Elke Bach

Damage to Natural and Synthetic Fibers Treated in Supercritical Carbon Dioxide at 300 bar and Temperatures up to 160°C

This paper examines and discusses fiber damage in cotton, viscose, polyester, poly amide 6.6, silk, and wool in supercritical carbon dioxide at 100. 120. 140, and 160°C for I and 4 hours at a pressure of 300 bar. For comparison, experiments are conducted for 4 hours at 160°C in nitrogen and air under atmospheric conditions. Damage is determined by fiber-specific reactions, staining tests, shrinkage, stress-strain measurements. viscosi metric molecular weight, and amino acid analyses. Shrinkage occurs only in polyamide 6.6 and polyester, and is comparable to water dyeing. During all treatments above 120°C in carbon dioxide, the degree of polymerization of polyamide 6.6 decreases, which is also detectable by stress-strain measurements. Polyester is not damaged by any treatment. Damaging effects on cotton, viscose, silk, and wool are only revealed by stress-strain measurements after 4 hours at 160°C in carbon dioxide, but not in nitrogen and air. The degree of polymerization of cellulose fibers starts to decrease slightly after 4 hours at 120°C, while amino acid analyses of silk and wool indicate damage only after 4 hours at 160°C. Generally, the combination of heat, treatment time, and carbon dioxide seems to be responsible for the damaging effects. The results show that except for polyamide 6.6, where treatment conditions are limited to 120°C at 300 bar for 1 hour, supercritical carbon dioxide is a suitable solvent for dyeing or other treatments, even for the most sensitive textiles up to 140°C. The treatment time at 160°C should not be longer than 1 hour.

An ultraviolet-spectrophotometric method with 2-cyanoacetamide for the determination of the enzymatic degradation of reducing polysaccharides

A rapid, facile, and sensitive uv-spectrophotometric assay has been developed for the determination of the enzymatic degradation of polysaccharides that generates reducing sugars. The assay was carried out with 2-cyanoacetamide in a single test tube. The solution was left at pH 9 by the addition of borate buffer within 5 min. Measurement of the reaction mixture at 274 nm allows a simple determination up to 600 mumol/liter of reducing sugars. The coefficient of variation was less than 2% on all measurements. The assay was developed with pectin and polygalacturonic acid from apples and has been compared with the Somogyi-Nelson method. The new assay was then exemplarily used for the determination of the enzymatic hydrolysis products of pectin from cotton.

Three-Dimensional Flow Calculation in a Textile Dyeing Process

Three-dimensional computational fluid dynamics simulation software provides deeper insight into dye liquor flow through a yarn bobbin and a dyeing vessel in a textile dyeing machine. In these calculations, the flow model is based on the Navier-Stokes equations for turbulent incompressible liquids, in which the yam package is described by a porosity model with the assumption of linear flow through the bobbins. The simulation results provide information on the static pressure and velocity distribution at every part of the dyeing vessel, which agrees with the experimental data obtained from static pressure measurements and from flow profiles in a polyester yam bobbin after treatment in a high temperature water dyeing plant.

NEW MATHEMATICAL MODEL FOR DETERMINING TIME-DEPENDENT ADSORPTION AND DIFFUSION OF DYES INTO FIBERS THROUGH DYE SORPTION CURVES IN COMBINATION SHADES. PART I: MATHEMATICAL FUNDAMENTALS

Dye uptake of textile substrates can be described as time-dependent by a new mathematical model, in which the sorption process is divided into fast and slow subprocesses. The fast subprocess describes the adsorption of the dye onto the fiber surface, and the slow one details the diffusion of the dye into the fiber. In addition, dye desorption is simultaneously considered along with adsorption. Relating this concept to the dyeing process, it is possible to divide the process into two parts—dye adsorption and diffusion. The model is verified by dyeing cotton with direct dyes, but the results are also transferable to other fibers and dye classes. Using this model, optimum dyeing parameters and dye combinations can be determined from the sorption curves, which are easily obtained by UV-VIS spectrophotometry.

Untersuchungen zum Schmelz- und Strukturverhalten von Polyethylenterephthalatfasern in Luft bei 1 bar und in überkritischem CO2 bis 280 bar

A comparative study was carried out as to the influence of CO 2 on changes of the fibre structure of thermofixed and unfixed PETP multifilament and monofilament fibres in relation to pressure and temperature. To this aim measurements were carried out on the glass transition-, the pre-melting- and the melting temperature with a dynamic heat flow difference calorimeter (DDC) in air at I bar, as well as in CO 2 at pressures up to 280 bar. In the thermograms taken under high pressure the melting point was clearly visible, in contrast to the glass transition- and pre-melting temperatures. Owing to its hydrophobic properties, the CO 2 is capable of diffusing into the fibre where it can act as a virtual contamination to the effect that the melting point at 280 bar is lowered by 13-14 C for all PETP fibres. Measurements of the pre-melting temperature, stress-strain behaviour and shrinkage after treatment of the PETP fibres at temperatures between 80 and 200 C in air and CO 2 show that particularly in the case of non-thermofixed PETP yarns at 280 bar structural changes are brought about from temperatures as low as 80 C upwards which are attributable to partial crystallite growth in the imperfect areas of the fibre polymers. In CO 2 at 280 bar. this results in higher pre-melting temperatures, increased shrinkage and higher elasticity of the fibres in contrast to air at I bar at comparable treatment temperatures. In the case of thermofixed fibres these effects are, as a rule, considerably less marked.

New Mathematical Model for Determining Time-Dependent Adsorption and Diffusion of Dyes into Fibers Through Dye Sorption Curves in Combination Shades Part II: Kinetic Data from Dyeing Cotton with a Trichrome Direct Dye System

Time-dependent dye uptake of textile substrates can be described by a new mathemat ical model that divides the dyeing process into two parts, dye adsorption and dye diffusion. Using this model, the influence of temperature (20-80°C) and NaCl concen tration (2.5-10.0 g/L) on the dye uptake of a trichrome dye combination of C.I. Direct Blue 225, C.I. Direct Violet 47, and C.I. Direct Yellow 27 on cotton is determined from sorption curves obtained by uv-vis spectroscopy. This model can demonstrate differences in temperature dependent dye uptake of the disordered inner and outer surfaces of the substrate and also displacement reactions that occur during dyeing.