Özgür Ceylan

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.

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.

The effect of water immersion on the thermal degradation of cotton fibers

The decomposition behavior of cotton fibers is examined using thermogravimetric analysis. The effect of the test parameters on the thermal degradation of raw cotton fibers is determined. Focus is given to the influence of water immersion on the thermal behavior of cotton fibers. For less mature fibers a clear difference is noted between the degradation profiles of the water-immersed and untreated samples. On the contrary, only a small change is noted on the degradation profile for more mature fibers after water immersion. The maturity and variations in water-soluble content of the fiber are found to be important factors influencing the thermal behavior of raw cotton fibers. Inductively coupled plasma atomic emission spectrometry (ICP-AES) is used to underpin the effect of water immersion on cotton fibers. This improved understanding for the role of maturity and water soluble constituents in thermal degradation of cotton fibers may lead to develop routes that improve thermal stability and smoldering characteristics of cotton fibers as relevant for future applications.

Electrospun polyamide 4.6 nanofibrous nonwovens: parameter study and characterization

The aliphatic polyamide 4.6 (PA 4.6) has unique properties compared to the commonly used polyamides 6 (PA 6) and 6.6 (PA 6.6). The purpose of this paper is to produce uniform and reproducible nanofibrous PA 4.6 structures. Therefore, a mixture of the solvent formic acid and the nonsolvent acetic acid is used to dissolve and electrospin the PA 4.6. First the steady-state behaviour of the process and the boundary limits of the solution parameters needed for steady-state electrospinning are investigated. Subsequently, the effect of several solution and process parameters on the fibre morphology is examined, using microscopic techniques and thermal analysis. The polyamide concentration is found to be the dominant parameter affecting the fibre diameter and morphology. Furthermore, tensile tests are performed on upscaled nanofibrous structures and electrospun under optimised steady-state conditions. It is shown that the PA 4.6 nanofibrous structures, compared to nanofibrous nonwovens of PA 6 and PA 6.6, have a higher stress and strain at break.

Dynamic moisture sorption behavior of cotton fibers with natural brown pigments

The moisture sorption behavior of white and naturally colored cotton fibers is studied by dynamic vapor sorption. Dark brown and brown fibers show a higher sorption capacity compared to beige and white fibers. The differences in sorption capacity are found to be related to the maturity and crystallinity index of the fibers. All fibers exhibited sorption hysteresis to varying degrees throughout the full relative humidity range. The variations in hysteresis behavior are mainly attributed to the differences in crystallinity index of the fibers. In addition the monolayer and polylayer moisture content is analyzed using the Hailwood Horrobin model. Monolayer sorption is most closely related to the crystallinity index and, to a lower extent, maturity of the fibers. For beige and white fibers monolayer sorption remains almost constant, whereas for darker fibers it shows a substantial increase with increasing color difference. In contrast, polylayer sorption shows a general increasing trend over the whole studied color spectrum. Also a noticeable relationship was found between the total hysteresis and the monolayer sorption. Yet such relation was less evident for polylayer sorption. This study contributes to the better understanding of the dynamic moisture sorption behavior of white and naturally colored cotton fibers. This improved understanding is important for optimal application of naturally colored cotton fibers in novel materials.

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.