The textile industry has been one of the largest consumers of water and is also responsible for polluting the environment with chemical treated waste. It is estimated that on an average to process one kilogram of textile material, 100-150 litres of water is required. Many companies are working towards cutting back on the usage of water by conserving, recycling, dye sublimation, and other new technologies.
Water is the key component and is used as a solvent in pre-treatment and finishing processes such as washing, bleaching, dyeing, rinsing, and scouring. According to the World Bank, textile dyeing and treatment are the source of 17-20% of industrial water pollution. Until a few years back, there was no substitute for dyeing fabrics but by using water. Thanks to dry dyeing, a waterless dyeing technique, this is possible now. This process makes use of carbon dioxide to dye textile materials. A super critical liquefied form of carbon dioxide dyes fabrics, providing same results as the conventional water based methods.
The dry dyeing method, a pioneering work of a Dutch company in textile dyeing, does not make use of water at all. Super critical is a state where matter can be expanded into a liquid or heavily pressurized and converted to gas. When carbon dioxide is heated to over 31°C and pressurized to above 74 bar, the super critical state is then achieved. Carbon dioxide's liquid like densities proves to be beneficial for dissolving hydrophobic dyes and the gas like densities, have low viscosities and diffusion properties.
The supercritical carbon dioxide technique is already being used in apparel dry cleaning, and has proved to be by far the best, most gentle, and the cleanest method to do so. There are various reasons as to why carbon dioxide is the best supercritical fluid for the dry-dyeing technique. It is a naturally occurring inexhaustible resource, physiologically compatible, and relatively inexpensive.
Carbon dioxide is readily available, is biodegradable, and does not release any form of volatile organic compounds. Moreover, it is non-toxic, non-flammable, and non-corrosive. These merits make it a very viable dyeing alternative. The biggest merit of using carbon dioxide is that it can be recovered, and reused again from the process of dyeing, making it a cost-effective option.
This method of waterless dyeing is also used for printing on garments. The water-based dyeing techniques involve drying the garment, once it has been colored, while this new innovative technique eliminates this process altogether.