Investigation the Effects of Different Composition of Chitosan/ Clay on the Nanocomposite Film Properties

Transcription

1 Ref: C0120 Investigation the Effects of Different Composition of Chitosan/ Clay on the Nanocomposite Film Properties Jafar HASHEMI, Department of Biosystem and Agriculture Machinery, Sari University of Agricultural Sciences and Natural Resources, Sari, Iran Marcos NEVES, School of Life and Environmental Science, College of Agrobiological Resource Scinces, University of Tsukuba, Japan Tomoyuki YOSHINO, Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, Ujina-Higashi, Minami-ku, Hiroshima, Japan Mitsutoshi NAKAJIMA, School of Life and Environmental Science, College of Agrobiological Resource Scinces, University of Tsukuba, Japan Abstract Nanocomposite film is one of the promising ways to modify biopolymer properties to make hybrid films with biopolymers and nano sized materials. The effect of nanoclay concentration on the water vapor permeability (WVP), water vapor transmission (WVTR), mechanical properties of the nanocomposite films was evaluated. In this study, chitosan nanocomposite films were prepared using a solvent-casting method by incorporation different concentrations of bentonite nanoclay. Concentrations of nanoclay greatly affect the WVP of biopolymer films at identical concentrations of chitosan. The lowest WVTR was observed in nanocomposite with 2%wt chitosan and 3%wt nanoclay. By adding nanoclay bentonite, the tensile strength (TS) of the nanocomposite films about 20% to 60% were improved. Also the elongation of nanocomposite films decreased with increasing amount of nanoclay. Further increasing clay content to 3 wt%, the WVP and E decreased and TS of nanocomposites film increased in chitosan 2 wt%. It is implied that three percentage of nanoclay not only decreased the WVP by aiding the role of chitosan but also modified the rheological properties of nanocomposite film. Adding nanoclay to chitosan polymer could be enhunced mechanical and WVP properties of nanocomposite film than pure chitosan film. Keywords: Chitosan, Mechanical properties, Nanoclay, WVP 1. Introduction Edible films and coatings have received considerable attention in recent years because of their advantages over synthetic films. Polysaccharides used for edible films include cellulose, starch derivatives, pectin derivatives, seaweed extracts, microbial fermentation gums and chitosan (Krochta and Mulder, 1997). Among the active biomolecules, chitosan has a great potential for a wide range of food applications due to its biodegradability, biocompatibility, antimicrobial activity, non-toxicity and film-forming capacity (Arvanitoyannis, 1999; Tharanathan and Kittur, 2003; Cha and Chinnan 2004). It can form semi-permeable coatings, which can modify the internal Proceedings International Conference of Agricultural Engineering, Zurich, /5

2 atmosphere, thereby delaying ripening and decreasing transpiration rates in fruits and vegetables (Ribeiro et al., 2007). Chitosan biopolymer has several advantages over other types of disinfectants and synthesis polymer such as biodegradability, gas barrier (increasing shelf life), and antimicrobial (increasing of spoilage time). But it has some demerit include of low mechanical properties, high water vapor permeability (Vargas et al., 2009). One of the promising ways to modify biopolymer properties such as inherent water sensitivity, relatively low stiffness and strength, and low thermal stability, is to make hybrid films with biopolymers and nano sized materials, which are known as nanocomposite films. It is consisting of nanolayers of silicates and organic polymers have recently evoked intense research interests in the materials science society. To design proper edible antimicrobial films to be used in food preservation can be considered as one of the major challenges for food technologists in the next few years. In the future, these films will be tailor made to solve some specific problems for a given product. The objectives of this study were to prepare composite films based on chitosan & nanoclay to gain some of the high mechanical strength of nanoclay and some of the superior biological properties of chitosan, to enhancing the water vapor barrier properties and mechanical properties and also to evaluate the morphology of surface structure of prepared film at two concentration of composite materials. 2. Materials and methods Chitosan medium molecular weight (448877, Sigma-Aldrich, Japan) with 75% deacetylation degree and 50,000 g/mol molecular weight were used. Nanoclay hydrophilic bentonite, (CAS: , Sigma-Aldrich, USA) was used in this experiment. Bentonite clay consists of about 1 nm thick layers and stacked in 5-10 µm multilayer stacks. To preparation of film, a clear chitosan aqueous solution (2 and 3 wt %) was prepared by dissolving powdery chitosan corresponding to desired weight ratio of acetic acid (1%, v/v) and stirring for 2 hrs. The glycerol (3% v/v) and Tween-20 (1% v/v) were added and the solution were stirred for 10 hrs at 55 o C. Nanoclay solutions with two compositions (1, and 3 %wt) were prepared by dispersing appropriate amounts of clay powder in distilled water and vigorously stirring for 12h at room temperature prior to nanocomposite solution. The chitosan solution was slowly added to the clay suspension at 55 o C. The nanocomposite chitosan/clay solution was cast by pouring certain amount of the solution onto aluminum plate (10 13 cm 2 ). The specimens of the nano-composite films were kept in a desiccator with silica gel at room temperature before use (Bhuvaneshwari et al., 2007). Sample codes denoted the materials were used during the chitosan/clay film solution. The first character indicated nanoclay bentonite (NB). The numbers were the concentration of the nanoclay and chitosan (%). The other character showed the chitosan with medium molecular weight (CM). A ph of nanocomposite solution was measured by ph-meter (Metrohm, 827 ph lab, Swiss) at 25 o C. The films thickness was measured using digital slide caliper. Water vapour permeability (WVP) was measured by using the Japanese method, JIS, K7129 (Yoshino et al., 2002). Cups consisted of cylindrical shape (7 cm in diameter and 2.1cm in depth) and cover ring to sealing. Cups were filled with calcium chloride, covered with a film, sealed with paraffin and placed in a desiccator chamber which conditioned at 37 C, 75% RH. The weight of the cup was measured intermittently at intervals of 12 h, up to 48 h. The WVP of the nanocomposite films was calculated using the equation 1, as follows: WL WVP (1) tap Where, WVP = water vapor permeability (10 12 g m/m 2 s Pa) W = increase in cup weight (g) L = thickness of film (m) t = measuring time (s) A = measuring area (m2) P = pressure difference in between outside and inside of the cup (Pa). Proceedings International Conference of Agricultural Engineering, Zurich, /5

3 The water vapor transmission rate (WVTR) was calculated using the equation 2, as follows: ( W W WVTR ) 1 2 (2) ta Tensile strength (TS) from each type of film will be measured by using of rheomete (Rheo meter, Shiba Soko, Japan). Samples were cut from the nanocomposite films by using a standard sample cutter (JIS Z1702; Rheotech, Tokyo, Japan). The tensile strength of the film was measured by pulling at a constant rate of 2 cm/min at room temperature by rheometer. Percentage of elongation (E%) at break of the film was calculated as the ratio of initial length to the final length at the point of sample rupture to the initial length of a specimen. 3. Results and Discussions The WVP, WVTR, and mechanical properties of chitosan and chitosan/clays nanocomposite films were measured and are summarized in Table 1. Table 1: The nanocomposite film properties at different concentration of chitosan and nanoclay Chitosan concentration (% wt) 2 3 Nano clay concentration (%w) Samples code NB 0 CM 2 NB 1 CM 2 NB 3 CM 2 NB 0 CM 3 NB 1 CM 3 NB 3 CM 3 Thickness (μm) WVP (10 12 g m/(m 2 s Pa)) WVTR (g/(m 2 h)) Tensile strength (kgf/mm 2 ) Elongation (%) Water vapor permeability As indicated in Table 1, the WVP of pure chitosan with 2 and 3%wt concentration was found to be and g.m/(m 2.s.Pa) respectively. The WVP values decreased with increasing in concentration of nanoclay in 2% chitosan treatments and the marked reduction occurred in the 3 wt% clay concentration. The reduction percentage of WVP for nanocomposite with 1 and 3wt% nanoclay were an approximately 18%, 54% compared with pure chitosan 2 w% film respectively. It shows that various concentrations of nanoclay greatly affect the WVP of biopolymer edible films at certain concentration of chitosan. The highest WVP is observed in samples with 1% nanoclay and 3% chitosan. The reason is not clear but it might be due to the surface properties and internal structure of the film. Therefore, it can deduce that the WVP decreased as the clay content increased in polymer matrix which is close to results obtained by Hale and Funda (2010). The relationship between WVP and TS should be considered. Normally, the lowest WVP agrees well with the highest TS. As clear from Table 1, the WVTR trend was similar to WVP trend at identical concentration of chitosan and clay. There is a marked difference of WVTR values in the nanocomposite with 2% and 3% chitosan in different percentage of nanoclay. Fig. 1 is shown the conditions of nanocomposite film after one week. As it is clear, the sample was covered with pure chitosan was damaged completely but the sample covered with nanocomposite (2% chitosan and 3% nanoclay) is still safe. As it was explained, the weight of both samples increased due to absorption of humidity but the amount of absorption was different. It can be interpreted that changing in internal environment of cup with nanocomposite film is slower than pure chitosan film. So, nanocomposite film with nanoclay Proceedings International Conference of Agricultural Engineering, Zurich, /5

4 be able to keeping the food for long time with minor and necessary changing in the inside environment. (a) NB 3 CM 2 (b) NB 1 CM 2 (c) NB 0 CM 2 Figure. 1: The nanocompisite films condition after 7 days in chitosan 2%wt 3.2 Tensile strength The mechanical property takes into account the response of membranes to an external stress which might be happed during the storage. Tensile testing provides an indication of the strength and elasticity of the edible film. As shown in Table 1, tendency of TS exhibited increasing with increase the percentage of nanoclay bentonite but the increasing value is different. When 1 and 3 wt% nanoclay bentonite was added, the percentage of TS of nanocomposite film was an approximately 58% and 20% increase compared with pure chitosan film with 2 %wt concentration respectively. As indicated in Table 1, further increasing clay content, the TS of nanocomposite films increased in compare of pure chitosan film but the amount of TS was higher for 1 wt% clay. It can be deduced that nanoclay not only decreased the WVP by aiding the role of chitosan but also modified the rheological properties of edible film. 3.3 Elongation at break point The obtained data of E% presented in Table 1. The elongation of nano composite with chitosan 3 wt% trend was similar to chitosan 2% trend at identical concentration of nanoclay. The elongation of the films decreased slightly with addition of nanoclay for samples with chitosan 2 wt%. The reduction percentage for nanocomposite with 1 and 3 wt% nanoclay were an approximately 59%, 62% compared with that of pure chitosan 2% respectively. The result shows that elasticity of an edible film or the ability of a membrane to deformation decreased due to locating the silicate layer between the polymer chains. Low values for elongation imply brittleness and minimum elasticity in the edible film which was confirmed by Bourtoom (2008). However, their mechanical properties and permeability are generally poorer than synthetic films Bourtoom (2008). 4. Conclusions The effect of different nanoclay concentration on the water vapor permeability, water vapor transmission, mechanical properties and morphology of surface structure of the nanocomposite films was evaluated. - The reduction percentage of WVP for nanocomposite with 1 and 3wt% nanoclay shows that various concentrations of nanoclay greatly affect the WVP of biopolymer films at identical concentration of chitosan. The lowest WVTR is belonging to nanocomposite with 2% chitosan and 3% nanoclay. - By adding nanoclay bantonite, the TS of the nanocomposite films about 20% to 60% were improved. Further increasing clay content to 3 wt%, the TS of Proceedings International Conference of Agricultural Engineering, Zurich, /5

5 nanocomposites film increased significantly in chitosan 2 wt%. It can be concluded that nanoclay with high concentration not only decreased the WVP by aiding the role of chitosan but also modified the rheological properties of edible film. - The pore spaces were observed in nanochomposite with different percentage of nanoclay due to the breaking of the bridges between particles. This condition might be affected on the mechanical properties and WVP of film. - Finally, increase in TS accompanied by decrease in WVP and elongation. It can deduce that by adding nanoclay, interactions between nanoclay and chitosan, leading to the formation of a new material with better mechanical and water vapor permeability properties than pure chitosan. 5. References Arvanitoyannis, I. S. (1999). Totally and partially biodegradable polymer blends based on natural and synthetic macromolecules: Preparation, physical properties, and potential as food packing materials. Journal of Macromolecular Science, Part C-Reviews in Macromolecular Chemistry and Physics, 39(2), Bhuvaneshwari, S., Sruthi, D., Sivasubramanian, V., kalyani, N., Sugunabai J. (2007). Development and characterization of chitosan film. International Journal of Engineering Research and Applications (IJERA). 1(2), Bourtoom, T. (2008). Edible films and coatings: characteristics and properties. International Food Research Journal 15(3), Cha, D.S. and Chinnan, M.S. (2004). Biopolymer-based antimicrobial packaging: Review. Crit. Rev. Food Sci.. Nutr. 44: Hale O., Funda T. (2010). Preparation and barrier properties of chitosan layered silicate nanocomposite films. Macromol. Symp., 298, Krochta, J. M. and Mulder-Johnson C. (1997). Edible and biodegradable polymer films: challenges and opportunities. Food Technology, 51(2), Ribeiro, C., Vicente, A., Teixeira, J. A., & Miranda C. (2007). Optimization of edible coating composition to retard strawberry fruit senescence. Postharvest Biology and Technology, 44, Tharanathan, R.N., and Kittur F.S. (2003). Chitin: The Undisputed Biomolecule of Great Potential. Crit Rev Food Sci Nut, 43(1), Vargas, M., Albors, A., Chiralt, A., and González-Martínez C. (2009). Characterization of chitosan -oleic acid composite films. Food Hydrocolloids, 23, Yoshino, T., Isobe, S., and Maekawa T. (2002). Influence of Preparation Conditions on the Physical Properties of Zein Films. JAOCS, 79 (4), Proceedings International Conference of Agricultural Engineering, Zurich, /5