Karen De Clerck

Polycaprolactone and polycaprolactone/chitosan nanofibres functionalised with the pH-sensitive dye Nitrazine Yellow

Nanofibres functionalised with pH-sensitive dyes could greatly contribute to the development of stimuli-responsive materials. However, the application of biocompatible polymers is vital to allow for their use in (bio)medical applications. Therefore, this paper focuses on the development and characterisation of pH-sensitive polycaprolactone (PCL) nanofibrous structures and PCL/chitosan nanofibrous blends with 20% chitosan. Electrospinning with added Nitrazine Yellow molecules proved to be an excellent method resulting in pH-responsive non-wovens. Unlike the slow and broad response of PCL nanofibres (time lag of more than 3h), the use of blends with chitosan led to an increased sensitivity and significantly reduced response time (time lag of 5 min). These important effects are attributed to the increased hydrophilic nature of the nanofibres containing chitosan. Computational calculations indicated stronger interactions, mainly based on electrostatic interactions, of the dye with chitosan (ΔG of -132.3 kJ/mol) compared to the long-range interactions with PCL (ΔG of -35.6 kJ/mol), thus underpinning our experimental observations. In conclusion, because of the unique characteristics of chitosan, the use of PCL/chitosan blends in pH-sensitive biocompatible nanofibrous sensors is crucial.

Damage-Resistant Composites Using Electrospun Nanofibers: A Multiscale Analysis of the Toughening Mechanisms

Today, fiber-reinforced polymer composites are a standard material in applications where a high stiffness and strength are required at minimal weight, such as aerospace structures, ultralight vehicles, or even flywheels for highly efficient power storage systems. Although fiber-reinforced polymer composites show many advantages compared to other materials, delamination between reinforcing plies remains a major problem limiting further breakthrough. Traditional solutions that have been proposed to toughen the interlaminar region between reinforcing plies have already reached their limit or have important disadvantages such as a high cost or the need for adapted production processes. Recently, electrospun nanofibers have been suggested as a more viable interlaminar toughening method. Although the expected benefits are numerous, the research on composite laminates enhanced with electrospun nanofibrous veils is still very limited. The work that has been done so far is almost exclusively focused on interlaminar fracture toughness tests with different kinds of nanofibers, where typically a trial and error approach has been used. A thorough understanding of the micromechanical fracture mechanisms and the parameters to obtain toughened composites has not been reported as of yet, but it is crucial to advance the research and design highly damage-resistant composites. This article provides such insight by analyzing the nanofiber toughening effect on three different levels for several nanofiber types. Only by combining the results from different levels, a thorough understanding can be obtained. These levels correspond to the hierarchical nature of a composite: the laminate, the interlaminar region, and the matrix resin. It is found that each level corresponds to certain mechanisms that result in a toughening effect. The bridging of microcracks by electrospun nanofibers is the main toughening mechanism resulting in damage resistance. Nevertheless, the way in which the nanofiber bridging mechanism expresses itself is different for each scale and dependent on parameters linked to a certain scale. The multiscale analysis of the toughening mechanisms reported in this paper is therefore crucial for understanding the behavior of nanofiber toughened composites, and as such allows for designing novel, damage-resistant, nanofiber-toughened materials.

Investigating the Halochromic Properties of Azo Dyes in an Aqueous Environment by Using a Combined Experimental and Theoretical Approach

The halochromism in solution of a prototypical example of an azo dye, ethyl orange, was investigated by using a combined theoretical and experimental approach. Experimental UV/Vis and Raman spectroscopy pointed towards a structural change of the azo dye with changing pH value (in the range pH 5-3). The pH-sensitive behavior was modeled through a series of ab initio computations on the neutral and various singly and doubly protonated structures. For this purpose, contemporary DFT functionals (B3LYP, CAM-B3LYP, and M06) were used in combination with implicit modeling of the water solvent environment. Static calculations were successful in assigning the most-probable protonation site. However, to fully understand the origin of the main absorption peaks, a molecular dynamics simulation study in a water molecular environment was used in combination with time-dependent DFT (TD-DFT) calculations to deduce average UV/Vis spectra that take into account the flexibility of the dye and the explicit interactions with the surrounding water molecules. This procedure allowed us to achieve a remarkable agreement between the theoretical and experimental UV/Vis spectrum and enabled us to fully unravel the pH-sensitive behavior of ethyl orange in aqueous environment.

Influence of Fiber Surface Purity on Wicking Properties of Needle-Punched Nonwoven after Oxygen Plasma Treatment

Polyester and meta-aramid nonwoven samples were treated at reduced pressure in a radiofrequency oxygen plasma for between 5 and 30 seconds. The hydrophilic effect of the plasma treatment was assessed by three consecutive vertical wicking tests on each sample. The influence of cleaning of the fiber surface before as well as after the plasma treatment was determined. The presence of fiber surface additives had a positive influence on first-time wicking. On the other hand, when the layer of surface additives is plasma treated rather than the fiber polymer surface, the treatment effect is easily washed away. Log(time) wicking curves and summed wicking height plots are introduced as a means to help the interpretation of wicking data.

Quality Control of Textile Electrodes by Electrochemical Impedance Spectroscopy

In this paper an electrochemical cell is developed to test and follow-up the quality of electrodes made of knitted, woven and non-woven conductive textile material. This cell is constructed of two electrodes planarly positioned against each other using a series of PVC plates. The obtained impedance, as a result of applied alternating potential and measured current signal, is equal to the resistance of the system electrode–electrolyte in the frequency region where no shift is observed in phase angle between applied potential and measured current. This resistance provides information about the properties and performance of the electrodes and a change of this resistance during the lifetime of the electrodes is an interesting parameter for quality control of the used electrodes. After characterization of the cell a range of textile electrodes (woven, non-woven and knitted) were investigated and compared. Results showed that the textile electrodes behave initially similar, obeying an equation that shows that the resistance is proportional to d, c –1and A –2/3, dbeing the distance between the electrodes, cthe electrolyte concentration and Athe electrode surface. However, after longer exposure some indication of corrosion and malfunction was detected.

Dye immobilization in halochromic nanofibers through blend electrospinning of a dye-containing copolymer and polyamide-6

‘Smart’ materials can be defined as materials that respond to a certain stimulus with a change in their properties. A specific class herein is halochromic textiles, i.e. fibrous materials that change color with pH. Such halochromic textiles play an important role in the continuous monitoring and visual reporting of the pH with applications in various fields, such as wound treatment and protective clothing. pH-sensitive nanofibrous nonwovens have high sensitivity and a fast response time, and are mostly fabricated by introducing a pH-responsive dye via dye-doping of the feed mixture before fabrication. However, this method suffers from leaching of the dye, which is an undesirable effect that not only reduces the output signal strength but can also be detrimental to the environment by causing, for instance, toxicological responses. In this paper, a new strategy is demonstrated for the reduction of dye leaching in electrospun, nanofibrous materials. Through blend electrospinning of polyamide-6 (PA6) with a dye-functionalized copolymer, large sheets of uniform, halochromic nanofibrous material can be fabricated showing a fast pH-sensitive color change. Polymeric entanglements within the nanofiber are proposed to immobilize the dye-functionalized copolymer in the PA6 matrix, resulting in drastically reduced dye leaching. Such stable nanofibrous, PA6-based, halochromic materials are particularly interesting in the design of new colorimetric sensors applicable in several sectors, including the biomedical field, agriculture, safety and technical textiles.

Filtration performance of electrospun polyamide nanofibres loaded with bactericides

Electrospinning is a process to generate nanofibrous nonwovens. With these nonwovens, many applications can be targeted, such as water filtration. In this paper, polyamide nanofibrous membranes are evaluated for their pore size, a key parameter in water filtration, and for their removal of microorganisms. To increase the removal efficiency to values exceeding the state of the art, innovative functionalization of the nanofibres is studied. The nanofibrous membranes are functionalized using a one step method. Different functionalization chemicals are investigated which are Ag nanoparticles and bactericides. Ag functionalized nanofibres are used as a reference medium to compare with a novel bactericide based functionalization system. It is seen that nanofibrous membranes functionalized with the bactericides exceed the normal removal efficiencies obtained by microfiltration membranes. Furthermore, knowledge is built up on how these bactericides are inserted in the nanofibres themselves.

Polyamide 6.9 nanofibres electrospun under steady state conditions from a solvent/non-solvent solution

Nanofibres can be processed into several high-end applications due to their unique characteristics, especially when based on a diversity of polymers with specific properties. This, however, requires that the nanofibrous structures are produced in a highly reproducible way. The article gives focus to polyamide (PA) 6.9, a less exploited PA though with interesting properties such as a very low moisture absorption. To trace and understand the dominant parameters that allow for the aimed reproducible characteristics, the influence of the solution parameters on the steady state behaviour during electrospinning as well as the resultant fibre morphology is followed by scanning electron microscopy and differential scanning calorimetry. Results show a significant effect of the amount of non-solvent acetic acid, added to the solvent formic acid, on the steady state behaviour and the fibre morphology. The non-solvent acetic acid broadens the steady state window by making the electrospin solutions more suitable to obtain uniform and reproducible nanofibrous structures with a narrow nanofibre diameter distribution. The mixture of the solvent formic acid and the non-solvent acetic acid strongly contributes to the future potentials of PA 6.9 nanofibres, with its leading to a smaller fibre distribution and moreover highly reproducible in time.

Moisture sorption in developing cotton fibers

The moisture sorption behavior of developing cotton fibers is studied by dynamic vapor sorption. Mature fibers show a typical sigmoidal isotherm, IUPAC type II, describing the adsorption on macroporous and non-porous adsorbents with a typical hysteresis. This is different from the type III isotherms exhibited by elongating fibers explained by the weak adsorbate–adsorbent interactions. The maximum sorption capacity clearly decreases throughout the cotton fiber development. This decrease is very rapid during the elongation phase of the fibers, but declines beyond 25 days post anthesis (DPA). This transition corresponds to the time point where the secondary cell wall becomes dominant over the primary cell wall, as confirmed with FT-IR. Also only little moisture hysteresis appeared during the elongation phase whereas from 25 DPA onwards a distinct hysteresis is observed that remains almost constant until maturation of the fiber. The study clearly elucidates the sorption mechanism during the elongation phase of the fiber to be different from the one during the secondary cell wall synthesis. This improved understanding of the cotton sorption behavior is important for optimal application of cotton fiber in novel materials.

B.1.I – Laundry Cleaning of Textiles

This chapter reviews the different aspects of textile cleaning and laundry detergents. A brief introduction to textiles, soils, and different detergent forms is given, and the key ingredients and cleaning mechanisms in a modern domestic laundry detergent (comprising surfactants, bleach, enzymes, builders, chelants, polymers, and others) are covered. Performance test methods and future trends are also analyzed. Over the past decades, a stream of innovations has led to more and more effective and efficient laundry detergents. These innovations were partly driven by the need to ensure compatibility with modern textiles and washing appliances. An even more important factor driving the innovations comes from the need to minimize environmental impact and from the consumer wish for increased performance and convenience. This approach has led to the development of superior products with readily biodegradable surfactants, new builders which replace phosphates, an optimized bleach system along with enzymes that take a more central role in many textile-cleaning products. Several other additives have been developed to strengthen specific performance areas and/or to deliver fabric care benefits. In addition to the formulation, the physical form of the laundry products has also evolved over time, from classical granules to liquids, then to compact granules and liquids, and more recently, to tablets and single-dose liquid laundry products (liquitabs).