Page 33 - Plastics Engineering

16 General Properties of Plastics

grades have crystal clarity and overall their low cost coupled with ease of
processing makes them used for such things as model aircraft kits, vending
cups, yoghurt containers, light fittings, coils, relays, disposable syringes and
casings for ballpoint pens. Polystyrene is also available in an expanded form
which is used for such things as ceiling tiles and is excellent as a packaging
material and thermal insulator.
Acrylonitrile-butadiene-styrene (ABS). ABS materials have superior
strength, stiffness and toughness properties to many plastics and so they
are often considered in the category of engineering plastics. They compare
favourably with nylon and acetal in many applications and are generally less
expensive. However, they are susceptible to chemical attack by chlorinated
solvents, esters, ketones, acids and alkalis.
Qpical applications are housings for TV sets, telephones, fascia panels, hair
brush handles, luggage, helmets and linings for refrigerators.
Polycarbonates. These materials also come within the category of engi-
neering plastics and their outstanding feature is extreme toughness. They are
transparent and have good temperature resistance but are attacked by alkaline
solutions and hydrocarbon solvents. Qpical applications include vandal-proof
street lamp covers, baby feeding bottles, machine housings and guards, camera
parts, electrical components, safety equipment and compact discs.
Polyethersulphone. This material is one of the new high temperature plas-
tics. It is recommended for load bearing applications up to 180°C. Even without
flame retardants it offers low flammability and there is little change in dimen-
sions of electrical properties in the temperature range 0-200°C. It is easily
processed on conventional moulding equipment. Applications include aircraft
heating ducts, terminal blocks, engine manifolds, bearings, grilles, tool handles,
non-stick coatings.
Modified Polyphenylene Oxide (PPO). The word modijied in this material
refers to the inclusion of high impact polystyrene to improve processability and
reduce the cost of the basic PPO. This material offers a range of properties
which make it attractive for a whole range of applications. For example, it
may be used at 100-150°C where it is rigid, tough and strong with good creep
resistance and hydrolytic stability. Water absorption is very small and there is
excellent dimensional stability. Applications include business machine parts,
flow values, headlight parts, engine manifolds, fascia panels, grilles, pump
casings, hair dryer housings, etc.

(c) Thermoplastic Rubbers
There are five types of thermoplastic rubbers currently available. These are
based on (i) Olefinics (e.g. Alcryn, Suntoprene) (ii) Polyurethanes (e.g. EZus-
tollun, Cuprolun, Pellethune) (iii) Polyesters (e.g. Hytrel, Arnitel) (iv) Styrenics
(e.g. Solprene, CuriJlex) and (v) Polyamides (e.g. Pebax, Dinyl) Some typical
properties are given in Table 1.4.