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the permittivity of the plastic and the permittivity of air. Permittivity is best described
as the ease with which plastic molecules can be polarized.
5. Dissipation Factor is a measure of heat dissipation and is a constant ratio of the
energy lost as heat compared to energy originally transmitted.
6. Arc Resistance is a time-rated value that measures the ability of a polymer to
withstand exposure to an electrical current across its surface before a conductive
path of carbon is created.
7. Comparative Tracking Index (CTI) is similar to arc resistance except that an
electrolyte (a solution of ammonium chloride) is placed on the surface of the plastic
being tested.
PROCESSING
The most important processing and physical properties for specialty polymers
include viscosity, shrinkage, and melt flow index. Blow moulding and extrusion
processes tend to use lower melt flow index, while injection moulding typically uses a
higher melt flow index.
1. Viscosity, a measurement of a fluid's resistance to flow, controls how well a resin
fills the cavities or voids in a mould.
2. Shrinkage is the maximum percentage of linear shrinkage that occurs after
drying, setting, and / or curing.
3. Melt flow index (MFI) is the output flow rate in grams that occurs during a 10
minute period.

REINFORCED PLASTICS (FRP): is a composite material made of a polymer
matrix reinforced with fibres, usually glass, carbon, basalt or aramid.
Reinforcement in plastics enhances the mechanical strength and reduces the
shrinkage. There are two types of reinforcement used in plastics.
Fibrous materials like cotton, nylon, polyester, rayon, glass, carbon, graphite etc.
Non fibrous mineral fillers like mica, talk, solid glass micro-spheres
Glass Fibre increases mechanical properties while Graphite give conductivity.
Thermoplastic Elastomer (TPE): To express it crudely, it can be said that
thermoplastic elastomers are positioned between plastic (thermoplastics) and
rubber (elastomers) in terms of structure and behaviour. Like thermoplastics, TPEs
become plastic due to the application of heat, and reveal elastic behaviour again on
cooling. In contrast to the chemical cross-linking which occurs in elastomers, TPE
involves purely physical cross-linking, which can be reversed via the further
application of heat.
COMPOUNDS are defined as plastic formulations obtained by mixturing of pure
basic plastics material along with fillers, reinforcements and/or additives
(stabilisers, anti-oxidants, UV-stabilizers) to achieve required properties and
performance. Compounding provides increased Viscosity, Flexural modulus,
Heat deflection temperature (HDT), Dimensional stability but decreased Izod
Impact, Mould shrinkage, Thermal expansion, Part cost.
Typical materials : PE, PP, PS, PVC, ABS, POM, PC, etc

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