Why use plastics

8/7/2019 Why use plastics

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Why use plastics

� Plastic are easily formed materials.

� The advantage to the manufacturer is that plastic products can be mass-produced and require less skilled staff .

� Plastics require little or no finishing, painting, polishing etc. Plastic isreferred to as a self-finishing material. Particular finishes can be achievedat relatively low cost.

� Plastics can be easily printed, decorated or painted.

� Plastics are corrosion resistant, and generally waterproof althoughcertain types of plastics such as UPVC can become brittle and it is possible

for the sun¶s rays to cause the colour of the plastic to fade. It becomesbleached.

� Plastics are lighter than metals, giving deeper sections for a givenweight, and hence stronger sections.



Origins of Plastics - synthetic plastics.

� The main source of synthetic plastics iscrude oil.

� Coal and natural gas arealso used.

� Petrol, paraffin,lubricating oils and high

petroleum gases are bi-products, producedduring the refining of crude oil.



Natural Plastics

� Natural µplastic products¶ occur in such things as animals¶ horns, animals¶milk, insects, plants and trees.

� Animals horns - Casein (glue)

� Animals milk - Formaldehyde (glue)

� Insects - Shellac (French polishing)

� Plants - Cellulose (table tennis balls), Cellulose acetate (cloth, photographic

film, handles), Cellophane (wrapping), Bitumen (roads, flat roofs)

� Trees - Latex (rubber)



Types of Plastics



Thermoplastics

� There are a wide range of thermoplastics, some that are rigid andsome that are extremely flexible.

� The molecules of thermoplastics are inlines or long chains with very fewentanglements. When heat is appliedthe molecules move apart, whichincreases the distance between them,

causing them to become untangled.This allows them to become soft whenheated so that they can be bent into allsorts of shapes.

� When they are left to cool the chainsof molecules cool, take their former position and the plastic becomes stiff

and hard again. The process of heating, shaping, reheating andreforming can be repeated manytimes.

Long chain molecules



Thermoplastics and PlasticMemory

Each time a thermoplastic is reheated it will try and return to itsoriginal shape, unless it has been damaged due to overheating or overstretching. This property is called plastic memory.

This is why a shape formed in thermoplastic becomes flat whenreheated.



Thermosetting plastics

� The molecules of thermosettingplastics are heavily cross-linked.They form a rigid molecular structure.

� The molecules in thermoplasticssit end-to-end and side-by-side.

� Although they soften when heatedthe first time, which allows them tobe shaped they becomepermanently stiff and solid andcannot be reshaped.

� Thermoplastics remain rigid andnon-flexible even at hightemperatures. Polyester resinand urea formaldehyde areexamples of thermosettingplastics.

Cross-linked molecules



Polythene

� High-density

polythene has been

used to manufacture

milk crates, bottles,buckets, bowl and

gear wheels.

� It is stiff, hard, can be

sterilised and is

dense.



LDPE

Low density polyethylene

� Makes bottles that requires flexibility

� Produces grocery bags and garbage bags,

shrink and stretch film and the coating for milk cartons



HDPE

High Density Polyethylene

� Used in milk, juice and water containers in order

to take advantage of its protective barrier properties

� Its chemical resistance properties make it a

good choice as container for householdchemicals and detergents.



Polystyrene

� Polystyrene is used tomake plates, cutleryand model kits.

� It is stiff hard andcomes in a widerange of colours.

� Image: cup andsaucer



Nylon

� Nylon is hard, tough, self-lubricating, has a highmelting point and hasvery good resistance towear and tear.

� It has been used to makeclothing, bearings andpropellers.

� Image: A nylon castor (wheel).



PVC� The rigid type is used to

make pipes, guttering

and roofing. It is very

lightweight and is

resistant to acids andalkalis.

� The plasticised type is

used for suitcases,

hosepipes, electrical

wiring and floor

coverings.

� Image: plumbing U-bend



PET

Polyethylene Terephthalate

� A clear, tough, polymer with exceptional gas andmoisture barrier properties.

� PET¶s ability to contain carbon dioxide

(carbonation) make it a good choice in soft drink

bottles.



Vinyl

Polyvinyl chloride, or PVC

� Excellent clarity, puncture resistance andcling

� Film vinyl can breathe, making it ideal for meats



PPPolypropylene

� High tensile strength, ideal for caps and lids with

threaded openings

� High melting point so can be hot-filled with products thatthen will cool

� Also used for products that need to be incubated, suchas yogurt



PSPolystyrene

� In its crystalline form, it is a colorless plastic plastic that can be clear and

hard.

� It can also be foamed to provide exceptional insulation properties. Foamed

or expanded polystyrene (EPS) is used for products such as meat trays,

egg cartons and coffee cups.

� It is also used for packaging and protecting appliances, electronics and

other sensitive products



Plastics Compared to Metals and

Ceramics Disadvantage

Lower useful thermal range

High creep, low yield strength

Low structural strength

Low heat dissipation

Low conductivity

UV degradation

Hard to color match

Affected by solvents

May cause fumes/fire hazard

Advantage

Ease of processing

Low brittleness

Lightweight products

Good thermal insulation

Good electrical insulation

Utility as clear material

Use without painting

Can be applied as solution

Waste can be burned

Characteristic

Low melting point

High elongation

Low density

Low thermal conductivity

Electrical resistance

Optical clarity (some types)

Easily colored

Solvent sensitivity

Flammable



Polymers²many atoms or

molecules� Natural or Synthetic

� Monomer = building block

� Polymer = chains (linked

groups)



History of PolymersDate

1868

1909

1919

1927

1927

1929

1936

1936

1938

1938

1938

1939

1939

Material

Cellulose Nitrate

Phenol-Formaldehyde

Casein

Cellulose Acetate

Polyvinyl Chloride

Urea-Formaldehyde

Acrylic

Polyvinyl Acetate

Polystyrene or Styrene

Nylon (Polyamide)

Polyvinyl Butyrate

Polyvinylidene Chloride

Melamine-Formaldehyde

Example Use

Figurines

Electrical equipment

Beauty accessories

Cellophane package wrapping

Pipe, Synthetic Leather

Lighting fixtures, Plywood glue

Brush backs, displays

Synthetic flooring

Disposable utensils

Hosiery

Safety glass interlayer

Saran wrap

Countertops, Cabinets



History of PolymersDate

1942

1942

1943

1943

1947

1948

19541956

1957

1957

1964

1964

Material

Polyester

Polyethylene

Fluorocarbon

Silicone

Epoxy

Acrylonitrile-Butadiene-Styrene

Polyurethane or UrethaneAcetal

Polypropylene

Polycarbonate

Ionomer

Polyimide

Example Use

Clothing, Boat hulls

Milk Jugs

Industrial gaskets, Non-stick liners

Gaskets, Tubing, Utensils

Glues

Luggage

Foam cushions, Shoe soles, WheelsAutomotive parts, Toilet parts

Living hinges, Safety helmets

Water bottles, Eye protection

Golf balls, Skin packages

Gears

Why use plastics

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