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clay nanocomposites
Accepted Manuscript Title: Preparation, characterization, mechanical, barrier and antimicrobial properties of chitosan/PVOH/clay nanocomposites Author: Aris Giannakas Maria Vlacha Constantinos Salmas Areti Leontiou Petros Katapodis Haralambos Stamatis Nektaria-Marianthi Barkoula Athanasios Ladavos PII: DOI: Reference:
S0144-8617(15)01250-3 http://dx.doi.org/doi:10.1016/j.carbpol.2015.12.072 CARP 10670
To appear in: Received date: Revised date: Accepted date:
3-11-2015 21-12-2015 29-12-2015
Please cite this article as: Giannakas, A., Vlacha, M., Salmas, C., Leontiou, A., Katapodis, P., Stamatis, H., Barkoula, N.-M., and Ladavos, A.,Preparation, characterization, mechanical, barrier and antimicrobial properties of chitosan/PVOH/clay nanocomposites, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.12.072 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Preparation, characterization, mechanical, barrier and antimicrobial properties of chitosan/PVOH/clay nanocomposites
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Aris Giannakas1, Maria Vlacha2, Constantinos Salmas1, Areti Leontiou1, Petros Katapodis3, Haralambos Stamatis3, Nektaria-Marianthi Barkoula2and Athanasios Ladavos1*
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Laboratory of Food Technology, Department of Business Administration of Food and Agricultural Enterprises, University of Patras, Agrinio 30100, Greece
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Department of Materials Science and Engineering, University of Ioannina, Ioannina 45110, Greece 3
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Department of Biological Applications & Technology, University of Ioannina, Ioannina 45110, Greece
E-mail addresses of all authors: [email protected] (A. Giannakas), [email protected] (M. Vlacha), [email protected] (C. Salmas), [email protected] (A.Leontiou), , [email protected] (P. Katapodis) [email protected] (H. Stamatis), [email protected] (N.-M. Barkoula) and [email protected] (A. Ladavos).
*Corresponding author: Athanasios Ladavos, Department of Business Administration of Food and Agricultural Enterprises, Laboratory of Food Technology, University of Patras, Agrinio 30100, Greece. Tel.: +302641074126, fax: +302641091703. E-mail: [email protected]
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Abstract
In the current study low molecular weight poly(vinylalcohol) (PVOH) was used to prepare chitosan/PVOH blends and chitosan/PVOH/montmorilonite nanocomposites via a reflux – solution–heat pressing method. The effect of PVOH content and montmorilonite type
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(hydrophylic vs. organically modified) on the morphology, mechanical, thermomechanical, barrier and antimicrobial properties of the obtained polymer blends and nanocomposite films
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was studied. Higher amounts of PVOH (20 and 30%) resulted in plasticization of the films,
with an increase in the elongation at break and decrease of the stiffness and the strength while
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effective blending between chitosan and PVOH chains was observed based on the XRD and DMA findings. Addition of PVOH was beneficial for water and oxygen barrier properties of
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the obtained films while it did not influence the antimicrobial activity of films against the growth of Escherichia coli. Intercalated structures were obtained after the addition of
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hydrophilic and organo-modified clays leading into stiffening of the nano-modified films and
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enhancement of their barrier and antimicrobial properties.
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Keywords: chitosan; polyvinylalcohol; nanocomposites; food packaging; antimicrobial
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1.
Introduction
Chitosan (CS), is a very promising biodegradable biopolymer, with good film forming properties and immense potential as active food packaging material due to its antimicrobial activity (Zheng & Zhu, 2003), non-toxicity and low oxygen permeability. CS the cationic (14)-2-amino-2-deoxy--D-glucan, is industrially produced in various quality grades from
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chitin, the second most abundant polysaccharide in nature (Muzzarelli, 2012;).
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Many strategies have been explored to improve the water resistance and mechanical
properties of chitosan based biodegradable films including the addition of plasticizers or other
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biodegradable aliphatic polyesters, such as poly-caprolactone, poly(butylene succinate), poly(lactic acid), poly(butylene terephthalate adipate), and poly(butylenesuccinate adipate).
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Poly vinylalcohol (PVOH) has been widely utilized for the preparation of blends and composites with several natural, renewable polymers (Chiellini, Corti, D’Antone, & Solaro,
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2003). PVOH is a semicrystalline, water-soluble synthetic polymer, with good biodegradability, excellent chemical resistance and good mechanical properties linked to the
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presence of -OH groups and their hydrogen bond formation ability (Abdelrazek, Elashmawi, & Labeeb, 2010). Many reports have been published on the preparation of blended CS/PVOH
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films for food packaging applications (Park, Jun, & Marsh, 2001; Bahrami, Kordestani, Mirzadeh, & Mansoori, 2003; Srinivasa, Ramesh, Kumar, & Tharanathan, 2003; Yang, Sua, Lang, Leub, & Yang, 2004; Nakano et al. 2007; Tripathi, Mehrotra, & Dutta, 2009; Parparita,
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Cheaburu, & Vasile, 2012; Bonilla, Fortunati, Ataré, Chiralt, & Kenny, 2014), biomedical uses (Costa-Júnior, Barbosa-Stancioli, Mansur, Vasconcelos, & Mansur, 2009; Naveen Kumar et. al. 2010) or other applications such as proton batteries (Kadir, Majid, & Arof, 2010). In Ref, Srinivasa et al., (2003) CS/PVOH films were prepared and found that an increment in the PVOH concentration resulted in an increase of the moisture content. In Ref. Tripathi, Mehrotra, & Dutta, (2009) a novel antimicrobial coating based on CS and PVOH was developed and evaluated its effect on minimally processed tomato by means of microbiological analyses. As previously reported (Bonilla Fortunati, Ataré, Chiralt, & Kenny,
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2014) biodegradable films of CS/PVOH blends were prepared. Reduction in the UVtransmittance and an increase of the antimicrobial activity upon the addition of chitosan was observed. In Ref. Yang et al., (2004) CS/PVOH films were prepared and an increase in the water vapor transmission rates of the membranes with increasing chitosan content was
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demonstrated, while the antibacterial activity of all tested membranes was similar. In recent years, many studies have been devoted in evaluating the benefits of clay addition in
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biodegradable polymers, especially for the control of the transport properties of the obtained
nanocomposite films (Ray, & Bousmina, 2005; Azeredo, 2009; Bordes, Pollet, & Avérous,
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2009; Rhim, Park, & Ha, 2013;Wang et al., 2005; Xu, Ren, & Hanna 2005; Rhim, Hong, Park, & Ng 2006; Tang et al., 2009; Haerudin et al., 2010). Although CS/PVOH blended
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films and CS/clay nanocomposites have attracted much attention there are only two publications dealing with CS/PVOH/clay nanocomposites. The Ref. Parida, Nayak, Binhani,
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& Nayak (2011) where CS/PVOH/Closite 30B nanocomposites have been applied for controlled release of the anticancer drug curcumin and the Ref. Huang, Mu, & Wang, (2012)
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packaging applications.
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where rod-like sepiolite has been used as reinforcing filler in CS/PVOH blends for food
In the current study the development of CS/PVOH blends films and CS/PVOH/clay nanocomposite films varying the PVOH content and type of clay nanofiller i.e. hydrophilic sodium–montmorillonite (NaMMT) and organically modified montmorillonite (OrgMMT)
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with dimethyl-dialkyl(C14-C18) amine groups are presented. The aim of the study is to improve the properties of CS/PVOH and CS/PVOH/clay nanocomposites films towards food packaging applications. In this direction: [i] A reflux - heat pressing method has been selected for the preparation of the CS/PVOH and CS/PVOH/clay nanocomposites films. This method was recently applied for the preparation of CS/clay nanocomposite films and proved to be beneficial for their morphological, mechanical and water barrier properties (Giannakas, Grigoriadi, Leontiou, Barkoula & Ladavos, 2014; Grigoriadi, Giannakas, Ladavos & Barkoula, 2015). [ii] While most studies discuss the effect of high molecular weight on the
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properties of CS/PVOH blends (Costa-Júnior, Barbosa-Stancioli, Mansur, Vasconcelos, & Mansur, 2009), in order to improve barrier properties of the obtained films, a low molecular weight PVOH has been used here. This study focuses on the morphology of the obtained CS/PVOH and CS/PVOH/clay films characterized using X-ray diffraction, the mechanical and thermomechanical response along with a series of properties that concern food packaging
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applications such as water sorption, water and oxygen barrier properties and antimicrobial
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activity.
2. Experimental
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2.1 Materials
The materials used were: (i) medium molecular weight CS, 190-310 kDa (MMW) with a
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deacetylation degree greater than 75%, (ii) NaMMT with commercial name Nanomer® PGV and OrgMMT with ~40% dimethyl-dialkyl (C14-C18) ammonium surfactant and commercial
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name Nanomer® - I44P, (iii) PVOH with low molecular weight (13.000-23.000) and hydrolysis degree 87-89% and (iv) glacial acetic acid (HAc) all purchased from Sigma–
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Aldrich.
2.2. Preparation of CS/PVOH blends and CS/PVOH/NaMMT, CS/PVOH/OrgMMT
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nanocomposites films
All films were prepared via a reflux-heat pressing method according to our previous publications (Giannakas, Grigoriadi, Leontiou, Barkoula & Ladavos, 2014; Grigoriadi, Giannakas, Ladavos & Barkoula, 2015). For the preparation of CS/PVOH blends and CS/PVOH/clay nanocomposites films a 2 %w/v CS solution was prepared by dissolving the CS powder in 1 v/v% aqueous HAc solution, under vigorous stirring for 24 h at 70◦C. Then the mixture (pH ≈ 4.4) was left to cool down at room temperature.
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Appropriate amount of the 2 w/v% CS solution was mixed with hot water containing PVOH in order to obtain final products with 10, 20 and 30 w/w% PVOH content, respectively. The mixtures were refluxed under stirring for 4h. Obtained solutions were cast onto plastic dishes (12 cm diameter). The castings were dried at ambient conditions (~22°C) for ~ 5 days and then received films were peeled off. After drying films were pressed for 5 minutes at 130°C
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under 3MPa constant pressure, using a hydraulic press with heated platens. For the
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preparation of the CS/PVOH/clay nanocomposites appropriate amounts of NaMMT or
OrgMMT were added in the PVOH solutions in order to achieve final 5 wt% clay content.
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The dispersions were left under vigorous stirring for 12h before the addition of the 2 w/v% CS solution and refluxed under stirring for 4h. Obtained dispersions were dried and pressed as
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described above. Code names and exact quantities used for the preparation of the films are presented in Table 1.
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Preparation of “blank” samples: Samples without the addition of PVOH, i.e. CS/NaMMT and CS/OrgMMT, as well as samples without CS, i.e. PVOH/NaMMT and PVOH/OrgMMT were
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prepared as “blank” samples for comparison (see Table 1). In all cases samples were refluxed under vigorous stirring for 4 h. The obtained dispersions were also dried and pressed as
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described above.
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2.3 X-ray diffraction (XRD) analysis
The XRD measurements of the films were performed on a Brüker D8 Advanced diffractometer with CuKa radiation (λ=1.5418Å). For the samples containing NaMMT or OrgMMT clays as nanofiller the d-spacing was estimated from the 001 reflection.
2.4 Mechanical properties The mechanical properties of the obtained CS/PVOH and CS/PVOH/clay nanocomposite films were assessed via tensile measurements, according to ASTM D638 using a Simantzü
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AX-G 5kNt instrument. Three to five samples of each film were clamped between the grips (30mm initial distance) and tensioned at a crosshead speed of 5mm/min. The shape of the samples was dumbbell with gauge dimensions of 10mm x 3mm x 0.22mm. Force (N) and deformation (mm) where recorded during the test. Based on these data and the gauge dimensions the stress, stain and Modulus of Elasticity were calculated. The strain and
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Modulus of Elasticity results can only be used for comparison, because the strain values are
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based on the rotational movement of the drive shaft.
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2.5 Thermomechanical properties
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The thermomechanical properties of the prepared films were measured on a NETZSCH DMA 242C apparatus. Dynamic temperature spectra of the samples were obtained in tensile mode
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at a vibration frequency of 1 Hz, at temperatures ranging from 40 – 200°C, at a rate of 3°C/min. In order to ensure linear viscoelastic response the amplitude of the deformation was
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set at 30 μm. Since the thermomechanical properties are sensitive to the moisture content the
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films were dried prior to measurement for 24h at 100ºC in order to remove unbound water.
2.6 Water sorption
Selected films were cut in small pieces (12 mm × 12 mm), desiccated overnight under
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vacuum and weighed to determine their dry mass. The weighed films were placed in closed beakers containing 30 ml of distilled water (pH = 7) and stored at 25◦C. The sorption plots were evaluated by periodical weighting of the samples until equilibrium was reached. The water gain (W.G.) was calculated as follows: W.G. (%)=(mWet −mDry)/mDry ×100
(1)
Where mWet and mDry are the weight of the wet and dry film, respectively.
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2.7 Water vapor permeability Water vapor permeability (WVP) of the prepared films was determined at 38◦C using the apparatus and methodology described in the ASTM E96/E 96M-05 and in our previous publication (Giannakas, Spanos, Kourkoumelis, Vaimakis, & Ladavos, 2008). Films with
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0.10 mm thickness were sealed by a rubber O-ring on top of Plexiglas test bottles containing dried silica gel. Bottles were placed in a glass desiccator in 50% relative humidity. Test
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bottles were weighed periodically for 24h and the WVP was calculated according equation (2):
(2)
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WVP=(G/t)/A
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where G is the weight gain of the tested bottles in g, t is the time in hours, G/t is the slope of
2.8 Oxygen Transmission Rate
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the straight line in the diagram G = f(t) and A (mm2) is the film’s permeation area.
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Oxygen transmission Rate (OTR) was measured by using an Oxygen Analyzer M8001 tester by SYSTECHIllinois, according to Standard Method D 3985-81 (ASTM 1989).
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Measurements were performed at 23°C in dry environment (0% RH). Oxygen transmission
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rate was obtained in cc O2/ m2/day. For each OTR value, at least two samples were tested.
2.9 Antimicrobial assay The antimicrobial activity of film on the growth of Escherichia coli was determined by a microtiter plate method. Bacteria were grown in LB medium overnight at 37oC. Culture of bacteria was diluted in fresh broth to approximately 106 cfu/ml. Then 150 μl of bacteria cells suspensions were inocubated into a sterile 96-well microplate. Chitosan discs with a diameter of 6 mm were added aseptically in each micro-culture. The microplates were agitated by the microplate reader and then incubated at 37 ± 1 oC for 4 h. Then the microplate were shaken
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for 1 min in order to achieve homogenous suspensions and 50 μl from each micro tube was transferred into a new microplate diluted with 200 μl of 50 mM phosphate buffer (pH 7.0). Turbidity was measured as absorbance at 600 nm. Each experiment was performed by
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triplicate.
3. Results and discussion
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3.1 XRD patterns
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XRD patterns of neat CS (Fig. 1a), CS/PVOH blends (Fig. 1b), as well as CS/clay (Fig 1a) and CS/PVOH/clay (Fig. 1c, d) nanocomposite films are shown in Fig. 1.
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Fig. 1
Neat CS sample presents two reflections, a wide one at 8-10o and a second, more intense, at
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21.6o. This pattern implies the existence of small and imperfect crystals (Rhim et al., 2006; Gartner et al., 2011) and can be associated with the application of the heat pressing process
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(Grigoriadi, Giannakas, Ladavos & Barkoula, 2015). The addition of both clay nanofillers into CS leads to shift of 001 reflection from 7.3o to 5.2o
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for NaMMT and from 3.47o to 2.48o for OrgMMT. This shift in lower angles indicates the formation of intercalated nanocomposite structure. Clay addition results in reduction of CS intensities and shift of CS’s 21.6o reflection to 19.7o and 20.0o for CS5NaMMT and
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CS5OrgMMT respectively. These changes suggest a substantial rearrangement in the supramolecular structure of biopolymer into clay galleries (Petrova et. al. 2012). XRD patterns of CS/PVOH blends are shown in Fig. 1b. As it is observed, the peak of neat CS at around 8-10o almost disappears while the peak at 21.6ο slightly shifts towards lower 2θ from 20.8◦ for CS10PVOH sample to 20.3◦ for both CS20PVOH and CS30PVOH samples. In Ref. Naveen Kumar et. al. (2010), reported a similar shift of CS’s peak at 20o with increasing PVOH content in CS/PVOH blends and suggested that the PVOH molecules expand the
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spacing between CS chains, which is indicative of chain interactions between the two materials, after heat pressing process. In Fig. 1c and Fig. 1d the influence of NaMMT and OrgMMT clays addition in the CS/PVOH matrices is being depicted while the calculated d001 values are tabulated in Table 1. As seen,
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both clay type addition results into the formation of intercalated nanocomposite structures. Based on the d001 values in Table 1 it could be said that the presence of PVOH facilitates the
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incorporation of CS chains into NaMMT clay but hinders it in the case of OrgMMT clay. This presumably suggests that the hydrophilic nature of NaMMT promotes the interaction between
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the clay and the polymer blend due to the hydrophilic nature of CS macromolecules (Rhim et
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al., 2006; Hu, Ren, & Hanna 2005).
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Table 1
3.2 Mechanical properties
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Typical stress-strain curves for tested polymer blends and nanocomposite films are presented in Fig. 2. The average values of the E Modulus, tensile strength and strain at break of all
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tested samples are provided in Table 1.
Fig. 2
As can be observed in Fig. 2 most of the tested films present a typical stress-strain behavior of
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semi-crystalline polymer while the addition of PVOH results in a distinct plastic flow region with higher strain at break values (up to 186% increase) and a pronounced decrease in stiffness and strength (up to 48 and 35 %, respectively). Overall different trends have been reported in the open literature on the effect of PVOH addition on the stiffness, strength and elongation of CS. In agreement with current findings, it has been reported (Srinivasa et al., 2003; Costa-Júnior, Barbosa-Stancioli, Mansur, Vasconcelos, & Mansur, 2009) that the addition of low molecular weight PVOH resulted in reduction of stiffness and strength and increase of elongation at break. On the contrary in most reports with medium and high
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molecular weight PVOH (Park, Jun, & Marsh, 2001; Bahrami, Kordestani, Mirzadeh, & Mansoori, 2003; Yang et al., 2004; Nakano et. al. 2007; Parparita, Cheaburu, & Vasile, 2012; Bonilla, Fortunati, Ataré, Chiralt, & Kenny, 2014) an increment in the strength with the PVOH addition was observed even at high PVOH contents. This enhancement was suggested to be due to the formation of hydrogen bonds between –OH and –NH2 of CS and –OH groups
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of PVOH (Park, Jun, & Marsh, 2001). On the other hand it seems that with low molecular
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weight PVOH, these hydrogen bonds are less formed and blending leads in phase separated systems. Thus PVOH behaves as plasticizer resulting in slight reduction in stiffness and
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strength and increase of the strain at break.
In Fig. 2b,c,d the effect of clay addition on the tensile response of CS/PVOH bends with
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various amounts of PVOH is depicted. With the addition of NaMMT/OrgMMT a pronounced enhancement of the stiffness and strength can be found followed in most cases by a
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significant decrease in the strain at break of the nanocomposite films. The increase of stiffness and strength is higher in the case of NaMMT in comparison to OrgMMT. More specifically
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for systems containing 10 w/w% PVOH the addition of clays causes an increase of E Modulus and strength values while the strain at break values are close or even higher than
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plain CS films (see Fig. 2b). As the PVOH content increases the modulus increment is less pronounced (see Fig. 2c and 2d), while strength continues to present high levels of enhancement (up to 50%). For systems containing 20 w/w% PVOH the strain at break
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decreases while films with 30 w/w% PVOH present very limited reduction in strain at break after clay addition. The increment of stiffness and strength with clay addition is in agreement with the results previously reported (Wang et al., 2005; Rhim et al., 2006; Tang et al., 2009; Haerudin et al., 2010) for CS/clay nanocomposite films and is attributed to strong interactions between -OH groups of clay platelets and neutralized amino groups of CS chains (Wang et al., 2005). The fact that NaMMT provides slightly higher enhancement compared to OrgMMT can be linked to the XRD findings presented in the previous paragraph where the presence of PVOH facilitated the incorporation of CS chains into NaMMT clay but hindered it in the case of OrgMMT clay. Finally the fact that CS30PVOH based nanocomposites
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present significant strength enhancement while retaining their ductility can be linked to more homogenous PVOH distribution along the CS chain in presence of clays. Preferential interactions between the CS, PVOH molecules and clay sheets’ edges may facilitate CS and PVOH interactions limiting potential phase separation.
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3.3 Thermomechanical properties
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Fig. 3 and Fig. 4 demonstrate the temperature dependence of the storage modulus (E’) and
damping factor (tanδ) of CS, CS/PVOH and CS/PVOH/MMT nanocomposite films. As seen
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in Fig. 3a, the addition of PVOH results in a decrease of the E’, which is pronounced in the glassy state and tremendous in the rubbery state. As seen in Fig. 3b-3d the addition of
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NaMMT results in clear enhancement in the E’ in both glassy and rubbery region of all CS/PVOH films accompanied with an increase of the Tg. A small change of the
observed after the addition of OrgMMT.
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thermomechanical response of the nanocomposites compared to the plain films is being
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Fig. 3
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Fig. 4
More information on the preferential interactions, the molecular mobility and the potential phase separation phenomena can be obtained observing the various transitions in the tanδ
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curves. As seen in Fig. 4a, CS films present a broad transition peak at app. 185ºC. This peak is associated with the Tg of CS although contradictory values have been reported in the open literature ranging between 60 and 203°C (Ogura, Kanamoto, Itoh, Miyashiro, & Tanaka, 1980; Quijada-Garrido, Iglesias-González, Mazón-Arechederra, & Barrales-Rienda, 2007; Grigoriadi et al., 2015). The reported values for the Tg of PVOH vary between 70 and 85ºC (Masci, Husu, Murtas, Piozzi, & Crescenzi, 2003; Yang et al., 2004; Nakano et al., 2007) Films containing 10 w/w% PVOH present three transition peaks at app. 78ºC, 122ºC and 155ºC, respectively. It is well accepted that in phase separated blends the transitions of the components remain unchanged, whereas effective blending leads into single transition
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(Menard, 2008). Thus the first peak in the CS/10PVOH system is close to the T g of PVOH, while the second and the third transitions are associated with mobility of interchain hydrogen bonding indicating different level of partial interactions between CS and PVOH. The addition of 20 w/w% PVOH results in two transition peaks at app. 90ºC and 150ºC. Two peaks are also found in systems with 30 w/w% PVOH at app. 100ºC and 140ºC. It can be concluded
although
systems
remain
phase
separated.
After
the
addition
of
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miscibility,
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that the higher amount of PVOH facilitates the blending process resulting in better
NaMMT/OrgMMT in CS10PVOH films (Fig. 4b) we observe that the two first peaks of the
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CS10PVOH blend tend to become one broad peak at app. 89-99 ºC, depending on the type of the clay. This suggests that clays may facilitate CS and PVOH interactions limiting potential
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phase separation. Similar trends are being observed for systems containing 20 and 30 w/w% PVOH, with very broad tanδ peaks between 80ºC and 150ºC. A clear shift of the tanδ curve of
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the CS30PVOHNaMMT system indicates also preferential interaction between the CS chains
3.4 Water Sorption
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in the blend and NaMMT.
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From the water sorption data in Fig. 5a it could be seen that PVOH and NaMMT addition results in slight increase of the %W.G. values while a decrease is found after OrgMMT addition. This increase has been attributed to the excess amount of hydroxyl groups (-OH) in
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the PVOH/CS blends (Bahrami, Kordestani, Mirzadeh, & Mansoori, 2003; Srinivasa et al., 2003; Hyder & Chen 2009) and uncovered –O or –OH adsorption sites in NaMMT which are eager to interact with water (Lavorgna, Piscitelli, Mangiacapra, Buonocore, 2010). In the case of OrgMMT these sites are significantly diminished due to the organic modification. It is interesting to note that after 120 min the %W.G. values of all tested films has reached equilibrium state (Fig.5b) and the total amount of the absorbed water is significantly lower than that reported by other researchers (Srinivasa et al., 2003; Hyder & Chen 2009; Parida et al., 2011). This reduction is associated with the heat pressing process used for the film
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formation and can be attributed to the denser packing of the CS chains and the elimination of pores (Grigoriadi et al., 2015). Next to that heat pressing results in quick evaporation of the unbound water and this in turn dramatically decreases the sites where water could be absorbed (Grigoriadi et al., 2015).
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Fig. 5
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3.5 Water vapor permeation and oxygen transmission rate
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Fig. 6 depicts the variation of the WVP and OTR as a function of the PVOH content and NaMMT/OrgMMT addition. Based on this figure it can be observed that PVOH addition
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leads to a decrease of both WVP and OTR of CS/PVOH blends which is more pronounced in the case of 20w/w% and 30 w/w% PVOH content, attributed to the formation of CS-PVOH
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intermolecular hydrogen bonds, which limit the intermolecular chain mobility. The addition of NaMMT and OrgMMT leads to an additional improvement of both water and oxygen
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barrier of the CS/PVOH based nanocomposites. Thus this study confirms that the addition of low molecular weight PVOH is beneficial for the WVP of CS films in agreement with Ref.
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Park, Jan, & Marsh (2001). Increase of WVP values with increasing PVOH content has been reported recently when high molecular weight PVOH was used (Kanatt, Rao, Chawla & Sharma, 2012).
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Regarding OTR values it should noted that all tested films with an average thickness from 60 to 120μm were impermeable to oxygen, in agreement with previous findings (Park, Jan, & Marsh 2001). Small values of oxygen permeation were measured for films with an average thickness of 30μm. Further improvement of water and oxygen barrier is obtained with the addition of NaMMT or OrgMMT which can be attributed to the intercalated structure of the nanocomposite films that results in the creation of a tortuous path delaying the transition of water vapor/oxygen (Yano, Usuki, Okada, Kurauchi and Kamigaito, 1993). Fig. 6
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3.6 Antimicrobial properties Figure 7 The antimicrobial activity of chitosan based films has been tested against the gram negative bacteria Escherichia coli. All the chitosan-PVOH films shows significant (p<0.05)
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antibacterial activity toward E. coli. The presence of PVOH at concentrations 10 to 30% in chitosan films did not show any significant difference compared to plain chitosan that exhibit
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25% inhibition of the bacteria growth at 4h (Fig. 7) (Kanatt et al 2012). The results are in
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agreement with the effect of chitosan-glycerol films on the inhibition growth of E. coli (Leceta, Guerrero, Ibarburu, Dueñas, & de la Caba, 2013) and shows that chitosan retains the
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antibacterial activity on the film surface even in 30% w/w lower content. The addition of NaMMT or OrgMMT enhances the antibacterial activity of the chitosan based films. More
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specifically, in chitosan based films the addition of NaMMT results in 40 to 44% growth inhibition while in films containing OrgMMT the inhibition were 42 to 53% (Fig. 7).
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Although NaMMT or OrgMMT does not have any particular antibacterial action it has been shown that when added in polymer matrices it leads into enhanced performance of chitosan
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(Wang, Du, Fan, Liu, and Hu 2005; Han, Lee, Choi, and Park 2010). This has been attributed to the high specific area of the clay platelets which can absorb the bacteria from the solution
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and immobilize them on their surface (Wang et al. 2005).
4. Conclusions
The current study discusses the effect of low molecular weight PVOH addition on the morphological, thermo-mechanical, antimicrobial and barrier properties of Chitosan based films. The addition of NaMMT and OrgMMT clays has been also studied. The following conclusions can be drawn based on the obtained results:
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PVOH addition: [i] functions as plasticizer resulting in higher strain at break and reduced stiffness and strength, [ii] improves water and oxygen barrier and [iii] does not significantly affects antimicrobial activity.
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NaMMT or OrgMMT addition: [i] results in pronounced enhancement of the stiffness and strength, [ii] facilitates CS and PVOH interactions limiting potential phase
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separation, [iii] further increases water and oxygen barrier and [iv] enhances
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antimicrobial activity up to 44% for NaMMT and up to 53% for OrgMMT.
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Gartner, C., Lopez, B. L., Sierra, L., Graf, R., Spiess, H. W., & Gaborieau, M. (2011). Interplay between Structure and Dynamics in Chitosan Films Investigated with Solid-State NMR, Dynamic Mechanical Analysis and X-ray Diffraction. Biomacromolecules, 12, 1380– 1386. Giannakas, A., Grigoriadi, K., Leontiou, A., Barkoula, N.-M., & Ladavos, A. (2014) Preparation, characterization, mechanical and barrier properties investigation of chitosan-clay nanocomposites. Carbohydrate Polymers, 108(1), 103-111.
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Giannakas, A., Spanos, C. G. , Kourkoumelis, N., Vaimakis, T., & Ladavos, A. (2008). Preparation, characterization and water barrier properties of PS/organo-montmorillonite nanocomposites. European Polymer Journal, 44(12), 3915–3921. Grigoriadi, K., Giannakas, A., Ladavos, A.K., & Barkoula, N.-M. (2015). Interplay between processing and performance in chitosan-based clay nanocomposite films. Polymer Bulletin,
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Haerudin, H., Pramono, A. W., Kusuma, D. S., Jenie, A., Voelcker, N. H., & Gibson, C. (2010). Preparation and characterization of chitosan/montmorilonite (MMT) nanocomposite
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Han, Y.S., Lee, S.H., Choi, K.H., and Park, I. (2010). Preparation and characterization of
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Huang, D., Mu, B., & Wang, A. (2012). Preparation and properties of chitosan/poly (vinyl alcohol) nanocomposite films reinforced with rod-like sepiolite. Materials Letters, 86, 69–72.
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Hyder, M.N., Chen, P. (2009). Pervaporation dehydration of ethylene glycol with chitosan– poly(vinyl alcohol) blend membranes: Effect of CS–PVA blending ratios. Journal of
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Kadir, M.F.Z., Majid, S.R., & Arof, A.K. (2010). Plasticized chitosan–PVA blend polymer electrolyte based proton battery. Electrochimica Acta, 55, 1475–1482.
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Kanatt, S.R., Rao, M.S., Chawla, S.P., & Sharma, A. (2012). Active chitosan polyvinyl alcohol films with natural extracts. Food Hydrocolloids, 29, 290-297. Lavorgna, M., Piscitelli, F., Mangiacapra, P., & Buonocore, G. G. (2010). Study of the combined effect of both clay and glycerol plasticizer on the properties of chitosan films. Carbohydrate Polymers, 82, 291–298. Leceta, I., Guerrero, P., Ibarburu, I., Dueñas, M.-T., & de la Caba, K. (2013). Characterization and antimicrobial analysis of chitosan-based films. Journal of Food Engineering, 116(4), 889-899.
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Masci, G., Husu, I., Murtas, S., Piozzi, A., & Crescenzi, V. (2003), Physical Hydrogels of Poly(vinyl alcohol) with Different Syndiotacticity Prepared in the Presence of Lactosilated Chitosan Derivatives. Macromolecular Bioscience, 3, 455–461. Menard, K. P. (2008) Dynamic Mechanical Analysis, A Practical Introduction, Second Edition CRC Press.
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Muzzarelli, R. A. A. (2012). Nanochitins and nanochitosans, paving the way to eco-friendly
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Nakano, Y., Bin, Y., Bando, M., Nakashima, T., Okuno, T., Kurosu, H., & Matsuo, M. (2007). Structure and Mechanical Properties of Chitosan/Poly(Vinyl Alcohol) Blend Films.
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Naveen Kumar, H.M.P., Prabhakar, M.N., Venkata Prasad, C., Madhusudhan Rao, K., Ashok
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Kumar Reddy, T.V., Chowdoji Rao, K., & Subha, M.C.S. (2010). Compatibility studies of chitosan/PVA blend in 2% aqueous acetic acid solution at 30 ◦C. Carbohydrate Polymers, 82,
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251–255. Ogura, K., Kanamoto, T., Itoh, M., Miyashiro, H., &Tanaka K. (1980). Dynamic mechanical
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Release of the Anticancer Drug Curcumin. Journal of Biomaterials and Nanobiotechnology, 2, 414-425.
Park, S.Y., Jun, S.T., & Marsh, K.S. (2001). Physical properties of PVOH/Chitosan - blended films cast from different solvents. Food Hydrocolloids, 15, 499-502. Parparita, E., Cheaburu, C. N., & Vasile, C. (2012). Morphological, thermal and rheological characterization of Polyvinyl alcohol/chitosan blends. Cellulose Chemistry and Technology, 46 (9-10), 571-581. Petrova, V. A., Nud’ga, L. A., Bochek, A. M., Yudin, V. E., Gofman, I. V., Elokhovskii, V. Yu., & Dobrovol’skaya, I. P. (2012). Specific Features of Chitosan–Montmorillonite
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Interaction in an Aqueous Acid Solution and Properties of Related Composite Films. Polymer Science, Ser. A, 54(3), 224–230. Quijada-Garrido, I., Iglesias-González, V., Mazón-Arechederra, J.M., & Barrales-Rienda, J.M. (2007). The role played by the interactions of small molecules with chitosan and their transition temperatures. Glass-forming liquids: 1,2,3-propantriol (glycerol) Carbohydrate
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Polymers, 68, 173-186.
Ray, S. S., & Bousmina, M., (2005). Biodegradable polymers and their layered silicate
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Rhim, J.-W., Hong, S.-I., Park, H.-M., & Ng, P. K. W. (2006). Preparation and
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Characterization of Chitosan-Based Nanocomposite Films with Antimicrobial Activity. Journal of Agricultural Food Chemistry, 54, 5814-5822.
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Rhim, J.-W., Park, H.-M., & Ha, C.-S. (2013). Bio-nanocomposites for food packaging applications. Progress in Polymer Science, 38, 1629– 1652.
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Siracusa,V., (2012). Food Packaging Permeability Behaviour: A Report. International Journal of Polymer Science, Volume 2012, Article ID 302029, 11 pages
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Srinivasa, P.C., Ramesh, M.N., Kumar, K.R., & Tharanathan, R.N. (2003). Properties and sorption studies of chitosan–polyvinyl alcohol blend films. Carbohydrate Polymers, 53, 431– 438.
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Tang, C., Chen, N., Zhang, Q., Wang, K., Fu, Q., & Zhang, X. (2009). Preparation and properties of chitosan nanocomposites with nanofillers of different dimensions. Polymer Degradation and Stability, 94, 124-131. Tripathi, S., Mehrotra, G.K., & Dutta, P.K. (2009). Physicochemical and bioactivity of crosslinked chitosan–PVA film for food packaging applications. International Journal of Biological Macromolecules, 45, 372–376. Wang, S.F., Shen, L., Tong, Y.J., Chen, L., Phang, I.Y., Lim, P.Q., & Liu, T.X. (2005). Polymer Degradation and Stability, 90, 123-131.
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Xu, Y., Ren, X., & Hanna, M. A. (2005). Chitosan/Clay Nanocomposite Film Preparation and Characterization. Journal of Applied Polymer Science, 99, 1684–1691. Yang, J. M., Sua, W. Y., Lang, Leub, T., & Yang, M.C. (2004). Evaluation of chitosan/PVA blended hydrogel membranes. Journal of Membrane Science, 236, 39–51. Yano, K., Usuki, A., Okada, A., Kurauchi, T., & Kamigaito, O. (1993). Synthesis and
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properties of polyimide–clay hybrid. Journal of Polymer Science A Polymer Chemistry, 31,
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2493–2498.
Zheng, L.-Y., & Zhu, J.-F. (2003). Study on antimicrobial activity of chitosan with different
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an
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molecular weights. Carbohydrate Polymers, 54, 527–530.
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Legends to Figures Figure 1. XRD patterns of tested CS/PVOH composite and CS/clay, CS/PVOH/clay nanocomposite films Figure 2. Effect of PVOH content and NaMMT/OrgMMT addition on the stress – strain
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response of CS, CS/PVOH and CS/PVOH/clay nanocomposite films. Figure 3. Effect of PVOH content and NaMMT/OrgMMT addition on the Storage
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Modulus (E’) of CS, CS/PVOH and CS/PVOH/clay nanocomposite films,
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Figure 4. Effect of PVOH content and NaMMT/OrgMMT addition on the damping factor (tanδ) of CS, CS/PVOH and CS/PVOH/clay nanocomposite films.
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Figure 5. (a) %W.G. values after 120min remaining in water of all tested films, calculated from water sorption plots. (b) Characteristic water sorption plots for selected films.
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Figure 6. (a) Water Vapor Permeability values and (b) Oxygen Transmission Rate values
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for all tested CS/PVOH composite and CS/PVOH/clay nanocomposite films. Figure 7. Effect of PVOH content and NaMMT/OrgMMT addition on antimicrobial
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assay against food pathogenic bacteria of E. coli. Bars indicate standard deviation (n=4).
Page 22 of 24
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NaMMT g-%
OrgMMT g-%
2θ (001)
d001 nm
2-100 2-95 2-95 2-90 2-80 2-70 -
0.33-10 0.50-20 0.85-30 0.33 0.33
0.11-5 0.11 -
2-85 2-75 2-65 2-85 2-75 2-65
0.23-10 0.53-20 0.92-30 0.23-10 0.53-20 0.92-30
0.11-5 0.11 -
7.13 3.47 5.23 2.48 4.89 3.01 4.65 4.81 4.69 2.56 2.42 2.62
1.24 2.54 1.64 3.63 1.75 2.93 1.90 1.85 1.88 3.43 3.66 3.36
d
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PVOH g-%
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CS NaMMT OrgMMT CS5NaMMT CS5OrgMMT PVOH CS10PVOH CS20PVOH CS30PVOH PVOHNaMMT PVOHOrgMMT CS10PVOH5NaMMT CS20PVOH5NaMMT CS30PVOH5NaMMT CS10PVOH5OrgMMT CS20PVOH5OrgMMT CS30PVOH5OrgMMT
CS g-%
ep te
sample code name
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Table 1. Designation and amounts (wt%) of Chitosan (CS), Poly-vinylalcohol (PVOH), Na-Montmorilonite (NaMMT) and organo modified Montmorilonite (OrgMMT) used for the preparation of the films. 2θ values of 001 clay reflection, d001, Young’s (E) Modulus, ultimate tensile strength (σuts) and % strain at break (εb).
0.12-5 0.13-5 0.15-5 -
0.12-5 0.13-5 0,13-5 0.15-5 0,15-5
E Modulus (MPa) 3515±261 3763±200 3546±467 1623±54 2812±451 2109±283 1822±118 3816±337 3239±606 2299±223 3473±258 2289±132 2356±248
σuts (MPa)
εb%
95.33±7.64 98.63±5.64 90.68±2.51 31.5±2.1 85.11±19.72 62.41±9.76 64.93±3.98 122.66±14.13 93.54±26.06 83.22±11.22 102.02±19.07 74.77±5.78 82.40±11.88
7.02±2.69 7.28±0.45 7.16±0.95 36.8±0.9 11.35±3.29 15.26±4.56 20.09±3.55 6.43±0.53 6.30±1.90 16.13±2.82 8.55±0.47 7.40±0.65 15.10±2.36
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Highlights Low molecular weight PVOH acts as plasticizer when blended with CS chains
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Addition of PVOH is beneficial for the water and oxygen barrier properties
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Addition of clay facilitates CS and PVOH interactions limiting phase separation
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Addition of clay leads into enhancement of barrier and antimicrobial properties
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S0144-8617(15)01250-3 http://dx.doi.org/doi:10.1016/j.carbpol.2015.12.072 CARP 10670
To appear in: Received date: Revised date: Accepted date:
3-11-2015 21-12-2015 29-12-2015
Please cite this article as: Giannakas, A., Vlacha, M., Salmas, C., Leontiou, A., Katapodis, P., Stamatis, H., Barkoula, N.-M., and Ladavos, A.,Preparation, characterization, mechanical, barrier and antimicrobial properties of chitosan/PVOH/clay nanocomposites, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.12.072 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Preparation, characterization, mechanical, barrier and antimicrobial properties of chitosan/PVOH/clay nanocomposites
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Aris Giannakas1, Maria Vlacha2, Constantinos Salmas1, Areti Leontiou1, Petros Katapodis3, Haralambos Stamatis3, Nektaria-Marianthi Barkoula2and Athanasios Ladavos1*
1
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Laboratory of Food Technology, Department of Business Administration of Food and Agricultural Enterprises, University of Patras, Agrinio 30100, Greece
2
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Department of Materials Science and Engineering, University of Ioannina, Ioannina 45110, Greece 3
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Department of Biological Applications & Technology, University of Ioannina, Ioannina 45110, Greece
E-mail addresses of all authors: [email protected] (A. Giannakas), [email protected] (M. Vlacha), [email protected] (C. Salmas), [email protected] (A.Leontiou), , [email protected] (P. Katapodis) [email protected] (H. Stamatis), [email protected] (N.-M. Barkoula) and [email protected] (A. Ladavos).
*Corresponding author: Athanasios Ladavos, Department of Business Administration of Food and Agricultural Enterprises, Laboratory of Food Technology, University of Patras, Agrinio 30100, Greece. Tel.: +302641074126, fax: +302641091703. E-mail: [email protected]
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Abstract
In the current study low molecular weight poly(vinylalcohol) (PVOH) was used to prepare chitosan/PVOH blends and chitosan/PVOH/montmorilonite nanocomposites via a reflux – solution–heat pressing method. The effect of PVOH content and montmorilonite type
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(hydrophylic vs. organically modified) on the morphology, mechanical, thermomechanical, barrier and antimicrobial properties of the obtained polymer blends and nanocomposite films
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was studied. Higher amounts of PVOH (20 and 30%) resulted in plasticization of the films,
with an increase in the elongation at break and decrease of the stiffness and the strength while
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effective blending between chitosan and PVOH chains was observed based on the XRD and DMA findings. Addition of PVOH was beneficial for water and oxygen barrier properties of
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the obtained films while it did not influence the antimicrobial activity of films against the growth of Escherichia coli. Intercalated structures were obtained after the addition of
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hydrophilic and organo-modified clays leading into stiffening of the nano-modified films and
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enhancement of their barrier and antimicrobial properties.
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Keywords: chitosan; polyvinylalcohol; nanocomposites; food packaging; antimicrobial
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1.
Introduction
Chitosan (CS), is a very promising biodegradable biopolymer, with good film forming properties and immense potential as active food packaging material due to its antimicrobial activity (Zheng & Zhu, 2003), non-toxicity and low oxygen permeability. CS the cationic (14)-2-amino-2-deoxy-
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chitin, the second most abundant polysaccharide in nature (Muzzarelli, 2012;).
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Many strategies have been explored to improve the water resistance and mechanical
properties of chitosan based biodegradable films including the addition of plasticizers or other
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biodegradable aliphatic polyesters, such as poly-caprolactone, poly(butylene succinate), poly(lactic acid), poly(butylene terephthalate adipate), and poly(butylenesuccinate adipate).
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Poly vinylalcohol (PVOH) has been widely utilized for the preparation of blends and composites with several natural, renewable polymers (Chiellini, Corti, D’Antone, & Solaro,
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2003). PVOH is a semicrystalline, water-soluble synthetic polymer, with good biodegradability, excellent chemical resistance and good mechanical properties linked to the
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presence of -OH groups and their hydrogen bond formation ability (Abdelrazek, Elashmawi, & Labeeb, 2010). Many reports have been published on the preparation of blended CS/PVOH
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films for food packaging applications (Park, Jun, & Marsh, 2001; Bahrami, Kordestani, Mirzadeh, & Mansoori, 2003; Srinivasa, Ramesh, Kumar, & Tharanathan, 2003; Yang, Sua, Lang, Leub, & Yang, 2004; Nakano et al. 2007; Tripathi, Mehrotra, & Dutta, 2009; Parparita,
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Cheaburu, & Vasile, 2012; Bonilla, Fortunati, Ataré, Chiralt, & Kenny, 2014), biomedical uses (Costa-Júnior, Barbosa-Stancioli, Mansur, Vasconcelos, & Mansur, 2009; Naveen Kumar et. al. 2010) or other applications such as proton batteries (Kadir, Majid, & Arof, 2010). In Ref, Srinivasa et al., (2003) CS/PVOH films were prepared and found that an increment in the PVOH concentration resulted in an increase of the moisture content. In Ref. Tripathi, Mehrotra, & Dutta, (2009) a novel antimicrobial coating based on CS and PVOH was developed and evaluated its effect on minimally processed tomato by means of microbiological analyses. As previously reported (Bonilla Fortunati, Ataré, Chiralt, & Kenny,
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2014) biodegradable films of CS/PVOH blends were prepared. Reduction in the UVtransmittance and an increase of the antimicrobial activity upon the addition of chitosan was observed. In Ref. Yang et al., (2004) CS/PVOH films were prepared and an increase in the water vapor transmission rates of the membranes with increasing chitosan content was
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demonstrated, while the antibacterial activity of all tested membranes was similar. In recent years, many studies have been devoted in evaluating the benefits of clay addition in
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biodegradable polymers, especially for the control of the transport properties of the obtained
nanocomposite films (Ray, & Bousmina, 2005; Azeredo, 2009; Bordes, Pollet, & Avérous,
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2009; Rhim, Park, & Ha, 2013;Wang et al., 2005; Xu, Ren, & Hanna 2005; Rhim, Hong, Park, & Ng 2006; Tang et al., 2009; Haerudin et al., 2010). Although CS/PVOH blended
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films and CS/clay nanocomposites have attracted much attention there are only two publications dealing with CS/PVOH/clay nanocomposites. The Ref. Parida, Nayak, Binhani,
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& Nayak (2011) where CS/PVOH/Closite 30B nanocomposites have been applied for controlled release of the anticancer drug curcumin and the Ref. Huang, Mu, & Wang, (2012)
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packaging applications.
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where rod-like sepiolite has been used as reinforcing filler in CS/PVOH blends for food
In the current study the development of CS/PVOH blends films and CS/PVOH/clay nanocomposite films varying the PVOH content and type of clay nanofiller i.e. hydrophilic sodium–montmorillonite (NaMMT) and organically modified montmorillonite (OrgMMT)
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with dimethyl-dialkyl(C14-C18) amine groups are presented. The aim of the study is to improve the properties of CS/PVOH and CS/PVOH/clay nanocomposites films towards food packaging applications. In this direction: [i] A reflux - heat pressing method has been selected for the preparation of the CS/PVOH and CS/PVOH/clay nanocomposites films. This method was recently applied for the preparation of CS/clay nanocomposite films and proved to be beneficial for their morphological, mechanical and water barrier properties (Giannakas, Grigoriadi, Leontiou, Barkoula & Ladavos, 2014; Grigoriadi, Giannakas, Ladavos & Barkoula, 2015). [ii] While most studies discuss the effect of high molecular weight on the
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properties of CS/PVOH blends (Costa-Júnior, Barbosa-Stancioli, Mansur, Vasconcelos, & Mansur, 2009), in order to improve barrier properties of the obtained films, a low molecular weight PVOH has been used here. This study focuses on the morphology of the obtained CS/PVOH and CS/PVOH/clay films characterized using X-ray diffraction, the mechanical and thermomechanical response along with a series of properties that concern food packaging
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applications such as water sorption, water and oxygen barrier properties and antimicrobial
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activity.
2. Experimental
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2.1 Materials
The materials used were: (i) medium molecular weight CS, 190-310 kDa (MMW) with a
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deacetylation degree greater than 75%, (ii) NaMMT with commercial name Nanomer® PGV and OrgMMT with ~40% dimethyl-dialkyl (C14-C18) ammonium surfactant and commercial
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name Nanomer® - I44P, (iii) PVOH with low molecular weight (13.000-23.000) and hydrolysis degree 87-89% and (iv) glacial acetic acid (HAc) all purchased from Sigma–
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Aldrich.
2.2. Preparation of CS/PVOH blends and CS/PVOH/NaMMT, CS/PVOH/OrgMMT
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nanocomposites films
All films were prepared via a reflux-heat pressing method according to our previous publications (Giannakas, Grigoriadi, Leontiou, Barkoula & Ladavos, 2014; Grigoriadi, Giannakas, Ladavos & Barkoula, 2015). For the preparation of CS/PVOH blends and CS/PVOH/clay nanocomposites films a 2 %w/v CS solution was prepared by dissolving the CS powder in 1 v/v% aqueous HAc solution, under vigorous stirring for 24 h at 70◦C. Then the mixture (pH ≈ 4.4) was left to cool down at room temperature.
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Appropriate amount of the 2 w/v% CS solution was mixed with hot water containing PVOH in order to obtain final products with 10, 20 and 30 w/w% PVOH content, respectively. The mixtures were refluxed under stirring for 4h. Obtained solutions were cast onto plastic dishes (12 cm diameter). The castings were dried at ambient conditions (~22°C) for ~ 5 days and then received films were peeled off. After drying films were pressed for 5 minutes at 130°C
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under 3MPa constant pressure, using a hydraulic press with heated platens. For the
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preparation of the CS/PVOH/clay nanocomposites appropriate amounts of NaMMT or
OrgMMT were added in the PVOH solutions in order to achieve final 5 wt% clay content.
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The dispersions were left under vigorous stirring for 12h before the addition of the 2 w/v% CS solution and refluxed under stirring for 4h. Obtained dispersions were dried and pressed as
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described above. Code names and exact quantities used for the preparation of the films are presented in Table 1.
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Preparation of “blank” samples: Samples without the addition of PVOH, i.e. CS/NaMMT and CS/OrgMMT, as well as samples without CS, i.e. PVOH/NaMMT and PVOH/OrgMMT were
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prepared as “blank” samples for comparison (see Table 1). In all cases samples were refluxed under vigorous stirring for 4 h. The obtained dispersions were also dried and pressed as
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described above.
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2.3 X-ray diffraction (XRD) analysis
The XRD measurements of the films were performed on a Brüker D8 Advanced diffractometer with CuKa radiation (λ=1.5418Å). For the samples containing NaMMT or OrgMMT clays as nanofiller the d-spacing was estimated from the 001 reflection.
2.4 Mechanical properties The mechanical properties of the obtained CS/PVOH and CS/PVOH/clay nanocomposite films were assessed via tensile measurements, according to ASTM D638 using a Simantzü
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AX-G 5kNt instrument. Three to five samples of each film were clamped between the grips (30mm initial distance) and tensioned at a crosshead speed of 5mm/min. The shape of the samples was dumbbell with gauge dimensions of 10mm x 3mm x 0.22mm. Force (N) and deformation (mm) where recorded during the test. Based on these data and the gauge dimensions the stress, stain and Modulus of Elasticity were calculated. The strain and
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Modulus of Elasticity results can only be used for comparison, because the strain values are
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based on the rotational movement of the drive shaft.
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2.5 Thermomechanical properties
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The thermomechanical properties of the prepared films were measured on a NETZSCH DMA 242C apparatus. Dynamic temperature spectra of the samples were obtained in tensile mode
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at a vibration frequency of 1 Hz, at temperatures ranging from 40 – 200°C, at a rate of 3°C/min. In order to ensure linear viscoelastic response the amplitude of the deformation was
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set at 30 μm. Since the thermomechanical properties are sensitive to the moisture content the
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films were dried prior to measurement for 24h at 100ºC in order to remove unbound water.
2.6 Water sorption
Selected films were cut in small pieces (12 mm × 12 mm), desiccated overnight under
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vacuum and weighed to determine their dry mass. The weighed films were placed in closed beakers containing 30 ml of distilled water (pH = 7) and stored at 25◦C. The sorption plots were evaluated by periodical weighting of the samples until equilibrium was reached. The water gain (W.G.) was calculated as follows: W.G. (%)=(mWet −mDry)/mDry ×100
(1)
Where mWet and mDry are the weight of the wet and dry film, respectively.
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2.7 Water vapor permeability Water vapor permeability (WVP) of the prepared films was determined at 38◦C using the apparatus and methodology described in the ASTM E96/E 96M-05 and in our previous publication (Giannakas, Spanos, Kourkoumelis, Vaimakis, & Ladavos, 2008). Films with
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0.10 mm thickness were sealed by a rubber O-ring on top of Plexiglas test bottles containing dried silica gel. Bottles were placed in a glass desiccator in 50% relative humidity. Test
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bottles were weighed periodically for 24h and the WVP was calculated according equation (2):
(2)
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WVP=(G/t)/A
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where G is the weight gain of the tested bottles in g, t is the time in hours, G/t is the slope of
2.8 Oxygen Transmission Rate
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the straight line in the diagram G = f(t) and A (mm2) is the film’s permeation area.
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Oxygen transmission Rate (OTR) was measured by using an Oxygen Analyzer M8001 tester by SYSTECHIllinois, according to Standard Method D 3985-81 (ASTM 1989).
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Measurements were performed at 23°C in dry environment (0% RH). Oxygen transmission
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rate was obtained in cc O2/ m2/day. For each OTR value, at least two samples were tested.
2.9 Antimicrobial assay The antimicrobial activity of film on the growth of Escherichia coli was determined by a microtiter plate method. Bacteria were grown in LB medium overnight at 37oC. Culture of bacteria was diluted in fresh broth to approximately 106 cfu/ml. Then 150 μl of bacteria cells suspensions were inocubated into a sterile 96-well microplate. Chitosan discs with a diameter of 6 mm were added aseptically in each micro-culture. The microplates were agitated by the microplate reader and then incubated at 37 ± 1 oC for 4 h. Then the microplate were shaken
Page 8 of 24
for 1 min in order to achieve homogenous suspensions and 50 μl from each micro tube was transferred into a new microplate diluted with 200 μl of 50 mM phosphate buffer (pH 7.0). Turbidity was measured as absorbance at 600 nm. Each experiment was performed by
ip t
triplicate.
3. Results and discussion
cr
3.1 XRD patterns
us
XRD patterns of neat CS (Fig. 1a), CS/PVOH blends (Fig. 1b), as well as CS/clay (Fig 1a) and CS/PVOH/clay (Fig. 1c, d) nanocomposite films are shown in Fig. 1.
an
Fig. 1
Neat CS sample presents two reflections, a wide one at 8-10o and a second, more intense, at
M
21.6o. This pattern implies the existence of small and imperfect crystals (Rhim et al., 2006; Gartner et al., 2011) and can be associated with the application of the heat pressing process
ed
(Grigoriadi, Giannakas, Ladavos & Barkoula, 2015). The addition of both clay nanofillers into CS leads to shift of 001 reflection from 7.3o to 5.2o
ce pt
for NaMMT and from 3.47o to 2.48o for OrgMMT. This shift in lower angles indicates the formation of intercalated nanocomposite structure. Clay addition results in reduction of CS intensities and shift of CS’s 21.6o reflection to 19.7o and 20.0o for CS5NaMMT and
Ac
CS5OrgMMT respectively. These changes suggest a substantial rearrangement in the supramolecular structure of biopolymer into clay galleries (Petrova et. al. 2012). XRD patterns of CS/PVOH blends are shown in Fig. 1b. As it is observed, the peak of neat CS at around 8-10o almost disappears while the peak at 21.6ο slightly shifts towards lower 2θ from 20.8◦ for CS10PVOH sample to 20.3◦ for both CS20PVOH and CS30PVOH samples. In Ref. Naveen Kumar et. al. (2010), reported a similar shift of CS’s peak at 20o with increasing PVOH content in CS/PVOH blends and suggested that the PVOH molecules expand the
Page 9 of 24
spacing between CS chains, which is indicative of chain interactions between the two materials, after heat pressing process. In Fig. 1c and Fig. 1d the influence of NaMMT and OrgMMT clays addition in the CS/PVOH matrices is being depicted while the calculated d001 values are tabulated in Table 1. As seen,
ip t
both clay type addition results into the formation of intercalated nanocomposite structures. Based on the d001 values in Table 1 it could be said that the presence of PVOH facilitates the
cr
incorporation of CS chains into NaMMT clay but hinders it in the case of OrgMMT clay. This presumably suggests that the hydrophilic nature of NaMMT promotes the interaction between
us
the clay and the polymer blend due to the hydrophilic nature of CS macromolecules (Rhim et
an
al., 2006; Hu, Ren, & Hanna 2005).
M
Table 1
3.2 Mechanical properties
ed
Typical stress-strain curves for tested polymer blends and nanocomposite films are presented in Fig. 2. The average values of the E Modulus, tensile strength and strain at break of all
ce pt
tested samples are provided in Table 1.
Fig. 2
As can be observed in Fig. 2 most of the tested films present a typical stress-strain behavior of
Ac
semi-crystalline polymer while the addition of PVOH results in a distinct plastic flow region with higher strain at break values (up to 186% increase) and a pronounced decrease in stiffness and strength (up to 48 and 35 %, respectively). Overall different trends have been reported in the open literature on the effect of PVOH addition on the stiffness, strength and elongation of CS. In agreement with current findings, it has been reported (Srinivasa et al., 2003; Costa-Júnior, Barbosa-Stancioli, Mansur, Vasconcelos, & Mansur, 2009) that the addition of low molecular weight PVOH resulted in reduction of stiffness and strength and increase of elongation at break. On the contrary in most reports with medium and high
Page 10 of 24
molecular weight PVOH (Park, Jun, & Marsh, 2001; Bahrami, Kordestani, Mirzadeh, & Mansoori, 2003; Yang et al., 2004; Nakano et. al. 2007; Parparita, Cheaburu, & Vasile, 2012; Bonilla, Fortunati, Ataré, Chiralt, & Kenny, 2014) an increment in the strength with the PVOH addition was observed even at high PVOH contents. This enhancement was suggested to be due to the formation of hydrogen bonds between –OH and –NH2 of CS and –OH groups
ip t
of PVOH (Park, Jun, & Marsh, 2001). On the other hand it seems that with low molecular
cr
weight PVOH, these hydrogen bonds are less formed and blending leads in phase separated systems. Thus PVOH behaves as plasticizer resulting in slight reduction in stiffness and
us
strength and increase of the strain at break.
In Fig. 2b,c,d the effect of clay addition on the tensile response of CS/PVOH bends with
an
various amounts of PVOH is depicted. With the addition of NaMMT/OrgMMT a pronounced enhancement of the stiffness and strength can be found followed in most cases by a
M
significant decrease in the strain at break of the nanocomposite films. The increase of stiffness and strength is higher in the case of NaMMT in comparison to OrgMMT. More specifically
ed
for systems containing 10 w/w% PVOH the addition of clays causes an increase of E Modulus and strength values while the strain at break values are close or even higher than
ce pt
plain CS films (see Fig. 2b). As the PVOH content increases the modulus increment is less pronounced (see Fig. 2c and 2d), while strength continues to present high levels of enhancement (up to 50%). For systems containing 20 w/w% PVOH the strain at break
Ac
decreases while films with 30 w/w% PVOH present very limited reduction in strain at break after clay addition. The increment of stiffness and strength with clay addition is in agreement with the results previously reported (Wang et al., 2005; Rhim et al., 2006; Tang et al., 2009; Haerudin et al., 2010) for CS/clay nanocomposite films and is attributed to strong interactions between -OH groups of clay platelets and neutralized amino groups of CS chains (Wang et al., 2005). The fact that NaMMT provides slightly higher enhancement compared to OrgMMT can be linked to the XRD findings presented in the previous paragraph where the presence of PVOH facilitated the incorporation of CS chains into NaMMT clay but hindered it in the case of OrgMMT clay. Finally the fact that CS30PVOH based nanocomposites
Page 11 of 24
present significant strength enhancement while retaining their ductility can be linked to more homogenous PVOH distribution along the CS chain in presence of clays. Preferential interactions between the CS, PVOH molecules and clay sheets’ edges may facilitate CS and PVOH interactions limiting potential phase separation.
ip t
3.3 Thermomechanical properties
cr
Fig. 3 and Fig. 4 demonstrate the temperature dependence of the storage modulus (E’) and
damping factor (tanδ) of CS, CS/PVOH and CS/PVOH/MMT nanocomposite films. As seen
us
in Fig. 3a, the addition of PVOH results in a decrease of the E’, which is pronounced in the glassy state and tremendous in the rubbery state. As seen in Fig. 3b-3d the addition of
an
NaMMT results in clear enhancement in the E’ in both glassy and rubbery region of all CS/PVOH films accompanied with an increase of the Tg. A small change of the
observed after the addition of OrgMMT.
M
thermomechanical response of the nanocomposites compared to the plain films is being
ed
Fig. 3
ce pt
Fig. 4
More information on the preferential interactions, the molecular mobility and the potential phase separation phenomena can be obtained observing the various transitions in the tanδ
Ac
curves. As seen in Fig. 4a, CS films present a broad transition peak at app. 185ºC. This peak is associated with the Tg of CS although contradictory values have been reported in the open literature ranging between 60 and 203°C (Ogura, Kanamoto, Itoh, Miyashiro, & Tanaka, 1980; Quijada-Garrido, Iglesias-González, Mazón-Arechederra, & Barrales-Rienda, 2007; Grigoriadi et al., 2015). The reported values for the Tg of PVOH vary between 70 and 85ºC (Masci, Husu, Murtas, Piozzi, & Crescenzi, 2003; Yang et al., 2004; Nakano et al., 2007) Films containing 10 w/w% PVOH present three transition peaks at app. 78ºC, 122ºC and 155ºC, respectively. It is well accepted that in phase separated blends the transitions of the components remain unchanged, whereas effective blending leads into single transition
Page 12 of 24
(Menard, 2008). Thus the first peak in the CS/10PVOH system is close to the T g of PVOH, while the second and the third transitions are associated with mobility of interchain hydrogen bonding indicating different level of partial interactions between CS and PVOH. The addition of 20 w/w% PVOH results in two transition peaks at app. 90ºC and 150ºC. Two peaks are also found in systems with 30 w/w% PVOH at app. 100ºC and 140ºC. It can be concluded
although
systems
remain
phase
separated.
After
the
addition
of
cr
miscibility,
ip t
that the higher amount of PVOH facilitates the blending process resulting in better
NaMMT/OrgMMT in CS10PVOH films (Fig. 4b) we observe that the two first peaks of the
us
CS10PVOH blend tend to become one broad peak at app. 89-99 ºC, depending on the type of the clay. This suggests that clays may facilitate CS and PVOH interactions limiting potential
an
phase separation. Similar trends are being observed for systems containing 20 and 30 w/w% PVOH, with very broad tanδ peaks between 80ºC and 150ºC. A clear shift of the tanδ curve of
M
the CS30PVOHNaMMT system indicates also preferential interaction between the CS chains
3.4 Water Sorption
ed
in the blend and NaMMT.
ce pt
From the water sorption data in Fig. 5a it could be seen that PVOH and NaMMT addition results in slight increase of the %W.G. values while a decrease is found after OrgMMT addition. This increase has been attributed to the excess amount of hydroxyl groups (-OH) in
Ac
the PVOH/CS blends (Bahrami, Kordestani, Mirzadeh, & Mansoori, 2003; Srinivasa et al., 2003; Hyder & Chen 2009) and uncovered –O or –OH adsorption sites in NaMMT which are eager to interact with water (Lavorgna, Piscitelli, Mangiacapra, Buonocore, 2010). In the case of OrgMMT these sites are significantly diminished due to the organic modification. It is interesting to note that after 120 min the %W.G. values of all tested films has reached equilibrium state (Fig.5b) and the total amount of the absorbed water is significantly lower than that reported by other researchers (Srinivasa et al., 2003; Hyder & Chen 2009; Parida et al., 2011). This reduction is associated with the heat pressing process used for the film
Page 13 of 24
formation and can be attributed to the denser packing of the CS chains and the elimination of pores (Grigoriadi et al., 2015). Next to that heat pressing results in quick evaporation of the unbound water and this in turn dramatically decreases the sites where water could be absorbed (Grigoriadi et al., 2015).
ip t
Fig. 5
cr
3.5 Water vapor permeation and oxygen transmission rate
us
Fig. 6 depicts the variation of the WVP and OTR as a function of the PVOH content and NaMMT/OrgMMT addition. Based on this figure it can be observed that PVOH addition
an
leads to a decrease of both WVP and OTR of CS/PVOH blends which is more pronounced in the case of 20w/w% and 30 w/w% PVOH content, attributed to the formation of CS-PVOH
M
intermolecular hydrogen bonds, which limit the intermolecular chain mobility. The addition of NaMMT and OrgMMT leads to an additional improvement of both water and oxygen
ed
barrier of the CS/PVOH based nanocomposites. Thus this study confirms that the addition of low molecular weight PVOH is beneficial for the WVP of CS films in agreement with Ref.
ce pt
Park, Jan, & Marsh (2001). Increase of WVP values with increasing PVOH content has been reported recently when high molecular weight PVOH was used (Kanatt, Rao, Chawla & Sharma, 2012).
Ac
Regarding OTR values it should noted that all tested films with an average thickness from 60 to 120μm were impermeable to oxygen, in agreement with previous findings (Park, Jan, & Marsh 2001). Small values of oxygen permeation were measured for films with an average thickness of 30μm. Further improvement of water and oxygen barrier is obtained with the addition of NaMMT or OrgMMT which can be attributed to the intercalated structure of the nanocomposite films that results in the creation of a tortuous path delaying the transition of water vapor/oxygen (Yano, Usuki, Okada, Kurauchi and Kamigaito, 1993). Fig. 6
Page 14 of 24
3.6 Antimicrobial properties Figure 7 The antimicrobial activity of chitosan based films has been tested against the gram negative bacteria Escherichia coli. All the chitosan-PVOH films shows significant (p<0.05)
ip t
antibacterial activity toward E. coli. The presence of PVOH at concentrations 10 to 30% in chitosan films did not show any significant difference compared to plain chitosan that exhibit
cr
25% inhibition of the bacteria growth at 4h (Fig. 7) (Kanatt et al 2012). The results are in
us
agreement with the effect of chitosan-glycerol films on the inhibition growth of E. coli (Leceta, Guerrero, Ibarburu, Dueñas, & de la Caba, 2013) and shows that chitosan retains the
an
antibacterial activity on the film surface even in 30% w/w lower content. The addition of NaMMT or OrgMMT enhances the antibacterial activity of the chitosan based films. More
M
specifically, in chitosan based films the addition of NaMMT results in 40 to 44% growth inhibition while in films containing OrgMMT the inhibition were 42 to 53% (Fig. 7).
ed
Although NaMMT or OrgMMT does not have any particular antibacterial action it has been shown that when added in polymer matrices it leads into enhanced performance of chitosan
ce pt
(Wang, Du, Fan, Liu, and Hu 2005; Han, Lee, Choi, and Park 2010). This has been attributed to the high specific area of the clay platelets which can absorb the bacteria from the solution
Ac
and immobilize them on their surface (Wang et al. 2005).
4. Conclusions
The current study discusses the effect of low molecular weight PVOH addition on the morphological, thermo-mechanical, antimicrobial and barrier properties of Chitosan based films. The addition of NaMMT and OrgMMT clays has been also studied. The following conclusions can be drawn based on the obtained results:
Page 15 of 24
-
PVOH addition: [i] functions as plasticizer resulting in higher strain at break and reduced stiffness and strength, [ii] improves water and oxygen barrier and [iii] does not significantly affects antimicrobial activity.
-
NaMMT or OrgMMT addition: [i] results in pronounced enhancement of the stiffness and strength, [ii] facilitates CS and PVOH interactions limiting potential phase
ip t
separation, [iii] further increases water and oxygen barrier and [iv] enhances
Ac
ce pt
ed
M
an
us
cr
antimicrobial activity up to 44% for NaMMT and up to 53% for OrgMMT.
Page 16 of 24
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ip t
Azeredo, H.M.C. (2009). Nanocomposites for food packaging applications. Food Research International, 42, 1240–1253.
cr
Bahrami, S. B., Kordestani, S. S., Mirzadeh, H., & Mansoori, P. (2003). Poly (vinyl alcohol) -
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Chitosan Blends: Preparation, Mechanical and Physical Properties. Iranian Polymer Journal, 12 (2), 139-146.
an
Bonilla, J., Fortunati, E., Atarés L., Chiralt, A., & Kenny, J.M. (2014). Physical, structural and antimicrobial properties of poly vinylalcohole chitosan biodegradable films. Food Hydrocolloids,
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Ac
Gartner, C., Lopez, B. L., Sierra, L., Graf, R., Spiess, H. W., & Gaborieau, M. (2011). Interplay between Structure and Dynamics in Chitosan Films Investigated with Solid-State NMR, Dynamic Mechanical Analysis and X-ray Diffraction. Biomacromolecules, 12, 1380– 1386. Giannakas, A., Grigoriadi, K., Leontiou, A., Barkoula, N.-M., & Ladavos, A. (2014) Preparation, characterization, mechanical and barrier properties investigation of chitosan-clay nanocomposites. Carbohydrate Polymers, 108(1), 103-111.
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Giannakas, A., Spanos, C. G. , Kourkoumelis, N., Vaimakis, T., & Ladavos, A. (2008). Preparation, characterization and water barrier properties of PS/organo-montmorillonite nanocomposites. European Polymer Journal, 44(12), 3915–3921. Grigoriadi, K., Giannakas, A., Ladavos, A.K., & Barkoula, N.-M. (2015). Interplay between processing and performance in chitosan-based clay nanocomposite films. Polymer Bulletin,
ip t
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cr
Haerudin, H., Pramono, A. W., Kusuma, D. S., Jenie, A., Voelcker, N. H., & Gibson, C. (2010). Preparation and characterization of chitosan/montmorilonite (MMT) nanocomposite
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Han, Y.S., Lee, S.H., Choi, K.H., and Park, I. (2010). Preparation and characterization of
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Huang, D., Mu, B., & Wang, A. (2012). Preparation and properties of chitosan/poly (vinyl alcohol) nanocomposite films reinforced with rod-like sepiolite. Materials Letters, 86, 69–72.
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Hyder, M.N., Chen, P. (2009). Pervaporation dehydration of ethylene glycol with chitosan– poly(vinyl alcohol) blend membranes: Effect of CS–PVA blending ratios. Journal of
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Kadir, M.F.Z., Majid, S.R., & Arof, A.K. (2010). Plasticized chitosan–PVA blend polymer electrolyte based proton battery. Electrochimica Acta, 55, 1475–1482.
Ac
Kanatt, S.R., Rao, M.S., Chawla, S.P., & Sharma, A. (2012). Active chitosan polyvinyl alcohol films with natural extracts. Food Hydrocolloids, 29, 290-297. Lavorgna, M., Piscitelli, F., Mangiacapra, P., & Buonocore, G. G. (2010). Study of the combined effect of both clay and glycerol plasticizer on the properties of chitosan films. Carbohydrate Polymers, 82, 291–298. Leceta, I., Guerrero, P., Ibarburu, I., Dueñas, M.-T., & de la Caba, K. (2013). Characterization and antimicrobial analysis of chitosan-based films. Journal of Food Engineering, 116(4), 889-899.
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Masci, G., Husu, I., Murtas, S., Piozzi, A., & Crescenzi, V. (2003), Physical Hydrogels of Poly(vinyl alcohol) with Different Syndiotacticity Prepared in the Presence of Lactosilated Chitosan Derivatives. Macromolecular Bioscience, 3, 455–461. Menard, K. P. (2008) Dynamic Mechanical Analysis, A Practical Introduction, Second Edition CRC Press.
ip t
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Kumar Reddy, T.V., Chowdoji Rao, K., & Subha, M.C.S. (2010). Compatibility studies of chitosan/PVA blend in 2% aqueous acetic acid solution at 30 ◦C. Carbohydrate Polymers, 82,
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Park, S.Y., Jun, S.T., & Marsh, K.S. (2001). Physical properties of PVOH/Chitosan - blended films cast from different solvents. Food Hydrocolloids, 15, 499-502. Parparita, E., Cheaburu, C. N., & Vasile, C. (2012). Morphological, thermal and rheological characterization of Polyvinyl alcohol/chitosan blends. Cellulose Chemistry and Technology, 46 (9-10), 571-581. Petrova, V. A., Nud’ga, L. A., Bochek, A. M., Yudin, V. E., Gofman, I. V., Elokhovskii, V. Yu., & Dobrovol’skaya, I. P. (2012). Specific Features of Chitosan–Montmorillonite
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Interaction in an Aqueous Acid Solution and Properties of Related Composite Films. Polymer Science, Ser. A, 54(3), 224–230. Quijada-Garrido, I., Iglesias-González, V., Mazón-Arechederra, J.M., & Barrales-Rienda, J.M. (2007). The role played by the interactions of small molecules with chitosan and their transition temperatures. Glass-forming liquids: 1,2,3-propantriol (glycerol) Carbohydrate
ip t
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Rhim, J.-W., Park, H.-M., & Ha, C.-S. (2013). Bio-nanocomposites for food packaging applications. Progress in Polymer Science, 38, 1629– 1652.
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Siracusa,V., (2012). Food Packaging Permeability Behaviour: A Report. International Journal of Polymer Science, Volume 2012, Article ID 302029, 11 pages
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Srinivasa, P.C., Ramesh, M.N., Kumar, K.R., & Tharanathan, R.N. (2003). Properties and sorption studies of chitosan–polyvinyl alcohol blend films. Carbohydrate Polymers, 53, 431– 438.
Ac
Tang, C., Chen, N., Zhang, Q., Wang, K., Fu, Q., & Zhang, X. (2009). Preparation and properties of chitosan nanocomposites with nanofillers of different dimensions. Polymer Degradation and Stability, 94, 124-131. Tripathi, S., Mehrotra, G.K., & Dutta, P.K. (2009). Physicochemical and bioactivity of crosslinked chitosan–PVA film for food packaging applications. International Journal of Biological Macromolecules, 45, 372–376. Wang, S.F., Shen, L., Tong, Y.J., Chen, L., Phang, I.Y., Lim, P.Q., & Liu, T.X. (2005). Polymer Degradation and Stability, 90, 123-131.
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Xu, Y., Ren, X., & Hanna, M. A. (2005). Chitosan/Clay Nanocomposite Film Preparation and Characterization. Journal of Applied Polymer Science, 99, 1684–1691. Yang, J. M., Sua, W. Y., Lang, Leub, T., & Yang, M.C. (2004). Evaluation of chitosan/PVA blended hydrogel membranes. Journal of Membrane Science, 236, 39–51. Yano, K., Usuki, A., Okada, A., Kurauchi, T., & Kamigaito, O. (1993). Synthesis and
ip t
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Zheng, L.-Y., & Zhu, J.-F. (2003). Study on antimicrobial activity of chitosan with different
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Page 21 of 24
Legends to Figures Figure 1. XRD patterns of tested CS/PVOH composite and CS/clay, CS/PVOH/clay nanocomposite films Figure 2. Effect of PVOH content and NaMMT/OrgMMT addition on the stress – strain
ip t
response of CS, CS/PVOH and CS/PVOH/clay nanocomposite films. Figure 3. Effect of PVOH content and NaMMT/OrgMMT addition on the Storage
cr
Modulus (E’) of CS, CS/PVOH and CS/PVOH/clay nanocomposite films,
us
Figure 4. Effect of PVOH content and NaMMT/OrgMMT addition on the damping factor (tanδ) of CS, CS/PVOH and CS/PVOH/clay nanocomposite films.
an
Figure 5. (a) %W.G. values after 120min remaining in water of all tested films, calculated from water sorption plots. (b) Characteristic water sorption plots for selected films.
M
Figure 6. (a) Water Vapor Permeability values and (b) Oxygen Transmission Rate values
ed
for all tested CS/PVOH composite and CS/PVOH/clay nanocomposite films. Figure 7. Effect of PVOH content and NaMMT/OrgMMT addition on antimicrobial
Ac
ce pt
assay against food pathogenic bacteria of E. coli. Bars indicate standard deviation (n=4).
Page 22 of 24
ip t cr
NaMMT g-%
OrgMMT g-%
2θ (001)
d001 nm
2-100 2-95 2-95 2-90 2-80 2-70 -
0.33-10 0.50-20 0.85-30 0.33 0.33
0.11-5 0.11 -
2-85 2-75 2-65 2-85 2-75 2-65
0.23-10 0.53-20 0.92-30 0.23-10 0.53-20 0.92-30
0.11-5 0.11 -
7.13 3.47 5.23 2.48 4.89 3.01 4.65 4.81 4.69 2.56 2.42 2.62
1.24 2.54 1.64 3.63 1.75 2.93 1.90 1.85 1.88 3.43 3.66 3.36
d
M
PVOH g-%
Ac c
CS NaMMT OrgMMT CS5NaMMT CS5OrgMMT PVOH CS10PVOH CS20PVOH CS30PVOH PVOHNaMMT PVOHOrgMMT CS10PVOH5NaMMT CS20PVOH5NaMMT CS30PVOH5NaMMT CS10PVOH5OrgMMT CS20PVOH5OrgMMT CS30PVOH5OrgMMT
CS g-%
ep te
sample code name
an
us
Table 1. Designation and amounts (wt%) of Chitosan (CS), Poly-vinylalcohol (PVOH), Na-Montmorilonite (NaMMT) and organo modified Montmorilonite (OrgMMT) used for the preparation of the films. 2θ values of 001 clay reflection, d001, Young’s (E) Modulus, ultimate tensile strength (σuts) and % strain at break (εb).
0.12-5 0.13-5 0.15-5 -
0.12-5 0.13-5 0,13-5 0.15-5 0,15-5
E Modulus (MPa) 3515±261 3763±200 3546±467 1623±54 2812±451 2109±283 1822±118 3816±337 3239±606 2299±223 3473±258 2289±132 2356±248
σuts (MPa)
εb%
95.33±7.64 98.63±5.64 90.68±2.51 31.5±2.1 85.11±19.72 62.41±9.76 64.93±3.98 122.66±14.13 93.54±26.06 83.22±11.22 102.02±19.07 74.77±5.78 82.40±11.88
7.02±2.69 7.28±0.45 7.16±0.95 36.8±0.9 11.35±3.29 15.26±4.56 20.09±3.55 6.43±0.53 6.30±1.90 16.13±2.82 8.55±0.47 7.40±0.65 15.10±2.36
Page 23 of 24
Highlights Low molecular weight PVOH acts as plasticizer when blended with CS chains
o
Addition of PVOH is beneficial for the water and oxygen barrier properties
o
Addition of clay facilitates CS and PVOH interactions limiting phase separation
o
Addition of clay leads into enhancement of barrier and antimicrobial properties
Ac
ce pt
ed
M
an
us
cr
ip t
o
Page 24 of 24