2. Introduction
Polymers. Macromolecules.
Natural & synthetic
Their unique properties have allowed them to replace metals.
strength: weight ratio
Designing with plastics
Cost of using plastics
Ease of manufacturing
3. Why use plastic?
plastic is cheaper than most metal
weighs a lot less (better fuel economy).
Plastic can be injection molded, vacuum molded, cast and generally
machined or "worked" faster and cheaper than metal.
for winter cold areas where the roads are salted, the corrosion
resistance of plastics
4. Bio-plastic green phones
Urethane bumpers
5. Types
Thermoplastics:
Amorphous structure. Secondary bonds. Linear & branched
polymers have weak secondary bonds. Return to their original
hardness when cooled. Reversible heating possible.
Examples:acrylics, nylon, PVC, polyethene
6. Types
Thermosets:
Cross-linked in a 3d network. Strength of bond. Hardness &
strength in material not affected by temperature.
Polymerization will require heat & pressure so that the shape
of the part is permanently set.(curing)
Irreversible. Decomposes. Chars.
7. Thermosets
Tg not sharply defined. Become rubbery over a narrow range.
Polymerization in 2 steps. At chemical plant & at
parts-producing plant.
Phenolics. Pots & pans.
Possess better insulating, mechanical & chemical properties.
Also better dimensional stability.
8. Disadvantages
they need to be painted for UV protection.
Tooling: Normally more expensive for plastic because of the surface
finish required (in the mold) and the number of cavities are
larger, thus increasing the cost.
9. Additives
Various chemical reactions were used to make cellulose in to
cellulose acetate. Photographic films. Packaging sheets.
So additives are added to impart certain specific properties.
Modify properties like stiffness, strength, color, flammability,
weatherability.
10. Additives
Fillers: improve mechanical properties. Decreases the cost/unit
weight.
Plasticizers: add flexibility & softness to the polymer by
reducing Tg .
Stabilizers: UV rays & oxygen tend to weaken & break the
primary bonds. Degradation.
Colorants
Flame retardants
11. Common thermoplastics
Cellulosics
Fluorocarbons
Polyamide (nylons)
Polycarbonates
Polyesters
Polyethylenes
Polypropylenes
Polystyrenes
PVC
12. 13. Acrylics
Acrylic is a useful, clear plastic that resembles glass, but has
properties that make it superior to glass in many ways. Common
brands of high-grade acrylic include Plexiglass.
moderate strength, good optical quality & weather resistance.
Transparent but can be made opaque. Generally resistant to
chemicals.
Typical applications: lenses, signs, automotive lenses, window
glazing, artificial nails, paints
14. Acrylic
For all of its advantages, there are two disadvantages of acrylic:
it is more expensive than glass, and if exposed to a direct flame
it will melt and eventually burn.
Has good impact strength, higher than that of glass or polystyrene,
but significantly lower than that of polycarbonate or engineering
polymers. In the majority of applications, it will not shatter but
instead breaks into large dull pieces.
15. Acrylonitrile-Butadiene-styrene
ABS is impact resistant, abrasion & chemical resistant.
Resistance to chemicals & corrosion. Does not ignite
easily.
Typical applications: pipes & fittings, tool handles,
telephones & appliances.
High performance at high & low temperatures. (-400 F to 1800
F)
16. Acrylonitrile-Butadiene-styrene
The main disadvantage to using ABS pipe fittings are that it is not
very durable when it comes to solvents or fatigue resistance. It
also has minimal UV resistance, so should not be left exposed to
the sun.
The nitrile groups from neighboring chains, being polar, attract
each other and bind the chains together, making ABS stronger than
pure polystyrene
17. 18. PVC Pipes
PVC has many advantages over pipes made of galvanized steel and
copper.
To begin with, it is the most lightweight of the three. This makes
it easier to install. Also, it is the least expensive of the three
types.
Also, it can withstand higher water pressure than the copper. Also,
PCV is non-conductive, will not rust, and is not as conducive to
condensation.
19. PVC PIPES
Another advantage is that PVC can be placed under concrete slab
without reacting to the concrete. Moreover, it is self-insulating.
That is why it can handle hotter temperature water.
20. Disadvantages
Even though it can withstand hot water temperatures, it is less
flame resistant. That is one of the biggest disadvantages of
PVC.
Also, PVC contains volatile compounds which are harmful to the
environment. Furthermore, some people have complained that PVC
pipes cause water to have a slight plastic taste.
21. Mechanical Properties
Elastic Modulus & tensile strength decrease with increasing
temperature. Toughness increases.
Water absorption. Adverse affect.
Solvents. Residual stresses.
Radiation & visible light.
Anisotropy due to cold rolling.
22. Physical Properties
Friction & wear (self-lubricating, TEFLON) (gears, roller skate
wheels, prosthetic joints)
Thermal & electrical conductivity
Low specific gravity (0.9-2.2)
High coefficient of thermal expansion
