Natural Polymers: Examples & Uses

The word “polymer” comes from the Greek words “poly,” which means many, and “meros,” which means parts or units. Each polymer molecule consists of a long chain of repetitive structural units, called monomers, linked together via covalent bonds. Polymers are present in almost every aspect of modern-day lives because of their vast spectrum of properties. While today, with the help of technology, we can synthesize many polymers in laboratories, naturally occurring polymers were used for their chemical properties long before they made their way to chemistry labs. In general, natural polymers are those polymeric materials that are found in nature or can be extracted from plants and animals. Natural Polymers are extensively crucial in many aspects of human life. For instance, our human body is made up of many natural polymers like nucleic acids, proteins, etc. Let’s take a look at some of the most commonly encountered natural polymers and their uses in everyday life.

Cellulose

Cellulose is an organic polysaccharide consisting of a linear chain of several hundred to over ten thousand linked D-glucose units having the formula ({C}_{6}{H}_{10}{O}_{5})_{n}). Cellulose is the major component of plant cell walls, which helps plants stay stiff and upright. Even though humans cannot digest cellulose, it is an important source of fiber in the diet. Cellulose aids digestion by allowing food to pass more readily through the intestines and pushing waste out of the body. The primary components of the plant cell wall are cellulose, hemicelluloses, and pectin. In the pharmaceutical sector, cellulose is primarily utilized as a diluent/binder in tablets for both the granulation and direct compression processes. Carboxylated methylcellulose is utilized in medication formulations as a binder, film-coating agent, and an ointment base.

Natural Rubber

Rubber, also known as latex, is an elastomer, a polymer that is prominently known for its elastic properties. Natural rubber is primarily harvested in the form of the latex from the rubber tree (Hevea brasiliensis). Latex is a stable dispersion (emulsion) of polymer microparticles in water that is extracted from the bark by cutting incisions and collecting the fluid in vessels, a technique known as “tapping.” After that, the latex is refined into rubber, which is ready for commercial use. Latex is allowed to agglomerate in the collection cup in large places. The coagulated lumps are collected and dried before being sold. Although 20,000 species of plants produce latex, only 2,500 species have been found to contain rubber in their latex. Natural rubber is widely employed in a variety of applications and products, both individually and in conjunction with other materials. Around 25 million tonnes of rubber are produced each year, of which 30 percent is natural. It is an essential raw material used in the creation of more than 40,000 products including medical equipment, surgical gloves, aircraft/car tires, pacifiers, clothes, toys, etc.

Wool

Wool is another type of naturally occurring polymer that we use in our daily life. Most of us are familiar with the warm clothes made of wool that we use in winters to comfort ourselves from cold weather.  Wool is one of the most reusable textile fibers present on our planet. It is obtained from sheep and other animals, including cashmere and mohair from goats, qiviut from muskoxen, hide and fur clothing from bison, angora from rabbits, and other types of wool from camelids. The polymeric structure of wool contains a group of proteins known as keratins linked together via covalent bonding.  In addition to its chemical complexity, wool also has a complex physical structure. The surface is made up of overlapping cuticles. Place it under a microscope and you see a scaly surface, which is very different from the smooth surface of synthetic fibers. These properties provide wool’s flexibility, elasticity, resilience, and good wrinkle recovery properties. It’s also what allows it to absorb both moisture and dyes so well. In addition to clothing, wool has been used for blankets, horse rugs, saddle cloths, carpeting, insulation, and upholstery. It is also used to cover piano hammers to absorb odors and noise. Wool can also be used for soundproofing in heavy machinery and speakers.

Bitumen

We depend vividly on roads to get us from one place to another. In fact, there are 33 billion meters of roads on Earth. The durability and the long-term satisfactory performance of roads are always influenced and affected to a greater extent by the employed ingredient materials and their inherent properties. Bitumen, otherwise known as Asphalt, is a thick-gooey substance, usually black or dark brown in color, derived as a natural by-product of the distillation of crude oil. Asphalt typically contains about 80% by weight of carbon; around 10% hydrogen; up to 6% sulfur; small amounts of oxygen and nitrogen; and trace amounts of metals such as iron, nickel, and vanadium.

Silk

Silk is a natural protein fiber, some forms of which can be woven into textiles. Natural silk is one of the strongest textile fibers, and this can be accounted for by the stretched-out molecular form. Silk (78% protein) is much stiffer than wool despite both being proteins made from amino acid chains. Silk fibers have fine draping qualities and are naturally crease-resistant and bring about a warm feel to the skin. The two most frequent amino acids present (glycine and alanine) in the polymer makeup about 75% of the polymer chain and fortunately have two of the simplest individual structures of all amino acids. Silk can come from many different insects, including caterpillars, spiders, and worms. The most economically viable silk is produced from mulberry silkworms because they can be raised in captivity and their silk can be mass-produced. The larva is born from an egg and must be fed mulberry leaves for up to one month before it is ready to create a cocoon of silk. Once it creates this cocoon, workers kill the larva inside using hot water or steam and then proceed with the rest of the manufacturing process.

Amber

Amber is heterogeneous in composition but consists of several resinous bodies more or less soluble in alcohol, ether, and chloroform, associated with an insoluble bituminous substance. Amber is a macromolecule produced by free radical polymerization of several precursors in the labdane family, e.g. communic acid, cummunol, and biformene. These labdanes are diterpenes (C20H32) and trienes, equipping the organic skeleton with three alkene groups for polymerization. As amber matures over the years, more polymerization takes place as well as isomerization reactions, crosslinking and cyclization. Heated above 200 °C (392 °F), amber suffers decomposition, yielding an oil of amber, and leaving a black residue which is known as “amber colophony”, or “amber pitch”; when dissolved in oil of turpentine or linseed oil this forms “amber varnish” or “amber lac.”Because of its unique properties, Amber has been adorned and studied extensively for centuries. It has been widely used for a variety of reasons including jewelry. If amber is heated under the right conditions, oil of amber is produced, and in past times this was combined carefully with nitric acid to create “artificial musk,” a resin with a peculiar musky odor. Although amber emits a distinctive “pinewood” scent when burned, modern goods such as perfume do not typically contain genuine amber because fossilized amber creates very little scent.

Shellac

Shellac is the name given to a material secreted by a parasitic female insect name Lac bug (Laccifer lacca). This insect is mainly found in the tropical rainforests of India and Thailand, making these countries two of the biggest exporters of Lac products in the world. These insects secrete a resinous material on the bark of the tree to form tunnels as they transverse the branches. This material is s cultivated and refined because of the commercial value of the finished product known as lac or shellac. The name “lac” is derived from a unit in the Indian numbering system for 100,000 and presumably refers to the huge numbers of insects that swarm on host trees. Typically, 50,000 to 300,000 female lac bugs are required to produce just 1 kg (2.2lb) of shellac. The chemical structure of shellac is very much like plastic, and hence, it is considered to be natural plastic with a melting point of 75 °C (167 °F). The earliest written evidence for the use of shellac originates from 3000 years ago; nonetheless, shellac was only commercialized in the early 1800s. Today, it is primarily used as a wood sealer and primer. It is the central element of the traditional “French polish” method of finishing furniture, fine string instruments, and pianos. Shellac is non-toxic in its pure form and possesses excellent odor, stain, and UV blocking properties, which makes it a desirable choice for wood furnish and primer. Shellac yields a range of warm colors from pale yellow through to dark orange-red and dark ochre, which makes it a traditional choice of dye for cotton and silk clothes. It is also used in the food industry as a glazing agent for several food items, particularly sweets.

Proteins

Protein is a linear polymer chain of amino acid residues called a polypeptide. A protein contains at least one long polypeptide in which at least 20 natural amino acids are linked by amide bonds. The individual amino acid residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In addition to the 20 natural amino acids, there are amino acids that are not directly synthesized from ribosomes, such as L-3,4-dihydroxyphenylalanine (DOPA), hydroxyproline (Hyp), tyrosine, and selenomethionine, and these compounds are synthesized via posttranslational modifications. Short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptide. Every cell in the human body contains proteins that have distinct cellular functions. Humans need protein in their diet to help their bodies repair cells and make new ones. Protein is also important for growth and development in children, teens, and pregnant women. Proteins allow cells to detect and react to hormones and toxins in their surroundings, and as the chief ingredient in antibodies, which help us resist infection, they play a part in protecting our bodies against foreign invaders. The lack of specific proteins in the brain may be linked to such mysterious, terrifying conditions as Alzheimer’s and Creutzfeldt-Jakob diseases.