no nanoparticle). cients of water in films containing high concentrations of 110 nm % CS Particle Size Tensile Strength nanoparticles. The permeation of water molecules through these in HPMC films (nm) (MPa) films is more difficult which results in a decrease in the WVP values. 6.3 no nanoparticle 30.7 ± 1.8a 14.3 no nanoparticle 39.7 ± 1.6b 20.7 no nanoparticle 38.5 ± 1.4b 6.3 110 66.9 ± 2.1d Oxygen permeability of films 14.3 82 58.4 ± 2.0c c Oxygen permeability of the HPMC films with and without CS20.7 59 58.0 ± 1.8 PMAA nanoparticles is summarized in Table 4. The O 2 P of the conDifferent letters within a column indicated significant difference at P < 0.05. trol HPMC film was 182.34 ± 1.11 cm3 μm m−2 d−2 kPa−1 . The Table 3 --- Effect of formulation and particle size of chi- O2P decreased significantly as the particle size of the CS-PMAA tosan nanoparticles added on elastic modulus, and per- nanoparticles was reduced in the HPMC films. This is indicative cent elongation on hydroxypropyl methylcellulose films that CS-PMAA nanoparticles act as oxygen barriers in HPMC films. produced from compression-molding. One-way ANOVA indicated that addition of nanoparticles signifi% CS-PMAA Particle Elastic Elongation cantly (P < 0.05) decreased the oxygen permeability of the HPMC in HPMC films size (nm) modulus (MPa) (%) films. It was found that O 2 P significantly decreased with increasing a particle sizes in the films. 0 (no nanoparticle) 900 ± 34 8.1 ± 0.7a 3.1 59 1212 ± 150b 8.8 ± 1.0a 3.1 82 1249 ± 120b 9.7 ± 2.1ab 3.1 110 1240 ± 92b 11.1 ± 1.0b Conclusions 6.3 59 1245 ± 140b 8.3 ± 1.0a his study is the first to investigate the incorporation of chi6.3 82 1472 ± 112c 10.7 ± 0.8b c c tosan nanoparticles into HPMC films. SEM images reveal that 6.3 110 1426 ± 59 16.8 ± 1.6 HPMC films become more compact and dense when chitosan 11.5 59 1313 ± 75bc 8.1 ± 1.0a 14.3 82 1389 ± 41c 11.3 ± 0.8b nanoparticles are added. The CS-PMAA nanoparticles occupy the 20.7 59 1364 ± 45c 8.1 ± 0.8a empty spaces of the porous HPMC matrix, increasing the collapse Different letters within a column indicated significant difference at P < 0.05. of the pores in the films. In this way, incorporation of chitosan
T
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filled thermoplastic starch. Cellulose fiber reinforced thermoplastic starch or silk fibroin (Av´erous and others 2001; Noshiki and others 2002) and in polypropylene composites loaded with residual softwood fibers (Angl`es and others 1999). Thus an improvement of mechanical properties of nanocomposites has been related to the ability of nanoparticles to induce additional reinforcement of the polymeric matrix (Kristo and Biliaderis 2007). Tensile strength values of the HPMC films synthesized with chitosan solution (without nanoparticles) were 30.7 ± 1.8, 39.7 ± 1.6, and 38.5 ± 1.4 MPa for 6.3%, 14.3%, and 20.7% CS-MAA added, respectively, as shown in Table 2. In addition, the TS for HPMC films containing only PMAA (no chitosan or CS-PMAA nanoparticles) was of 27.8 ± 1.2 MPa. Significant increases in tensile strength are apparent as nanoparticles are added into the films. Two-way ANOVA indicated that the addition of nanoparticle to HPMC films and its increase of particle size increased the tensile strength of the films. The tensile strength is strongly dependent on the variation of particle size in the films synthesized using the polysaccharide HPMC. The TS values increased with the increase in particle size at both concentrations. Nanoparticles with large sizes occupy the empty spaces of the porous HPMC film matrix, inducing the collapse of the pores in the films and thereby resulting in significant improvements in mechanical properties. The percentage elongation also increased significantly when particle size increased as shown in Table 3. By 2-way ANOVA, it was concluded that an increase in concentration of nanoparticles with same particle size increases the elastic modulus of the films. Increasing the CS-PMAA for films with 59 and 82 nm nanoparticles did not increased elongation of HPMC films. The influence of the particle size in the nano range (< 100 nm) is overriding the effect of the different concentrations on the elastic modulus of the HPMC films. However, increasing the concentration of nanoparticles for
Properties of novel hydroxypropyl methylcellulose films . . . Table 4 --- Oxygen permeability for hydroxypropyl methyl cellulose films with different chitosan nanoparticle sizes. Particle size of CS-PMAA in HPMC films
O 2 permeability (cm3 μm m−2 d−2 kPa−1 ) 182.3 ± 0.5d 142.3 ± 4.0c 136.1 ± 1.0b 110.7 ± 0.9a
No nanoparticles 110 nm 82 nm 59 nm
Different letters within a column indicated significant difference at P < 0.05.
that WVP decreases when nanoparticles are included into HPMC matrix films from 0.79 ± 0.03 to 0.46 ± 0.06 (6.3% CS-PMAA in HPMC films), 0.58 ± 0.05 (14.3% CS-PMAA in HPMC films), and 0.64 ± 0.04 (20.7% CS-PMAA in HPMC films) due to decreases in diffusion and solubility coefficients of water. The observed reductions in the WVP of films containing chitosan nanoparticles are promising as a means to improve final product quality and shelf stability. These results suggest that HPMC films with CS-PMAA nanoparticles are offer potential as films to be applied in packaging to foods in the future.
Acknowledgment The financial support given by USDA, ARS, WRRC and CNPq, FINEP/LNNA, and Embrapa/Labex (Brazil) is gratefully acknowledged.
References
N: Nanoscale Food Science Figure 4 --- Dependence of water vapor permeability of HPMC films on the CS-PMAA concentration for different particle sizes: (A) 59 nm; (B) 82 nm; and (C) 110 nm. Values show the means and error bars indicate the standard deviations. Different letters over bars indicate significant difference at P < 0.05.
nanoparticles in the films significantly improves the mechanical properties while improving film water barrier properties. Film solubility results demonstrated that the added nanoparticles decrease the solubility of the HPMC films to 94.5% (6.3% CS-PMAA), 96.4% (14.3% CS-PMAA), and 97.3% (20.7% CS-PMAA). WVP results show N36
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Ahvenainen R. 2003. Novel food packaging techniques. Boca Raton, Fla: CRC Press LLC. Angellier H, Molina-Boisseau S, Dufresne A. 2005. Mechanical properties of waxy maize starch nanocrystal reinforced natural rubber. Macromolecules 38(22):9161– 70. Angl`es MN, Salvad´o J, Dufresne A. 1999. Steam-exploded residual softwood-filled polypropylene composites. J Appl Polym Sci 74(8):1962–77. ASTM. 2002. Standard test methods for tensile properties of plastics. D638-02a. In Annual book of American Standard Testing Methods. Philadelphia, Pa.: ASTM. ASTM. 1995. Standard test method for oxygen gas transmission rate through plastic film and sheeting using a coulometric sensor. D3985-95. In Annual book of American Standard Testing Methods. Philadelphia, Pa.: ASTM. Av´erous L, Fringant C, Moro L. 2001. Plasticized starch–cellulose interactions in polysaccharide composites. Polymer 42(15):6565–72. Burdock GA. 2007. Safety assessment of hydroxypropyl methylcellulose as a food ingredient. Food Chem Toxicol 45(12):2341–51. Coma V, Martial-Gros A, Garreau S, Copinet A, Salin F, Deschamps A. 2002. Edible anti-microbial films based on chitosan matrix. J Food Sci 67(3):1162–9. Dogan N, McHugh TM. 2007. Effects of microcrystalline cellulose on functional properties of hydroxypropyl methylcellulose microcomposite films. J Food Sci 72(1):16– 22. Dufresne A, Vignon MR. 1998. Improvement of starch film performances using cellulose microfibrils. Macromolecules 31(8):2693–6. Gontard N, Guilbert S, Cuq JL. 1992. Edible wheat gluten films: influence of the main process variables on film properties using response surface methodology. J Food Sci 57(1):190–5. Hong SI, Krochta JM. 2004. Whey protein isolate coating on LDPE film as a novel oxygen barrier in the composite structure. Packag Technol Sci 17(1):13–21. Kristo E, Biliaderis CG. 2007. Physical properties of starch nanocrystal-reinforced pullulan films. Carbohydr Polym 68(1):16–22. McHugh TH, Avena-Bustillos R, Krochta JM. 1993. Hydrophilic edible films: modified procedure for water vapor permeability and explanation of thickness effects. J Food Sci 58(4):899–903. Moller H, Grelier S, Pardon P, Coma V. 2004. Antimicrobial and physicochemical properties of chitosan-HPMC-based films. J Agric Food Chem 52(21):6585– 91. Morillon V, Debeaufort F, Blond G, Capelle M, Voilley A. 2002. Factors affecting the moisture permeability of lipid-based edible films: a review. Crit Rev Food Sci 42(1):67–89. Moura MR de, Aouada FA, Mattoso LHC. 2008. Preparation of chitosan nanoparticles using methacrylic acid. J Colloid Interface Sci 321(2):477–83. No HK, Meyers SP, Prinyawiwatkul W, Xu Z. 2007. Applications of chitosan for improvement of quality and shelf life of foods: a review. J Food Sci 72(5):87–100. Noshiki Y, Nishiyama Y, Wada M, Kuga S, Magoshi J. 2002. Mechanical properties of silk fibroin–microcrystalline cellulose composite films. J Appl Polym Sci 86(13):3425–9. Okada A, Usuki A. 1995. The chemistry of polymer-clay hybrids. Mater Sci Eng C 3(2):109–15.
Properties of novel hydroxypropyl methylcellulose films . . . Turowski M, Deshmukh B, Harfmann R. 2007. A method for determination of soluble dietary fiber in methylcellulose and hydroxypropyl methylcellulose food gums. J Food Compos Anal 20(5):420–9. Wu Y, Yang W, Wang C, Hu J, Fu S. 2005. Chitosan nanoparticles as a novel delivery system for ammonium glycyrrhizinate. Int J Pharm 295(1–2):235– 45. Yakimets I, Paes SS, Wellner N, Smith AC, Wilson RH, Mitchell JR. 2007. Effect of water content on the structural reorganization and elastic properties of biopolymer films: a comparative study. Biomacromolecules 8(5):1710–22.
N: Nanoscale Food Science
Orts WJ, Shey J, Imam SH, Glenn GM, Guttman ME, Revol JF. 2005. Application of cellulose microfibrils in polymer nanocomposites. J Polym Environ 13(4):302–6. Perez-Gago MB, Krochta JM. 2001. Denaturation time and temperature effects on solubility, tensile properties, and oxygen permeability of whey protein edible films. J Food Sci 66(5):705–10. Schuetz P, Caruso F. 2002. Multilayer thin films based on polyelectrolyte-complex nanoparticles. Colloids Surf A 207(1–3):33–40. Sorrentino A, Gorrasi G, Vittoria V. 2007. Potential perspectives of bionanocomposites for food packaging applications. Trends Food Sci Technol 18(2):84–95.
Vol. 73, Nr. 7, 2008—JOURNAL OF FOOD SCIENCE
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