Cotton and Other Natural Cellulose Fibers

Cotton fibers are the most important natural cellulose fibers. Cotton fibers are one of the purest somces of cellulose. The cellulose content in cotton fibers is in the range of 88.0% - 96.0%. The noncellulosic components of cotton fibers include proteins, pectic substances, sugars, wax, and organic acids. Table 4.1 shows the contents of different components in dried cotton fibers. The actual contents of different components may vary, depending on the variety and matiuity of cotton and envirorunental conditions such as climate, soil, water source, farming method, etc. Treatments can remove most of the noncellulosic components, and the cellulose content of the treated cotton fibers could be more than 99%. 

In addition to cotton fibers, they are mar r other types of natural cellulose fibers. One major difference between cotton and other natural cellulose fibers is the cellulose content. Cotton fibers are the purest and other natural cellulose fibers have significantly lower content of cellulose. For example, both cotton and kapok are seed fibers, but cotton has the highest cellulose content and kapok has the lowest (13 wt%). The cellulose contents of other natural cellulose fibers are in the range of 40%-90%. Table 4.2 shows the cellulose contents of several natural cellulose fibers. 

Source Wakelyn, P.J., et al.. Cotton Fiber Chemistty and Technology, CRC press, 2007.  

Source Mwaikambo, L. Y., African Journal of Science and Technology, 1, 120-133,2006.  

---

What is the major difference between the chemical compositions of cotton and other natural cellulose fibers ... 

Another major difference among different natural cellulose fibers is their morphology. Kapok fibers are obtained from the seed pods of the tropical kapok tree. Like cotton, kapok fibers are unicellular fibers. However, kapok fibers do not collapse and twist after dried (Figure 5.6). Dried kapok fibers have circitlar, hollow (lumen) cross-sectional stmcture with total wall thicknesses of aroimd 2 /rm and fiber diameters ranging from 15 to 35 //m. As a result, kapok fibers have lower densities (0.31-0.38 g/cm ) than most other natural cellulose fibers. 

Uses/Sources. Wood contains 50-70% cellulose cotton and other textile fibers of plant origin contain 65-95% rayon is prepared by dissolving natural cellulose and then precipitating it from solution, with some loss of crystallinity. Cellulose is made into cellophane film and is used to form fibers, resins, coatings and gums. 

Except cotton and kapok, most of the natural cellulosic fibers are multicellular. They are usually used as groups of individual cells or as bundles of fiber in industrial applications. As a term, a fiber , or a technical fiber [14], refers to a bundle of individual cells bound together by hemicellulose, lignin and other non-cellulosic materials [12]. However, the individual fiber cell is drastically stronger than the fiber bundle [56]. For example, the individual fiber of flax is as stiff as aramid [65]. The individual fiber cell has a lumen inside which imparts a hollow structure to the fiber as seen in Figure 11.7. As an example, okra fibers have a void content of 18-32% [15]. The interface between two cells is called middle lamella [14]. 

Textile fibers are normally broken down into two main classes, natural and man-made fibers. All fibers which come from natural sources (animals, plants, etc.) and do not require fiber formation or reformation are classed as natural fibers. Natural fibers include the protein fibers such as wool and silk, the cellulose fibers such as cotton and linen, and the mineral fiber asbestos. Man-made fibers are fibers in which either the basic chemical units have been formed by chemical synthesis followed by fiber formation or the polymers from natural sources have been dissolved and regenerated after passage through a spinneret to form fibers. Those fibers made by chemical synthesis are often called synthetic fibers, while fibers regenerated from natural polymer sources are called regenerated fibers or natural polymer fibers. In other words, all synthetic fibers and regener-... 

The image in Fig. 7.26 resembles the supermolecular structure of cellulose of cotton or bast fibers. For other natural celluloses, the ratio between crystallites and non-crystalline domains, as well as sizes of these constituents, can vary in a wide range. The proposed model permits explaining various physico-mechanical, physicochemical, chemical, and biological properties of natural cellulose. 

Natural cellulose fibers also are called plant fibers or vegetable fibers. Natural cellulose fibers include cotton together with flax, jute, jute, ramie and other fibers produced by plants. Natural cellulose fibers can be classified to seed, bast, leaf, and fruit fibers. Figure 4.1 shows the classification of natnral cellnlose fibers. 

Horns and hooves were the raw materials for the early polymer preparations. These materials were ground up and treated in various ways so that they could be fabricated into such items as combs to use for ladies hair, and other specialty things of that sort. The next development was the use of cellulose from cotton or from wood as the raw material which was studied for making films and fibers. Work on the cellulose structure had provided information that it was a hydroxylated product, and by converting the hydroxyls to esters, the natural cellulose could be turned into a soluble material, which was spun into fibers and cast into films to make the first cellulose rayon-type material and cellulose films. 

Nature has long used reactions such as these to produce interesting solids such as cotton (seed pod), hemp (grass), and silk (cocoons for worms while they develop into moths) as fibers that we can strand into rope or weave into cloth. Chemists discovered in the early twentieth century that cellulose could be hydrolyzed with acetic acid to form cellulose acetate and then repolymerized into Rayon, which has properties similar to cotton. They then searched for manmade monomers with which to tailor properties as replacements for rope and sdk. In the 1930s chemists at DuPont and at ICl found that polyamides and polyesters had properties that could replace each of these. [Linear polyolefins do not seem to form in nature as do condensation polymers. This is probably because the organometaUic catalysts are extremely sensitive to traces of H2O, CO, and other contaminants. This is an example where we can create materials in the laboratory that are not found in nature.]... 

---