| | SLO | ENG | Piškotki in zasebnost

Večja pisava | Manjša pisava

Iskanje po katalogu digitalne knjižnice Pomoč

Iskalni niz: išči po
išči po
išči po
išči po
* po starem in bolonjskem študiju


11 - 14 / 14
Na začetekNa prejšnjo stran12Na naslednjo stranNa konec
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: 1996; Prenosov: 54
URL Povezava na celotno besedilo

Inhibition properties of TRITON-X-100 on ferritic stainless steel in sulphuricacid at increasing temperature
Regina Fuchs-Godec, Gregor Žerjav, 2009, izvirni znanstveni članek

Opis: The inhibiting action of a non-ionic surfactant of the TRITON-X series (TRITON-X-100) on stainless steel type X4Cr13 in 1.0 M H2SO4 solution at five different temperatures was investigated by the potentiodynamic polarisation measurements. The inhibition efficiency has been calculated in the presence and in the absence of the inhibitor. The experimental data suggest that the inhibition efficiency increases with increasing concentration of the TRITON-X-100, and decreases with the increasing temperature. Adsorption of the non-ionic surfactant used here obeys the Flory- Huggins isotherm. The thermodynamic parameters, such as, the heat of adsorption, adsorption entropy, and the adsorption free energy, have been calculated by employing thermodynamic equations. Kinetic parameters, also been evaluated.
Ključne besede: non-ionic surfactants, corrosion inhibitors, sulphuric acid, Flory-Huggins adsorption isotherm
Objavljeno: 31.05.2012; Ogledov: 1396; Prenosov: 63
.pdf Celotno besedilo (332,60 KB)
Gradivo ima več datotek! Več...

Supercritical fluid adsorption and desorption of lipids on various adsorbents
Mojca Škerget, Željko Knez, 2007, izvirni znanstveni članek

Opis: In present work the feasibility of using supercritical fluid chromatography (SFC) for separation of free fatty acids (FFA) and triglycerides has been examined. Lipids such as oleic acid and sunflower oil (containing 96% of triglycerides) were used; adsorption and desorption on adsorbents such as silica gel and neusilin using supercritical $CO_2$ as mobile phase was investigated. The experiments were performed at 40 °C and in the pressure range from 13 to 30 MPa. Adsorption kinetic lines were determined by analysingbreakthrough curves. Several parameters such as rate of adsorption and desorption, loading, desorbed quantity and diffusion coefficients in solid phase were calculated.
Ključne besede: supercritical fluid chromatography, lipids, oleic acid, triglycerides, adsorption, desorption
Objavljeno: 31.05.2012; Ogledov: 1686; Prenosov: 68
.pdf Celotno besedilo (167,88 KB)
Gradivo ima več datotek! Več...

Localized dissolution kinetics of low carbon steel
Aljana Petek, Valter Doleček, 2007, izvirni znanstveni članek

Opis: Localized dissolution of low carbon steel in saturated calcium hydroxide with different amount of sodium chloride has been investigated, using a dc technique. Potentiokinetic polarization curves indicated that pitting potentials ($E_{pit}$) decrease linearly with the log of chloride concentration. The rate of pit nucleation (1/$t_i$), and the rate of pits growth increases with increasing concentration of $Cl^-$ ions. Initiation of pitting attack could be ascribed to the adsorption of $Cl^-$ ions on the oxide surface. Adsorption of $Cl^-$ ions is physisorption and follow the Langmuir isotherm with $Δ_{ads}G^0$ = -21.1 kJ/mol.
Ključne besede: pitting corrosion, adsorption isotherm, low carbon steel, simulated interstitial solution
Objavljeno: 31.05.2012; Ogledov: 1701; Prenosov: 80
.pdf Celotno besedilo (105,67 KB)
Gradivo ima več datotek! Več...

Iskanje izvedeno v 0.13 sek.
Na vrh
Logotipi partnerjev Univerza v Mariboru Univerza v Ljubljani Univerza na Primorskem Univerza v Novi Gorici