Rheological and Antimicrobial Properties of Silica and silver Nanoparticles-reinforced K-carrageenan/hydroxyethyl Cellulose Composites for Food Packaging Applications

Sustainable food packaging lms were developed using a combination of k-Carrageenan (C), hydroxyl ethyl cellulose (H), silicon dioxide (SiO 2 ), and silver (Ag) nanoparticles. The CH-SiO 2 /Ag nanocomposites showed promising results, mainly due to their transparency, exibility, low cost, and environmental friendliness. The structure and uniform morphology of the CH-SiO 2 /Ag nanocomposites were determined by FT-IR, XRD, and SEM analysis. Barrier properties (water vapor permeability-WVP), thermal properties (T 5% loss, char yield), and mechanical properties determined for the CH and CH-SiO 2 /Ag nanocomposites, which improved by 3.3–1.9 ×10 − 9 gm/m 2 Pas (WVP), 59.1-115.7 o C (T 5% ), 13.4–29.3 % (char yield), 23.8–41.5 MPa(tensile strength), and 22.3–28.9 (EB), respectively. The contact angles of the CH-SiO 2 /Ag nanocomposites were in the range of 60.1–76.4. The UV transmittance of the CH composites decreased with the addition of SiO 2 and Ag nanoparticles. However, the transparency of the composites was not affected, and it inhibited UVA and UVB rays by the addition of Ag nanoparticles. The increased decreased higher than 2 /Ag nanocomposite has potential for packaging and other biomedical applications.


Introduction
These days there is a great attention on the terms environment friendly, green synthesis, sustainable, biocompatible and biodegradable, in the area of material science research. Particularly, in polymers and plastics being used in many sectors for packaging ( Tippabattini et al. 2013). However, it is damaging our ecosystem, human and animal health, due to unrealizable utilization (Zhili et al. 2017; Rhim et al. 2014). Owing to the above concerns, biopolymer-based composites are an immediate alternative with reasonable parameters such as low cost, biodegradability, biocompatibility, and low toxicity, and are available from sustainable natural resources.
Carrageenan is a linear and high molecular weight biopolymer derived from red seaweed (Eucheuma spinosum) and is available in different structures such as kappa, iota, and alpha carrageenan. It was classi ed based on the composition of 3, 6 -anhydro-galactose and ester sulfate groups. Kappa-carrageenan However, both k-Carrageenan and hydroxyethyl cellulose are mechanically weak and have poor barrier properties (Mithilesh et  To overcome these disadvantages, the incorporation of two more biopolymers and the addition of inorganic additives is the best method (Lokesh et al 2014; . The above disadvantages are easily overcome by the preparation of two or more biopolymers based on the addition of inorganic additives such as In this work, we prepared a synergistic composition based on k-carrageenan, hydroxyethyl cellulose, Ag, and SiO 2 nanoparticles. We focused and thoroughly studied the rheological properties of the CH-SiO 2 /Ag nanocomposites. In addition, the effect of Ag and SiO 2 on the water barrier, contact angle, and mechanical properties were systematically explored.

Materials And Methods
K-Carrageenan (Ash content 40.0% and viscosity min 10.0 in 0.30% in water at 25 o °C), 2-hydroxyethyl cellulose (molecular weight M v ~ 1,300,000), and SiO 2 (particle size 50 nm, BET) were purchased from Sigma Aldrich, South Korea and used as received. Glycerin, sodium citrate, epichlorohydrin, and citric acid were purchased from Dajang Chemicals, South Korea. A silver colloid (Nanomix-silver 30 000 ppm) was obtained from Meiji Nanotech (Seoul, Korea). All reagents were used as received.
Preparation of CH-SiO 2 /Ag nanocomposite lms CH with various concentrations of SiO 2 (0, 2.5, 5, 7.5, and 10 wt%) and Ag nanoparticles were prepared by the solvent evaporation method. First, k-carrageenan (0.5g) and hydroxyethyl cellulose (0.5g) were dispersed in glycerin (3g) to ensure that there was no particle agglomeration. Then, 75 mL of distilled water was added with continuous stirring and the temperature was increased to 80 o C for 15 min. The crosslinking agent of epichlorohydrin (4 wt%) was added to the above solution. Subsequently, citric acid (0.5g) and sodium citrate (0.5g) were mixed one by one in the reaction mixture at same condition. SiO 2 was dispersed in ethanol separately in sonicated for 60 min at 50 o C. The dispersed SiO 2 was mixed with the hydrogel reaction mixture and continuously stirred for another 60 min. The temperature was reduced to 50 o C and 0.25 mL of silver colloid solution was added with vigorous stirring. Finally, the CH-SiO 2 /Ag nanocomposite hydrogel was spread on the glass plate and dried at ambient temperature, and then removed from the glass plate, under dried conditions. Similarly, the same procedure was followed for all the (a) CH (b) CH-SiO 2 -2.5 wt% (c) CH-SiO 2 -5 wt % (d) CH-SiO 2 -7.5 wt% (e) CH-SiO 2 -10 wt% (f) CH-SiO 2 -10 wt% /Ag nanocomposite preparations.

FT-IR
The FT-IR spectra of the CH-Ag composites are shown in Fig. 1 Further, w by the addition or increasing content of SiO 2 nanoparticles, this peak shifted slightly, and the intensity of the peak for the CH-SiO 2 -10 wt% composites increased. The XRD patterns of the CH-SiO 2 -10 wt% /Ag nanocomposites all the materials dispersed well, and the amorphous structure of k-C was not affected and altered by the incorporation of HEC, SiO 2 , and Ag nanoparticles. UV UV-VIS spectroscopy is a very important technique for studying the transmittance and absorption of food packaging composite lms. Figure 3 and Table 1 show that the transmittance of the CH and CH-SiO 2 -10 wt% /Ag nanocomposites are in the ranges of 92.2-89.7 and 91.5-89.5 % at 800 nm and 600 nm, respectively.
There was no signi cant reduction in their transmittance. However, at 280 nm, the transmittance decreased to 71.7-56.6 % for CH and CH-SiO 2 -10 wt% /Ag composites, respectively. The transmittance of the CH composites decreased from 800 to 280 nm from 92.2% to 71.7 %, and for the CH-SiO 2 -10 wt% composite is 90.7% to 64.1 %. The addition of SiO 2 nanoparticles gradually decreased the transmittance, but the addition of

TGA
The rate of decomposition and thermal stability of the CH and CH-SiO2-10 wt% /Ag nanocomposites were studied by TGA under nitrogen atmosphere ( Table 2 and Fig. 4). The initial thermal degradation of the CH composites is very low. The 5% gravimetric loss of the CH composites was 59.

Rheology
The storage modulus (G') and loss modulus (G') were studied for the 3D structure and coordination bonds However, the rate of increase of G' shows that the elastic properties of the gelling hydrogel dominate. Figure 7 shows the loss modulus of the CH composites. It was observed as very steep in the low frequency region.
When the frequency is increased, it minimizes the slippage level and maintains a reasonable level. In the highfrequency region (20-100 rad/s), G'' increased, which indicated that the nanocomposites exhibited a more elastic behavior for the materials. The concentrations of SiO 2 and Ag played an important role in the G' and G'' of the CH composites.
The complex viscosity versus frequency of the CH and CH-SiO 2 -10 wt% /Ag nanocomposites is shown in From the dynamic viscoelastic results of G' and G' and the complex viscosity of CH and CH-SiO 2 -10 wt% /Ag nanocomposites showed strong interactions between CH and SiO 2 and Ag nanoparticles. Figure S4 shows the shear dependent viscosity results for the CH-SiO 2 -10 wt% /Ag nanocomposites. The viscosity of the CH composites decreased at a low shear rate. This shear thinning or non-Newtonian behavior of composites is due to the molecular disentanglements in their structure and aligned with the ow direction (Hadi et al. 2020).
The viscosity of the CH composites was 51.2 Pas, which increased to 261.0 Pas by the addition of 10 wt% of SiO 2 nanoparticles at a 1/s shear rate (Fig. 9). At low shear rates, the viscosity of the nanocomposite is higher than that of neat CH, but the high shear rate decreases signi cantly. This may be attributed to the coalescence of nanoparticles, which leads to a decrease in the surface area and interaction between the nanoparticles and polymer matrices.
The full range of shear stress versus shear rate of CH and CH-SiO 2 -10 wt% /Ag composites is shown in reported. The effect of SiO 2 and Ag nanoparticles is more pronounced at low shear rates, and it (or the relative effect) diminishes with increasing shear rates due to shear thinning. Moreover, the trend of the viscosity and shear stress with shear rate is very similar to the reported composites.

Antimicrobial properties
The antimicrobial properties of the CH and CH-SiO 2 -10 wt% /Ag nanocomposites were studied by the well diffusion method and the results of their inhibition zone of the CH-SiO 2 -10 wt% /Ag nanocomposite lms are shown in Table 3. This study was broadly performed using four different gram positive and two different   These developed CH-SiO 2 -10 wt% /Ag nanocomposites are suitable for active food processing in biomedical applications.