Properties of the Naturally Colored Cottons

Textile is among the industries in which harmful substances would arise. The disposal of the drainage after dyeing and finishing causes environmental pollution. On the other hand, questions are frequently raised regarding textile fibers and their impact on the environment, workplace and their product safety. It is reported that fabrics made by using synthetic fibers would cause health hazards to the users.

Cotton, here means the white cotton, has been the most important textile material. It is understood that bleaching, mercerizing and dyeing of the cotton goods would cause environmental problems. The usage of pesticide, chemical fertilizer, and weed killer during cotton planting, the chemical treatment during textile manufacturing，lead to chemical deposits in the cotton fiber, these are harmful to the customers.

Naturally colored cotton is considered to be disease-resistant during its growth, no traditional pesticides are needed. If organic fertilizer is deployed, the grown colored cotton may be regarded as totally chemical free. Naturally colored cotton is environmentally frigidly as its goods need no dyeing. Colored cotton is not a new concept，its cultivating history can date back to 5000 years ago. Later, owing to its lower yield and inferior quality compared with that of the white cotton, colored cotton had not been frequently mentioned until the 1970s, when people began to aware the importance of the environmental protection. Breeding research over the last 30 years in this field has led to improvement in yields, fiber quality and color intensity. China began its research work on colored cotton in the 1990s. To date, 4 colored cotton research centers have been set up, plantations specialized in colored cotton have been run successfully for continuous several years in the provinces of Sichuan, Gansu, Henan, Xinjiang and Hainan in China. Colors of the cultivated cotton include brown, green, purple, grey and orange. The growing area of the colored cotton in China had reached 20,000 hectares in the year of 2003. It is estimated that in 30 years the colored cotton yield in China would take 30% of its total cotton output.

In order to use the colored cotton effectively, thorough understanding of the colored cotton fibers is necessary.

Structures and properties of the colored cottons

Table 1 gives some of the substances extracted from the colored cottons. White cotton is included for comparison.

Table 1. Some compositions of the colored cotton

The table reveals that the fat content in the colored cottons is larger than that of the white cotton. And there is no lignin in the white cotton when larger amount of it is noticed in the colored cottons. As has been recognized that both fat and lignin are considered to be hydrophobic. One may estimate that the ability of the moisture absorption of the colored cotton goods would be lower than that of the white. The table also shows that the pectin content in the white cotton is the highest.

Table 2 illustrates the major physical properties of the colored cotton fibers. For the sake of comparison, the white cotton is also included.

Table 2. Cotton fibers physical properties

Usually the colored fibers are finer than the white fiber, especially for the green one, it measures 6750 meters per gram. The strength of the finer fibers is usually weaker than that of the thicker ones, anyway, the yam evenness may be better because more fibers can be included in a definite yam cross section.

The brown cotton fiber is the longest, when fibers are twisted to form the yam, longer fibers offer more connection areas among the fibers, resulting in greater friction among the fibers and hence the yam strength. Compared to other fibers, the tenacity of the green cotton fiber is the lowest. One may expect its lower yam strength.

Suggestions in using the colored cottons

Based on the physical properties of the colored cottons and the spinning practice, some suggestions are listed below for using the colored cottons effectively and economically.

• Naturally colored cottons are recommended to blend with white cotton because they are usually shorter, finer and weaker and because of their higher price. Add certain percentage of white cotton in the yam can reduce the initial cost of the yam. On the other hand, the color shade of the yam can be adjusted by using various blending ratios.
• Blending with synthetic fibers. Synthetic staples such as polyester, nylon etc. can be blended with colored cotton in yarn spinning. It is recommended that the content of the synthetic fiber should not be higher than 10%. This can increase the strength of the yarn greatly. Too much synthetic fiber content will deteriorate the environmental character of the colored cotton.
• Since the limited color variety, colored cottons with different hue can be blended to spin the yarn of expected colors.