One type of plastic, known as polyethylene, is composed of extremely long molecules that each contain over , carbon atoms. These long, chainlike molecules give plastics unique properties and distinguish plastics from materials, such as metals, that have short, crystalline molecular structures. Although some plastics are made from plant oils, the majority are made from fossil fuels.
Fossil fuels contain hydrocarbons compounds containing hydrogen and carbon , which provide the building blocks for long polymer molecules.
These small building blocks, called monomers, link together to form long carbon chains called polymers. The process of forming these long molecules from hydrocarbons is known as polymerization. The molecules typically form viscous, sticky substances known as resins, which are used to make plastic products.
Ethylene, for example, is a gaseous hydrocarbon. When it is subjected to heat, pressure, and certain catalysts substances used to enable faster chemical reactions , the ethylene molecules join together into long, repeating carbon chains.
These joined molecules form a plastic resin known as polyethylene. Joining identical monomers to make carbon chains is called addition polymerization, because the process is similar to stringing many identical beads on a string. Plastics made by addition polymerization include polyethylene, polypropylene, polyvinyl chloride, and polystyrene.
Joining two or more different monomers of varying lengths is known as condensation polymerization, because water or other by-products are eliminated as the polymer forms. Condensation polymers include nylon polyamide , polyester, and polyurethane.
For example, elastomers are plastics composed of long, tightly twisted molecules. These coiled molecules allow the plastic to stretch and recoil like a spring. Rubber bands and flexible silicone caulking are examples of elastomers. These side chains give plastics some distinguishing characteristics. For example, when chlorine atoms substitute for hydrogen atoms along the carbon chain, the result is polyvinyl chloride, one of the most versatile and widely used plastics in the world.
The addition of chlorine makes this plastic harder and more heat resistant. Different plastics have advantages and disadvantages associated with the unique chemistry of each plastic. For example, longer polymer molecules become more entangled like spaghetti noodles , which gives plastics containing these longer polymers high tensile strength and high impact resistance.
However, plastics made from longer molecules are more difficult to mold. This table lists the monomers for several major plastics, as well as the properties and uses of each type of plastic.
These terms refer to the different ways these types of plastics respond to heat. Thermoplastics can be repeatedly softened by heating and hardened by cooling. Thermosetting plastics, on the other hand, harden permanently after being heated once. The reason for the difference in response to heat between thermoplastics and thermosetting plastics lies in the chemical structures of the plastics. Thermoplastic molecules, which are linear or slightly branched, do not chemically bond with each other when heated.
Instead, thermoplastic chains are held together by weak van der Waal forces weak attractions between the molecules that cause the long molecular chains to clump together like piles of entangled spaghetti. Thermoplastics can be heated and cooled, and consequently softened and hardened, repeatedly, like candle wax.
For this reason, thermoplastics can be remolded and reused almost indefinitely. Thermosetting plastics consist of chain molecules that chemically bond, or cross- link, with each other when heated.
When thermosetting plastics cross-link, the molecules create a permanent, three-dimensional network that can be considered one giant molecule. Once cured, thermosetting plastics cannot be remelted, in the same way that cured concrete cannot be reset. The different molecular structures of thermoplastics and thermosetting plastics allow manufacturers to customize the properties of commercial plastics for specific applications.
Because thermoplastic materials consist of individual molecules, properties of thermoplastics are largely influenced by molecular weight. For instance, increasing the molecular weight of a thermoplastic material increases its tensile strength, impact strength, and fatigue strength ability of a material to withstand constant stress. Instead, many properties of thermosetting plastics are determined by adding different types and amounts of fillers and reinforcements, such as glass fibers.
Thermoplastics may be grouped according to the arrangement of their molecules. Highly aligned molecules arrange themselves more compactly, resulting in a stronger plastic. For example, molecules in nylon are highly aligned, making this thermoplastic extremely strong. The degree of alignment of the molecules also determines how transparent a plastic is. Thermoplastics with highly aligned molecules scatter light, which makes these plastics appear opaque.
Thermoplastics with semialigned molecules scatter some light, which makes most of these plastics appear translucent. Thermoplastics with random amorphous molecular arrangement do not scatter light and are clear.
Amorphous thermoplastics are used to make optical lenses, windshields, and other clear products. Air, heat, and molds are used to shape the plastic during its formation. Plastic is an increasingly popular manufacturing material because it is relatively durable, inexpensive, and versatile. Many different processes are used to make plastic products, and in each process, the plastic resin must be softened or sufficiently liquefied to be shaped.
A Forming Thermoplastics How Thermoplastics are Formed Thermoplastics are plastics that can be hardened and melted more than once. In the calendering process, continuous plastic sheets are formed by forcing hot plastic between successive sets of heated rollers. Injection molding uses a screw to push plastic through a heated tube into a mold.
Extrusion is a continuous process that heats plastic pellets in a long barrel. A screw pushes the heated plastic through a die opening to form objects such as garden hose and piping. In thermoforming a hot plastic sheet is draped over a mold and a vacuum draws the plastic down into the mold.
Blow molding forms containers from soft, hollow plastic tubes that have a mold fitted around the outside. The tube is heated, and air injected into the heated tube expands the plastic against the walls of the mold. Although some processes are used to manufacture both thermoplastics and thermosetting plastics, certain processes are specific to forming thermoplastics. For more information, see the Casting and Expansion Processes section of this article. The mold is then opened and the plastic cast removed.
Thermoplastic items made by injection molding include toys, combs, car grills, and various containers. A2 Extrusion Plastic Pellets and Extrusion Early in the manufacturing process, small pellets of nylon a synthetic resin are stirred and melted. Once melted, the blue plastic mixture will be forced into the desired shape in a process called extrusion. Extrusion is a continuous process, as opposed to all other plastic production processes, which start over at the beginning of the process after each new part is removed from the mold.
In the extrusion process, plastic pellets are first heated in a long barrel. In a manner similar to that of a pasta-making or sausage-stuffing machine, a rotating screw then forces the heated plastic through a die device used for forming material opening of the desired shape. As the continuous plastic form emerges from the die opening, it is cooled and solidified, and the continuous plastic form is then cut to the desired length.
Melted thermoplastic forced through extremely fine die holes can be cooled and woven into fabrics for clothes, curtains, and carpets. A3 Blow Molding Blow molding is used to form bottles and other containers from soft, hollow thermoplastic tubes. First a mold is fitted around the outside of the softened thermoplastic tube, and then the tube is heated.
Next, air is blown into the softened tube similar to inflating a balloon , which forces the outside of the softened tube to conform to the inside walls of the mold. Once the plastic cools, the mold is opened and the newly molded container is removed.
Blow molding is used to make many plastic containers, including soft-drink bottles, jars, detergent bottles, and storage drums. A4 Blow Film Extrusion Blow film extrusion is the process used to make plastic garbage bags and continuous sheets. This process works by extruding a hollow, sealed-end thermoplastic tube through a die opening. As the flattened plastic tube emerges from the die opening, air is blown inside the hollow tube to stretch and thin the tube like a balloon being inflated to the desired size and wall thickness.
The plastic is then air-cooled and pulled away on take-up rollers to a heat-sealing operation. The heat-sealer cuts and seals one end of the thinned, flattened thermoplastic tube, creating various bag lengths for products such as plastic grocery and garbage bags.
For sheeting flat film , the thinned plastic tube is slit along one side and opened to form a continuous sheet. The air inflates the plastic tube like a balloon, until a bag with the desired shape, size, and wall thickness is formed. A5 Calendering The calendering process forms continuous plastic sheets that are used to make flooring, wall siding, tape, and other products. These plastic sheets are made by forcing hot thermoplastic resin between heated rollers called calenders. A series of secondary calenders further thins the plastic sheets.
Paper, cloth, and other plastics may be pressed between layers of calendered plastic to make items such as credit cards, playing cards, and wallpaper. Products made from thermoformed sheets include trays, signs, briefcase shells, refrigerator door liners, and packages. In a vacuum-forming process, hot thermoplastic sheets are draped over a mold. Air is removed from between the mold and the hot plastic, which creates a vacuum that draws the plastic into the cavities of the mold.
When the plastic cools, the molded product is removed. In the pressure-forming process, compressed air is used to drive a hot plastic sheet into the cavities and depressions of a concave, or female, mold.
Vent holes in the bottom of the mold allow trapped air to escape. B Forming Thermosetting Plastics Thermosetting plastics are manufactured by several methods that use heat or pressure to induce polymer molecules to bond, or cross-link, into typically hard and durable products. How Thermosetting Plastics are Formed Thermosetting plastics are plastics that cannot be remelted once they have hardened.
Compression molding forms thermosetting plastic objects in a steel mold. When heat and pressure are applied, the softened plastic squeezes into all parts of the mold to form the desired shape. Laminating binds layers of materials together in a plastic matrix. The layers are fused when heated plates melt the plastic and squeeze the material together.
First, thermosetting resin is placed into a steel mold. The application of heat and pressure, which accelerate cross-linking of the resin, softens the material and squeezes it into all parts of the mold to form the desired shape. Once the material has cooled and hardened, the newly formed object is removed from the mold.
This process creates hard, heat-resistant plastic products, including dinnerware, telephones, television set frames, and electrical parts. B2 Laminating The laminating process binds layers of materials, such as textiles and paper, together in a plastic matrix.
This process is similar to the process of joining sheets of wood to make plywood. Resin-impregnated layers of textiles or paper are stacked on hot plates, then squeezed and fused together by heat and pressure, which causes the polymer molecules to cross-link. The best-known laminate trade name is Formica, which is a product consisting of resin-impregnated layers of paper with decorative patterns such as wood grain, marble, and colored designs.
Formica is often used as a surface finish for furniture, and kitchen and bathroom countertops. Thermosetting resins known as melamine and phenolic resins form the plastic matrix for Formica and other laminates. Electric circuit boards are also laminated from resin-impregnated paper, fabric, and glass fibers. B3 Reaction Injection Molding RIM Strong, sizable, and durable plastic products such as automobile body panels, skis, and business machine housings are formed by reaction injection molding.
In this process, liquid thermosetting resin is combined with a curing agent a chemical that causes the polymer molecules to cross-link and injected into a mold. Most products made by reaction injection molding are made from polyurethane. How Both Types of Plastics are Formed Both types of plastic, thermoplastics and thermosetting plastics, can be formed through casting and expansion processes. Casting forms plastic objects in a mold. After the plastic is poured in the mold, additives mixed into the plastic cause the resin to harden.
Expansion processes inject gases into the plastic melt, creating a foam plastic from the tiny bubbles trapped inside. Styrofoam contains a chemical that produces gas as it is heated. As the styrofoam cools and hardens, tiny bubbles left inside the material from the gas create a foam plastic. C1 Casting The casting process is similar to that of molding plaster or cement.
Fluid thermosetting or thermoplastic resin is poured into a mold, and additives cause the resin to solidify. Photographic film is made by pouring a fluid solution of resin onto a highly polished metal belt.
A thin plastic film remains as the solution evaporates. The history of man-made fibres began at the end of the 19th century with the first semi-synthetic or regenerated materials van Oosten and although completely synthetic polymers were developed in the early 20th century, many fibres that are now in common use were not fully exploited until the s and s. Isotactic polypropylene was successful from the early s due to the new catalysts for polymerisation developed by Ziegler and Natta in Brydson It became an important plastic being used in many different forms and applications through a range of manufacturing processes.
A large proportion of PP is used in fibres as constituents of fabrics, upholstery and carpets. Many industrial uses involve ropes, woven and non-woven fabrics and reinforcements. Since the s the production, consumption and applications of this polymer have increased through the application of even more efficient catalysts and property enhancements and today PP is the most common fibre used all over the world.
The usefulness of PP depends on the retention of its properties during a prolonged service life. For instance, under mild conditions, unstabilised PP will retain its properties for long periods of time. However in most applications, exposure to heat and light will occur which accelerates oxidative degradation. The properties that make PP widely used as a fibre do not prevent the fibre from deteriorating over time when exposed to daylight and UV radiation Lemaire et al.
This new discovery launched Phillips into an entirely new industry: The manufacture of a family of polyolefin plastics that included both the polypropylenes and polyethylenes. Phillips management nurtured the new plastics from laboratory discovery to commercial-scale production in less than six years — no small feat for an oil company new to the plastics industry!
Today, chromium catalysts still account for most of the world's HDPE. Hundreds of different grades of resin are produced globally by a variety of manufacturing processes from scores of different variants on the original chromium catalyst. A lot of empiricism and some serendipity is needed for success in the field of industrial catalysis Company marketing executives were wildly optimistic, expecting that the product would be a big hit and that the Phillips would not be able to keep it on the shelves.
Inventories piled up in the warehouses. The turnaround came from an unlikely source — a large ring of plastic tubing called the hula hoop. Phillips president Paul Endacott was so delighted that he kept a hoop in his office for impromptu demonstrations.
The toy's popularity continued long enough for Phillips to improve the production process and expand the number of available product grades. The hula hoop craze helped pave the way for more practical uses, such as commercial and industrial tubing. The discovery of crystalline polypropylene and the development of HDPE launched what is now a multibillion-dollar industry.
The list below gives only a small idea of the impact of these plastics, which are used in thousands of applications. Polypropylene and HDPE play a role in the management of serious environmental issues. They are used in medical care and in public health and are essential materials in a variety of manufacturing industries and consumer-product companies.
Importantly, these plastics also have created industries that provide thousands of jobs and business opportunities in this country and around the world. Food and drink containers Household product bottles Outdoor furniture Toys Trash and lawn bags. Cable jacketing Oil and gas lines Packaging films Tanks and drums Wire insulation. It is hard to do justice to plastic because it serves so many functions, assumes so many guises, satisfies so many desires, and so quickly recedes into relative invisibility as long as it does its job well.
In a little more than a century, plastics have spread throughout the material world, moving from almost no presence at all to near ubiquity. Considering their similar backgrounds, it seems fitting that J. Banks would eventually come together as a team. The two grew up in small towns barely miles apart.
Hogan was born in and spent his childhood in southwestern Kentucky, near the small town of Lowes. Banks was born two years later, in , and grew up in the southeastern Missouri community of Piedmont. Both of their mothers were teachers. Banks' mother, Maude, was a music teacher before she married.
Hogan's mother, Alma, taught elementary school. Banks' father, James, was a dentist in Piedmont. Hogan's father, Charles, was well known in Lowes as a farmer, mechanic and proprietor of a local store.
Banks received a B. Hogan received a B. After the war ended, both men joined Phillips as research chemists — Hogan in and Banks in In , they began their now famous collaboration. After their discovery of polypropylene and the development of HDPE, the two men continued to make important contributions. Banks went on to discover olefin metathesis, a key factor in the growth of the synthetic chemical business.
Hogan continued to develop the chromium catalyst for ethylene polymerization and led a research team dedicated to exploring chromium catalysts. Both men climbed the Phillips ladder, achieving the level of senior research associate. Hogan and Banks retired in the same year, Two years later, they received the Society of Chemical Industry's Perkin Medal for their contributions to chemistry.
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