Evaluation of physicochemical properties of emulsified nanobiocomposite films based on carboxymethyl cellulose-nano silver

Introduction: Over the years, the biological effects ofsynthetic plastics and food packaging waste have raised global concerns about the limitations of their disposal methods. Thus, in the last two decades, there has been a growing interest in the development and growth of biopolymers and technologies that reduce the dependence on fossil fuels. Also, the use of stable bionanocomposite materials has grown significantly (Weber et al., 2002; Sorrentino et al., 2007). CMC is water soluble and has the ability to form flexible and strong films. Carbohydrate films usually have good mechanical properties and good oxygen retention. However, resistance to moisture penetration is weak due to the nature of their hydrophilicity (Rhim et al., 2013). Therefore, in recent years, a lot of research has been done on improving the properties of these films and improving their inhibitory, thermal, physical and mechanical properties. Recently, production of nanocomposites is one of the newest ways to improve the inhibitory, thermal and mechanical properties of food packaging based on biopolymers (Sinha and Bousmina 2005; Rhim 2007; Bordes et al., 2009) On the other hand, another way to improve the inhibitory properties and increase the hydrophobic properties of CMC films is to produce emulsion films and use hydrophobic compounds such as fats in their composition. Fatty acids, such as oleic acid, can potentially improve the moisture retention properties of hydrophilic films. Bioanocomposite refers to a material consisting of two phases, a matrix and a filler, with a filler measuring 1-100 nm. The fillers used include organic compounds (clay particles, cellulose nanoparticles, chitosan and chitin nanoparticles, carbon nanotubes) and inorganic compounds (nanosilver, titanium, dioxide, iron, silica) (De Azerdo et al., 2009). Silver nanoparticles have been used in the production of active packages due to their strong tensile properties on a wide range of microbes, high thermal stability and low volatility (Kumar and Manstedt 2005). According to library studies, the effect of silver nanoparticles on CMC emulsified films has not been investigated. Therefore, the aim of this study was to study the optical properties, water vapor permeability, thermal properties and topographic characteristics of CMC emulsified films.
Material and method: To make emulsified films based on carboxymethyl-cellulose-silver nanoparticles, 3 g of CMC powder was dissolved in 180 ml of distilled water and stirred continuously on a magnetic stirrer at 65 ˚C for 45 minutes. After the clear gel was formed, 1 ml of oleic acid (0.3 g / g CMC) and tween 80 (1% by weight of oleic acid) were added to the solution as emulsifiers. Then, in order to homogenize the solution, the Ultra-Turrax T25 homogenizer was used (24000 rpm for 6 min). Different percentages of silver nanoparticles (0.5, 1 and 2 wt % based on CMC) were transferred to 100 ml Erlenmeyer flasks and 20 ml of distilled water was added. In order to better disperse the nanoparticles, they were placed in an ultrasonic bath for 10 minutes.  It was then added to the carboxymethylcellulose-oleic acid solution and stirred for 5 minutes. In the last step, 1.5 ml of glycerol as a plasticizer was slowly added to different parts of the solution and placed on a magnetic stirrer for 20 minutes. Finally, for uniform distribution of the dissolved nanoparticles, it was placed in an ultrasonic bath for 5 minutes. Finally, 50 g of this solution was dried in glass jars at 55 ˚C for 18 hours. Then, the effect of incorporation of the Ag silver nanoparticles on CMC emulsified film optical properties, Water vapor permeability, thermal properties and topographic characteristics were investigated.
Results and discussion: The aim of this study was to prepare emulsion films based on CMC and evaluation effect of silver nanoparticles on their physicochemical properties. The amount of WVP decreased significantly with increasing nanoparticle concentration (P <0.05). Silver nanoparticles, by being in the empty spaces of the biopolymer matrix and creating zigzag paths, the path for moving water vapor make hard and long. The rate of transmission in the UV-C (240 nm) range in the CMC film control and samples containing 2% nano silver were 0/01% and percentage of transmission wavelengths in UV-A (nm ٣٦٠) in CMC film was 78.16%% which by addition of silver nanoparticles, decreased to 11.11%. Also, the rate of inhibition of visible waves (600 nm) by addition of nanoparticles increased. The results of the DSC test showed that Tg by addition of silver nanoparticles decreased from 86/65 ˚C to 83.61˚C, but their thermal resistance increased. According to the X-ray test, the peak intensity of the peaks decreased and their size expanded in 2% concentration. This indicates the uniform distribution of nanoparticles in the biopolymer matrix. Images obtained from AFM show that CMC emulsion films control have a relatively smooth surface. But in nanocomposite films containing 2% silver nanoparticles, surface roughness of the film increased and the uniformity surface their decreased.
Conclusion: In this study, emulsion nanocomposite films based on CMC were produced and the effect of silver nanoparticles in different concentrations on its structural properties was studied. The nanoparticles increased film's resistance to WVP, and the film's resistance to UV-VIS waves was improved. The results of XRD showed that the nanoparticles at a concentration of 2% were well distributed in the biopolymer matrix. However, they almost retained their crystalline form. The Tg of the film decreased at concentration of 2% nanoparticles and their surface roughness increased.