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1.
The interaction ability of cellulosic materials as a function of fine structure and Helmholtz surface energy
Tatjana Kreže, Karin Stana-Kleinschek, Volker Ribitsch, Zdenka Peršin, Majda Sfiligoj-Smole, 2005, izvirni znanstveni članek

Opis: Many chemical or physical modification processes significantly influence the accessibility of fiber forming polymers by causing structural changes. The wettability and sorption ability improvements of polymeric materials are major tasks during finishing processes. Different pre-treatment processes are used in order to improve the accessibility of dissociable groups, hydrophilicity, dyeability, and whiteness. These are usually alkaline purification, chemical bleaching and mercerization. In a previous paper we presented the data for structural characteristics (density, crystallinity index, molecular orientation, void volume, diameter and the specific inner surface of void, etc.) of untreated regenerated cellulose fibers (viscose, modal and lyocell) [41]. We now compare the influence of different pre-treatment processes on fiber structure and the accessibility of the chemical groups of these fibers. In order to improve the accessibility, two pre-treatment processes were used: chemical bleaching of fibers and tensionless alkali treatment. The influence of these pre-treatment processes on the structure parameters was evaluated using viscosity measurements (determination of polymerization degree (DIN 54 270)) and iodine sorption ability measurements according to the Schwertassek method (determination of crystallinity index) [13, 16]. The reactivity and accessibility in a polar environment was determined using tensiometry. Contact angles between the fibers and liquids of different polarities were determined using the powder contact angle method and calculated from a modified Washburn equation [26, 28]. The surface free (Helmholtz) energy of differently treated fibers was determined from the contact angle data using the Owens-Wendt-Raeble-Kaelble approximation [30, 33, 35]. The differences in the accessibility of raw and pre-treated regenerated cellulose fibers obtained using tensiometry are compared with the results of the conventional method used to determine moisture adsorption (DIN 54 351, DIN 53 802). In regard to raw fibers, viscose shows the most hydrophilic characteristic: adsorbs the highest amount of moisture, has the fastest penetration velocities (Fig. 6), the smallest contact angle, and the highest SFE (Fig. 8). Modal fibers have the largest contact angle, the lowest SFE, and they adsorb the smallest amount of water vapor. Pre-treatments increase the sorption ability and the surface free (Helmholtz) energy while they decrease the contact angle. This makes the material more accessible to water and chemicals used in the finishing processes although the crystallinity index increases. The main modification in polymer properties caused by the treatments is an increase in the fiber SFE caused by an increase of the fiber surfaces because of swelling in the alkaline medium (washing, slack-mercerization), and due to an increase of accessible OH- and COOH-groups (bleaching). This enables the formation of an increased number of hydrogen bridges between the water molecules and the OH- and COOH-groups. Our investigations confirm the results published earlier thatthe main property necessary for the proper sorption behavior of cellulose materials are the accessible, less ordered regions and not the degree of crystallinity.
Ključne besede: regenerated cellulose fibers, fiber pre-treatment, iodine sorption, cristallinity, tensiometry, contact angle, Helmholtz surface energy, water adsorption
Objavljeno: 01.06.2012; Ogledov: 1668; Prenosov: 36
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2.
Tuning of poly(ethylene terephtalate)(PET)surface properties by oxygen plasma treatment
Aleš Doliška, Metod Kolar, 2011, izvirni znanstveni članek

Opis: Modification of surface properties of poly(ethyleneterephtalate) (PET) thin films by treatment with weakly ionized oxygen plasma was studied by contact angles of water and diiodomethane (DIM) drops. Samples were exposed to oxygen plasma with the ion density of 5 x 1015/m[sup]3 and the neutral oxygen atom density of 3 x 1021/m[sup]3. Just after the treatment they were characterized by contact angle measurements. Results showed a quick decrease of the water contact angle in the first few seconds of plasma treatment, while prolonged treatment did not cause any substantiated modification. The contact angles of DIM, on the other hand, remained rather constant for the first several secondsof plasma treatment, and increased after prolonged treatment. It was found that the dispersion component of the surface free energy decreased with increasing treatment time, while the polar component increased with treatment time. The results were explained by surface functionalization as well as by roughness effects.
Ključne besede: poly(ethylene terephtalante), PET, oxygen plasma, contact angle, hydrophilic, functionalization
Objavljeno: 01.06.2012; Ogledov: 1097; Prenosov: 22
.pdf Celotno besedilo (329,87 KB)
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3.
Substrate-induced coagulation (SIC) of nano-disperse titania in non-aqueous media : the dispersibility and stability of titania in N-methyl-2-pyrrolidinone
Angelika Basch, Simona Strnad, Volker Ribitsch, 2009, izvirni znanstveni članek

Opis: Dispersions of 1 wt% titandioxide (titania or TiO2) were investigated with respect to their stability in non-aqueous media. The objective of this work was to find conditions for the substrate-induced coagulation (SIC) process in N-methyl-2-pyrrolidinone (NMP). The SIC process is a dip-coating process that enhances adsorption of fine dispersed particles on a pre-conditioned surface. The wetting behavior of titania and NMP was investigated by the powder contact angle method. The absorption process of the polar solvent NMP on the acid oxide TiO2and Aerosol OT (AOT) (bis-2-ethylhexyl sodium sulfosuccinate) was also investigated and a polar or hydrophilic interaction was found. The stability of titania in NMP dispersions and the influence of the solvent AOT and the electrolyte LiCl was investigated. By studying the electrophoretic mobilities of titania particles in NMP and the influence on solutes by the electrophoretic method phase analysis light scattering (PALS) and the electroacoustic method this paper explores suitable conditions for non-aqueous substrate-induced coagulation of titania.
Ključne besede: contact angle, non-aqueous dispersions, electrophoretic mobilities, substrate-induced coagulation, titandioxide, zeta potential
Objavljeno: 01.06.2012; Ogledov: 1185; Prenosov: 49
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