Thermosetting and Thermoplastics

Everything you need to know about SYLLABUS-LISTED plastics in concise form

1. Geometrical and Mechanical Engineering
Drawing: Unit 2 Module 2
Plastics
A plastic material of a wide range of synthetic/semi-synthetic organic solids that are mouldable. They
are typically organic polymers of high molecular mass but usually contain other substances. Most are
synthetic and commonly derived from petrochemicals.
Properties
Low cost, ease of manufacture, versatility, imperviousness to water, usually low melting point, electrical
insulator (except stretch-oriented polyacetylene). Some may decompose to toxic substances when
heated.
Thermoplastics
A thermoplastic, also called a thermo-softening plastic is a plastic which becomes pliable or
mouldable above a specific temperature and returns to a solid state upon cooling.
Most thermoplastics have a high molecular weight. More aesthetically pleasing, expensive
forming process, less resistance to mechanical creep, not suitable for use in EXTREMELY
temperatures, little to no cross-linking in microstructure, eco-friendly forming process.
Polyvinyl Chloride (PVC)
PVC comes in two forms, rigid (for construction in pipe and in doors and windows) and are made more
flexible by addition of plasticizers (phthalates). [Add ease of work, used for cables, lowers glass
transition temperature, increased flexibility and durability]
Properties
High hardness, high moduli of elasticity (rigid-type), very low moduli of elasticity (flexible), poor heat
stability, small expansion coefficient, good flame retarding, electrical insulator
Uses
PVC pipes, electric cable insulation, uPVC in place of wood, signs, clothing, furniture

Polytetrafluoroethylene (PTFE)
PTFE is a fluorocarbon solid which cannot be wet by water
Properties
High strength, toughness and self-lubricating down to 5K. Good flexibility above 194K, highly corrosion
resistant, third lowest coefficient of friction, subject to creep, electrical insulator

2. Uses
Wiring in aerospace and computing, printed circuit boards, TEFLON, plain bearings, gears
Polyethylene
The most common plastic, mixture of organic compounds.
Properties
Relatively low melting point, corrosion resistant (from acids and bases), burns slowly with a blue flame
High-Density Polyethylene (HDPE)
Density >= 0.941g/cm
3
, Low degree of branching low tensile strength, used in milk jugs, detergent
bottles, garbage containers and water pipes.
Medium-Density Polyethylene (MDPE)
Density 0.926-0.940g/cm
3
Good shock and drop resistance, less notch sensitive than HDPE, stress
cracking resistance also better. Used in gas pipes and fittings, sacks, shrink film and carrier bags.
Low-Density Polyethylene (LDPE)
Density 0.910-0.940g/cm
3
, lower tensile strength, increased ductility, used for rigid containers and
plastic film applications.

Polystyrene (PS)
Synthetic aromatic polymer, can be rigid or foamed.
Properties
Clear, hard, brittle, low melting point, poor barrier to oxygen and water, glassy at RTP, can be cast into
moulds for fine detail, slow to biodegrade
Uses
Protective packaging, containers, lids, bottled, trays, napalm-B

Polypropylene
Properties
Tough, flexible, used as an engineering plastic when copolymerized with ethylene, good resistance to
fatigue, chain degradation due to sunlight, corrosion resistant, resilient to impact and freezing, can be
joined by heat fusion, heat resistant, light weight, durable
Uses
Plastic hinges, as a dielectric, kettles, food containers, carpets, rugs, ropes, PVC alternative, electrical
cables, plastic mouldings (bottle tops, bottles, and fittings), clothing, and EPP toy aircraft.

3. Polyamide - Nylon
Macromolecule with repeating units, artificial and natural.
Properties
Very elastic, strong, high crystallinity, high tensile strength when drawn using heated rolls at high
speeds, clear, colourless or milky, easily dyed, good electrical insulator.

Polymethylmethacrylate (Perspex)
Shatter resistant which is also called acrylic glass
Properties
Moderate strength, easy handling and processing, low cost, brittle when loaded, prone to scratching,
varieties block visible light while allowing transmission on IR light
Uses
Transparent glass substitute (submersibles, aircraft, riot control, aquariums), daylight radiation,
implants, acrylic paint

Thermo-Setting Plastics
A thermosetting resin (a.k.a. a thermoset) is a petrochemical that irreversibly cures by heat, chemical
reaction or suitable irradiation. More complex forming procedure, more resistance to creep/chemical
erosion, heavily cross-linked.
Epoxy
An epoxy is the end cured product of an epoxy-resin, typically two resins that need to be mixed together
before use.
Bakelite
Properties
Heat resistant, electrical insulator, brittle, complexity of production, hard, dense, tend to well in areas of
perpetual dampness
Uses
Wire insulation, brake pads, whistles, cameras, gun-grips, table-top games, heat-shields
Melamine
Properties

4. Fire retardant,
Uses
Kitchen utensils and plates, high-pressure laminates, countertops, cabinets and furniture making