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Household items made of various kinds of plastic.
Plastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce costs. Monomers of Plastic are either natural or synthetic organic compounds.
The word is derived from the Greek past (plastikos) meaning fit for molding, and past (plastos) meaning molded. It refers to their malleability, or plasticity during manufacture, that allows them to be cast, pressed, or extruded into a variety of shapesâ€such as films, fibers, plates, tubes, bottles, boxes, and much more.
The common word plastic should not be confused with the technical adjective plastic, which is applied to any material which undergoes a permanent change of shape (plastic deformation) when strained beyond a certain point. Aluminium, for instance, is plastic in this sense, but not a plastic in the common sense; in contrast, in their finished forms, some plastics will break before deforming and therefore are not plastic in the technical sense.
There are two types of plastics: thermoplastics and thermosetting polymers. Thermoplastics will soften and melt if enough heat is applied; examples are polyethylene, polystyrene, polyvinyl chloride and polytetrafluoroethylene (PTFE). Thermosets can melt and take shape once; after they have solidified, they stay solid.
Plastics can be classified by chemical structure, namely the molecular units that make up the polymer's backbone and side chains. 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 cross-linking.
Other classifications are based on qualities that are relevant for manufacturing or product design. Examples of such classes are the thermoplastic and thermoset, elastomer, structural, biodegradable, and electrically conductive. Plastics can also be classified by various physical properties, such as density, tensile strength, glass transition temperature, and resistance to various chemical products.
Due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper clips to spaceships. They have already displaced many traditional materials, such as wood; stone; horn and bone; leather; paper; metal; glass; and ceramic, in most of their former uses.
The use of plastics is constrained chiefly by their organic chemistry, which seriously limits their hardness, density, and their ability to resist heat, organic solvents, oxidation, and ionizing radiation. In particular, most plastics will melt or decompose when heated to a few hundred degrees celsius.While plastics can be made electrically conductive to some extent, they are still no match for metals like copper or aluminium. Plastics are still too expensive to replace wood, concrete and ceramic in bulky items like ordinary buildings, bridges, dams, pavement, and railroad ties.
Common thermoplastics range from 20,000 to 500,000 in molecular mass, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as repeat units, derived from monomers; each polymer chain will have several thousand repeating units. The vast majority of plastics are composed of polymers of carbon and hydrogen alone or with oxygen, nitrogen, chlorine or sulfur in the backbone. (Some of commercial interests are silicon based.) The backbone is that part of the chain on the main "path" linking a large number of repeat units together. To customize the properties of a plastic, different molecular groups "hang" from the backbone (usually they are "hung" as part of the monomers before linking monomers together to form the polymer chain). This fine tuning of the properties of the polymer by repeating unit's molecular structure has allowed plastics to become such an indispensable part of twenty first-century world.
Some plastics are partially crystalline and partially amorphous in molecular structure, giving them both a melting point (the temperature at which the attractive intermolecular forces are overcome) and one or more glass transitions (temperatures above which the extent of localized molecular flexibility is substantially increased). The so-called semi-crystalline plastics include polyethylene, polypropylene, poly (vinyl chloride), polyamides (nylons), polyesters and some polyurethanes. Many plastics are completely amorphous, such as polystyrene and its copolymers, poly (methyl methacrylate), and all thermosets.
Molded plastic food replicas on display outside a restaurant in Japan.
The firsthuman-made plastic was invented by Alexander Parkes in 1855 ; he called this plastic Parkesine (later called celluloid). The development of plastics has come from the use of natural plastic materials (e.g., chewing gum, shellac) to the use of chemically modified natural materials (e.g., rubber, nitrocellulose, collagen, galalite) and finally to completely synthetic molecules (e.g., bakelite, epoxy, polyvinyl chloride, polyethylene).
In 1855, an Englishman from Birmingham named Alexander Parkes developed a synthetic replacement for ivory which he marketed under the trade name Parkesine, and which won a bronze medal at the 1862 World's fair in London. Parkesine was made from cellulose (the major component of plant cell walls) treated with nitric acid and a solvent. The output of the process (commonly known as cellulose nitrate or pyroxilin) could be dissolved in alcohol and hardened into a transparent and elastic material that could be molded when heated. By incorporating pigments into the product, it could be made to resemble ivory.
Bois Durci is a plastic moulding material based on cellulose. It was patented in Paris by Lepage in 1855. It is made from finely ground wood flour mixed with a binder, either egg or blood albumen, or gelatine. The wood is probably either ebony or rose wood, which gives a black or brown resin. The mixture is dried and ground into a fine powder. The powder is placed in a steel mould and compressed in a powerful hydraulic press whilst being heated by steam. The final product has a highly polished finish imparted by the surface of the steel mould.
The first plastic based on a synthetic polymer was made from phenol and formaldehyde, with the first viable and cheap synthesis methods invented in 1909 by Leo Hendrik Baekeland, a Belgian-born American living in New York state. Baekeland was searching for an insulating shellac to coat wires in electric motors and generators. He found that mixtures of phenol (C6H5OH) and formaldehyde (HCOH) formed a sticky mass when mixed together and heated, and the mass became extremely hard if allowed to cool. 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 were strong and fire resistant. The only problem was that the material tended to foam during synthesis, and the resulting product was of unacceptable quality.
Baekeland built pressure vessels to force out the bubbles and provide a smooth, uniform product. He publicly announced his discovery in 1912, naming it bakelite. It was originally used for electrical and mechanical parts, finally coming into widespread use in consumer goods in the 1920s. When the Bakelite patent expired in 1930, the Catalin Corporation acquired the patent and began manufacturing Catalin 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 even molecule found in nature. It was also the first thermosetting 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. Thermoset plastics are tough and temperature resistant.
Bakelite was cheap, strong, and durable. It was molded into thousands of forms, such as radios, telephones, clocks, and 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 have been largely replaced by cheaper and less brittle plastics, but they are still used in applications requiring its insulating and heat-resistant properties. For example, some electronic circuit boards are made of sheets of paper or cloth impregnated with phenolic resin.
Phenolic sheets, rods and tubes are produced in a wide variety of grades under various brand names. The most common grades of industrial phenolic are Canvas, Linen and Paper.
Polystyrene and PVC
Plastic piping and firestops being installed at Nortown Casitas, North York (Now Toronto), Ontario, Canada. Certain plastic pipes can be used in some non-combustible buildings, provided they are firestopped properly and that the flame spread ratings comply with the local building code.
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 IG Farben of Germany.
Polystyrene is a rigid, brittle, inexpensive plastic that has been used to make plastic model kits and similar knick-knacks. 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 "open cell" 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 flotation devices. In the late 1950s, high impact styrene was introduced, which was not brittle. It finds much current use as the substance of toy figurines and novelties.
PVC has side chains incorporating chlorine atoms, which form strong bonds. PVC in its normal form is stiff, 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 chemical processing, and in this form it is now used for shrink-wrap, food packaging, and rain gear.
The real star of the plastics industry in the 1930s was polyamide (PA), far better known by its trade name nylon. Nylon was the first purely synthetic fiber, introduced by DuPont Corporation at the 1939 World's Fair in New York City.
In 1927, DuPont had begun a secret development project designated Fiber66, under the direction of Harvard chemist Wallace Carothers and chemistry department director Elmer Keiser Bolton. Carothers had been hired to perform pure research, and he worked to understand the new materials' molecular structure and physical properties. He took some of the first steps in the molecular design of the materials.
His work led to the discovery of synthetic nylon fiber, which was very strong but also very flexible. The first application was for bristles for toothbrushes. However, Du Pont's real target was silk, particularly silk stockings. Carothers and his team synthesized a number of different polyamides including polyamide 6.6 and 4.6, as well as polyesters.
General condensation polymerization reaction for nylon
It took DuPont twelve years and US$27 million to refine nylon, and to synthesize and develop the industrial processes for bulk manufacture. With such a major investment, it was no surprise that Du Pont spared little expense to promote nylon after its introduction, creating a public sensation, or "nylon mania".
Nylon mania came to an abrupt stop at the end of 1941 when the USA entered World War II. The production capacity that had been built up to produce nylon stockings, or just nylons, for American women was taken over to manufacture vast numbers of parachutes for fliers and paratroopers. After the war ended, DuPont went back to selling nylon to the public, engaging in another promotional campaign in 1946 that resulted in an even bigger craze, triggering the so called nylon riots.
Subsequently polyamides 6, 10, 11, and 12 have been developed based on monomers which are ring compounds; e.g. caprolactam.nylon 66 is a material manufactured by condensation polymerization.
Nylons still remain important plastics, and not just for use in fabrics. In its bulk form it is very wear resistant, particularly if oil-impregnated, and so is used to build gears, plain bearings, and because of good heat-resistance, increasingly for under-the-hood applications in cars, and other mechanical parts.
Natural rubber is an elastomer (an elastic hydrocarbon polymer) that was originally derived from latex, a milky colloidal suspension found in the sap of some plants. It is useful directly in this form (indeed, the first appearance of rubber in Europe is cloth waterproofed with unvulcanized latex from Brazil) but, later, in 1839, Charles Goodyear invented vulcanized rubber; this a form of natural rubber heated with, mostly, sulfur forming cross-links between polymer chains (vulcanization), improving elasticity and durability.
The first fully synthetic rubber was synthesized by Lebedev in 1910. In World War II, supply blockades of natural rubber from South East Asia caused a boom in development of synthetic rubber, notably Styrene-butadiene rubber (a.k.a. Government Rubber-Styrene). In 1941, annual production of synthetic rubber in the U.S. was only 231 tons which increased to 840 000 tons in 1945. In the space race and nuclear arms race, Caltech researchers experimented with using synthetic rubbers for solid fuel for rockets. Ultimately, all large military rockets and missiles would use synthetic rubber based solid fuels, and they would also play a significant part in the civilian space effort.
Due to their insolubility in water and relative chemical inertness, pure plastics generally have low toxicity in their finished state, and will pass through the digestive system with no ill effect (other than mechanical damage or obstruction).
However, plastics often contain a variety of toxic additives. For example, plasticizers like adipates and phthalates are often added to brittle plastics like polyvinyl chloride (PVC) to make them pliable enough for use in food packaging, children's toys and teethers, tubing, shower curtains and other items. Traces of these chemicals can leach out of the plastic when it comes into contact with food. Out of these concerns, the European Union has banned the use of DEHP (di-2-ethylhexyl phthalate), the most widely used plasticizer in PVC. Some compounds leaching from polystyrene food containers have been found to interfere with hormone functions and are suspected human carcinogens.
Moreover, while the finished plastic may be non-toxic, the monomers used in its manufacture may be toxic; and small amounts of those chemical may remain trapped in the product. The World Health Organization's International Agency for Research on Cancer (IARC) has recognized the chemical used to make PVC, vinyl chloride, as a known human carcinogen. Some polymers may also decompose into the monomers or other toxic substances when heated.
The primary building block of polycarbonates, bisphenol A (BPA), is an estrogen-like endocrine disruptor that may leach into food. Research in Environmental Health Perspectives finds that BPA leached from the lining of tin cans, dental sealants and polycarbonate bottles can increase body weight of lab animals' offspring. A more recent animal study suggests that even low-level exposure to BPA results in insulin resistance, which can lead to inflammation and heart disease.
As of January 2010, the LA Times newspaper reports that the United States FDA is spending $30 million to investigate suspicious indications of BPA being linked to cancer.
Bis(2-ethylhexyl) adipate, present in plastic wrap based on PVC, is also of concern, as are the volatile organic compounds present in new car smell.
The European Union has a permanent ban on on the use of phthalates in toys. In 2009, the United States government banned certain types of phthalates commonly used in plastic.
Plastics are durable and degrade very slowly; the molecular bonds that make plastic so durable make it equally resistant to natural processes of degradation. Since the 1950s, one billion tons of plastic has been discarded and may persist for hundreds or even thousands of years. In some cases, burning plastic can release toxic fumes. Burning the plastic polyvinyl chloride (PVC) may create dioxin. Also, the manufacturing of plastics often creates large quantities of chemical pollutants.
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.
By 1995, 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 as filler, though 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.
To assist recycling of disposable items, the Plastic Bottle Institute of the Society of the Plastics Industry devised a now-familiar scheme to mark plastic bottles by plastic type. A plastic container using this scheme is marked with a triangle of three cyclic arrows, which encloses a number giving the plastic type:
Plastics type marks: the resin identification code
1. PET (PETE), polyethylene terephthalate: Commonly found on 2-liter soft drink bottles, water bottles, cooking oil bottles, peanut butter jars.
2. HDPE, high-density polyethylene: Commonly found on detergent bottles, milk jugs.
3. PVC, polyvinyl chloride: Commonly found on plastic pipes, outdoor furniture, siding, floor tiles, shower curtains, clamshell packaging.
4. LDPE, low-density polyethylene: Commonly found on dry-cleaning bags, produce bags, trash can liners, and food storage containers.
5. PP, polypropylene: Commonly found on bottle caps, drinking straws, yogurt containers.
6. PS, polystyrene: Commonly found on "packing peanuts", cups, plastic tableware, meat trays, take-away food clamshell containers
7. OTHER, other: This plastic category, as its name of "other" implies, is any plastic other than the named #1â€œ#6, Commonly found on certain kinds of food containers, Tupperware, and Nalgene bottles.
Unfortunately, recycling plastics has proven difficult. The biggest problem with plastic recycling is that it is difficult to automate the sorting of plastic waste, and so it is labor intensive. Typically, workers sort the plastic by looking at the resin identification code, though common containers like soda bottles can be sorted from memory. Other recyclable materials, such as metals, are easier to process mechanically. However, new mechanical sorting processes are being utilized to increase plastic recycling capacity and efficiency.
While containers are usually made 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 and colors of plastics. In a case like this, the resources it would take to separate the plastics far exceed their value and the item is discarded. However, developments are taking place in the field of Active Disassembly, which may result in more consumer product components being re-used or recycled. Recycling certain types of plastics can be unprofitable, as well. For example, polystyrene is rarely recycled because it is usually not cost effective. These unrecycled wastes are typically disposed of in landfills, incinerated or used to produce electricity at waste-to-energy plants.
Biodegradable (Compostable) plastics
Research has been done on biodegradable plastics that break down with exposure to sunlight (e.g., ultra-violet radiation), water or dampness, bacteria, enzymes, wind abrasion and some instances rodent pest or insect attack are also included as forms of biodegradation or environmental degradation. It is clear some of these modes of degradation will only work if the plastic is exposed at the surface, while other modes will only be effective if certain conditions exist in landfill or composting systems. Starch powder has been mixed with plastic as a filler to allow it to degrade more easily, but it still does not lead to complete breakdown of the plastic. Some researchers have actually genetically engineered bacteria that synthesize a completely biodegradable plastic, but this material, such as Biopol, is expensive at present. The German chemical company BASF makes Ecoflex, a fully biodegradable polyester for food packaging applications.
Some plastics can be obtained from biomass, including:
Â¢ from pea starch film with trigger biodegradation properties for agricultural applications (TRIGGER).
Â¢ from biopetroleum.
Oxo-biodegradable (OBD) plastic is polyolefin plastic to which has been added very small (catalytic) amounts of metal salts. As long as the plastic has access to oxygen (as in a littered state), these additives catalyze the natural degradation process to speed it up so that the OBD plastic will degrade when subject to environmental conditions. Once degraded to a small enough particle they can interact with biological processes to produce to water, carbon dioxide and biomass. The process is shortened from hundreds of years to months for degradation and thereafter biodegradation depends on the micro-organisms in the environment. Typically this process is not fast enough to meet ASTM D6400 standards for definition as compostable plastics.
Price, environment, and the future
The biggest threat to the conventional plastics industry is most likely to be environmental concerns, including the release of toxic pollutants, greenhouse gas, litter, biodegradable and non-biodegradable landfill impact as a result of the production and disposal of petroleum and petroleum-based plastics. Of particular concern has been the recent accumulation of enormous quantities of plastic trash in ocean gyres.
For decades one of the great appeals of plastics has been their low price. Yet in recent years the cost of plastics has been rising dramatically. A major cause is the sharply rising cost of petroleum, the raw material that is chemically altered to form commercial plastics.
With some observers suggesting that future oil reserves are uncertain, the price of petroleum may increase further. Therefore, alternatives are being sought. Oil shale and tar oil are alternatives for plastic production but are expensive. Scientists are seeking cheaper and better alternatives to petroleum-based plastics, and many candidates are in laboratories all over the world. One promising alternative may be fructose.
Common plastics and uses
A chair made with a polypropylene seat
Food containers, appliances, car fenders (bumpers), plastic pressure pipe systems.
Packaging foam, food containers, disposable cups, plates, cutlery, CD and cassette boxes.
High impact polystyrene (HIPS)
Fridge liners, food packaging, vending cups.
Acrylonitrile butadiene styrene (ABS)
Electronic equipment cases (e.g., computer monitors, printers, keyboards), drainage pipe.
Polyethylene terephthalate (PET)
Carbonated drinks bottles, jars, plastic film, microwavable packaging.
Polyamides (PA) (Nylons)
Fibers, toothbrush bristles, fishing line, under-the-hood car engine mouldings.
Polyvinyl chloride (PVC)
Plumbing pipes and guttering, shower curtains, window frames, flooring.
Cushioning foams, thermal insulation foams, surface coatings, printing rollers. (Currently 6th or 7th most commonly used plastic material, for instance the most commonly used plastic found in cars).
Compact discs, eyeglasses, riot shields, security windows, traffic lights, lenses.
Polyvinylidene chloride (PVDC) (Saran)
Wide range of inexpensive uses including supermarket bags, plastic bottles.
Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS)
A blend of PC and ABS that creates a stronger plastic. Used in car interior and exterior parts, and mobile phone bodies.
Polymethyl methacrylate (PMMA)
Contact lenses, glazing (best known in this form by its various trade names around the world; e.g., Perspex, Oroglas, Plexiglas), aglets, fluorescent light diffusers, rear light covers for vehicles.
Heat-resistant, low-friction coatings, used in things like non-stick surfaces for frying pans, plumber's tape and water slides. It is more commonly known as Teflon.
Polyetheretherketone (PEEK) (Polyetherketone)
Strong, chemical- and heat-resistant thermoplastic, biocompatibility allows for use in medical implant applications, aerospace mouldings. One of the most expensive commercial polymers.
Polyetherimide (PEI) (Ultem)
A high temperature, chemically stable polymer that does not crystallize.
Phenolics (PF) or (phenol formaldehydes)
High modulus, relatively heat resistant, and excellent fire resistant polymer. Used for insulating parts in electrical fixtures, paper laminated products (e.g., Formica), thermally insulation foams. It is a thermosetting plastic, with the familiar trade name Bakelite, that can be moulded by heat and pressure when mixed with a filler-like wood flour or can be cast in its unfilled liquid form or cast as foam (e.g., Oasis). Problems include the probability of mouldings naturally being dark colours (red, green, brown), and as thermoset difficult to recycle.
One of the aminoplasts and used as a multi-colorable alternative to phenolics. Used as a wood adhesive (for plywood, chipboard, hardboard) and electrical switch housings.
Melamine formaldehyde (MF)
One of the aminoplasts, and used as a multi-colorable alternative to phenolics, for instance in mouldings (e.g., break-resistance alternatives to ceramic cups, plates and bowls for children) and the decorated top surface layer of the paper laminates (e.g., Formica).
Polylactic acid (PLA)
A biodegradable, thermoplastic found converted into a variety of aliphatic polyesters derived from lactic acid which in turn can be made by fermentation of various agricultural products such as corn starch, once made from dairy products.
Biodegradable and heat resistant, thermoplastic composed of modified corn starch.
Effects of Plastics
In this era of many astonishing industrial developments, probably no industry has under gone such rapid growth and development as the plastics industry. According to most authorities in this field, the plastics industry really began in 1868. A young American printer, named John Wesley Hyatt, was searching for a new material to be used as a substitute for ivory in the making of billiard balls.
This new plastic was called Bakelite. Many new plastics have been made since Bakelite. Production of plastics has increased over 2000% since Bakelite was first produced, and there are now more than twenty known types. Research along the lines of plastics has given a great impetus to research and invention in many other different fields of endeavor. Millions of dollars are spent yearly in plastics research, trying to find new plastics and to improve the existing ones. Much research will be done in the future to lower the cost of producing plastics so that their consumption will become greater. In spite of the varied and widespread application of plastics in practically every phase of everyday life, the possibilities of this wonderful new material have been by no means exhausted. It seems safe to say that if the application and use of plastics continue to increase at the present rate, we may be living in a "Plastics Age."
An apt definition of plastics has been given by the head of the Monsanto Plastics Research who says, "Plastics are materials that, while being processed, can be pushed into almost any desired shape and then retain that shape."
The major chemicals used to make plastic resins pose serious risks to public health and safety. Many of the chemicals used in large volumes to produce plastics are highly toxic.Some chemicals, like benzene and vinyl chloride, are known to cause cancer in humans; many tend to be gases and liquid hydrocarbons, which readily vaporize and pollute the air. Many are flammable and explosive. Even the plastic resins themselves are flammable and have contributed to numerous chemical accidents. The production of plastic emits substantial amounts of toxic chemicals(eg. ethylene oxide, benzene and xylenes) to air and water. Many of the toxic chemicals released in plastic production can cause cancer and birth defects and damage the nervous system, blood, kidneys and immune systems. These chemicals can also cause serious damage to ecosystems.
Ethylene oxide is used as a sterilant in hospitals. It is also the principle metabolite of ethene, a precursor to polyethylene plastics and other synthetic chemicals. Ethylene oxide can be measured by gas chromatography in air or biological specimens. Ethylene oxide reacts in the body with hemoglobin.
Many food containers for meats, fish, cheeses, yogurt, foam and clear clamshell containers, foam and rigid plates, clear bakery containers, packaging "peanuts," foam packaging, audio cassette housings, CD cases, disposable cutlery, and more are made of polystyrene. J. R. Withey in Environmental Health Perspectives 1976 Investigated styrene and vinyl chloride monomer as being similar: "Styrene monomer readily migrates from food contained in it. It makes no difference whether the food or drink is hot or cold, or contains fat or water. ...It is not inconceivable that the animal body behaves as a 'sink' for styrene monomer until the lipid portion of the animal body either becomes saturated (although death would probably occur prior to this event) or the tissues are equilibrated at the same concentration as the exposure atmosphere."
PVC is used for many products including: flooring, toys, teethers, clothing, raincoats, shoes, building products like windows, siding and roofing, hospital blood bags, IV bags and other medical devices. One of it's major ingredients is chlorine. When chlorine-based chemicals are heated in the presence of hydrocarbons they create dioxin, a known carcinogen and endocrine disruptor. All PVC production releases dioxin. Other sources of dioxin are: production and use of chemicals, such as herbicides and wood preservatives, oil refining, burning coal and oil for energy, all car and truck exhaust, cigarette
Plasticizers are used in PVC that migrate into a blood recipient via the blood bag, IV bag, IV tubing. Children's toys are made with pvc.
Anyone who receives blood, is on kidney dialysis, or has tubes either inserted in them or has liquid or air transported to their body is at risk. About 85% of medical waste is incinerated, accounting for ten percent of all incineration in the U.S.Approximately five to fifteen percent of medical waste needs to be incinerated to prevent infectious disease. The remaining waste, while not posing any danger from infectious pathogens, is very dangerous when burned. It contains high volumes of chlorinated plastics including PVC (also the toxic substances mercury, arsenic, cadmium and lead.)
Pyrolysis is a process of thermal degradation in the absence of oxygen. Plastic & Rubber waste is continuously treated in a cylindrical chamber and the pyrolytic gases are condensed in a specially-designed condenser system.This yields a hydrocarbon distillate comprising straight and branched chain aliphatic, cyclic aliphatic and aromatic hydrocarbons. The resulting mixture is essentially the equivalent to petroleum distillate.The plastic / Rubber is pyrolised at 370Ã‚ÂºC -420Ã‚ÂºC and the pyrolysisgases are condensed in a series of condensers to give a low sulphur content distillate.
TYPES OF PYROLYSIS TECHNIQUES:
In our study, we intended to divide pyrolysis into pyrolysis with the use of catalysts and pyrolysis without the use of catalysts. Pyrolysis process, which uses catalysts, can take place in two different kinds of batch reactor
Pyrolysis using expensive catalysts:
Here the catalysts used are metal promoted silica-alumina or mixtures of metal hydrogenation catalysts with HZSM-5. The optimization of waste plastic as a function of temperature in a batch mode reactor gave liquid yields of about 80% at a furnace temperatures of about 600 degrees centigrade and one hr residence time. The pyrolysis oil obtained at the temperature of maximum yield are relatively heavy in nature. However, hydroprocessing at relatively low hydrogen pressures (200-500psiag) at 430-450 degrees centigrade either thermally or catalytically converts them into a much lighter product. Sodium carbonate or lime addition to the pyrolysis and coprocessing reactors results into an effective chlorine capture and the chlorine content of pyrolysis oil reduces to about 50-200ppm and that of the hydroprocessed oils to 1-10ppm. The volatile product from this process is scrubbed and condensed yielding about 10-15%gas and 75-80% of a relatively heavy oil product.
Pyrolysis using synthesized catalysts from fly ash:
Table 2 shows chemical compositions of the catalysts and fly ash obtained from coal fired power plants. To use fly ash as synthesized catalyst it was treated in NaOH solution for more 24 hrs, washed by distilled water and dried. To make another synthesized catalysts this catalyst can be impregnated in the nickel nitrate solution. So two types of catalysts were made for the pyrolysis of PE and PP of olefin series.
Component Mordenite HY SilicaAlumina Fly Ash
SiO2 91.7 74.9 87 53.56
Al2O3 8.23 24.0 13 27.71
Na2O3 0.03 1.1 - 0.37
Fe - 0.03 - 5.53
SiO2/Al2O3 (-)18.9 5.31 6.69 1.93
The setup of the pyrolysis batch reactor is shown in Figure 1. The mechanical agitator was installed in the batch type reactor wrapped around with electric heater for controlling the pyrolysis temperature of waste plastic. The organic vapor pyrolyzed from waste plastics can pass the catalytic cracker bed or not when catalyst is charged with waste plastics in the reactor. After that, the vapor is discharged through 1st and 2nd condenser for product oil conversion. These two condensers are maintained at different temperatures, 70 and 10. Pyrolysis oil collected from each condenser was analyzed by SIMDIS GC to investigate the catalytic properties and the pyrolysis conditions. The yields of pyrolysis oil from polyethylene and polypropylene were 75 to 89%
Pyrolysis without the use of catalysts:
The process carried out is the same in this case also but catalysts are not used. Instead the temperature parameters are varied.
Commercial technology (CFFLS pyrolysis technology):
CFFLS (Consortium for fossil fuel liquefaction science) technology is implemented by USA.Here; plastic is subjected to a very simple pretreatment process of shredding of waste to 1-10cm size. The shredded materials are then subjected to magnetic and eddy current cleaning steps. In pyrolysis at about 600 degrees centigrade for 1hr about 80% of oil yield is obtained, which is relatively low in chlorine content (1-10ppm).
Future prospects of pyrolysis technology:
Pyrolysis is a very promising and reliable technology for the chemical recycling of plastic wastes. Countries like UK, USA, and Germany etc have successfully implemented this technology and commercial production of monomers using pyrolysis has already begun there.
Pyrolysis offers a great hope in generating fuel oils, which are heavily priced now. This reduces the economical burden on developing countries. The capital cost required to invest on pyrolysis plant is low compared to other technologies. So, this technology may be the beacon light in the future to a world, which is now on the verge of acute fuel shortage.
Indian scenario and conclusion:
According to one estimate in India about 80000 tons of municipal solid waste is generated everyday of which plastics comprise of only 4-6%. A scientific and systematic approach in recycling the plastic waste in India is still in its infancy. Unscientific and haphazard landfilling is in operation in urban areas and in rural areas practically there is absence of any treatment.
The reasons are many. Both the government and private industrial sectors failed to initialize the development of indigenous technologies related to this area. Except well-established industries like Reliance polymers etc, others are not investing in a venture like this.
Nevertheless, India has already taken its first step in this direction. In
the course of time, with the potential that our country has, India will surely make the most of chemical recycling methods and achieve great profits and progress by adapting pyrolysis.
Plastics have become an integral part and parcel of our lives due to its economic value, easy availability, easy processability, light-weight, durability and energy efficiency, besides other benefits.
Since plastics are re-usable and recyclable, there should not have been any problem of disposal of the plastics waste, however due to our poor littering habits and inadequate waste management system/infrastructure, plastics waste management, disposal continues to be a major problem for the civic authorities, especially in the urban areas.
Though various steps have already been either taken or initiated by the Government and the legal/civic authorities to reduce the problem of this waste management, an innovative invention by Prof. Alka Umesh Zadgaonkar of the Department of Applied Chemistry, G.H. Raisoni College of Engineering, Nagpur, Maharashtra, has created a hope and scope to tackle this problem more easily and more environmentally-friendly manner.
She has invented a catalyst system, which converts polymeric materials into liquid, solid and gaseous fuels.
Under controlled reaction conditions, plastics materials undergo random de-polymerization and is converted into three products:
a) Solid Fuel â€œ Coke
b) Liquid Fuel â€œ Combination of Gasoline, Kerosene, Diesel and Lube Oil
c) Gaseous Fuel â€œ LPG range gas
The process consists of two steps:
i) Random de-polymerization
- Loading of waste plastics into the reactor along with the Catalyst system.
- Random de-polymerization of the waste plastics.
ii) Fractional Distillation
- Separation of various liquid fuels by virtue of the difference in their boiling points.
One important factor of the quality of the liquid fuel is that the sulphur content is less than 0.002 ppm â€œ which is much lower than the level found in regular fuel.
All plastics are polymers mostly containing carbon and hydrogen and few other elements like chlorine, nitrogen, etc. Polymers are made up of small molecules, called monomers, which combine together and form large molecules, called polymers.
When this long chain of polymers break at certain points, or when lower molecular weight fractions are formed, this is termed as degradation of polymers. This is reverse of polymerization or de-polymerization.
If such breaking of long polymeric chain or scission of bonds occur randomly, it is called ËœRandom depolymerizationâ„¢. Here the polymer degrades to lower molecular fragments.
In the process of conversion of waste plastics into fuels, random depolymerization is carried out in a specially designed reactor in the absence of oxygen and in the presence of coal and certain catalytic additives. The maximum reaction temperature is 350oC. There is total conversion of waste plastics into value-added fuel products.
Unique features of the process and product obtained are:
Â¢ All types of Plastics Waste including CDâ„¢s and Floppies having metal inserts, laminated plastics â€œ can be used in the process without any cleaning operation. Inputs should be dry.
Â¢ Bio-medical plastics waste can be used.
Â¢ About 1 litre of Fuel is produced from 1 kg of Plastics Waste. Bye-products are Coke and LPG Gaseous Fuel.
Â¢ Any possible dioxin formation is ruled out during the reaction involving PPVC waste, due to the fact that the reaction is carried out in absence of oxygen, a prime requirement for dioxin formation.
Â¢ This is a unique process in which 100% waste is converted into 100% value-added products.
Â¢ The process does not create any pollution.
Though the fuel so produced from the plastics waste could be used for running a four-stroke/100 cc motorcycle at a higher mileage rate, the inventor agrees that separation of petrol from the liquid fuel could be a complex generation. Nevertheless the product is good enough for use as an alternative clean fuel in boilers and other heating systems.
It is, however, not the first time that fuel has been produced out of plastics waste. A Japanese company, M/s. Ozmotec, is already manufacturing fuel out of plastics waste at an industrial plant in Japan employing the Pyrolysis process. However, Prof. Zadgaonkarâ„¢s process is a continuous one and hence is cheaper, whereas the Japanese technology is a batch process and is comparatively costlier.
A live demonstration of the production of Liquid Fuel was made in the presence of ICPE led team in the laboratory. Three kgs of plastics scrap was used to produce about 2 litres of Liquid Fuel in about 3 hrs. The reaction was terminated after the trial demo. The fuel obtained was used in smooth running of a motorcycle, which was experienced by the visiting members. However, the inventor does not wish to claim the product as a substitute for Petrol or Diesel at this stage. The present use would be as a fuel for running boilers and other heating purposes.
The process is also carried out in absence of oxygen & in the presence of coal and certain hybrid catalytic additive.
The reaction parameters viz. temperature and pressure for a batch were extremely high in initial stages.
Later with the use of hybrid catalyst the maximum reaction temperature were brought down to a greater extend.
1.Feed System :
Feed consists of all type of plastic scrap
The system essentially consist sorters and sizing equipment like of Crusher
The material is crushed in to uniform size for ease of handling and melting
This process of sizing and grading the waste is semi automatic.
The feeder consists of a driving motor, electric heater and control panel.
The granular crushed/cut/shredded waste plastic melts and injected in the melting vessel.
In melter vessel, the feed is heated to 275Ã‚Â°C -410Ã‚Â°C.
The heat required for the melting will be supplied by the gas generated from the plant.
The molten plastic will be drawn from the overflow end of melter vessel to Dechlorinate.
Here the waste plastic is heated with catalytic additive which helps in removal of chlorine.
The hydrocarbons free from HCl shall be used for heating purpose
The molten plastic is taken out and subjected to depolymerization
The molten waste plastic free of chlorine is allowed to flow over a heated surface at 300 - 350 OC
polymers are highly heat sensitive due to the limited strength of the covalent bonds
Hence The breaking of chemical bonds under the influence of heat occurs
Here complex hydrocarbons breaks into simpler molecules to increase the quality and quantity of lighter, more desirable products.
It is also known as unzipping reaction.
Reduces pollution helps in waste plastic degradation.
Cheaper and quality fuel.
Perfect solution for waste plastic, rubber, tyre management.
Raw material readily available.
Plant is energy self sufficient.
This study shows without doubt that one-way PET bottles are as Ëœecologically favourableâ„¢ as refillable glass under non-deposit circumstances. A plausible alternative could be to revise the Packaging Ordinance, such that ecologically favourable packaging systems would be included in a deposit without being discriminated when compared to refillable packaging. It cannot be explained to consumers that they should return the empty bottles to the store if they are
subsequently transported to the other side of the world for recycling. This way we are losing environmental gain that is the prime reason behind bottles collection. This study has shown that it does not matter whether collected PET is recycled into polyester fibre, sheet, strapping or back into PET bottles: they all offer equal benefits to the ecological profile of PET. Mandatory or semi mandatory requirements to recycle PET bottles into PET bottles would be ridiculous. Public perception does not always match reality. Not many people comprehend that PET bottles, even for single use, are as good as their glass counterparts. This calls for further improvements in balanced, reputable education, and independent and irrespective of local political