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Q 6

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Q 6 PLASTICS * * Mr.Breslin/Mr. Harvey St. Oliver P.P. School Engineering Dept. * Mr.Breslin/Mr. Harvey St. Oliver P.P. School Engineering Dept. * Mr.Breslin/Mr ... – PowerPoint PPT presentation

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Title: Q 6


1
Q 6
  • PLASTICS

2
Short History of Plastics
  • 1862 first synthetic plastic
  • 1866 Celluloid
  • 1891 Rayon
  • 1907 Bakelite
  • 1913 Cellophane
  • 1926 PVC
  • 1933 Polyethylene
  • 1938 Teflon
  • 1939 Nylon stockings
  • 1957 velcro
  • 1967 The Graduate

3
  • Any solid substance that can be moulded into a
    new shape under pressure is said to be plastic.
  • When referring to plastics we talk about
    polymers, mainly because plastic is a state,
    condition, property.
  • e.g. metals when heated to a certain temp are
    said to be plastic and certain polymers when
    moulded are no longer plastic after moulding.
  • Plastics can be any colour and can be moulded
    into complex shapes.

4
  • Numerous items such as household equipment, toys,
    building materials, decorative objects,
    containers, packaging, aircraft parts, motor car
    parts, safety screens, etc are made form
    plastics.

5
  • Plastics can have a wide range of properties
    e.g. plastic grill on front of motor car must be
    decorative and tough where as a plastic drinking
    cup must be able to withstand temps up to 100
    degrees
  • Plastics can be hard or soft, transparent or
    opaque, rigid flexible. They are poor conductors
    of heat and electricity. Plastics are suitable
    for insulation

6
TYPES OF PLASTICS
  • Plastics are divided into three main categories
  • 1.) Natural plastics
  • 2.) Modified Natural Plastics
  • 3.) Synthetic Plastics

7
Natural Plastics
  • Decorative objects have been made as far back as
    the 1860s form natural plastics. Items such as
    spoons, combs, Knife and tool handles, horn cups
    etc.
  • The most popular natural plastics are
  • AMBER
  • ANIMAL HORN
  • SHELLAC
  • NATURAL RUBBER

8
Amber
  • Amber is a resinous substance which oozes from
    pine trees and solidifies. It is fairly soft and
    can be carved into shape and polished.
  • Pine trees that produce amber usually grow in the
    Baltic region

9
Animal Horn
  • Animal horn is composed completely of keratin.
  • This is a fibrous protein which is found in
    the outer layers of the skin, finger nails, hair
    and animal horns.

10
Natural Rubber
  • Natural rubber is a cream coloured elastic
    material extracted from the rubber tree. It is
    more often referred to as a Natural polymer.

11
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12
Shellac
  • Shellac is a resinous substance. It is produce by
    the parasitic insects which live on trees,
    generally in India. Shellac was once important as
    an adhesive and wood polish.
  • Lact insect

13
How Plastics are Classified
14
Introduction
  • We use plastics daily, anything from plastic
    garbage bags to compact discs to the cars we
    drive incorporate some type of polymer.
  • Most common material used is production of
    polymers is petroleum. (oil)
  • These materials contain the basic elements that
    are used in forming polymers...carbon, hydrogen,
    oxygen, nitrogen, chlorine, and fluorine.

15
CARBON
  • Considered to be the backbone of
    polymerization.
  • A general model of a monomer is below

H            H               C 
C                 H          "X"
16
Polymerization
  • Polymers are macromolecules because smaller
    molecules are joined together to form polymer
    chains.
  • This process is called polymerization.
  • For a monomer to polymerize, it must be capable
    of forming at least two covalent bonds,  one on
    the front, one on the back.

17
Network Structure
  • Some of these monomers are poly functional,
    meaning that three or more bonds can be formed,
    resulting in a network.
  •   This network structure determines the
    properties of the material.
  •   There are two classifications of
    polymerization addition and condensation, with
    addition being the most common.
  •   During the addition polymerization process
    atoms add onto one another to form the polymer
    chains.
  •   No atomic change takes place, atoms simply
    connect to the "arms" of their neighbor. 

18
Branched Polymers
  • Structural branching can be achieved by causing
    a macromolecule to grow at several locations
    rather than just at the ends.
  •   These polymers will not  pack together as
    tightly as linear polymers.
  •   An example of a branched polymer is low density
    polyethylene however high-density polyethylene
    remains essentially linear.

19
Thermoplastics
  • A polymer formed through the addition process
    is called a thermoplastic material.
  • Properties of thermoplastics in general are
    that they become soft when heated and harder when
    cooled.
  •   These materials have no strong bonds between
    individual molecules and can be softened by heat
    and remolded.
  •   Thermoplastics are recyclable materials.

20
Cross Linking
Thermoplastics may have varying degrees of cross
linking ranging from none to heavy.
21
ADDITION POLYMERISATION
  • Adding together of large number of mers so that
    they form into long CHAIN-LIKE molecule
  • Example Polymerisation of Ethylene
  • Catalyst added to Ethylene molecule.

22
  • Weaker Bond is broken down, leaving Carbon atom
    free to link up with other carbon atoms
  • Weak Bond is attacked by a Free Radical
  • Element.

Chain stopper
Free radical
  • Weak Bond contains two electrons,
  • one which is attacked by radical other is left.

23
  • New molecule behaves like a radical and the
    process is repeated continuously.
  • Several thousand molecules can be joined together
    this way in a single second until eventually a
    chain stopper is incorporated which terminates
    the process

24
  • The result is that the pot is now full of a large
    number of interwoven chain molecules, twisted
    around each other like spaghetti.
  • Where these chains touch off each other Secondary
    Bonds are formed. Therefore the Secondary Bonds
    provide the three dimensional structure. These
    bonds are much weaker than Primary Bonds, and are
    susceptible to heat.

25
CONDENSATION POLYMERISATION
  • Used to produce Thermosetting Plastics
  • It forms a Strong Primary Bond with cross-linking
    between chains
  • Two monomers react chemically to form a new
    molecule with water eliminated as a by-product
  • The polymer produced cannot be re-softened, has
    high tensile strength and high melting point

26
Phenol Formaldehyde is an example
Phenol
Phenol
Formaldehyde
27
Phenol Formaldehyde
  • Each of the Phenol molecules give up a Hydrogen
    atom, and the Formaldehyde molecule gives up an
    Oxygen atom, and these join to form water.

WATER
28
CO-POLYMERISATION
  • This type of polymerisation involves adding
    together different types of Mers.
  • This allows many different polymers to be
    manufactured
  • Example Polyvinylchloride, this is a
    combination of PVC and POLYETHYLENE

29
CO-POLYMERISATION
30
THERMOPLASTICS THERMOSETTING
Chemical Bonding CovalentBonding Secondary Bonding Weak Van Der Walls Forces ii) Polymerisation Process Addition Polymerisation Chemical Bonding Covalent Bonding Primary Bonding Strong 3-D structure held together by strong rigid cross links ii) Polymerisation Process Condensation Polymerisation
31
THERMOPLASTIC THERMOSETTING
iii) Internal Structure Linear Branched Chains iv) Properties Low Melting Point Allows for easy moulding Easily disrupted by heat Low tensile strength Branched structures have higher tensile strength than linear Ideal for recycling iii) Internal Structure Cross Linked Structure iv) Properties High Melting point High tensile strength Good thermal insulation Can withstand high temperatures without loosing rigidity Stiff and less flexible
32
Thermosetting Plastics
Primary covalent bonding giving 3-D
structure. Internal structure is
cross-linked. They are rigid, strong,
inflexible and cannot be remoulded. High
melting point.
33
Thermo Plastics
  • Bonded by weak van-der-waals forces between
    adjacent chains.
  • Internal structure can be linear or branched.
  • They are soft,

34
  • Polyethylene terephthalate (PET) used in bottles,
    carpets and food packaging
  • Polypropylene (PP) used in food containers,
    battery cases, bottle crates, automotive parts
    and fibres
  • Polystyrene (PS) used in dairy product
    containers, tape cassettes, cups and plates
  • Polyvinyl chloride (PVC) used in window frames,
    flooring, bottles, packaging film, cable
    insulation, credit cards and medical products.

35
Compare
Thermoplastic
Thermoset
Elastomer (Rubber)
36
Additives
  • Catalysts plus the application of heat and
    pressure are used to accelerate reactions between
    substances.
  • Other agents are added to achieve desired
    properties of the material.
  • Some of those include plasticizers, fillers,
    reinforcing agents, and stabilizers.

37
COMMON TERMINOLOGY
  • LINEAR STRUCTURE this type of chain results
    from the process of Addition Polymerisation.
  • The chain molecules are bonded together along
    their length by weak Vander walls Forces
  • Bonds are so weak heat and high pressure can
    overcome them
  • Polymer material with Linear structures have a
    low melting point and tensile stength. ie
    Elastomers

38
  • BRANCHED CHAINS this type of chain results from
    addition ploymerisation.
  • Weak Van Der Walls forces bond the molecular
    chains together along their length
  • Side Branching means each chain has greater
    surface area and More Van der Walls forces
  • The cumulative effect of these Van der Wall
    forces gives a stiffer, stronger chain structure
    with a higher melting point. I.e. Polyethylene

39
  • CROSSLINKING - In condensation, a strong rigid
    3-D network is formed by primary covalent bonds
    between adjacent chains.
  • These bond and are called crosslinks and give the
    polymer higher tensile strength, rigidity and
    resistance to heat.
  • Thermosetting plastics are formed due to
    crosslinking.

40
  • FILLER These are materials that are added to
    polymers to increase their volume and strength
  • GRP Glass reinforced plastic known as Fibre
    glass consists of a polymer mixed with glass
    fibres. This increases the tensile strength of
    the material
  • PIGMENTS have the function of giving colour to
    the polymer

41
  • LUBRICANTS make a polymer easier to mould.
    Various types of waxes are used in small amounts
    for this purpose
  • PLASTICISERS are added to polymers to improve
    their flexibility. They achieve this by altering
    the forces of attraction between molecules of the
    polymer
  • NATURAL RUBBER have linear chain molecules
    which are folded in nature. They are both plastic
    and elastic

42
NATURAL RUBBER
  • This is the sap from the rubber tree. Its polymer
    chains are of a folded nature and are bonded by
    weak Van-der-Walls forces.
  • Natural rubber is both plastic and elastic.

43
SYNTHETIC RUBBER
  • These are natural rubbers which are processed
    with sulphur. This is called VULCANISATION.
  • Vulcanised rubber have folded chains, which are
    cross-linked. This causes the chains to be
    permanently bonded.
  • They are more durable and less flexible than
    natural rubbers

44
AMORRPHOUS POLYMER
  • These structures are random and disorganised.
    They have a low tensile strength and melting
    point.
  • Example - Thermoplastics

45
CRYSTALLINE POLYMER
  • This structure is arranged in a regular geometric
    pattern. This gives a strong rigid structure with
    high tensile strength

46
VAN DER WALLS FORCES
  • These are bonding forces between polymer chains
    as a result of addition polymerisation.
  • They are weak secondary bonds and are easily
    broken by heat and pressure.

47
ELASTOMERS
  • A group of polymers consisting of linear chains
    that are coiled, entangled and are subject to
    minimal cross-linking.
  • This irregular internal structure and bonding
    arrangement allows these materials to be very
    elastic at room temperature.

48
  • ELASTIC MEMORY This is the ability of a
    thermoplastic to return to its original shape
    when heated
  • MONOMER - This is a single polymer unit. Polymers
    are made from many mers.
  • CATALYST a substance that speeds up a chemical
    reaction. ie salt in boiling water
  • STABILISER helps to prevent the degrading
    effects of heat, ultraviolet light on the polymer
  • PROMOTERS are similar to catalysts in that they
    speed up a chemical reaction
  • INHIBITOR prohibits a reaction from occur

49
CO-POLYMER
  • This is a polymer formed when two different mers
    are linked together in the same polymer chain.
  • This new polymer may have a mixture of new
    improve properties, it is similar to alloying in
    metals.

50
PARISON
  • In BLOW MOULDING, a tube called a parison is
    extruded between the two halves of a split mould.
    The mould closes around the parison and air is
    blown into it at either end, forcing it out
    against the wall of the mould.The component is
    allowed to cool before being removed from the
    mould. Using this process, thermoplastic
    materials can be moulded into bottles and drums.

51
EXAMPLE PARISON
52
Reinforcing Agents
  • Added to improve mechanical properties and
    increase strength, impact resistance, stiffness,
    and hardness.
  • Various types of fibers are used as reinforcing
    agents.
  • These fibers may include glass fibers, carbon
    fibers, or even metal fibers.

53
Composites
Short Fibers
Long Fibers
54
Plasticizers
  • They lower the glass temperature.
  •   Glass is quite brittle and thus the glass
    temperature is very important for changing the
    properties of some materials.

55
Fillers
  • Polymer filler materials
  • These additives control the mechanical
    properties, such as material strength, of the
    polymer.
  • They reduce the amount of expensive polymer used.
  • Fillers such as chalk, wood flour and glass
    fibre can be used.

56
Stabilizers
  • Added to maintain the integrity of plastic
    during forming and service.
  •   These agents may be as simple as carbon black
    to prevent degradation of strength through
    reaction to ultraviolet light.
  •   Sometimes, lead compounds are added to increase
    or stabilize the material against weathering, if
    used in an outdoor product

57
Extenders
  • Organic materials such as oils or waxes.
  •   Extenders are added to reduce the volume of
    plastic material needed per unit area required.

58
Molecular Arrangement and Structural Properties
  • Molecular arrangement determines the size and
    weight of the plastic molecule.
  • As molecular size and weight increases, it
    affects several mechanical properties.
  •   Among those most affected are strength,
    stiffness, and hardness.
  •   Molecular arrangement also affects the
    viscosity of the plastic.  This property is very
    important for processes that involve molding.

59
Two Types of Structure
  • Two general types of structure that relate to
    properties of polymers.
  • Crystalline and amorphous
  •   Crystalline thermoplastics is much higher as
    temperature increases compared to amorphous

60
Crystalline Structure
  • The structure is arranged in a regular
    geometrical pattern.
  • This gives a strong rigid 3-dimensional structure
    with high tensile strength and melting point, as
    in thermosetting plastics

Examples  Nylon, polypropylene,.
61
Amorphous Structure
  • Here the chain structure is random and
    disorganised.
  • This structure has a lower tensile strength and
    melting point

Examples  Polystyrene, acrylic, polyvinyl
chloride.
62
General Characteristics and Properties Electrical
resistance
  • Primarily due to covalent bonding.
  • Locks the electrons into relatively fixed
    positions. 
  • Electrical conductivity increases with the
    hydroscopic materials.
  • Some plastics absorb and hold water more
    easily.
  • In this case ionic conduction may be present.

63
General Characteristics and Properties Thermal
Conductivity
  • Plastics have very low thermal properties and
    are relatively good insulators against heat and
    cold.
  •   Since electrons are closely bound by covalent
    bonds, and there are larger spaces between atoms,
    heat transfer is inhibited.
  •   Voids are often present and create insulating 
    "gas" pockets.
  • Example Insulation in walls.

64
Density
  • Plastics exhibit very low densities unless
    heavier reinforcing materials are added.
  •   Typically, commercial plastics range from about
    .3 to .75 pounds per cubic foot.
  •   

65
Corrosion Resistance
  • Excellent tolerance to corrosion.
  •   Large size of plastic molecules prevent
    transitions into solution.
  •   Plastics are subject to a special type of
    corrosion called swelling.
  •   This happens due to the large molecules
    allowing solvent agents (like grease and oil) to
    penetrate.
  • Example outside furniture

66
Manufacturing Processes and Materials
  • Polymer Processing

67
The following processes are used when working
with plastics
Injection Molding Compression Molding Transfer
Molding Rotational Molding Extrusion Blow
Molding     
Blown film extrusion Thermoforming Calendaring
Fibering Foaming Laminating
68
Introduction
  • Polymers can be made into various shapes and
    forms including resins, powders, granules, or
    sheets

69
Injection Molding
  • Plastic granules of the thermoplastic materials
    are fed into the hopper.
  • A plunger forces the plastic along the machine
  • barrel where they are melted by the heaters and
    compacted by the torpedo.
  • The softened polymer is then forced into the
    mould where it solidifies.
  • The mould is opened and the plastic product is
    ejected.

70
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71
APPLICATIONS
  • GOLF TEES
  • MILK CRATES

72
Extrusion
  • This process is used to produce items of uniform
    profile such as curtain rails and plumbing pipes.
  • Plastic granules are fed from a hopper through a
    die by a rotating screw.
  • The plastic is heated in the chamber before it
    enters the die and cooled by air jets or water as
    it leaves the die.

73
Extrusion Cont.
  • The extruded products can be cut into lengths or
    coiled.
  • Polythene, PVC and nylon are commonly extruded.

74
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75
APPLICATIONS
  • Products of of uniform profile such as curtain
    rails and plumbing pipes etc

76
Making Fiber Optic Cable
77
Compression Molding
  • This process is suitable for thermosetting
    plastics. It uses a split mould formed to the
    shape of the object to be moulded.
  • The combination of heat and pressure allows a
    measured amount of polymer to be shaped.
  • The polymer can be in powder or slug form..

78
Compression Molding
  • As the mould closes, the application of heat
    triggers the chemical reaction of crosslinking
    and the object sets (curing).
  • The mould is opened and the object is removed.
  • These mouldings can have a high quality finish
    requiring only the removal of flash.

79
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80
Compression Molding a Composite
81
APPLICATIONS
  • ELECTICAL SOCKETS
  • MICROWAVE DISHES

82
Transfer Molding
  • The powder is placed in a compartment above the
    mould where it is heated.
  • A plunger forces the molten polymer into the
    mould cavity where the polymer takes the shape of
    the cavity and solidifies.
  • It can be used to produce thermosetting objects
    with high definition such as plug tops.

83
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84
APPLICATIONS
  • Car Doors
  • Baths
  • Boats

85
Blow Molding
  • An extruded thick-walled tube, called a parison,
    is placed in the mould.
  • The mould closes and air is blown into the
    parison.
  • The parison takes the shape of the mould.

86
Blow Molding
  • Compare to blowing up a balloon inside a bottle.
  • After cooling, the split mold opens and the
    part is ejected.
  • Economical method of producing plastic bottles,
    hollow toys, balls. 

87
Blow Moulding
88
APPLICATIONS
  • PLASTIC BOTTLES
  • PLASTIC CONTAINERS

89
Calendaring
  • Continuous lengths of sheets are produced in
    thermoplastics by calendaring.
  • The material passes through a series of heated
    rollers to gradually produce the
  • desired thickness of material.
  • These sheets may then be cut to size or collected
    in a roll.

90
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91
APPLICATIONS
  • PLASTIC FLOORING

92
Foaming
  • Plastics can also be produced as foams
  • Polyurethane, polyethyelene, and polystyrene
    are some of the foaming type materials.
  • Use of these materials is varied...from
    expanded polyethylenes and polystyrene
    (styrofoaming
  • materials...such as drinking cups) to insulating
    foams or packing materials to structural foam
    used in construction.
  •  

93
Foaming
  • Elastomer foams (foam rubber) are produced in a
    number of ways including molding and compressed
    extrusion.
  •   Products include cushions, flotation devices,
    and many others. 
  • Recent advances in foaming and reinforcing
    materials such as kevlar have allowed for
    innovative structural composite materials.

94
Kevlar is a composite material used in bullet
proof vests
95
Thermoforming
  • Primarily for forming thermoplastic sheet stock
    into desired shapes.
  • Most common name is vacuum forming.
  •   Sheet of thermoplastic is placed over a mold
    and heated.
  •   Mold cavity is evacuated of air causing the
    sheet to be pushed into or over the mold by
    atmospheric pressure.
  •   Vacuum pressure and heat range varies with type
    and thickness of material being formed.
  • Products include disposable packing trays,
    household storage bins,

96
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97
APPLICATIONS
  • HOUSEHOLD STORAGE TRAYS
  • WASTE DISPOSAL BINS

98
Laminating
  • Thin layers of materials bonded together.
  • High strength plastics can be produced by layers
    of paper or cloth coated with resin being bonded
    together.
  • Heat and pressure can be used.
  •  
  • Products produced include kitchen counter tops
    and reinforced insulating tubes.

99
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100
Laminated Plastic Kitchen Worktop
101
Fiber Drawing
  • Modification of extrusion and is used to
    produce synthetic fibers such as rayon, nylon,
    and polyester.
  • Extrusion die has a small slit or has
    multi-orifices (called a spinneret).
  • Small fibers are extruded through the die and
    then post die conditioned.
  •   Conditioning processes may be chemical
    treatments to harden the fiber, dye or coloring
    the material, or mechanical treatments for
    crystallization.

102
Fiber Drawing Cont.
  • Oriented and crystallized plastic is strong in
    the longitudinal direction weakening the material
    in the lateral direction.
  • Since process is for producing fibers, this is
    desirable if the product is made into fabric.

103
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104
Pultrusion
105
Filament Winding
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