2. GLASS TRANSITON TEMP. OF SOME
THERMOPLASTICS
POLYETHYLENE--PE -110 °C
POLYPROPYLENE---PP -18 °C
POLYVINYL
ACETATE--PVA
29 °C
POLYVINYL
CHLORIDE--PVC
82 °C
POLYSTYRENE---PS 75-100 °C
7. Polyvinyl Chloride (PVC)
Applications
• Pipe, valves and fittings
• Thermoformed parts for transportation, exhibits
and machinery parts
• Pollution control equipment parts
• Packaging
The IAPD Plastics Primer, Module 3
9. Polyethylenes (PE)
Key Characteristics
• Classified by density and molecular
weight
• Excellent chemical resistance
• Zero moisture absorption
• Light weight (1/8 weight of steel)
• Excellent insulator
• High impact strength
The IAPD Plastics Primer, Module 3
11. Low Density Polyethylene (LDPE)
Key Characteristics
• Good chemical resistance
• Very flexible
• High impact strength
• Low heat resistance (60-79°C/140-
175°F)
• Used extensively in packaging industry
The IAPD Plastics Primer, Module 3
12. High Density Polyethylene (HDPE)
Key Characteristics
• Higher rigidity and tensile strength than
low and medium density polyethylenes
• Good formability
• Slightly lower impact strength than LDPE
The IAPD Plastics Primer, Module 3
13. Low Density Polyethylene (LDPE)
High Density Polyethylene (HDPE)
Applications
• Films
• Industrial trash bags
• Liners
• Shipping bags
• Marine industry
• Playgrounds
• Bathrooms
• Pipe
• Automotive
The IAPD Plastics Primer, Module 3
18. Polypropylenes (PP)
Key Characteristics
• Excellent chemical resistance
• Excellent fatigue strength — referred to as
“living hinge”
• Lower impact strength than polyethylenes
• Available in homopolymer and co-polymer
• Co-polymer offers better impact, clarity
and cold temperature properties
The IAPD Plastics Primer, Module 3
24. Polystyrene PS
• ITS inexpensive.
• IT can be hard or soft.
• It can be shaped into just about anything.
• Toys
• Hairdryers
• Drinking cups
• Computers
• Packaging
• Car parts
• Kitchen appliances
• StyrofoamTM is one brand of polystyrene foam
25. Polystyrene (PS)
Limitations
• Low impact resistance
• Brittle after UV exposure
• Cannot be used at elevated temperatures
• Mechanical stress
26. Properties of Polystyrene PS
1. The Glass transition temperature of
Polystyrene is 100º C.
2. It melts at 240ºC .
3. It softens in acetone (nail polish
remover).
4. It is recyclable.
27. FLUORINATED THERMOPLASTICS
• Fluoropolymers, or fluoroplastics, are a family of
fluorine-containing thermoplastics that exhibit
some unusual properties. These properties include
inertness to most chemicals, resistance to high
temperatures, extremely low coefficient of
friction, weather resistance, and excellent
dielectric properties.
• Mechanical properties are normally low but can be
enhanced with glass or carbon fiber or
molybdenum disulfide fillers.
35. PROCESSING OF PLASTIC MATERIALS
There are different methods to process the plastic
materials and forming several products
36. Polymers are formed by many low temperature
processes.
Extrusion
Film Blowing
Injection Molding
Blow Molding
Compression Molding
Reaction Injection Molding
Polymer Processing Methods
37. PROCESSING OF PLASTIC MATERIALS
Injection Molding PROCESS
• Injection molding is a manufacturing
technique for making parts from
thermoplastic material.
• Molten plastic is injected at high pressure
into a mold, which makes the product's
shape.
38. INJECTION MOLDING PROCESS
• The mold is made usually either steel or
aluminum.
• Injection Molding is the most common
method of production, with some
commonly made items including bottle
caps and outdoor furniture .
39. The polymer is heated to the liquid state, but it is prepared
in metered amounts, and the melt is forced into a mold to
create the part. It is not a continuous process. Many toys are
made by injection molding.
INJECTION MOLDING PROCESS
41. INJECTION MOLDING PROCESS
• There is two types of injection molding machines
1- Plunger Type
• 2- Screw Type
• In injection molding process plastic granules from a
hopper are inserted into the injection cylinder onto
the surface of a rotating screw which carries them
forward and moves to the dies and during the whole
path constant pressure is maintained and constant
heating to melt the plastic grains and after giving
them desired shape they made cool in open air or in
water.
44. The polymer is heated to the liquid state and
forced through a die under pressure resulting in
an endless product of constant cross section.
60% of polymers are prepared in this way.
Examples: tubing, pipes, window frames, sheet,
insulated wire.
Extrusion Process
45. .
• Using the same method as extrusion the
material coming out of the die is blown into a
film.
• An example is plastic wrap.
Film Blowing Process
47. Blow Molding (Vacuum molding) Process
• The melted polymer is put into a mold, then
compressed air is used to spread the polymer
into the mold. It is used to make many
containers such as plastic soda containers
and milk jugs.
48. BLOW MOLDING PROCESS
• Blow Molding is accomplished by vertically
extruding a hollow tube of molten plastic.
This tube is called a "parison" in blow
molding terms. The parison is then clamped
between two mold halves and expanded into
the desired shape by inflating it with
compressed air. After cooling, a hollow part
emerges.
51. Solid polymer is placed in a mold, the mold is heated
and puts pressure on the polymer to form the part.
COMPRESSION MOLDING PROCESS
52. COMPRESSION/TRANSFER MOLDING PROCESS
• These type of molding is used for the materials like Phenol-
formaldehyde, Urea-formaldehyde and melamine-
formaldehyde
CHARACTERISTICS
Tooling Cost - high
Production Rate -high
Tolerances are held tightly using injection molding
No trimming is required
Wide variety of rubber compounds give varying costs
and material properties.
53. COMPRESSION/TRANSFER MOLDING PROCESS
• Compression and Transfer Molding is
accomplished by placing a pre-weighed
amount of rubber in a matched metal mold
and closing the mold. The heat and pressure
cause the rubber to liquefy and flow into the
voids in the tool where it chemically reacts
and hardens into the final shape. Very large
shapes can be molded in compression
presses.
55. TRANSFER MOLDING PROCESS
• In the Resin Transfer Molding, or RTM process, dry ( i.e.,
unimpregnated ) reinforcement is pre-shaped and
oriented into a skeleton of the actual part known as the
preform, which is inserted into a matched die mold. The
mold is then closed, and a low-viscosity thermoset resin is
injected into the tool. During this time, the resin "wets
out" the fibers and the air is displaced and escapes from
vent ports placed at the high points. Heat is applied to the
mold to activate the polymerization that solidifies the
resin. The resin cure begins during filling and continues
after the filling process. Once the part develops sufficient
green strength, it is moved or demolded.
56. REACTION INJECTION MOLDING PROCESS
Liquid monomers are placed in the
mold avoiding the need to use
temperature to melt the polymer or
pressure to inject it. The monomers
polymerize in the mold forming the
part.
58. THERMOSETS
• Thermosetting resins are used in molded and laminated
plastics. They are first polymerized into a low-molecular-
weight linear or slightly branched polymer or oligomer,
which is still soluble, fusible, and highly reactive during
final processing. Thermoset resins are generally highly
filled with mineral fillers and glass fibers. Thermosets are
generally catalyzed and/or heated to finish the
polymerization reaction, cross-linking them to almost
infinite molecular weight. This step is often referred to as
cure. Such cured polymers cannot be reprocessed or
reshaped. The high filler loading and the high cross-link
density of thermoset resins results in very high densities
and very low ductility, but very high rigidity and good
chemical resistance.
59. Phenolic Resins
Phenolic resins combine the high reactivity of phenol and
formaldehyde to form prepolymers and oligomers called resoles and
novolacs. These materials are combined with fibrous fillers to give a
phenolic resin, which when heated provides rapid, complete cross
linking into highly cured structures. The high crosslinked aromatic
structure has high hardness, rigidity, strength, heat resistance,
chemical resistance, and good electrical properties.
Uses. Phenolic applications include automotive uses (distributor caps,
rotors, brake linings), appliance parts (pot handles, knobs, bases,
electrical/electronic components (connectors, circuit breakers,
switches), and as an adhesive in laminated materials (e.g., plywood).
60. Epoxy Resins
The most common epoxy resins are prepared from
the reaction of bisphenol A and epichlorohydrin to
yield low-molecular-weight resins that are liquid
either at room temperature or on warming. Each
polymer chain usually contains two or more epoxide
groups. The high reactivity of the epoxide groups
with amines, anhydrides, and other curing agents
provides facile conversion into highly crosslinked
materials. Cured epoxy resins exhibit hardness,
strength, heat resistance, electrical resistance, and
broad chemical resistance.
61. Epoxy Resins
• Uses. Epoxy resins are used in glass reinforced,
high-strength composites in aerospace, pipes,
tanks, pressure vessels; encapsulation or casting of
various electrical and electronic components
(printed wiring boards, etc.); adhesives; protective
coatings in appliances, flooring, and industrial
equipment; and sealants.
62. Unsaturated Polyesters
Unsaturated polyesters are prepared by the condensation
polymerization of various diols and maleic anhydride to give a very
viscous liquid that is dissolved in styrene monomer. The addition of
styrene lowers the viscosity to a level suitable for impregnation and
lamination of glass fibers. The low-molecularweight polyester has
numerous fumarate ester units that provide easy reactivity with
styrene monomer. Properly formulated glass-reinforced unsaturated
polyesters are commonly referred to as sheet molding compound
(SMC), or reinforced plastics. In combination with reinforcing materials
such as glass fiber, cured resins offer outstanding strength, high
rigidity, impact resistance, high strength-to-weight ratio, and chemical
resistance. SMC typically is formulated with 50% calcium carbonate
filler, 25% long glass fiber, and 25% unsaturated polyester.
63. Unsaturated Polyesters
• The highly filled nature of SMC results in high
density and brittle easily pitted surface. Bulk
molding compound (BMC) is formulated similar to
SMC except -in. chopped glass is used. The shorter
glass length gives easier process but lower strength
and impact.
Uses. The applications include large body parts
for automobiles, trucks, trailers, buses, and
aircraft, small- to medium-sized boat hulls and
associated marine equipment, building panels,
housing bathtub and shower stalls, appliances,
and electrical/electronic components.
64. Alkyd Resins
• Alkyd resins are based on branched prepolymers from
glycerol, phthalic anhydride, and glyceryl esters of fatty
acids. Alkyds have excellent heat resistance, are
dimensionally stable at high temperatures, and have
excellent dielectric strength (14 MV/m), high resistance to
electrical leakage, and excellent arc resistance.
Uses. Alkyd resin applications include drying oils in enamel
paints, lacquers for automobiles and appliances; and
molding compounds when formulated with
reinforcing fillers for electrical applications (circuit breaker
insulation, encapsulation of capacitors and resistors, and
coil forms).
65. Diallyl Phthalate
Diallyl phthalate (DAP) is the most widely used compound in
the allylic family. The neat resin is a medium-viscosity liquid.
These low-molecular-weight prepolymers can be reinforced
and compression molded into highly cross-linked,
completely cured products. The most outstanding properties
of DAP are excellent dimensional stability and high
insulation resistance. In addition, DAP has high dielectric
strength, excellent arc resistance, and chemical resistance.
Uses. DAP applications include electronic parts, electrical
connectors, bases and housings. DAP is also used as a
coating and impregnating material.
66. Amino Resins
The two main members of the amino family of thermosets are:
The melamine
Urea resins
They are prepared from the reaction of melamine and urea with
formaldehyde.
These materials exhibit extreme hardness, scratch resistance, electrical
resistance, and chemical resistance.
Uses.
The melamine Resins are used for dinnerware, decorative laminates,
countertops, tabletops, furniture surfacing, switchboard panels, circuit
breaker, arc barriers, armature, slot wedges, adhesives, coatings.
The urea resins are used in particleboard binders, decorative housings,
closures, elecrical parts, coatings, and paper and textile treatment.
68. Processing of thermosetting plastics
Thermosets are usually processed by using the
following molding techniques.
• Compression molding.
• Transfer molding.
• Injection molding.
70. COMPRESSION MOLDING PROCESS OF
THERMOSETTING PLASTICS
• Step 1
The mold consists of two
halves into which cavities are
machined material is placed on
the lower mold.
The mold driven by hydraulic
cylinder is heated by electric
heater.
71. COMPRESSION MOLDING PROCESS
Step 2
• Heated molds
compress the material
allowing it to fill the whole
cavity chemical reaction take
place and the part is cured.
72. COMPRESSION MOLDING PROCESS
Step 3
• After curing the part
the molds are open and
the part is ejected from
the molds. The excess material
called as flash is then trimmed.
73. Advantages of compression molding process
• Lowest cost.
• Better for large parts.
• Lower labor cost.
• Minimum wastage of material & improved efficiency.
• Internal stresses are minimum.
• High dimensional stability and shrinkage is minimum.
74. Transfer molding process of thermosetting
plastics
• Step 1
The molds heated by
electric heater are open
and the material is placed
In the transfer pot .
75. Transfer molding process
Step 2
• The molds are closed the
plunger compresses the
material which passes
through gate into
cavities.
76. Transfer molding process
Step 3
• After punching the molds
are open the cured part is
ejected . The flash are then
trimmed.
77. Advantages of transfer molding process
• 1- It is quick method because loading material in “pot” takes
less time than loading in each mold cavity.
• 2- The flash produced in transfer molding are comparatively
less.
78. Injection molding process of thermosetting
plastics
Injection molding is done with the help of two
mechanisms.
• 1- with plunger
• 2- with a reciprocating rotating screw
