Jelena Vasiljević

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.

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.

Cotton fiber hot spot in situ growth of Stöber particles

Textured cotton substrates are drawing interest as a new class of non-wetting and non-fouling materials. We investigated the effect of temperature, solvent and substrate presence on the in situ particle growth process for the production of self-cleaning, wash-resilient and air-permeable superhydrophobic and oleophobic cotton textiles. By comparing the size of particles grown in solution with those grown on cotton fibers, we show that the uniform solution growth follows a faster reaction rate. In general, the cotton surface favors the production of hierarchical structures that provide a liquid-repellent behavior, when combined with low surface free energy nanocoatings, such as an organically modified silane precursor or perfluoro ethers. In addition, the influence of an oil-based lubricant on the pinning effect was evaluated. On the basis of these findings, we present a low-cost method to manufacture nanostructured coatings to achieve optimal roughness and liquid repellence.

Combining polyNiPAAm/chitosan microgel and bio-barrier polysiloxane matrix to create smart cotton fabric with responsive moisture management and antibacterial properties: influence of the application process

Smart cotton fabric with simultaneous temperature and pH responsive moisture management and antibacterial properties was prepared by applying poly-(N-isopropylacrylamide)/chitosan microgel in combination with bio-barrier-forming sol–gel precursor dimethyloctadecyl (3-(trimethoxysilyl)propyl) ammonium chloride. Two application processes were used: one-step, which included deposition of a mixture of PNCS microgel and Si-QAC mixture (PNCS/SiQ (1S)), and two-step, comprising deposition of PNCS microgel followed by Si-QAC (PNCS + SiQ (2S)) and vice versa, i.e., deposition of Si-QAC followed by the PNCS microgel (SiQ + PNCS (2S)). Different analysis, i.e., nuclear magnetic resonance, thermogravimetry and dynamic light scattering were used to characterize the poly-(N-isopropylacrylamide)/chitosan microgel, while scanning electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy analysis were employed to determine the morphological and chemical properties of the modified cotton samples. Their functional properties were assessed by the moisture content, water vapor transmission rate, water retention capacity and antibacterial activity against Escherichia coli. While Si-QAC granted excellent antibacterial activity, it also influenced swelling/deswelling activity of the poly-(N-isopropylacrylamide)/chitosan microgel. Accordingly, it slightly impaired moisture content and water retention capacity at conditions when microgels swell but increased water repulsion from the poly-(N-isopropylacrylamide)/chitosan microgel at conditions that trigger its coil-to-globe transition. The application process greatly influenced the washing fastness of the coatings, and the PNCS + SiQ (2S) application process appeared most promising. In this case, the poly-(N-isopropylacrylamide)/chitosan microgel acted as a carrier for the sol–gel precursor dimethyloctadecyl (3-(trimethoxysilyl)propyl) ammonium chloride, causing its gradual release to the fiber surface triggered by a variation of temperature and pH and thus preserving its excellent antibacterial activity after five laboratory washings. To assure complete synergistic activity of both components in the coating, further optimization of the sol–gel precursor dimethyloctadecyl (3-(trimethoxysilyl)propyl) ammonium chloride concentration is necessary.Graphical Abstract

Influence of N-, P- and Si-based Flame Retardant Mixtures on Flammability, Thermal Behavior and Mechanical Properties of PA6 Composite Fibers

This research investigated the influence of two flame retardant (FR) mixtures consisting melamine cyanurate (MeCy) and aluminum diethylphosphinate (AlPi), and MeCy and sodium aluminosilicate (SASi) at different weight ratios, on the flammability, thermal behavior and mechanical properties of polyamide 6 (PA6) composite yarns produced by meltspinning. The morphological and chemical properties of PA6/FR filaments were investigated by scanning electron microscopy and Fourier-transform infrared spectroscopy, flame retardancy by vertical burning test UL-94, thermal behavior by thermogravimetric and differential scanning calorimetric analyses, and mechanical properties by tensile tests. The results indicate that within the UL 94 V2 rating, the composite yarns differed significantly from each other in their burning and dripping behavior. The incorporation of both mixtures, MeCy+AlPi and MeCy+SASi, into the PA6/FR yarns significantly decreased the afterflame time relative to pristine PA6, confirming a lower production of flammable volatiles. This phenomenon was attributed mainly to MeCy, which caused an immediate extinguishment of the flame after the withdrawal of the igniting flame. Compared to one component MeCy, the incorporation of the MeCy+SASi mixture enhanced the thermooxidative stability of the PA6/FR yarns because of their additive effect at higher concentrations. In contrast, an antagonistic effect was obtained for the MeCy+AlPi mixture, irrespective of the concentration. Since the incorporation of MeCy+SASi did not drastically reduce the tensile properties of filaments, this mixture enables the production of the PA6/MeCy+SASi composite yarns with the enhanced flame retardancy and thermo-oxidative stability.