M.L. Gulrajani

Optimization of a Single-Stage Preparatory Process for Cotton Using Sodium Hypochlorite

A single-stage preparatory process for cotton fabrics, based on a self emulsifiable solvent-assisted system using sodium hypochlorite has been investigated using a second- order response surface design. The proposed process works at a low temperature (40°C) and thus leads to a considerable energy savings. The properties of single-stage bleached fabrics are comparable with those of conventionally bleached fabrics.

Kinetics of Bleaching Agent Decomposition in a Single-Stage Preparatory Process Part I: Hydrogen Peroxide Bleaching

In a single-stage preparatory process, hydrogen peroxide decomposes at a faster rate in the presence of pH buffers, whereby the activation energy is lowered. A relatively slower rate of peroxide decomposition is achieved in fabrics containing acrylic size. The damage to cellulose assessed in terms of the copper number and carboxyl content is slightly higher for acrylic-sized fabrics than starch-sized fabrics.

Factors Influencing the Critical Dissolution Time of Textile Fibers

The dissolution of the fiber takes place on penetration of the solvent sufficient enough to break down the intermolecular forces to an extent that molecular chains become virtually free, and this is observed as a mechanical failure of the fiber under tension due to the load. The tension on the fiber influences the critical dissolution time (CDT) significantly. Since the tension leads to the orientation of the molecular chains, it appears that the increase in CDT is due to the restriction to the diffusion of phenol molecules into the oriented space of the fiber kept under tension. The results imply that in addition to the crystallinity, the size, and the stability of the crystalline portions of the fiber, the orientation also influences the CDT.

Effect of Dye-Polymer Interaction on the Stress-Strain Characteristics of Dyed Polyethylene Terephthalate Fiber

The mechanical properties of undyed (treated under conditions identical to those of dyeing) and dyed polyester fibers, dyed with PNA (a model disperse dye), C.I. Disperse Yellow I, and Red 17 were investigated. It was observed that the presence of these dyes causes perceptible changes in the mechanical behavior of the fibers. While PNA (model dye) acts as a plasticizer, the disperse dyes cause hindrance to the movement of the molecular chains of the polymer..

Role of Phenol in High Temperature Dyeing of Polyester

The dyeing characteristics of a polyester fabric have been investigated in the presence of phenol with CI disperse orange 13. Phenol increases the acceleration factor largely because of the lowering of TD, particularly at lower dyeing temperatures. The increased solubility of the dye in the phenol solution seems to promote higher exhaustion as well as equilibrium dye uptake.

Kinetics of Bleaching Agent Decomposition in a Single-Stage Preparatory Process Part II: Sodium Hypochlorite Bleaching

In a single-stage fabric preparation process, the rate of decomposition of sodium hypochlorite is high at pH 9 compared to pH 10 and 11, both in the absence and presence of cotton. The extent of chlorate formation is high in the absence of cotton, whereas oxygen evolution is greater in the presence of cotton. The degradation of cotton is minimum at higher alkaline conditions. Around 30-35% more sodium hy pochlorite is required in the single-stage process compared to conventional bleaching.

Dye-Induced Changes in the Mechanical and Physical Properties of Dyed Nylon 6 Fibers

The effect of the presence of dyes in nylon 6 fibers has been studied. It is seen that the presence of acid, disperse, and reactive dyes brings about perceptible changes in the stress-strain characteristics of the dyed fibers. From the results it was concluded that the physical hindrance by the dye molecules is independent of the forces binding the dye to its site in the fiber phase. The dye participates in the structural rearrangements of the fiber during dyeing with disperse and disperse reactive dyes, and this is detected by the increase in critical dissolution time of the dyed fibers. However, such a phe nomenon is not observed in the case of fibers dyed with acid dyes.

Aggregation of Disperse Dyes

Aggregation of disperse dyes in polyester has long been a controversial issue. Hoffmann et al. E5] and many others have shown that the dispersion of disperse dyes takes place in monomeric form, while there are others [1-3, 7, 10] who have concluded that aggregation takes place in hydrophobic fibers. Findings of Giles and Shah E3] appear to give direct proof of the aggregated state of disperse dyes; however, their results have been subjected to serious objections [6]. This short paper describes an investigation of aggregation of dyes in the presence and absence of a nonionic

Dye-Induced Structural Changes and Mechanical Properties of Polyethylene Terephthalate Fibers

Disperse dyes participate in the structural modifications of polyester fibers during dyeing. The change in the mechanical properties of the disperse-dyed polyester fibers over the blank-treated ones is, however, due to mechanical hindrance of the dye, which is dependent on the structure and the concentration of dye in the fiber. The dye-induced structural change has little or no effect on the mechanical properties.