Effect Of Microwave Irradiation On The Micro-structure Of Wool And Application In Its Dyeing And Finishing

Microwave has wavelength between about 1mm and 1m corresponding to frequency from 300MHz up to 300GHz. Microwaves are high frequency radio waves which are capable of penetrating many materials and causing heat to be generated in the process. The ability of a substrate to absorb microwave energy is determined by its polarity. When an electrical field is applied at microwave frequencies, the polar molecules rotate in an attempt to rearrange their dipole moment with the changing electrical field. Energy is absorbed and heat is generated by the internal friction between the rotating molecules. In recent years, some new techniques and methods for saving energy and pollution-free in textile processing have been studied. The use of microwave heating method in textile dyeing and finishing has been the subject of considerable importance because of various advantages such as uniformity, flexibility, less energy and high efficiency. Wool has been widely used as a high-quality textile material due to its good elasticity, flexility, wettability, biodegradability and biocompatibility. Compared with other natural fibers or synthetic polymers, wool has a relatively higher dielectric constant (ε). Microwave irradiation is one of powerful techniques of non-contact heating, because the dielectric substances with large dielectric constant vigorously fever by vibration and rotation of permanent dipoles in microwave field. Wool has higher polarization ability in microwave field compared with other natural fibers or synthetic polymers. The use of high efficient microwave heating method in wool dyeing and finishing to achieve energy savings and high efficiency has been the subject of considerable.A number of studies have investigated the application of microwave in textile dyeing and finishing, however, few studies have investigated application of microwave in wool dyeing and finishing. In this paper, wool fabrics in different humid state were treated with microwave. The micro-structure and property change of wool fabrics in different humid state during microwave irradiation, dyeing behavior of wool pretreated by microwave, microwave pad dyeing process of wool and microwave curing for antimicrobial finishing of wool were studied. In addition, the study also penetrates into thermal efficiency, special microwave efficiency and non-thermal efficiency of microwave when chitosan biguanidine hydrochloride was synthesized under microwave irradiation. Contents and conclusions of the studies are mainly as follows.Wool fabrics in different humid state were treated with microwave. The micro-structure and property change of wool fabrics in different humid state during microwave irradiation was studied with stress put on discussing the effect of microwave irradiation at different power and treatment time on physical properties, crystallinity, surface morphological structure, the concentration of cystine S-S bonds, the concentration of the a-helical conformation and the degree of disorder for protein molecules chain of wool in different humid state. It can be concluded from the investigated report that microwave irradiation could impact the physical properties of wool fabrics in different humid state. The crystallnity and concentration of the a-helical conformation of the treated wool in nature humid state with microwave irradiation increased. The crystallnity and concentration of the a-helical conformation of the treated wool in dry state and wet state with microwave irradiation decreased. Microwave treatment improves ordered degree for nature humid wool fine structure and decreases ordered degree for dry and wet wool fine structure. The microwave treatment caused an obvious damaging effect of the surface scale-like structure of the wool fibres. The wool fiber in wet state lost its original scale-like structure after higher power microwave treatment. The concentration of cystine S-S bonds in microwave-treated wool fibres is lower than that of the untreated wool fibres. The cystine S-S gradually decreases with an increasing irradiation power.Wool was pretreated with microwave and then dyed with Lanasol reactive dye and Palatin 1:1 metal complex dye by conventional exhaust dyeing process. Adsorption behavior and diffusion coefficient were also studied. A higher dye uptake rate and increased diffusion coefficient of treated fibers are observed in the dyeing test, but the adsorption behavior keeps constant in the microwave treatment. Microwave pretreatment has a slightly damaging effect on the surface scale-like structure of wool, which results in the reduction of the concentration the S-S bonds in keratin. It was considered that destroy of the surface improved the absorption of dye molecules by the wool fibres during dipping and the diffusion of dye molecules into the wool fibres.Microwave pad dyeing process of wool dyed by Realan reactive dyes and Lanasol reactive dyes were carried out. Influences of various dyeing process conditions including galactomannan dosage, urea dosage, sodium bisulphite dosage, pH value, microwave irradiation power, microwave treatment time and cold batching time before microwave fixation on K/S values and fixation of dyed fabric were investigated by using single factor experimentation and orthogonal experimental design. Fixation, levelness of dyeing, dye penetration, breaking strength and breaking elongation of dyed wool fabric were compared among cold pad batch dyeing process, microwave pad dyeing process and conventional exhaust dyeing process. The optimal microwave pad dyeing conditions were found to be:microwave irradiation power 700W, microwave treatment time 5 minutes,40g/L galactomannan,20g/L sodium bisulphite,100 g/L urea. Microwave heating at 700W for 3 minutes produced almost same or more fixations compared with 24 hours cold batching. Higher uniformity was achieved with microwave heating. To improve the penetrating property of microwave pad dyeing process for wool, wool fabric was pretreated with dichlorinated isocyanurate (DCCA). It was found that the chlorination-treated wool fibres had significantly improved colour yield and penetrating property compared to untreated wool. The conventional exhaust dyeing process leads to the requirement for long continuous dyeing times at higher temperature, which can lead to certain impairments of the wool material as a consequence of fibre damage. Microwave pad dyeing process of chlorination-treated wool could minimize fibre damage in the dyeing by the exhaustion method, in particular to reduce the dyeing time, the energy consumption of the actual dyeing process still further.Antimicrobial chitosan guanidine hydrochloride and chitosan biguanidine hydrochloride have been synthesized by the guanidinylation reaction of chitosan. Antimicrobial properties of guanidinylated chitosan treated wool fabric were assessed. Wool fabrics were oxidized by hydrogen peroxide, crosslinking mechanism among finishing agent guanidinylated chitosan, crosslinking agent citric acid and wool was analyzed after oxidization. An alternative microwave curing system was used for curing guanidinylated chitosan treated wool fabric. The effects of microwave curing at different irradiation power and treatment time on the physical properties and adsorption capacity of guanidinylated chitosan on wool fabrics have been examined. Guanidinylated chitosan modifications can effectively improve the antimicrobial properties of wool fabric. Guanidinylated chitosan and citric acid did not crosslink with the wool fibers if wool fabrics were not oxidized by hydrogen peroxide and after oxidization, citric acid produce esterification and transamidation with the -OH group and the -NH2 group of the wool and guanidinylated chitosan to form a crosslink. The use of the microwave curing system effectively reduced the drying and curing time when compared to the conventional drying and curing system. The microwave-cured sample showed a significant improvement in whiteness and adsorption capacity at 700W power for 2min when compared with the conventionally cured sample. Retention of breaking strength was similar between microwave-cured sample and conventionally cured sample. The microwave-cured sample showed higher uniformly and degree of crosslinking and antimicrobial activity compared with the conventionally cured sample.The study penetrates into thermal efficiency, special microwave efficiency and non-thermal efficiency of microwave when chitosan biguanidine hydrochloride was synthesized under microwave irradiation. Microwave heating method can increase the reaction rate over the conventional heating method. Time is saved and efficiency is enhanced markedly. Enhancement of reaction rate for microwave heating is due to high heating rate of the reaction system and special microwave efficiency. Existence or non-existence of non-thermal efficiency depends on interaction mechanism between microwave and chemical reaction and further development of unbalance theory.It can be summarized that microwave irradiation treatment technique has significant potential for dyeing and finishing of wool fabric as microwave is a clean, environmentally friendly, highly efficient heating technology. Research for the micro-structure and property change of wool fabrics in different humid state during microwave irradiation lays foundations for further application of microwave in dyeing and finishing of wool fabrics.