Developments in Cotton for Denim

Cotton growers are continuously struggling for a reasonable price for their cotton. There is now a move towards a fair-trade practice with cotton, which should enable cotton growers to be paid a fair price for their product. In this respect, there is an increasing trend towards the cultivation and production of organic cotton for denim manufacture. This is generally understood to be cotton that is not genetically modified and grows without the use of synthetic agricultural chemicals, which includes both fertilizers and pesticides.

Organic cotton production and trade is also promoted as a more viable and sustainable alternative to conventional cotton production. However, cotton growers generally do not adopt new production techniques unless they are profitable. Organic cotton yields are generally lower than conventional ones, and even lower than what might be acceptable in view of lower production costs. Nevertheless, some consumers are willing to pay a premium for denim garments made from certified organic cotton fiber and labelled as such. Although production of organic cotton is expanding rapidly, conventional cotton still accounts for about 99.9% of total world output.

In recent years, naturally colored cotton has also become important for denim in view of its ecofriendly character. Cotton occurs naturally in different colors like creamy white, brown, green, blue and pink. The color is a genetically controlled characteristic, and the accumulation of pigments in the fiber lumen starts before boll bursting. However, the complete expression of color takes place only when the boll bursts open and the fiber is exposed to sunlight. It takes about a week for the fiber to develop a complete natural color. It is interesting to note that while sunlight is essential for the development of color, continuous exposure leads to color fading. Some genotypes may show color fading with time and washing, while others may not. Brown color in some genotypes may intensify after several washings. Naturally colored cotton has some inherent drawbacks, which include low yield potential, short fiber length, limited colors and instability of colors. It also requires specialized harvesting techniques and facilities, making it more expensive to harvest than white cotton. As the fiber length is short, the spinning is more complicated as compared to white cotton. Even though companies like Levi Strauss has shown interest in naturally colored cotton, in general the market for colored cotton can be considered a niche market.

Another area of development is genetically modified cotton, which has been engineered to be insect resistant or tolerant to herbicides. One of the commercial varieties is Bacillus thuringiensis (BT) cotton, which is resistant to bollworms. Bacillus thuringiensis is a very common bacterium occurring in the soil and capable of producing crystal proteins that have insecticidal action. These proteins are toxic to certain types of insects (moths such as bollworms) that attack cotton, and the action is specific to those insects. The target insect must ingest the crystal protein for the protein to be effective. BT cotton was first planted on a commercial scale in 1996 in Australia and the United States. Genetically modified cotton has been officially approved for commercial release in some countries and experimentation is under way in several other countries. Monsanto, USA, has a dominant position and controls about 80% of commercially grown genetically modified cotton. Many scientific studies have also been undertaken for converting cotton fiber into new and innovative denim textile material. In this respect, an experimental study has been undertaken for improving the physical appearance by using low torque ring spun yarns. In this work, the residual weft torque in the cotton yarn was reduced. Low torque cotton yarns of 84 and 58 tex linear density with different twist levels were produced on a modified ring spinning machine. The results from the study showed that the low torque yarns possessed fewer yarn snarling turns. This enabled denim to improve fabric smoothness and appearance. There are many other research studies undertaken on cotton fiber used in the production of denim. These include modified rotor spinning of denim warp yarns, testing of physical properties of different types of denim fabrics and enzyme treatments on denim products.

Cotton is often blended with other fibers like lycra to produce desired effects on denim. This imparts a high degree of extensibility to the yarn that is used in denim, to produce tightly fitting garments. These are particularly used for the manufacture of ladies’ denim jeans. Blending the cotton fiber with the DuPont fiber T400 polyester enables the fabric to be more bleach resistant and withstand chlorine more effectively. DuPont has also created a knitted stretch denim called Veloflex, which contains 96% cotton and 4% lycra. The fabric is reputed to have soft hand, is supple and it enables designers to create slim cut jeans that provide comfort and freedom of movement.

The developments in blending cotton fibers with lycra have also led to some leading companies collaborating to bring improved performance on denim stretch fabrics. Invista, the holder of the lycra brand, and Lenzing AG, a leading producer of man-made cellulosic, have worked together to improve the aesthetic performance of stretch fabrics. The outcomes included the delivery of unique solutions to the denim industry with the combination of Invista’s patented lycra dualFX fabric technology with Lenzing’s lyocell fiber, for the improvement of stretch cellulosic fabrics and reinvention of lyocell fiber.

One of the innovative cottons finishing technologies from Cotton Inc. USA is Stay True Cotton, which helps indigo dyed denim retain its original color longer. A very small quantity of dye is released during home laundering of these garments, giving it an environmentally friendly appeal. Wicking Windows is a moisture management technology for cotton that transfers moisture away from the body and reduces absorbent capacity for faster drying. Fabrics treated with this technology show 1400% improvement in one-way transfer of moisture to the outside of the fabric over their untreated cotton equivalent. Cotton fabrics made with TransDRY technology offer comfort and softness of cotton while staying dry, keeping the wearer cooler and more comfortable. Another technology, termed Storm Denim, is a super repellent finish that protects the wearer from moderate rain, snow and wet conditions, while maintaining the natural comfort and breathability of cotton.

There are also studies to replace cotton in denim with more sustainable fibers. In this respect, the researchers at Herriot-Watt School of Textiles and Design, in the United Kingdom, have developed jeans using a fiber made from sustainable wood instead of cotton, and it is claimed that this could be the key to cutting carbon emissions in the denim jeans industry around the world. The developed jeans have cotton like qualities but use only one fifth of the water and energy needed to manufacture conventional jeans.