In recent years, there has been a lot of news about outbreaks and diseases in the world, which negatively affect human life, including coronavirus, influenza, hepatitis, Salmonella and E. coli infections [1] . Therefore, consumers focused extremely on medical products, and then as a natural consequence, the use of textiles on medical, hygiene, and health care fields has become significantly widespread with new antimicrobials, fibers, and technologies. Medical Textiles Market is strongly growing due to the rising both U.S. healthcare expenditure and demand from the Asia Pacific region under the COVID-19 outbreak. For example, The U.S. healthcare expenditure has increased from around US$ 1.1 trillion in 2010 to about US$ 1.8 trillion in 2020. As a result of all these, Medical Textiles Market is estimated to will reach US$ 16.8 billion J o u r n a l P r e -p r o o f by 2024 from US$ 12.2 billion in 2019, with a growth rate of more than 5% every year [2, 3] .
Biocidal functionalization on textiles have also been studied extensively, and many chemicals have been explored and developed for inhibiting the growth of bacteria and preventing infections and diseases in medical applications. Many antimicrobials such as organometallics and metal ions (especially silver ions) [4] [5] [6] [7] , phenols [8] [9] [10] [11] [12] [13] , biguanides, quaternary ammonium salts [14] [15] [16] , organo-silicones and N-halamines [17] [18] [19] have been used in textile industry for decades. N-halamines can have the forms of amine, amide, and imide as a biocidal agent. They offer many advantages and benefits over other biocides, such as they have potent, broad-spectrum, generally nonleaching, rechargeable, relatively inexpensive, and hydrophobic character. Their lethal action occurs with the transfer of the oxidative chlorine to the cell membrane of the microorganisms. Their most distinctive property is that they can be recharged again (by converting N-H bond to N-Cl) by aqueous chlorine exposure when oxidative halogen ion (chlorine, bromine, or iodine) inactivates the microorganisms and then is vanished. They can easily be polymerized on the surfaces, be modified to produce desirable functional groups for attaching to surfaces, be impregnated into polymeric materials, and be incorporated on surfaces, as a biocide [20] [21] [22] [23] .
For medical textiles, modification and functionalization are also significant to obtain active groups on the surface using textile-wet processes. However, attachments of any chemical and surface treatment to inert polymers such as polyester and polypropylene are complicated and a big challenge due to lack of surface tethering (functional) groups [24, 25] . While there are methods such as spin coating and layer by layer assembly to impart functionality to inert substrates, these methods are not universally applicable as they only provide stable functionality on high surface tension substrates. Therefore, J o u r n a l P r e -p r o o f pretreatment is generally required to increase the surface tension of the inert surface or to form reactive groups on the surface. Unfortunately, the formation of functional properties on the surface was proven to be unsuccessful for polyester in conventional textile applications [24, 26] . At the same time, the growth of consumer's demand for innovative technologies and value-added textile materials, Governmental rules, and increasing environmental concerns force the textile industry to develop green technologies [27] [28] [29] [30] .
Considering all of the above, modification, functionalization, and processing of materials could be easily carried out through supercritical fluids. They offer several specific physical, chemical, and toxicological advantages to reduce the consumption of energy, water (wastewater), chemicals, and also get functional properties on the polymer surfaces [26, 31, 32] . Since the late 1990s, supercritical fluids related studies have increased exponentially, and carbon dioxide (CO2) is the most desirable among them. Besides being non-flammable and non-toxic, due to its cheapness, CO2 is widely used as the supercritical fluid. Its critical coordinates are low conditions (Tc=31°C and Pc=7.38 MPa), and it also becomes gaseous and is spontaneously separated from the processed products when pressure is decreased to 60 bar or less. So, it can be industrialized without high equipment and operating costs [31, 33, 34] . In a supercritical state, CO2 shows low viscosity, high permeation and diffusion abilities like that of gases combined with high density, and has a solvating power similar to liquid solvents. Therefore, CO2 in the supercritical state has both high solvating power to chemicals and swelling and plasticizing efficiency to hydrophobic polymers [26, [35] [36] [37] [38] [39] [40] [41] . For example, polyester can be easily functionalized in supercritical CO2 (scCO2) state.
However, medium and small molecular weight compounds (monomers, cross-liners, initiators, etc.) can dissolve and quickly diffuse into polyester in scCO2 [33, 37, 42] .
Many functional chemicals such as polysiloxanes, N-halamines, and fluoropolymers are soluble in scCO2 and served as the anchoring tool to attach functional groups to the surface of the substrate without the need of polymerization since this application does not require reactive sites on substrates, as well [43, 44] . As a result, scCO2 is highly suited to textile processes such as pre-treatment, dyeing, and finishing for modification and functionalization of surfaces.
In this study, we focused on the antibacterial functionalization of polyester with Nhalamine in scCO2. Firstly, N-(2-methyl-1-(4-methyl-2,5-dioxo-imidazolidin-4yl)propan-2yl)acrylamide (HA) was synthesized and polymerized by free radical polymerization, and then their structures were confirmed by NMR and FTIR, respectively. The presence of N-halamine on the polyester surface was also investigated by FTIR. The properties of color, mechanical, and durability to abrasion were measured, and also stability, rechargeability, and durability to washings of the antibacterial properties were examined after scCO2 treatments. 
HA was synthesized according to the procedure described in Kocer et al [45] . The synthesis and polymerization reactions of HA were given in The obtained polymer was filtered as white powder form. Its structure was confirmed by NMR and FTIR spectroscopies. 1 
The schematic description of the apparatus used for scCO2 applications was described in Fig. 2 [35] . This apparatus was equipped with motor, temperature and time controllers, heating and cooling systems, a rotary pattern where the vessels are mounted, and a high-temperature oil bath. The vessels are stainless steel cylinders (internal volume=290 mL, Pmax=30 MPa, and Tmax=130 °C ) and equipped with closure with Teflon seal, safety valve, and needle valve used to fill and vent the CO2. The PET sample (16x24 cm, ca. 10 g) was wrapped around a stainless-steel perforated beam, and 5% of HA homopolymer (HP) (owing to fabric weight, ca 0.5 g) was placed at the bottom of the vessel which was then filled with CO2 up to predetermined temperature and pressure during durations from 1 to 24 hours. For easy filling of CO2, the vessels were cooled in a separate freezer for 15 minutes. Then, the vessels were mounted on the pattern rotating inside the oil bath. The experiments have been done considering poor solubility, and it was decided to accomplish at different durations; 1, 3, 6, 12, and 24 hours, while keeping pressure and temperature constant (at 120 °C , 25 MPa). After J o u r n a l P r e -p r o o f treatments, samples were removed from vessels, rinsed with acetone to remove loosely attached polymers on the surface, and dried at ambient temperature. 
Chlorination was applied after scCO2 treatments for activating N-halamines with halogen ions. For chlorination, 10% aqueous solution at pH 7 was prepared from household bleach (6% sodium hypochlorite). After samples were chlorinated for 1 h, the unbonded chlorine on samples was removed by washing with water, and by drying at 45 °C for 1 h. The chlorination mechanism was provided in Fig. 3 . 
1 H (400 MHz) NMR spectra were recorded with 16 scans on a Bruker spectrometer equipped with SampleXPress autosampler, using the Bruker TopSpin 2.1 software.
The sample was prepared by dissolving 5 mg of monomer in 1 mL deuterated dimethyl sulfoxide (DMSO-d 6 ). The spectra were collected at ambient temperature at 30 °C and chemical shift values were given in parts per million (ppm).
FTIR spectrum was obtained using Thermo Nicolet iS50 FTIR spectrometer attenuated total reflectance (ATR) accessory to characterize monomer, polymers, and fabrics.
While recording spectra, 32 scans were made at 2 cm -1 spectral resolution, and scanning range was from 400 to 4000 cm -1 .
Color values were determined using Datacolour CHECK II Plus spectrophotometer, and the measurements were taken according to AATCC Test Method 173. The samples were folded twice and measurement was conducted in reflectance mode under the condition of D65 illuminantand 10° standard observer. The averages of four measurements were reported as color values (L*, a*,b*) and color difference (∆E).
The samples were conditioned for 24 hours at 20±2 °C and 65±4% RH before tensile tests, and then they were subjected to tensile testing only in accordance with the warp direction, using ISO 13934-1 test method on Instron test machine. Briefly, the strips in 25x150 mm size were tested using a 50 kN of the load cell with 100 mm of the gauge length, and 10 cm/min of speed, at room temperature. The mean value and standard deviation (SD) were calculated using SPSS.V25 software and the averages of three measurements were reported as breaking strength (MPa) and breaking extension (%).
The determination of loaded chlorine on the surfaces was made with iodometric/thiosulfate titration [46] . The ethanol with 0.1 N acetic acid (90/10; v/v) was prepared and 0.25 g potassium iodide was dissolved in this solution, then the samples were added to the final solution. Titration was made with 0.005 N sodium thiosulfate solution until the color of the solution is yellow to clear. The weight percent of loaded chlorine (Cl + %) on samples were calculated according to Eq. 1 given below:
where V and N are the volume (L) and concentration (mol/L) and of titrant sodium thiosulfate, respectively, and W is the weight percentage of the sample (g). The mean values and standard deviations of five measurements were reported as the loaded chlorine.
The durability of scCO2 treatments against abrasion was measured for 9000 cycles, Muller-Hilton II agar media, and plates were incubated for 24 h at 37 °C. The viable colonies were counted (in CFU/mL), and the bacterial reduction was determined.
Reduction rate (R%) of bacteria was calculated using the formula (Eq. 2): J o u r n a l P r e -p r o o f
The hydantoin ring configuration of HA monomer was obtained by Bucherer-Bergs reaction and polymerized according to the procedure described in Kocer et al [45] . 1 H NMR spectrum of HA monomer was given in Fig. 4 J o u r n a l P r e -p r o o f
Surface characterization of before and after scCO2 treatment was performed by FTIR to determine the chemical changes and confirm the presence of treatment on the PET.
It was first observed the most obvious HA presence in the surface for 6 hours, comparing 1 and 3 hours, and therefore, this spectrum was provided in Fig. 5 with spectra of HA polymer and untreated PET fabric together. As seen in Figure HA treated PET in scCO2 for 6 hours.
For textile materials, color values and color change are one of the most important fabric quality characteristics, and it is a significant aspect to take into consideration after any surface treatments. The color values were measured after scCO2 treatments with and without HA, and the results were presented in Table 1 It was found that both sorption and swelling increase with pressure, and that higher values are reached when specific CO2/polymer interactions can occur and when the mobility of the polymeric chains is higher (or the crystallinity is lower) [60] . As a result, the swelling and CO2/polymer interactions are both enhanced by increasing CO2 density (via pressure increase or temperature decrease). In turn, density improves solute loading, by polymer plasticization and increase of internal diffusion coefficients [60] . swelling). As a general conclusion of these works, the processing conditions can be optimized by getting change the temperature and/or time to reduce this loss further because the running with accurate processing time and temperature is critical knowledge for not getting worse the mechanical properties of PET. These results suggested that scCO2 treatments did not affect the mechanical properties of PET fabrics dramatically and exhibited satisfactory results.
J o u r n a l P r e -p r o o f 
For scCO2 studies, the treatments with 5% HA were carried out at 120 °C , 25 MPa for different processing times considering chemical solubility in scCO2. The increases of 1.6, 1.8, and 1.9% on fabric weights were observed in Fig. 7 , considering 6, 12, and 24 hours processing times. However, hydantoin acrylamide on the surface must be activated by any aqueous treatment using halogen ions (converting the N-H bond to N-Cl). After chlorination treatment, the presence of oxidative chlorine (Cl + ) bonded to HA on the PET was measured by analytical titration of treated samples, and chlorine loadings (Cl + %) concerning process time were shown in Fig. 7 . Although the chlorine loading is relatively low comparing previously described studies [38, 51, 61, 62] , the treated PET samples provided fast inactivation against E. coli as shown in the antibacterial tests (Fig. 8 ) and the effects of these treatments were not surprising.
Earlier works have reported that with a chlorine loading of 0.04% would be sufficient for getting antibacterial activity [61, 63] , hence, PET-HA (6 hours), PET-HA (12 hours), and PET-HA (24 hours) samples would still provide antibacterial efficacy. As seen in 
The stability and rechargeability of oxidative chlorine (Cl + ), and the durability of HA compound on the PET surface are essential against washes because of the chlorine stability of N-Cl bond and antibacterial property. The tests were applied to PET-HA (6 hours) samples, and the treatments were performed on chlorinated samples before washes (A), chlorinated before washes and rechlorinated after washes (B), and unchlorinated before washes, but chlorinated after washes (C), as presented in Fig. 9 .
The chlorinated PET samples (A) lost the most of their first chlorine loadings quickly with increasing washes, and the chlorine content decreased from 0. 25 
The durability of treatments against abrasion was tested, and the remained chlorine on the surface was determined by titration after defined abrasion cycles. The results were shown in Fig. 11 about 23% of chlorine remained on the surface after the 9000 cycles. This indicated that the polymer was still standing on the surface. Hence, the durability of the treatments against the repeated friction could consider good since they had higher values than the critical value (0.04%) in literature [39, 65] . Fig. 11 . Durability to abrasion of fabrics treated in scCO2.
The functionalization of polyester is more challenging than cotton and other related fibers because of the lack of functional groups within the molecular structure. This study investigated the antibacterial functionalization of polyester fabrics with Nhalamine in scCO2 medium for different processing times. Therefore, HA was This study points out the new application for sustainable fabrication of biocidal polyester using N-halamine by resource-efficient and eco-friendly scCO2 technique.
The scCO2 technology can create a new opportunity to focus on nonreactive polymers such as polyester for getting surface functionalization and modification, which would help reduce the cost of production and the environmental pollution with textile finishings.
The authors declare no conflict of interest.