K. De Clerck

The effect of temperature and humidity on electrospinning

Electrospinning is a process that generates nanofibres. Temperature and humidity affect this process. In this article the influence of humidity and temperature on the formation and the properties of nanofibres are studied using cellulose acetate (CA) and poly(vinylpyrrolidone) (PVP) as target materials. The experiments indicate that two major parameters are dependent of temperature and have their influence on the average fibre diameter. A first parameter is the solvent evaporation rate that increases with increasing temperature. The second parameter is the viscosity of the polymer solution that decreases with increasing temperature. The trend in variation of the average nanofibre diameter as a function of humidity is different for CA and PVP, which can be explained by variations in chemical and molecular interaction and its influence on the solvent evaporation rate. As the humidity increases, the average fibre diameter of the CA nanofibres increases, whilst for PVP the average diameter decreases. The average diameter of nanofibres made by electrospinning change significantly through variation of temperature and humidity.

The Use of pH-indicator Dyes for pH-sensitive Textile Materials

The development of halochromic textile materials could lead to interesting end-use applications as it offers the potential for flexible pH-sensors with a first warning signal. Research on halochromic textiles, especially on the development of these materials using a simple and economic beneficial dyeing process, is however very limited. Therefore, we studied color-changing textile materials with a pH-sensitivity based on the dyeing of conventional textiles with standard watersoluble pH-indicator dyes. In a first broad screening, a set of pH-indicators is evaluated on their dyeing performance and their color change with a change in pH. After this, some promising indicators (Brilliant Yellow and Alizarin) are selected and studied in more detail. It was found that the indicators show different characteristics on the textile materials compared with the solution due to dye—fiber interactions. The properties of the pHindicator dyes are also dependant on the fiber type. Moreover, in case of Brilliant Yellow this thesis was confirmed by Raman spectroscopy. Generally, it can be concluded that it is feasible to develop a pH-sensor with pH-indicator dyes and conventional textile materials using a standard dyeing process.The development of halochromic textile materials could lead to interesting end-use applications as it offers the potential for flexible pH-sensors with a first warning signal. Research on halochromic textiles, especially on the development of these materials using a simple and economic beneficial dyeing process, is however very limited. Therefore, we studied color-changing textile materials with a pH-sensitivity based on the dyeing of conventional textiles with standard watersoluble pH-indicator dyes. In a first broad screening, a set of pH-indicators is evaluated on their dyeing performance and their color change with a change in pH. After this, some promising indicators (Brilliant Yellow and Alizarin) are selected and studied in more detail. It was found that the indicators show different characteristics on the textile materials compared with the solution due to dye-fiber interactions. The properties of the pHindicator dyes are also dependant on the fiber type. Moreover, in case of Brilliant Yellow this thesis was confirmed by Raman spectroscopy. Generally, it can be concluded that it is feasible to develop a pH-sensor with pH-indicator dyes and conventional textile materials using a standard dyeing process.

Kinetics and mechanism of the oxidation of sodium dithionite at a platinum electrode in alkaline solution

Abstract In this paper the oxidation of sodium dithionite in alkaline solution was studied by cyclic voltammetry at a stationary and rotating platinum disk electrode. The reaction proceeds in two steps, with sulfite as a relatively stable intermediate and sulfate as final product. It was possible to quantitatively analyze the kinetics of the oxidation wave making use of the experimental evidence that the reaction rate is not dependent on pH, with a reaction order of 0.5 with respect to sodium dithionite and a charge transfer coefficient of 0.5. The proposed mechanism of the overall electron transfer reaction consists of five consecutive steps starting with the adsorption of dithionite, followed by decomposition into SO 2 − , which releases an electron in the rate determining step and finally two more chemical steps leading to the formation of sulfite. The predicted behavior by this mechanism is in agreement with the experimentally observed one.

Structure changes and water filtration properties of electrospun polyamide nanofibre membranes

Nanofibre membranes are studied extensively in water treatment. Inappropriate storage, however, could alter their performance, e.g. regarding water filtration. This shows the need for investigating this effect in more detail so as to offer a solution for long-term behaviour and stability. In this study, polyamide nanofibre membranes were treated under different conditions, simulating the diverse storage conditions and to simulate their use in water filtration systems. Under all these different settings, nanofibre properties (scanning electron microscope pictures, dimensional changes, tensile strength) and water filtration performance (clean water permeability (CWP), bacterial removal) were investigated. The results demonstrate that, as soon as the dimensional change of a membrane is >2%, the CWP, tensile strength and bacterial removal significantly decrease. These dimensional changes occurred when the membrane became dry after it had been in contact with water. As such, it is important to keep the membrane either in dry or in wet conditions to store its unique properties. When heat-treated, the membrane had a higher tensile strength and kept its morphology and characteristics better during storage.

Innovative screening of novel bioengineered cotton fibers containing oligochitin

The aim of this paper is to establish a test method for the screening of bioengineered cotton fibers with an improved reactivity through the incorporation of positively charged nitrogen moieties. For this purpose a spectrophotometric method based on the absorption of a negatively charged dye (Acid Orange 7) is extensively studied. The processing parameters have been optimized for analyzing small amounts of fibers and the feasibility of the method is examined by using two other well established techniques for nitrogen analysis. Good correlations were obtained between the different methods, however, the reproducibility of the Acid Orange 7 was superior to the other two methods. Moreover, statistically significant differences were found between fibers from cotton lines designed to produce oligochitin and control fibers without oligochitin. This shows that the proposed method is capable of accurately detecting increased nitrogen levels in bioengineered cotton fibers.

Nanofibrous textiles in medical applications

Abstract: Nanofibrous textiles may have a great potential in the medical field because of their unique characteristics that meet the criteria for medical applications. After a general introduction on nanofibres, this chapter will elaborate on the possibilities of nanofibres in wound dressings, drug delivery systems and tissue engineering applications. These case studies will prove the enormous potential of nanofibres in various medical domains.

Moisture sorption in naturally coloured cotton fibres

Increasing environmental concerns have stimulated an interest in naturally coloured cottons. As many commercial and technical performance aspects of cotton fibres are influenced by their response towards atmospheric humidity, an in-depth research on moisture sorption behaviour of these fibres using dynamic vapour sorption is carried out. Significant differences were observed in sorption capacity and hysteresis behaviour of brown and green cotton fibres. These differences are mainly attributed to the variations in maturity and crystallinity index of the fibres. This study provides valuable insights into the moisture sorption behaviour of naturally coloured cotton fibres.