Arthur D. Broadbent

Decolorization Of Textile Dye Solutions

Results are presented on the use of ozone to decolorize textile dye solutions. The results describe the rates of reaction and the stoichiometry for the use of ozone to decolorize a simulated wastewater containing a bisazo acid dye (Acid Red 158). These rates of reaction are not sensitive to pH and are only mildly affected by temperature. The effects of a combination of an uncolored organic compound on the rates of reaction were investigated because if ozone reacts preferentially with uncolored compounds, its use might not be economical. Guar gum used in the textile industry as an aid in dyeing carpets increases the consumption of ozone by 20–60% for the conditions studied and has a small effect on the reaction rate. The competition found is not severe enough to make ozone treatment uneconomical.

Air Flow Through Textiles at High Differential Pressures

Air flow through fabrics at relatively high differential pressures is studied both ex perimentally and theoretically. An extension of a previous model for fluid flow through a bed of fibers takes into account the geometric irregularities and deflection of the fibers, successfully predicting that the pressure drop across the fabric is a linear function of the air flow rate up to the pressure corresponding to critical flow conditions. It also correctly predicts values for the elastic moduli of the various fibers. The influence of fiber swelling induced by wetting on air permeability is examined. At high differential pressures (55 kPa), a decreased air flow rate is found only for wool fabrics. Under the conditions of the standard fabric air permeability test (differential pressure 12.3 Pa), water blocking the channels in the wet fabric is not removed, so the air permeability is much less than that for the conditioned fabric.

Modeling the influence of dye distribution on the perceived color depth of a filament array

This paper presents a model of the reflection, refraction, and absorption of light rays by a dyed cylindrical filament according to classical laws of optics. Overall light transmit tance and reflectance of a single filament are then assumed to apply to a complete layer of such filaments. The optical behavior of the entire filament array is derived by adding successive filament layers with the same or different amounts and distributions of dye. Each filament contains a light-absorbing dye that may be evenly distributed throughout it, or located in a ring close to the filament periphery (ring dyed). The model also considers the case where only filaments near the surface of the array are colored, while those in the interior are not. The calculations predict how the various different distributions of the dye in the filament array influence the perceived color depth. The results are discussed in relation to previous work and to practical dyeing experience.

Pre-drying Textile Fabrics with Infrared Radiation

A number of different fabrics were pre-dried in a pilot-scale electric infrared oven, using tubular radiant heaters placed evenly above and below the web. For most of the fabrics, the degree of drying, for given conditions using both medium- and short-wave sources, was independent of the nature of the fibers and the material construction. The textile simply served as an inert support for a sheet of water. This was true provided the wet fabric was thick enough to avoid any significant transmission of the radiation incident on it, and its final water content was not much below the critical value cor responding to the end of the constant rate drying period. At the optimum fabric width, the energetic efficiency for pre-drying using this particular oven was 73% for medium- wave quartz tubes and 56% for short-wave T-3 tubes. The lower efficiency of the short- wave sources was a consequence of decreased absorption of radiation by the wet web at wavelengths below 1.5-2.0 μm. The effects of source-web distance and fabric width were determined with the aid of view factor calculations based on the specific geometry of the dryer. The drying rate was not greatly influenced by variations in the rate of air flow. There was a contribution from convective heat transfer between the warm air and the textile, but this was difficult to assess.

Numerical Control of a Continuous Infrared Dryer

This study compares the relative performance of distinct microcomputer control algorithms for drying a textile sheet in an infrared oven. The process responses to changes in the set point as well as perturbations in the traveling velocity of the sheet and the inlet humidity of the sheet are analyzed. Feedback, feedforward, and hybrid control algorithms are considered. The results indicate that the performance of the feedback control algorithm is negatively affected by the time delay associated with the traveling of the sheet in the dryer. The feedforward control algorithm exhibits more rapid dynamics, but falls short of reaching the set point because of model imperfection. The hybrid control algorithm, combining the feedback and feedforward controls, gives the best results overall.

Modeling the Effects of Filament Radius and Photochemical Dye Fading on the Perceived Color Depth of a Filament Array

An optical model is used for simulating the effects of varying filament radii on the perceived color strength of an array of parallel filament layers representing a textile fabric. As the filament radius decreases, the color yield also decreases in direct proportion. The model predicts that the concentration of dye in the filaments, required to achieve a given color strength, is inversely proportional to the filament radius in agreement with practical experience in dyeing microfiber fabrics. New equations are also derived to calculate the light absorption by each individual filament layer at a given dye concentration. The degree of photochemical dye fading in each layer is simulated using these respective absorbed light intensities leading to a decrease in the overall color strength. Repeated calculations of the absorbed light intensities and decreasing dye concentration and color strength show that pale colors will fade more rapidly than deep colors and that fading will be faster when the filament radius is decreased. Both these results agree with practical observations of the light fastness of dyeings. For deep colors, the upper filament layers absorb all the incident light, and filaments in the center of the array undergo minimal fading, resulting in significant dye concentration gradients in the filament matrix.

Modeling light reflection from colored filament assemblies

The model describes the reflection, refraction and absorption of light rays by a single cylindrical filament according to the classical laws of optics. The overall light transmittance and reflectance of a single filament are then assumed to apply to an entire layer of such filaments. The optical behavior of the entire filament assembly is derived by adding successive filament layers, with the same optical characteristics, to those already present. The model describes the effects of varying the relative refractive index of the filament material and the filament radius on the transmittance and reflectance of the filament matrix, and in individual filaments, influences the perceived color depth. The dye may be evenly distributed throughout each filament or located in a ring close to the filament periphery. The model also considers the case where filaments near the surface of the assembly are colored while those in the interior are not. The results are discussed in relation to practical coloration experience.

Measuring the Water Content of a Textile Fabric Using a Radio Frequency Sensor

Application of radio frequency sensors for the automatic control of a pilot-scale infrared drying range for textiles is described. This was most successful for the classical proportional-integral-differential (PID) negative feedback control system, but with some important restrictions—the drying of a single fabric with a relatively low initial water content and at constant tension. The radio-frequency sensor detects changes in water content of the textile from capacitance variations arising from changes in the dielectric constant of the wet fabric. This parameter was influenced by many variables in addition to the amount of water in the fabric. In particular, the dielectric constant depended on the characteristics of the fabric and was very sensitive to the presence of ionic substances in the water. Thus, this sort of sensor is less appropriate for control of textile drying under industrial conditions.

Simulating Textile Padding with Vacuum Extraction Part I: Influence of Process Variables Under Ideal Conditions

Mass balance equations were developed for several equipment configurations used for textile padding, followed by vacuum extraction and solution recycling. The effects of changes in process variables on the amount of chemical in the bath and that retained by the fabric were simulated for both transitory and steady-state operation. The time to reach a new steady state after a perturbation of the process depended on the nature of the variable changed, the kind of equipment, and whether the vacuum extracted solution was recycled and to which container. Systems for which the chemical solution is metered and the bath level maintained by water make-up have quite different char acteristics from those with bath make-up by a chemical solution alone. The process simulations permitted comparison of the response times for different equipment types, along with useful information for equipment selection, process optimization, and pre diction of the influence of process changes.

Simulating Textile Padding with Vacuum Extraction Part II: Perturbations of the Bath Concentration

Mass balance equations have been solved to simulate textile padding followed by vacuum extraction and recycling for seven equipment configurations. These equations include five parameters describing a number of perturbations that change the con centration of the chemical solution being applied: evaporation of the solution under vacuum, incomplete recovery of the chemical after vacuum extraction, preferential absorption of the chemical or of water from the applied solution before the pad nip or between the nip and the vacuum extractor, hydrolysis of the reactive group of a dye or chemical, and desorption of water or chemical already present in the fabric being treated. Methods for determining numerical values for the parameters describing these effects are given. In addition, the model also includes bath overflow and deviation of the extracted solution to a recovery unit. A number of typical process simulations are given, demonstrating time dependence and magnitude of concentration changes for single or combinations of effects. Since the conditions for steady-state operation are easily calculated, the required quantity of chemical in the fabric can be maintained constant from the start of the process.