The dye fixation process by the contact-type dry heat fixation (CDHF) technique was investigated when cotton fabrics are dyed with a reactive dye by the ink-jet printing. The dye fixation ratio was measured as a function of the water regain of fabrics and the temperature at the fixation treatment. At first, the time dependence of the water regain and the dye fixation ratio during the treatment was observed. Although the water regain drops sharply within 2 seconds, the practical level of dyeing was achieved if the fabrics are treated with enough amount of water and with high enough temperature. The amount of water and the temperature required are 29 wt% and 120 °C, respectively. The diffusion of dye molecules into the inside of the polymer matrix was confirmed by the model experiment using a cellophane film. In this dyeing system, the diffusion of dye molecules occurs very quickly, followed by the relatively slow dye fixation. Water molecules are very good plasticizer for the cotton fiber. The activation diffusion model may successfully describe the diffusion behavior observed in this study rather than the pore diffusion model which is often used for the explanation for the dip dyeing of cotton.
To identify some fine histological features of wool fiber cross-sections by scanning electron microscopy (SEM), the preparation method by the differential dissolution of section with a proteolytic enzyme was investigated. Wool fibers were embedded in epoxy resin and were sectioned into about 25 μm thickness. The resultant sections were mounted on the SEM sample stage and were surface etched by enzyme (Savinase: Nobozymes Japan industry) solution followed by SEM observation. By using this method for preparing specimens, this differential digestion of components revealed the relatively distinct histological structure of the fiber in the SEM images with good resolution, where the cystine-poor endocuticle, cell membranes, nuclear remnants, and intermacrofibrillar material of the intact wool cross-sections were partially dissolved away. For the wool fiber oxidized under aqueous acidic conditions with Caro's salt, especially, the macrofibrils were observed in an electron scattering zone (concave circular structure) at the center of each one over the orthocortex, but not over the paracortex. Because of this differentiation, it was possible to distinctly discriminate between the ortho- and pracortex cell types of the fiber. In addition, this method will undoubtedly be valuable for assessing the extent of damage in fiber resulting from various physical and chemical treatments.
An investigation was conducted into the reaction selectivity of azo dye decoloration by peroxidase (POD). The effects of pH and the addition of p-iodophenol on decoloration rate were investigated using 3 types of dye in single-dye and mixed-dye systems. The addition of p-iodophenol accelerated decoloration. In the mixed-dye system, a pH of 8.0 resulted in the highest decoloration rate. HPLC was used to determine the decoloration rate of individual dyes in the mixed-dye system. The decoloration reaction of Orange I proceeded swiftly, decoloration of Orange II was slowed, and decoloration of Orange G was accelerated. The reaction mechanism in the mixed-dye system is considered to be as follows. Orange I reacts much faster than the other dyes, producing radicals immediately after the reaction commences and then decomposing. Meanwhile, since Orange II has a higher oxidation potential than Orange I, the reaction between Orange II and POD begins after completion of the Orange I reaction. The reaction with Orange G, which has a higher oxidation potential than Orange II, commences even later. Some of the Orange II radicals produced undergo radical reactions with Orange G, transferring electrons to Orange G and reverting to Orange II. As a result, the Orange II reaction is inhibited more than in an Orange II-only system. Conversely, when p-iodophenol was introduced into the mixed-dye system, the reaction selectivity was lost as p-iodophenol radicals reacted simultaneously with all 3 dyes.
Biomax® was irradiated using electron beam (EB) or gamma-rays (γ-rays) in air or vacuum at 25 °C. Inherent viscosities, melting points, and melting enthalpies of the irradiated samples decreased with increasing irradiation dose, indicating that irradiation treatment degrades the polymer chain. The degree of chain-scission of Biomax® irradiated with γ-rays in air was higher than that irradiated with γ-rays or EB in vacuum because of oxidative chain-scission by oxygen in air. Biodegradability of Biomax® was promoted with increasing dose due to the decrease in crystallinity.