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Introduction:

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 (plastikos) meaning fit for molding,

and (plastos) meaning molded. It refers to their malleability, orplasticity

during manufacture, that allows them to be cast, pressed, orextruded into a variety of

shapessuch as films, fibers, plates, tubes, bottles, boxes, and much more.

The common wordplastic should not be confused with the technical adjectiveplastic,

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.

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Overview

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 ordecompose

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.

Chemical structure

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 frommonomers;

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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 orsulfurin 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 molecularstructure,

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.

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History

The firsthuman-made plastic was invented by Alexander Parkes in 1855[7]; 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).

Types

Cellulose-based plastics

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 elasticmaterial 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 flourmixed 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.

Bakelite

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.

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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.

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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 namestyrene foam orStyrofoam. Foam plastics

can be synthesized in an "open cell" form, in which the foam bubbles are

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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 impactstyrene 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 inits 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

forshrink-wrap, food packaging, and rain gear.

Nylon

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 Fairin 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

directorElmer 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.

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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.[9]

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 ofparachutes 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.

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Rubber

Natural rubber is an elastomer (an elastic hydrocarbon polymer) that was originally

derived fromlatex, 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.

Synthetic rubber

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.

Toxicity

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 andphthalates 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

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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 ofpolycarbonates, bisphenol A (BPA), is an estrogen-like

endocrine disruptor that may leach into food. Research in Environmental HealthPerspectives 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 wrapbased on PVC, is also of concern, as

are the volatile organic compoundspresent in new car smell.

The European Union has a permanent ban on on the use ofphthalates in toys. In 2009,

the United States government banned certain types of phthalates commonly used in

plastic.

Environmental issues

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, themanufacturing of plastics often creates large quantities of chemical pollutants.

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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 ofthe 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 softdrinkbottles, water bottles, cooking oil bottles, peanut butter jars.

2. HDPE, high-density polyethylene: Commonly found on detergent bottles, milkjugs.

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, yogurtcontainers.

6. PS, polystyrene: Commonly found on "packing peanuts", cups, plastictableware, meat trays, take-away food clamshell containers

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7. OTHER, other: This plastic category, as its name of "other" implies, is anyplastic other than the named #1#6, Commonly found on certain kinds of food

containers, Tupperware, and Nalgenebottles.

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-energyplants.

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 engineeredbacteria that synthesize a completelybiodegradable plastic, but this material, such as Biopol, is expensive at present. The

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German chemical company BASF makes Ecoflex, a fully biodegradable polyester for

food packaging applications.

Bioplastics

Some plastics can be obtained from biomass, including:

from pea starch film with trigger biodegradation properties for agriculturalapplications (TRIGGER).

from biopetroleum.

Oxo-biodegradable

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 formcommercial plastics.

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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

Polypropylene (PP)

Food containers, appliances, car fenders (bumpers), plastic pressure pipe

systems.Polystyrene (PS)

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.

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Polyethylene terephthalate (PET)

Carbonated drinks bottles, jars, plastic film, microwavable packaging.

Polyester(PES)

Fibers, textiles.

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.

Polyurethanes (PU)

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).

Polycarbonate (PC)

Compact discs, eyeglasses, riot shields, security windows, traffic lights,

lenses.

Polyvinylidene chloride (PVDC) (Saran)

Food packaging.

Polyethylene (PE)

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.

Special-purpose plastics

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.

Polytetrafluoroethylene (PTFE)

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)

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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.

Urea-formaldehyde (UF)

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.

Plastarch material

Biodegradable and heat resistant, thermoplastic composed of modified corn

starch.

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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.

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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.)

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Pyrolysis:

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 370C -420C

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.

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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.

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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%

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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

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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

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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.

Random Depolymerization:

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.

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The Process

Under controlled reaction conditions, plastics materials undergo random de-

polymerization and is converted into three products:

a) Solid FuelCoke

b) Liquid FuelCombination of Gasoline, Kerosene, Diesel and Lube Oil

c) Gaseous FuelLPG 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 ppmwhich is much lower than the level found in regular

fuel.

Principals Involved

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 Random depolymerization. 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

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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:

All types of Plastics Waste including CDs and Floppies having metal inserts,laminated plastics can be used in the process without any cleaning

operation. Inputs should be dry.

Bio-medical plastics waste can be used.About 1 litre of Fuel is produced from 1 kg of Plastics Waste. Bye-products

are Coke and LPG Gaseous Fuel.

Any possible dioxin formation is ruled out during the reaction involvingPPVC waste, due to the fact that the reaction is carried out in absence of

oxygen, a prime requirement for dioxin formation.

This is a unique process in which 100% waste is converted into 100% value-added products.

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. Zadgaonkars 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.

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Zadgaonkars Process:

The process is also carried out in absence of oxygen & in the presence of coal andcertain 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.

Steps Involved:

1.Feed System

2. Premelter

3.Melter

4.Dechlorination

5.Reactor

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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 meltingThis process of sizing and grading the waste is semi automatic.

2.Pre-melting/Feeder

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.

3.Melter

In melter vessel, the feed is heated to 275C -410C.

The heat required for the melting will be supplied by the gas generated from the

plant.

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4.Dechlorination

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

5.Reactor Section

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.

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Advantages

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.

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Conclusion

This study shows without doubt that one-way PET bottles are as ecologically

favourable as refillable glass under non-deposit circumstances. A plausiblealternative 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

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Reference