Lidija Fras

Determination of the adsorption character of cellulose fibres using surface tension and surface charge

Abstract.The reactivity and adsorption properties of cellulose fibres are critical for successful treatment because behavior during the finishing process is determined by both structure and surface properties. The fine structure of natural cellulose fibres i.e. cotton, is different from the regular viscose, modal and new types of regenerated cellulose fibres i.e. lyocell, which are clarified by different hydrophilic/hydrophobic character of fibres and different adsorption properties. Tensiometry, seldom used in fibre characterization was used to obtain the differences in the adsorption properties of different cellulose fibres. The surface tension, contact angle and adsorption were measured, and then compared with various methods for determining water adsorption. Currently some additional methods especially sensitive to surface properties (electrokinetic properties of fibres) are being applied in order to characterize the adsorption character and reactivity of the fibre surfaces. The streaming potential was measured due to the fact that the interaction properties are strongly influenced by electric charges on the surface, and from these values the zeta potential (ζ) was calculated as a function of the pH and the surfactant concentration in the liquid phase. As with the results of fibre reactivity and adsorption properties obtained by conventional methods, the electrokinetic character of the materials and their adsorption ability determined using the tensiometry also show the same phenomena. The natural fibres have the smaller hydrophilic character and they are less reactive than the regenerated ones, so the ζmax of cotton is the highest and the contact angle ϕ the greatest [1, 2, 3]

Mild and Selective Oxidation of Cellulose Fibers in the Presence of N-Hydroxyphthalimide

The oxidation reaction of regenerated cellulose fibers mediated by N-hydroxyphthalimide (NHPI) and various cocatalysts at room temperature for different time intervals and various amounts of low concentration sodium hypochlorite solution has been investigated to produce oxidized cellulose (OC), a biocompatible and bioresorbable polymer. The results revealed that the nonpersistent phthalimide-N-oxyl (PINO) radical generated in situ from NHPI in both, metallic or metal-free systems, is a powerful agent in this kind of transformation. Moreover, the reaction converts highly selectively C(6) primary hydroxyl groups to carboxylic groups under mild reaction conditions and shorter reaction times than previously reported. The amounts of negatively charged groups in OC were determined by means of potentiometric titration. Further characterization of the products were accomplished by using Fourier transform infrared spectroscopy/attenuated total internal reflection spectroscopy (FT-IR/ATR), environmental scanning electron microscopy (ESEM), and X-ray and energy-dispersive X-ray (EDX) spectroscopy. Notably, water retention values of the oxidized fibers increased by 30% in comparison with the original nonoxidized sample, as a result of the introduction of hydrophilic carboxylate groups.

Comparison study of TEMPO and phthalimide-N-oxyl (PINO) radicals on oxidation efficiency toward cellulose

Regenerated cellulose fibers, type viscose, have been oxidized with sodium hypochlorite and catalytic amounts of sodium bromide by using two different protocols: first, involving the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and second, employing N-hydroxyphthalimide (NHPI). The reactions were carried out at room temperature and pH=10.5 for 2.5h. Viscose oxidized samples were analyzed and compared in terms of the negative charged groups content, as determined by potentiometric titration and methylene blue adsorption, morphologies and crystallinities changes, as well as changes in the degree of polymerization. The highest content of the carboxylic groups and the best preservation of the morphology and molecular weight of the original material have been found in the case of using NHPI/anthraquinone as oxidation mediators. TEMPO-mediated oxidation leads to the highest depolymerization and cause significant degradation of the cellulosic material.

4 – Active textile dressings for wound healing

Aqueous medium containing several nutrients and vitamins is essential for cell metabolism and growth. The wound exudate serves as a transport medium for a variety of bioactive molecules. The various cells in the wound communicate with one another via mediators such as enzymes, growth factors, and hormones to ensure and enhance the healing processes. The wound exudate also provides the various cells of the immune system with ideal conditions for destroying invading pathogens such as bacteria, foreign bodies, and necrotic tissues, diminishing the rate of infection. There are several types of moist/smart wound dressing; in this chapter, we discuss the following types: alginate fibres, chitosan fibres, nanofibres, maggots, medical-grade active Leptospermum or manuka honey, hydrogels, and antibacterials.