how is plastic made

8/9/2019 How is Plastic Made

1/20

How Is Plastic Made?

Plastic: Any of various complex organic compounds produced by polymerization, capable of being molded, extruded, cast into various shapes and films, or drawn into filaments used as textile fibers. --Webster's Dictionary

That's an interesting definition, you may be thinking, but how is plastic actually made? What's involvedin the plastics manufacturing process?

Th e Basics of Plastic Manufacturing

The term "plastics" encompasses organic materials, such as the elements carbon (C), hydrogen (H),nitrogen (N), chlorine (Cl) and sulfur (S), which have properties similar to those naturally grown inorganic materials such as wood, horn and rosin. Organic materials are based on polymers, which areproduced by the conversion of natural products or by syththesis from primary chemicals coming from oil,natural gas or coal.

The plastic manufacturing process begins by heating the hydrocarbons in a "cracking process." Here, inthe presence of a catalyst, larger molecules are broken down into smaller ones such as ethylene(ethene) C2H4, propylene (propene) C3H6, and butene C4H8 and other hydrocarbons. The yield of ethylene is controlled by the cracking temperature and is more than 30% at 850C and such products asstyrene and vinylchloride can be produced in subsequent reactions. These are then the startingmaterials for several other types of plastics. Therefore, this process results in the conversion of thenatural gas or crude oil components into monomers such as ethylene, propylene, butene and styrene.

These monomers are then chemically bonded into chains called polymers. Different combinations of monomers yield plastic resins with different properties and characteristics. Each monomer yields aplastic resin with different properties and characteristics. Combinations of monomers producecopolymers with further property variations.

The resulting resins may be molded or formed to produce several different kinds of plastic products withapplication in many major markets. The variability of resin permits a compound to be tailored to aspecific design or performance requirement. This is why certain plastics are best suited for someapplications while others are best suited for entirely different applications. For instance, impact strengthmeasures the ability of a material to withstand shock loading. Heat resistance protects the resin fromexposure to excessive temperatures. Chemical resistance protects the resin from breakdown due toexposure to environmental chemicals.

Some examples of material properties in plastic product applications are:

- Hot-filled packaging used for products such as ketchup- Chemical-resistant packaging used for products such as bleach- Impact strength of car bumpers

Th e Structure of Polymers

Polymers are created by the chemical bonding of many identical or related basic units and thoseproduced from a single monomer type are called homopolymers. These polymers are specifically madeof small units bonded into long chains. Carbon makes up the backbone of the molecule and hydrogenatoms are bonded along the carbon backbone.

Polymers that contain primarily carbon and hydrogen are classified as organic polymers. Polypropylene,polybutylene, polystyrene and polymethylpentene are examples of these.


2/20

Even though the basic makeup of many polymers is carbon and hydrogen, other elements can also beinvolved. Oxygen, chlorine, fluorine, nitrogen, silicon, phosphorous and sulfur are other elements thatare found in the molecular makeup of polymers. Polyvinyl chloride (PVC) contains chlorine. Nyloncontains nitrogen. Teflon contains fluorine. Polyester and polycarbonates contain oxygen. There arealso some polymers that, instead of having a carbon backbone, have a silicon or phosphorousbackbone and these are considered inorganic polymers.

Th e Additives

When plastics emerge from reactors, they do not have the desired properties that make it a material of choice, that is, it is considered a raw material. In order to achieve a commercial product, the plastic issubject to further treatment and the inclusion of additives which are selected to give it specifiedproperties. Most polymers are blended with additives during raw material processing into their finishedparts. Additives are incorporated into polymers to alter and improve their basic mechanical, physical or chemical properties. Additives are also used to protect the polymer from the degrading effects of light,heat, or bacteria; to change such polymer properties as flow; to provide product color; and to providespecial characteristics such as improved surface appearance or reduced friction.

T ypes of Additives:

- antioxidants: for outside application- colorants: for colored plastic parts- foaming agents: for styrofoam cups- plasticizers: used in toys and food processing equipment

T wo C h aracterizations of Plastic

A Thermoset is a polymer that solidifies or "sets" irreversibly when heated. Similar to the relationshipbetween a raw and a cooked egg, once heated, a thermoset polymer can't be softened again and oncecooked, the egg cannot revert back to its original form. Thermosets are valued for their durability andstrength and are used primarily in automobiles and construction, although applications such asadhesives, inks and coatings are also significant. Other examples of thermoset plastics and their product applications are:

Polyuret h anes:

- mattresses- cushions- insulation- ski boots- toys

Unsaturated Polyesters:

- lacquers- varnishes- boat hulls- furniture

Epoxies:

- glues- coating for electricalcircuits- helicopter blades

A Thermoplastic is a polymer in which the molecules are held together by weak secondary bondingforces that soften when exposed to heat and return to its original condition when cooled back down toroom temperature. When a thermoplastic is softened by heat, it can then be shaped by extrusion,molding or pressing. Ice cubes are a common household item which exemplify the thermoplasticprinciple. Ice will melt when heated but readily solidifies when cooled. Like a polymer, this process maybe repeated numerous times. Thermoplastics offer versatility and a wide range of applications. Theymake up the greatest share of plastics used in food packaging because they can be rapidly andeconomically formed into any shape needed to fulfill the packaging function. Examples include milk jugsand soda bottles. Other examples of thermoplastics are:

Polyet h ylene: Polypropylene: Polyvinyl c h loride


3/20

- packaging- electrical insulation- milk and water bottles- packaging film- house wrap- agricultural film

- carpet fibers- automotive bumpers- microwave containers- external prosthesesyes

(PVC):

- sheathing for electricalcables- floor and wall coverings- siding

- credit cards- automobile instrumentpanels

Processing Met h ods

There are a variety of different processing methods used to convert resins into finished products. Someinclude:

Extrusion - This continuous process is used for the production of semi-finished goods such as films,sheet profiles, tubs and pipes. They are termed "semi-finished" because they must be further processedbefore they become useful articles. Plastic material is first loaded into a hopper and then fed into a longheated chamber through which it is moved by the action of a continuously revolving screw. At the end of the heated chamber, the molten plastic is forced out through a small opening called a die that is cast inthe shape of the finished product. As the plastic extrusion comes from the die, it is fed onto a conveyor belt where it is cooled by blowers or by immersion in water. The operation's principle is the same as thatof a meat mincer but with added heaters in the wall of the extruder. Examples of products include lawnedging, pipe, film and window trim.

Injection molding - Since this process can produce moldings of high quality and with great accuracy, itis very widespread. It is predominately used for thermoplastics but smaller amounts of thermosets andelastomers are also processed this way. In injection molding, plastic material is also put into a hopper,which feeds into a heating chamber. A plunger pushes the plastic through the heating chamber wherethe material is then softened into a fluid state. At the end of this chamber, the resin is forced into aclosed mold. Once the plastic cools to a solid state, the mold opens and the finished product is ejected.This process is used to make such items as butter tubs, yogurt containers, closures, fittings and razors.

Blow molding - Blow molding is a process used in conjunction with extrusion. The die forms a moltentube of thermoplastic material. Using compressed air, the tube is then blown to conform to the interior of a chilled mold which clamps around the tube. Overall, the goal is to produce a uniform melt, form it intoa tube with the desired cross section and blow it into the exact shape of the product. This process isintended for use in manufacturing hollow plastic products and its principal advantage is its ability toproduce hollow shapes without having to join two or more separately molded parts. This method is usedto make items such as commercial drums and bottles.

Rotational Molding - This process is relatively simple in concept since heat is used to melt and fuse aplastic resin inside a closed mold without using pressure. Rotational molding consists of a moldmounted on a machine capable of rotating on two axes simultaneously. Solid or liquid resin is thenplaced within the mold and heat is then applied. Rotation distributes the plastic into a uniform coating onthe inside of the mold until the plastic part cools and sets. This process is used to make hollowconfigurations. Common rotationally molded products include shipping drums, storage tanks and someconsumer furniture and toys.

ReferenceWeb site : www.plasticsresource.com

Back


4/20

Plastic

The term " plastics " covers a range of synthetic or semi-synthetic polymerization products. They arecomposed of organic condensation or addition polymers and may (often) contain other substances toimprove performance or economics. There are few natural polymers generally considered to be" plastics ". Plastics can be formed into objects or films or fibers. Their name is derived from the fact that

many are malleable, having the property of plasticity. Plastics are designed with immense variation inproperties such as heat tolerance, hardness, resiliency and many others. Combined with thisadaptability, the general uniformity of composition and light weight of plastics ensures their use inalmost all industrial segments.

Polymerization is a process of reacting monomer molecules together in a chemicalreaction to form linear chains or a three-dimensional network of polymer chains .There are many forms of polymerization and different systems exist to categorizethem.

The main categories area.addition polymerization b. step-growth polymerization.

"Plastic " may also refer to any material characterized by deformation or failure under shear stress

Plastics can be classified in many ways but most commonly by their polymer back-bone (polyvinyl chloride, polyethylene, acrylic, silicone, urethane, etc.) . Other classifications include thermoplastic vs.thermoset, elastomer vs. engineering plastic, addition or condensation, and Glass transitiontemperature or T g.

Many plastics are partially crystalline and partially amorphous in molecular structure, giving them both amelting point (the temperature at which the covalent bonds dissolve) and one or more glass transitions

(temperatures at which the degree of cross-linking is substantially reduced.) Plastics are polymers: long-chains of atoms bonded to one another. These chains are made up of manyrepeating molecular units, or " monomers ". The vast majority of plastics are composed of polymers of carbon alone or with oxygen, nitrogen, chlorine or sulfur in the back-bone. (Some of commercial interestare silicon based.) The back-bone is that part of the chain on the main "path" linking the multitude of monomer units together. To customize the properties of a plastic different molecular groups "hang" fromthe back-bone (usually they are "hung" as part of the monomers before linking monomers together toform the polymer chain). This customization by pendant groups has allowed plastics to become such anindispensable part of 21st century life by fine-tuning the properties of the polymer.

The development of plastics has come from the use of natural materials (e.g. chewing gum, shellac) tothe use of chemically modified natural materials (e.g. natural rubber, nitrocellulose) and finally to

completely man-made molecules (e.g. epoxy, polyvinyl chloride, polyethylene). 01 Natural polymers

People have been using artificial organic polymers for centuries in the form of waxes and shellacs. Aplant polymer named "cellulose" provides the structural strength for natural fibers and ropes, and by theearly 19th century natural rubber, tapped from rubber trees, was in widespread use.


5/20

Eventually, inventors learned to improve the properties of natural polymers. Natural rubber wassensitive to temperature, becoming sticky and smelly in hot weather and brittle in cold weather. In 1834,two inventors, Friedrich Ludersdorf of Germany and Nathaniel Hayward of the US, independentlydiscovered that adding sulfur to raw rubber helped prevent the material from becoming sticky.

In 1839, the American inventor Charles Goodyear was experimenting with the sulfur treatment of natural

rubber when, according to legend, he dropped a piece of sulfur-treated rubber on a stove. The rubber seemed to have improved properties, and Goodyear followed up with further experiments, anddeveloped a process known as " vulcanization " that involved cooking the rubber with sulfur. Comparedto untreated natural rubber, Goodyear's " vulcanized rubber " was stronger, more resistant to abrasion,more elastic, much less sensitive to temperature, impermeable to gases, and highly resistant tochemicals and electric current.

Vulcanization remains an important industrial process for the manufacture of rubber in both natural andartificial forms. Natural rubber is composed of an organic polymer named " isoprene ". Vulcanizationcreates sulfur bonds that link separate isoprene polymers together, improving the material's structuralintegrity and its other properties.

02. Cellulose based plastics: celluloid and rayon

All Goodyear had done with vulcanization was improve the properties of a natural polymer. The nextlogical step was to use a natural polymer, cellulose, as the basis for a new material.

Inventors were particularly interested in developing synthetic substitutes for those natural materials thatwere expensive and in short supply, since that meant a profitable market to exploit. Ivory was aparticularly attractive target for a synthetic replacement.

An Englishman from Birmingham, named Alexander Parkes developed a "synthetic ivory" named"pyroxlin", which he marketed under the trade name "Parkesine", and which won a bronze medal at the1862 World's fair in London. Parkesine was made from cellulose treated with nitric acid and a solvent.The output of the process hardened into a hard, ivory-like material that could be molded when heated.

However, Parkes was not able to scale up the process to an industrial level, and products made fromParkesine quickly warped and cracked after a short period of use. An American printer and amateur inventor named John Wesley Hyatt took up where Parkes left off. Parkes had failed for lack of a proper softener, but Hyatt discovered that camphor would do the job very nicely.

Hyatt was something of an industrial genius who understood what could be done with such ashapeable, or "plastic", material, and proceeded to design much of the basic industrial machineryneeded to produce good-quality plastic materials in quantity. Since cellulose was the main constituentused in the synthesis of his new material, Hyatt named it "celluloid". It was introduced in 1863.

One of the first products were dental pieces, and sets of false teeth built around celluloid provedcheaper than existing rubber dentures. However, celluloid dentures tended to soften when hot, makingtea drinking tricky, and the camphor taste tended to be difficult to suppress.

Celluloid's real breakthrough products were waterproof shirt collars, cuffs, and the false shirt frontsknown as "dickies", whose unmanageable nature later became a stock joke in silent-movie comedies.They didn't wilt and didn't stain easily, and Hyatt sold them by trainloads. Corsets made with celluloidstays also proved popular, since perspiration didn't rust the stays, as it would if they had been made of metal.

Celluloid proved extremely versatile in its field of application, providing a cheap and attractivereplacement for ivory, tortoiseshell, and bone, and traditional products that had used these materials


6/20

were much easier to fabricate with plastics. Some of the items made with cellulose in the 19th centurywere beautifully designed and implemented. For example, celluloid combs made to tie up the longtresses of hair fashionable at the time are now jewel-like museum pieces. Such pretty trinkets were nolonger only for the rich.

Celluloid could also be used in entirely new applications. Hyatt figured out how to fabricate the material

in a strip format for movie film. By the year 1900, movie film was a major market for celluloid. However, celluloid still tended to yellow and crack over time, and it had another, more dangerousdefect: it burned very easily and spectacularly, unsurprising given that mixtures of nitric acid andcellulose are also used to synthesize smokeless powder.

Ping-pong balls, one of the few products still made with celluloid, sizzle and burn if set on fire, and Hyattliked to tell stories about celluloid billiard balls exploding when struck very hard. These stories mighthave had a basis in fact, since the billiard balls were often celluloid covered with paints based onanother, even more flammable, nitrocellulose product known as "collodion". If the balls had beenimperfectly manufactured, the paints might have acted as primer to set the rest of the ball off with abang.

Cellulose was also used to produce cloth. While the men who developed celluloid were interested inreplacing ivory, those who developed the new fibers were interested in replacing another expensivematerial, silk.

In 1884, a French chemist, the Comte de Chardonnay, introduced a cellulose-based fabric that becameknown as "Chardonnay silk". It was an attractive cloth, but like celluloid it was very flammable, aproperty completely unacceptable in clothing. After some ghastly accidents, Chardonnay silk was takenoff the market.

In 1894, three British inventors, Charles Cross, Edward Bevan, and Clayton Beadle, patented a new"artificial silk" or "art silk" that was much safer. The three men sold the rights for the new fabric to theFrench Courtauld company, a major manufacturer of silk, which put it into production in 1905, usingcellulose from wood pulp as the "feedstock" material.

Art silk became well known under the trade name "rayon", and was produced in great quantities throughthe 1930s, when it was supplanted by better artificial fabrics. It still remains in production today, often inblends with other natural and artificial fibers. It is cheap and feels smooth on the skin, though it is weakwhen wet and creases easily. It could also be produced in a transparent sheet form known as"cellophane".

03. Bakelite (p h enolic)

The limitations of celluloid led to the next major advance, known as "phenolic" or "phenol-formaldehyde"plastics. A chemist named Leo Hendrik Baekeland, a Belgian-born American living in New York state,was searching for an insulating shellac to coat wires in electric motors and generators. Baekeland foundthat mixtures of phenol (C6H5OH) and formaldehyde (HCOH) formed a sticky mass when mixedtogether and heated, and the mass became extremely hard if allowed to cool and dry.

He continued his investigations and found that the material could be mixed with wood flour, asbestos, or slate dust to create "composite" materials with different properties. Most of these compositions werestrong and fire-resistant. The only problem was that the material tended to foam during synthesis, andthe resulting product was of unacceptable quality.

Baekeland built pressure vessels to force out the bubbles and provide a smooth, uniform product. Hepublicly announced his discovery in 1909, naming it "bakelite". It was originally used for electrical and


7/20

mechanical parts, finally coming into widespread use in consumer goods in the 1920s. When theBakelite patent expired in 1927, the Catalin Corporation acquired the patent and began manufacturingCatalin plastic using a different process that allowed a wider range of coloring.

Bakelite was the first true plastic. It was a purely synthetic material, not based on any material or evenmolecule found in nature. It was also the first "thermoset" plastic. Conventional "thermoplastics" can be

molded and then melted again, but thermoset plastics form bonds between polymers strands when"cured", creating a tangled matrix that cannot be undone without destroying the plastic. Thermosetplastics are tough and temperature resistant.

Bakelite was cheap, strong, and durable. It was molded into thousands of forms, such as radios,telephones, clocks, and, of course, billiard balls. The U.S. government even considered making one-cent coins out of it when World War II caused a copper shortage.

Phenolic plastics are still in widespread use. For example, some electronic circuit boards are made of sheets of paper or cloth impregnated with phenolic resin.

04. Polystyrene and PVC

After the First World War, improvements in chemical technology led to an explosion in new forms of plastics. Among the earliest examples in the wave of new plastics were "polystyrene" (PS) and"polyvinyl chloride" (PVC), developed by the I.G. Farben company of Germany.

Polystyrene is a rigid, brittle plastic that is now used to make plastic model kits, disposable eatingutensils, and similar knicknacks. It would also be the basis for one of the most popular "foamed"plastics, under the name "styrene foam" or "Styrofoam". Foam plastics can be synthesized in an "opencell" form, in which the foam bubbles are interconnected, as in an absorbent sponge, and "closed cell",in which all the bubbles are distinct, like tiny balloons, as in gas-filled foam insulation and floatationdevices.

PVC has side chains incorporating chlorine atoms, which form strong bonds. PVC in its normal form isstiff, strong, heat and weather resistant, and is now used for making plumbing, gutters, house siding,enclosures for computers and other electronics gear. PVC can also be softened with chemicalprocessing, and in this form it is now used for shrink-wrap, food packaging, and raingear.

05. Nylon


8/20

The real star of the plastics industry in the 1930s was "polyamide" (PA), far better known by its tradename, "nylon". Nylon was the first purely synthetic fiber, introduced by Du Pont Corporation at the 1936World's Fair in New York City.

In 1927, Du Pont had begun a secret development project designated "Fiber66", under the direction of aHarvard chemist named Wallace Carothers. Carothers had been hired to perform pure research, and

not only investigated new materials, but worked to understand their molecular structure and how itrelated to material properties. He took some of the first steps on the road to "molecular design" of materials.

His work led to the discovery of synthetic nylon fiber, which was very strong but also very flexible. Thefirst application was for bristles for toothbrushes. However, Du Pont's real target was silk, particularlysilk stockings.

It took Du Pont twelve years and $27 million USD to refine nylon and develop the industrial processesfor bulk manufacture. With such a major investment, it was no surprise that Du Pont spared littleexpense to promote nylon after its introduction, creating a public sensation, or "nylon mania". Nylonmania came to an abrupt stop at the end of 1941, when America entered World War II. The productioncapacity that had been built up to produce nylon stockings, or just "nylons", for American women, wastaken over to manufacture vast numbers of parachutes for fliers and paratroopers. After the war ended,Du Pont went back to selling nylon to the public, engaging in another promotional campaign in 1946 thatresulted in an even bigger craze, triggering off "nylon riots".

Nylon still remains an important plastic, and not just for use in fabrics. In its bulk form it is very wear-resistant, and so is used to build gears, bearings, bushings, and other mechanical parts.

06. Synt h etic rubber

Another plastic that was critical to the war effort was "synthetic rubber", which was produced in a varietyof forms.

First synthetic rubber polymer was obtained by Lebedev in 1910 Practical synthetic rubber grew out of studies published in 1930 written independently by American Wallace_Carothers, Russian scientistLebedev and the German scientist Hermann Staudinger. These studies led in 1931 to one of the firstsuccessful synthetic rubbers, known as "neoprene". Neoprene is highly resistant to heat and chemicalssuch as oil and gasoline, and is used in fuel hoses and as an insulating material in machinery.

In 1935, German chemists synthesized the first of a series of synthetic rubbers known as "Bunarubbers". These were "copolymers", meaning that their polymers were made up from not one but twomonomers, in alternating sequence. One such Buna rubber, known as "GR-S" ("Government Rubber Styrene), is a copolymer of butadiene and styrene, became the basis for US synthetic rubber productionduring World War II.

Worldwide natural rubber supplies were limited, and by mid-1942 most of the rubber-producing regionswere under Japanese control. Military trucks needed rubber for tires, and rubber was used in almost


9/20

every other war machine. The US government launched a major (and largely secret) effort to developand refine synthetic rubber. A principal scientist involved with the effort was Edward Robbins.

By 1944 a total of 50 factories were manufacturing it, pouring out a volume of the material twice that of the world's natural rubber production before the beginning of the war.

After the war, natural rubber plantations no longer had a stranglehold on rubber supplies, particularlyafter chemists learned to synthesize isoprene. GR-S remains the primary synthetic rubber for themanufacture of tires.

Synthetic rubber would also play an important part in the space race and nuclear arms race. Solidrockets used during World War II used nitrocellulose explosives for propellants, but it was impracticaland dangerous to make such rockets very big.

During the war, California Institute of Technology (Caltech) researchers came up with a new solid fuel,based on asphalt fuel mixed with an oxidizer, such as potassium or ammonium percholorate, plusaluminum powder, which burns very hot. This new solid fuel burned more slowly and evenly thannitrocellulose explosives, and was much less dangerous to store and use, though it tended to flowslowly out of the rocket in storage and the rockets using it had to be stockpiled nose-down.

After the war, the Caltech researchers began to investigate the use of synthetic rubbers instead of asphalt as the fuel in the mixture. By the mid-1950s, large missiles were being built using solid fuelsbased on synthetic rubber, mixed with ammonium perchlorate and high proportions of aluminumpowder. Such solid fuels could be cast into large, uniform blocks that had no cracks or other defects thatwould cause nonuniform burning. Ultimately, all large military rockets and missiles would use syntheticrubber based solid fuels, and they would also play a significant part in the civilian space effort.

07. Plastics explosion: acrylic, polyet h ylene, etc

Other plastics emerged in the prewar period, though some wouldn't come into widespread use until after the war.

By 1936, American, British, and German companies were producing polymethyl methacrylate (PMMA),better known as acrylic. Although acrylics are now well-known for the use in paints and synthetic fibers,such as "fake furs", in their bulk form they are actually very hard and more transparent than glass, andare sold as glass replacements under trade names such as "Plexiglas" and "Lucite". Plexiglas was usedto build aircraft canopies during the war, and it is also now used as a marble replacement for countertops.

Another important plastic, "polyethylene" (PE), sometimes known as "polythene", was discovered in1933 by Reginald Gibson and Eric Fawcett at the British industrial giant Imperial Chemical Industries(ICI). This material evolved into two forms, "low density polyethylene" (LDPE), and "high densitypolyethylene" (HDPE).


10/20

PEs are cheap, flexible, durable, and chemically resistant. LDPE is used to make films and packagingmaterials, while HDPE is used for containers, plumbing, and automotive fittings. While PE has lowresistance to chemical attack, it was found later that a PE container could be made much more robustby exposing it to fluorine gas, which modified the surface layer of the container into the much tougher "polyfluoroethylene".

Polyethylene would lead after the war to an improved material, "polypropylene" (PP), which wasdiscovered in the early 1950s by Giulio Natta. It is common in modern science and technology that thegrowth of the general body of knowledge can lead to the same inventions in different places at about thesame time, but polypropylene was an extreme case of this phenomenon, being separately inventedabout nine times. It was a patent attorney's dream scenario, and litigation wasn't resolved until 1989.

Polypropylene managed to survive the legal process, and two American chemists working for PhillipsPetroleum of the Netherlands, J. Paul Hogan and Robert Banks, are now generally credited as the"official" inventors of the material. Polypropylene is similar to its ancestor, polyethylene, and sharespolyethylene's low cost, but it is much more robust. It is used in everything from plastic bottles to carpetsto plastic furniture, and is very heavily used in automobiles.

Polyurethane was invented by Friedrich Bayer & Company of Germany in 1937, and would come intouse after the war, in blown form for mattresses, furniture padding, and thermal insulation. It is also usedin non-blown form for sports wear as "lycra".

In 1939, I.G. Farben Industrie of Germany filed a patent for "polyepoxide" or "epoxy". Epoxies are aclass of thermoset plastic that form cross-links and "cure" when a catalyzing agent, or "hardener", isadded. After the war they would come into wide use for coatings, "adhesives", and composite materials.

Composites using epoxy as a matrix include glass-reinforced plastic, where the structural element isglass fiber, and "carbon-epoxy composites", in which the structural element is carbon fiber. Fiberglass isnow often used to build sport boats, and carbon-epoxy composites are an increasingly importantstructural element in aircraft, as they are lightweight, strong, and heat-resistant.

Two chemists named Rex Whinfield and James Dickson, working at a small English company with thequaint name of the "Calico Printer's Association" in Manchester, developed "polyethylene terephthalate"(PET or PETE) in 1941, and it would be used for synthetic fibers in the postwar era, with names such as"polyester", "dacron", and "terylene".

PET is more impermeable than other low-cost plastics and so is a popular material for making bottlesfor Coca-Cola and other "fizzy drinks", since carbonation tends to attack other plastics, and for acidicdrinks such as fruit or vegetable juices. PET is also strong and abrasion resistant, and is used for making mechanical parts, food trays, and other items that have to endure abuse. PET films,tradenamed "Mylar", are used to make recording tape.

One of the most impressive plastics used in the war, and a top secret, was "polytetrafluoroethylene"(PTFE), better known as "teflon", which could be deposited on metal surfaces as a scratchproof andcorrosion-resistant, low-friction protective coating. The polyfluoroethylene surface layer created byexposing a polyethylene container to fluorine gas is very similar to teflon.


11/20


12/20

pollutants, and required use of the Earth's limited supply of fossil fuels. However, it should be noted thatplastics only consume 4% of world's oil production. Furthermore, it can be claimed that the use of plastics helps the environment by saving water and oil. For example, plastics make cars lighter, thussaving oil and reducing CO 2 emissions.

By the 1990s, plastic recycling programs were common in the United States and elsewhere.

Thermoplastics can be remelted and reused, and thermoset plastics can be ground up and used asfiller, though the purity of the material tends to degrade with each reuse cycle. There are methods bywhich plastics can be broken back down to a feedstock state.

To assist recycling of disposable items, the Plastic Bottle Institute of the Society of the Plastics Industrydevised a now-familiar scheme to mark plastic bottles by plastic type. A recyclable plastic container using this scheme is marked with a triangle of three "chasing arrows", which enclose a number givingthe plastic type:

Plastics type marks: the resin identification code

- PETE - Polyethylene Terephthalate , Commonly found on: 2-litre soft drink bottles, cooking oil bottles,peanut butter jars.- HDPE - High Density Polyethylene , Commonly found on: detergent bottles, milk jugs.- PVC - Polyvinyl Chloride , Commonly found on: plastic pipes, outdoor furniture, shrink wrap, water bottles, salad dressing and liquid detergent containers.- LDPE - Low Density Polyethylene , Commonly found on: dry cleaning bags, produce bags, trash canliners, food storage containers.- PP - Polypropylene - , Commonly found on: bottle caps, drinking straws- PS - Polystyrene , Commonly found on: packaging pellets or "Styrofoam peanuts," cups, plastictableware, meat trays, take away food clam shell containers- OTHER - This plastic category, as its name of "other" implies, is any plastic other than the named #1-#6, Commonly found on: certain kinds of food containers and Tupperware.

Unfortunately, recycling plastics proved difficult. The biggest problem with plastics recycling is that it isdifficult to automate the sorting of plastic waste, and so it is labor-intensive. While containers are usuallymade from a single type and color of plastic, making them relatively easy to sort out, a consumer product like a cellular phone may have many small parts consisting of over a dozen different types andcolors of plastics. As the value of the material is low, recycling plastics is unprofitable. For this reason,the percentage of plastics recycled in the US is very small, somewhere around 5%. Even so the

American Plastics Council spends about 20 million dollars a year on an ad campaign that tries toconvince the public that plastic recycling works.


13/20

Recently it was shown, however, that for post-consumer plastic waste, gasification offers a solution for the recycling of such material.

Research has been done on "biodegradable" plastics that break down with exposure to sunlight. Starchcan be mixed with plastic to allow it to degrade more easily, but it still doesn't lead to completebreakdown of the plastic. Some researchers have actually genetically engineered bacteria that

synthesize a completely biodegradable plastic, but this material is expensive at present. BASF makeEcoflex, a fully biodegradable polyester for food packaging applications. The disadvantage of biodegradable plastics is that the carbon that is locked up in them is released into the atmosphere asthe greenhouse gas carbon dioxide when they degrade.

So far, these plastics have proven too costly and limited for general use, and critics have pointed outthat the only real problem they address is roadside litter, which is regarded as a secondary issue. Whensuch plastic materials are dumped into landfills, they can become "mummified" and persist for decadeseven if they are supposed to be biodegradable. In this regard though plastics are no worse than food or paper which also fails to degrade in landfills.

There have been some success stories. The Courtauld concern, the original producer of rayon, cameup with a revised process for the material in the mid-1980s to produce "Tencel". Tencel has many

superior properties over rayon, but is still produced from "biomass" feedstocks, and its manufacture isextraordinarily clean by the standards of plastic production.

09. Price and t h e future

One of the great appeals of plastics have been their low price, as compared to other materials.However, in recent years the cost of plastics has been rising dramatically. The cause of the increase isthe sharply rising cost of petroleum, the raw material that is chemically altered to form commercialplastics. As the cost of plastic hinges on the cost of petroleum, should petroleum prices continues torise, so will the cost of plastic. In 2004, the higher price of plastic drove a number of plastic toymanufacturers out of business.

Fears of dwindling petroleum supplies are becoming very real, with publications such as USA Today

reporting that current oil reserves will only last 40 years. Alternate reserves such as oil shale and tar oil(tar sand) do exist, but the cost of production is much higher than with current sources. Thus, even if alternative sources are used, costs will continue to rise.

Scientists are seeking cheaper alternatives to plastic. Some plastic alternatives are: graphite, fiberglass,carbon fiber, graphene, carbon nanotubes, diamond, aerogel, carbon nanofoam, cellulose soybeanplastic (bioplastic), and other carbon-based non-petroleum materials. Some of these alternatives are tooexpensive or not malleable enough, but can be used in some plastic applications. Some are many timesthe strength of plastic, but crack if made thin like cellophane. The most promising alternatives to plasticare graphene, carbon nanotube, and carbon nanofoam. All three of these are made of nanocarbons,products of the new nanotechnology. Nanocarbons are very cheap, 100 times stronger than steel,slicker than Teflon, lightweight, and can be made very thin, made to stretch, and built into any shape -all the things plastic can do. In addition, nanocarbon manufacturing is low- to non-polluting. Already

bowling balls, golf balls, sports equipment, and water-proof cotton balls have been made of nanocarbons.

10. Common plastics and t h eir typical uses

a . polyet h ylene (P E)wide range of uses, very inexpensive


14/20

Polyethylene or polyethene is an engineering thermoplastic heavily used in consumer products. Itsname originates from the monomer ethene used to create the polymer.

In the polymer industry the name is sometimes shortened to PE, similar to how other polymers likepolypropylene and polystyrene are shortened to PP and PS, respectively. In the United Kingdom thepolymer is called polythene. (e.g. in the Beatles song Polythene Pam).

The ethene molecule (known almost universally by its non-IUPAC name ethylene), C2H4 is CH2 = CH2,Two CH2 connected by a double bond, thus

Polyethylene is created through polymerization of ethene. It can be produced through radicalpolymerization, anionic polymerization, and cationic polymerization. This is because ethene does nothave any substituent groups which influence the stability of the propagation head of the polymer. Eachof these methods results in a different type of polyethylene.

Classification of polyet h ylenes

Polyethylene is classified into several different categories based mostly on its mechanical properties.The mechanical properties of PE depend significantly on variables such as the extent and type of branching, the crystal structure, and the molecular weight.

UHMWPE (ultra high molecular weight PE)HDPE (high density PE)LDPE (low density PE)LLDPE (linear low density PE)UHMWPE is polyethylene with a molecular weight numbering in the millions, usually between 3.1 and5.67 million. The high molecular weight results a very good packing of the chains into the crystalstructure. This results in a very tough material. UHMWPE is made through metallocene catalysispolymerization.

HDPE has little branching and thus stronger intermolecular forces and tensile strength. The lack of branching is ensured by an appropriate choice of catalyst (e.g. Ziegler-Natta catalysts) and reactionconditions.

LDPE has many more branches than HDPE, which means that the chains do pack into the crystalstructure as well. It has therefore less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility. LDPE is createdby free radical polymerization.


15/20

LLDPE is a substantially linear polymer, with significant numbers of short branches, commonly made bycopolymerization of ethylene with longer-chain olefins.

UHMWPE is used in high modulus fibers and in bulletproof vests. The most common household use of HDPE is in containers for milk, liquid laundry detergent, etc; the most common household use of LDPEis in plastic bags. LLDPE is used primarily in flexible tubing.

Recently, much research activity has focused on Long Chain Branched polyethylene. This is essentiallyHDPE, but has a small amount (perhaps 1 in 100 or 1000 branches per backbone carbon) of very longbranches. These materials combine the strength of HDPE with the processability of LDPE.

b . polypropylene (PP)food containers, appliances

Polypropylene (PP) is a thermoplastic polymer, used in a wide variety of applications, including foodpackaging, textiles, laboratory equipment, and polymer banknotes. An addition polymer made from themonomer propylene, it is unusually resistant to many chemical solvents, bases and acids.

Most commercial polypropylene has a level of crystallinity intermediate between that of low density

polyethylene (LDPE) and high density polyethylene (HDPE); its Young's modulus is also intermediate. Although it is less tough than LDPE, it is much less brittle than HDPE. This allows polypropylene to beused as a replacement for engineering plastics, such as ABS. Polypropylene has very good resistanceto fatigue, so that most plastic living hinges, such as those on flip-top bottles, are made from thismaterial.

Polypropylene has a melting point of 320 degrees farenheit and 160 degrees celsius. Food containersmade from it will not melt in the dishwasher, and do not melt during industrial hot filling processes. For this reason, most plastic tubs for dairy products are polypropylene sealed with aluminium foil (both heat-resistant materials). After the product has cooled, the tub are often given lids of a cheaper (and lessheat-resistant) material, such as LDPE or polystyrene. Such containers provide a good hands-onexample of the difference in modulus, since the rubbery feeling of LDPE with respect to PP of the samethickness is readily apparent.

A rubbery PP can be also be made by a specialized synthesis process, as discussed below. Unliketraditional rubber, it can be melted and recycled, making it a thermoplastic elastomer.

c . polystyrene (PS)packaging foam, food containers, disposable cups, plates and cutlery

Polystyrene is a polymer made from the monomer styrene, a liquid hydrocarbon that is commerciallymanufactured from petroleum. At room temperature, polystyrene is normally a solid thermoplastic, butcan be melted at higher temperature for molding or extrusion, then resolidified. Styrene is an aromaticmonomer, and polystyrene is an aromatic polymer.

Polystyrene was first manufactured by BASF in the 1930s, and is used in numerous plastic products.Pure solid polystyrene is a colorless, harder plastic with limited flexibility which can be cast into moldswith fine detail. Polystyrene can be transparent or can be made to take on various colors. It iseconomical and is used for producing plastic model assembly kits, plastic cutlery, and many other objects where a fairly rigid, economical plastic of any of various colors is desired. Polystyrene fabricatedinto a sheet can be stamped (formed) into economic, disposable cups, glasses, bowls, lids, and other items, especially when high strength, durability, and heat resistance are not essential. A thin layer of transparent polystyrene is often used as an infra-red spectroscopy standard.


16/20

Polystyrene's most common use, however, is as expanded polystyrene, which is a mixture of about 5%polystyrene and 95% air. This is the lightweight material of which coffee cups and takeaway foodcontainers are made. The voids filled with trapped air give expanded polystyrene low thermalconductivity. It is also used as insulation in building structures, as packing material for cushioning insideboxes, as non-weight bearing architectural structures (such as pillars) and also in crafts and modelbuilding, particularly architectural models. Foamed between two sheets of paper, it makes a more-uniform substitute for corrugated cardboard tradenamed Foamcore.

In the USA it is made by the Dow Chemical Company under the tradename Styrofoam. The wordstyrofoam is often used by the general public in the United States to indicate any brand of polystyrenefoam (see genericized trademark).

Expanded polystyrene used to contain CFCs but other, more environmentally-safe blowing agents arenow used.

Because it is an aromatic hydrocarbon, polystyrene is flammable and burns with an orange-yellow flamegiving off soot, as opposed to non-aromatic hydrocarbon polymers such as polyethylene, which burnwith a light yellow flame (often with a blue tinge) and no soot.

d . polyet h ylene terep h th alate (P ET E)beverage containers

Polyethylene terephthalate (aka. PET, PETE, PETP) is a plastic resin of the polyester family that is usedto make beverage, food and other liquid containers, as well as for some other thermoformingapplications. It is also one of the most important raw materials used in man-made fibers. Depending onits processing and thermal history, it may exist both as an amorphous (transparent) and as a semi-crystalline (opaque and white) material. It can be synthesized by a transesterification reaction betweenethylene glycol and dimethyl terephthalate.

e . Polyamide (PA) (Nylon)fibres, toothbrush bristles, fishing line

Nylon is a synthetic polymer, a plastic, invented on February 28, 1935 by Wallace Carothers at DuPontof Wilmington, Delaware, USA. The material was announced in 1938 and the first nylon products; anylon bristle toothbrush made with nylon yarn (went on sale on February 24, 1938) and more famously,women's stockings (went on sale on May 15, 1940). Nylon fibres are now used to make many syntheticfabrics, and solid nylon is used as an engineering material.

f . polyester fibres, textiles

Polyester is a category of polymers, or, more specifically condensation polymers, which contain theester functional group in their main chain. Although polyesters do exist in nature, polyester generallyrefers to the large family of synthetic polyesters (plastics) which includes polycarbonate and above allpolyethylene terephthalate (PET). PET is one of the most important thermoplastic polyesters.

The first synthetic polyester, glycerine phthalate, was used in the First World War for waterproofing.Natural polyesters have been known since around 1830.

g . polyvinyl c h loride (PVC)plumbing pipes, flooring, erotic clothing

Polyvinyl chloride (PVC) is a widely-used plastic. In terms of revenue generated, it is one of the mostvaluable products of the chemical industry. Globally, over 50% of PVC manufactured is used in


17/20

construction. As a building material PVC is cheap, and easy to assemble. In recent years, PVC hasbeen replacing traditional building materials such as wood, concrete and clay in many areas. Despiteappearing to be an ideal building material, concerns have been raised about the environmental andhuman health costs of PVC.

Polyvinyl chloride is produced from its monomer, vinyl chloride (chemical formula CH2=CHCl). PVC is a

hard plastic that is made softer and more flexible by the addition of plasticizers, the most widely usedbeing phthalates.

There are many uses for PVC including vinyl siding, window profiles, gramophone records (hence theones made of this material are sometimes called vinyl records) pipe/plumbing/conduit fixtures, beanbags; and, in its soft form, for clothing, upholstery (car seats), flooring, roofing membranes, electricalcables, etc

h . polycarbonatecompact discs, eyeglasses

Polycarbonates are a particular group of thermoplastics. They are easily worked, mold, andthermoformed; as such, these plastics are very widely used in modern manufacturing. They are called

polycarbonates because they are polymers having monomers groups linked together by carbonategroups (-O-CO-O-) in a long molecular chain.

The most common type of polycarbonate plastic is one made from Bisphenol A, where groups fromBisphenol A are linked together by carbonate groups in a polymer chain. This polycarbonate is a verydurable material, and can be laminated to make bullet-proof "glass", though bullet-resistant would bemore accurate. The characteristics of polycarbonate are quite like those of polymethyl methacrylate(acrylic), but polycarbonate is stronger and thus more expensive. This polymer is mainly transparentand has better light transmission characteristics than glasses.

Polycarbonate has :a density of 1.20 g/cm3a use range from -100C to +135C

a melting point around 250Ca refractive index equal to 1.585 0.001a light transmission index equal to 90% 1%Polycarbonate is becoming more common in housewares as well as laboratories and in industry. It isoften used to create protective features, for example in banks as well as vandal-proof windows andlighting lenses for many buildings. Other products made from polycarbonate include sunglass/eyeglasslenses, compact discs and DVDs.

i. acrylonitrile butadiene styrene (ABS)

electronic equipment cases (e.g. computer monitors, printers, keyboards)

Acrylonitrile butadiene styrene, or ABS, (chemical formula ) is acommon thermoplastic used to make light, rigid, moulded products such as pipes, golf club heads (usedfor its good shock absorbance), enclosures and toys including LEGO Bricks. It is a copolymer made bypolymerizing styrene and acrylonitrile in the presence of polybutadiene. The proportions can vary from15% to 35% acrylonitrile, 5% to 30% butadiene and 40% to 60% styrene. The result is a long chain of polybutadiene criss-crossed with shorter chains of poly(styrene-co-acrylonitrile). The nitrile groups fromneighbouring chains, being polar, attract each other and bind the chains together, making ABS stronger than pure polystyrene. The styrene gives the plastic a shiny, impervious surface. The butadiene, arubbery substance, provides resilience even at low temperatures. ABS can be used between -25C and+60C.


18/20

Production of 1 kg of ABS requires the equivalent of about 2 kg of oil for raw materials and energy.

Today, ABS is produced through a special process called grafting, rather than the copolymerization of acrylonitrile, styrene, and butadiene. In grafting, butadiene is polymerized first, then the cyanide andphenyl groups are added through a special chemical reaction.

j . polyvinylidene ch

loride (PVDC)food packaging

Polymerizing vinylide chloride with monomers such as acrylic esters and unsaturated carboxyl groups,forming long chains of vinylide chloride. The copolymerization results in a film with molecules bound sotightly together that very little gas or water can get through. The result is a barrier against oxygen,moisture, chemicals and heat-qualities used to protect food, consumer and industrial products. PVDC isresistant to oxygen, water, acids, bases, and solvents.

11. Special purpose plastics

a . T eflonheat resistant, low-friction coatings

Teflon is the brand name of a polymer compound discovered by Roy J. Plunkett (1910-1994) of DuPontin 1938 and introduced as a commercial product in 1946.

Teflon is polytetrafluoroethylene (PTFE), a polymer of fluoride and ethylene.Teflon is also used as the trade name for a polymer with similar properties, perfluoroalkoxy polymer resin (PFA)

PTFE has the lowest coefficient of friction of any solid material. It is used as a non-stick coating for pansand other cookware. PTFE is very unreactive, and so is often used in containers and pipework for reactive chemicals. Its melting point varies between 260 C (FEP) and 327 C (PTFE), depending onwhich specific Teflon polymer is being discussed.

PTFE is sometimes said to be a spin-off from the US space program with more down-to-earthapplications; this is an urban legend, as teflon cooking pans were commonplace before Yuri Gagarin'sflight in 1961. PTFE was discovered serendipitously by Roy Plunkett of DuPont in 1938, whileattempting to make a new CFC refrigerant, when the perfluorethylene polymerized in its storagecontainer. DuPont patented it in 1941, and registered the Teflon trademark in 1944.

Its first significant use was in the Manhattan Project, as a material to contain highly-reactive uraniumhexafluoride, when it was known as K416.

It was first sold commercially in 1946 and by 1950, DuPont was producing over a million pounds(weight) per year in Virginia.

Teflon has been supplemented with another DuPont product, Silverstone, a three-coat fluoropolymer system that produces a more durable finish than Teflon. Silverstone was released in 1976.

Amongst many other industrial applications, PTFE is used to coat certain types of hardened, armour-piercing bullets, so as to reduce the amount of wear on the firearm's rifling. These are often mistakenlyreferred to as "cop-killer" bullets on account of PTFE's supposed ability to ease a bullet's passagethrough body armour. Any armour-piercing effect is, however, purely a function of the bullet's velocityand rigidity rather than a property of PTFE.


19/20

PTFE has excellent electrical properties especially at radio frequencies, making it eminently suitable for use as an insulator in cables and connector assemblies. Combined with its high melting temperaturethis makes it the material of choice as a high performance substitute for the weaker and more meltablepolyethylene that is commonly used in low-cost applications.

Due to its low friction, it is used for applications where sliding action of parts is needed: bearings,

bushings, gears, slide plates, etc. In these applications it performs significantly better than nylon andacetal; it is comparable with UHMWPE, where teflon displays lower resistance to wear than UHMWPE.For these applications, versions of teflon with mineral oil or molybdenum disulfide embedded asadditional lubricants in its matrix are being manufactured.

b . Polyuret h aneinsulation foam, upholstery foam

A polyurethane is any polymer consisting of a chain of organic units joined by urethane links. It is usedin adhesives, elastomers, foams (both foam rubber and rigid materials), fibers, seals, gaskets,condoms, carpet underlayment, and hard parts.

Production

Polyurethane can be made in a variety of textures and hardnesses by varying the particular monomersused and adding other substances.

Softer polyurethane can be made by adding flexible Polyethylene glycol segments between urethanelinks. This strategy is used to make spandex fibers, as well as foam rubber. Careful control of viscoelastic properties can lead to memory foam, which is much softer at skin temperature than at roomtemperature.

Polyurethane foam (including foam rubber) can be produced by adding a small amount of water to oneof the liquid precursors of polyurethane before they are mixed together. This modifies the polymerizationreaction, causing carbon dioxide to be released as the material cures. Gas is generated throughout theliquid, creating relatively uniform bubbles which then harden to form a solid foam as polymerization

progresses. The small proportion of reactions affected by the water result in urea linkages -NC(O)N-,rather than urethane linkages, so that the resulting material should technically be called poly(urethane-co-urea).

c . Bakeliteinsulating parts in electrical fixtures (it is a thermoseting plastic, aka phenol formaldehyde or phenolicresin, that can be molded by heat and pressure when mixed with a filler like woodflour or can be cast init's unfilled liquid form.)

While commonly referred to as Bakelite, the correct generic designation is phenolics. Phenolics areheat-resistant, thermosetting plastics based on a chemically stable resin(polyoxybenzylmethylenglycolanhydride, the first plastic). Bakelite was developed about 1907-1909 byDr. Leo Baekeland, an American chemist of Belgian descent. It is formed by combining phenol andformaldehyde under heat and pressure. Radios, telephones and electrical insulators were made of phenolics in the past due to its insulating and heat-resistant properties.

Bakelite distributor rotorDue to its hardness and durability when cooled, it was considered as a materialfor making pennies during World War II, due to copper being needed for shell casings. Several patternswere made in 1942, but steel was used instead in 1943 and recycled shell casings in 1944 and 1945.

Bakelite Corp. was formed in 1922 from General Bakelite Co., Condensite Corp. and Redmanol Co. Thecompany was acquired by Union Carbide and Carbon Corp. in 1938.


20/20

Bakelite Limited was formed in 1927 from the amalgamation of three suppliers of phenol formaldehydematerials: the Damard Lacquer Company Limited of Birmingham; Mouldensite Limited of Darley Daleand Redmanol Limited of London. Around 1928, A new factory opened in Tyseley, Birmingham inSeptember 1931. It was demolished in 1998.

Phenolics are little used in consumer products today due to the cost and complexity of its production

and its brittle nature, but old phenolic products, especially kitchenware and toys, have become quitecollectible in recent years. One prevalent use for phenolics because of its heat-resistance is in moldeddisc brake cylinders.

ReferenceWeb site : en.wikipedia.org

Back

how is plastic made

Documents