Plastics
Plastics Background
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Definition the term plastics,
as it is commonly used today
refers to a large group of
synthetic materials which are
made from a number of
common substances such as
coal, salt, oil, natural gas,
cotton, wood, and water
Simple chemicals are pulled
from the material to produce
monomers. Which are capable
of reacting with one another,
are produced.
Monomers are then built up in
a chainlike molecules called
polymers
Types of Plastics
Developments have produce over 40
groups or families of plastics. Each with
its own characteristics, such as light
weight, heavy weight, heat-resistant,
hard, soft, clear, or opaque.
 Two general classifications
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Thermoplastics
Thermosetting plastics
Thermoplastics
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Become soft when heated and hard when cooled,
regardless of the number of times the process is
repeated
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This is due to the fact that linear molecular chains can
move together when heated and cooled.
Types of plastics – acrylics, celluloses, polyethylene,
polyvinyl chloride (PVC), polystryrene, polyallomers,
polycarbonates, polyimide, polypropylene, polysulfone,
phenylene oxide nylons, methyl pentenes, ionomer,
fluroplastics, acetal and acrylonitrile butradiene styrene
(ABS)
Thermosetting plastics
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Are also chainlike in
molecular structure but the
curing and hardening
process involves the
formation of cross-links
between molecules in
adjacent chains. Resulting
in complex chains that are
no longer free to move.
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Types – alkyds, aminous
(urea and melamine
formaldehyde),
diallylphthalate (DAP),
epoxies, furan, phenolics,
polyesters, polyurethane,
and silicones
Production of Plastics
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Process of uniting monomers to form
polymers is known as polymerization
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Accomplished by either a condensation or an
addition process
Raw material can come in any of the
following forms
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Granules
Powder
Beads
Liquid resins
Production of Plastics
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The raw material is then produced into the following forms
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Additions to plastics
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Sheets
Films
Tubing
Rods
Solid or semisolid shape
Plasticizers – added for workability
Fillers – are added to produce bulk
Fibers – added for strength and durability
Hardeners – added to induce setting
Plastics products are formed by a number of methods –
injection molding, blow molding, expandable bead molding,
compression molding, transfer molding, rotational
modeling, form modeling, extrusion thermoforming,
laminating, casting, and calendaring
Injection Molding
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Measured amounts of
powder or granules are fed
into the intake end of the
heated barrel of a molding
machine. And forced
forwarded by a ram.
Heated to temperatures of
300 to 650 c
Pressure from 5000 to
40000 psi
Thermoplastics and
thermosets are used.
Blow Molding
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Three processes
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Extrusion blow molding – an extruder produces a hollow
tube called a parison which is captured between the two
halves of a hollow mold. The mold is close and air is blown
into the tube forcing it to expand.
Injection blow molding – process is same except the tube
(parison) is injected molded on a steel rod and the rod is
removed prior to closing the mold
Stretch blow molding – involves, stretching the parison in
the axial direction before blowing.
Polyethylene is typically used, but PVC, polystyrene, and
polypropylene are also used.
Bottles and water cans are typical shapes produced
Expandable Bead Molding
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Process used to produce lightweight products of
polystyrene foam
Small granules together with a small amount of
an expanding agent are placed in a rolling drum
and steam heated
Heat softens the granules and the expanding
agent enlarges their size
Cooled and transferred to a mold
Again heated to 135 c and until they fused
together
Flotation equipment, shipping containers, rigid
insulation are typical products
Compression Molding
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Simplest form of molding
A measured amount of powder is place in a
heated mold then closed
Heat and pressure are applied to the plastic
material which melts and flows to all parts of
the mold
Transfer Molding
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Differs from
compression molding
in that in the transfer
molding process the
molding compound is
liquefied outside the
molding chamber
Transfer to the mold
under pressure
There the forming and
setting takes place
Rotational Molding
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Used to form hollow units with complex shapes
and heavy walls
A pre measured amount of powder or liquid
resin is placed in the bottom half of a cold
mold and the mold is closed
Mold is heated and rotated. Then allowed to
cooled
Form Molding
Made by mixing an expanding agent with
either granules or powder and then
heating it
 Heat melts the plastic and causes the
formation of a gas which expands the
molten material into foamed structure
 Quickly cooled to set the material
 Insulation is made in this manner
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Extrusion Thermoforming
Is used to produce materials which have a
constant cross section
 Heat material is pushed through a die
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Laminating
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Bonding together a number of layers of
materials to form a single sheet.
Casting
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Liquid plastic are poured into molds and
set
Calendaring
Form of extrusion
 Plastic material is fed to a pair of revolving
rollers which extrude a thin film or sheet
between them
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Properties of Plastics
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Transparency (acrylics, methyl pentenes, polycarbonates, ionomer,
polysulfone)
resistance to discoloration (acrylics)
good resistance to weathering (acrylics, epoxy, silicone, polyvinyl chloride)
good dimensional stability (fluoroplastics, polycarbonates, phenylene,
oxide, polyvinyl chloride, urea, melamine)
toughness (Cellulosics, ionomer, nylone, phenoxies, polycarbonates,
polyethylene)
high impact resistance (acrylics, ethyl cellulose, polypropylene, polyimide,
polycarbonates)
abrasion resistance (nylons, polyallomers, polyimide, polypropylene)
low moisture absorption (fluoroplastics, phenylene oxide, polypropylene,
diallyl phthalate, silicone)
ductility (phenoxies, acrylics, nylons)
good adhesive qualities (epoxy, phenolics, amino resins)
good resistance to chemicals (nylons polyethylene, phenylene oxide,
polypropylene, polysulfone, diallylphthalate)
Additives for plastics
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not all properties of plastics are positive ones, additives are
necessary to reinforce another property.
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Antioxidants
antistatic agents
coloring agents
coupling agents
Fillers
reinforcing agents
flame retardants
foaming agents
Lubricants
Plasticizers
Preservatives
processing aids
ultraviolet stabilizers
Plastics in Construction
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Structural Applications
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For use in structural applications plastics need to be
reinforced
Glass fiber, jute, cotton, sisal, asbestos, and synthetic
and metallic fibers are used
Flat sheets – glazing
Thermoformed shapes – roof shapes, curtain wall
Glass fiber structural shapes – used where corrosion is a
problem (like steel members)
Plastic foam boards – decking, roofing
Fabrics – balloons over a pool
Foamed insulation – insulating materials
Nonstructural applications
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resilient flooring – vinyl tile, vinyl-cushioned flooring,
linoleum, cork tile, rubber flooring
Non resilient flooring – plastic terrazzo – plastic topping –
carpets – tufted carpet – woven carpet - loomed carpet –
knitted carpet – needle punched carpet
interior finishes – wall coverings
moisture control – vapor barriers
plastic pipe – pvc
caulking and sealing compounds
paints and varnishes
lights and sunscreens
adhesives
material coatings