A study of "waste-extracted" colorants and their application in textile wet processing

Abstract

Due to the change of requisitions of living standard, "green" revolution brings people aware of environmental damage caused by the industries. Dye Manufacturers are forced to shift their concern on the proper use of dyestuffs and their traditional production methods. The increasing use of synthetic dyes arouses our awareness about the harmful effect imposed on the natural habitat. After the announcement of the twenty two carcinogenic azo dyes by the German Government, many dye manufacturers have given up the use of these carcinogenic azo dyes in dyeing process irrespective of their brilliant colours and higher fastness properties. Along with the continuous identification of the defects of synthetic dyes, some manufacturers recently shift their attention back to the revitalisation of "green" dyes. The objectives of the dissertation are to soothe the environmental pressures that come from the continuous discovery of adverse effects of synthetic dyes leading to environmental deterioration, enforcement of strict environmental legislation on dyes and persistent accumulation of waste materials in the society. This research project has the cherished aim to extract "value'' or "materials" from daily waste products such as fruit peels, tea residues and wilted flower petals, and change them into a form that can be applied to the textile industry. These new materials do not contain any harmful substances that will affect the environment and threaten the existence of human lives. By converting these waste materials into useful substances, two advantages can be obtained: (1) minimising the amount of waste products generated and (2) reducing the production cost of dyeing. The research study has established an effectively simplified method for the extraction of "green" dyes from the commonly waste products, i.e. fruit peels. Chinese tea and flower petals. The optimum extraction parameters including the solvent selection, "green" dye concentration, temperature and time have been investigated. The selected materials were divided into two categories. One type was water-soluble such as Chinese tea and flower petal which required water for extraction. The other type was water-insoluble such as fruit peels which required solvent for extraction. The extraction methodology depended on the physical properties of the "green" dyes and their inherited chromophore systems. Furthermore, the thermodynamic behaviours of "green" dyes on wool fabric have been investigated including (1) the standard affinity and enthalpy change in dyeing process, (2) the dyeing mechanism between colorants and fibre surface, and (3) the time of half-dyeing and the activation energy required for the "green" dye to diffuse into the fabric. From the findings, the affinity of "green" dye for wool fabric was found to be relatively low. However, the dyeing process could be conducted at room temperature because of lower activation energy required to proceed the dyeing reaction. In addition, the structure of "green" mordants and the chromophore system of "green" dyes have been identified using a number of instrumental techniques including IR, HPLC and AAS. The results illustrated that the fundamental dyeing mechanism, kinetic reaction and intermolecular force were related to the structure of "green" mordants and the chromophore system of "green" dyes. The next investigation was focused on maximising the absorption of "green" dye by wool fabric under optimum dyeing conditions. In the first part of the experiment, mathematical models have been developed using an experimental design approach named "Response Surface Methodology". The mathematical models could illustrate the relationships between the uptake of different "green" dyes by wool fabric and different dyeing parameters including dye concentration, pH value, temperature, time and Glauber salt concentration. The optimum wool dyeing conditions for "green" dyes could be calculated from the mathematical models through mathematical approach. The second part of experiment was aimed at improving the absorption behaviour of "green" dyes on wool fabrics. Two commonly wasted "green" mordants derived from eggshell and ginger were used. The optimum conditions for the extraction of "green" mordants have been determined using the method of "Response Surface Methodology". After the application of "green" mordant, a significant increase in dye uptake and improvement of the colour fastness properties such as light, washing and rubbing was achieved. Furthermore, the conventional methods of using heavy metal mordants such as alum, potassium dichromate, copper sulphate, ferrous sulphate and tannic acid in the dyeing of wool fabric were compared with the newly developed "green" mordants. Their effects on the environment were evaluated by analysing the BOD. COD, pH, turbidity, temperature, colour and heavy metal content of the dyebath after dyeing. In conclusion, the waste-extracted "green" dyes and "green" mordants have been successfully applied to wool dyeing process. The goals of producing environmentally friendly "green" dye and adding values to the waste products have also been achieved. Their effects on dye uptake, colour fastness properties and the environment are in positive approach.