The link that binds agricultural products and renewable resources

Private companies have been disposed to reconsider domestic agricultural resources as alternative materials for manufacturing processes.

For many centuries, agricultural products were the main sources of raw materials for the manufacturing of soap, paints, ink, lubricants, grease, paper, cloth, drugs, and a host of other nonfood products.During the early 1900s, the advances in organic synthesis in Western Europe and the United States led to the use of coal as an alternative resource; in the 1940s, oil and natural gas were added as starting materials as a result of great advances in catalysis and polymer sciences. Since then the Petrochemical industry has grown rapidly as the result of the abundance and low price of the starting materials as well as the development of new products, such as nylon and other polymers, water based paints, and detergents.

However with the rapidly increasing economies of the nations of the world, these developments did not ever result in reduction in the utilisation of agricultural products as industrial materials. Although specific nonfood crops, such as linseed or cotton, may have suffered from these development, animal fats, vegetable oils, starch, cellulose, and other renewable agricultural resources still are used extensively in industry, and many new uses have been developed since the 1950s.

Mainly the energy and raw material crises of the 1970s with the resulting price increases for oil and natural gas, but also the recognition that many major industrial nations depend on imported agricultural raw materials have resulted in an upsurge in research and development. Private companies have been disposed to reconsider domestic agricultural resources as alternative materials for manufacturing processes.

Fats and Oils:Animal fats, marine and vegetable oils, and their fatty acid derivatives have always played a major role in the manufacturing of many industrial products. Some of these commodities are produced solely for industrial end uses, examples are linseed, tung, castor, and sperm whale oils. Others, such as tallow and soybean oil, are used for both edible and industrial products.

Most fats and oils are triglycerides; that is, they consist of a glycerine molecule esterified with three identical or different fatty acids. Some are used in their original state, with minor chemical modification or formulation. Examples are drying oils in paints and castor and rapeseed oils as lubricants. Hydrogenation of fats and oils leads to solid products for candles and waxes. Soybean and linseed oils are also epoxidized for use as stabilizers in polyvinyl chloride, or made into alkyds for paints.

A large proportion of fats and oils are split to glycerine and fatty acids or converted into fatty methyl esters. They, in turn, are used directly or converted to fatty amines or fatty alcohols. Monounsaturated fatty acids, such as oleic or erucic acid, are split further by oxidation of the double bond to produce a mixture of mono and dicarboxylic acids. Oleic acid is thus converted to pelargonic and azeleic acids and erucic acid to pelargonic and brassylic acids. All of these products serve as starting materials for manufacture of soaps, detergents, lubricants and plasticizers. The energy crises of the 1970s led to serious consideration of vegetable oils and their simple esters as emergency fuels to replace diesel fuels, especially for farming operations.

Carbohydrates:Starch, cellulosics, and gums also have been used for many centuries as industrial materials, whereas sugarcane and sugar beet, have mainly satisfied world food needs.

(a) Starch:Starches from potato, maize, and many other crops have been used as thickening agents and adhesives for a variety of industrial applications and as substrates in fermentation and enzyme mediated processes for the manufacturing of many products. Unmodified as well as derivatized starches play a major role in the production of paper and textiles.

The most prominent fermentation product from starch is industrial ethanol, used both as solvent and as fuel extender in gasoline. Economic and technical developments have led to fermentation alcohol becoming cheaper than ethanol from petrochemical ethylene. Research since the 1940s has created new industrial products, including the so-called super slurper and related water-absorbing polymers insoluble starch xanthate, which is used to clean up waste-water from the metal plating industry, water-soluble laundry bags, biodegradable plastics, and encapsulating agents for pesticides.

(b) Cellulose: The main use of celluslose has been in fiber form for manufacturing paper and textile products, and the principle sources are hard and softwoods. Other prominent sources are cotton and flax, as well as biogases and straw from agricultural residues. Although petrochemical research has led to the production of many types and large quantities of synthetic fibers, manufacture of cellulose-based products has not decreased appreciably worldwide. Cellulose has also been modified chemically for manufacturing plastics (celluloid), fibers (rayon viscose), and thickening agents like carboxyl methyl cellulose and so on. However, the development of synthetic plastics and fibers has drastically cut the use of cellulose for these purposes.

Since cellulose is so abundant in nature, much effort has been expended to explore the potential of this material for fermentation processes. Although this is easy to accomplish with starch, so far no economical route for preparing glucose from cellulose has been developed. In addition to the cellulose-to-glucose conversion being more difficult, cellulose normally is closely associated with lignin, which in itself is a rather inaccessible polymer. However, once achieved, such conversion would revolutionize utilization of cellulose as well as of hemicelluloses, a polymer of pentose sugars, and also a major constituent of plant materials.

(c) Gum: Plant gums, including guar, tragacanth, and gum arabic have served as thickening agents for a long time and for many purposes. Most industrial nations of the world depend on imports for these materials. They cannot be supplemented or replaced by microbial polysaccharides, such as santhan gum, which are made by fermentative conversion of starch. One prominent use of gums is in drilling fluids for secondary oil recovery.

Hydrocarbons:Natural rubber and turpentine are excellent examples of plant-derived hydrocarbons. The development of synthetic rubbers during and after World War II has never threatened the demand for natural rubber; there is generally a world shortage. Turpentine is a product of the wood and paper pulp industry and is used as a solvent and thinner in paints and varnishes.

Novel Crops: The threat that industrial nations of the world might be separated from part or all of their traditional sources of raw materials through political and economic upheavals or natural calamities has resulted in a renewed effort to develop additional crops for local agriculture. In the United States, research has provided a number of candidate species that either are now in commercial development or are ready for the time when circumstances warrant such development.

Examples are jojoha, a liquid wax ester to replace sperm whale oil, guayule (alternate source of natural rubber), Kenaf, a paper fiber with annual yields much higher than available from trees, and cramble and meadow foam. There is also active research involving cupbea species, vermonia and several other promising plants.

First Published:May 23, 2020, 8:46 p.m.