Studies on methylcellulosepectinmontmorillonite

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Carbohydrate Polymers 136 (2016) 1218–1227

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Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol

Studies on methylcellulose/pectin/montmorillonite nanocomposite films and their application possibilities Nayan Ranjan Saha a , Gunjan Sarkar a , Indranil Roy a , Dipak Rana b , Amartya Bhattacharyya a , Arpita Adhikari a , Asis Mukhopadhyay c , Dipankar Chattopadhyay a,∗ a

Department of Polymer Science and Technology, University of Calcutta, 92 A.P.C. Road, Kolkata 700009, India Department of Chemical and Biological Engineering, Industrial Membrane Research Institute, University of Ottawa, 161 Louis Pasteur St. , Ottawa, ON K1N 6N5, Canada c Department of Jute and Fiber Technology, Institute of Jute Technology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700019, India b

a r t i c l e

i n f o

Article history: Received 22 June 2015 Received in revised form 12 October 2015 Accepted 13 October 2015 Available online 23 October 2015 Keywords: Methylcellulose Pectin Montmorillonite Nanocomposites Mechanical properties Transdermal drug delivery

a b s t r a c t Films based on methylcellulose (MC) and pectin (PEC) of different ratios were prepared. MC/PEC (90:10) (MP10 ) gave the best results in terms of mechanical properties. Sodium montmorillonite (MMT) (1, 3 and 5 wt%) was incorporated in the MP10 matrix. The resulting films were characterized by X-ray diffraction and transmission electron microscopy, and it was found that nanocomposites were intercalated in nature. Mechanical studies established that addition of 3 wt% MMT gave best results in terms of mechanical properties. However, thermo-gravimetric and dynamic mechanical analysis proved that decomposition and glass transition temperature increased with increasing MMT concentration from 1 to 5 wt%. It was also observed that moisture absorption and water vapor permeability studies gave best result in the case of 3 wt% MMT. Optical clarity of the nanocomposite films was not much affected with loading of MMT. In vitro drug release studies showed that MC/PEC/MMT based films can be used for controlled transdermal drug delivery applications. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction In the last few decades, with increasing population and urbanization, the use of petroleum based non-biodegradable polymers has been drastically increased and coincidentally, it increases the percentage of non-biodegradable material in solid waste. Hence, polymer scientists are trying to replace non-biodegradable polymers with biodegradable polymers. The replacement of petroleum based non-biodegradable polymers with biodegradable polymers in packaging applications is one of the promising ways to reduce non-biodegradable solid wastes. Edible films made up of biodegradable polymers are used for carrying food additives, such as antioxidants, antimicrobial agents, flavours, vitamins and colors (Appendini & Hotchkiss, 2002; Kester & Fennema, 1986; Krochta & De Mulder-Johnston, 1997). Biodegradable polymers from renewable resources have some disadvantages with respect to synthetic polymers. Biodegradable polymers such as methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), cellulose acetate, starch,

∗ Corresponding author. E-mail address: [email protected] (D. Chattopadhyay). http://dx.doi.org/10.1016/j.carbpol.2015.10.046 0144-8617/© 2015 Elsevier Ltd. All rights reserved.

pectin, chitosan, lignin, poly(vinyl alcohol) (PVA), and polyester have lowered mechanical properties, water resistance, barrier properties and thermal properties compared to synthetic polymers. Therefore, an improvement of properties for biodegradable polymers is necessary for the replacement of non-biodegradable polymers. Researchers have proposed various routes in improving the properties of biodegradable polymers, including the blending of biodegradable polymers with synthetic (Arvanitoyannis, Biliaderis, Ogawa, & Kawasaki, 1998; Bhattacharya, 1998) or with natural polymers (Coffin, Fishman, & Cooke, 1995; Xu, Kim, Hanna, & Nag, 2005) or by incorporating nanofillers such as various types of layered silicate (Tang & Alavi, 2012), mica flakes (Alves, Costa, & Coelhoso, 2010) and also by inter and intra molecular crosslinking (Simkovic, Laszlo, & Thompson, 1996). Among biodegradable polymers, MC is widely used because of its various advantages, e.g. biocompatibility, low cost, easy to prepare coating film and edible film. MC has greater mechanical properties compared to many other biodegradable polymers such as HPMC, chitosan, starch, etc., but it has some limitations for different applications. Blending of one polymer with another polymer/s have great interest as it is economical and the properties of a polymer blend are better with respect to individual

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polymers which are used for making the blend (Long, Katherine, & Lin, 2006). In the recent past, blending of various natural polymers have been tested to develop the desirable properties for various applications (Abugoch, Tapia, Villamán, Yazdani-Pedram, & Díaz-Dosque, 2011; Coffin & Fishman, 1994; Kristo, Biliaderis, & Zampraka, 2007; Miyamoto, Yamane, Seguchi, & Okajima, 2011; Roh & Shin, 2006; Wu, Wang, Wang, Bian, & Li, 2009; Yoo & Krochta, 2011; Zhai, Zhao, Yoshii, & Kume, 2004). The chemical structure of polymers and the interactions between polymers are the key factor to improve the properties of blends (Rhim, 2012). Pectin (PEC) is a natural, non-toxic linear polysaccharide, generally extracted from a plants cell wall. PEC is a methylated ester of d-galacturonic acid. PEC is divided into two classes with respect to a degree of methylation (DM), such as low-methoxyl pectins (DM < 50%) and high-methoxyl pectins (DM > 50%) (Bierhalz, Silva, & Kieckbusch, 2012). PEC has great potential to carry drugs into the gastrointestinal tract via gel beads, matrix tablets and film-coated dose form (Tripathi, Mehrotra, & Dutta, 2010). It is used in edible films for food packaging applications (Mariniello et al., 2003). It is reported that the incorporation of 30% (w/w) pectin in alginate film increases nearly 30% in tensile strength and 20% in modulus (Gohil, 2011). Therefore, the same pectin can be used for making blends with MC for the improvement of mechanical properties. Nowadays polymer/layered silicate nanocomposite generates an enormous interest to academia and industries, because nanocomposites gives a more promising improvement in various properties compared to virgin polymers and conventional particulate filler polymer composites. When reinforced materials are filled with a nano-scale level (at least one dimension in nanometer range) into a polymer matrix, it is known as a nanocomposite (Rhim, 2011). In the year 1993, scientists of Toyota group successfully prepared a polymer–clay nanocomposite with an improvement in the tensile strength as well as tensile modulus and heat distortion temperature compared with pure polymer for lightweight applications (Kojima et al., 1993; Usuki et al., 1993; Usuki, Kato, Okada, & Kurauchi, 1997). There are various types of layered silicates available in nature, such as montmorillonite (MMT), smectite, hectite, saponite, kaolinite, mica etc. MMT is the most commonly used clay because of its easy availability and low cost. It is a phyllosilicate with an octahedral alumina sheet sandwiched between two tetrahedral silica sheets. The layers of MMT are negative in nature and this charge is neutralized by a counter cation (generally Na+ cation), which are situated in the gap between the layers (Cyras, Manfredi, Ton-That, & Vázquez, 2008). Ketorolac tromethamine (KT) is a non-steroidal antiinflammatory drug. It is a heteroaryl acetic acid derivative. On the other hand, KT has great potential to be used as an analgesic agent compared to narcotic analgesics since it is non-addictive in nature with the absence of respiratory side effects (Litvak & McEvoy, 1990). KT is 800 times more effective than aspirin (Buckley & Brogden, 1990). KT is administered by oral, intramuscular or intravenous routes for the treatment of moderate to severe pain for short periods of time (biological half-life ∼4–6 h). Frequently administrations of KT often give some gastrointestinal side effects (Bo-Yeon et al., 2005; Gillis & Brogden, 1997). Due to analgesic activity, anti-inflammatory activity and low molecular weight, KT has a potential for use in transdermal administration (Alsarra, Bosela, Ahmed, & Mahrous, 2005; Cordero, Camacho, Obach, Domenech, & Vila, 2001; Tiwari, Pai, & Udupa, 2004). Furthermore, transdermal delivery of KT would reduce the therapeutic dose and also reduce the side effect in the gastrointestinal tract. In this work we have selected MC, pectin and MMT to make nanocomposite films of different compositions by the solution mixing process. This process has some advantages over a melt mixing process. In a solution mixing process, solvent soluble drugs, food preservative, etc., can be incorporated and this film can then be

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used as a patch for drug delivery, anti-fungal film, etc., respectively. Whereas, films made by a melt mixing process are difficult to use in former applications, as many drugs and food preservatives are sensitive to high temperature. The prepared nanocomposite films are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA), and dynamic mechanical analysis (DMA) to analyze the role of MMT percentage in nanocomposite films. Mechanical properties, moisture absorption and water vapor permeability (WVP) are also measured to see the effect of pectin and MMT in the as prepared nanocomposite films with the objective to use in packaging applications. Again drug (KT) loaded nanocomposite films are also subjected for the in vitro transdermal drug release study to see the availability of KT from drug loaded films. 2. Materials and methods 2.1. Materials Methyl cellulose (MC) (4000 cps) was purchased from Central Drug House Pvt. Ltd., New Delhi, India. Unmodified montmorillonite clay (MMT) was obtained from Nanocor, USA with a cation-exchange capacity of 100 mequiv./100 g. Pectin (PEC) (mol. wt. ∼3 × 104 –1 × 105 Da) was purchased from Loba Chemie Pvt. Ltd., Mumbai, India. Ketorolac tromethamine (KT) was a gift sample received from Unichem Labs Ltd., Mumbai, India. Dialysis membrane (LA390) was purchased from Hi-Media Laboratories Pvt. Ltd., Mumbai, India. Materials are used without further purification. 2.2. Preparation of MC and PEC blend films The solution mixing technique was used to prepare the blends of the MC and PEC of different weight ratios. PEC solution was prepared by dissolving a measured amount of PEC in distilled water. Then a different amount of 2% (w/v) MC solution was added to the previously prepared PEC solution with vigorous stirring at room temperature. The solution mixtures were then transferred into a petri plate at room temperature. Thin films of average thickness were obtained after the evaporation of water. Compositions of blend films are given in Table S1. It is noted that MP10 indicates a blend containing 10 wt% PEC and 90 wt% MC. 2.3. Preparation of MC/PEC/MMT nanocomposite films MC/PEC/MMT nanocomposites were prepared by the solution mixing process. At first MMT suspensions of different concentration (1, 3 and 5 wt%) were prepared by dispersing a predetermined amount of MMT in distilled water with vigorous stirring using a magnetic stirrer followed by sonication. On the other hand, the PEC solution was added into a 2% (w/v) MC solution with an appropriate ratio. Then, the MMT suspension was added into the MC/PEC solution with continuous stirring and followed by sonication at room temperature. The resultant solutions were transferred into a petri plate at room temperature. Thin films of average thickness were obtained after the evaporation of water. Compositions of nanocomposites are given in Table S1. It is noted that MP10 M1 indicates a blend containing 10 wt% PEC, 90 wt% MC and 1 wt% MMT. 2.4. Preparation of drug loaded MC/PEC/MMT nanocomposite (patch) films A predetermined amount of MMT was dispersed in distilled water. This MMT suspension was added into the mixture of 2% (w/v) MC and PEC solution with an appropriate ratio. Next, the measured amount of drug (KT) solution was added to the resultant solution with continuous stirring followed by sonication at

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room temperature. Then the total mixtures were transferred into a petri plate at room temperature. Thin films of average thickness were obtained after the evaporation of water. Compositions of drug loaded nanocomposites are depicted in Table S1. It is noted that MK, MP10 K and MP10 M1 K indicate blends containing MC with 100 mg KT, MP10 with 100 mg KT and MP10 M1 with 100 mg KT, respectively. 2.5. Characterizations 2.5.1. Mechanical property The mechanical property of solution cast films of pure MC, MP10 and MP10 /MMT nanocomposites was determined according to the ASTM method D882-95a using Zwick Roell (ZO10). Initial separation between two grips, width and cross-head speed were set at 22 mm, 5 mm and 5 mm/min, respectively. Tensile strength was determined by the ratio of the maximum load and the initial cross sectional area in MPa unit, and % elongation was calculated by the percentage value of the film length at rupture to the initial length (Kołodziejska & Piotrowska, 2007). The test was carried out at room temperature with regular humidity conditions. 2.5.2. X-ray diffraction (XRD) The morphology of the nanocomposite films was investigated by the X-ray diffraction technique. The XRD analysis of the samples was performed using X-PERT-PRO Panalytical diffractometer at room temperature using Cu K␣ ( = 1.5406 nm) as the X-ray source and at a generator voltage of 40 kV and a current of 30 mA. The rate of scan was 1◦ /min. The basal spacing of MMT in the nanocomposite films was calculated by Bragg’s law as follows (Eq. (1)) (Mondal, Mollick, et al., 2013): d=

 2 sin 

(1)

where d is the basal spacing (nm),  indicates the wavelength of X-ray source (nm) and  is the angel of X-ray incidence. 2.5.3. Transmission electron microscopy (TEM) Morphology of the nanocomposite films was explored by using transmission electron microscopy (TEM). The TEM measurement was performed using JEOL TEM (HRTEM, JEOLJEM 2100) at an accelerating voltage of 120 kV. A measured amount of MMT was dispersed in distilled water. Then, MMT suspension was added into the mixture of MC and PEC solution with an appropriate ratio, maintaining the total mixture concentration at about 1 g/l. One drop of the resultant mixture was placed onto a copper grid (300 mesh) and dried under a lamp. The copper grid was subjected for the TEM analysis. 2.5.4. Thermo-gravimetric analysis (TGA) Thermal properties of films of pure MC, MP10 and MP10 /MMT nanocomposites were measured using the Perkin Elmer (PYRIS 1) TGA instrument. Samples of 10–15 mg were heated from room temperature to 500 ◦ C in alumina crucible. The heating rate was 5 ◦ C/min in dinitrogen atmosphere with a flow rate of 30 mL/min.

2.5.6. Moisture absorption For the measurement of moisture absorption of MP10 and MP10 /MMT nanocomposites, the films were cut in the dimension of 3 mm × 3 mm. The thicknesses of the films were ∼0.07 mm. The films were heated at 60 ◦ C under vacuum for 24 h and also cooled under vacuum conditions. Then the cooled films were immediately weighted and considered as the initial weight. Next, the films were placed in an environment at 75% constant relative humidity (RH) in a locked glass container containing a saturated sodium chloride (NaCl) solution (ASTM E104-85) for 24 h (Mondal, Bhowmick, et al., 2013). Films were taken out from the glass container, immediately weighed and then considered as the final weight. The moisture absorption of the films was calculated using the following Eq. (2) (Rimdusit, Jingjid, Damrongsakkul, Tiptipakorn, & Takeichi, 2008). Moisture absorption (%) =

Wf − Wi × 100 Wi

(2)

where Wi and Wf are the initial and final weight of the films, respectively. 2.5.7. Water vapor permeability (WVP) The water vapor permeability of MP10 and MP10 /MMT nanocomposite films was measured using the modified ASTM E9600 (ASTM, 2000) method (Mondal et al., 2015). Films were sealed in a 60 mm circular opening of a glass permeation cell containing calcium chloride (∼0% relative humidity inside the cell). Then, the permeation cell was kept in a desiccator containing a saturated solution of NaCl to maintain a 75% constant relative humidity gradient across the film. The weight of the permeation cell was measured every 24 h until the weight was constant. The WVP of the samples were calculated using the following Eq. (3): Q =

W ×L S

(3)

where W is the increase in the permeation cell weight per 24 h, L is the thickness (cm) of specimens, S is the exposed area (cm2 ) of the specimen and Q is the water vapor transmission rate (g/cm2 /24 h). 2.5.8. UV–visible spectroscopy The optical clarity of the pure MC, MP10 and MP10 /MMT nanocomposite films was measured by the Perkin-Elmer Lambda 25 UV/Vis spectrophotometer. The samples were cut in rectangular shapes. The scan range was 200–800 nm and an empty compartment was used as reference. Absorbance values were converted into transmittance values using the Lambert–Beer equation and plotted against the wavelength. 2.5.9. In vitro drug release study In vitro release studies of KT from nanocomposite films (patches) were performed in a Franz diffusion cell following the procedure as mentioned in the research article of Sarkar et al. (2014). A cellulose acetate based dialysis membrane (LA390, width ∼25.27 mm, diameter ∼15.9 mm and capacity ∼1.99 ml/cm) was used as a human skin replica to study the KT release from the drug loaded nanocomposite films. 3. Results and discussion

2.5.5. Dynamic mechanical analysis (DMA) Dynamic mechanical analyses of nanocomposite films were carried out in a Perkin Elmer DMA 8000 instrument. The dimensions of the samples were ∼13.02 mm × 3 mm × 0.1 mm. The analysis was performed in tensile mode (tension rectangle) at a frequency of 1 Hz in the temperature range of 40–230 ◦ C at the temperature swipe rate of 2 ◦ C/min. The test samples were subjected to deformation at 5 ␮m amplitude.

3.1. Mechanical properties Biodegradable polymers are the next generation packaging materials. But mechanical properties of biodegradable polymers are inferior to the polymers that come from petroleum sources. Therefore, improvement of mechanical properties of biodegradable polymers is a challenging job for scientists. Many processes

N.R. Saha et al. / Carbohydrate Polymers 136 (2016) 1218–1227 Table 1 Mechanical properties of MC and PEC blends. Sample name

Initial tensile modulus (0.01% strain) (GPa)

MC MP10 MP20 MP30 MP40

1.91 2.02 1.90 1.82 1.78

± ± ± ± ±

0.12 0.16 0.18 0.14 0.17

Tensile strength (MPa) 78.78 87.71 75.44 71.19 60.11

± ± ± ± ±

1.54 2.18 1.60 1.20 2.34

Elongation at break (%) 47.14 49.05 34.24 28.46 25.45

± ± ± ± ±

1.2 0.9 1.8 0.8 1.4

are developed to improve the mechanical properties of biodegradable polymers like one biodegradable polymer is incorporated to another biodegradable polymer matrix (Coffin et al., 1995) or the incorporation of some inorganic filler materials into a single polymer matrix (Mondal, Bhowmick, et al., 2013) or into the polymer blends (Alboofetileh, Rezaei, Hosseini, & Abdollahi, 2013; Alves et al., 2010). Table 1 shows the tensile modulus at 0.01% strain, tensile strength and % elongation at break of pure MC and different combinations of MC and PEC blends. From Table 1, it is clear that the MC and PEC weight ratio of 90:10 (MP10 ) gives the best result, i.e. maximum improvement in tensile modulus, tensile strength and elongation at break and beyond 10 wt% PEC in MC, mechanical properties decrease due to the brittle nature of pure PEC. Therefore, the films were not prepared beyond MC:PEC weight ratio of 60:40. Then, MP10 composition is mixed with different concentrations (1, 3 and 5 wt%) of MMT to prepare nanocomposite films for further studies.

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Fig. 1a shows the stress vs strain curves of MP10 /MMT nanocomposites. From Fig. 1a, we have calculated and plotted the tensile strength, tensile modulus and % elongation at break in Fig. 1b, c and d, respectively. Fig. 1b shows the tensile strength of MP10 and MP10 /MMT nanocomposites. From Fig. 1b, it is clear that the tensile strength of a MP10 film is 87.04 MPa. With loading of 1, 3 and 5 wt% MMT in the MP10 the tensile strength is enhanced from 87.04 to 99.57 MPa, 108.50 MPa and 97.43 MPa, respectively. It means tensile strength is improved by 14.40, 24.47 and 11.93% with respect to MP10 films with loading of 1, 3 and 5 wt% MMT, respectively. A similar behavior was observed in the case of various biodegradable polymer based nanocomposite films such as agar (Rhim, 2011), starch (Alamsi, Ghanbarzadeh, & Entezami, 2010; Avella et al., 2005; Cyras et al., 2008; De Carvalho, Curvelo, & Agnelli, 2001; Huang, Yu, & Ma, 2006), chitosan (Casariego et al., 2009) and soy protein (Kumar, Sandeep, Alavi, Truong, & Gorga, 2010a, 2010b). Here it is clear that MP10 M3 gives the best reinforcement. Fig. 1c shows the tensile modulus of MP10 and MP10 /MMT nanocomposites at 0.01% strain. From Fig. 1c, it is apparent that the tensile modulus has increased from 2.08 GPa for the MP10 to 2.53, 3.56 and 2.95 GPa with 1, 3 and 5 wt% MMT loading, respectively. Therefore, the results indicate that the maximum improvement in tensile modulus is about 66.69% with a loading of 3 wt% of MMT in the MP10 . The surface area of the MMT layer exposed into the MP10 matrix is playing the key role for the improvement in tensile strength and as well as tensile modulus by adding only 3 wt% of MMT in the MP10 . In the case of MP10 M5 , the tensile strength

Fig. 1. Mechanical properties of MP10 /MMT nanocomposite films at different concentration of MMT (a) stress–strain curve, (b) tensile strength, (c) initial tensile modulus (0.01% strain) and (d) elongation at break.

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value of tensile strength and tensile modulus of MP10 M5 is less compare to MP10 M3 . Fig. 1d shows the % elongation at break of MP10 and MP10 /MMT nanocomposites. This result shows that % elongation at break decreases with an increase in the percentage of MMT loading to the MP10 . The % elongation at break of MP10 decreased from 49 to 45.26%, 40.88% and 34.34% with loadings of 1, 3, and 5 wt% MMT, respectively. In the case of filler reinforced films, increasing the concentration of the reinforcing particles induces brittleness in the films. This kind of observation is also common for nanocomposite films (Cyras et al., 2008; Pereda, Dufresne, Aranguren, & Marcovich, 2014; Rhim, 2011). It is due to the reinforcement effect of MMT to the MP10 , where the mobility of the polymer chains gets restricted through MMT layers. 3.2. Morphology of nanocomposites

Fig. 2. XRD pattern of (a) pure MMT, (b) MP10 , (c) MP10 M1 , (d) MP10 M3 and (e) MP10 M5 .

and tensile modulus are less than MP10 M3 , the reason behind this observation is the agglomeration of MMT layers in the case of MP10 M5 . Agglomeration of MMT layers may decrease the availability of hydroxyl groups in hydroxyl rich MMT layers (Ma, Xu, Ren, Yu, & Mai, 2003). As a result, hydrogen bonding between inorganic MMT layers and polymer matrix are getting weaker. Therefore, the

X-ray diffraction (XRD) is an effective method to verify intercalated and exfoliated structure of nano clay in a polymer matrix. In the case of intercalated nanocomposite structure, the repeated layered structure of the clay mineral is preserved. During the intercalation process polymer chains are incorporated into the clay galleries and lead to the increase in basal spacing. However, in the case of an exfoliated nanocomposite structure, the layered structure of clay is destroyed and no peak is observed (Tunc¸ & Duman, 2010). Fig. 2 shows the XRD patterns of MMT powder, and MP10 /MMT nanocomposites. The diffraction peak of pure MMT powder is observed at 6.75◦ and leads to an interlayer basal spacing of 1.308 nm. The diffraction peaks of MP10 /MMT nanocomposites are observed at 4.41◦ , 4.43◦ and 4.49◦ corresponding to the inter layer basal spacing of 2.001, 1.992 and 1.962 nm with loading of 1, 3 and 5 wt% MMT, respectively. From the results, it can be concluded that the nanocomposites of MP10 /MMT are intercalated in nature, this is probably due to the polar interactions between the hydroxyl groups of the polymer matrix and clay layers. It is also

Fig. 3. TEM images of MP10 /MMT nanocomposites, (a, c and e) at low magnification and (b, d and f) at high magnification of 1, 3 and 5 wt% MMT loaded MP10 , respectively.

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Fig. 4. (I) TGA, (II) DTG, (III) storage modulus and (IV) tan ı curves of (a) pure MC, (b) MP10 , (c) MP10 M1 , (d) MP10 M3 and (e) MP10 M5 as a function of temperature.

observed from Fig. 2 that with an increase in concentration of MMT loading to the MP10 , the intensity of the MMT peak also increases. Transmission electron microscopy is an effective method to visualize the dispersion and the texture, which means morphology of nano clay into the polymer matrix. The TEM micrograph of MP10 /MMT nanocomposites is shown in Fig. 3. Dark thread type lines are implying the thick MMT sheets and the gap between the two adjacent sheets represents the interlayer/basal spacing of MMT layers. Fig. 3a, c and e shows the low magnification images and Fig. 3b, d and f shows the high magnification images of MP10 /MMT nanocomposites with loadings of 1, 3 and 5 wt% of MMT, respectively. The basal spacing of MP10 M3 is calculated from Fig. 3b and it is found that the average distance between two layers is 2.12 nm, which is close to the result obtained from XRD analysis. From the images, it is clear that the MMT layers are well oriented, showing that it correlates with the XRD analysis data as the morphology of MMT layers in the polymer matrix are intercalated in nature. It is also apparent from TEM images that with the increasing concentration of MMT from 1 wt% to 5 wt%, more and more MMT layers are agglomerated and that is why mechanical properties decrease beyond 3 wt% of MMT. 3.3. Thermo-gravimetric analysis (TGA) Fig. 4I shows the thermal degradation curves and Fig. 4II shows the first order derivative curves (DTG) of weight loss of

the pure MC, MP10 and MP10 /MMT nanocomposites as a function of temperature. The first weight loss is observed in the range of 210–320 ◦ C. Here, 10% weight loss is occurred in the case of MP10 and MP10 /MMT nanocomposites but not in pure MC. This weight loss is due to the decomposition of PEC. It is also an evidence of PEC content (∼10 wt%) in MP10 and MP10 /MMT nanocomposites. From Fig. 4II, it is apparent that with an increase in MMT loading the peaks corresponding of PEC are shifted towards the higher temperature. From the DTG curves (Fig. 4II), it is clear that with loadings 1, 3 and 5 wt% MMT to the MP10 , the thermal stability of the first weight loss enhances from 237 to 239.6 ◦ C, 242.3 ◦ C and 244.8 ◦ C, respectively. Then, the major weight loss was observed in the range of 300–425 ◦ C, which is mainly due to the structural decomposition of MC (Mondal, Bhowmick, et al., 2013; Mondal, Mollick, et al., 2013). Beyond 425 ◦ C all polymer chains are decomposed, only inorganic MMT is stable at this temperature. From the DTG curves, it can be interpreted that with loadings 1, 3 and 5 wt% MMT to the MP10 matrix, the thermal stability increases from 357.8 to 362.08 ◦ C, 363.8 ◦ C and 365.4 ◦ C, respectively in terms of 50% weight loss. In the case of pure MC (from Fig. 4II), 354.3 ◦ C is the temperature at which 50% of the sample weight is lost. Hence, it can be concluded that the incorporation of MMT enhances the thermal stability of the MP10 , because MMT has good heat insulation properties and prevents the permeation of volatile material of the matrix through MMT layers.

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Fig. 5. (I) Moisture absorption and (II) water vapor permeability (WVP) of MP10 /MMT nanocomposite films of different MMT concentration.

3.4. Dynamic mechanical analysis (DMA) Fig. 4III and IV shows the storage modulus (E ) and loss angle tangent (tan ı) curve of pure MC, MP10 and MP10 /MMT nanocomposites as a function of temperature at a fixed frequency (1 Hz). The storage modulus indicates the temperature dependence elastic modulus and tan ı or damping factor which is a measure of glass transition temperature (Tg ) of the nanocomposites. The peak of the tan ı curve indicates the Tg value. From Fig. 4III, it is apparent that MP10 /MMT nanocomposites possess a higher storage modulus (around 40 ◦ C) than pure MC as well as the MP10 and a significant drop in the storage modulus is observed as the temperature increases. The storage modulus (around 40 ◦ C) increases with the wt% of MMT since it increases the stiffness of MP10 /MMT nanocomposites. The reason behind this observation is the incorporation of rigid alumina and silicate layers in the polymer matrix. From Fig. 4IV, it can be interpreted that the Tg of MP10 shifts to a higher temperature from 200.39 to 204.54 ◦ C, 211.06 ◦ C and 212.37 ◦ C with 1, 3 and 5 wt% MMT loading, respectively. From the results, it can be concluded that MMT layers play the role of reinforcing filler which not only increases the modulus and tensile strength, but also improves Tg which is very important from an application point of view. The reason behind the improvement in mechanical properties and Tg is the restricted mobility of polymer chains in the presence of MMT layers (Hsueh & Chen, 2003). 3.5. Moisture absorption Fig. 5I shows the moisture absorption of MP10 and MP10 /MMT nanocomposites. Moisture absorption decreases with the incorporation of MMT. Similar kind of results were observed by other researchers in the case of nanocomposites made of MMT and biodegradable polymers such as starch (Cyras et al., 2008; Huang, Yu, & Ma, 2004), agar (Rhim, 2011), methyl cellulose (Rimdusit et al., 2008; Tunc¸ & Duman, 2010), hydroxypropylmethylcellulose (Mondal, Bhowmick, et al., 2013; Mondal, Mollick, et al., 2013) and chitosan (Pereda et al., 2014). This is due to the hydrogen bonding interactions between negatively charged layers of MMT and polymer molecules (Cyras et al., 2008). With loadings of 1, 3 and 5 wt% of MMT in MP10 matrix the moisture absorption decreases from 14 to 13.61%, 12.01% and 13.1%, respectively. In the case of MP10 M5 nanocomposite, the moisture absorption value is slightly higher than that of the MP10 M3 nanocomposite. It is due to the agglomeration of MMT layers in the MP10 M5 nanocomposite which is clear from TEM images. With the agglomeration of MMT, the hydroxyl groups of MMT probably make hydrogen bonds between MMT

layers and therefore, more polymer molecules are free to interact with water molecules in MP10 M5 nanocomposite compared to MP10 M3 nanocomposite. 3.6. Water vapor permeability (WVP) Permeability of moisture is very important for food packaging applications. The permeability of moisture through the film should be as low as possible (Benbettaïeb, Kurek, Bornaz, & Debeaufort, 2014). In comparison to synthetic polymers, biodegradable polymers have a lower barrier property (Kołodziejska & Piotrowska, 2007). For improvement of barrier properties, clay is incorporated into the polymer matrix for lowering the permeability of moisture and gases through the polymer matrix. Fig. 5II shows the water vapor permeability of MP10 and MP10 /MMT nanocomposites. Due to the incorporation of MMT to MP10 , the water vapor permeability decreases. With loadings of 1, 3 and 5 wt% of MMT in the MP10 matrix the water vapor permeability decreases from 4.98 × 10−5 to 4.58 × 10−5 , 4.27 × 10−5 and 4.5 × 10−5 g/cm2 /day, respectively. The decrease in water vapor permeability of polymer/clay nanocomposite films is mainly due to the impermeable clay layers incorporated into the polymer matrix which created a tortuous path; and hindered water vapor diffusion through nanocomposites (Mondal, Bhowmick, et al., 2013; Mondal, Mollick, et al., 2013; Rimdusit et al., 2008). In the case of MP10 M5 nanocomposite, water vapor permeability is slightly greater than that of the MP10 M3 nanocomposite. It may be due to the agglomeration of MMT layers in the MP10 M5 nanocomposite which is apparent from TEM images. 3.7. UV–visible spectroscopy analysis of nanocomposite films Optical clarity of the pure MC, MP10 and MP10 /MMT nanocomposite films is investigated by using a UV–visible spectrophotometer. Generally, exfoliated nanocomposites are more transparent compared to an intercalated nanocomposite, because aggregated layers scatter light strongly. From Fig. 6, it is clear that with an increasing amount of MMT loading to the polymer matrix the optical clarity decreases slightly. From Fig. 6, it can also be concluded that MMT layers are well dispersed in the polymer matrix. 3.8. In vitro transdermal release of Ketorolac tromethamine (KT) The cumulative amount of drug released from the pure MC and MMT loaded nanocomposite film samples in phosphate buffer saline media of pH 7.4 at 37 ◦ C is shown in Fig. 7. Fig. 7 shows that

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such as a ‘pore’ mechanism and the ‘partition’ mechanism. Drug permeation follows both mechanisms, but in practical, one mechanism is predominant over another to control the drug release pattern (Zentner, Cardinal, & Kim, 1978). Here all the polymers are hydrophilic in nature and are in contact with water, hence they get swelled. Therefore, here the drug release pattern follows ‘pore’ mechanism (Ofori-Kwakye & Fell, 2001). In the case of ‘pore’ mechanism, drugs diffuse through the pores from the polymer matrix. MC apparently swells and creates pores in the films, leading to an increase in drug permeability from films through pores. Addition of PEC to MC matrix leads to a decrease in the release of drug. It is because the swell ability of PEC is lesser than MC, and restricts the diffusion of drug molecules through films. On the other hand, the incorporation of MMT to the polymer matrix increases the tortuous path which restricts the diffusion of drug molecules through interlayer spaces of MMT. For the purpose of precisely understanding the release mechanism, the drug release kinetics data obtained from all drug loaded films is fitted to the following equation: Mt = Kt n M∞ Fig. 6. The % transmittance of (a) pure MC, (b) MP10 , (c) MP10 M1 , (d) MP10 M3 and (e) MP10 M5 against wavelength.

where Mt /M∞ is the fraction of drug released at time t, K is a constant related to the properties of the drug delivery system and n is the diffusion exponent that characterizes the drug release mechanism. When the value of n is 0.5, it indicates that the drug release process follows the anomalous drug diffusion mechanism. The values of n calculated according to the above method are found to be 0.59, 0.61, 0.58, 0.6 and 0.62 for the formulations MK, MP10 K, MP10 M1 K, MP10 M3 K, and MP10 M5 K, respectively. Thus, the nanocomposites follow the anomalous drug diffusion controlled release mechanism. Therefore, the effect of drug immobilization in the MMT gallery also has a significant impact on the drug release profile as compared to PEC containing nanocomposites (MP10 K). Pure MC formulation exhibits a burst release followed by first order kinetics whereas PEC and MMT containing drug loaded formulations follows zero order kinetics with sustained release characteristics. In conclusion, both kinds of drug release follow the anomalous drug diffusion mechanism but it transforms from first order to zero after the incorporation of the MMT layers into the polymer matrix. 4. Conclusions

Fig. 7. Cumulative drug (KT) release from drug loaded nanocomposite films (a) MK, (b) MP10 K, (c) MP10 M1 K, (d) MP10 M3 K and (e) MP10 M5 K.

the KT is continuously released for over 7 h from all films. It is clear that the release of KT is considerably slower and hence controlled with the addition of PEC and MMT in different MC based nanocomposite formulations. An initial burst release of KT of 5–13% is observed from all formulations and this bursting may be due to the saturation of the drug molecules on the nanocomposite surface during storage. The cumulative amount of drug released from formulations containing PEC and MMT (MP10 K, MP10 M1 K, MP10 M3 K, and MP10 M5 K) is at a slower rate than the formulation (MK) without PEC and MMT. From the results it can be concluded that the rate of release of the drug decreases with the addition of PEC and MMT in MC based nanocomposites formulations. The cumulative percentage of drug release from prepared nanocomposites films after 4 h is 84.93, 73.26, 68.93, 60.18 and 51.92% for MK, MP10 K, MP10 M1 K, MP10 M3 K, and MP10 M5 K, respectively. Drug permeation through the polymer matrix generally follows two mechanisms,

In this work, we have successfully prepared MC/PEC/MMT nanocomposite films which can be used for food packaging and as well as a patch for the controlled delivery of a transdermal drug. Initially films with different weight ratios of MC and PEC were prepared and found that only MC:PEC (90:10) gave a strong and tough film. It is observed that a nanocomposite film based on 3 wt% MMT loaded MC/PEC/MMT gave the best results in terms of mechanical properties, moisture absorption and water vapor permeability, but thermal stability, glass transition temperature and time of drug release increased with increasing concentration of MMT from 1 to 5 wt%. Hence, it can be concluded that 3 wt% MMT loaded MC/PEC/MMT nanocomposite film is suitable for packaging applications whereas, 5 wt% MMT loaded MC/PEC/MMT nanocomposite film gives a better performance in terms of controlled release of a transdermal drug. Acknowledgements Nayan Ranjan Saha likes to thank the University Grant Commission (UGC), Govt. of India, for his fellowship. Gunjan Sarkar likes to thank the University Grant Commission, Govt. of India, for his

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fellowship under Rajiv Gandhi National Fellowship (RGNF) scheme. Indranil Roy and Amartya Bhattacharyya like to thank the TEQIP, India, for their fellowship. Arpita Adhikari likes to thank the Department of Science & Technology (DST), New Delhi, Govt. of India, for her fellowship under Women Scientist Scheme WOS-B (SoRF) [Internship mode]. Also, we like to thank the Centre for Research in Nanoscience and Nanotechnology, University of Calcutta, for providing instrumental facility. Again we like to thank HASETRI, JK Tyre, Rajasthan, India for providing TGA facility. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.carbpol.2015.10.046. References Abugoch, L. E., Tapia, C., Villamán, M. C., Yazdani-Pedram, M., & Díaz-Dosque, M. (2011). Characterization of quinoa protein–chitosan blend edible films. Food Hydrocolloids, 25(5), 879–886. Alamsi, H., Ghanbarzadeh, B., & Entezami, A. A. (2010). Physicochemical properties of starch–CMC–nanoclay biodegradable films. International Journal of Biological Macromolecules, 46(1), 1–5. Alboofetileh, M., Rezaei, M., Hosseini, H., & Abdollahi, M. (2013). Effect of montmorillonite clay and biopolymer concentration on the physical and mechanical properties of alginate nanocomposite films. Journal of Food Engineering, 117(1), 26–33. Alsarra, I. A., Bosela, A. A., Ahmed, S. M., & Mahrous, G. M. (2005). Proniosomes as a drug carrier for transdermal delivery of ketorolac. European Journal of Pharmaceutics and Biopharmaceutics, 59(3), 485–490. Alves, V. D., Costa, N., & Coelhoso, I. M. (2010). Barrier properties of biodegradable composite films based on kappa-carrageenan/pectin blends and mica flakes. Carbohydrate Polymers, 79(2), 269–276. Appendini, P., & Hotchkiss, J. H. (2002). Review of antimicrobial food packaging. Innovative Food Science and Emerging Technologies, 3(2), 113–126. Arvanitoyannis, I., Biliaderis, C. G., Ogawa, H., & Kawasaki, N. (1998). Biodegradable films made from low density polyethylene (LDPE), rice starch, and potato starch for food packaging applications. Carbohydrate Polymers, 36(2), 89–104. Avella, M., De Vlieger, J. J., Errico, M. E., Fischer, S., Vacca, P., & Volpe, M. G. (2005). Biodegradable starch/clay nanocomposite films for food packaging applications. Food Chemistry, 93(3), 467–474. Benbettaïeb, N., Kurek, M., Bornaz, S., & Debeaufort, F. (2014). Barrier, structural and mechanical properties of bovine gelatin–chitosan blend films related to biopolymer interactions. Journal of the Science of Food and Agriculture, 94(12), 2409–2419. Bhattacharya, M. (1998). Stress relaxation of starch/synthetic polymer blends. Journal of Materials Science, 33(16), 4131–4139. Bierhalz, A. C. K., Silva, M. A. D., & Kieckbusch, T. G. (2012). Natamycin release from alginate/pectin films for food packaging applications. Journal of Food Engineering, 110(1), 18–25. Bo-Yeon, K., Hea-Jeong, D., Thanh-Nguyen, L., Won-Jea, C., Chul-Soon, Y., Han-Gon, C., et al. (2005). Ketorolac amide prodrugs for transdermal delivery: Stability and in vitro rat skin permeation studies. International Journal of Pharmaceutics, 293, 193–202. Buckley, M. M. T., & Brogden, R. N. (1990). Ketorolac: A review of its pharmacodynamics and pharmacokinetic properties, and therapeutic potential. Drugs, 39, 86–109. Casariego, A., Souza, B. W. S., Cerqueira, M. A., Teixeira, J. A., Cruz, L., Díaz, R., et al. (2009). Chitosan/clay film’s properties as affected by biopolymer and clay micro/nanoparticles’ concentrations. Food Hydrocolloids, 23(7), 1895–1902. Coffin, D. R., & Fishman, M. L. (1994). Physical and mechanical properties of highly plasticized pectin/starch films. Journal of Applied Polymer Science, 54(9), 1311–1320. Coffin, D. R., Fishman, M. L., & Cooke, P. H. (1995). Mechanical and microstructural properties of pectin starch films. Journal of Applied Polymer Science, 57(6), 663–670. Cordero, J. A., Camacho, M., Obach, R., Domenech, J., & Vila, L. (2001). In vitro based index of topical anti-inflammatory activity to compare a series of NSAIDs. European Journal of Pharmaceutics and Biopharmaceutics, 51, 135–142. Cyras, V. P., Manfredi, L. B., Ton-That, M. T., & Vázquez, A. (2008). Physical and mechanical properties of thermoplastic starch/montmorillonite nanocomposite films. Carbohydrate Polymers, 73(1), 55–63. De Carvalho, A. J. F., Curvelo, A. A. S., & Agnelli, J. A. M. (2001). A first insight on composites of thermoplastic starch and kaolin. Carbohydrate Polymers, 45(2), 189–194. Gillis, J. C., & Brogden, R. N. (1997). Ketorolac. A reappraisal of its pharmacodynamic and pharmacokinetic properties and therapeutic use in pain management. Drugs, 53, 139–188. Gohil, R. M. (2011). Synergistic blends of natural polymers, pectin and sodium alginate. Journal of Applied Polymer Science, 120(4), 2324–2336.

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