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New Jersey Scuba Diving

Polymer Materials

Polymer materials - rubbers, plastics, and silicones - are not really of interest as artifacts. They are, however, among the most important materials to divers: without neoprene, nylon, and a bewildering range of other polymer materials, we would not have most of the equipment that makes diving possible !

A polymer is a chemical compound with high molecular weight consisting of a number of structural units linked together by covalent bonds. The simple molecules that may become structural units are themselves called monomers; two monomers combine to form a dimer, and three monomers, a trimer. A structural unit is a group having two or more bonding sites. A bonding site may be created by the loss of an atom or group, such as H or OH, or by the breaking up of a double or triple bond, as when ethylene, H2C=CH2, is converted into a structural unit for polyethylene, -H2C-CH2- .

Polyethylene
Polyethylene - the simplest polymer: ---CH2-CH2-CH2-CH2-CH2---

Incidentally, stick a hydrogen "H" onto each end of this illustration in place of the squiggly lines, and you have C11H24 - a fairly common form of gasoline ! Many artificial polymers are synthesized from fuel oils; there is no clear delineation between the two. Likewise, many polymers combust just as readily as fuel oils, although often with toxic products, especially those containing chlorine.

In a linear polymer, the structural units are connected in a chain arrangement and thus need only be bifunctional, i.e., have two bonding sites. When the structural unit is trifunctional ( has three bonding sites, ) a nonlinear, or branched, polymer results. Ethylene, styrene, and ethylene glycol are examples of bifunctional monomers, while glycerin and divinyl benzene are both polyfunctional. Polymers containing a single repeating unit, such as polyethylene, are called homopolymers. Polymers containing two or more different structural units, such as phenol-formaldehyde, are called copolymers.

All polymers can be classified as either addition polymers or condensation polymers. An addition polymer is one in which the molecular formula of the repeating structural unit is identical to that of the monomer, e.g., polyethylene and polystyrene. A condensation polymer is one in which the repeating structural unit contains fewer atoms than that of the monomer or monomers because of the splitting off of water or some other substance, e.g., polyesters and polycarbonates.

Many polymers occur in nature, such as silk, cellulose, natural rubber, and proteins. In addition, a large number of polymers have been synthesized in the laboratory, leading to such commercially important products as plastics, synthetic fibers, and synthetic rubber. Polymerization, the chemical process of forming polymers from their component monomers, is often a complex process that may be initiated or sustained by heat, pressure, or the presence of one or more catalysts.


Rubber

Rubber is any solid substance that upon vulcanization becomes elastic; the term includes natural rubber ( caoutchouc ) and synthetic rubber. The term elastomer is sometimes used to designate synthetic rubber only and is sometimes extended to include caoutchouc as well.

Chemistry and Properties

Natural Rubber
Natural Rubber

All rubber-like materials are polymers, which are high molecular weight compounds consisting of long chains of one or more types of molecules, such as monomers. Vulcanization ( or curing ) produces chemical links between the loosely coiled polymeric chains; elasticity occurs because the chains can be stretched and the crosslinks cause them to spring back when the stress is released. Natural rubber is a polyterpene, i.e., it consists of isoprene molecules linked into loosely twisted chains. The monomer units along the backbone of the carbon chains are in a cis arrangement and it is this spatial configuration that gives rubber its highly elastic character. In gutta-percha, which is another natural polyterpene, the isoprene molecules are bonded in a trans configuration leading to a crystalline solid at room temperature. Unvulcanized rubber is soluble in a number of hydrocarbons, including benzene, toluene, gasoline, and lubricating oils.

Rubber is water repellent and resistant to alkalies and weak acids. Rubber's elasticity, toughness, impermeability, adhesiveness, and electrical resistance make it useful as an adhesive, a coating composition, a fiber, a molding compound, and an electrical insulator. In general, synthetic rubber has the following advantages over natural rubber: better aging and weathering, more resistance to oil, solvents, oxygen, ozone, and certain chemicals, and resilience over a wider temperature range. The advantages of natural rubber are less buildup of heat from flexing and greater resistance to tearing when hot.

Rubber TireVulcanization is the treatment of rubber to give it certain qualities, e.g., strength, elasticity, and resistance to solvents, and to render it impervious to moderate heat and cold. Chemically, the process involves the formation of cross-linkages between the polymer chains of the rubber's molecules. Vulcanization is accomplished usually by a process invented by Charles Goodyear in 1839, involving combination with sulfur and heating. A method of cold vulcanization ( treating rubber with a bath or vapors of a sulfur compound ) was developed by Alexander Parkes in 1846.

Rubber for almost all ordinary purposes is vulcanized; exceptions are rubber cement, crepe-rubber soles, and adhesive tape. Hard rubber is vulcanized rubber in which 30% to 50% of sulfur has been mixed before heating; soft rubber contains usually less than 5% of sulfur. After the sulfur and rubber ( and usually an organic accelerator, e.g., an aniline compound, to shorten the time or lower the heat necessary for vulcanization ) are mixed, the compound is usually placed in molds and subjected to heat and pressure. The heat may be applied directly by steam, by steam-heated molds, by hot air, or by hot water. Vulcanization can also be accomplished with certain peroxides, gamma radiation, and several other organic compounds.

Rubber TreeThe finished product is not sticky like raw rubber, does not harden with cold or soften much except with great heat, is elastic, springing back into shape when deformed instead of remaining deformed as unvulcanized rubber does, is highly resistant to abrasion and to gasoline and most chemicals, and is a good insulator against electricity and heat. Many synthetic rubbers undergo processes of vulcanization, some of which are similar to that applied to natural rubber. The invention of vulcanization made possible the wide use of rubber and aided the development of such industries as the automobile industry.

Natural Rubber

Natural rubber is obtained from the milky secretion ( latex ) of various plants, but the only important commercial source of natural rubber ( sometimes called Para rubber ) is the tree Hevea brasiliensis. The only other plant under cultivation as a commercial rubber source is guayule ( Parthenium argentatum ) a shrub native to the arid regions of Mexico and the SW United States. The easiest way to see raw latex for yourself is to pick a Dandelion. The sticky white liquid that drips from the broken stem is latex.

Rubber TreeTo soften the rubber so that compounding ingredients can be added, the long polymer chains must be partially broken by mastication, mechanical shearing forces applied by passing the rubber between rollers or rotating blades. Thus, for most purposes, the rubber is ground, dissolved in a suitable solvent, and compounded with other ingredients, e.g., fillers and pigments such as carbon black for strength and whiting for stiffening; antioxidants; plasticizers, usually in the form of oils, waxes, or tars; accelerators; and vulcanizing agents. The compounded rubber is sheeted, extruded in special shapes, applied as coating or molded, then vulcanized. Most Para rubber is exported as crude rubber and prepared for market by rolling slabs of latex coagulated with acid into thin sheets of crepe rubber or into heavier, firmly pressed sheets that are usually ribbed and smoked.

An increasing quantity of latex, treated with alkali to prevent coagulation, is shipped for processing in manufacturing centers. Much of it is used to make foam rubber by beating air into it before pouring it into a vulcanizing mold. Other products are made by dipping a mold into latex ( e.g., rubber gloves ) or by casting latex. Sponge rubber is prepared by adding to ordinary rubber a powder that forms a gas during vulcanization.

Vibram SoleSurgical TubingMost of the rubber imported into the United States is used in tires and tire products; other items that account for large quantities are belting, hose, surgical tubing, insulators, valves, and gaskets. Vibram is a trade name for both a rubber formulation and a tread design used extensively in footwear, dating back to the 1930s. Uncoagulated latex, compounded with colloidal emulsions and dispersions, is extruded as thread, coated on other materials, or beaten to a foam and used as sponge rubber. Used and waste rubber may be reclaimed by grinding followed by devulcanization with steam and chemicals, refining, and remanufacture.

Latex PaintMost white glues, such as Elmer's, are latex-based. The solvent in Elmer's all-purpose school glue is water. When the water evaporates, the polyvinylacetate (PVA) latex that has spread into a material's pores and crevices forms a flexible bond. Another use for latex that is often overlooked is in paint. Most modern water-based paints ( as well as driveway sealers, etc ) use synthetic latex for a binding agent, which acts much as it does in glue. So chances are, your walls are coated with rubber !

Synthetic Rubber

The more than one dozen major classes of synthetic rubber are made of raw material derived from petroleum, coal, oil, natural gas, and acetylene. Many of them are copolymers, i.e., polymers consisting of more than one monomer. By changing the composition it is possible to achieve specific properties desired for special applications. The earliest synthetic rubbers were the styrene-butadiene copolymers, Buna S and SBR, whose properties are closest to those of natural rubber. SBR is the most commonly used elastomer because of its low cost and good properties; it is used mainly for tires. Other general purpose elastomers are cis-polybutadiene and cis-polyisoprene, whose properties are also close to that of natural rubber.

Among the specialty elastomers are copolymers of acrylonitrile and butadiene that were originally called Buna N and are now known as nitrile elastomers or NBR rubbers. They have excellent oil resistance and are widely used for flexible couplings, hoses, washing machine parts, and gloves. Butyl rubbers are copolymers of isobutylene and 1.3% isoprene; they are valuable because of their good resistance to abrasion, low gas permeability, and high dielectric strength. Neoprene ( polychloroprene ) is particularly useful at elevated temperatures and is used for heavy-duty applications. Of course, Neoprene foam is the primary material of most diving suits.O-ringNeoprene is a common material for o-rings, and is also used as the basis of many contact cements.

Ethylene-propylene rubbers (RPDM) with their high resistance to weathering and sunlight are used for automobile parts, hose, electrical insulation, and footwear. Urethane elastomers are called Spandex and they consist of urethane blocks and polyether or polyester blocks; the urethane blocks provide strength and heat resistance, the polyester and polyether blocks provide elasticity; they are the most versatile elastomer family because of their hardness, strength, oil resistance, and aging characteristics. They have replaced rubber in elasticized materials. Other uses range from airplane wheels to seat cushions. Other synthetics are highly oil-resistant, but their high cost limits their use. Silicone rubbers are organic derivatives of inorganic polymers, e.g., the polymer of dimethysilanediol. Very stable and flexible over a wide temperature range, they are used in wire and cable insulation. AquaSeal is a urethane cement.

Spandex
Spandex - what would the '80s have been without it ?

History

Pre-Columbian peoples of South and Central America used rubber for balls, containers, and shoes and for waterproofing fabrics. Mentioned by Spanish and Portuguese writers in the 16th century, rubber did not attract the interest of Europeans until reports about it were made (1736-51) to the French Academy of Sciences by Charles de la Condamine and Francois Fresneau. Pioneer research in finding rubber solvents and in waterproofing fabrics was done before 1800, but rubber was used only for elastic bands and erasers, and these were made by cutting up pieces imported from Brazil. Joseph Priestley is credited with the discovery c.1770 of its use as an eraser, thus the name rubber.

The first rubber factory in the world was established near Paris in 1803, the first in England by Thomas Hancock in 1820. Hancock devised the forerunner of the masticator ( the rollers through Rubber Bandwhich the rubber is passed to partially break the polymer chains, ) and in 1835 Edwin Chaffee, an American, patented a mixing mill and a calendar ( a press for rolling the rubber into sheets. )

In 1823, Charles Macintosh found a practical process for waterproofing fabrics, and in 1839 Charles Goodyear discovered vulcanization, which revolutionized the rubber industry. On March 17, 1845, the fist rubber band was patented by Stephen Perry of London. In the latter half of the 19th century the demand for rubber insulation by the electrical industry and the invention of the pneumatic tire extended the demand for rubber. In the 19th century wild rubber was harvested in South and Central America and in Africa; most of it came from the Para rubber tree of the Amazon basin.

Despite Brazil's legal restrictions, seeds of the tree were smuggled to England in 1876. The resultant seedlings were sent to Ceylon ( Sri Lanka ) and later to many tropical regions, especially the Malay area and Java and Sumatra, beginning the enormous East Asian rubber industry. Here the plantations were so carefully cultivated and managed that the relative importance of Amazon rubber diminished. American rubber companies, as a step toward diminishing foreign control of the supply, enlarged their plantation holdings in Liberia and in South and Central America.

During World War I, Germany made a synthetic rubber, but it was too expensive for peacetime use. In 1927 a less costly variety was invented, and in 1931 Neoprene was made, both in the United States. German scientists developed Buna rubber just prior to World War II. When importation of natural rubber from the East Indies was cut off during World War II, the United States began large-scale manufacture of synthetic rubber, concentrating on Buna S. Today synthetic rubber accounts for about 60% of the world's rubber production.

Edible Rubber

Chewing GumChicle is the name for the gum obtained from the latex of the sapodilla tree ( Manilkara zapota ) a tropical American evergreen. The sapodilla ( known also by many other common names ) is widely cultivated in tropical regions, including south Florida, for its fruit, which is plum-sized with translucent yellow-brown flesh. Large-scale cultivation of the tree for latex is impractical because it can be tapped only infrequently and varies widely in yield.

Chicle is collected during the rainy season from wild trees in the rain forests. Natives, called chicleros, cut zigzag gashes in the tree trunk and collect the sap in bags. The collected material is boiled until it reaches the correct thickness and is then molded into blocks. These are exported, chiefly to the United States, for use in making chewing gum. Unsystematic and excessive tapping of the sapodilla ( especially in the Yucatan peninsula, where it was most abundant ) is leading to its depletion and has necessitated increasing use of chicle substitutes from other latex-producing plants.

Chewing gum is a confection consisting usually of chicle, flavorings, and corn syrup and sugar or artificial sweeteners. Prehistoric people are believed to have chewed resins. Spruce resin was chewed as a thirst quencher by Native Americans, from whom pioneers adopted the custom. Refined paraffin was later used and then chicle, which was probably first imported into the United States through Mexico. A chicle gum was patented in 1869 by William and Semple.

In the present-day manufacture of chewing gum blocks of chicle are ground, melted, and cleared in a whirling vat, and then the flavorings and other ingredients are added. The gum is rolled through sheeting machinery and chopped into sticks or into candy-coated pellets. Insoluble plastics may be mixed with or substituted for the chicle. The United States is the major producer, exporter, and consumer, of chewing gum.


Plastics

A plastic is any organic material with the ability to flow into a desired shape when heat and pressure are applied to it and to retain the shape when they are withdrawn. Rubbers are really a subset of plastics, known as elastomers, although there is no clear dividing line between the two: many rubbers are quite stiff and hard, and many plastics are stretchy like rubber.

Composition and Types of Plastic

Dive FinA plastic is made up principally of a binder together with plasticizers, fillers, pigments, and other additives. The binder gives a plastic its main characteristics and usually its name. Thus, polyvinyl chloride ( PVC ) is both the name of a binder and the name of a plastic into which it is made. Binders may be natural materials, e.g., cellulose derivatives, casein, or milk protein, but are more commonly synthetic resins. In either case, the binder materials consist of very long chainlike molecules called polymers.

Cellulose derivatives are made from cellulose, a naturally occurring polymer; casein is also a naturally occurring polymer. Synthetic resins are polymerized, or built up, from small simple molecules called monomers. Plasticizers are added to a binder to increase flexibility and toughness. Fillers are added to improve particular properties, e.g., hardness or resistance to shock. Pigments are used to impart various colors. Virtually any desired color or shape and many combinations of the properties of hardness, durability, elasticity, and resistance to heat, cold, and acid can be obtained in a plastic.

There are two basic types of plastic: thermosetting, which cannot be resoftened or reshaped after being subjected to heat and pressure; and thermoplastic, which can be repeatedly softened and remolded by heat and pressure. When heat and pressure are applied to a thermoplastic binder, the chainlike polymers slide past each other, giving the material "plasticity." However, when heat and pressure are initially applied to a thermosetting binder, the molecular chains become cross-linked, thus preventing any slippage if heat and pressure are reapplied.

Ashtray
This genuine plastic ashtray was recovered from inside the Stolt Dagali.

Molding of Plastic

Plastics are available in the form of bars, tubes, sheets, coils, and blocks, and these can be fabricated to specification. However, plastic articles are commonly manufactured from plastic powders in which desired shapes are fashioned by compression, transfer, injection, or extrusion molding.

In compression molding, materials are generally placed immediately in mold cavities, where the application of heat and pressure makes them first plastic, then hard. The transfer method, in which the compound is plasticized by outside heating and then poured into a mold to harden, is used for designs with intricate shapes and great variations in wall thickness. Injection-molding machinery dissolves the plastic powder in a heating chamber and by plunger action forces it into cold molds, where the product sets.

The operations take place at rigidly controlled temperatures and intervals. Extrusion molding employs a heating cylinder, pressure, and an extrusion die through which the molten plastic is sent and from which it exits in continuous form to be cut in lengths or coiled.

Environmental Considerations

Plastics are so durable that they will not rot or decay as do natural products such as those made of wood. As a result great amounts of discarded plastic products accumulate in the environment as waste. It has been suggested that plastics could be made to decompose slowly when exposed to sunlight by adding certain chemicals to them. Plastics present the additional problem of being difficult to burn. When placed in an incinerator, they tend to melt quickly and flow downward, clogging the incinerator's grate. They also emit harmful fumes; e.g., burning polyvinyl chloride gives off hydrogen chloride gas. see Water Pollution

Early Plastics

Natural polymers with plastic-like properties have been used for centuries. These include shellac, tortoiseshell, and horn, as well as many resinous tree saps. Shellac is derived from insects; tortoiseshell is actually from sea turtles, primarily Hawksbills; while horn may be derived from any suitable animal, primarily cattle and sheep. Hard rubber Vulcanite and Gutta Percha were introduced in the 1840s. Bois Durci was developed in the 1850s from animal blood, a byproduct of Paris slaughterhouses. All of these materials could be processed with heat and pressure into articles such as hair combs and items of jewelry.

The first man-made plastic was an invention of English scientist Alexander Parkes. He unveiled Parkesine at the 1862 London International Exhibition. Parkesine, an organic material that could be heated and molded but would retain its shape when cooled, was made by dissolving cellulose nitrate in just a bit of solvent. Unlike rubber, Parkesine could be colored or transparent, and could be carved into any shape. In 1866, four years after the exhibition, Parkes formed the Parkesine Company; it failed after only two years due to high production costs.

35mm filmNone of these materials was of any great industrial significance. The first really important man-made plastic, Celluloid, was discovered circa 1869 by the American inventor John W. Hyatt and manufactured by him in 1872. Celluloid is a transparent, colorless synthetic thermoplastic ( ie meltable and reshapeable ) made by treating cellulose nitrate ( nitrocellulose ) with camphor and alcohol. Celluloid was the first important synthetic plastic and was widely used as a substitute for more expensive substances, such as ivory, amber, horn, and tortoise-shell. Newark NJ was once a major center of celluloid production.

Celluloid is highly flammable, and has been superseded by newer plastics with more desirable properties. It has been used for combs, brush handles, billiard balls ( although they had a tendency to explode ), knife handles, buttons, and other useful objects. Celluloid was also originally used for photographic and movie film. The inevitable breakdown of this natural plastic puts many old films and photos at risk, and most modern photographic films are based on synthetic cellulose acetate rather than celluloid. Surprisingly, celluloid is also edible, at least if you are a goat. It is still used to make ping-pong balls.

Synthetic plastics did not come into modern industrial use until the production of Bakelite in 1909 by the American chemist L.H. Baekeland. Bakelite, or polyoxybenzyl- methylenglycolanhydride, is a synthetic thermosetting (permanent) resin. Bakelite is a condensation polymer of formaldehyde and phenol. In practice, the phenol and formaldehyde are first polymerized to a small extent by using the proper choice of catalyst and temperature. The resulting prepolymer, called a resol, is a low-melting, soluble material, which can then be combined with a filler ( usually cotton linters or wood fibers ) and a pigment and heated under pressure in a mold to yield an object of the desired shape. The pure resin is colorless or amber-colored and very brittle; various fillers, pigments, and other additives are used to give it the desired properties depending on its application. Heating of the prepolymer results in extensive cross-links between the polymer chains, resulting in a tightly bound three-dimensional network.

Salt Shakers
Bakelite salt shakers from the Mohawk

Bakelite is tough, hard, dimensionally stable and strong, and highly resistant to heat, moisture and most chemicals. It is easily machined and carved, as well as molded, and largely replaced celluloid after its introduction in the early 20th century. Bakelite has been widely used both alone, to form whole objects, and in combination with other materials, as a laminate or a surface coating. It was used as a substitute for hard rubber and amber as well as celluloid. Commercial uses of Bakelite included insulation for electrical apparatus ( since it is a nonconductor ) and the manufacture of certain machinery gears. It was also used for phonograph records and many other articles, useful and ornamental, and as diverse in character as buttons, billiard balls, pipestems, and umbrella handles. Bakelite distributor caps were fitted on Model-T Fords in the 1920s. During the Great Depression, Bakelite sold more than any other commercial product, and was loved by the public for its brilliant and cheerful colors and its affordability. It found extensive use during World War II, but was finally rendered obsolete soon after by newly developed materials like lucite, fiberglass, vinyl and acrylics, although it is still produced in Japan.

Neither Celluloid nor Bakelite are used any more. Celluloid deteriorates over time, but Bakelite is much more durable, and many old Bakelite objects, from telephones to radios to jewelry, are now sought-after as antiques. Pre-World War II shipwrecks such as the Mohawk can yield fine Bakelite artifacts which survive well in the water and are easily cleaned and conserved.


BakeliteBakelite: A Revolutionary Early Plastic

Text by Lloyd Fadem and Stephen Z. Fadem, MD Photographs by Doug Congdon-Martin

IT IS HARD TO BELIEVE that one can combine two unlikely substances like carbolic acid and formaldehyde to produce a beautiful and versatile substance such as phenolic resin or "Bakelite, " a revolutionary, non-flammable, early plastic. "The material of a thousand uses, " as it was called, made a splash in the 1920s, '30s and '40s.

Around the turn of the century, the Belgian born scientist Dr. Leo Baekeland, working as an independent chemist, came upon the compound quite by accident. Anyone familiar with the newspaper printing business is aware of the Velox used as a proof; that was his first discovery. Velox was invented in 1899 and is still in use today. After selling the rights to this product to Eastman Kodak for three quarters of a million dollars, he started developing a less flammable bowling alley floor shellac; bowling was becoming the latest rage in New York City. Dr. Baekeland soon realized that a resin that was both insoluable and infusible could have a much wider appeal when used as a molding compound. He obtained a patent and started the Bakelite Corporation around 1910.

BakelitePhenolic resin could be produced in a multitude of colors, commonly yellow, brown, butterscotch, green and red. Ommitting the pigment could produce a transparent or translucent effect. The resin could be molded or cast, depending on variations in the formula. For molding, the formula was cooked until resinous, spread out in thin sheets to harden, then ground to a fine consistency. At this point, powdered fillers and pigment were added, to enable the resin to be molded and to add color. This mixture was then put through hot rollers which created large sheets of colored, hardened resin. These sheets were then ground into a very fine powder which was molded under high heat and pressure into the final product form. As a molded material the resin's drawback was the limited range of colors which could be created. For casting, the formula was modified slightly, enabling the resin to be poured into lead molds and then cured in ovens until it polymerized into a hard substance. The liquid resin could be tinted to any color or "marbelized" by mixing two colors together.

For the first ten years or so after its introduction, the resin was used primarily to make electrical and automobile insulators and heavy industrial products. Eventually, uses for the resin spread into the consumer market. Castings were made in the shape of cylinders or blocks, and then sold to novelty and jewelry makers. Industrial designers began experimenting with the new material. Fine craftsmen sculpted the molded products on fast wheels with razor-like tools to carve out designs that the world has not seen since; after World War II, most companies switched to creating designs through the use of patterned molds, instead of hand-carving. Bakelite replaced flammable celluloid, previously the most popular synthetic material for molded items, as a major substance for jewelry production.

BakeliteThe process to the collector of today may not be significant, as Bakelite is now treasured for its unique, unreproducible beauty. A deeply carved half inch bangle bracelet may sell for $225.00, and a two and one half inch bangle may command $900.00. Bakelite often acquires a patina within a few months to a few years of its date of production, and metamorphisizes into a completely different appearing color. The red, white and blue Bakelite designs of yesterday have mellowed into lovely yellows, reds and blacks, enhancing further the value of those rare pieces which have continued to maintain their original color and luster.

Bakelite's many uses allowed it to become a standard item in the family home of the 1930s and 1940s. It was frequently found in the kitchen, in the form of flatware handles, rabbit or chicken napkin holders, salt and pepper shakers, or serving trays. During the Depression Bakelite sold more than any other commercial product, and was loved by the public for its brilliant and cheerful colors and its affordability.

When the Bakelite patent expired in 1927, it was acquired by the Catalin Corporation that same year. They began mass production under the name "Catalin, " using the cast resin formula which enabled Catalin to add 15 new colors to the original five produced by the Bakelite Corporation, which used the limited color range molded formula, as well as the now-famous marbelized effect. One of their most notable products was the Fada bullet radio. The Catalin Corporation was responsible for nearly 70% of all phenolic resins that exist today.

Bakelite-Catalin was sold mostly by Saks Fifth Avenue, B. Altman and Bonwit Teller, but was also on the shelves of F.W. Woolworth and Sears. To the wealthy socialites, whose husbands had fallen on tough times during the Depression, with Tiffany diamonds and Cartier jewelry now well beyond their means, the vibrantly colorful carved jewelry adorned with rhinestones became de riguer for cocktail parties and formal dinners. Yet, Catalin and Bakelite were within everyone's reach with Depression prices ranging from twenty cents to three dollars. Diana Vreeland, editor of Vogue, often spoke of the versatility of Bakelite, as did Elsa Schiaparelli, who was constantly contracting with the Bakelite and Catalin Corporations for exclusive buttons for her dress designs.

But in 1942 Bakelite and Catalin suspended sales of their colorful cylinders to costume jewelry manufacturers in order to concentrate on the wartime needs of a nation which had totally shifted its focus. Defense phones and aviator goggles, as well as thousands of other Bakelite products, found their way to armed forces around the world. The scheme shifted from the 200 vibrant colors which brightened the dark days of the Depression to basic black, the no-nonsense symbol of a nation at war. By the end of the war, new technology had given birth to injection-molded plastics, and most manufacturers switched to less labor-intensive and more practical means of developing products. The next generation of plastics had been born - lucite, fiberglass, vinyl and acrylic - and they were molded into products commonplace in our everyday lives today.

Bakelite and Catalin became obsolete, but survive in the hearts of collectors who hunt flea markets, swap meets and antique shows for the Depression treasures of a generation now consigned to the pages of history. Bakelite was given a boost in the mid-1970s by artist, photographer, and flea market icon Andy Warhol who fell in love with Bakelite carvings and whimsical Martha Sleeper pins, and amassed one of the largest collections.

Upon Warhol's untimely death in 1987, Bakelite reached the high prices which it ironically had never been able to command during its peak in the Depression. It is still quite possible and most exciting to discover that a deeply carved bracelet or a Martha Sleeper designed pin purchased for $10.00 in a junk shop has a real value between $900.00 and $1,500.00!

In conclusion, Bakelite, an early plastic, represented an affordable solution for a unique and short time in history when a nation hinged on the edge of economic disaster and needed a cheerful substitute for the lost elegance of the 1920s. Now, while its usefulness as a practical product has long been replaced, Bakelite exists as a treasure. The prospective collector should acquire a sense and appreciation for Bakelite's true value, and a network of reliable dealers to purchase from.

Several books on the market are invaluable Bakelite aids to the new collector; they are identified below.

Lloyd Fadem is a well known collector and mid-century enthusiast whose interest lies in architectural and industrial design of the thirties, forties and fifties. He is currently working on the book, "Cool Stuff." - Stephen Z. Fadem, M.D., is a prominent Houston nephrologist whose hobby is history, with a current fascination on the development of American technology and its impact upon our everyday lives. He is collaborating with his brother on the book "Cool Stuff."

Copyright 1996 Deco Echoes Publications
all rights reserved

Shipwrecks from after the turn of the century ( that's 1900, not 2000, kiddies ) to World War II can yield many fine artifacts in an early plastic material known as Bakelite. Bakelite actually has significant value to collectors as art and antiques. Bakelite artifacts are fun to find. They are generally colorful, and need very little attention to restore to display condition. A little scrubbing with an old toothbrush and a weak acid solution or even vinegar will remove most stains and encrustation - no soaking or other bother required. You can even put them through the dishwasher. Then perhaps a little silicone spray or furniture polish to shine it up, and put it on the shelf. All plastics should be kept away from direct sunlight, as the UV degrades the material.

Bakelite tray handles
A set of Bakelite tray handles from the Mohawk.

Nothing remarkable about these except for the fact that they are in near-perfect condition, not even discolored, while the chromed-steel trays themselves had completely dissolved in the seawater. Black Bakelite seems to be the toughest of all the varieties. The upper one is upsidedown, showing the molded-in brass fasteners.


Modern Plastics

New uses for plastics are continually being discovered. Following World War II, optical lenses, artificial eyes, and dentures of acrylic plastics, splints that X-rays may pierce, nylon fibers, machine gears, fabric coatings, wall surfacing, and plastic lamination were developed. More recently a hydrophilic, or water-attracting, plastic suitable for use in non-irritating contact lenses has been developed. Plastics reinforced with fiberglass are used for boats, automobile bodies, furniture, and building panels.

Nylon
Nylon

Weight BeltNylon is a synthetic thermoplastic material characterized by strength, elasticity, resistance to abrasion and chemicals, low moisture absorbency, and capacity to be permanently set by heat. After 10 years of research E. I. du Pont de Nemours & Company introduced nylon in 1938 as monofilaments for bristles and in 1940 as multifilament yarn for hosiery. Nylon is now manufactured also in the form of sheets, coatings, and molded plastics and used in a variety of products, including fabrics, surgical sutures, thread, insulating wire coverings, mosquito netting and screening, gears and bearings, rope, and tire cords. There are a variety of nylons, all being polyamides frequently made from diamines and dicarboxylic acids. The most generally useful of these is nylon-66, made from hexamethylene amine and adipic acid. Velcro is typically made of nylon.

Delrin is a polyacetal resin that was developed in 1959. It is a tough, translucent, white material which resembles nylon and polypropylene but is somewhat harder. Originally marketed as "synthetic stone", its solvent resistant properties coupled with a good dimensional stability allow Delrin to find all kinds of uses as a substitute for nonferrous metal castings in machine parts, dry-run bearings, and gears, and in other light engineering applications.

PolyesterPolyester is a synthetic fiber produced by the polymerization of the product formed when an alcohol and organic acid react. The outstanding characteristic of polyesters is their ability to resist wrinkling and to spring back into shape when creased. In addition, polyesters have good dimensional stability, wash and dry easily and quickly, and have excellent wash-and-wear or minimum-care characteristics; one of their principal uses is in apparel fabrics of this kind. Microfiber, which was introduced in 1986, is a variety of polyester that has extremely thin filaments ( half as thick as silk fibers. ) Thinsulate and Polartec are polyester microfibers. Polyesters are also used in casement curtains, throw rugs, and as a cushioning or insulating material. Mylar, Dacron, and Tyvek are varieties of polyester.

Polystyrene is a widely used plastic; it is a polymer of styrene. Polystyrene is a colorless, transparent thermoplastic that softens slightly above 212°F and becomes a viscous liquid at around 365°F. It is resistant to acids, alkalies, oils, and alcohols. It is produced either as a solid or as a foamed plastic marketed under the trade name Styrofoam. Its many uses include electrical and thermal insulation, translucent window panels, storage-battery cases, and toilet articles.

ABS LegoABS plastic is commonly used in dive gear. A wide spectrum of ABS plastics can be produced by varying the proportions of the three 3 constituent monomers - Acrylonitrile, Butadiene and Styrene, with properties tailored to meet specific requirements. In addition to this great versatility, ABS plastics in general are distinguished by great toughness and high impact strength ( even at low temperatures ), good dielectric properties and excellent dimensional stability. To this is added extremely fine gloss appearance, very wide coloring possibilities and ready availability. All these attributes meant that when ABS was introduced in the mid 1950s, plastics could for the first time offer real competition with many traditional materials such as metals, for making highly durable moldings with great consumer appeal. One of the earliest applications was the famous Lego brick from Denmark.

PVC PipeVinyl plastics are a group of thermoplastics used in molded products, flexible tubing, material for raincoats, and laminated safety glass. Vinyl plastics are polymers and copolymers of vinyl derivatives ( i.e., derivatives of ethylene, H2C-CH2, ) e.g., vinyl chloride ( H2C=CHCl ) and vinyl acetate ( H2C=CH-OOC-CH3. ) Polyvinyl chloride is an important member of this group. Polytetrafluoroethylene, or Teflon, is also sometimes classed as a vinyl polymer. Polyolefins are a group of vinyl plastics that are polymers of various alkenes, or olefins. The most important are polyethylene and polypropylene.

Polyvinyl chloride ( PVC ) is a thermoplastic that is a polymer of vinyl chloride. Resins of polyvinyl chloride are hard, but with the addition of plasticizers a flexible, elastic plastic can be made. This plastic has found extensive use as an electrical insulator for wires and cables. It is both waterproof and fire-resistant. Cloth and paper can be coated with it to produce fabrics that may be used for upholstery materials and raincoats. Most plumbing pipe is today made out of PVC. When burned, PVC materials give off a number of hazardous and polluting chlorine compounds.

PolypropylenePolypropylene is a plastic noted for its light weight, being less dense than water; it is a polymer of propylene. It resists moisture, oils, and solvents. Since its melting point is 250°F, it is used in the manufacture of objects that are sterilized in the course of their use. Polypropylene is also used to make textiles, ropes that float, packaging material, and luggage. For diving, polypropylene is the material of choice for floating dive flag lines and lightweight waterproof equipment boxes.

Polyethylene is the most widely used plastic. It is a polymer of ethylene H2C=CH2, having the formula (-CH2-CH2-)n, and is produced at high pressures and temperatures in the presence of any one of several catalysts, depending on the desired properties for the finished product. Polyethylene is resistant to water, acids, alkalies, and most solvents. Its many applications include films or sheets for packaging, shower curtains, unbreakable bottles, pipes, buckets and bins, drinking glasses, and insulation for wire and cable. Polyethylene products are typically labeled LDPE or HDPE, which stands for Low-Density Polyethylene and High-Density Polyethylene.

Polyurethanes are a group of plastics that may be either thermosetting or thermoplastic. Polyurethane can be made into both flexible and rigid foams. The flexible foam is often used in furniture and automobile cushions, in mattresses, and for carpet backings. The rigid foam is used for the thermal insulation of refrigerators, trucks, and buildings. In the furniture industry the rigid foam is molded into mirror frames, chair shells, and other parts that were formerly made from wood. Some polyurethanes are highly elastic materials that are resistant to chemical attack and to abrasion. They are used in such things as solid rubber tires and shoe heels. Lycra, a fiber used in stretch clothing, is a polyurethane. Polyurethanes are also used as decorative and protective coatings, exhibiting high gloss, hardness, and toughness.

PolycarbonatePolycarbonates are a group of clear, thermoplastic polymers used mainly as molding compounds. Polycarbonates are prepared by the reaction of an aromatic difunctional phenol with either phosgene or an aromatic or aliphatic carbonate. The commercially important polycarbonates use 2,2-bis (4-hydroxyphenol)-propane (bisphenol A) and diphenyl carbonate. This polymer is a clear plastic with a slight yellow discoloration. It has excellent electrical properties and a high impact strength.

Polyacrylics are a group of thermoplastics that are transparent and highly decorative. The polyacrylics, or acrylic plastics, are polymers ( and copolymers ) of derivatives of acrylic acid, H2C-CH-COOH. The best-known acrylic plastic is polymethyl methacrylate, sold under the trade names Plexiglas and Lucite. It takes a high polish, is clear and colorless, and is transparent to visible and ultraviolet light. Since it is a thermoplastic, it can be shaped while hot to form a number of objects, such as windshields for airplanes and transparent ornamental objects. Other esters of acrylic acid and methylacrylic acid similarly polymerize and copolymerize to transparent thermoplastics, differing somewhat in hardness and in softening temperatures. Orlon and Rayon are acrylic polymers. Rayon, based on cellulose, is one of the oldest plastics, dating to 1892. It was the first man-made fiber, originally known as "artificial silk", and it is the basis of many textiles, as well as cellophane and Scotch Tape.

CyanoacrylateCyanoacrylate, C5H5NO2 ( or Crazy Glue ) is an acrylic resin that cures ( forms its strongest bond ) almost instantly. In glue form, the cyanoacrylate molecules ( monomers ) are suspended in an acid stabilizer which inhibits polymerization. The mixture cures within seconds on contact with water ( specifically, hydroxyl ions. ) This is convenient, since virtually any object you might wish to glue will have at least trace amounts of water on its surface ( especially fingers. )

Cyanoacrylate undergoes a process called anionic polymerization: the molecules start linking up when they come into contact with water, whipping around in chains to form a durable plastic mesh. The glue thickens and hardens until the thrashing molecular strands can no longer move, resulting in an incredibly strong, permanent waterproof bond. Super-glue fuming is sometimes used in criminal investigations to detect latent fingerprints. Another interesting application is the use of cyanoacrylate to close wounds in place of stitches.

Epoxy resins are a group of synthetic resins used to make plastics and adhesives. These materials are noted for their versatility, but their relatively high cost has limited their use. High resistance to chemicals and outstanding adhesion, durability, and toughness have made them valuable as coatings. Because of their high electrical resistance, durability at high and low temperatures, and the ease with which they can be poured or cast without forming bubbles, epoxy fiberglass boatresin plastics are especially useful for encapsulating electrical and electronic components. Epoxy resin adhesives can be used on metals, construction materials, and most other synthetic resins. They are strong enough to be used in place of rivets and welds in certain industrial applications.

Fiberglass is a thread made from glass. It is made by forcing molten glass through a kind of sieve, thereby spinning it into threads. Fiberglass is strong, durable, and impervious to many caustics and to extreme temperatures. For those qualities, fabrics woven from the glass threads are widely used for industrial purposes. Fiberglass fabrics can also be made to resemble silks and cotton and are used for curtains and drapery. A wide variety of materials are made by combining fiberglass with plastic resins. These materials, which are rust proof, are molded into the shape required or pressed into flat sheets. Boat hulls, automobile bodies, and roofing and ceiling compositions are some of the uses to which such material is put.

Acetate is one of the most important forms of artificial cellulose-based fibers; the ester of acetic acid. The first patents for the production of fibers from cellulose acetate appeared at the beginning of the 20th century. During World War I, production of acetylcellulose began on an industrial scale for military applications. Acetate fibers are basically delivered in the form of a continuous textile yarn. Their principal use is in the production of widely used consumer goods, such as men's shirts, women's blouses, underwear, ties, bathing suits, jersey jackets and sweaters, suit fabrics, coats, and sports clothing.

KevlarKevlar is a high-strength synthetic fiber similar to Nylon. It was first produced by the DuPont corporation in the early 1960s, and arrived in commercial products in the 1970s. Kevlar is very strong and very light: by weight about five times as strong as steel. It is a polymeric aromatic amide, an aramid polymer containing a benzene ring, linked together through amide (nitrogen) groups. Because of the high ratio of carbon to hydrogen atoms, Kevlar requires high concentrations of oxygen before it starts to burn, leading to very low flammability. The planar aromatic rings polymerize in rigid chains, and hydrogen bonding between the hydrogen atoms of one chain, and oxygen of another leads to a strong planar sheet structure. When the material is made into fibers, the flat sheets are spun 360 degrees around the fiber axis, forming the cylindrical fiber shape. Kevlar has a high price at least partly because of the difficulties caused by the use of concentrated acid in its manufacture. An early use for Kevlar was to replace steel cords in car tires. It is now commonly used in bulletproof vests and other types of light armor and extreme sports equipment.


Silicones

Silicone

silicone mouthpieceSilicone ( properly polysiloxane ) is an inorganic polymer in which atoms of silicon and oxygen alternate in a chain; various organic radicals ( the "R"s above, ) such as the methyl group, CH3, are bound to the silicon atoms. Silicones, which are unusually stable at extreme temperatures ( both high and low, ) may occur as liquids, rubbers, resins, or greases. Silicones are prepared from halides of organic silicon compounds by decomposition. Such compounds are chosen and used in mixtures that allow the desired molecular weight and degree of cross-linking to be obtained in the final polymer.

Apart from use in cast and molded products such as mouthpieces and mask skirts, silicone compounds such as RTV ( Room Temperature Vulcanize, in case you were wondering ) are also used as flexible adhesives and caulks, bonding a wide range of materials including glass, metal, and rubber. Silicone foams are used as fire barriers. Some surgical tubing is made of silicone, although most is latex. Other silicone formulations are used as lubricants and low-friction coatings. Silicones are also used to make the heat resistant tiles on the bottom of the space shuttle, and hair conditioners that don't cause buildup. For scuba diving, silicones are commonly used to form regulator mouthpieces and mask skirts.

SiliconeSilly Putty
Silicones find uses from molded products to adhesives and caulks to lubricants to ...

Polydimethylsiloxane does something strange when mixed with boric acid, or B(OH)3. The resulting mixture is soft and pliable, and you can mold it into any shape easily with your fingers. But it is also very bouncy. What's more, push it gently and it gives way, but hit it hard with a hammer and it cracks ! Strangely, if you spread it over newspaper, and pull it away, it gets printed with a mirror image of the newspaper text. No industrial use was ever found for his wonder material, but tons of it has been sold as toy called Silly Putty.

Other inorganic polymers have been synthesized with backbones of pure silicone, germanium, tin, and alternating phosphorus and nitrogen atoms.


Biological Polymers

protein molecule
Model of a portion of a typical protein molecule

We are polymers ! Or at least, we are based largely on polymer materials - proteins and nucleic acids or DNA are both organic polymers. Therefore, without polymers, there would definitely be no scuba diving.

Proteins

Protein is any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight. Hundreds of protein molecules have been isolated in pure, homogeneous form; many have been crystallized. All contain carbon, hydrogen, and oxygen, and nearly all contain sulfur as well. Some proteins also incorporate phosphorous, iron, zinc, and copper. Proteins are large molecules with high molecular weights (from about 10,000 for small ones [of 50-100 amino acids] to more than 1,000,000 for certain forms); they are composed of varying amounts of the same 20 amino acids, which in the intact protein are united through covalent chemical linkages called peptide bonds. The amino acids, linked together, form linear unbranched polymeric structures called polypeptide chains; such chains may contain hundreds of amino-acid residues; these are arranged in specific order for a given species of protein.

protein moleculeA protein molecule that consists of but a single polypeptide chain is said to be monomeric; proteins made up of more than one polypeptide chain, as many of the large ones are, are called oligomeric. Based upon chemical composition, proteins are divided into two major classes: simple proteins, which are composed of only amino acids, and conjugated proteins, which are composed of amino acids and additional organic and inorganic groupings, certain of which are called prosthetic groups. Conjugated proteins include glycoproteins, which contain carbohydrates; lipoproteins, which contain lipids; and nucleoproteins, which contain nucleic acids.

Classified by biological function, proteins include the enzymes, which are responsible for catalyzing the thousands of chemical reactions of the living cell; keratin, elastin, and collagen, which are important types of structural, or support, proteins; hemoglobin and other gas transport proteins; ovalbumin, casein, and other nutrient molecules; antibodies, which are molecules of the immune system; protein hormones, which regulate metabolism; and proteins that perform mechanical work, such as actin and myosin, the contractile muscle proteins.

Nucleic Acids

DNA moleculeNucleic acid any of a group of organic substances found in the chromosomes of living cells and viruses that play a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis. In most organisms, nucleic acids occur in combination with proteins; the combined substances are called nucleoproteins. Nucleic acid molecules are complex chains of varying length. The two chief types of nucleic acids are DNA ( deoxyribonucleic acid ), which carries the hereditary information from generation to generation, and RNA ( ribonucleic acid ), which delivers the instructions coded in this information to the cell's protein manufacturing sites.

A substance that he called nuclein ( now known as DNA ) was isolated by 1869 by Friedrich Miescher, but it was only in the last half of the 20th century that that research revealed its significance as the material of which the gene is composed, and thus its function as the chemical bearer of hereditary characteristics. RNA was first made by laboratory synthesis in 1955. In 1965 the nucleotide sequence of tRNA was determined, and in 1967 the synthesis of biologically active DNA was achieved. The amount of RNA varies from cell to cell, but the amount of DNA is normally constant for all typical cells of a given species of plant or animal, no matter what the size or function of that cell. The amount doubles as the chromosomes replicate themselves before cell division takes place; in the ovum and sperm the amount is half that in the body cells.

The chemical and physical properties of DNA suit it for both replication and transfer of information. Each DNA molecule is a long two-stranded chain. The strands are made up of subunits called nucleotides, each containing a sugar (deoxyribose), a phosphate group, and one of four nitrogenous bases, , guanine, thymine, and cytosine, denoted A, G, T, and C, respectively. A given strand contains nucleotides bearing each of these four. The information carried by a given gene is coded in the sequence in which the nucleotides bearing different bases occur along the strand. These nucleotide sequences determine the sequences of amino acids in the polypeptide chain of the protein specified by that gene.

Between the genes, or coding loci, on the DNA of higher organisms, there are long portions of DNA, often referred to as "junk" DNA, that code no proteins. Sometimes junk DNA occurs within a gene; when this occurs, the coding portions are called exons and the noncoding (junk) portions are called introns. Junk DNA makes up 97% of the DNA in the human genome. Little is known of its purpose.

In 1953 the molecular biologists J. D. Watson, an American, and F. H. Crick, an Englishman, proposed that the two DNA strands were coiled in a double helix. In this model each nucleotide subunit along one strand is bound to a nucleotide subunit on the other strand by hydrogen bonds between the base portions of the nucleotides. The fact that adenine bonds only with thymine (A-T) and guanine bonds only with cytosine (G-C) determines that the strands will be complementary, i.e., that for every adenine on one strand there will be a thymine on the other strand. It is the property of complementarity between strands that insures that DNA can be replicated, i.e., that identical copies can be made in order to be transmitted to the next generation.


compiled from various sources


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I make no claim as to the accuracy, validity, or appropriateness of any information found in this website. I will not be responsible for the consequences of any action that is based upon information found here. Scuba diving is an adventure sport, and as always, you alone are responsible for your own safety and well being.

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