Barbara Simončič

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.

A study of dye-surfactant interactions. Part 1. Effect of chemical structure of acid dyes and surfactants on the complex formation

Abstract The study of the interactions between anionic azo dyes C.I. Acid Orange 7 (AO7) and C.I. Acid Red 88 (AR88), with different surfactants, i.e., the cationic surfactants dodecylpyridinium chloride (DPC) and cetylpyridinium chloride (CPC) and the anionic surfactant sodium dodecylsulphate (SDS), in submicellar concentration ranges has been researched by a potentiometric technique using a surfactant-cation-sensitive membrane electrode. The e.m.f. measurements versus surfactant concentration have been performed for the systems CPC-AO7, DPC-AO7, DPC-AR88 and SDS-AO7 in pure water at 25°C. Experimental measurements give the option to determine the concentration of free and of bound surfactant cations at a given stoichiometric concentration and calculation of the dye-surfactant complex formation constant, K, and the standard free enthalpy change, ΔG°. The results show that under the same experimental conditios the complex formation between CPC and AO7 takes place at much lower surfactant concentration than between DPC and AO7, accompanied by much higher values of K. It can be seen from the shapes of the binding isotherms that the binding of DPC to AO7 is most likely cooperative. The results indicate that in the DPC-AR88 system, where more hydrophobic dye AR88 is used, the dye-surfactant interactions are stronger compared to DPC-AO7 system. Such observations enable the conclusion, to be made that, beside the electrostatic attractive interactions, the noncoulonic interactions are also very important for the formation of the complex between the oppositely-charged dyes and surfactants. The study of the interactions between the same-charged dye AO7 and surfactant SDS shows that they do not interact with one another in the whole measured concentration range. The most logical explanation for this is that the repulsive electrostatic interactions prevent the formation of the complex between the same charged AO7 and SDS.

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.

A study of dye–surfactant interactions. Part 3. Thermodynamics of the association of C.I. Acid Orange 7 and cetylpyridinium chloride in aqueous solutions

Abstract The association of C.I. Acid Orange 7 (D) and the surfactant cetylpyridinium chloride (S) was studied at 15, 25, 35 and 45°C in the presence of 0, 0.05 and 0.1 mol/kg NaCl, by potentiometric titration, using a surfactant cation sensitive membrane electrode. By using the association constant (K1) for the first step of the association [D−+S+ ↔(DS)°], the standard free energy change, standard enthalpy change, and standard entropy change of the association were calculated at low surfactant concentrations. The unitary entropy of association was negative, suggesting that hydrophobic interactions do not play a major role in the initial interaction between dye and surfactant. On the other hand, in the second step [S++(DS)° ↔(DS2)+], the unitary entropy change in the medium-level surfactant concentration domain was highly positive, indicating that water-structure contributions are appreciable in the stabilisation of the (DS2)+ species. It was shown that a further stepwise association is not very likely in the third domain, and that a neutral quadruple species of type (SD)2° may be present in the solution. Further increases in surfactant concentration led to a very steep increase in bound surfactant as the concentration of free surfactant ions approached the c.m.c. point. It was also shown that the addition of a simple electrolyte (e.g. NaCl) decreased K1, mainly due to interference with the interaction of dye and surfactant ions. Since long range Coulombic interactions are absent in the second association step, the increase in K2 with increasing NaCl concentration can be mainly attributed to short range hydrophobic interactions.

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.

Functionalization of cotton with poly-NiPAAm/chitosan microgel: Part II. Stimuli-responsive liquid management properties

Stimuli-responsive microgel, based on synthetic polymer (poly-NiPAAm) and biopolymer (chitosan), was incorporated onto cotton fabric surface by pad-dry-cure method using 1,2,3,4-butanetetracarboxylic acid (BTCA) as crosslinker. In order to assess the moisture management properties of cotton functionalized with responsive microgel, the effects of temperature, relative humidity and concentration of microgel on water vapour transmission rate (WVTR) and moisture content (MC) were quantified. Since the use of experimental design is considered as a highly attractive feature in dealing with experiments and variables of this nature, the effects were quantified by using a central composite design. The regression equations obtained from the statistical analysis allowed the prediction of WVTR and MC at different ambient conditions. Material properties such as crease recovery and whiteness were also measured. The results indicate that both relative humidity and temperature significantly influence studied responses (WVTR and MC), showing that good perspiration can be achieved at lower humidity levels and at higher temperatures. The observed phenomena are attributed to controlled expansion (or contraction) of the surface incorporated microgel, which acts as a sensor of temperature and as a valve to regulate the water vapour permeability of functionalized cotton.

Influence of Repellent Finishing on the Surface Free Energy of Cellulosic Textile Substrates

The aim of this research is to investigate the influence of a fluorochemical repellent treatment with and without an added durable press finish on the surface free energy changes of a cellulosic textile substrate as well as the durability of the finishing agents. For this purpose, contact angles are measured based on the goniometric-sessile drop tech nique. Different theoretical models are chosen to calculate the solid surface free energy and its dispersive and polar components. A statistical evaluation of the results with ANOVA (P < 0.01 ) shows that the values of the surface free energy components of the finished textile substrate depend on a theoretical model as well as the chosen liquid combinations. Coating the textile substrate with fluoropolymer repellents alone and in combination with the durable press finish changes the highly hydrophilic polar cellulosic fabric into an almost apolar low energy solid. Laundering of the finished substrate in a surfactant aqueous solution decreases oil repellency, and a full rearrangement of the fluorocarbon polymer film on the textile surface is achieved after the heat treatment. What is also achieved is excellent durability of the fluoropolymer film on the textile substrate.

Preparation and performance of silver as an antimicrobial agent for textiles: A review:

This article reviews select contemporary silver (Ag) compounds used for the chemical modification of textile fibers, including colloidal Ag, Ag salts, and Ag powder. The routes of their application, the chemical methods of preparation, and the strengths and drawbacks of the individual application processes are reviewed. The most important additives employed in the preparation of colloidal Ag nanoparticle (Ag NP) solutions and their influences on the properties of the colloidal Ag are discussed. Furthermore, the mechanism of the antimicrobial activity of Ag when incorporated into textile fibers is presented in particular. Different factors related to the application processes and the properties of the fibers themselves are addressed in the context of the efficiency of Ag as an antimicrobial agent in textiles.

A study of dye–surfactant interactions. Part 2. The effect of purity of a commercial cationic azo dye on dye–surfactant complex formation.

Abstract The interactions between the cationic azo dye C.I. Basic Yellow 25 and the cationic surfactant cetylpyridinium chloride have been studied by potentiometry, UV/VIS spectrophotometry and 1 H NMR. The effect of the purity of the commercial sample of the dye on the dye–surfactant interactions has been investigated. The results show that the cetylpyridinium chloride forms a complex with one of the components of the commercial sample of the dye in aqueous solution. The concentration of this component is decreased by purification of the commercial dye sample. The results also indicate that there are no dye–surfactant interactions in solutions of the cationic and nonionic components of the dye. According to this observation, we conclude that the surfactant cetylpyridinium chloride does not form a complex with the dye component in the commercial sample of C.I. Basic Yellow 25, and that the reduction of the free surfactant cation concentration in the solution causes reduction of the levelling action of the surfactant in the system involving the same charged dye and surfactant.