Fabrication of C6-Fluorocarbon-dendrimer-based superhydrophobic cotton fabrics for multifunctional aspects

C6-Fluorocarbon-dendrimer has been applied to the cotton knit fabric to develop oil–water repellent, oil–water separation, acid-resistant, self-cleaning, UV-resistant, and antibacterial properties. The C6-Fluorocarbon (FC)-dendrimer-coated 100% cotton single jersey knitted fabric samples were prepared using the “pad-dry-cure” method. The 90 g/L and 100 g/L FC-dendrimer-treated cotton fabrics showed excellent water repellency and oil–water separation as well as good self-cleaning performance. However, air permeability and heat conductivity were reduced by 13%, 15%, and 40%, 54%, for 90 g/L and 100 g/L FC-dendrimer-treated cotton fabrics compared to untreated fabrics. The presence of FC-dendrimer in the treated fabric was confirmed by FTIR, SEM, EDX, and XRD analyses. SEM analysis was employed to study the morphology of deposited FC-dendrimer particles on the fabric surface. TGA and DTA evaluated thermal performance. The FC-dendrimer-treated fabric also showed acid resistance, self-cleaning performance, and UV resistance attribute. In addition, Bacterial population growth appears to be less in the FC-dendrimer-treated sample than in the untreated sample. Overall, the result suggests that FC-dendrimer can be a valuable ingredient in the manufacture of multifunctional products.


Introduction
The rapid growth in protective textiles and their services has created a severe need to apply functional finishes. Recent market surveys have shown that apparel consumers worldwide are demanding functionality in their purchased products. According to recent research, the global market of functional textiles is expected to reach USD 4.72 billion by 2020, growing at a CAGR (Compound annual growth rate) of 33.58 percent between 2015 and 2020 (Majumdar et al. 2020). "Protective" textiles are garments or fabrics which protect the wearer from environmental hazards. Some of the best examples of protective and functional textiles are those which are water resistant, oil repellent, acid resistant, flame retardant, fade resistant, UV resistant, stain removing, antimicrobial resistant and soil repellent.
Protective properties of clothing can be assured by many types of finishes, including paraffin (Abo-Shosha et al. 2008), silicone (Sun et al. 2017), stearic acid-melamine-based compound (Dashairya et al. 2019), fluoropolymer (Jain et al. 2018) and so on. However, paraffin repellents do not repel oil and are generally not durable for laundering and dry cleaning. Additionally, fabrics treated with paraffinbased finishes are less permeable by air and vapour, resulting in poor wearer comfort (Schindler and Hauser 2004). Silicone repellents offer moderate durability for laundering and dry cleaning and no oil or soil repellency. Wastewater, particularly from residual baths of the finish application processes, is toxic to fish (Dong et al. 2015). Silicone compounds like tetraethoxysilane (TEOS) modified cotton fabric showed good water-repellent properties (Wang et al. 2007). However, TEOS exhibited toxicity and may cause potent respiratory hazards (Omae et al. 1998). In addition, stearic acid-melamine repellent finishes release of formaldehyde is a problem for human health and the environment (Schindler and Hauser 2004).
C6 Fluorocarbon (FC) polymer is primarily effective for liquid repellent and soil release finishes. Fluorocarbon finished product showed good resistance to water absorption, excellent adhesion properties and better transmission of water. The transmission of water vapour through a piece of fabric is the essential component of thermal comfort (Shekar et al. 2001). The efficiency of FC compounds is due to the bond structure between the F and C atoms. The C-F (1.35 Å) bond length is shorter than the C-C (1.54 Å) bond. As a result, the C-F bond is more substantial than the C-C bond (Atav and Bariş 2016). FC compounds have a low boundary surface tension of 10-20 mN/m (Schindler and Hauser 2004). C6 Fluorocarbon (FC) polymer is also environmentally friendly. C6 fluorocarbon polymers degrade more quickly in the environment than C8 fluorocarbon polymers (Danish Environmental Protection Agency 2005). Figure 1a shows the chemical structure of a fluorocarbon polymer on a fibre surface (Schindler and Hauser 2004).
On the other hand, dendrimers are highly branched molecules having a well-defined size, shape, molecular weight, and monodispersity compared to linear polymer. Dendrimers have a tree-like form consisting of a central core, branches and terminal group, having diameters in the 2-10 nm range. Dendrimer has very low polydispersity and high functionality (Tomalia et al. 1985). There are different types of dendrimers like polypropylene imine (PPI) dendrimers, poly amido amine (PAMAM) dendrimers, tecto dendrimers, chiral dendrimers, hybrid dendrimers, micellar dendrimers, multiple antigen peptide dendrimers, amine-terminated hyperbranched dendritic polymers. Dendrimers terminated with amine end-groups are named amino-terminated dendrimers. End groups are generally called the surface group of the dendrimer or terminal group. The novel characteristics of amineterminated dendritic polymers have many reactive end groups, globular shapes, and multi-valency, making them suitable for a wide range of applications; particularly, in textile engineering (Akbari and Kozłowski 2019). In this research, amine-terminated hyperbranched dendritic polymers are used.
Dendrimers are used along with FC to enhance water repellence by changing the nanostructure of the cloth's surface. Dendrimer's core molecules exhibited a large number of branched organic atoms (Windisch et al. 2000). Fabric treated with FC-dendrimer had higher oil and water repellency ratings than fabric treated with fluorocarbon polymer (Atav and Bariş 2016). Namligoz et al. (2009) also found that polymeric dendrimers containing FC had better Fig. 1 a Fluorocarbon polymer on fibre surface. Where m = 6-10, X and Y are co-polymers mainly stearylacrylates, R=H or CH 3 (polyacrylic or polymethacrylic acid esters), and A is the fibre surface; b A dendrimer structure synthesized from three distearyl-amines or amides and a tri-functional isocyanate X (N=C=O) results for water, oil, and stain repellency than conventional FC in performance and washing resistance. It is assumed that FC-dendrimer provides more functional groups on the surface of the textiles than one. On the other hand, the dendrimer has a well-known regular structure, built up over several generations, starting from a core and containing a surface with a high density of end groups (functional groups). The number of end groups increases exponentially with the number of generations building up the dendrimer.
Fluorocarbon polymers are applied together with dendrimers, causing self-organization where the fluorocarbon chains are enriched on the surface and co-crystallize with the dendrimers. Dendrimers are highly branched oligomers with non-polar chains forming a star brush structure. The resulting polar and non-polar sandwich arrangements are highordered, causing equal or better repellency effects, with lower fluorocarbon amounts than dendrimerfree FC finishes. Other advantages include low condensation temperature (80-130 °C), high abrasion resistance, good wash permanence, and a soft feel. A hypothetical structure of a dendrimer is shown in Fig. 1b (Schindler and Hauser 2004). In addition, the hydrocarbon dendrimer is more environmentally friendly and economical than the FC polymer (Atav and Bariş 2016). Hydrocarbon dendrimer-treated fabric could withstand more water hydrostatic pressure than FC-treated fabric. The breathability of hydrocarbon dendrimer-treated fabric was more than that of FC polymer-treated fabric (Chowdhury 2018a).
Generally, water-proof fabrics have lamination, high-density tight weaving, and solid coating, all of which block air and water vapour movement. As a result, the wearer feels discomfort due to the condensation of sweat inside the clothing. FC-dendrimer repellent finishes overcome these problems by developing a permeable layer that allows water vapour, heat, and air to pass through the dress due to the dendrimer macromolecule's ability to build up crystal structures in the nano range on the fabric surface. Water-repellent fabrics can be used for various types of protective garments against rain, snow, cold and active sportswear (Krishnan 1991;Roey 1992;Chinta and Satish 2014;Colleoni et al. 2011).
Several research articles on fluorocarbon polymer have previously been published. However, there hasn't been enough research done on FC-dendrimer. Both compounds are solely used on textiles to make the oil and water-resistant (De et al. 2005;Midha et al. 2014;Crews and Clark 1990;Lee et al. 1999;Khoddami et al. 2012;Sayed and Dabhi 2014;Shekar et al. 2001Shekar et al. , 1999Behera and Hari 2010;Wang et al. 2011;Zhou et al. 2013;Cerne and Simoncic 2004;Lidija and Simoncic 2008;Chowdhury 2018b). To the best of our knowledge, the oil-water separation, acid-resistance, self-cleaning, flame retardant, UV protection properties and antibacterial activity of FC-dendrimer treated fabric have not been evaluated. Using only one major chemical, FC-dendrimer, this study aimed to produce several functional qualities. Water-repellent chemicals have traditionally been applied to woven cloth. However, woven cloth has significant comfort constraints, such as limited moisture absorption, low air permeability, and reduced suppleness compared to knitted fabric (Ajgaonkar 1998). Therefore, cellulosic knitted fabrics are used in this investigation.
In light of this information, the current research aims to investigate the various functional properties of 100% cotton-knitted fabric treated with C6-fluorocarbon resin with dendrimers, including oil-water separation, acid resistance, self-cleaning, UV protection factor, antimicrobial activity, and thermal comfort properties, as well as the water-oil repellent property. The contact angle, spray rating test, hydrostatic pressure, and vapour permeability were used to determine the water-resistance qualities. In addition, the morphology and surface composition of treated fabrics were studied using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. In this research, the optimum concentration of fluorocarbon dendrimers suitable for particular end usage has been studied. Statistical analysis has also been used to determine the acceptable thermal comfort properties for different concentrated-fluorocarbon-dendrimer-treated fabrics at a 5% level of significance.

Sample preparation
Five samples with the formulation of 60, 70, 80, 90, and 100 g/L FC-dendrimer resin plus 15 g/L blocked polyisocyanate, and 10 g/L polysiloxane compound were prepared. At first, the 100% cotton single jersey knitted fabrics with a shape of 12 inches × 12 inches were taken. A solution was prepared according to the recipe, and a material-to-liquor ratio of 1:30 was used. After that, the samples passed through two nip rollers on a padding machine to squeeze out any excess solution at two bar pressures, leaving the fabric with a more limited amount of the chemical remaining. Then the samples were dried at 100 °C. Finally, the samples were cured at 150 °C, for two minutes, with the help of a mini-stenter machine. 100% cotton-bleached single jersey knitted fabrics were used in this study and defined as untreated. The sample preparation process is shown in Fig. 2.

Instrumental analysis
Fourier-transform infrared (FT-IR) spectra of treated and untreated samples were obtained by an FTIR spectrophotometer (Spectrum-100, Perkin Elmer, USA), over a scanning range of 400-4000 cm −1 was used to carry out the test. The dried sample was ground into powder using a mortar-pastle and about 1% of the powder was mixed with dried KBr to make pellets.
The crystallinity of the treated and untreated samples was evaluated by X-Ray diffraction (XRD) analysis using X' Pert PRO diffractometer (PAN Analytical, Auckland, New Zealand). The XRD was carried out using Cu-Kα radiation, of wavelength λ = 0.15406 nm, as the X-ray source. The operating voltage and current were 40 kV and 30 mA, respectively, at room temperature. The sample holder was placed in the X-ray goniometer and a 2 scanning range over 5°-50°, was used.
The 'd' spacing was evaluated according to Bragg's law: where λ is the X-ray wavelength and d is the interplane spacing.
The full width of the peak at the half-maximum (FWHM) value of the XRD pattern was used to estimate the crystal diameter, using the Scherrer formula (Jenkins and Snyder 1996): (1) λ = 2d Sin In this equation, K (= 0.9) is the Scherrer constant, λ = 0.15406 nm, (theta) is the Bragg diffraction angle, and β is the full width of the peak in the X-ray pattern line at half peak height in radians.
The crystalline percentage (Cr%) of treated and untreated samples was calculated from the XRD pattern, using the following equation (Ye and Farriol 2005): where I 200 and I am represents the crystalline region and amorphous region of cellulose fibers.
The energy dispersive X-ray spectroscopy (EDX) is used to analyze the elemental composition present in a sample. The contents of carbon (C), nitrogen (N), oxygen (O) and fluorine (F) of the treated cotton were measured by EDX (JEOL-6300F, Germany).
A scanning electron microscope was used to study the surface morphology of the cotton fabric both before and after treatments. SEM (Model-Phenom G2 pro, Netherland) was performed to investigate the surface morphology at × 3000 magnifications.
A simultaneous TGA and DTA thermal analyzer (Jupiter, Germany) was used to study both the FCdendrimer-treated and untreated samples. The samples, approximately 10 mg each, were heated from 20 to 800 °C with a heating rate of 20 °C per minute in a nitrogen atmosphere. The mass of the sample and its temperature were recorded continuously, to determine the mass lost.
(2) D = Kλ βCosθ Functional properties A spray rating tester (Model no: 333A, Mesdan Lab, Italy) helped assess the fabric's water repellency. AATCC Test Method TM 22-2005 was followed in such assessment. For testing, a piece of cloth of 180 mm in diameter was stretched tightly in embroidery hoops. They were held at a 45 o angle. Then 250 mL of water was sprayed on it from 150 mm height. The fabrics were rated between 0 and 100 based on photographic pattern, with the stages of 100, 90, 80, 70, 50, and 0. Zero (0) ratings revealed completely wetting, whereas 100 ratings pointed out that upper and lower surfaces were completely dry. A wash durability test was carried out to check the water repellency after washing several times. Industrial washing machines washed treated fabrics according to AATCC 124-2018AATCC 124- (2018 standard. In the present experiment, washing was done just five times. The treated cotton fabric sample was assessed for contact angle measurement with water using the goniometer (DSA 100, Kruss, Germany) sessile drop technique. 5 μL of water was dropped at points on the sample in five places, at room temperature (Siddiqui et al. 2017). The average value of contact angles was used. The drops were photographed.
A drop test was also carried out, to observe the repellent properties of the treated fabric against aqueous dye solution and paraffin oil (Singh and Singh 2016).
The ability of the treated fabric to repel oil was tested by the 3 M Oil Repellency Test (Khoddami et al. 2015). In this test, a drop of oil was dropped onto the sample while lying flat on a smooth, horizontal surface. The droplets were observed for 30 s  Table 1. FC-dendrimer coated (treated) fabric was used to perform an oil-water separation test, according to the Yang et al. (2019) method, with some amendments. For this purpose, a mixture of oil and water, 50 mL hexane, and 50 mL red-dyed was poured on FC-dendrimer-coated fabric contained in a funnel placed on a conical flask. The filtrate mixed solution was collected in the flask and the FC-dendrimer coated (treated) fabric separated them. The following formula was used to measure the efficiency of separation.
where V b is the volume of oil before separation and V a is the volume after separation.
An acid drop test tested acid resistance. 20 μL of 98% sulfuric acid was dropped on the fabric with a micropipette. A digital camera was then recorded the ensuing damage (Wang et al. 2018).
Self-cleaning tests, for both untreated cotton and FC-dendrimer-polymer-coated cotton, were carried out according to Yang et al.'s (2019) method, with some modifications. Very fine Methylene Blue (MB) dye powder was used as a surrogate for soil. The Methylene Blue powder was placed on untreated cotton and treated cotton fabric and then water flowed on the surface of the fabrics. After cleaning with water, the sample was dried, and an image of the samples was taken.
A UV spectrophotometer (Shimadzu 1650, Japan) was used to measure the ultraviolet protection factor, and the factor was calculated according to the AATCC Test Method: TM 183-2004 (2010) by the following equation: In this equation: E λ is erythermal spectral effectiveness, S λ is solar spectral irradiancies, λ is the wavelength in nm, T λ is spectral transmission and Δ λ is wavelength intervals (in nm).
Disc diffusion process was used to determine zone of inhibition for both treated and untreated samples.

Physical properties
Fabric weight per unit area was measured according to the Standard ASTM-D 3776-96 (2002). The thickness of the fabric was measured using James Heal's thickness gauge followed B.S. 2544:1954 (1954).

Mechanical properties
A Trust Burst tester for bursting strength test, ASTM D 3786-87 (1987) applied a force to the fabric plane at 90°, under specified conditions, until it ruptured the cloth.
A hydrostatic pressure test was evaluated according to the AATCC Test Method 127-2008 (2009). The lower surface of the tested fabric was subjected to a hydrostatic pressure head, increasing the pressure at a constant rate, until leakage appeared at three points on the upper surface of the test specimen. A reservoir with a circular test area of 100 ± 5 cm 2 , containing distilled or deionized water (Majumdar et al. 2020), supplied the water applied to the fabric surface. Results were obtained from water pressure by a millibar (Mb).
The abrasion resistance was tested according to ASTM D 4966-98 (1989) using a Martindale Abrasion Tester.
Comfort properties A Lee disc apparatus was used to measure the ability of the samples to conduct heat by the following formula (Vigneswaran et al. 2009): where K is the ability of the sample to conduct heat, m is the brass disc mass, s is the specific heat of the disc material, d is the specimen thickness (in mm), d dt is the cooling rate, a is the area of the specimen crosssection, t 1 is the highest temperature persisting over time, and t 2 is the lowest temperature persisting over time.
The air permeability of the fabric was tested by the airflow thod (BS 5636 1990). The BS 7209 test (1990) was used to measure the water vapour permeability of the sample using the following formula: In the above equation, M is mass loss (in grams), A is the sample's exposed area in m 2 , and t is the time elapsed between weighing of the assembly (in hours).

Statistical analysis
Statistical analysis was used to investigate the acceptable level of thermal comfort properties. For this purpose, the Chi-square distribution Test Method was carried out at a 5% level of significance (Gupta 2002).

Results and discussion
The manuscript has been organized so that the confirmation tests, such as FTIR, XRD, EDX, SEM, and TGA, are discussed. Second, functional properties such as water and oil repellent, oil-water separation, acid resistance self-cleaning, UV protection and antibacterial have been addressed. Physical and mechanical properties have been addressed in the third section. Fourth, thermal conductivity, air permeability, and water vapour permeability have all been explored as comfort properties. Finally, the comfort data were analyzed statistically. Each result will be analyzed and discussed below.

FTIR spectra
In Fig. 3a, FTIR spectra of untreated cotton fabric, or simply cotton fabric, show a broad peak at 3331 cm −1 signifying the OH stretching vibration of cellulose hydroxyl groups in the region of 3100-3600 cm −1 . The untreated cotton fabric spectra also showed typical characteristic peaks at 1428 cm −1 and 2900 cm −1 , which may be C-H bending and stretching bands, respectively. (Chung et al. 2004). Wavenumber 3331 cm −1 of cotton fabric has been converted into little high wave numbers of FC-dendrimer treated cotton fabrics as shown in Fig. 3b-f, which indicated intermolecular hydrogen bond formation. The peak at 2900 cm −1 of cotton fabric has been shifted to a little lower wavenumber of the FC-dendrimer-treated fabrics except for 60 g/L. A peak at 1427 cm −1 has also changed after FC-dendrimer treatment. These changes indicate that FC-dendrimer was successfully attached to the treated cotton fabric.

XRD analysis
The X-ray diffraction of untreated and FC-dendrimertreated fabrics both shows distinctive peaks, at a 2θ angle in the crystal planes of (1-10), (110), (200) and (004) as shown in Fig. 4. This result agrees with the similar observation for cellulosic fibre of Altınışık et al. (Altınışık et al. 2013). The crystallinity percentages of 60 g/L, 70 g/L, 80 g/L, 90 g/L, and 100 g/L FC-dendrimer-treated samples were 81. 44, 79.98, 80.76, 79.83, and 77.93%, respectively ( Table 2). The crystallinity percentage of the treated samples slightly decreased compared to those of the untreated sample (82.21%), the peak intensity of the treated fabric also decreased when the 2 value at the crystal plane was (200). The crystallinity percentage of the FC-dendrimer-treated samples gradually decreased as the FC concentration increased. As a result, the FC-dendrimer-treated fabric exhibited a slightly lower level of crystallinity. On the other hand, the full width at half maximum (FWHM) value of the     FC-dendrimer-treated sample was greater than that of the untreated sample.
The full width at half maximum (FWHM) value is inversely proportional to the crystal diameter. As the concentration of FC-dendrimer treated cotton fabric increases, the full width at half maximum value increases corresponding to the decrease of the crystal diameter of the sample according to the Scherrer formula (Eq. 2, Table 2). Thus, the crystal diameter of all FC-dendrimer-treated cotton fabrics was lower than that of the untreated fabrics. A positive correlation was clear between crystallite diameter and crystallinity percentage.
No major difference is seen in the inter-plane spacing of untreated and FC-dendrimer-treated fabric, as shown in Table 2. The X-ray diffraction shows that the characteristic peaks of untreated and FC-dendrimer-treated fabric are almost the same. Thus, the cotton fibre cellulose did not produce any remarkable changes after FC-dendrimer incorporation. A small change in FTIR results supports the small change in X-ray diffraction results.
Energy-dispersive X-ray spectroscopy (EDX) analysis The EDX photograph of untreated fabric and that of FC-dendrimer treated fabrics is shown in Fig. 5. The weight percentages of carbon atoms were 49. 85, 52.15, 53.44, 53.91, 55.80, 56.08% for untreated, 60 g/L, 70 g/L, 80 g/L, 90 g/L, 100 g/L FC-dendrimer-treated cotton fabrics, respectively, are listed in Table 3. The weight percentages of oxygen atoms were 50. 15, 47.53, 45.97, 45.14, 43.09, and 41.97% for untreated, 60 g/L, 70 g/L, 80 g/L, 90 g/L and 100 g/L FC-dendrimer treated cotton fabrics, respectively. The weight percentages of oxygen atoms in FC-dendrimer-treated fabric were less than that in untreated fabric. Smaller oxygen peaks in FCdendrimer-treated fabric indicate that few hydroxyl groups (-OH), which attract water molecules¸ are present. But the weight percentages of carbon atoms are greater in the treated fabric. The greater weight percentage and higher carbon peaks in FC-dendrimertreated fabric imply that the number of hydrocarbon groups has increased. Hence, the hydrophobicity of treated cotton fabric increases with the increased concentration of fluorocarbon polymer.

Scanning electron microscopy (SEM) study
The surfaces of both the treated and untreated fabrics were studied using a scanning electron microscope. The untreated fabric has a smooth surface, as shown in Fig. 6a, but the treated fabrics had rough and uneven surfaces, as shown in (Fig. 6b-f) compared to the untreated fabric. Granular materials are visible in Fig. 6e. That gave the treated fabric an uneven surface and provided evidence that the water repellent agent was successfully attached to the untreated fabric surface. After the FC-dendrimer treatment, the surface texture of the cotton fabric became similar to that of non-wettable fabrics. Among the samples, the uneven appearance of the surface of those treated with 90 g/L and 100 g/L concentrations of FC-dendrimer treatment was most prominent. This result is similar to the outcome of Jeyasubramanian et al. (2016).

Thermal analysis
The thermal behaviour of untreated fabric and FCdendrimer-treated fabric were evaluated by the study of TGA and DTA thermograms. The weight loss percentage, DTA peak temperature and char residue percentage are shown in Table 4. The TGA thermogram represents the weight loss percentage of the specimen and shows three stages of thermal degradation. In the first stage, weight loss occurred, in the untreated, 60, 70, 80, 90 and 100 g/L FC-dendrimer treated fabrics are 6, 5, 5, 3, 4 and 6% respectively, at 100 °C that are due to loss of moisture, low molecular weight solvent and expulsion of gases. Major weight losses were observed in the second stage at DTA 1st peak temperature, as shown in Table 4. The DTA at 1st peak temperatures of the untreated fabric, 60, 70, 80, 90 and 100 g/L. FC-dendrimer-treated fabrics were observed at 377, 379, 376, 380, 382 and 382 °C, respectively. A more-pronounced degradation occurred at this temperature due to the breakdown of glycosidic linkages and hydrogen bonds, leading to the formation of organic compounds. The final-stage residual char was obtained at DTA 2nd peak temperature (Table 4). From Table 4, the DTA peak temperature or decomposition temperature of FC-dendrimer-treated fabrics was greater than in untreated fabrics. Considering the 1st peak temperature as well as the 2nd peak temperature, it can be said that the thermal stability of FC-dendrimer treated fabric has been slightly improved. The char residue of 100 g/L FC-dendrimer-treated fabric was higher than that of untreated fabric. In contrast, the char residue of 90 g/L FC-dendrimer treated fabric is similar to that of untreated fabric. On the other hand, char residue rates of 60, 70, and 80 g/L FCdendrimer-treated fabrics are slightly lower than untreated cotton fabric. The use of polysiloxane might have catalyzed cellulose decomposition and resulted in decreased residue after degradation (Flynn 2002). As the add-on percentage was higher with the increase of concentration of FC-dendrimer, this might be the cause of increased residual char % at 100 g/L FC-dendrimer.
Spray test results Table 5 shows spray-test results for FC-dendrimertreated fabric. The spray test readings, according to AATCC-22, of 60, 70, 80, 90 and 100 g/L FC-dendrimer-treated samples were 80, 90, 90, 100 and 100, respectively. According to the rating chart (AATCC -22 method), 90 g/L and 100 g/L showed the highest rating. This rating implies that there was "No sticking or wetting of the upper surface". When the concentrations of FC-dendrimer were 90 g/L and 100 g/L, the weight gain percentage was maximum. As a result, the thickness of the treated fabric also increased. So, the treated fabric showed excellent water resistance performance. Again, at 70 g/L and 80 g/L, the treated sample had a rating of "90" meaning "Slight random sticking or wetting". After fifteen times launderings, the spray rating value for all five samples remained unchanged. After twenty times launderings, the spray rating value for the 60 and 70 g/L FC-dendrimer-treated samples has decreased. The spray rating value for the 80, 90 and 100 g/L FC-dendrimer-treated samples was decreased after twenty-five times launderings. Moreover, with the increase in launderings more than 30 times, the spray rating values of five FC-dendrimertreated samples also deteriorated.
Repellent finishes achieve repellence because they reduce the free energy on the fibres' surface. A drop of liquid will spread if the adhesive interactions, between the fibres and the liquid droplets, are greater than the cohesive internal interactions within the liquid. A drop of liquid will not spread, if the adhesive interactions between the fibres and the liquid droplets, are lower than the cohesive internal interactions within the liquid. Surfaces that exhibit low interaction with liquids "low-surface energy" surfaces (Schindler and Hauser 2004). After five launderings, the spray rating value for all five samples remained unchanged.

Water contact angle of the samples
Contact angle measurement is the best method to use to evaluate the water repellency of a hydrophobic surface. The static contact angle is the angle between a liquid and the surface created when the liquid contacts the surface. If the water contact angle is 0 ≤ ≤ 90 • , the surface is defined as "hydrophilic". If the water contact angle is 90 ≤ ≤ 180 • , the surface is defined as "hydrophobic". Water repellency increases when cotton fabric with low surface energy is used.
Water contact angle indicates whether a surface is hydrophilic or hydrophobic as it measures how much spread a drop of liquid will achieve on the surface. The surface will become more hydrophilic if oxidizing agents or ionizable groups are introduced to the cotton surface. As a result, the water contact angle will become smaller. On the other hand, if hydrocarbons are introduced to the surface, the surface will become more hydrophobic, and the water contact angle will increase. Therefore, to measure the water contact angle, a droplet of water is placed on the surface. The height and width of the water's spread are then recorded to calculate the angle. The 100 g/L and 90 g/L FC-dendrimer treated cotton fabric provided excellent water repellence: its water contact angle measured between 154 • and 144 • , as shown in Fig. 7e and f. Figure 7b-d show that 60 g/L, 70 g/L and 80 g/L FC-dendrimer-treated cotton fabrics have exhibited water contact angles of 124 • , 122 • and 136 • , respectively. Hence FCdendrimer treated cotton fabric became hydrophobic and hydrophobicity increases with the increase of FCdendrimer concentration.

Drop test results
In this case, the sample was prepared using a mixture of 100 g/L FC-dendrimer, 15 g/L blocked polyisocyanate and 10 g/L polysiloxane compound. A coloured water droplet and paraffin oil spread easily on an untreated fabric surface respectively, as shown in Fig. 8a and b. On the other hand, coloured water droplets and paraffin oil did not spread on the FC-dendrimer treated fabric surface in Fig. 8c. Here the spherical shape of the water and oil droplets is observed distinctly. Thus, FC dendrimer-treated cotton fabrics are water and oil-repellent.

Oil repellence
The surface tension and density of paraffin oil are 31.5 mN/m and 0.86 kg/dm 3 , respectively, as shown in Table 1. Kasturiya & Bhargava (Kasturiya and Bhargava 2003) found that the critical surface tension for FC-dendrimer polymer-coated surfaces is 6-28 mN/m. Yet, for bleached cotton, this critical surface tension is 44 mN/m. When FC-dendrimer was applied to bleached cotton fabric, the surface tension is reduced to 6-28 mN/m. Paraffin oil did not penetrate the FC-dendrimer-treated fabric, as the surface tension of paraffin oil is greater than that of the FC-dendrimer-treated fabric. On the other hand, paraffin oil easily penetrates the bleached cotton fabric since the surface tension of paraffin oil is less than that of the bleached cotton fabric. So, it can say that the 60 g/L, 70 g/L, 80 g/L, 90 g/L and 100 g/L FC-dendrimer treated fabric showed a paraffin oil repellent.
The surface tension and density of n-heptane are 19.8 mN/m and 0.69 kg/dm 3 , respectively. The surface tension of n-heptane is less than that of the other organic oils used in the oil repellence test, as shown in Table 1. N-heptane organic oil can easily wet 60 g/L, 70 g/L, and 80 g/L FC-dendrimer-treated fabric, but not 90 g/L and 100 g/L FC-dendrimer-treated fabric. Therefore, according to the oil repellence test chart, 90 g/L and 100 g/L FC-dendrimer-treated fabric showed an oil repellency rating of 8 (eight) as shown in Table 1. A high value of water contact angle also indicated a high degree of oleophobicity. The water contact angle of 90 and 100 g/L FC-dendrimertreated fabrics are 154° and 144° as in Fig. 7e and f. The surface tension and density of n-octane are 21.4 mN/m and 0.70 kg/dm 3 , respectively. N-octane organic oil can easily wet 60 g/L and 70 g/L FC-dendrimer-treated fabric but not 80 g/L FC-dendrimertreated fabric. So, 80 g/L FC-dendrimer-treated fabric achieved an oil repellence rating of 7 (seven), according to Table 1. N-decane organic oil cannot wet the 60 g/L and 70 g/L FC-dendrimer-treated fabric, as the surface tension of n-decane is higher than that of n-octane. So, 60 g/L and 70 g/L FC-dendrimer-treated fabric achieved an oil repellency rating of 6 (six) according to Table 1. The oil repellence ratings of all the FCdendrimer-treated samples are illustrated in Fig. 9. Oil-water separation Oil-water separation becomes a crucial issue due to considerable oily wastewater from agricultural and industrial activities. On the other hand, improper disposal of used motor oil, oil spills, or leaks from ships or tankers have considerably contaminated watercourses and our food chain. (Wang et al. 2016;Cao and Cheng 2018;Yuan et al. 2018;Baig et al. 2019).
All concentrated FC-dendrimer-treated fabrics exhibited hydrophobic characteristics because the surface tension of water is fixed. On the other hand, FC-dendrimer-treated fabric showed oleophobic and oleophilic characteristics determined by the different surface tensions of the different organic oils tested. For example, n-decane cannot penetrate the 60 g/L and 70 g/L FC-dendrimer-treated fabric, but n-octane can do so easily. As a result, a mixture of n-octane and water can be separated by 60 g/L and 70 g/L FC-dendrimer-treated fabric. Similarly, a mixture of n-heptane and water has been separated by 60, 70 and 80 g/L FC-dendrimer-treated fabric. In addition, It may also separate the n-hexane and water mixture using any FC-dendrimer-treated fabric as the surface tension (18.43 mN/m) of n-hexane organic oil is less than that of all the FC-dendrimer-treated fabric.
50 mL water and 50 mL n-hexane were mixed and used 100 g/L FC-dendrimer-treated fabric for separation. After separation, the collected water remaining was still about 50 mL. The collected oil decreased a little in volume due to the absorbency of cotton and volatilization. The coated cotton would let the oil permeate until saturation in the parts which make contact with it. The FC-dendrimer-treated cotton, however, showed an excellent oil-water separation.
The separation efficiency of FC-dendrimer-treated cotton was 97-99%, as calculated according to Eq. (4). A schematic diagram of oil-water separation is shown in Fig. 10. Materials which can repel water even amidst oily pollutants are very useful in seawater. Thus, as described earlier, FC-dendrimer-coated fabric with dual functionality is a promising material for anti-wetting, self-cleaning, support for aquatic floating devices and as a filtration material for rapid, continuous oil-water separation. Among the possible applications of acid-resistant fabric are petroleum, chemistry, metallurgy, and electroplating. Workers in these industries need clothing made of such fabric to protect them from the dangerous acids they work with. In the past, clothing was made acid-resistant by coating it with rubber or hydrocarbon resins. These resins created a continuous film on the textile, which closed its empty spaces, stopping the intrusion of acid (Forsberg et al. 2014). Gal'braikh (2005) proved that fluoropolymers effectively resist corrosive solutions, including acid. Wang et al. (2011) and Zhou et al. (2013) used fluorinated polymers, which resisted acid most effectively.
The acid resistance performance of the untreated fabric and 100 g/L FC-dendrimer treated fabrics is shown in Fig. 11. Initially, 100 g/L FC-dendrimer was not affected by an acid droplet (Fig. 11a). But the untreated fabric was affected by acid droplets to some extent (Fig. 11b). After 30 min, the treated fabric was washed with water. Colour change had taken place where the acid droplet had landed in Fig. 11c. A large area of untreated fabric was burnt by the acid droplet after 30 min (Fig. 11d).

Self-cleaning
Water-resistant finishes are chemical additions to clothing that enhance the hydrophobic nature of the surface of a fabric. Completely hydrophobic surfaces also must be self-cleaning. Hydrophobic and selfcleaning attributes are exhibited in many surfaces of nature, such as the wings of butterflies, the leaves of cabbage and lotus, the elephant's ears and Indian cress. The surface of lotus leaves has protruding nubs, as proven by Scanning Electron Microscopy.
Epicuticle wax crystalloid encloses each nub. Due to these crystalloids, lotus leaves clean themselves and have a water contact angle (WCA) of 160. From this model, researchers have created artificial surfaces with water contact angles greater than 90 o (Guo et al. 2011;Lin et al. 2011;Li et al. 2014;Xu et al. 2010).
In super-hydrophilic coatings, the surface is cleaned by the sheeting effect of water. Complex organic substances on the surface are broken down into carbon dioxide and water. Superhydrophobic coatings have air pockets that get trapped between the nano-structured substrate and water droplets. The formation of a composite solid/air/liquid interface leads to an increase in the contact angle (CA) of liquid droplets. Increased contact angle leads to de-wetting of the surface. Then the droplet rolls off easily, taking away dirt and pollutants with it. Figure 12a shows that methylene blue dye powder spread widely on the untreated fabric surface due to the capillary effects of cotton fibers. The coated cotton surface has extremely little adhesion to methylene blue dye powder. However, water droplets quickly and easily removed dirt-like methylene blue dye powder on the superhydrophobic cotton surface. Thus, the surface in Fig. 12b-f is clean and dry. Among the treated samples, 80 g/L, 90 g/L and 100 g/L FC-treated samples showed better self-cleaning performance than the 60 g/L and 70 g/L FC-treated samples. UV protection factor (UPF) The United States Environmental Protection Agency has stated that 80% of the sun's UV rays reach the Earth, damaging human skin (The United States Environmental Protection Agency 2004), even in cold climates (Skin Cancer Foundation 2015). For this reason, it is essential to wear UV protective garments on cloudy or rainy days and sunny days. Therefore, there is a strong demand for UV-resistant garments all over the world. There are three kinds of UV light: (1) UV-A (315-400 nm), The ozone layer absorbs UV-C radiation. UV-A and UV-B radiation reach the earth's surface. These are the ones that can cause serious health problems. Ultraviolet radiation (UV-R) on earth is comprised of UV-A and UV-B rays. Its wavelength range is 280-400 nm.  Clothing serves as a link window between the outside environment and the human body. It can reflect, absorb, or scatter solar waves. Thus, ordinary clothing is usually not enough to protect the human body from the harmful effects of UV radiation. For this reason, UV-resistant finishing on textiles is necessary. Table 6 illustrates that the UPF value gradually increased with increasing FC-dendrimer concentration. The relationship between UPF rating and transmittance value is inversely proportional. The UPF value of the 100 g/L FC-dendrimer-treated samples was 4.42 for UV-R, nine times greater than that of the untreated sample. Pande and Crooks (2011) identified the absorbance peak at 280-285 nm which is caused by the dendrimer structure. A dendrimer is a key component for maximizing the ultra-violet protection capacity of FC-dendrimer-treated clothing.

Antimicrobial activity
Clothing that fights germs is better for human health and now-a-day it is essential in a medical environment. If clothing is water-, oil-and dirt-repellant and UV-protective and antimicrobial, this is almost ideal in many applications (Attia et al. 2017).
Antimicrobial clothing materials can be active or passive. Passive materials do not contain bioactive substances. Only the surface structure of the passive material can resist microbial contamination. Examples include "the lotus effect" and the micro-domainstructured surface. The key is to make it impossible for microbial cells to adhere to the fibre's surfaces. Active antimicrobial clothing contains bioactive substances which kill microbes (Russell and Chopra 1996;Beumer et al. 2000).
Recently, modified dendrimers have been proposed to develop antimicrobial properties for applications to textiles. Ghosh et al. (2010) observed effective antimicrobial activities of the modified-dendrimer treated fabric against Staphylococcus aureus (S. aureus).
Clear microbial inhibition zones were not found for treated fabrics in Fig. 13b-f. However, bacterial population growth seems to be less in the FCdendrimer-treated samples in Fig. 13b-f than in the untreated sample in Fig. 13a. Among the treated samples, 100 g/L FC-dendrimer treated fabric (Fig. 13f) showed the lowest bacterial population growth. The bacterial population was assessed by visual inspection. Around the untreated sample, the area is more ambiguous than the treated fabric. More ambiguity indicates a higher bacterial population.
FC-dendrimer polymer has no active antimicrobial properties. But it can act as a passive antimicrobial agent, due to converting fabric surfaces to superhydrophobic surfaces. Hydrophobic and super-hydrophobic fabrics resist bacterial adherence by making it a slippery surface like that of lotus leaves.

GSM and thickness measurement
After FC-dendrimer treatment, the GSM and thickness of the treated fabrics increased markedly compared to that of the untreated fabric (Table 7). The FC-dendrimer might close some pores in the fabric, creating a chemical coating. That was the reason behind the thickness and weight increases of the fabric. Both GSM and thickness gradually increased with increased FC-dendrimer concentration.

Bursting strength and hydrostatic pressure measurement
Bursting strength is the amount of pressure that ruptures the fabric. The increase or decrease in bursting strength is mainly a function of the smoothness or roughness of the treated fabric's surface. Generally, a smooth surface increases bursting strength and vice-versa. The SEM image revealed that microroughness was developed on fluorocarbon-treated cotton ( Fig. 13b-f) in comparison to the untreated cotton fabric. Micro-surface roughness increases with the increased water contact angle of the treated fabric. But, visually, FC-dendrimer-treated cotton fabric showed a smooth surface. It is assumed that softening agents, like non-ionic polysiloxane, were the main contributing factors to the treated fabric's visual smoothness and smooth feel. In the present study, Table 8 shows that the bursting strength of treated fabric increases with the increase of the FC-dendrimer concentration. The SEM result did not support the present outcome. The true explanation for this is still unclear. Hydrostatic pressure means the pressure needed for water to penetrate a fabric. Hydrostatic pressure increased after FC-dendrimer coating, compared to that of untreated fabric. Table 8 shows this increase. Hydrostatic pressure increases gradually with the increase of coating because the FC-dendrimer polymer coating on the fabric becomes denser as its concentration increases. A denser coating makes the fibre more water-repellent. The highest hydrostatic pressure (180 mbar) and lowest hydrostatic pressure (158 mbar) were reached with coatings of 100 g/L, and 60 g/L treated fabrics, respectively. Hydrostatic pressure is directly proportional to the water repellency property. High hydrostatic pressure indicates a high water-repellent property. So, it can say that 100 g/L FC-dendrimer finished fabric exhibits the highest water repellency.

Abrasion resistance measurement
The aim of this experiment is to see if the treated fabrics could withstand abrasion. The spray rating remained unchanged after 5000 rub cycles and is shown in Table 9. On the other hand, water repellency decreased a little after 10,000 rub cycles. Water spray rating of 60 g/L FC-dendrimer treated fabric was maintained at 4 using the ASTM D4966-98 (1989) standard. After 10,000 rub cycles, 70 g/L FCdendrimer treated fabric maintains a 4-5 spray rating. 80, 90, 100 g/L FC-dendrimer treated fabrics showed the best abrasion resistance. Thermal conductivity is heat flow through a material. Table 10 illustrates that the least conductivity existed in 100 g/L FC-dendrimer-treated fabric, and maximum conductivity was observed in 60 g/L concentration. The thermal conductivity value decreased as the thickness and GSM of the treated sample gradually increased. As the FCdendrimer concentration increased, the rate of heat transfer decreased. The thermal conductivity rate of 90 g/L and 100 g/L FC-dendrimer-treated fabric was decreased to 40% and 54%, respectively, due to their greater thickness. Moreover, it is assumed that changing the surface morphology of the treated fabric also created barriers to thermal conductivity. SEM study revealed that the FC-dendrimer polymer filled the pores of the untreated fabrics and deposited small amounts of granular material on the surface of the treated fabric, which would reduce thermal conductivity in the treated sample.
The calculated values for thermal conductivity of 60 g/L, 70 g/L and 80 g/L FC-dendrimer-treated fabric are less than the tabulated values as shown in Table 10, so the null hypothesis is accepted. The null hypothesis is a typical statistical theory that suggests that no statistical relationship and significance exists in a set of given single observed variable, between two sets of observed data and measured phenomena. On the other hand, the calculated values of 90 g/L and 100 g/L FC-dendrimer-treated fabrics are greater than the tabulated values: as a result, the null hypothesis is rejected. Therefore, thermal conductivity will not be hampered by 60 g/L, 70 g/L and 80 g/L FC-dendrimer treatment. But the comfort properties of the fabric will be significantly and negatively affected by 90 g/L and 100 g/L FC-dendrimer treatment. Air permeability Comfort and breathability are closely related to air permeability. The air permeability rate of 60 g/L, 70 g/L, 80 g/L, 90 g/L and 100 g/L FC-dendrimer treated fabric was 829, 818, 790, 750 and 733 m 3 / m 2 /h, respectively, as shown in Table 11. The highest air permeability value existed in 60 g/L fabric, and the air permeability of 90 g/L and 100 g/L treated fabrics were 13% and 15% lower, respectively, than that of untreated fabric. As the concentration of FCdendrimer coating materials increased, the pickup percentage gradually increased and, as a direct result, the air permeability value declined. Cross-linking networks may form on the waterrepellent finish. The FC-dendrimer treatment results in blocking some pores, which may be responsible for less air permeability. These are some of the factors that may create less air permeability.
The critical chi-square value is evaluated at a 5% level of significance with two degrees of freedom. For each sample, we took three observations. The calculated values for 60 g/L and 70 g/L FC-dendrimertreated fabrics are less than the tabulated values as shown in Table 11, so the null hypothesis is accepted. On the other hand, the calculated value for 80 g/L, 90 g/L and 100 g/L is greater than the tabulated value (Table 11), so the null hypothesis is rejected. The 80 g/L, 90 g/L and 100 g/L FC-dendrimer-treated fabric observation did not achieve a sufficient value for accepting the null hypothesis, but the 60 g/L and 70 g/L FC-dendrimer-treated fabric observation did.
Thus, we conclude that 60 g/L and 70 g/L FC-dendrimer treatment will not hamper the air permeability or comfort of the fabric. But this will not hold at higher levels of FC-dendrimer concentration.

Water vapour permeability
Clothing should be able to let water vapour pass through it. Otherwise, heat accumulates in the body as humid water vapour is impacted between clothing and the body. Similarly, perspiration should pass through clothing. Lighter fabrics (less mass per square meter and thickness) permit the easy passage of water vapour through the fabrics.
The water vapour permeability rate decreased with the increased concentration of FC-dendrimer, as shown in Table 12. The water vapour permeability of 60 g/L, 70 g/L, 80 g/L, 90 g/L, and 100 g/L FC-dendrimer-treated fabrics were 1249, 1240, 1231, 1221 and 1212 g/m 2 /day, respectively.
The calculated values of 60 g/L and 70 g/L FCdendrimer-treated fabrics are less than the tabulated value, as shown in Table 11, so the null hypothesis is accepted. On the other hand, the calculated values of 80 g/L, 90 g/L and 100 g/L FC-dendrimer-treated fabrics are greater than the tabulated values: as a result, the null hypothesis is rejected.
It may determine that FC-dendrimer treatment at 60 g/L and 70 g/L does not affect on water vapour permeability or comfort qualities. However, treatment with 80, 90, and 100 g/L FC-dendrimer significantly reduces comfort qualities.

Conclusion
The purpose of this experiment was to test whether FC-dendrimer treatment could improve the characteristics of cotton fabric to make it more functional and protective. In that sense, this experiment was a success. FC-dendrimer and crosslinking agents produce a fabric that is water-, oil-and dirt-repellent, as well as UV-protective. As the amount of FC-dendrimer concentration increases, these properties of the treated fabric intensify. An increase in the surface hydrophobicity, reduction of surface energy and lowering of the number of hydroxyl functional groups on the cotton fabric surface are achieved by FC-dendrimer coating, enhancing its repellence and allowing unwanted water, oil and dirt to slide off so that the fabric self-cleans. High contact angle values for liquids mean that FC-dendrimer-treated cotton fabrics have become hydrophobic. The treated cloth effectively separates water/oil combinations on its surface due to its hydrophobic properties.
Results showed that fabric coated with 60, 70, and 80 g/L FC-dendrimer displayed the best performance in comfort. On the other hand, 90 and 100 g/L showed the best result in terms of water resistance. Therefore, FC-dendrimer treatment can produce more suitable textiles than untreated cotton for a wide range of functions, including anti-wetting, self-cleaning, oil-water separation, antimicrobial articles and protective textiles.

Limitations
In this study, the spray rating did not change after five machine washes. On the other hand, the spray rating did not change after 5000 rub cycles. Furthermore, 70, 80, and 100 g/L FC-dendrimer treated fabric still maintained their hydrophobicity even after 10,000 rub cycles. As a result, after five machine washes and 10,000 rub cycles, the self-cleaning, oil-water separation, hydrophobic, antibacterial, and UV resistance all preserved their efficacy. All the self-cleaning, oil-water separation, antibacterial and UV-resistant properties mainly depend on the hydrophobic performance of the fabric for this study.
Some literature revealed that fluorocarbon-treated fabric has become unusable after 50 (fifty) washing cycles and 50,000 rub cycles. So, this issue of persistence of the effects of treatment needs further investigation.
Several types of dendrimers are available in the market. In this study, FC-dendrimer (Rucostar EEE6, Rudolf, Germany) has been used.
A detailed mechanism of FC-dendrimer interaction with the fabric was not shown. For this reason, it was not possible to demonstrate the cross-linking network between FC-dendrimer and cotton fabric. Furthermore, due to a lack of specific information on the FC-dendrimer chemical structure, it did not clearly describe the process of UV resistance. These will be of great interest to researchers for future investigation. In order to develop the flame retardant property, flame retardant monomers would be used with the FC-dendrimers compound.
Funding This research received no external funding.

Conflict of interest
The authors declare they have no conflicts of interest.
Ethical standard This article does not involve the participation of humans or animals.