Brigita Tomšič

Structures of Novel Antimicrobial Agents for Textiles - A Review

In this article we review some of the contemporary antimicrobial agents used in textiles, including quaternary ammonium compounds, N-halamines, chitosan, polybiguanides, triclosan, nanoparticles of noble metals and metal oxides, and bioactive plant-based products. According to their mechanism of antimicrobial activity, toxicity, durability and ecological acceptability, these agents can be divided into biocides and biostats, leaching and bound antimicrobials, controlled-release and barrier-forming agents, and agents of poor and good washing resistance. In view of the need for ecologically friendly antimicrobial finishing, much research has focused on the synthesis of antimicrobial agents where the leaching antimicrobials have been replaced with the bound antimicrobials. The latter have mostly been prepared using polymerizable quaternary ammonium salts with acrylate groups, alkyltrialkoxysilanes with incorporated quaternary ammonium groups, reactive cationic dyes, appropriate crosslinking agents, complexes with cyclodextrines, and encapsulated nanoparticle agents embedded into polymer matrices of various compositions.

Structural Properties and Antibacterial Effects of Hydrophobic and Oleophobic Sol−Gel Coatings for Cotton Fabrics

In a continuation of previous studies, the wetting properties of the hydrophobic diureapropyltriethoxysilane [bis(aminopropyl)-terminated polydimethylsiloxane (1000)] (PDMSU) sol-gel hybrid, which forms washing-resistant water-repellent finishes on cotton fabrics, were further investigated. The addition of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) to PDMSU resulted in a highly apolar low-energy surface on aluminum with gammaStotal equal to 14.5 mJ/m2 and a DetlaGiwi value of -82 mJ/m2. Mixed PFOTES-PDMSU finishes applied on cotton fabrics increased the water contact angles (thetaw) from approximately 130 degrees (PDMSU) to 147 degrees, also imparting oleophobicity (thetadiiodomethane=130 degrees, thetan-hexadecane=120 degrees) to the finished cotton fabrics. Washing caused breakage of the coatings integrity as established from SEM, which was attributed to the partial removal of PFOTES from the composite films, also shown by subtractive IR attenuated total reflectance (ATR) and XPS spectral measurements made on washed and unwashed fabrics. The antibacterial properties of the PFOTES-PDMSU-finished fabrics were assessed with the transfer method (EN ISO 20743:2007), revealing that the reduction of Escherichia coli bacteria on unwashed cotton fabrics was nearly 100%. Moreover, for washed (10 times) cotton fabrics a much higher bacterial reduction was noted for the PFOTES-PDMSU finishes (60.6+/-10.8%), surpassing PDMSU (30.4+/-6.1%) and commercial fluoroalkoxysilane (FAS) (21.9+/-5.7%) finishes. The structure of PFOTES-PDMSU gels, xerogels, and the corresponding coatings was investigated by analyzing the 29Si NMR and IR ATR spectra and comparing them with the spectra of PFOTES and octameric (T8) PFOTES based polyhedra. The results revealed the tendency of PFOTES to condense in octameric silsesquioxane polyhedra (T8), coexisting in the PDMSU sol-gel network with cyclic tetramers (T4(OH)4) and open cube-like species (T7(OH)3). The presence of -OH-functionalized PFOTES silsesquioxanes, established even in coatings heat-treated at 140 degrees C (15 min), also explained the excellent washing fastness of PFOTES finishes on cotton fabrics. The regenerative nature of the water- and oil-repellent properties of washed PFOTES-PDMSU-finished cotton fabrics was attributed to the surface mobility of the T8 PFOTES based polyhedra, ousted from the coating interior during consecutive washings.

The surface modification of cellulose fibres to create super-hydrophobic, oleophobic and self-cleaning properties

The surface modification of cellulose fibres was performed with the use of low-pressure water vapour plasma, followed by the application of a pad-dry-cure sol-gel coating with the water- and oil-repellent organic-inorganic hybrid precursor fluoroalkyl-functional siloxane (FAS), with the aim of creating the “lotus effect” on the cotton fabric surface. The tailored “lotus effect” was confirmed by measurements of the contact angle of water (154°) and n-hexadecane (140°), as well as by measurements of the water sliding angle (7°), which were used to identify the super-hydrophobic, oleophobic and self-cleaning properties of the modified fibres. The chemical and morphological changes caused by modifications of the fibres were investigated by XPS, FTIR, AFM and SEM. The results show that the plasma pre-treatment simultaneously increased the surface polarity, average roughness, and surface area of the fabric. The application of the FAS coating after plasma pre-treatment caused only a slight increase in the surface roughness, accompanied by a decrease in the surface area, indicating that the architecture of the surface was significantly changed. This result suggests that the surface pattern affected the “lotus effect” more than the average surface roughness. The plasma pre-treatment increased the effective concentration of the FAS network on the fabric, which resulted in enhanced repellency before and after repetitive washing, compared with that of the FAS-coated fabric sample without the plasma pre-treatment. Despite the fact that the plasma pre-treatment increased the concentration of the oxygen-containing functional groups on the fabric surface, this phenomenon insignificantly contributed to the adhesion ability and, consequently, the washing fastness of the FAS coating.

Functionalization of cellulose fibres with DOPO-polysilsesquioxane flame retardant nanocoating

The preparation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-functionalised polysilsesquioxane (Si-DOPO)-coating was described and its flame retardant efficiency for cotton fabric was thoroughly investigated. The 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide–vinyltrimethoxysilane (DOPO–VTS) was synthesized and applied to cotton fabrics at different concentrations using a sol–gel process. The structure of the synthesized DOPO–VTS was characterized using Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The characteristics of the Si-DOPO coatings formed on the cotton fibres were investigated using X-ray photoelectron spectroscopy, time-of-flight-secondary ion mass spectrometry and scanning electron microscopy. The flame retardant properties of the Si-DOPO-coated cotton samples were evaluated by thermogravimetric analyses, vertical flame spread tests and cone calorimetry analyses. The Si-DOPO coating increased the thermo-oxidative stability of the cotton fibres by increasing the stability of the protective char and inhibited cellulose fibres degradation. The Si-DOPO coating did not decrease the time of flaming combustion but did completely stop the vigorous combustion of the fibres. The results also suggest that the flame retardation by the Si-DOPO coating is due to the quenching of active radicals from the decomposing cellulose and the cellulose phosphorylation by the DOPO component as well as the silicon oxide formation by the silsesquioxane component on the fibre surface. These findings indicate that the flame retardant efficiency of the Si-DOPO coating can be ascribed to the combined activity of phosphorus acting in both gas and condensed phases and silicon acting in the condensed phase.

Multifunctional superhydrophobic/oleophobic and flame-retardant cellulose fibres with improved ice-releasing properties and passive antibacterial activity prepared via the sol–gel method

In this research, a two-component sol–gel inorganic–organic hybrid coating was prepared on a cotton fibre surface. An equimolar sol mixture of the precursors 1H,1H,2H,2H-perfluorooctyltriethoxysilane (SiF) and P,P-diphenyl-N-(3-(trimethoxysilyl)propyl) phosphinic amide (SiP) was applied to cotton fabric samples using the pad-dry-cure method. The surfaces of the untreated and coated cotton fibres were characterised using scanning electron microscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight-secondary ion mass spectrometry. The functional properties of the coated cotton fabric samples were investigated using static contact angle measurements with water and n-hexadecane, the ice-releasing test, antibacterial testing against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, thermogravimetric analysis in an air atmosphere, and vertical flammability tests. The results reveal the formation of a nanocomposite two-component inorganic–organic hybrid polymer network that is homogenously distributed over the cotton fibre surface. The presence of the SiP component in the two-component inorganic–organic hybrid coating did not hinder the functional properties imparted by the presence of the SiF component and vice versa, illustrating their compatibility. The cooperative action of the SiF and SiP components in the two-component coating provided the cotton fabric with exceptional multifunctionality, including simultaneous superhydrophobicity and high oleophobicity, passive antibacterial activity, and improved thermo-oxidative stability.

Antimicrobial wool, polyester and a wool/polyester blend created by silver particles embedded in a silica matrix

A two-step antimicrobial finishing procedure was applied to wool (WO) and polyester (PES) fabrics and a WO/PES fabric blend, in which the pad-dry-cure method was performed to create a functional silica matrix through the application of an inorganic-organic hybrid sol-gel precursor (RB) followed by the in situ synthesis of AgCl particles on the RB-treated fibres using 0.10 and 0.50mM AgNO3 and NaCl. The bulk concentration of Ag on the cotton fibres was determined by inductively coupled plasma mass spectroscopy. The antimicrobial activity was determined for the bacteria Escherichia coli and Staphylococcus aureus, and the fungus Aspergillus niger. The results showed that the highest concentration of the adsorbed Ag compound particles was on the WO samples followed by the WO/PES and PES samples. The antimicrobial activity of the finished fabric samples strongly depended not only on the amount of adsorbed Ag but also on the properties of the fabric samples. Whereas Ag biocidal activity was generated for the finished PES samples at Ag particle concentrations of less than 10mg/kg, the 34-times higher Ag particle concentration on the WO samples was insufficient to impart satisfactory antimicrobial activity because Ag chemically binds to the thiol groups on wool. The presence of wool fibres in WO/PES samples decreased the antimicrobial protection of the fabric blend compared with that of the PES fabric. A lethal concentration of adsorbed Ag compound particles for bacteria and fungi was produced only through the treatment of the WO and WO/PES samples with 0.5mM AgNO3.

Influence of oxygen plasma pre-treatment on the water repellency of cotton fibers coated with perfluoroalkyl-functionalized polysilsesquioxane

Oxygen plasma pre-treatment was applied to cotton fabric with the aim of improving the water repellency performance of an inorganic-organic hybrid sol-gel perfluoroalkyl-functionalized polysilsesquioxane coating. Cotton fabric was pre-treated with low-pressure oxygen plasma for different treatment times and operating powers. Afterward, 1H,1H,2H,2H-perfluorooctyltriethoxysilane (SiF) was applied to the cotton fabric samples using the pad-dry-cure method. The surfaces of the untreated and modified cotton fibers were characterised using Fourier transform infrared spectroscopy, Xray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The water repellency of the SiF-coated fabric samples was evaluated using static and sliding contact angle measurements with water. The results show that the plasma treatment with the shortest treatment time (10 s) and the lowest operating current (0.3 A) increased the atomic oxygen/carbon ratio of the cotton fiber surface from 0.6 to 0.8 and induced the formation of a nano-sized grainy surface. Increasing the plasma treatment time and/or operating current did not intensify the surface changes of the cotton fibers. Such saturation effects were explained by the large influence of reactive oxygen atoms during the plasma treatment. The measured static water contact angles on the surface of the untreated and plasma pre-treated and SiF-coated cotton fabrics showed that the oxygen plasma pre-treatment enabled the increase of the water contact angle from 135° to ≈150°, regardless of the applied plasma treatment time and discharge power. This improvement in the hydrophobicity of the SiF coating was followed by a decrease in the sliding angle of water droplets by more than 10° compared to the plasma untreated and SiF-coated sample characterized by a water sliding angle of 45°. Additionally, measurements of the water sliding angle revealed that the increase of the static contact angle from 149° to 150° corresponded to a drop of the water sliding angle from 33 to 24°, which suggests that the plasma pre-treatment of 20 s at an operating current of 0.3 A produced the best water-repellent performance of the SiF-coated cotton fabric.

Bacteriostatic photocatalytic properties of cotton modified with TiO2 and TiO2/aminopropyltriethoxysilane

A new route for the functionalization of cotton fibres with organic–inorganic hybrid materials is proposed using titanium tetraisopropoxide (TiP) and aminopropyltriethoxysilane (APTES). The antimicrobial and photocatalytic activities of the new cotton finishes based on titania and mixed titania/amino-silica hybrids were tested by monitoring the growth of Escherichia coli (ATCC 25922) on the surfaces of functionalized fabrics under exposure to UV radiation and in the dark. Transmission electron microscopy revealed the amorphous nature of the hybrids and confirmed their similarity to other bactericidal aminofunctionalized polymers. Attenuated total reflection infrared spectra showed the protonated amino groups of the APTES in the TiP/APTES hybrid and the presence of Si–O–Ti bonding within the sol–gel hybrids between silica and titania by analogy with previous transmission and ATR infrared studies. Several analytical techniques were employed to establish the presence of the TiP and TiP/APTES modified cotton fibres. ATR measurements proved to be a very useful tool to study also the silane/–C–OH interactions between the hybrid materials and the cotton fibres, revealing the presence of covalent (i.e., –Si–O–C–) bonding with the OH functional group of cellulose. The advantages of the cotton finishes were demonstrated by the measured photocatalytic bacteriostatic effect, which persisted even after 15 washings; in contrast, the aminofunctionalized polymeric finishes, only showed a sufficient bacteriostatic effect. Furthermore, the TiP finishes were photocatalytically active, while the TiP/APTES finishes were not. The ultraviolet protective factor, degree of polymerization of the finished cotton samples were also investigated and revealed the suitability of the proposed method.

Characterisation and functional properties of antimicrobial bio-barriers formed by natural fibres

Antimicrobial bio-barriers formed on cotton (CO), silk (SE), and woollen (WO) fabrics were prepared by the application of 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (Si-QAC) at 11 concentrations ranging from 0.5% to 20% using an exhaustion method. The presence of the Si-QAC coating on the treated fabric samples was detected by X-ray photoelectron spectroscopy. The bromophenol blue reagent was used to determine the concentration of quaternary ammonium groups in the coating. The antimicrobial activity of the coated fibres against Gram-negative and Gram-positive bacteria (Escherichia coli and Staphylococcus aureus), fungi (Aspergillus niger and Chaetomium globosum), and soil microflora was assessed using standard microbiological methods. The antimicrobial protection of the fibres increased with increases in the applied concentration of Si-QAC. The fibre type strongly influenced the antimicrobial activity of Si-QAC. Si-QAC was most effective for CO fibres, less effective for WO fibres, and least effective for SE fibres, suggesting that Si-QAC is less accessible for interactions with microorganisms when applied to protein fibres than to cellulose. Although Si-QAC reduced the microbial growth, it did not significantly hinder the biodegradability or sustainability of the coated fibres when exposed to soil microflora. The extent of rotting was more influenced by the morphological and chemical properties of the fibres than by the presence of Si-QAC.

Sol–gel technology for functional finishing of PES fabric by stimuli-responsive microgel

The possibility of incorporating a stimuli-responsive microgel into a silica matrix by the sol–gel method was studied. This method allows the preparation of a novel class of functional finishes for textile material modification, which is aimed at the creation of simultaneous stimulus-responsive behaviour and functional protective properties. Using a pad-dry-cure method, a thermo- and pH-responsive microgel (PNCS) based on poly-(N-isopropylacrylamide) (poly-NiPAAm) and chitosan was embedded into a silica matrix on a previously activated polyester (PES) fabric. The matrix was composed of a model sol–gel precursor, vinyltrimethoxysilane (VTMS), in combination with hydrophilic fumed silica nanoparticles (SiO2). Functionalized PES fabric samples were characterised by determining the morphological and chemical properties using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The stimuli (temperature and pH) responsiveness of the functionalized PES fabric was established by measuring its porosity, wicking ability, moisture content, drying rate, water vapour transmission rate and water uptake. In order to assess the washing fastness of the surface modifying systems, the tests were done before and after five consecutive washings. The results showed that sol–gel technology is an appropriate method for the incorporation of PNCS microgel on PES fibre surface. Because of the elasticity of the sol–gel matrix, the VTMS/SiO2 polysiloxane film had no adverse influence on the swelling/deswelling effect of the PNCS microgel, thus retaining and even enhancing its stimulus response.