Folded chain concept of fiber structure

Colloid and Polymer Science - The fringed fibril concept of fiber structure is suported by the high longitudinal and smaller lateral tensile strength and elastic modulus, but one experiences...     

Determination of caffeine and associated compounds in food, beverages, natural products, pharmaceuticals, and cosmetics by micellar electrokinetic capillary chromatography

A method is described for quantitating caffeine, theobromine, theophylline, paracetamol, propyphenazone, acetylsalicylic acid, salicylic acid, and codeine phosphate in corresponding real samples of food, beverages, natural products, pharmaceuticals, and cosmetic preparations by micellar electrokinetic capillary chromatography. The separation is carried out at 25 degrees C and 25 kV, using a 20mM phosphate buffer (pH 9.0), 80mM sodium dodecyl sulfate, and 7.5% (v/v) acetonitrile. UV detection is at 210 nm. The method is shown to be specific, accurate (recoveries over the range 98.9-101.2%), linear over the tested range (correlation coefficients >/= 0.9993), and precise (relative standard deviation below 2.1%). The method is applied for the quantitative analysis of these compounds in different foods, beverages, natural products, pharmaceuticals, and cosmetic products.     

Inverse gas chromatography analysis of spruce fibers with different lignin content

Unbleached TMP spruce fibers were stepwise delignified by KMnO₄/H₂SO₄ and five partly delignified samples were obtained. Fibers were characterized in terms of carboxylic groups, lignin and hemicelluloses content. IGC measurements were performed in the untreated fibers and in the five delignified fiber samples, as well as in microcrystalline cellulose (MCC). Different parameters, such as the dispersive component of the surface free energy (g_s ^d \gamma_{{_{s} }}^{d} ), the free energy and the enthalpy of adsorption with nonpolar probes ( \Updelta G_a^d \Updelta G_{a}^{d} and \Updelta H_a^d \Updelta H_{a}^{d} , respectively), as well as the specific interactions with polar probes, quantified by the free energy and the enthalpy of adsorption ( \Updelta G_a^s \Updelta G_{a}^{s} and \Updelta H_a^s \Updelta H_{a}^{s} , respectively), were determined. The values of g_s ^d \gamma_{{_{s} }}^{d} and \Updelta G_a^d \Updelta G_{a}^{d} are for all samples lower than for pure cellulose and vary slightly with the amount of lignin. For small contents of lignin, the values of \Updelta G_a^s \Updelta G_{a}^{s} of the acidic probes decrease with the delignification whereas those of the basic probes increase, pointing to a rather acidic character of the fibers due to the increase of the relative amount of the carbohydrates. The values for MCC corroborate these findings. Despite the substantial variation in the carboxylic group content during delignification, no clear tendencies were detected regarding the affinity with the basic probes.