Chemical Resistance of Plastics 3. Dimensional Stability 4. Ductility of Plastics 5. Durability of Plastics 6. Electric Insulation 7. Finishing 8. Fire Resistance 9.
Fixing Humidity Maintenance Melting Point Optical Property Recycling of Plastics For, example, the higher is the bitumen content; the better is the fatigue life, provided all the other parameters are kept unchanged. But with the increase of bitumen content, the resistance to rutting may decrease. Increase in bitumen content not accompanied by adequate amount of air voids will result in the fall of stability of the mix, the chances of bleeding will increase.
The only way to increase bitumen content keeping sufficient air voids VA is by maximizing VMA and suitably gradation can be designed. Same grades of bitumen are generally used for construction of these layers. Generally same grades of bitumen are used for construction of these layers. Stiffer grade of bitumen has higher value of stiffness, and it causes lesser stains to the pavement layers and also it is expected to show lesser rutting. On the other hand, higher fatigue life as observed for bituminous mixes with softer grade of bitumen [Das ], indicates greater longevity of the pavement against fracture.
It can be shown computationally [Das and Pandey , Das ] that if a pavement is constructed with softer grade of bitumen at the lower layer, and harder grade at the top layer, the pavement is expected to last longer, than a pavement constructed with same grades for both the layers — this technique is known as rich-bottom pavement construction [Harvey et.
Coated bituminous mix The generation of waste plastics is increasing day by day. The major polymers are namely polyethylene, polypropylene, polystyrene show adhesion property in their molten state. The plastic coated aggregate bitumen mix and plastic modified bitumen forms better materials for flexible pavement construction as the mixes shows higher Marshall Stability value and suitable Marshall Coefficient.
Hence the use of waste plastics for flexible pavement is one of the best methods of easy disposal of waste plastics. The use of polymer coated aggregate is better than the use of polymer modified bitumen in many aspects. The studies on the thermal behaviour and binding property promoted a study on the preparation of plastic waste-bitumen blend and its properties to find the suitability of the blend for road construction.
In a few cases, the rock dust itself when mixed with water forms slurry which acts as a binding medium. The aggregates may be classified into natural and artificial aggregates.
The natural aggregates again are classified as coarse aggregates consisting of crushed rock aggregates or gravels and fine aggregates or sand. The blast furnace slag obtained as by-product from blast furnaces is the one extensively used as road construction material. Stone aggregate used for road work should be hard, tough, durable and hydrophobic for bituminous surface. Gravel should be well graded 6. Sand should be sharp, well graded, clean of all silts, clay and organic matter.
The quantity of aggregates used in first coat of surface dressing should be 0. On the other hand, the quantity of aggregate used in second coat of surface dressing should be 0. Bitumen Bitumen is used as binders in pavements constructions. Bitumen may be derived from the residue left by the refinery from naturally occurring asphalt. When petroleum crude is refined in a refinery, they are separated by fractional distillation in the order of decreasing volatility. On distillation of the residual bituminous residue, straight-run bitumen is obtained.
This bitumen is known as penetration grade bitumen or steam refined petroleum bitumen. The grades of bitumen used for pavement construction is known as paving grades and that used for water proofing of structures is known as industrial grades. The grade of straight run bitumen is chosen depending upon the climatic conditions of the region in which surface dressing is to be constructed. Heavier grade cut backs, rapid setting emulsions or heavier grade tars may also be used. The grade of basic bitumen is altered either by controlled refining or by mixing with diesel oil or other oils.
For single dressings on WBM base course, quantity of bitumen needed ranges from 17 to kg per 10 m2 areas and 10 to 12 kg per 10 m2 area in case of renewal of black top surfacing. For second coat of surface dressing, the quantity of bitumen needed ranges from 10 to 12 kg per 10 m2 area. Bulk bitumen Lorries with tanks of capacity ranging from to litres are used to transport bulk bitumen.
The paving bitumen available in India is classified into two categories: Paving bitumen from Assam petroleum denoted as A-type and designated as grades A35, A90, etc. Paving bitumen from other sources denoted as S-type and designated as grades S35, S90, etc. Important properties of bitumen are: Viscosity of bitumen should be adequate at the time of mixing and compaction.
It is achieved by heating prior to mixing and by use of cutbacks and emulsion. In presence of water bitumen should not strip off from aggregate.
Bitumen should be durable in all seasons. It should not become too soft during summers and develop cracks during winters. Cut-back bitumen: The asphaltic bitumen is very often mixed with comparatively volatile solvents to improve the workability of the material.
The solvent gets evaporated leaving behind the particles together. This cutback bitumen is classified into slow, medium and rapid curing depending upon the type of solvent used.
Emulsions: An emulsion is a mixture of normally two immiscible liquids. Asphalt gets broken up into minute globules in water in the presence of the emulsifiers.
It improves the workability of bitumen or asphalt. As a result of emulsification, asphalt is available at normal temperature in the liquid form. Some important groups in these classifications are the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can also be classified by the chemical process used in their synthesis, such as condensation, polyaddition, and crosslinking. There are two types of plastics: thermoplastics and thermosetting polymers. Thermoplastics are the plastics that do not undergo chemical change in their composition when heated and can be moulded again and again.
Examples include polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polytetrafluoroethylene PTFE In the thermosetting process, a chemical reaction occurs that is irreversible. The vulcanization of rubber is a thermosetting process.
Before heating with sulfur, the polyisoprene is a tacky, slightly runny material, but after vulcanization the product is rigid and non-tacky.
The properties of plastics are defined chiefly by the organic chemistry of the polymer. Since the s, one billion tons of plastic have been discarded and may persist for hundreds or even thousands of years.
Perhaps the biggest environmental threat from plastic comes from nurdles, which are the raw material from which all plastics are made. They are tiny pre-plastic pellets that kill large numbers of fish and birds that mistake them for food. Prior to the ban on the use of CFCs in extrusion of polystyrene and general use, except in life-critical fire suppression systems; see Montreal Protocol , the production of polystyrene contributed to the depletion of the ozone layer; however, non-CFCs are currently used in the extrusion process.
Thermoplastics can be remelted and reused, and thermoset plastics can be ground up and used as filler, although the purity of the material tends to degrade with each reuse cycle. There are methods by which plastics can be broken back down to a feedstock state. Classification of plastic waste a Polyethylene LDPE Low Density Poly-Ethylene : Low density poly-ethylene this plastic waste available in the form of carry bags generally in stores these plastic bags are very thin and also easily available.
It is available in the form of plastic bottles and mat sheets etc. Waste plastic shredding Shredding is the process of cutting the plastic into small sizes between 2. Agglomerater and Scrap Grinder.
In Agglomerater, thin films of poly-ethylene and polypropylene carry bags are shredded and in Scrap Grinder a solid plastic material are shredded i. In this process a thin plastic waste carry bags cut in small pieces with the help of fix and rotator blades this whole process required minutes for shredding. X mm ht. Rotatory knives Fix knives Ph induction A. Length of blademm. They are sieved and the plastic pieces passing through 4.
These plastic pieces are added slowly to the hot bitumen of temperature around C. The mixture stirred well using mechanical stirrer for about minutes. Polymer-bitumen mixtures of different compositions can be prepared and used for carrying out various tests.
Homogeneity can be obtained approximately up to 1. Beyond this composition, the variation of softening point is much higher for the top and bottom layer of the test samples showing that there is a separation of polymer from bitumen on standing. This shredded plastic waste is added over hot aggregate with constant mixing to give a uniform distribution. The plastic get softened and coated over the aggregate.
Segregation 2. Cleaning process 3. Shredding process 4. Collection process Two processes used in the construction of plastic roads 1. As a result, this thermoplastic is used to make optical lenses, watch crystals, aircraft windshields, skylights, and outdoor signs. Because PMMA can be cast to resemble marble, it is also used to make sinks, countertops, and other fixtures.
A8 Polyamide Polyamides PA , known by the trade name Nylon, consist of highly ordered molecules, which give polyamides high tensile strength. Some polyamides are made by reacting dicarboxylic acid with diamines carbon molecules with the ion — NH2 on each end , as in nylon-6,6 and nylon-6, The two numbers in each type of nylon represent the number of carbon atoms in the diamine and the dicarboxylic acid, respectively.
Other types of nylon are synthesized by the condensation of amino acids. Velcro Loops and Hooks This color-enhanced electron microscope image shows the tiny nylon hooks and loops that give Velcro its unique fastening ability.
Due to the strength of nylon, Velcro can be fastened and unfastened thousands of times. Velcro fastens when dry or wet, and is used in sports shoes, jackets, tents, sleeping bags, and countless other products—even spacesuits.
Therefore, nylons are commonly used for mechanical applications, such as gears, bearings, and bushings. Nylons are also extruded into millions of tons of synthetic fibers every year.
The most commonly used nylon fibers, nylon-6,6 and nylon-6 single number because this nylon forms by the self-condensation of an amino acid are made into textiles, ropes, fishing lines, brushes, and other items.
B Thermosetting Materials Because thermosetting plastics cure, or cross-link, after being heated, these plastics can be made into durable and heat-resistant materials.
The most commonly manufactured thermosetting plastics are presented below in order of decreasing volume of production.
Alkyl groups are chemical groups obtained by removing a hydrogen atom from an alkane—a hydrocarbon containing all carbon-carbon single bonds. Most types of polyurethane resin cross- link and become thermosetting plastics.
However, some polyurethane resins have a linear molecular arrangement that does not cross-link, resulting in thermoplastics. Thermosetting polyurethane molecules cross-link into a single giant molecule. Thermosetting polyurethane is widely used in various forms, including soft and hard foams. Soft, open-celled polyurethane foams are used to make seat cushions, mattresses, and packaging.
Hard polyurethane foams are used as insulation in refrigerators, freezers, and homes. Thermoplastic polyurethane molecules have linear, highly crystalline molecular structures that form an abrasion-resistant material. Thermoplastic polyurethanes are molded into shoe soles, car fenders, door panels, and other products.
B2 Phenolics Phenolic phenol-formaldehyde resins, first commercially available in , were some of the first polymers made. Phenolic plastics are hard, strong, inexpensive to produce, and they possess excellent electrical resistance. Phenolic resins cure cross-link when heat and pressure are applied during the molding process. Phenolic resin-impregnated paper or cloth can be laminated into numerous products, such as electrical circuit boards.
Phenolic resins are also compression molded into electrical switches, pan and iron handles, radio and television casings, and toaster knobs and bases.
B3 Melamine-Formaldehyde and Urea-Formaldehyde Urea-formaldehyde UF and melamine-formaldehyde MF resins are composed of molecules that cross-link into clear, hard plastics. Properties of UF and MF resins are similar to the properties of phenolic resins.
Melamine-formaldehyde resins are easily molded in compression and special injection molding machines. MF plastics are more heat-resistant, scratch-proof, and stain-resistant than urea-formaldehyde plastics are.
MF resins are used to manufacture dishware, electrical components, laminated furniture veneers, and to bond wood layers into plywood. Urea-formaldehyde resins form products such as appliance knobs, knife handles, and plates. UF resins are used to give drip-dry properties to wash-and-wear clothes as well as to bond wood chips and wood sheets into chip board and plywood.
Unsaturated polyesters an unsaturated compound contains multiple bonds cross- link when the long molecules are joined copolymerized by the aromatic organic compound styrene see Aromatic Compounds.
Unsaturated polyester resins are often premixed with glass fibers for additional strength. Both types of compounds are doughlike in consistency and may contain short fiber reinforcements and other additives. Sheet molding compounds are preformed into large sheets or rolls that can be molded into products such as shower floors, small boat hulls, and roofing materials.
Bulk molding compounds are also preformed to be compression molded into car body panels and other automobile components. Epoxies are tough, extremely weather-resistant, and do not shrink as they cure dry.
Epoxies cross-link when a catalyzing agent hardener is added, forming a three- dimensional molecular network. Because of their outstanding bonding strength, epoxy resins are used to make coatings, adhesives, and composite laminates. Epoxy has important applications in the aerospace industry.
All composite aircraft are made of epoxy. Epoxy is used to make the wing skins for the F and F fighters, as well as the horizontal stabilizer for the F fighter and the B-1 bomber. B6 Reinforced Plastics Reinforced plastics, called composites, are plastics strengthened with fibers, strands, cloth, or other materials.
Thermosetting epoxy and polyester resins are commonly used as the polymer matrix binding material in reinforced plastics. Organic synthetic fibers such as aramid an aromatic polyamide with the commercial name Kevlar offer greater strength and stiffness than glass fibers, but these synthetic fibers are considerably more expensive.
The Boeing aircraft makes extensive use of lightweight reinforced plastics. Other products made from reinforced plastics include boat hulls and automobile body panels, as well as recreation equipment, such as tennis rackets, golf clubs, and jet skis.
For example, the early Egyptians soaked burial wrappings in natural resins to help preserve their dead. People have been using animal horns and turtle shells which contain natural resins for centuries to make items such as spoons, combs, and buttons. During the midth century, shellac resinous substance secreted by the lac insect was gathered in southern Asia and transported to the United States to be molded into buttons, small cases, knobs, phonograph records, and hand-mirror frames.
During that time period, gutta-percha rubberlike sap taken from certain trees in Malaya was used as the first insulating coating for electrical wires.
In order to find more efficient ways to produce plastics and rubbers, scientists began trying to produce these materials in the laboratory. In American inventor Charles Goodyear vulcanized rubber by accidentally dropping a piece of sulfur-treated rubber onto a hot stove.
Goodyear discovered that heating sulfur and rubber together improved the properties of natural rubber so that it would no longer become brittle when cold and soft when hot. In British chemist Alexander Parkes synthesized a plastic known as pyroxylin, which was used as a coating film on photographic plates.
The following year, American inventor John W. Hyatt began working on a substitute for ivory billiard balls. Hyatt added camphor to nitrated cellulose and formed a modified natural plastic called celluloid, which became the basis of the early plastics industry.
These early plastics based on natural products shared numerous drawbacks. For example, many of the necessary natural materials were in short supply, and all proved difficult to mold.
Finished products were inconsistent from batch to batch, and most products darkened and cracked with age. Furthermore, celluloid proved to be a very flammable material. Due to these shortcomings, scientists attempted to find more reliable plastic source materials.
In American chemist Leo Hendrik Baekeland made a breakthrough when he created the first commercially successful thermosetting synthetic resin, which was called Bakelite known today as phenolic resin. Use of Bakelite quickly grew. It has been used to make products such as telephones and pot handles. The chemistry of joining small molecules into macromolecules became the foundation of an emerging plastics industry.
Between and , the I. Farben Company of Germany synthesized polystyrene and polyvinyl chloride, as well as a synthetic rubber called Buna-S. In Du Pont made a breakthrough when it introduced nylon—a material finer, stronger, and more elastic than silk.
By acrylics were being produced by German, British, and U. That same year, the British company Imperial Chemical Industries developed polyethylene. In the German company I. Farbenindustrie filed a patent for polyepoxide epoxy , which was not sold commercially until a U.
After World War II , the pace of new polymer discoveries accelerated. In a small English company developed polyethylene terephthalate PET. In the postwar era, research by Bayer and by General Electric resulted in production of plastics such as polycarbonates, which are used to make small appliances, aircraft parts, and safety helmets. In Union Carbide Corporation introduced a linear, heat-resistant thermoplastic known as polysulfone, which is used to make face shields for astronauts and hospital equipment that can be sterilized in an autoclave a device that uses high pressure steam for sterilization.
Today, scientists can tailor the properties of plastics to numerous design specifications. Modern plastics are used to make products such as artificial joints, contact lenses, space suits, and other specialized materials.
As plastics have become more versatile, use of plastics has grown as well. By the year , annual global demand for plastics is projected to exceed million metric tons billion lb. As municipal landfills reach capacity and additional landfill space diminishes across the United States, alternative methods for reducing and disposing of wastes— including plastics—are being explored.
Some of these options include reducing consumption of plastics, using biodegradable plastics, and incinerating or recycling plastic waste. A Source Reduction Source reduction is the practice of using less material to manufacture a product. For example, the wall thickness of many plastic and metal containers has been reduced in recent years, and some European countries have proposed to eliminate packaging that cannot be easily recycled.
Plastics are therefore not considered biodegradable. However, researchers are working to develop biodegradable plastics that will disintegrate due to bacterial action or exposure to sunlight. For example, scientists are incorporating starch molecules into some plastic resins during the manufacturing process. When these plastics are discarded, bacteria eat the starch molecules.
This causes the polymer molecules to break apart, allowing the plastic to decompose. Researchers are also investigating ways to make plastics more biodegradable from exposure to sunlight. Prolonged exposure to ultraviolet radiation from the sun causes many plastics molecules to become brittle and slowly break apart. Researchers are working to create plastics that will degrade faster in sunlight, but not so fast that the plastic begins to degrade while still in use.
C Incineration Some wastes, such as paper, plastics, wood, and other flammable materials can be burned in incinerators. The resulting ash requires much less space for disposal than the original waste would. Because incineration of plastics can produce hazardous air emissions and other pollutants, this process is strictly regulated.
D Recycling Plastics All plastics can be recycled. Thermoplastics can be remelted and made into new products. Thermosetting plastics can be ground, commingled mixed , and then used as filler in moldable thermoplastic materials.
Highly filled and reinforced thermosetting plastics can be pulverized and used in new composite formulations.
Collecting, sorting, and recycling plastics is an expensive process. Although automated plastic sorting machines are being developed, many recycling operations sort plastic by hand, as shown here.
Only about 5 percent of plastic products in the United States are reused. Chemical recycling is a depolymerization process that uses heat and chemicals to break plastic molecules down into more basic components, which can then be reused. Another process, called pyrolysis, vaporizes and condenses both thermoplastics and thermosetting plastics into hydrocarbon liquids.
Collecting and sorting used plastics is an expensive and time-consuming process. While about 35 percent of aluminum products, 40 percent of paper products, and 25 percent of glass products are recycled in the United States, only about 5 percent of plastics are currently recovered and recycled.
Once plastic products are thrown away, they must be collected and then separated by plastic type. Most modern automated plastic sorting systems are not capable of differentiating between many different types of plastics.
However, some advances are being made in these sorting systems to separate plastics by color, density, and chemical composition. For example, x-ray sensors can distinguish PET from PVC by sensing the presence of chlorine atoms in the polyvinyl chloride material.
Other factors can adversely affect the quality of recycled plastics. These factors include the possible degradation of the plastic during its original life cycle and the possible addition of foreign materials to the scrap recycled plastic during the recycling process. For health reasons, recycled plastics are rarely made into food containers. Instead, most recycled plastics are typically made into items such as carpet fibers, motor oil bottles, trash carts, soap packages, and textile fibers.
To promote the conservation and recycling of materials, the U. In the Plastic Bottle Institute of the Society of the Plastics Industry established a system for identifying plastic containers by plastic type.
0コメント