Photodegradation of bisphenol A polycarbonate ; structure mmechanism and methods of stabilization.

1. B Y
MOHAMED MAHMOUD ABDUL-MONEM
F A L L 2 0 1 7
D E G R A D A T I O N A N D S T A B I L I Z A T I O N O F M A T E R I A L S
Bisphenol A Polycarbonate
Photodegradation

2. Contents
 Structure of Polycarbonate (PC)
 Properties of PC
 Processing of PC
 Applications of PC
 Mechanism of photodegradation of PC
 Stabilization of Polycarbonate
 References

3. Strucrutre
 Polycarbonates are a very special class of
thermoplastics.
 Polymers containing carbonate groups
(−O−(C=O)−O−)

4. Properties
 They exhibit a unique combination of properties, for
instance they have :
1. Excellent toughness compared to other
thermoplastics.
2. High transparency.
3. Dimensional stability over a wide temperature
range.
4. Good electrical properties
5. Lightweight

5. Processing
Interfacial synthesis :
 Phosgene COCl2
+
 Sodium salt of
bisphenol A

6. Processing
Melt-phase
transesterification :
Bisphenol A
+
Diphenyl carbonate

7. Applications
1. Glazing and sheet applications, such as transparent
panels for greenhouses.
2. Electrical and electronics applications, such as
computers and, mobile phones, and optical media,
such as compact discs.
3. Moreover, they can also be used in medical and
health care.
4. Bottles and packaging.
5. Automotive parts.

11. Photodegradation of Bisphenol A Polycarbonate
 On extended exposures to (UV) light, BPA-PC slowly
degrades, turning progressively more yellow (oxidation
of phenolic groups) eventually leading to a decrease in
its physical properties.
 This is particularly so for the ester groups and the
aromatic rings which are strong UV absorbers.
 The absorbed energy can cause the rupture of covalent
bonds initiating photo-oxidation and photo-Fries
reactions.

12. Mechanism of polycarbonate
photodegradation
1.Photo-fries:
 The photo-Fries reaction is promoted by radiation of
short wavelengths (<310 anm) and does not require
oxygen to occur.
 In the photo-Fries mechanism, the energy absorbed
from UV radiation promotes the scission of the
carbonate linkage, forming two primary free radicals.

14. Mechanism of polycarbonate
photodegradation
2.Photo oxidation:
 For samples exposed to sunlight and air, photo-
oxidation has been reported to be the predominant
reaction, which occurs via a three-stage reaction.
 Photo-oxidation is favored by wavelengths in the
290–350 nm range.

15.  Hydrogen atoms are abstracted from the methyl
groups, forming a free radical and thus initiating a
chain scission reaction which propagates the
reaction.
 In the presence of oxygen, the methyl side chains are
photo-oxidised into hydroperoxide intermediates,
which are transformed into tertiary alcohols and
ketones.

17. Stabilization of Polycarbonate
1.UV absorbers
 There are different groups of UVAs.
 The most important groups are:
1. Hydroxybenzophenones,
2. Hydroxyphenyl benzotriazoles,
3. Cyanoacrylates,
4. Hydroxyphenyl triazines.

18. 2.Hindered amine light stabilizers
 Hindered amine light stabilizers (HALS) absorb no
light in the wavelengths between 300 and 400 nm,
and act by catalyzing the termination step of the
oxidation cycle.
 HALS act to inhibit degradation of the polymer by
continuously and cyclically removing free
radicals that are produced by photo-oxidation of the
polymer.

19.  HALS react with the initial polymer peroxy radical
(ROO•) and alkyl polymer radicals (R•) formed by
the reaction of the polymer and oxygen.
 By these reactions HALS are oxidised to their
corresponding aminoxyl radicals.

20. References
 1..Diepens M and Gijsman P.Photodegradation of
bisphenol A polycarbonate with different types of
stabilizers. Polymer Degradation and Stability
.2010;95: 811-817
 2. Burn LS et al. The effects of ultraviolet radiation
on polycarbonate glazing. Durability of building
materials and components.1999; 884-898.