Synthesis and optimization of Novel Chitosan/Cellulose Acetate Natural Polymer Membrane for water treatment

Chitosan (Ch) and Cellulose Acetate (CA) natural polymer in addition to other samples with different mass fractions of Chitosan/Cellulose Acetate (Ch/CA) were synthesized via simple casting route. Prepared samples were studied using FT-IR and UV/vis spectroscopic techniques. Structural variations due to the process of blending were retraced using X-ray diffraction data (XRD) and morphological investigation using scanning electron microscopy (SEM). Obtained spectral data reveals compatibility and complexation between polymer constituents identified through presence of polymer characteristic peaks with small variation in both intensity and position along with change in the value of optical energy gap from UV optical absorption spectral data. XRD pattern indicate the semicrystalline nature of the studied sample with an observable change in the crystallinity. Moreover, scanning electron microscopic (SEM) micrographs reveals homogenous structure without any evidence for agglomerations nearly in all compositions.


Introduction
Water is essential to all forms of life and makes up 50-97% of the weight of all plants, animals and about 70% of the human body. Despite its importance, water is the most poorly managed resource in the world. The main sources of water pollution are domestic sewage, industrial effluent, and agricultural runoff. Sodium, copper, chromium, lead and mercury are some of the more common effluent pollutants discharged from industries which causes a number of hazardous diseases. So there is a very urgent need to control heavy metal emissions into the environment [1][2][3][4].
Nowadays filtration, microfiltration and even ultrahigh filtration were performed using polymeric membranes [5]. Natural degradable polymers and their composites are amongst these materials. Many efforts were made to enhance their workability via blending [6] or adding dopant in the nanoscale [7].
Chitosan consider one of the unique renewable and abundant cationic polysaccharide polymeric material results from the deacetylation process of Chitin and characterized their biodegradability and nontoxicity. Chitosan is a functional biopolymer used extensively pharmaceutics, food and in biological applications as immune enhancing partner, anti-tumoral and anti-fungal agent [8][9][10].
Cellulose is the primary component of the core composition of living plant cell wall and may be considered as the major constituent of plant biomass which are the most abundant biopolymer on the earth. Cellulose acetate was synthesized through reaction of cellulose, acetic acid, and acetic anhydride [7] The most of commercially synthetic artificial membranes in the separation industry are made of polymeric matrices. Which may be a single virgin polymer or mix of two different polymers with various characteristic that result in a new material with unique properties for different applications Present work aims to synthesis and optimized a novel biodegradable Chitosan/Cellulous Acetate (Ch/CA) natural polymeric membrane prepared via green route (solvent free) method to be used in water treatment applications.

Materials
Commercial grade Cellulose acetate was supplied from winlab co., UK. Commercial grade Chitosan (poly-2-aminoglucose) of deacetylation degree DD = 93% was supplied by SIGMA Aldrich Co.
Polymeric membrane of varying weight fractions were prepared. Chitosan was dissolved in 2% aqueous solution of acetic acid while cellulose acetate was dissolved in glacial acetic acid. Prepared solution added to each other drop wise and vigorously stirred at room temperature for about 3 hours. Obtained solution were then poured in plastic petri dishes kept at about 50 C until all solvent traces was evaporated. Dry films peeled from the dishes and kept in a vacuum dissector until use. Table 1 shows the chemical composition of prepared thin membrane.

Methods
Fourier transform infrared (FT-IR) experimental data were collected for three different samples from each composition with 32 scan for each using Nicolet is10 spectrophotometer in the spectral range 4000-400 cm -1 with a resolution 4 cm -1 . X-ray diffraction scans (XRD) obtained using DIANO corporation (USA) equipped with CuK radiation (=1.79026Ǻ), the tube operated at 30 kV within the Bragg angle (2) ranging between [5-80]. Ultraviolet/visible (UV/Vis.) absorption spectra were measured at the wavelength region of [200-600] nm using a spectrometer (Perkin-Elmer UV/Vis). SEM micrographs were performed on thin polymeric films of suitable thickness after coating with gold layer of thickness around 2 nm via JEOL JSM-6510LV, USA, operating at 20 kV accelerating voltage.

X-ray diffraction
Figure (1) reveals X-ray diffraction (XRD) of virgin basic samples (chitosan and cellulose acetate) prepared via casting route without any further treatment. Obtained data approved the semi crystalline nature of both samples with two halos around 15, 20.7 in case of chitosan and for cellulose acetate associated with (101) and (020) planes. These characteristic halos previously described by Sudha et al [11] and Mututuvari et al. [12].  (2) shows XRD experimental data of the prepared polymer blend with variable concentration of both samples. First insight for the complex spectra reveal the amorphous character of all prepared samples with obvious increase in amorphousity. Disappearance characteristic crystalline peaks present in virgin constituent is a good indication for complexion and interaction between these polymers and allow homogenous distribution of both polymers their prepared films or membranes with all ratios.
Maxima of XRD peaks was found to be varied with increasing content of chitosan pointing to variation of characteristics and role of each constituent in synthesized samples. Obvious change of the 2Ɵ angle observed at maximum intensity in synthesized samples of low chitosan content up to (20%) followed by gradual decrease tell sample containing about 50% chitosan.

FTIR absorption spectra
Infrared spectroscopy given a variable non-destructive, rapid and accurate technique that used for the identification of specified functional groups especially in case of organic compounds different route can be All samples shows the characteristic sharp absorption edge located between 205-245 nm shifts to higher wavelength with increasing chitosan content. This shift indicate some type of variation in the optical energy gap that can be related to the change in degree of crystallinity or amorphucity in the synthesized sample. The remind spectral range (visible section) shows nearly no change and characterized by the absence of any sharp or broad band. The band located in the UV section may be attributed mainly to unsaturated C=O and/or C=C bands assigned to π→π* transition within the polymeric matrices. The knick or shoulder appears at about 300-450nm in the blend samples arising from N double bond and may be assigned to n→π* transitions within the polymeric matrices [16,17].

Scanning electron microscopic analysis (SEM)
Detailed information about surface morphology and topography associated with variable change in composition and interactions may be retraced using SEM route. Figure (6.a-g) shows the flaky nature of both chitosan and cellulose acetate matrix in different concentrations. Presented images shows the formation of homogenous structure with fair distribution of both polymers by naked eye resulting from the nature of preparation route involving dissolution process in aqueous solution containing 2% acetic acid in case of chitosan and glacial acetic acid in case of cellulose acetate samples. Expect in the case of higher concentration of both partner (CA/Ch) samples (c, d, e, f and g).