By:
Dr. Sukalyan Sengupta, Civil & Environmental Eng. Department
Dr. Bal Ram Singh, Chemistry & Biochemistry Department
University of Massachusetts Dartmouth
By: www.turi.org

Introduction

The textile industry produces and uses approximately 1.3 million tonnes of dyes, pigments and dye precursors, valued at around $23 billion, almost all of which is manufactured synthetically.

However, synthetic dyes have some limitations, primarily, (i) their production process requires hazardous chemicals, creating worker safety concerns, (ii) they may generate hazardous wastes, and (iii) these dyes are not environment friendly. This research explores methods where natural dyes are produced from plant tissue and fungal species.

Until the second half of the nineteenth century, all dyes used in textiles were naturally derived. However, with the synthesis of mauveine by Perkin in 1856, the synthetic dye industry has grown at a vigorous rate and all but totally eradicated the use of natural dyes. The large number of synthetic dyes in use today bears witness to the creativity and innovation of textile chemists in successfully satisfying the dyers demands for simple, reproducible application processes, and the consumers demand for quality products at a reasonable price. Thus, even though the availability of natural dyes has been known for centuries, the reasons synthetic dyes have been so popular are:

They are simple to produce in large quantities,
They can be manufactured at a reasonable price ($10 100/kg),
They can provide the variety of colors that are demanded by todays consumers,
They provide high color-fastness (i.e., the dye is very strongly bound to the fabric and does not detach after repeated washing cycles).

However, manufacturing of synthetic dyes suffers from the following limitations:

1. Environmentally Unfriendly: The production of synthetic dyes requires strong acids, alkalis, solvents, high temperatures, and heavy metal catalysts. For example, production of a dye designated as Color Index Mordant Blue 23 states, Treat 4,8-diamino-1,3,5,7-tetrahydroxy-2,6- anthraquinonedisulfonic acid with boiling alkali or dilute acid and convert to the sodium salt or Treat 1,5-dinitro-anthraquinone with fuming sulfuric acid in the presence of sulfur sufficient to produce S2O3 at 1300C, hydrolyze with water, and convert to the sodium salt.

2. Increase in Cost of Feedstock or Energy: Petroleum is the starting material for all synthetic dyes and thus the price of dyes is sensitive to the price of petroleum. Also, since synthesis is energy intensive (uses super-heated steam, boiling acids, etc.), the process is sensitive to energy prices and also generates greenhouse gases.

3. Hazardous Waste Generation: Since synthetic production of dyes needs very toxic and hazardous chemicals, it also generates a hazardous waste, the disposal of which is a major environmental and economic challenge. Moreover, some facilities that produced dyes in the past are now Superfund sites due to intentional dumping or accidental spills of toxic and hazardous wastes.

4. Increasing Transportation Costs: Since dyes are hazardous materials and are produced at central
facilities, transportation of dyes from manufacturing plants to textile dyeing and printing facilities is a major cost item and a logistic challenge.

5. Toxic and Allergic Reactions: There are occupational safety issues involved since production processes use the toxic and hazardous materials and conditions described above.