Products From Nontraditional Crops

How Crops Can Provide Raw Materials for the Chemical Industry

by Shelby Thames, Distinguished University Research Professor and Professor of Polymer Science, University of Southern Mississippi, Hattiesburg; Robert Kleiman, National Center for Agricultural Utilization Research, ARS, USDA, Peoria, IL; and L. Davis Clements, Director, Agricultural Materials, CSRS, USDA, Washington, DC.

Nature has produced an estimated 300,000 different plant species, of which we use only a few hundred in organized agriculture. In 1957, USDA initiated a program that collected plants worldwide from a number of sources. The idea was to take a close look at these plants chemically and see if any new and different materials in them could be useful to humanity.

About 8,000 different species were collected, most of which had never been examined before. Their chemical compositions were analyzed for potential sources of starch, protein, oil, fiber, gum, and medicinal components, as well as for any special individual characteristics. For example, researchers found over 100 different, never-before-discovered oils.

This effort to utilize new species, as well as to develop new uses for traditional crops, is possible because nature offers renewable, reliable "living factories" for an incredible array of chemical materials.

Agriculture in the United States is accustomed to identifying crops as specific commodities (corn, soybeans, cotton, etc.) in relation to the traditional food, feed, and fiber markets. To fully explore potential uses of a crop, we must view it not simply as a commodity but as a complex raw material that has specific functional groups suitable for producing industrial products. The utility of a given crop as a resource for the chemical industry depends upon the chemical composition and structure of the materials found in that crop.

All crops are made up of many types of materials. For example, the corn plant has starches, oil, zein (protein), and a number of lesser components in each kernel. The cobs and stalks contain cellulose (a long chain, or polymer, of sugar molecules containing six carbon atoms), hemicellulose (a polymer of sugar molecules containing five carbons), and lignin (a polymer made up of six-member carbon-hydrogen rings). Each of these materials contains chemically distinct structural units that can react with other chemical structures to form new materials. These reactive chemical units are referred to as the "chemical functionality" of the material.

Its specific chemical functionality is the basis for each material's use as an industrial resource. For this reason, when we consider industrial uses for both traditional and nontraditional agricultural products, we group crop resources in terms of their primary materials: starches, oils, proteins, lignocellulosics, and other natural products such as naturally derived chemicals. We will examine in more detail the functionalities and uses for three of these materials: oils, starches, and lignocellulosics.

Vegetable Oils

A major ingredient in many plants is the oil that can be extracted from their fruits or seeds. Seed oils have been used for millenia as an energy component of food and almost as long in nonfood applications. The ancient Egyptians used castor oil in their paints and as a lubricant, and Biblical passages refer to olive oil as a source of fuel in lamps.

Seed oils from traditional crops, such as soybeans, provide raw materials for many of the products that we use every day; from the soap we wash with, to the grease we use to lubricate our automobiles.

USDA 067-10-2A

Seed oils from traditional crops such as soybeans, corn, cotton, coconuts, and flax provide raw materials for many of the products that we use every day. From the soap we wash with, to the grease we use to lubricate our automobiles, combines, and military equipment, vegetable oils are a prime ingredient. In addition, a number of new crops, such as crambe, rapeseed, lesquerella, and others, produce oils with unique compositions. The oil from these new crops is used for products ranging from lubricants to plastics and from cosmetics to industrial chemicals.

Seed oils consist primarily of a chemical form called a triglyceride. These triglycerides are liquids at room temperatures and insoluble in water. Some triglycerides are stable at high temperatures because they are either saturated (nonreactive) or partially unsaturated (somewhat reactive). These oils, used in cooking, include corn oil, peanut oil, safflower oil, olive oil, and sunflower oil. Others, with high levels of chemical unsaturation, are valuable either because they are chemically reactive or because they contain unusual chemical structures.

Vegetable oils can react with other materials to form either a much thicker liquid (a lubricant) or solids.

The oils can be used directly for dust control or as carriers for pesticides. Alcohols such as methanol or ethanol can react with the oil's triglyceride to give what is called a fatty acid ester, which is useful, among other things, as a substitute diesel fuel. Vegetable oils can be converted to glycerol (used in cosmetics, synthetic fibers, explosives, etc.) and fatty acids through the chemical addition of water to the triglyceride.

The fatty acids of soybean oil and tall oil (from wood, primarily pine) are used to make materials included in hot-melt glues and in the curing component of epoxy glues, while the fatty acids in coconut oil are the major ingredient in soaps and detergents. Other uses for fatty acids include fabric softeners, cosmetics, plastics,paints, coatings, inks, antifoaming agents, minerals processing agents, and mold release agents in foundries. In short, whether we realize it or not, we use vegetable oils in our everyday life for many things we would be hard pressed to do without.

New crops, such as lesquerella, produce oils with unique compositions that are opening up new applications as raw materials for products from lubricants to cosmetics.

Ken Hammond/USDA 92BW0693-35

Many new uses of seed oils are now being developed to take advantage of their natural functionalities. Soybean oil has been modified to replace petroleum in inks for newspaper printing. (The 1991 and 1992 Yearbooks of Agriculture were printed with soy ink.) A number of nylons based on oils from other crops, particularly nylon-11 and nylon-13,13, are being evaluated for use as engineering plastics in the automotive industry. New, flexible coatings and paints can be made from rapeseed and crambe oils.

The functionality of each oil is unique. The fatty acids in each oil are different, and therefore each oil's ability to react is different. The unsaturated bonds in the fatty acids that make up the triglycerides are reactive; that is, they can combine with other chemicals easily. So, when we deliberately add oxygen, sulfur, or phosphorus to the unsaturated bonds in a triglyceride, we can make a lubricant, a rubber additive, or a wax. The reactivity of unsaturated bonds in fatty acids also leads to the production of raw materials necessary in the manufacture of nylons, polyesters, waxes, and other products.