5. Fibers from Cotton Stalks

The most prominent and oldest known natural cellulose fiber, cotton, has been grown and used for textiles since time immemorial. Cotton was grown in about 34.2 million hectares, and about 26 million tons of cotton was produced worldwide in 2012. In addition to the seed from which cotton fibers are harvested, cotton plants consist of stalks and leaves that are left as by-products, equivalent to 3–5 times the weight of the cotton fiber produced. Cotton stalks consist of an outer bark (20 % by weight of the stalk) and inner pith. The outer bark is fibrous and could be utilized as a source for fibers similar to the bast fibers produced from jute or flax plants. Treating the outer bark of cotton stalks with 2 N NaOH at boil for 1 h resulted in fibers with fineness of about 50 denier. These fibers had strength similar to cotton but lower elongation. When used as reinforcement for polypropylene composites, cotton stalk fibers provided similar tensile and flexural properties compared to jute fibers. Cotton stalks were treated at 150 °C in a mixture of 20 % sodium sulfide, 2 % anthraquinone, 2 % sodium silicate, and different concentrations of sodium hydroxide for 30 min. Concentration of sodium hydroxide considerably influenced the composition and properties of the fibers as seen in Table 5.1 [12Zho]. Substantially finer fibers (0.9 tex) have been produced by the high-temperature treatment reported by Zhou et al. compared to those produced by Reddy and Yang [09Red]. So far, no reports have been available on the processing of cotton stalk fibers into textiles or on the bleaching and dyeing of the cotton stalk fibers.