A Glimpse of Industrial Polymers

CONTENTS 2

What is ‘polymer’ and ‘plastic’?

Two types of polymerization reactions

Chain polymerization examples

Step growth polymerization examples

Comparison of two types

Rubber, Vulcanization, Synthetic elastomers

Synthetic Fibers

Synthetic Films

Biodegradable plastic

• Polymers are large molecules that are formed from

relatively small molecular fragments known as monomers

that are bonded together repetitively.

• Wool, cotton, silk, wood and leather are examples of

natural polymers that have been known and used since

ancient times. This group includes biopolymers such as

proteins and carbohydrates that are constituents of all

living organisms.

• Synthetic polymers, which includes the large group known

as plastics, came into prominence in the early twentieth

century.

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POLYMERIZATION REACTION

Converts monomers into macromolecule. May involve catalysts.

(i) Step growth or Condensation and (ii) Addition or Chain reactions are the two main types of polymerization reactions.

Condensation reaction

• Addition reaction

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ADDITION POLYMERS 8

One of the major breakthroughs in polymer chemistry

occurred in the early 1950s when the German chemist Karl

Ziegler discovered a group of catalysts that could efficiently

polymerize ethylene.

At about the same time, Giulio Natta (Italian) made the first

isotactic (and crystalline) polyethylene.

The Zieglar - Natta catalysts revolutionized polymer

chemistry by making it possible to control the stereo-

regularity of these giant molecules. The two shared the

1963 Nobel Prize in Chemistry.

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Step growth polymerization requires that the monomers

possess two or more kinds of functional groups that are

able to react with each other in such a way that parts of

these groups combine to form a small molecule (often

H2O) which is eliminated from the two pieces. The now-

empty bonding positions on the two monomers can then

join together .

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Thermoset polymer Bakelite 14

Phenolic resins

These are made by condensing one or more types of phenols

(hydroxy - substituted benzene rings) with formaldehyde, as

illustrated above. This was the first commercialized synthetic

molding plastic.

The brown material (usually bulked up with wood powder)

was valued for its electrical insulating properties (light

fixtures, outlets and other wiring devices).

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Making plastics from polymer

• A plastic contains a polymerized organic substance of large

molecular weight as an essential ingredient, is solid in its

finished state, and in its processing into finished articles

can be shaped by flow. Plasticizers, fillers etc., are also

added to alter the properties of the plastic products.

• Thermosetting plastics are processed by heat curing to

produce an infusible or insoluble product.

• Thermoplastics are processed by heating to soften them

and cooling to harden them. Process may be repeated.

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Commercial step growth polymers

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Raw Materials

Monomers: vinyl chloride, ethylene, propylene and similar simple hydrocarbons

Chemical intermediates : phenol, formaldehyde, hexamethylenetetramine, phthalic anhydride, methyl acrylate and methacrylate

Other raw materials: plasticizers, fillers, and reinforcements are also added to alter the properties of the plastic products.

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RUBBER

Vulcanization creates disulfide cross-links that prevent the

polyisoprene chains from sliding over each other. The

degree of cross-linking can be controlled to produce a

rubber having the desired elasticity and hardness. More

recently, other kinds of chemical treatment (such as

epoxidation) have been developed to produce rubbers for

special purposes.

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Vulcanization creates disulfide cross-links that prevent the

polyisoprene chains from sliding over each other. The

degree of cross-linking can be controlled to produce a

rubber having the desired elasticity and hardness. More

recently, other kinds of chemical treatment (such as

epoxidation) have been developed to produce rubbers for

special purposes.

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Synthetic Fibers and their Applications

Polyamides –They are used in home furnishings, especially carpets.

Acrylics and Modacrylics – polyacrylonitrile is the major component of several industrial textile fibers.

Spandex – It is used in foundation garments, hose, swimwear and other elastic products.

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Other Synthetic Fibers

Polyolefins – They excel in special cases, such as ropes, laundry nets, carpets, blankets and backing for tuffed carpets, but are difficult to dye and their melting point is low.

Fluorocarbons – It is widely used in pump packings and shaft bearings.

Glass Fibers – are used for electrical insulation in motors and generators, structural reinforcement of plastics, fire-proof wall coverings and tire cords.

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Films

are made from different polymers such as polyesters, polyvinyl chloride, etc.

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3 Common Types of Film Processing

Slit-die process – produces flat sheets by extruding the molten polymer through a slit-die into a quenching water bath or onto a chilled roller.

Blow-extrusion Process – produces tubular film by using air pressure to force the molten polymer around a mandrel.

Calendering – preparation of film is produced by feeding a plastic mix of polymer, stabilizer, and plasticizers between two heated roll where it is squeezed into a film.

Biodegradable disposable plastic 27

Interest in biodegradable disposable plastic items has steadily grown

because of the environmental problems caused by non-degradable

synthetic polymers.

Disposable packaging materials used to ship and protect purchased

items as well as disposable containers used for food and drink are of

special interest.

The idea that one time use items can be disposed of with the peace of

mind, that they will not remain for centuries in a landfill, or as litter, is

one of the tenets driving the recent interest in "green" technologies and

lifestyles.

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With packaging materials, the reduction in usage of raw

materials, re-use and recycling is of course the best route to

sustainable lifestyle.

However, for various reasons, in practice, much of the

material ends up being discarded to a landfill or accidentally

shows up as litter.

For these instances, it is advantageous to have a plastic

material that would biodegrade when exposed to

environments where other biodegradable materials are

undergoing decay.

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What is Biodegradable?

Biodegradation is degradation caused by

biological activity, particularly by enzyme action

leading to significant changes in the material's

chemical structure. In essence, biodegradable

plastics should breakdown cleanly, in a defined

time period, to simple molecules found in the

environment such as carbon dioxide and water.

Polymer Science and Technology Books 30

F. W. Billmayer, Textbook of Polymer Science 3rd

edition, 1984, John Wiley & Sons, Singapore

F. Rodriguez, Principles of Polymer systems, 4th

edition, 1996, Taylor & Francis.

Dryden’s Outline of Chemical Technology for 21st

Century, 3rd edition, chapter V a) Polymerization

Fundamentals, b) Polymerization Technology.