Synthesis and characterization of high flux and antibacterial film nanocomposite based on epoxy-zeolite NaA

INTRODUCTION

Polymers due to properties and low cost are widely used in various industries application, but, polymers have the low total strength and poor fraction toughness which limit their applications in structural components [1-3]. Numerous fillers use to improve properties polymer such as nano-clay, zeolite, carbon black, carbon nanotubes compound with the polymers epoxy resin is a thermoplastic polymer which has unique properties such as excellent adhesion, chemical resistance, and high tensile strength [4-7]. Adding nanoparticles such as zeotype materials in the matrix of polymer improve the thermal stability of the produced composite [8-12]. Industrial applications of epoxy-based polymer materials are extensive and include adhesives, coatings and composite materials such as fiber and fiberglass [13].

Hard water has high concentrations of Ca²⁺ and Mg²⁺ ions and has serious problems for the industry also limit its use. Due to cation exchange ability zeolites can reduce water hardness [14]. The use of zeolites in polymers makes it easy to separate them from solutions and reduce their cost considerably [15].

Zeolite NaA incorporated into the polyamide polymer matrix improves membrane permeability and silver exchange zeolite-polyamide nanocomposites exhibit antibacterial properties [4].

Zeolites are crystalline microporous and mesoporous structures of alumina silicates, which have high porosity. These structures have three-dimensional pore and cavities. Zeolite cavities have the negative charge that neutralized by cation elements. These cations are often loosely bound and easily replaceable, supplying increase to the ion replacement properties of zeolites without damaging the zeolite framework [16-18].

Zeolite NaA displays the LTA (Linde Type A) structure. The pore diameter is small at 4.2Å and has the larger cavity of minimum free diameter 11.4Å. The general formula for zeolite materials is Mx / n [(Al₂O₃) x (SiO₂) y] mH₂O. For zeolite LTA, the Si to Al ratio is one and the pores size of its related to the type of counter cation (K⁺, Na⁺ and Ca²⁺). One application of Na-LTA zeolites is in detergent as water softener. It can also be with the ion exchange process and the replacement of silver ions in the structure zeolite the antibacterial property given to the specimen [17, 19, 20].

The target of this work was to expand the thin high-performance nanocomposite membranes with the combination of the zeolite NaA and epoxy polymer for effective calcium removal from water also to improve the water permeability at the same time. NaA zeolite ion exchange with silver and copper were used to improve the anti-bacterial nanocomposite membrane.

MATERIALS AND METHODS

Epoxy resin (based bisphenol A type, KFR-120, Kukdo Chemical), modified amine hardeners, tetraethylorthosilicate (TEOS, 98 wt. %), aluminum nitrate (Al (NO₃)₃.9H₂O), ethanol (EtOH, 99 wt. %), and solid NaOH were obtained from Merck.

Synthesis of Zeolite NaA

First 4. 5 ml of TEOS and 5 g of aluminum nitrate were added to 20 ml of the ethanol/water solution mix gently until aluminum nitrate was completely dissolved. Then 25 ml of 0.25 M sodium hydroxide were added to the previous solution gently mix until the gel is created. Then gel is heated under microwave radiation at 100 ° C for 1 minute. After crystallization, the product solid was separated by centrifugation, washed by deionized water several times, dried overnight at 105 °C. To improve antibacterial properties of nanocomposites first Na ion in the structure of zeolite exchanged with Ag and Cu. 1 g of the zeolite were added separately to 0.01 M solutions of AgNO₃ and Cu(NO₃)₂ then was put under reflux at 90°C for 16 h with magnetic stirring. Silver and cooper ions exchange with sodium ions and produce Ag-LTA zeolite and Cu-LTA. The product solid was separated by centrifugation, washed by deionized water several times, dried overnight at 105 °C.

Synthesis of zeolite NaA/epoxy nanocomposite films

Various loading ratios ranging from 0 to 3 wt.% of the zeolite NaA added into epoxy and curing agent mixtures. The mixture was sonication for 30 minutes subsequently de-gassed at 25 °C for 1 h under the vacuum. Nanocomposite films were fabricated on the glass layer by spin coating process at 1000 rpm for 60 s and aging at 60 °C for 10 min. 1% wt% Ag-LTA and Cu-LTA zeolite were added to the epoxy mixture for investigated the antibacterial activity of the nanocomposite.

Membrane performance evaluation

The calcium ion absorption performance for nanocomposite and composite films were evaluated by a bench-scale cross-flow filtration system with a total internal volume of 50 mL and an active surface area of 15 cm². The water flux was computed at the pressure of 2 bar at 25 ^oC. The water flux (J) and and ion removal (R) membranes were determined using the following equations [16, 21]:

 (1)

 (2)

V is the volume of permeate water (L), A is the effective surface membrane area (m²), Δt is the filtration time (h), C_p (mg/L) and C_f (mg/L) are the salt concentration of penetration and feed solutions, respectively. The feed water contained 300 mg/L CaCl₂ solution.

The NaA zeolite that dispersed into the cross‐linked epoxy polymer capable as the ion exchanger, adsorption Ca²⁺ and releases Na⁺. Calcium solutions were prepared using CaCl₂. 2H₂O.

Antibacterial assay

For antibacterial activities, E. coli and S. aureus were selected according to the standard method 24 hours cultured to obtain a logarithmic growth phase. Mueller-Hinton agar is employed for growth medium [22]. 1ml each bacterium was added to the culture medium and then cultured on a plate surface with the sterile swabs. zeolite AgA/epoxy and zeolite CuA/ epoxy nanocomposite was prepared the centimeter square and placed on the culture medium and incubated at 37 °C for 24 h. Antibacterial activity investigated by measuring the diameter of inhibition zone (DIZ) [23].

RESULTS AND DISCUSSION

The bonding interactions between the cross‐linked epoxy and zeolite NaA nanoparticles were analyzed employ a Perkin Elmer, Fourier Transform Infrared (FTIR), from 4000 to 400 cm⁻¹ using a thin layer of the sample on a 25×4mm KRS-5 disc. Fig. 1 shows the FTIR spectra of cross‐linked epoxy, zeolite and epoxy nanocomposite (containing 3 wt.% zeolite nanoparticle) in the range of 4000-400 cm⁻¹. Fig. 1a the peak of the oxirane ring observed at 915 cm^-1 which attribute to the C-O of the oxirane group [24-26]. However, in Fig. 1c the oxirane ring peaks disappear, perhaps reacted with the OH on the surface of the zeolite. The peaks at 990 cm⁻¹ and 462 cm⁻¹ correspond to the asymmetric stretching vibration of inner tetrahedral and the bending vibration modes of T–O bonds in TO4 tetrahedral of zeolite structure (where T = Si or Al), respectively. The peak at 1655 cm⁻¹ is attributed to the bend vibration of OH group in the adsorbed water on zeolite pore [27].

Fig. 2(a)–(c) show the SEM (Philips XL-30ESM) top surface of synthesized epoxy polymer, zeolite, and nanocomposite (containing 3 wt.% zeolite nanoparticle). Fig. 2b shows synthesized zeolite NaA has cubic morphology and flower-like with slightly different sizes. Fig. 2c depicts the morphology of surface nanocomposite, clearly seen zeolite uniformly distributed in the polymer matrix.

Crystallinity and structure of nanocomposite and zeolite, were analyzed employing an were recorded by a Philips, X-ray diffractograms using Ni-filtered Cu Kα radiation. XRD was used to investigate the structure of zeolite NaA/epoxy nanocomposite as shown in Fig. 3. The XRD patterns show the zeolite NaA has a crystalline phase and the nanocomposite has an amorphous phase. XRD patterns of zeolite NaA match well with that of standard Na₉₆ Al₉₆ Si₉₆ O₃₈₄ 216 H₂ O (JCPDS-No. 39-0222).

The TGA of epoxy polymer and zeolite NaA/ epoxy nanocomposite depict in Fig. 4. The results of the thermal gravimetric analysis (TGA) shows that adding zeolite improves the composite thermal stability. In the Fig. 4a, shows the thermal decomposition of the epoxy polymer starts at 350 ° C, while the nanocomposite decomposes at 400 ° C. Zeolite materials have thermal and chemical stability [15]. Zeolite Na can absorb carbon dioxide and reduces emissions of carbon dioxide from burning polymer.

The water contact angle values of the epoxy cross-linked membrane and epoxy cross-linked membrane containing various amounts of nano zeolite NaA in organic phase exhibit in Fig. 5. NaA zeolite is very hydrophilic and cation exchangeable could improvement interaction between the nanocomposite surface and the polar water, thereby increasing the water flux and reduced the contact angle in the epoxy films [14, 28]. The pure epoxy cross-linked membrane showed a high contact angle of 91°. after the incorporation of zeolite NaA nanofiller the contact angle of epoxy cross-link membranes decreases, with increase zeolite NaA loading from 1 wt% to 3 wt%, which means the improve of membrane surface hydrophilicity.

The Fig. 6 show the effect of zeolite weight loaded into the matrix of the cross‐linked epoxy polymer on water permeability, cation adsorption of the nanocomposite. Increase the amount of zeolite loaded into the polymer matrix from 0 to 3 wt.% increases the water flux from 10 to 54 L/m2 h.The NaA zeolite dispersed into the matrix cross‐linked epoxy films creates a new flow path for water crossing through this film. Therefore, adding NaA zeolite into epoxy polymer increases water absorption and permeability [29, 30]. Increasing the amount of zeolite loaded in the range of 0 to 3 wt.% into the cross‐linked epoxy polymer matrix increases the absorption of calcium ion from 4 to 99 percentage.

The image in Fig. 7 illustrates the antibacterial activity of AgA zeolite /epoxy and CuA zeolite /epoxy nanocomposites. The results of the study showed the growth inhibition zone for AgA zeolite/epoxy nanocomposites is 1 mm larger than the CuA zeolite/epoxy nanocomposite. Increased antibacterial properties of nanocomposites due to the release of Ag+ and Cu²⁺ ions to the medium containing bacteria.

CONCLUSION

Nanocomposite epoxy/zeolite NaA film was prepared by loaded of zeolite NaA in the epoxy matrix and homogenization by ultrasonic. Water flux and thermal stability of the membranes significantly enhanced by incorporation of zeolite NaA. The evaluation of the antibacterial properties of the nanocomposite containing AgA and CuA zeolite the membrane against E. coli and S. aureus indicated antibacterial activity.

CONFLICT OF INTEREST

The authors declare that there is no conflict of interests regarding the publication of this manuscript.