Natural Cellulose Fibers from Renewable Resources

Keywords

Natural cellulose fiber • Cotton cultivation • Bast fiber • Alternative fiber

For centuries, mankind has been clothed using natural cellulose and protein fibers that have been almost entirely derived from dedicated sources. Cultivation of fiber crops and rearing of silkworms and sheep have been the traditional methods of obtaining cellulose and protein fibers, respectively. However, fiber crops were not just sources for clothing, but the by-products generated were major sources for food and means for substantial income. For instance, cotton seeds have been used as a source for oil and also as animal feed. Among the different types of fibers, natural cellulose fibers, mainly cotton, have been the most common source for fibers. Recently, the cultivation of cotton and other natural fibers has been declining due to the difficulties in growing cotton, better profits from biofuel crops such as corn and soybeans, and limited technological improvements in processing and using cotton-based textiles. Similarly, the supply of petroleum resources required for synthetic fibers at affordable prices could be questionable in the near future. At any given time, it can be expected that fuel needs would predominate the use of petroleum resources for textile fibers. In addition, increasing consumption, espe­cially in the developing countries, constraints on the natural resources required to produce fibers, and inability to increase the supply proportionate to the demand are expected to make most of the current fibers either too expensive or unavailable for commodity applications. This scenario is neither unrealistic nor unforeseeable. The production of natural fibers such as cotton is declining due to cotton farmers shifting to more profitable biofuel crops such as corn and soybeans. These biofuel crops are also less demanding in terms of resources required for cultivation, harvesting, and processing into final products. The decrease in cotton production could escalate further due to the demand for biofuels.

Attempts to find alternative sources for the natural cellulose fibers in current use have met with limited success due to cost and quality restrictions. Unlike cultivating exclusive fiber crops that require dedicated land, large amounts of water, energy, and labor, the residues such as stalks (stems), leaves, and husks left after harvesting cereal grains contain cellulose that can be extracted in the form of fibers. Similarly, coproducts obtained during the processing of cereal grains for food or fuel contain proteins that can be used to develop regenerated protein fibers. These by-products and coproducts of agricultural processing are available in abundance, are annually renewable, and are inexpensive. However, such agricul­tural by-products and coproducts have been relatively unexplored for fibrous applications. Attempts have been made to study the potential of using these by-products and coproducts to develop fibers, but there are no reports on commer­cial production of fibers or fibrous products from agricultural residues.

Corn, wheat, rice, and sorghum are the most common staple foods that are extensively grown across the world. Cultivation of these cereal crops inevitably generates substantial amounts of lignocellulosic by-products such as leaves, stems, husks, cobs, and straw, roughly equivalent to the amounts of grains harvested. In many instances, such as cotton, the amounts of by-products generated are typically much higher than the weight of the grain or fibers produced. These by-products are mostly been burned or buried on the ground, but traditional uses include animal feed and bedding, as fuel by burning, and to some extent as agricultural mulches. Increasing costs of agriculture and demand for sustainable raw materials have directed attention to understand the potential of using the by-products and coproducts generated during agricultural production and processing for various applications.