Functional Finishing of Polyester Fabric With Polystyrene-acrylic/zno Nanocomposite for Effective Dyes Filtration


 Organic dyes such as Methyl Orange (MO) and Methylene Blue (MB) are widely used in different industries, becoming one of the leading emerging water contaminants. It is urgent to develop the most suitable materials for effective elimination of the dyes as they are non-biodegradable and are not removed efficiently by the traditional treatment methods. The present work applied polystyrene-acrylic/ZnO nanocomposite on the polyester surface by blade coating and one-bath pad methods. Features of surface chemical modifications were determined by FTIR, SEM analysis, WCA, N2 adsorption-desorption isotherms. The functionalised layer can create unprecedented function of filter textile material depending on the way of treatment. The possibility of using such fabrics as ﬁlters was explored for MO and MB in the concentration of 100 ppm. Water purification occurred by 60% from methylene blue and 40% from methylene orange flowing through the padded polyester filter and the covered polyester filter for 2 min, respectively. Moreover, it was shown that a colourless reduced form of MB – leuco-methylene blue (LMB) could be created. The functionalised layer of the developed filters through hydrogen bonding between the –OH groups of styrene-acrylic molecules and the –N(CH3)2 groups on LMB can stabilise LMB.


Introduction
Water pollution by industrial e uent like organic dyes is now one of the critical issues worldwide. The growing concentration of dyes pollutants in water is hazardous and causes signi cant environmental problems due to the reducing the photosynthetic activity and oxygen enrichment of aquatic organisms by decreasing light transmittance 1 .
Various physicochemical approaches have been made to remove the dyes from water, such as chemical precipitation 2 , ltration 3 , and coagulation and occulation processes 4 . Filtration is one of the easiest ways to remove pollutants from wastewater. The development and implementation of new types of lters with higher ltering capabilities have great importance.
Polymer nanocoated textiles can show good results as water lters due to the material's high physical and mechanical resistance 5 . By controlling the nishing processes of the textile material, it is easy to create the required porosity and possible to increase the lter life and save material facilities. Nano llers in the polymer composition can provide high durability for fabrics because nanoparticles have a large surface area-to-volume ratio and high surface energy, thus presenting better fabric a nity and increasing durability 6 . Furthermore, was investigated the photoactivity of modi ed textiles in the decontamination of organic dyes 7,8 and degradation of gaseous pollutants 9 . Moreover, the nanoparticles can penetrate into certain parts of the substrate, such as pores, holes, and crevices, and they lock mechanically to the substrate. Where the voids between the nanoparticles can be utilised as ltration channels, as a result, ltration performance can be increased.
Currently, the production of photoactive textiles incorporated with photocatalytic particles is of great interest. Considerable research devoted to the preparation and investigation of such materials impregnation of textiles in the dip-coating method. Han and Bai immobilised different layers of titanium dioxide onto the surface of polypropylene fabric. They con rmed that methyl orange dye solution degradation under UV and visible lights could be greatly improved over one layer of titanium dioxide coating. Also, such fabrics can be used for the photocatalytic oxidation of phenol from water 10 .
Zhang and Zhu immobilised Fe-doped TiO 2 on the surface of polyamide fabric under hydrothermal conditions. Coating demonstrated improved photocatalytic activity against methylene blue 11 . Ag-TiO 2 was synthesised by photo-reducing Ag + ions to Ag metal and then coated on cotton fabric using the paddry-cure method. The coated fabric showed high e ciency against methylene blue under the normal laboratory environment conditions 12 .
In the present work, polymer composition for the nishing of polyester textile was created by mixing acrylic copolymer, melamine cross-linked agent and ZnO nanoparticles. Polyester material was treated by polymer composition using coating and padded method. Developed textile material was used in the ltration of organic dyes from the model wastewater.

Finishing polyester method
Polymer compositions with ZnO nanoparticles were used for treatment of polyester fabric by two methods: one bath pad method and blade coating method. For this purpose two different composition were developed (Table 4). The covering was implemented by the blade coating method. As shown in Fig. 14, the polymer composition is applied to the fabric while being run at tension under a oating knife blade. The distance between the fabric and the knife was 1 mm, which determines the thickness of the coating. The polymer composition had to be highly viscose to prevent soaking through the fabric. The coating was dried under 100 0 C for 30 minutes to x the covering on the polyester surface. This sample was labelled as covered polyester.
The padding technique, widely regarded as a textile nishing technique, usually refers to a bre coating to apply micro or nanomaterials or chemical compositions. As shown in Fig. 15, the fabric was submerged in the polymer composition for 90% pick-up and then dried at 100°C for 30 minutes. This sample was labelled as padded polyeste.

Water absorption test
The sample was dried rst at 38.5 C to get a constant weight, noted as W 0 (g). Then immersed the samples in deionized water for 1h, took out the fabric and absorbed the surface water droplets with lter papers (the whole process should take no more than 1 min), weighted the fabric and recorded as W 1 (g).
The water adsorption capacity of fabric was calculated by the following equation: Thickness and surface density The areal density PA (g/m2) was calculated according to Eq. (1): where m is mass (g) measured by an electronic balance, and A is area (m2).
Fourier transform infrared (FTIR) spectrum of produced lters was recorded with the help of spectrometer Avatar 360 (Nicolet) in the range of 508 and 4000 cm − 1 (resolution 1.93 cm − 1, 200 scans, 1 s per scan).
Microstructure investigation were performed by a scanning electron microscope (SEM) ZEISS Auriga Compact equipped with EDAX energy-dispersive X-ray spectroscope (EDS) and eld emission scanning electron microscopy MIRA 3 FE-SEM microscope (TESCAN, Czech Republic) equipped with a highresolution cathode (Schottky eld emitter) and with three-lens Wide Field Optics™ design.
A ltration study was carried out with a textile lter when 25.0 ml (100 ppm solutions) of dye at pH ∼6.0 in a dynamic mode moved through the lter with an average speed of 0,21 ml/sec. The concentration of dyes was measured on a Helios Gamma UV-vis spectrophotometer (Thermo electron corporation, UK) for MB in the region 200-700 nm and MO − 300-600 nm. Filtration was conducted by the vacuum ltration method (Fig. 16), using a Buchner porcelain funnel and ltration glass ask. According to this technique, a dye solution was vacuum-ltered through produced lters. The water from the funnel penetrates the lter and ows into a conical beaker by reducing the pressure with a water pump.
The amount of dye adsorbed onto the fabric surface at equilibrium, Q e (mg/g), was calculated by the following expression: where C 0 and C e are the initial and equilibrium dye concentrations in mg/L respectively, V is the volume of solution (L) and m is the mass of the lter (g).
The ltration e cient (retention in %) was calculated by the following: where C 0 is the mass concentration of dyes in the upstream, and C is the mass concentration of dye in the downstream.

Results
The structure and properties of the yarn and fabric were optimised considering the characteristics of lter fabrics (Table 1). Different types of surface treatment of polyester lead to different types of etching due to chemical modi cation. The surface becomes smooth, which leads to deterioration of wettability.  The Finishing process happens due to the mechanism shown in Fig. 1. Partially esteri ed melamine can be linked covalently to polyester fabrics and styrene-acrylic binder by curing at 140-150 0 C through transamidation. At these temperatures, the primary amino groups of the melamine can react with the carboxylic acids groups of styrene-acrylate and with accessible ester groups at the surface of the polyester bre.
Polymer matrix and textile material can stabilise nanoparticles. Such stabilisation provides xing the nanoparticles to each other or xing the particle layer on the support layer. Such treatment enabled a diversity of textile materials and their pore geometries. High ow resistance is possible during ltration if the particles used as llers are selected by size.
Surface chemical modi cations of nished polyester fabric were determined by an FTIR analysis in the range of 500-4000 cm − 1 . Figure 2 shows the FTIR spectra obtained for the untreated polyester, padded polyester and covered polyester. In untreated polyester, the presence of ester, alcohol, anhydride, aromatic ring, and heterocyclic aromatic rings can be seen. An absorption peak at the wavelength of 1710 cm − 1 is related to the stretching vibration of the carbonyl group (C = O), the peak at 700 cm − 1 attributed to the out-of-plane bending vibration of the C-H on the benzene ring, and the peak at 1014 cm − 1 is assigned O-H out-of-plane bending in terminal carboxylic groups 13 . This is a reason that there is still alcohol and anhydride as residual reactants left in the polyester. The carboxyl, ester, anhydride and alcohol groups showed that the polyester fabric was not pure. There is not much change in the padded polyester since the intensity and position of absorption peaks were not changed too much. Cleary can be seen an The observed absorption bands (Fig. 2b, c)

Water absorption test
Water absorption (retention) test results of the lter materials are given in Fig. 3. The standard polyester fabric absorbs a minimal amount of water (0.8 %) into its structure. Water absorption decreases dramatically at padded polyester. Polymer nanocomposite applied to the polyester surface made a signi cant contribution to the water absorbency of lter media. It was detected that the differences between the water absorption values of padded and covered polyester occurred because of the low adsorption property of the polymer composition that is due to their ability to decrease the porous diameter and change fabric structure.
The structure of the surfaces The structure of the coated surfaces was characterized by scanning electron microscopy (SEM). The SEM images were used to investigate the change in the surface morphology of the untreated, padded and covered polyester fabric, as shown in Fig. 4  The SEM images show that the structure of treated polyester is relatively bulky, and the structure of the polymer composition is relatively dense. Due to the fact that polymer composition consists of ZnO nanoparticles, on the surface of textile can be formed cross-linked structure which has crosslinked units with components of composition and polyester bres. As a result, the structure became crisscross and intertwined, so the lter pore size decreased. This factor can't be ignored, as the combination of polymer nanocomposite surface and polyester substrate will increase the ltration resistance and improve the ltration e ciency. Produced layer decreases the possibility for the penetration of the dye molecules into the bres and lets them rather adsorbed on the surface.
The result of the elemental mapping performed on the surface of the padded polyester fabric sample is shown in Fig. 5. The nanoscale ZnO particles can be clearly seen well distributed on the surface of polyester. The particle size plays a primary role in determining their adhesion to the bre. It is reasonable to expect that the largest particle agglomerates will be easily removed from the bre surface. In contrast, the smaller particles in the polymer composition will penetrate deeper and adhere strongly to the fabric matrix.

Hydrophobicity
Hydrophobicity improved by modi cation of the lters using polymer composition. The results of the studied lters are shown in Fig. 6. When the polyester textile material was deposited with polymer composition, the contact angle was dramatically increased, indicating that the hydrophobicity of the surface was greatly improved. This nding is in contradiction with the results of polymer nanocomposite lm formed on the glass surface reported in previous studies. The polymer lm exhibit smoothness surface 16 . Polyester fabric is characterised by hairiness which forms an unregular surface. As the polymer lm texture is created on the surface of textile ber, polymer nanocomposite build-up hierarchical structures and increases surface roughness 17 , which signi cantly improve the hydrophobic properties of treated polyester fabric 18 . The primary reason that produced lters realises hydrophobicity is that polluted water droplets can be stably supported on the hierarchical structure of the lter surface, and dyes could form pockets in the interface.
Low-temperature nitrogen adsorption-desorption isotherms Figure 7 shows the nitrogen adsorption-desorption isotherms obtained at 77 K for polyester textile material prepared with different treatment techniques. The covered and padded polyester exhibit steep type III isotherms, indicating the occurrence of macroporous. Additionally, the development of mesoporosity is indicated by the pronounced desorption hysteresis loops that appear for samples. Covered polyester shows a wide hysteresis loop, and the desorption curve is steeper than the adsorption branch, indicating that the samples have various pore types and pore diameter distributions. Padded  Table 2. It is pointed out that the surface area available to the nitrogen vapour is greatly dependent upon the way of polyester treatment. Polymer nanocomposite lm was also tested and showed a non-porous structure with low speci c surface values of 8.7 m 2 /g. A small hysteresis loop can be seen, which indicates the presence of some pores or holes in the network.

Pore Size Distribution
The proper selection of lter material is an essential factor in achieving e cient ltration. Pore size measurements Fig. 8 shows the distribution of the pore size.
The average pore size of untreated polyester is ~ 3.4 nm, covered polyester is ~ 3.08 nm, and padded polyester is ~ 3.4 nm. Total pore volume is 0.036 cm 3 /g, 0.028 cm 3 /g and 0.065 cm 3 /g, respectively. The pore size of covered polyester is smaller compared with untreated and padded polyester. Moreover, the average pore size of untreated polyester is the same as padded. Two more maximums of pore distribution 4.2 nm and 12.4 nm at padded polyester, indicate that pores are not regular. The surface of the polyester substrate consists of a large number of bres that can interweave and pile up with each other, contributing to the formation of some large pores between the bres. On the other hand, the accumulation of bres on the surface may result in partial blockage of the pores and, therefore, some small pores formed. 19 Filtration experiment The possibility of using such fabrics for lters was explored with methylene blue and methyl orange solution. The size of the methylene blue molecule is around 13.82 Å 20 . The methyl orange molecules have a larger size ~ 26.14 Å 21 . Considering the length of the dyes molecules and the dimension of the pores in lters, organic dyes can easily enter into the pores. It was shown that the concentration of MB decreased from 100 ppm to 60 ppm using the padded polyester, and the content of MO declined from 100 ppm to 40 ppm assisting the covered polyester ( Fig. 9-10). These observations indicate that organic dyes of different nature can be effectively removed from the water by using the suitably processed textile lter. It is evident that the covered technology almost totally encloses the pores. Meanwhile, padded technology decries the ratio between bres and form the solid covering of the pores. and solutions after ltration Filtration e ciency It was noticed that thru the ltration process, the movement of the dyes particles typically deviates from the water ow, especially as they approach the bre. During the ltration Brownian diffusion, the electrostatic effect and the gravity effect happened. The electrostatic effect rmly attaches the particles to the surface of the bres. Results are presented in Table 3.

Discussion
Used technology for treating polyester fabric provides a unique method to lower the energy barrier between the polymer nanocomposition and the lter surface and thus increase the deposition of dyes particles on the surface of the lter. Unionised dyes molecules diffuse through the covered and padded lter because both polymer matrix and dye are hydrophobic. Moreover, pores are covered with polymer composition in padded polyester, which increases the lter adsorption capacity. In covered polyester, all interactions can happen on the surface of the lter. Furthermore, in covering technology, polymer nanocomposition cover the pores, which two times reduce their size (Fig. 11 ).
The pH of the dye solution was 6.00, which is below the pH ZPC of the surface of treated polyester. The surface of developed lters exhibits basic properties (Table 3). Decreasing the pH of the surface indicates an increase in the concentration of H + ions in the solution. Padded polyester with pH ZPC 6.3 releasing H + ions induces a positive charge on the terminal nitrogen of the methyl orange. The positively charged terminal group in methyl orange helps in adsorption through the anion-exchange mechanism. The maximum dye removal e ciency of MO using covered polyester could be attributed to the electrostatic attraction between positively charged surfaces (ZnOH + ). 22,23 . It was recognized that the removal e ciency of MB is lower than MO due to the bigger size of MB anions. Some MB anions could be excluded because of the lters 'sieve effect', others could be adsorbed on the surface of the lter by an electrostatic attraction. Ion exchange mechanism can be created between the nitrogen of the amino groups of MB, the nitrogen of the -NH 2 group of melamine in polymer composition and oxygen of the carbonyl group of the styrene-acrylate.
1. Methyl orange b)Methylene blue Figure 12. Possible mechanism of interaction Most researchers were focused on detecting the highly coloured form of MB; meanwhile, its colourless reduced form, leuco-methylene blue (LMB), has not been the subject of much interest. In this article, we report the results of the formation of LMB, which was previously not considered when determining the adsorption properties of materials. Such observations are not surprising, as the LMB is colourless and weakly absorbs in the near UV range and absorbs more strongly in the far UV (l max = 256 nm).
Several works reported chemical transformation between the highly coloured oxidised form of MB and its stable colourless reduced LMB. In that time, the system's colour changed from blue to colourless, corresponding to the hydrogenation of MB to LMB. MB to LMB was reduced using ascorbic acid 24 25 , acrylate media 26 an ionic liquid 27 and nitrogen environment. Well known, MB is characterized by two main peaks one at 662 nm due to the substitution of the N(CH 3 ) 2 group on the heteroaromatic ring (responsible for colour), and the other at 292 nm, associated with localized bands of the unsaturated heteroaromatic system.
Results of ltration with the developed lters show that the intensity of these peaks markedly decreased. Also, the spectra showed an increase in the peak at 246 nm, which is responsible for LMB formation. Filtration with a covered polyester observed the disappearance of the absorption band associated with LMB (246 nm) and the formation of a hypsochromic shift up to 225 nm. This observation further con rmed that the MB molecules were mineralised during the ltration instead of discoloured 28 . In this case, probably occurred the injection of electrons into the ZnO nanoparticles on the surface of the lte 29 .
Using the lter produced from padded polyester, it is observed that the original blue colour of the dye disappeared and formed a colourless LMB. The spectrum shows a steady decrease in two absorption maximum (664 and 292 nm) and the appearance of a new band at 246 nm due to the formation of LMB (Fig. 13).
For a pure polyester lter, a decrease in the optical density of the dye is also observed but not so signi cant. The lters were inactive for MB recovery to LMB. In the absence of the polymer composition on the lter surface, there was no marked decrease in the absorption of the dye.
The problem of detecting MB dye is that the colourless LMB can quickly switch back to the original blue colour MB through a hydrogenation/oxidation reaction mechanism when the system is exposed to oxygen or air. In the case of developed lters, styrene-acrylic copolymer can stabilise LMB through hydrogen bonding between the -OH groups of styrene-acrylic molecules and the -N(CH 3 ) 2 groups on LMB, and then e ciently slow down the fast recolouration process (oxidative dehydrogenation process) at ambient conditions 30 .
In conclusion, a cost-effective and straightforward process successfully fabricated two types of new textile nanocomposite lters.
The main ndings of this study are listed below: It is indicated developed lters were fabricated with suitable thickness, lightweight property and great exibility for practical application.
Microstructure observation revealed that the way of polymer nanocomposite applying changed the pore structure in the lter material. Using the covered method, pores diameter decreased, which is attributed to the formation of polymer nanocomposite covering on the surface of polyester textile material. The padded method didn't reduce the pore size, moreover, polymer nanocomposition seeps all the textile material.
Due to the hydrophobic property of produced lters, the dyes molecules would be absorbed on the surface of the lter, which led to high removal e ciency.
It was shown that in the time of using methylene blue dye, a colourless reduced form of methylene blue -leuco-methylene blue could be created. The functionalised layer of the developed lters can stabilise leuco-methylene blue, keep it colourless and don't let it switch on back to methylene blue form.
Declarations Figure 2 FTIR spectra of a) Polyester; b) Padded polyester; c) Covered polyester.

Figure 3
Water absorption test.
Page 17/21   Nitrogen adsorption-desorption isotherms Concentration of organic dyes after ltration Figure 11 Scheme of produced lters Figure 12 Possible mechanism of interaction Figure 13 UV/vis spectra recorded for methylene blue solution before and after ltration Figure 14 Page 21/21 The Blade coating method (covering of polyester) Figure 15 One-bath pad method Figure 16 Vacuum ltration method