Chapter 6 discusses plastics, defining them as organic polymers that can be molded when heated and retain their shape upon cooling. It covers various types of polymers, including linear, branched, and crosslinked polymers, as well as their synthesis through addition and condensation polymerization. The chapter also distinguishes between thermoplastics, which can be reshaped multiple times, and thermosetting plastics, which cure permanently, and outlines different molding processes including injection, extrusion, and compression molding.

1. CHAPTER 6
PLASTIC

2.  An organic polymer material ( with carbon and
hydrogen base ) with the ability to flow into a
desired shape when heat and pressure are applied to
it and retain the shape when they are withdrawn.
 In more technical terms, a plastic is a material that
can be heated and molded so that it keeps its
molded shape after it cools.
DEFINITION

3. POLYMERS

4.  Polymer molecules are very large
macromolecules consisting of long flexible
chains with carbon atoms as a backbone.
POLYMERS

5.  Polymer is composed of a large number of repetitive
structures called mer.
 A single mer is called monomers.
 Thus, a polymer is made up of thousands of monomers
joined chemically together to form a large molecule.
POLYMERS

6. POLYMER STRUCTURE

7. MOLECULAR STRUCTURE

8.  Linear polymers are those in which the mer units are
joined together end to end in single chains. These
long chains are flexible and may be thought of as a
mass of spaghetti where each circle represents a mer
unit.
 Some of the common polymers that form with linear
structures are polyethylene, polyvinyl chloride,
polystyrene, polymethyl methacrylate, nylon, and the
fluorocarbons.
LINEAR POLYMERS

9.  Polymers may be synthesized in which side-
branch chains are connected to the main ones,
these are fittingly called branched polymers.
 The branches, considered to be part of the main-
chain molecule, result from side reactions that
occur during the synthesis of the polymer.
BRANCHED POLYMERS

10.  In crosslinked polymers, adjacent linear chains
are joined one to another at various positions by
covalent bonds.
 The process of crosslinking is achieved either
during synthesis or by a nonreversible chemical
reaction that is usually carried out at an elevated
temperature.
CROSSLINKED POLYMERS

11.  Trifunctional mer units, having three active
covalent bonds, form three-dimensional
networks and are termed network polymers.
 These materials have distinctive mechanical and
thermal properties; the epoxies and phenol-
formaldehyde belong to this group.
NETWORK POLYMERS

12.  Polymerisation is the process of forming a polymer.
 This process can be classified as addition
polymerisation and condensation polymerisation.
POLYMERISATION

13.  The process chemically combines similar
monomer to form a long chain of molecule
(linear molecule).
ADDITION POLYMERISATION

14.  Two or more chemically different monomers are
polymerised to form a cross linked or linear
polymer, along with a by-product such as water
or ammonia.
CONDENSATION POLYMERISATION

15. EXAMPLE OF PLASTIC PRODUCT

16. There are two types of plastics:
1)Thermoplastics
2)Thermosetting
TYPES OF PLASTICS

17.  Thermoplastics are the plastics that do not undergo
chemical change in their composition when heated
and can be moulded again and again.
THERMOPLASTICS

18.  Deformable at higher temperatures and becomes
hard again after cooling.
 Can be softened and hardened by heating and cooling
any number of times.
 Since the flow easily by heating, they are suitable for
processing by extrusion or injection moulding.
 Easy to be machined on.
THERMOPLASTICS POLYMER

19. Thermoplastics
Long chain molecules

20.  Polyethylene
 Polypropylene
 Polystyrene
 Polyvinyl Chloride (PVC)
 Polymethyl Methacrylate (Perspex)
 Polyamide (Nylon)
Example of thermoplastics

21. EXAMPLE THERMOPLASTICS

22. DENTAL THERMOPLASTICS

23. SOCKET MADE OF
THERMOPLASTIC

24.  A thermosetting plastic, also known as a
thermoset, is polymeric material that
irreversibly cures. The cure may be done
through heat (generally above 200 °C
(392 °F)), and involve a chemical reaction.
THERMOSETTING

25.  Are soft or soften upon heating.
 Cannot be re-softened once they have set and
hardened.
 Due to cross-linking of molecule chains,
thermosetting materials are hard, tough, non-swelling
and brittle.
 Ideal for moulding and casting into components.
THERMOSETTING POLYMER

26. Thermosetting plastics
Cross-linked molecules

27.  Phenol fomaldehyde
 Expoxide
 Polyester
 Urea formaldehyde
 Melamine formaldehyde
Examples of thermosetting plastics

28. THERMOSET TOILET SEAT PRODUCT

29. MOULDED PART

30. No. Thermoplastics Thermosetting
1 Composed of chain molecules Cross linked molecules
2 Addition polymerisation Condensation polymerisation
3 Deforms at high temperature Cannot be deformed at high
temperature
4 Plasticity increases with
temperature
Plasticity does not increase with
temperature
5 Easily moulded and remoulded
into any shapes
Cannot remoulded into new
shapes
Comparison between thermoplastics and
thermosetting plastics

31. 1) Injection Moulding
2) Extrusion Moulding
3) Compression Moulding
4) Blow Moulding
Plastic Production Process

32. INJECTION
MOULDING PROCESS

34. Step 1: Plastic granules are melted
down and with screw injected into
the mold.

35. Step 2: The mold is held under
pressure (hold pressure) until the
plastic material cools and hardens.

36. Step 3: Once the material ( plastic )
hardens, the mold is opened and the
part is removed from mould.

37. Step 4 : Mould again closed and
the process can be repeated.

38. EXTRUSION MOULDING
PROCESS

40.  Process that supplies a continuous stream of
thermoplastic material with equally cross
section where it is directly produced through a
shaping tool or to some other subsequent
shaping process(dies) placed directly on the
end of the extrusion machine.
Extrusion Moulding Process

41. Extrusion Moulding Process

42.  Working principles-
1.The pellets or resins are inserted into the hopper
2.The material then fed into the heated cylinder by rotating
screw
3.When the material become softer,it will be forced continously
by the rotating screw ram.
4.The products or outcomes are formed into continous shape.
5.After the product exiting from the die,it will be cooled by
air,water or become cold by interact with cold roll surface
where then it will be solidifies while rolling
6.Extruded product such as pipe,rod,etc,extrude this way
because it can be curved or bended after extruded with
hotwater by sinking it in it.
Extrusion Moulding Process

43. Extrusion Moulding Product

44. COMPRESSION
MOULDING PROCESS

45. Compression Moulding

46. Compression Moulding

47. Compression Moulding

48.  Compression moulding is principally used for
thermosetting plastics.
 Preheated resin is placed into a hot mould cavity.
The upper section of the mould is subsequently
forced down onto the resin to create the desired
product shape. The applied pressure and heat
forces the liquified polymer to fill the cavity.
Compression Moulding

49.  Following the compression, a period of heating is
required to force cross-linking of the thermosetting
polymer.
 Throughout the process heat and pressure are
maintained until the polymer has cured.
Compression Moulding Process

51. Compression moulding is a high-volume, high-
pressure plastic moulding method that is suitable
for moulding complex, high-strength objects.
And with its short cycle time and high production
rate, many organizations in the automotive
industry have chosen compression moulding to
produce parts.

52. BLOW MOULDING
PROCESS

53.  Working principle for extrusion blow moulding
method :
 The resins or pellets are inserted into the hopper,
 With gravity manipulating, the materials enter the
injection or extrusion chamber or cylinder which
surrounded with heater,
 When the materials become softened ( plasticizers
), it will be injected or extruded using screw
rotator or torpedo plunger,
 The hot and softened material is called a parison.
 The materials will be flow straight to the nozzle
and enter the mould cavity.

54.  Top of the parison will be cut off using a blade,
 The air then blowed into the parison through a
cavity at the top of the mould,
 The plastic will be cooled, then solidified in the
mould under water system cycling in the
channels in the mould,
 After that the mould and the product will be
retrieved,
 The connecting opener will retrieved the
product using ejector pin to eject the product
out the mould.

55. The resins or pellets are inserted into the hopper.

56. The materials are heated and become softened. Then it will be
injected by using screw rotator.

57. The materials will be flow straight to the nozzle and enter the
mould cavity.

58. Top of the parison will be cut off using a blade.
The air then blowed into the parison through a
cavity at the top of the mould.

59. The plastic will be cooled, then solidified in the
mould under water system cycling in the
channels in the mould.
After that the mould and the product will be
retrieved,

60. Parison (blue) Blown bottle
(blue)

61. Plastic engineering
application
 Advantages
1. Excellent electrical
insulation properties
2. Transparent and
translucent
3. Easy coloured
4. Ease of fabrication
5. Good wear and scratch
resistance
 Disadvantages
1. Plastics produces toxic
fumes when it is burnt
2. Low heat resistant
3. Softer and less elastic
than metal
4. Brittle at low
temperature