The document summarizes the types and causes of degradation and aging of rubbers. There are several types of degradation, including oxidation at lower and higher temperatures, oxidation accelerated by heavy metals, degradation aided by heat and moisture, crack formation from dynamic and static stresses, and changes caused by light and oxygen. Oxidation occurs as oxygen reacts with double bonds in the rubber, leading to chain scission and crosslinking that degrade the material properties. Other factors like ozone, UV light, heat, and stresses can also cause cracking and property changes. Proper compounding with antioxidants, waxes, and other additives can help prevent various degradation pathways.

1. DEGRADATION AND
AGING OF RUBBERS
Presented By:
Sherin Peter
M. Tech.
School of Chemical Sciences

2. Preface :
Introduction
Types of degradation
Summary
Conclusion

3. Introduction
 What is aging..?
It is a collective term for changes in property of materials that occur on longer
term storage without the action of chemicals that lead to partial or complete
degradation
or
Rubber degradation is a change in the properties—tensile strength, color, shape,
etc.—of a rubber product under the influence of one or more environmental factors
such as heat, light or chemicals such as acids, alkalis and some salts

4. Types of Degradation
 Oxidation at lower and high temperature
 Oxidation accelerated by heavy metal compound
 Degradation aided by heat and moisture
 Crack formation by dynamic stress
 Degradation by static ozone action
 Crack formation by high energy light and oxygen
 Changes in surface luster and other process

5. Oxidation at lower and high temperature
 Diene rubber take up O2 and partially given off CO2 and H2O and create active radical
 At low temperature O2 absorption is proportional and at elevated temperature it is like
autocatalytic one
 Types of reaction occurs are;
 Molecular chain cleavage and molecular network loosens
 Crosslinking leading to higher crosslink density
 Free radicle bound chemically and remain inactive

6. Oxidation accelerated by heavy metal compound
 Also called rubber rubber - poison aging
 Heavy metal compounds of Cu and Mn have catalytic activity on oxidation
 Cu and CuO are in slow aging but Cu - Oleate have aggressive aging
 It can be made inactive by reactants which converts it into a suitable coordination complex

7. Degradation aided by heat and moisture
 The property change occurs in presence of moisture
 Softening ; Decomposition of crosslinking and hydrolysis of water sensitive structure
 Hardening ; Inter and Intermolecular network formation
 Shifting of crosslinks without total number

8. Crack formation by dynamic stress
 When rubber is subjected to prolonged mechanical stress, Crack will develop in surface
 Crack on surface can lead till the article break
 Crack formation can be happen in total absence of O3 and O2 but will accelerate in
presence
 Higher crosslink density and sulphur rich crosslink are preferred.

9. Degradation by static ozone action
 Also called static ozone crack formation
 Double bond containing vulcanisates exposed in O3 containg environment, crack will
develop perpendicular to direction of applied stress.
 The extend of crack propagation and speed of crack formation is proportional to amount of
ozone present.
RCH=CHRʹ RCH CHRʹ
O O
O

10. Types of Degradation
 Oxidation at lower and high temperature
 Oxidation accelerated by heavy metal compound
 Degradation aided by heat and moisture
 Crack formation by dynamic stress
 Degradation by static ozone action
 Crack formation by high energy light and oxygen
 Changes in surface luster and other process

11. Summary :
Chemical changes occurring on ageing.
 The long molecular chain which form the major structure will cut into smaller pieces

12.  The linear molecular chain may tied together by crosslinks
 The nature of the chemical side groups along molecular chains maybe modified.

13. DEGRADATION BY OXYGEN
 It is accelerated by increasing temperature above 60°C.
 Only 1– 2 % of combined oxygen is enough to render the rubber product useless.
 Oxygen attacks double bond.
 Oxidation causes Chain scission and Cross linking resulting in the loss of elastic
properties of vulcanizates.
 Both occur simultaneously - the one which prevails, determines the final product
properties

14.  Scission predominates in polymers like NR, IR, IIR .
 Scission results in the decrease of molecular weight leading to softening of the
aged / over cured vulcanizates, reduction in tensile properties etc.
 Cross linking predominates in case of polymers like BR, SBR, NBR, CR .
 Cross linking results in brittleness, gelation and reduction in elongation of the
polymer.
 The ‘cure system’ selection also influences the ageing resistance of the rubber
product. The ‘Conventional Cure’ Systems are more prone to oxidative
degradation than the ‘Semi EV’ or ‘EV Cure’ systems.

15. POLYMER DEGRADATION CHEMISTRY
initiation of
degradation-
free radicals
form
Propagation-
Peroxy
radicals form
Formation of
unstable
hydro
peroxides
Hydro peroxides
decompose to
form alkoxy &
hydroxy radicals

17. Continue..
 Propagation stage is very rapid and continues till termination occurs
 Propagation reaction is an autocatalytic oxidation reaction
 Propagation continue till the formation of stable product

18. Termination
 The termination stage proceeds as follows
CHAIN SCISSION
CROSSLINKING

19. DEGRADATION BY OZONE
 Unsaturated polymers which contain electron donating groups (e.g. methyl
groups in NR) are more vulnerable to ozone attack.
 The unsaturated polymers containing electron-withdrawing groups (e.g. Chlorine
in CR, Bromine in BIIR) are less vulnerable to ozone attack due to the
deactivating effect imposed on the double bonds by the halogen atoms.
 Ozone reacts with the double bonds in the rubber molecule causing chain
scission. The chain scission results in the formation of surface cracks in the
direction perpendicular to the applied strain.
 In addition to large number of double bonds present in the highly unsaturated
rubbers, ozone also reacts with saturated polymers and the polysulphide chains at
a comparatively slower rate.

20.  The rubber surface which is not stressed also undergoes reaction with
ozone to form oxidized film but does not show typical ozone cracks.
 No crack growth occurs unless the specific stress value is exceeded. This
value is known as ‘Critical Stress Value’.
 When the rubber is stressed just above the critical stress value, the ozone
cracks are few in numbers but are large in length and depth.
 As the stress is increased to a high stress value, the ozone cracks
increase in number and are finer in size.
 Under strain the ozonides easily decompose and break the double bonds
resulting in the appearance of surface cracks and as this mechanism repeats,
the cracks grow deeper.

21. OZONATION REACTION

22. Sl. No Type of Degradation Primary cause Type of physical failure Counter Measure
1 Heat aging
Heat, Heat +
Oxygen
Post vulcanization, Cyclisation,
Reversion, Elasticity and tensile
loss
Reversion stable cures &
Anti oxidents
2 Light aging
U.V, Light,
Humidity, Heat ,
Oxygen
Formation of non-oriented crack, Anti oxidents
3 Natural aging
Storage condition,
Light, Humidity,
Heat , Oxygen
Change in molecular mass and
gel formation in raw rubber,
Elasticity and tensile loss in
vulcanized rubber
Stabilizer

23. Sl. No Type of Degradation Primary cause Type of physical failure Counter measure
4 Ozone cracking
Mechanical stress
, Ozone
Extensive cracking
perpendicular to force causing
strain on the surface, Deep
crack on the thick specimen
Wax bloom anti-
ozonent
5 Flex cracking
Mechanical stress
, Ozone, Oxygen,
Mecahnical flaws
Stiffnesss and Cracking
Anti flex cracking,
Anti degradants.
6
Metal ion catalysed
aging
Cu, Mn, Fe, ion
and their soluble
fatty acid salts +
oxygen
Rapid loss in elasticity and
tensile strength
Anti oxidant
7 Hydrolysis
Hot water or
steam
Hydrolysis --

24. Reference ;
 Rubber technology Handbook ( Hanser publication ) - Wenner Hofmann
( 264-268, 492)
 Rubber engineering ( IRI – chapter 19 ) - 807-852
 The Vanderbilt latex handbook - George G. Winspear
- 237-241
 Wikipedia / Rubber aging

25. THANK YOU