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.

Novel Applications and Environmental Aspects of Denim

Novel applications and environmental aspects of denim includes different topics. They consist of novel varieties of denim fabrics, non-apparel applications of denim, recovery and recycling of denim waste, effluent treatment in denim and jeans manufacture, and the environmental impacts of denim manufacture.

Novel denim varieties

Apart from the well-known standard denim, several novel varieties of denim fabrics exist, and they are finding extensive application in the fashion industry. Stretch denim, pseudo denim, generic denim and reverse denim are some interesting variants, and from the viewpoint of manufacturers and consumers, stretch denim has a huge potential. Cotton blends of lyocell, wool, silk, polyester, linen, hemp, etc. are also available on a commercial scale. The use of different fibres in combination with cotton has also improved the functionality of the denim material.

The coloration and washing techniques possible now on denim are innumerable, and the functional finishes are adding a different dimension to denim. As sustainability is becoming a major focus globally, use of biodegradable fibres in denim is ever increasing. Some sustainable varieties include denim made of polylactic acid, soybean and bamboo fibres. Other such variants include organic cotton denim and denim dyed with natural dyes without using metallic mordants.

Non-apparel applications

Known well for apparel use, denim is now finding novel applications in other sectors, including furniture, home interiors and automobiles. These alternative applications can increase the market share of denim considerably in industrial sectors where it was never thought to enter. Denim has become an interesting substrate to designers and technologists to create new products satisfying the changing consumer trends as well as the demands on creativity and unique products.

Denim has a significant market potential for being used in several fields. Denim and home textiles are two important and popular sectors of the textile industry, and it is possible to generate a synergistic effect and a different market by combining their aspects. If new denim fabrics are used for non-apparel applications, especially in-home interior textiles, furnishings, curtains, etc., it can create value addition to denim. But the utilisation of used denim garments to produce non-apparel denim articles is an environmentally friendly approach and will be more economical in achieving new market shares.

Recovery and recycling

Denim and jeans waste are creating a municipal dumping problem, and a proper recycling of this waste can result in novel products for other industrial sectors. In general practice, the denim waste is either dumped in municipal landfills or incinerated in solid waste incinerators. Waste denim can be recovered from the denim mill as well as from the jeans manufacturing units. Apart from this virgin material, the used jeans and garments can also be recovered systematically. Denim recycling possibilities are unlimited, and the adoption of an effective strategy will reduce the environmental impact and simultaneously contribute to the competitiveness of the industry, by addressing increasing issues of raw material access.

Denim is usually triturated and converted into nonwoven felts for the insulation in construction and automotive industries, but it is possible to shred the fabrics to get them back into a similar kind of fibre to virgin cotton. There is an increasing attention for this high end recycling of denim, and a number of fashionable products are already available in the market with a high content of recycled denim fibres. Nowadays the possibility of manufacturing denim from other waste materials is also becoming important.

Effluent treatments

Denim warp dyeing as well as the garment dyeing, washing and finishing processes result in huge effluent volumes, and their treatment is essential. The wastewater can be treated by several treatment methods based on biological or physicochemical processes, but it is not easy to decompose this type of wastewater to meet the discharge levels set by standards. However, a comprehensive treatment process that enables the reuse of this wastewater and process chemicals will be the preferable alternative in terms of environmental and economical considerations.

Rather than effluent treatment, effluent reduction at the source by implementing different ecological processes is receiving more attention nowadays. For pollution prevention, minimisation of the use of chemicals, dyes and water, as well as good housekeeping practices, should be considered. Combining different processing stages can also reduce the water and energy consumption, thereby increasing the productivity and decreasing production costs.

Environmental impacts

The overall environmental impact of denim manufacture is significant, especially in areas such as cotton growing, dyeing and washing, and many consumers are not aware of this aspect. In the case of denim, there are some inherent limitations, such as the ever-preferred use of indigo, its low affinity for cotton and poor fastness properties. As with other sectors, Life Cycle Assessment techniques are utilised to assess the impact of denim and to identify the possibilities for improving its environmental profile.

Improvements in each step of denim manufacture will offer significant reductions in the overall environmental impact as well as cost savings for the industry. Among all the processing steps, industrial as well as household laundries seem to offer the highest potential for improvement. Indeed, modern technologies have helped reducing the overall impact to some extent, but there is still a long way to go. Some of these possibilities include the use of organic cotton, reduction of dyes and chemicals, and producing less complex wastewater. Other environmentally friendly alternatives include electrochemical reduction, minimal application technologies and reduced water washing. It is very clear that the consumers will soon look for denim that has been manufactured with the highest environmental standards, maintaining sustainability throughout its life cycle.