Amorphous and crystalline plastics

An alternative classification of plastics is by their shape. They may be crystalline (with shape) or amorphous (shapeless).
Amorphous plastics
Amorphous plastics basically are of three major types:
ABS:acrylonitrile butadiene styrene
ABS/PC blend
PC:polycarbonate.
Amorphous engineering plastics have the following properties:
High stiffness
Good impact strength
Temperature resistance
Excellent dimensional stability
Good surface finish
Electrical properties
Flame retardance (when required)
Excellent transparency (polycarbonate only).

In the automotive industry use is made of the good mechanical properties (even at low temperatures), the thermal resistance and the surface finish. The applications are:
1.Body embellishment
2.Interior cladding
3.Lighting where,apart from existing applications of back lamp clusters,polycarbonate is expected to replace glass for headlamp lenses.

Semi-crystalline plastics
Semi-crystalline plastics are in two basic types:
Polyamide 6 and 66 types
Polybutylene terephthalate (PBT).
Semi-crystalline plastics have the following prop-
erties:
High rigidity
Hardness
High heat resistance
Impact resistance
Abrasion,chemical and stress crack resistance.
The semi-crystalline products find major application in the automotive sector,where full use is made of the mechanical and thermal properties, together with abrasion and chemical resistance.
Examples include:
1.Underbonnet components
2.Mechanical applications
3.Bumpers,using elastomeric PBT for paint on-line
4.Body embellishment (wheel trims,handles, mirrors)
5.Lighting,headlamp reflectors.

Blended plastics
Blended plastics have been developed to overcome
inherent specific disadvantages of individual plas-
tics. For large-area body panels,the automotive
industry demands the following properties:
Temperature resistance
Low-temperature impact resistance
Toughness (no splintering)
Petrol resistance
Stiffness.
Neither polycarbonate nor polyester could fulfil totally these requirements. This led to the combination of PC and PBT to form Macroblend PC/PBT, which is used for injection moulded bumpers.