Page 316 - Carrahers_Polymer_Chemistry,_Eighth_Edition

9 Naturally Occurring

Polymers—Plants

There may be many ways to divide nature. One way is to divide it according to being alive, that is, self-
replicating and the ability to be dead, and nonliving such as rocks and sand. Again, we have two further
main divisions—plant and animal. In this, and the following chapter, we will deal with materials that
are alive or once were alive. With the exception of lignin, the general chemical groups that constitute
animals and plants are the same on the macrolevel. Both base their ability to replicate on nucleic acids

that form genes containing the blueprint for their life. But, the two classifications do differ in the major
building material. Animals have as their basic building material proteins while plants have as their
basic building material polysaccharides. All of the basic building and genetic materials are polymeric.
Industrially, we are undergoing a reemergence of the use of natural polymers as feedstocks and
materials in many old and new areas of application. Since natural polymers are typically regeneratable
or renewable resources, nature continues to synthesize them as we harvest them. Many natural poly-
mers are available in large quantities. For instance, cellulose makes up about one-third of the bulk of
the entire vegetable kingdom, being present in corn stocks, tree leaves, grass, and so on. With the real-
ization that we must conserve and regulate our chemical resources comes the awareness that we must

find substitutes for resources that are not self-renewing, thus, the reason for the increased emphasis in

polymer chemistry toward the use and modification of natural, renewable polymers by industry.
Natural feedstocks must serve many human purposes. Carbohydrates as raw materials are valu-
able due to their actual or potential value. For example, commercial plants are already utilizing
rapidly reproducing reengineered bacteria that metabolize cellulose wastes converting it to more
protein-rich bacteria that is harvested and then used as a protein source feed meal for animals.
Further, natural materials can be used in applications now reserved largely for only synthetic poly-
mers. There is available sufficient natural materials to supply both food and polymer needs.

When plant or animal tissues are extracted with nonpolar solvents, a portion of the material
dissolves. The components of this soluble fraction are called lipids and include fatty acids, triacylg-
lycerols, waxes, terpenes, prostagladins, and steroids. The insoluble portion contains the more polar
plant components, including carbohydrates, lignin, proteins, and nucleic acids.
Many renewable feedstocks are currently summarily destroyed (through leaving them to rot or
burning) or utilized in a noneconomical manner. Thus, leaves are “ritualistically” burned each fall.
A number of these seemingly useless natural materials have already been utilized as feedstock
sources for industrial products with more becoming available.
Just to bring natural polymers a little closer to home, the following might be our breakfast from
the viewpoint of natural polymers. This breakfast includes polymers derived from both the animal
and plant kingdoms.

Milk Coffee Cake
Proteins Gluten
Fruit Starches
Starches Dextrins
Cellulose Scrambled Eggs
Pectin Ovalbumin
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