STRUCTURAL AND OPTICAL CHARACTERISTICS OF POLY(VINYL ALCOHOL)/ CARBOXYMETHYL CELLULOSE/CURCUMIN NANOCOMPOSITES

Curcumin nanoparticles (CurNP’s) were successfully synthesized, characterized, and used as a cross-linking dopant of polyvinyl alcohol/ sodium carboxymethyl cellulose (PVA/CMC) semi-natural polymer blend. Synthesized nanocomposite films of (PVA/CMC/CurNP’s) were characterized using Fourier transforms infrared FTIR spectroscopy and tested for their resistance of different bacterial grams. Obtained data shows that studied PVA polymerized and cross-linked with CMC as a result for hydrogen bonding between the carboxylic groups and with the non-substituted hydroxyl groups of the cellulose molecule. The optical energy gap was found to be sensitive for the CurNP’s doping level, and the indirect transition was dominant in the studied samples. The addition of CurNP’s appears to increase the activity index of all samples against both gram-negative and positive bacteria, and their activity increases with increasing dopant level until a specific optimal concentration.


INTRODUCTION
Curcumin is an enormously influential, non-toxic, bioactive agent found in turmeric and has been known for centuries as a household remedy to many ailments. The only detriment is that it suffers of low aqueous solubility and poor bioavailability. Nanoparticles of curcumin (nano curcumin) were prepared by a procedure based on a wet-milling approach. They were found to have a fine particle size distribution in the range of 240nm. On the contrary to curcumin, nano curcumin was found to be freely dispersible in water in the absence of any surfactants. The chemical structure of nano curcumin was the same as that of curcumin, and there was no modification during nanoparticle preparation. A minimum restrained concentration of nano curcumin was determined for various bacterial and fungal strains and was compared to that of curcumin. Curcumin, the agent responsible for the characteristic yellow-orange color and the solid spicy taste of curries, is the principal polyphenol derived from the root of the turmeric plant (Curcuma longa). In addition to its uses in the food industry as a spice and food-coloring agent, curcumin has commonly been used as an herbal remedy for inflammatory disorders, such as arthritis, colitis, and hepatitis. Former research has revealed that curcumin possesses pharmacological effects, including antitumor, anti-inflammatory, and anti-infectious activities [1][2][3][4].
Cellulose is the largest polymer on earth, which, as well as the most common organic compound. The bulk of cellulose is commonly used in manufacturing paper and cardboard goods like raw material, and a limited fraction is used in the manufacture of commodity materials and value-added carboxymethyl cellulose and methylcellulose, etc. [5]. In addition, by-products such as carboxymethyl cellulose, methylcellulose, ethylcellulose, hydroxypropyl cellulose, cyanoethyl cellulose, and so on can be chemically modified to pay for value-added cellulose in all these cellulosic products that are converted. Because of its broad commercial applications concerning volume demand, CMC is synthesized in substantial quantities. A wide variety of uses, including food additives, pharmaceuticals, cosmetics, papers, adhesives, lithography, ceramics, detergents, and fabrics, are recognized within numerous industries [6,7]. In all cellulose ether product groups, CMC is one of the largest market shareholders with such diverse applications along with its low pricing. Carboxymethyl cellulose (CMC) is a type of cellulose ether that is soluble in water. It is one of the essential cellulose derivatives produced in the presence of an alkali catalyst by reacting cellulose with acetic acid. Due to its hydrophilicity, non-toxicity, excellent biocompatibility, and low price, CMC has outstanding pharmaceutical and biomedical applications. However, the electrospinning of CMC is highly difficult due to the very poor solubility of organic solvents. The CMC nanofibers were successfully manufactured in previous studies by combining them with polymers such as polyethylene oxide (PEO), poly (vinyl alcohol) (PVA) [8,9].
Poly(vinyl alcohol) (PVA) is a water-soluble polyhydroxy polymer, used in practical applications because of its simple preparation, excellent chemical resistance and physical properties, ideal mechanical properties, and is fully biodegradable and inexpensive. The -OH groups can be a source of hydrogen bonding (H-bonding) and thus assist in polymer blend forming. There are excellent film formation, emulsifying, and adhesive properties of polyvinyl alcohol. It is oil, grease, and soap resistant as well. It is odorless, non-toxic, with high tensile strength, flexibility, and high resistance to oxygen and scent. Owing to the desirable nature of comparatively small -OH groups bound to alternate carbon atoms of PVA, the chemical composition of PVA favors the development of intramolecular hydrogen bonding, so it is used in the preparation of different membranes and hydrogels [10].
The presented study aims to introduce a clear insight into the role of curcumin nanoparticles in the physical characteristics of CMC/PVA cross-linked polymer blend and their correlation with their bioactivity against pathogenic grams.

EXPERIMENTAL
Polyvinyl alcohol (PVA) of molecular weight 6000 g/mol supplied by Acros Organics (USA) in combination with sodium carboxymethyl cellulose (CMC) provided by Lanxess (Germany) were used for blend biofilm preparation. Curcumin from (Curcuma longa) was supplied by herbal house centers (Egypt). Curcumin nanoparticles were prepared using hydrothermal route adopting 2 g curcumin powder with 2 mL dimethyslsulfoxide (DMSO) with 30 mL bidistilled water at 60 °C for about 12 h.
The echo-friendly solvent casting route was used for the preparation of blend films and other nanocomposite films doped with CurNP's adopting water as a common solvent. Calculated amounts of both polymers were dissolved separately in deionized water with vigorous stirring at room temperature. The two solutions were mixed, and appropriate amounts of CurNPs were added, as shown in table (1). Obtained viscous solutions were poured in a polypropylene Petridishes and positioned in a 50 °C regulated oven until evaporation of all solvent traces. Function groups of the studied films were investigated using (Nicolet is 10) single-beam spectrophotometer within the mid-range between 4000-400 cm -1 . UV/Vis. Electronic spectral data were recorded using JASCO V-570 double-beam spectrometer. The size and morphology of synthesized nanoparticles were investigated using the JEOL-JEM-1011 transmission electron microscope (TEM).

RESULTS AND DISCUSSION
Characterization of synthesized nano curcumin UV/Vis. optical absorption spectrum of synthesized curcumin shown in Figure 1 reveals the appearance of a strong UV absorption band located at 220 nm attributed by several authors to the presence of iron impurities in the extract even at ppm-level. Such a peak followed by another peak in the same region at about 350 nm is generally assigned and confirms the presence of organic chromospheres within the extract [11,12]. Besides, such peaks can be related to unsaturated groups and heteroatoms such as sulfur, nitrogen, and oxygen. The spectrum also shows a visible broad band centered at 425 nm attributed to the formation of curcumin in the nano-form with a shoulder at about 470 nm in their descending lope. It is well known that bulk curcumin showed a visible absorption band at 450 nm [12], which means that nano curcumin usually shows a blue shift. Transmission electron microscopic images approve the formation of spherical CurNP's with a radius of about 65 nm.

FT-IR optical absorption spectra of studied materials
FTIR can reveal the chemical changes by producing absorption spectrum. It can be seen that FTIR spectra of original curcumin and curcumin nanoparticles did not show significant differences.    [14][15][16]: (i) a broad medium intensity band at 3340 cm -1 was assigned to the hydroxyl group in the main structure, (ii) a sharp, intense band at 1735 cm -1 and another band at 1100 cm -1 corresponds to the C-O stretching vibrations in the acetate group, (iii) bands at 2940 and 2910 cm -1 attributed for the aliphatic backbone C-H stretching vibrations and (iv) the band at 1335 cm -1 has been assigned to the combination frequencies of (CH·OH).
Additionally, the spectrum of the CMC sample shows the following absorption bands: The band located at about 2980 cm -1 was assigned for C-H stretching vibrations. The band at 1185 cm -1 attributed for C-O stretching vibrations of ether groups results from carboxymethylation of cellulose or ether linkage of cellulose compartment in combination with that arising from the two types of ether present in CMC. A strong band at 3223 cm -1 results from O-H stretching of the non-substituted hydroxyl groups of cellulose. The band located at 816 cm -1 attributed to the C-O stretching of alcohol. Two broad bands initially located at 3225 and 3495 cm -1 are correlated with intramolecular hydrogen bonding in CMC sodium salt molecules [17][18][19].
Finally, FTIR of cross-linked polymer blend shows notable variations in the spectral bands resulting from PVA polymerization and increase in the hydrogen bonding result in a broadness of the band extended from 3000 to 3600 cm -1 . The previous may explain the formation of hydrogen bonding between the carboxylic groups themselves and with the non-substituted hydroxyl groups of the cellulose molecule. Therefore, it was suggested that interaction of such blend might be assigned to hydrogen bonding. Figure 4 reveals FTIR absorption spectra of pristine synthesized CurNP's dopant with CMC/PVA cross-linked blend films. It was suggested that CurNP's could interact with both CMC and/or PVA causing cross-linking of the polymeric matrix as indicated in Scheme 1. Two major observations were recorded with the addition of CurNP's. Obtained spectral data show maintenance of the bands at the UV region without a change in their position. The observed band in the visible region shows broadness and increasing intensities with increasing curcumin content combined with splitting in the observed shoulders attributed to the hydrogen bonding and interactions between polymeric matrices and dopant material. Mode of transition can be estimated from analysis of the optical band gap calculated from both fundamental absorption edge (Eg = hc/λ) or via Tauc's plots of energy (h) versus (h) 1/2 or (h) 2 for both direct and indirect energy gap respectively. Figure 6 shows Tauc's plot and their use for the estimation of optical energy gap from their extrapolated lines. The estimated energy gap for the blend sample and their nanocomposites containing different content of curcumin nanoparticles were listed in Table 2.

Antibacterial tests
Antimicrobial activity tests of studied nanocomposite films were tested against different pathogenic grams. Two streams of each gram were studied, gram-positive (B. subtilis and S. aureus) and gram-negative (E. coli and P. aeruginosa) bacteria are shown in Figure 7. The experiment was conducted at pH 7 and 37 °C with distilled water and compared with that free of dopant nanoparticles [22]. Antimicrobial resistance against various grams can be interpreted in terms of three different mechanisms: enzymatic breakdown of antibacterial medications, changes in antimicrobial target bacterial proteins, and changes in antibiotic membrane permeability.
The relation between curcumin nanoparticles content (mL/wt) drawn against the diameter of inhibition zone (mm) reveals three important facts: (1) the inhibition zone of samples containing curcumin nanoparticles shows a larger inhibition zone compared with a pure blend (70CMC/30PVA), (2) the increase of CurNP's content is usually combined with an increase in the inhibition zone, (3) higher concentrations 7.5 and 10 shows a gradual and small variation, and (4) Gram-negative bacteria usually show higher activity.

CONCLUSION
Curcumin nanoparticles (CurNP's) were successfully synthesized from Curcuma longa using a solvent-free hydrothermal route. The formation of CurNP's was approved via the formation of a visible band located at 425 nm while transmission microscope micrographs indicate the formation of spherical CurNP's with a radius of about 65 nm. Synthesized CurNP's were used as a dopant cross-linker for PVA/CMC nanocomposite films. Synthesized films were observed to be sensitive for the CurNP's doping level especially in the visible region and the indirect transition was dominant. Samples containing CurNP's shows higher biological activity against different pathogenic grams with respect to the undoped polymer blend while higher concentrations 7.5 and 10 show gradual and small differences and gram-negative bacteria usually show higher activity.