Natural Cellulose Fibers from Renewable Resources

Keywords

Wheat straw • Rice straw • Fiber extraction • Lignin • Interlocked structure

Wheat is the fourth most popular crop in the world with a production of 675 million tons in 2012. About 1-1.2 tons of straw are generated per acre and wheat straw accounts for about 50 % by weight of the cereal produced. Straw is mainly used as animal fodder and bedding, for thatching, and for artistic works, and in many countries, wheat straw is burnt to prevent soilborne diseases. Extensive studies have been done to understand the potential of using wheat straw for pulp and paper production. However, wheat straw has a waxy covering on the surface and a unique morphological structure that makes it difficult for alkali to penetrate into the straw and separate fiber bundles with the length, fineness, and tensile properties required for textile and other high-value fibrous applications. As seen in Fig. 3.1, the individual cells or ultimate fibers in wheat straw have serrated edges that get interlocked with each other. It was found that a pretreatment with detergent and mechanical separation with steel balls were necessary before the alkaline treatment to obtain fiber bundles from wheat straw [07Red]. Fiber bundles obtained from wheat straw had tensile properties similar to kenaf as seen in Table 3.1. About 20 % fibers were obtained, but the fiber bundles obtained were considerably coarser than cotton and linen.

Similar to wheat, rice is also one of the most widely grown crops with a world production of about 720 million tons in 2012. Unlike other cereal straws, rice straw contains up to 15 % silica and 15 % lignin that makes it difficult to be processed into pulp and paper. Efforts to use rice straw as a source for fuel to power biomass plants have also not been economically attractive. In many countries, rice straw is mostly burnt and in developing countries used as animal feed and bedding and also for thatching. In addition to the straw, processing of rice removes the outer covering or the husk, equivalent to about 20 % by weight of the grain. The ultimate cells in rice straw are considerably smaller (0.6 mm in length and 8.1 pm in width) which makes the straw sensitive to fiber extraction conditions. As seen in Table 3.1, relatively

Table 3.1 Tensile properties and moisture regain of wheat and rice straw fibers compared with cotton, linen, and kenaf fibers

coarse rice straw fibers (240 tex) with length ranging from 2.5 to 8 cm were obtained after alkali and enzyme treatment [06Red]. Fibers obtained from rice straw had similar tensile properties compared to fibers obtained from wheat straw and jute. Rice straw fibers were blended with cotton (50:50 ratio) and processed on short staple cotton machinery into a 20s Ne yarn. The yarns were knitted into fabrics and dyed using reactive dyes.

References

[06Red] Reddy, N., Yang, Y.: J. Agric. Food Chem. 54, 8077 (2006)

[07Red] Reddy, N., Yang, Y.: J. Agric. Food Chem. 55, 8570 (2007)