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RADIATION DEGRADATION
In normal service it is UV radiation which causes
degradation
Depending on the polymer type two modes of change
may be indicated.
1) Reduction in molecular mass
Polymer softens and may ultimately become a liquid
2) Cross-linking
Polymer embrittles.
Combination of 1) and 2) also possible
Protection
1) Add UV stabilisers
2) Add pigments
3) Add waxes
INTRODUCTION
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In a normal environment it is UV
radiation which is the major problem.
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A -
hv
B
(A - B) excited state
deexcitation
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A+B
degradation i.e bond scission
Such
excitations may be specific to given
molecular groups
TYPE OF RADIATION

Type of radiation
Wavelength
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 rays
5*10E-11 to 5*10E-12 m
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X rays soft
2*10E-9 to 1*10E-10 m
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X rays hard
1*10E-10 to 1*10E-11 m
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UV
4*10E-7 to 1.8*10E-7 m
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Visible light
4.2*10e-7 to 6.5*10E-7 m
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IR light
1*10e-5 to 7.5*10E-5 m
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far
1*10E-4 to 1*10E-5 m
 i.e. type of radiation determines the energy of the
radiation.
 Radiation excites the molecule and if excitation
sufficiently high bonds will break.
EFFECT OF RADIATION EXPOSURE
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1- Polymer crosslinks due to side group
bond breakages
 Example:- Polyethylene, Polypropylene,
Polystyrene, Polyamides and Rubbers
 In general, polymer with this chain
structure.
H
------CH2 – C –
X
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2 - Polymers which show a reduction in molecular mass.
 Example:- Polyisobutylene, polymethylmethacrylate,
Polymethylstyrene, P.T.F.E., Cellulose.
 In general, polymer with this chain structure.
X
------CH2 – C –
Y
The tendency to degrade is related to:a) Absence of a tertiary hydrogen atom.
b) A weaker than average main chain C – C
bond.
c) The presence of unusually strong bonds elsewhere in
the molecule e.g. C – F bonds
PROTECTION
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1) Add UV stabilizers i.e. molecules which
preferentially absorb UV radiation (see
antioxidant)
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2) Add waxes - Such waxes must have a limited
polymer solubility so that they bloom to the
surface
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3) Pigmentation e.g. carbon black.
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preferential absorption of UV by the pigment
Thank You
See You Next Lecture