History And Uses Of Polymers Biology Essay

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Polymer is a huge molecule also known as macromolecule composed of replicating structural units linked by chemical bonds of covalent. Polymers are considered in the fields of polymer physics, polymer science and polymer chemistry. Natural Polymers (from the Greek poly meaning "many" and meros meaning "parts") are found in many forms such as horns of animals, tortoise shell, shellac (from the lac beetle), rosin (from pine trees), asphalt, and tar from distillation of organic materials. One of the most useful of the natural polymers was rubber, obtained from the sap of the hevea tree. (Rubber was named by the chemist Joseph Priestley who found that a piece of solidified latex gum was good for rubbing out pencil marks on paper. In Great Britain, erasers are still called "rubbers".) Natural rubber had only limited use as it became brittle in the cold and melted when warmed. In 1839, Charles Goodyear discovered, through a lucky accident, that by heating the latex with sulfur, the properties were changed making the rubber more flexible and temperature stable. That process became known as vulcanization

Another common name for many synthetic polymers is plastic which comes from the Greek word "plastikos", suitable for molding or shaping. Many objects in daily use from packing, wrapping, and building materials include half of all polymers synthesized. Other uses include textiles, TV's, CD's, automobiles, and many other all are made from polymers.

HISTORICAL DEVELOPMENT:

Starting in 1811, Henri Braconnot did pioneering work in derivative cellulose compounds, perhaps the earliest important work in polymer science. The development of vulcanization later in the nineteenth century improved the durability of the natural polymer rubber, signifying the first popularized semi-synthetic polymer. In 1907, Leo Baekeland created the first completely synthetic polymer, Bakelite, by reacting phenol and formaldehyde at precisely controlled temperature and pressure. Bakelite was then publicly introduced in 1909. Its original use was to make billiard balls. Rayon, the first synthetic fiber was developed as a replacement for silk in 1911.

Although many polymers were made in the following years, the technology to mass produce them was not developed until World War II, when there was a need to develop synthetic rubber for tires and other wartime applications and nylon for parachutes. Since that time, the polymer industry has grown and diversified into one of the fastest growing industries in the world. Today, polymers are commonly used in thousands of products as plastics, elastomers, coatings, and adhesives. They make up about 80% of the organic chemical industry with products produced at approximately 150 kg of polymers per person annually in the United States.

RUBBER, A Natural Polymer::

Natural latex is found in the inner bark of many trees, especially those found in Brazil and the Far East. The white sticky sap of plants such as milkweed and dandelions is also a latex. Latex will turn into a rubbery mass within 12 hours after it is exposed to the air. The latex protects the tree or plant by covering the wound with a rubbery material like a bandage.

Natural rubber is a polymer of isoprene (2-methyl-1,3-butadiene, see Figure 1) in the form of folded polymeric chains which are joined in a network structure and have a high degree of flexibility (See Figure 2). Upon application of a stress to a rubber material, such as blowing up a balloon or stretching a rubber band, the polymer chain, which is randomly oriented, undergoes bond rotations allowing the chain to be extended or elongated (See Figure 3). The fact that the chains are joined in a network allows for elastomeric recoverability since the cross-linked chains cannot irreversibly slide over one another. The changes in arrangement are not constrained by chain rigidity due to crystallization or high viscosity due to a glassy state.

Since latex will solidify in air, a stabilizer is added to prevent polymerization if the latex is to be stored or shipped in liquid form. The stabilizer is usually 0.5 to 1% ammonia. When the ammonia is removed by evaporation or by neutralization, the latex will solidify into rubber.

Figure 2: Schematic sketch of a typical Figure 3: Elastic deformation

elastomeric network. of a rubber chain.

Make a Rubber Ball from Rubber Latex:

Safety Precautions:

Wear safety goggles at all times in the laboratory.

When noting the odor of the rubber latex, cup your hand and waft the vapors toward you. Do not

take a deep breath of the material.

Make sure the rubber ball is submerged under water when squeezing out the excess liquid to

prevent it squirting onto anyone.

Materials Needed:

Rubber latex

Vinegar

Stirring rod

Paper cup

Measuring devices

Procedure:

Measure 20 mL of rubber latex into a paper cup.

Carefully, smell the material. Describe its odor.

Pour a few drops of latex onto the palm of your hand. Spread it out using your

fingure. Observe any changes that take place.

Add 20 ml of water to the latex in the cup and stir.

Add 20 mL of vinegar to the cup and stir the mixture.

Remove the mass from the cup and stirring rod with your fingers. Carefully

squeeze the mass while washing it underwater. Form the mass into a ball by

repeatedly rotating it and squeezing it.

Dry the rubber with a paper towel.

Drop the rubber on the floor and describe what happens.

BAKELITE, The First Synthetic Polymer:

Bakelite, a phenol-formaldehyde polymer, was the first completely synthetic plastic, first made by Leo Baekeland in 1907. Baekeland and an assistant started their research in 1904 looking for a synthetic substitute for shellac. Bakelite was commercially introduced in 1909. Bakelite was first used to make billiard balls, but, later, was used to make molded insulation, valve parts, knobs, buttons, knife handles, many types of molded plastic containers for radios and electronic instruments, and more.

Safety Precautions:

Wear safety goggles at all times in the laboratory

Formalin is an irritant to the skin, eyes, and mucous membranes.

Phenol is toxic via skin contact. It is listed as a carcinogen.

Glacial acetic acid is an irritant and can cause burns on contact.

Work under a hood and wear gloves and protective clothing when working

with these materials

Materials needed:

Phenol-formaldehyde reaction mixture (freshly prepared solution should be

available. The reaction mixture is made by mixing 25 g 36-40%

formaldehyde + 20 g phenol + 55 mL glacial acetic acid.)

Hydrochloric acid, HCl, concentrated

150-mL beaker

stirring rod

Procedure:

Under a hood, measure 25 mL of the phenol-formaldehyde reaction mixture

into a 150-mL beaker . Place the beaker on a white paper towel.

Add 10 mL of concentrated hydrochloric acid, slowly, with stirring.

Add additional hydrochloric acid, dropwise, with stirring. (You will need

approximately 2 mL of HCl.) As the polymerization point is reached, a white

precipitate will form and dissolve. At the point where polymerization begins,

the white precipitate will not dissolve.

Continue to stir as the plastic forms and becomes pink in colour.

Wash the plastic well before handling.

Describe the properties of the plastic.

RAYON, The First Synthetic Fiber:

What may be considered as the first precursor to Rayon, Louis Marie Hilaire Bernigaut, Comte de Chardonnet worked on a process of producing threads of an "artifical silk" made from collodion in 1884. Chardonnet's silk was finally marketed in 1891, but was short-lived after a young lady's ball gown when up in a puff of smoke after being touched by the lighted cigar of her escort. Charles F. Cross and Edward J. Bevan patened their formula for viscose, a cellulose polymer, in 1892 and were soon manufacturing items of their new Viscoid. The first viscose thread was made by Charles Topham Jr. and commericially produced in 1899. Rayon, made from regenerated cellulose in 1926, marketed by Du Pont, was finally used as a replacement for silk.

Safety Precautions:

Wear safety goggles at all times in the laboratory.

Ammonia fumes are irritating eyes, and mucous membranes. Work in a well ventilated

area.

Materials needed:

Copper(II) sulfate pentahydrate, CuSO4â‹…5 H2O

Ammonia, NH3, concentrated

Sulfuric acid, H2SO4, 5% solution

Filter paper

Funnel

Plastic dropper

Stirring rod

Procedure:

Dissolve 5.0 g of copper(II) sulfate pentahydrate in 25 mL of deionized water. Working under a hood, add concentrated ammonia solution dropwise, with stirring, to

form a light blue-green copper(II) hydroxide, Cu(OH)2, precipitate persists. Allow the precipitate to settle for a few minutes. The remaining liquid should be light blue or colorless. If necessary, add an additional drop or two of the ammonia solution to check for completeness of precipitation of the copper(II) sulfate. Avoid an excess of ammonia. Collect the precipitate by gravity filtration. Wash the solid with two 5 mL portions of cold water.

Transfer the precipitate to a 150-mL beaker. The filtrate can be discarded.

Under a hood, add 25 mL of concentrated ammonia solution to the beaker. Srit to dissolve the

solid.

Obtain two pieces of filter paper. Tear them into pieces and add them to the dark blue copperammonia solution. Stir to dissolve the filter paper.

Obtain 100 mL of 5% sulfuric acid in a 250-mL beaker.

Fill a plastic dropper with the blue cellulose-copper-ammonia solution. Place the tip of the

dropper below the surface of the 5% sulfuric acid solution and squirt its contents into the solution.

Dark blue threads will form which will slowly bleach to white. Repeat with the rest of the

cellulose-copper-ammonia solution.

Wash the rayon well with water before handling.

Record your observations of the rayon.

POLYSTYRENE, An Addition Polymer:

Polystyrene is used to make many types of containers such as videocassette cases, compact disk jewel boxes, tableware (forks, knives and spoons), and cafeteria trays. A foamed form of polystyrene is used to make coffee cups, grocery store meat trays, and building insulation.

To minimize fumes in the laboratory, this procedure uses a styrene casting resin.

Safety Precautions:

Wear safety goggles at all times in the laboratory. Styrene is harmful by inhalation. It is an irritant to the eyes and respiratory system. Work in a well ventilated area. Methyl ethyl ketone is an irritant. Work in a well ventilated area.

Materials needed:

Styrene casting resin

Casting resin catalyst, methyl ethyl ketone

Half of a small petri dish

Stirring rod

Optional: A clean dry coin, such as a penny

Procedure:

Measure 15 mL of styrene casting resin into a paper cup.

Add 5 drops of catalyst to the resin. Stir well.

Pour the resin mixture into a clean half of a petri dish. Allow the mixture to sit, undisturbed, for approximately one hour or until hard.

If desired, a clean, dry penny can be added to the resin after it has set for about 5 minutes. To

avoid air bubbles, coat the penny with a small amount of the mixed resin before adding it to the resin mixture in the petri dish.

NYLON, A Condensation Polymer:

Nylon was the result of research directed by Wallace Hume Carothers at du Pont. The research team was interested in duplicating the characteristics of silk. Nylon gained rapid acceptance for use in stockings and in making parachutes. Carothers, however, was subject to bouts of depression and in 1937, shortly before du Pont placed nylon stockings on the market, Carothers committed suicide by drinking cyanide.

Safety Precautions:

Wear safety goggles at all times in the laboratory.

The materials in this experiment are considered toxic. They are irritants to the eyes and mucous membranes. Wear gloves and work in a well ventilated area.

Materials needed:

Hexamethylenediamine (1,6-hexanediamine), 5% aqueous solution Sebacoyl chloride (or adipyl chloride), 5% solution in cyclohexane Sodium hydroxide, NaOH, 20% aqueous solution

Beaker, 50 mL

Forceps

Stirring rod.

Procedure:

Pour 10 mL of hexamethylenediamine solution into a 50 mL beaker.

Add 10 drops of 20% sodium hydroxide solution. Stir.

Carefully add 10 mL of sebacoyl chloride solution by pouring it down the wall of the tilted beaker. Two layers should be evident in the beaker and there should be an immediate formation of a polymer film at the interface between the two liquids.

Using forceps, pick up the mass at the center and slowly draw out the nylon, allowing a "rope" to be formed. Use a stirring rod to wrap the rope and continue to pull it slowly from the mixture interface.Wash the nylon well with water before handling.

Stir any remaining solutions left in the beak to form additional polymer. Wash the nylon well with water.

Commercially, nylon is made by mixing the components in bulk. Nylon thread, rod, and sheet are made by melting and forming or extruding the polymer.

SODIUM POLYACRYLATE, A Copolymer:

Superabsorbants were originally developed by the United States Department of Agriculture in 1966. This material consisted of a grafted copolymer of hydrolyzed starch-polyacrylonitrile (polyacrylonitrile is commonly known as Acrilan, Orion, or Creslan). The intended use was for additives for drilling fluid in off-shore secondary oil recovery operations and as agricultural thickeners. These materials were followed by synthetic superabsorbants that are

polyacrylic and polyacrylonitrile based. Some of these materials are capable of absorbing up to 2000 times their weight of distilled water.

When a starch-hydrolyzed polyacrylonitrile superabsorbant is mixed with glycerin or ethylene glycol, the resulting firm gel has a rubbery texture and is very strong and resilient. This material can absorb about 300 to 400 times its

weight in distilled water and can "grow" many times its original size. This material was formed into various shapes and sold under names such as "Grow Creatures". The process is reversible and, on standing in air, the grow creature will shrink almost to its original size on drying. It can be grown and dried many times.

A useful application of "Super Slurper" is in the liners of Pampers and other disposable diapers. Under this application, the polymer gel can absorb up to 90 times its weight in liquid.

Super-absorbent material, sold under the name "Water Grabber" or "Water Lock" is available from garden supply stores and can be found in the garden department of some variety stores.

Safety Precautions:

There are no safety hazards with the materials used in this experiment.

Materials Needed:

Sodium polyacrylate

Sodium chloride, NaCI

Paper cup, 5 oz

Stirring rod

Disposable diaper

Newspaper

Procedure:

Measure a level ½ teaspoon of superabsorbent material and place the material in a 5 oz paper or plastic cup.

Add 100 mL of water to the cup.

Record your observations.

Add 1/2 teaspoon of salt, sodium chloride, to the mixture. Record your observations.

Sodium polyacrylate from a disposable diaper:

To obtain the superabsorbant material from a disposable diaper: Obtain an ultra-absorbent diaper. Spread out some newspaper on a table top or the floor.

Slowly, take the diaper apart. Observe the different layers. What is the function of each layer?

Shake the cotton well to remove any superabsorbent material. Throw the waste cotton into the trash. Rub the outside liner of the diaper to remove any superabsorbent material adhering to the plastic.

Transfer the powder and cotton on the newspaper to a 5 oz. plastic or paper cup. Remove any loose cotton, leaving the powder in the cup. Add 50 mL of water to the powder in the cup and stir. Observe the material in the cup for about a minute. Record your observations.

Testing a disposable diaper: Open a disposable diaper on the bench top.

Add water, 100 mL at a time, until the diaper does not hold additional water.

Record the amount of water held by the diaper.

Some Inorganic Polymers:

Some examples of-Inorganic Polymers: (Ref.: H. R. Allcock, Scientific American, 230, 66, March 1974)

Glass: made of rings and chains of repeating silicate units. Glass fibers (fiberglass) are used in textiles and in many construction materials.

Bricks, concrete and ceramics are three-dimensional polymers.

Polyphosphazenes: general formula (NPCl2) n . Formed from reacting NH4Cl with PCl5 at 250°C for several hours. Can be substituted to alter properties.

Materials Needed:

Sulfur

Safety Precautions:

It is recommended that a hot plate be used in heating the sulfur in this preparation. This will prevent the sulfur from igniting and burning to form toxic sulfur dioxide, a strong irritant. Keep the beaker of sulphur covered with a watch glass to minimize sulfur vapors escaping from the beaker.

Procedure:

Heat ordinary sulfur to a temperature between 140-170°C. The sulfur will turn red and become viscous above 159°C. At 175°C, the viscosity of the molten sulfur begins to decrease.

Pour the hot melt into water in a thin stream. When cool, it forms rubbery fibers of the Polymeric sulfur. The polymer is not stable at room temperature and it will eventually harden, returning to its normal yellow color, when the molecules reform into eight-membered rings.

SILLY PUTTY, An Inorganic Polymer:

Silly Putty is a silicone polymer marketed by Binney & Smith Inc. Easton, PA 18042, and with similar products marketed under other names by other companies. It comes packaged in small egg-shaped containers and is usually pink in color. Some forms of Silly Putty contain phosphorescent material that will allow it to glow in the dark.

Silly Putty is a non-Newtonian fluid which has dilantant properties. That is, it tends to dilate (or expand) when sheared resulting in an increased viscosity under stress. For this reason, Silly Putty has some unique properties:

a) Under low stress, such as slowly pulling the Silly Putty apart, the putty flows forming thin strands.

b) Under high stress, such as a sharp pull, the putty breaks.

c) If rolled into a ball and dropped, the putty will bounce.

d) If the ball of putty is placed on a table top and hit with your hand, the ball will hardly be deformed. If hit

with a hammer, the putty will shatter. Yet, if you squeeze gently, the ball will flatten.

e) If you stuff the putty through a tube, it will swell as it emerges from the open end. This is known as dieswell.

(This works well with freshly prepared putty as the putty tends to harden with age.)

The Preparation of Silly Putty

Materials needed:

dimethyldichlorosilane, SiCl2(CH3)2

diethyl ether, anhydrous, (C2H5)2O

sodium hydrogen carbonate, NaHCO3, saturated aqueous solution

boric oxide, B2O3 sometimes called boric acid, fused)

sodium sulfate, Na2SO4, anhydrous

safety shield

flask, 250-mL, and 125-mL

separatory funnel

test tube, Pyrex, 25 x 250 mm

stirring rod

Safety Precautions

Wear safety goggles at all times in the laboratory.

Dimethyldichlorosilane reacts violently with water to produce heat and toxic and corrosive fumes (HCl).

Avoid skin contact and use it only in a fume hood.

Ether is extremely flammable, avoid the use of flames in the laboratory during this procedure.

When washing the ether solution with sodium hydrogen carbonate, carbon dioxide is released building up pressure in the separatory funnel. Vent the funnel often.

Procedure

This procedure must be carried out in a fume hood or in an area with excellent ventilation and behind a safety shield.

To a 250-mL flask add 20 mL of dimethyldichlorosilane and 40 mL of anhydrous ether. Hydrolyze the solution by adding 40 mL distilled water DROPWISE, allowing the reaction to cease before adding additional water. (If water is added too rapidly, the reaction will proceed vigorously and may spatter from the flask. Avoid inhaling any vapors from the flask.)

After the water addition is complete, transfer the reaction mixture to a separatory funnel and drain off and discard the water layer. Wash the remaining ether solution with 10 mL portions of saturated sodium hydrogen carbonate, venting often, until it is no longer acid (and no more CO2 forms), then wash with 10 mL of distilled water. Drain the ether layer into a 125-mL flask containing 2 grams Na2SO4 and allow to dry for 15-20 minutes.

Filter the solution into a 100-mL beaker and transfer to a water bath or steam bath to evaporate the ether.

Determine the mass of the residual silicone oil. Add about 5% of the silicone oil's mass of boric oxide, and stir for a few minutes. Transfer the mixture to a Pyrex test tube and heat in an oil bath at 200`C for three hours. Allow the silly putty to cool.

NOTE: Initially, the silly putty will be a clear, colorless to slightly yellow material. It will cure within one week to a white solid with properties closer to the commercially available Silly Putty. As it is used, it will pick up foreign matter and become gray in color slowly improving its properties.

Application and future prospective:

Macromolecular science has had a major impact on the way we live. It is difficult to find an aspect of our lives that is not affected by polymers. Just 50 years ago, materials we now take for granted were non-existent. With further advances in the understanding of polymers, and with new applications being researched, there is no reason to believe that the revolution will stop any time soon.

Wood cellulose, a versatile and renewable natural resource, has potential for use as a reinforcement for synthetic organic polymers. During the past 80 years a number of materials using the reinforcing properties of wood cellulose have found major markets. Forms of wood cellulose proposed as reinforcements include: wood fibers, cellulose fibers, microfibillar, and microcrystalline cellulose. Recent attention has been given to them as fillers/reinforcements in thermoplastics and elastomers. Most cellulosic composites derive their existence from their comparatively low materials cost and the filling rather than reinforcing properties of cellulose. However, cellulose chains have a potential stiffness much higher than glass and in the same range as superstiff aramid fibers.

In this paper I examined different uses and preparation for different polymers. And at last I

came to the conclusion that polymers are useful to human being in every aspect of life. Almost all the substances we use for our convenience are made of different types of polymers.

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