Saminathan Ratnapandian

Research conducted in this thesis

Exhaust dyeing of natural dyes is traditional and has been adopted widely by hobbyists and craftspeople. Consequently, previous researchers have concentrated most of their efforts on regularising and improving this method [40, 94, 95, 106]. The rising commercial interest in the use of natural dyes encourages research into the use of continuous colouration methods. Hence, this research investigated the padding of natural dyes. Commercially available natural dyes in powder form and laboratory grade chemicals were used to standardise and further simplify the process.

The study was conducted in progressive stages to obtain answers to:

1. 
   How mordants are to be used with the selected natural dyes during padding?
   
2. 
   What are the ideal padding parameters for a given dye concentration?
   
3. 
   What means of improving the dye uptake may be employed?
   
4. 
   Whether there is a potential for additional benefits from such improvement techniques? and,
   
5. 
   What is the feasibility of a colouring process that uses chemicals with a lower environmental impact as compared to current practices?
   

At every stage of experimentation the depth of shade was measured and desirable fastness properties were evaluated. Keeping in line with the objective of utilising renewable resources, cotton and wool were selected for use as the textile substrates. In summation, sustainability in industrial-scale use of natural dyes as measured by the lowering of resultant environmental impact was the focus of this thesis.

1. Chapter outline

Chapter 2 lays out the research methodology of this study. It discusses the design of the experiments and gives details of the materials used.
Chapter 3 describes the padding process and optimisation steps involved. Specialised evaluation techniques used to gain an intimate understanding of dyeing mechanism are detailed. The results obtained are discussed.
Chapter 4 describes investigations regarding atmospheric pressure plasma pretreatment to improve natural dye uptake. Innovative applications of utilising this technology are explored.
Chapter 5 reveals the results of studies on whether including chitosan in the pad liquor of natural dyes produces darker shades. The resultant antimicrobial characteristics are also analysed.
Chapter 6 outlines the investigations into dyeing with indigo dye by the padding process. The effectiveness of using chemicals with a lower environmental impact is presented. The use of these chemicals in printing has also been evakuated. Finally, a comparison is drawn between using these chemicals in combination with natural and synthetic indigo.
Chapter 7 gives the overall conclusions drawn considering the results of the study. Future research directions are outlined.

2. Expected outcomes and potential benefits

It is expected that a better understanding of the pad-dyeing mechanism for natural dyes will be acquired. The insight into a) how mordants help to fix the selected dyes; and b) the unique relationship between individual dye and mordant will aid in optimising the process parameters for the selected natural dyes. The process will be improved by integrating atmospheric-pressure plasma technology or byproducts (chitosan) to obtain darker shades. Such improvement methods are also expected to result in additional benefits. Indigo colouration by using chemicals with lower environmental impact and the vat dyeing process will increase the scope of the use of this dye. The findings in this thesis are likely to encourage industrial trials in the padding of natural dyes. In summation, sustainability in the industrial-scale use of natural dyes is expected.

26

Chapter 2