RUBBER COMPOUNDING PRESENTATION DONE BY WAYNE MUTATAVIKWA AND TAFADZWA MUSHAIKE

Rubber technology

1. WAYNE MUTATAVIKWA H140058W
TAFADZWA MUSHAIKE H140057P
RUBBER COMPOUND

2. RUBBER COMPOUNDING
What is rubber compounding?
Why we are doing?
How can we do it successfully?

3. DEFINITION OF RUBBER COMPOUNDING
•is the art and science of selecting and combining
elastomers and additives to obtain an intimate
mixing that will develop the necessary physical
and chemical properties for a finished product.

4. OBJECTIVE OF RUBBER
COMPOUNDING
•To secure certain properties in the finished
product to satisfy service requirements
•To attain processing characteristics necessary for
efficient utilization of available equipment
•To achieve the desirable properties and
processability at lowest possible cost.

5. TO BE SUCESSFUL IN
COMPOUNDING
•Must understand the properties and function
of hundreds of elastomers and rubber
chemicals
•Must also have intimate knowledge of the
equipment used for mixing, extrusion,
calendering, molding and vulcanization.

6. PROCEDURE FOR
COMPOUND DEVELOPMENT
1.Set specific objectives (properties, price,etc.).
2.Select base elastomer(s).
3.Study test data of existing compounds.
4.Survey compound formulations and properties
data presented by material suppliers in their
literature .
5.Choose a starting formulation.
6.Develop compounds in laboratory to meet
objectives.

7. TO BE CONTINUED
7.Estimate cost of compound selected for
further evaluation.
8.Evaluate processability of compound in
factory.
9.Use compound to make a product sample
10.Test product sample against performance
specification.

8. CLASSIFICATION OF
COMPOUNDING INGREDIENTS
1.Elastomers
2.Vulcanizing Agents (Curatives)
3.Accelerators
4.Activators and Retarders
5.Antidegradants(Antioxidants, Antiozonants,
Protective Waxes)
6.Processing Aids(Peptizers, Lubricants, Release
Agents)

9. TO BE CONTINUED
7.Fillers (Carbon Blacks, Non-black Materials)
8.Plasticizers, Softeners, and Tackifiers
9.Color Pigments
10.Special Purpose Materials(Blowing Agents,
Reodorants, etc,)

10. REQUIREMENTS OF RUBBER
COMPOUND FOR GOOD
PROCESSING
1.Uniform plasticity and recovery.
2.Uniform scorch rate.
3.Uniform rate of cure.

11. VULCANIZING AGENTS
•To cause chemical reaction resulting in
crosslinking of elastomer molecules.
•Sulfur is by far the most widely used.

12. WHAT IS VULCANIZATION?
The treatment that accomplishes cross-linking of
elastomer molecules
•Makes the rubber stiffer and stronger but retain
extensibility
•The long-chain molecules become joined at
certain tie points, which is reduces the ability to
flow
–Soft rubber has 1 or 2 cross-links per 1000
mers
–As the number of cross-links increases, the
polymer becomes stiffer (e.g., hard rubber)

13. VULCANIZING PROCESS

14. VULCANIZING AGENTS
Sulfur
•Rhombic sulfur is most common.
Insoluble sulfur
•At curing temperatures, sulfur reverts to
rhombic S8 sulfur
•Available in sulfur/oil mater batch.
Peroxides
•Most peroxides are available as a liquid (90% -
98% active), as powders (40% -50% active), or as
pastes made from silicone fluids and gums (20% -
80% active) to facilitate handling and dispersion.

15. TO BE CONTINUED
Activators
•Zinc oxide and stearic acid are used.
Coupling agents
•Promotors of surface adhesion between
dissimilar materials, e.g., glass and polymers.
Silane and titanate
•Curing agents-chemicals that cause crosslinking.
•Inhibitorsused to establish shelf life
•Catalyst (hardeners) start reactions. Organic
peroxides used to cross-link elastomers as well as
Benzoyl peroxides and MEK.

16. ACCELERATORS / PROMOTERS
•Use to reduce vulcanization time, or cure time
by increasing the speed of vulcanization
•Most are organic substance containing both
nitrogen and sulfur.
•Inorganic accelerator was widelyused years
ago (litharge, lime, and magnesia)

17. ORGANIC ACCELERATORS
TYPE EXAMPLE TYPICAL USE
Aldehyde-amine butyral dehyde andanilineReaction product of Fast
curing accelerator for
reclaim,hardrubber and
self-curingcements
Amines Hexamethyleneand
tetramine
Delayed action slow
accelerator for natural
rubber
Guanidines Diphenyl guanidine Secondary accelerator to
activate thiazole type
accelerator
Thioureas Ethylene thiourea(ETU) Fast curing acceleratorfor
Neoprene,Hypalon and
Epichlorohydrin
Thiazoles Benzothiazyldisulfide
(MBTS)
Safe-processing
moderately fast curing
acceleratorIsoprene,SBR,
Nitrile,Butyl and
EPDM

18. ORGANIC ACCELERATORS
TYPE EXAMPLE TYPICAL USE
Thiurams Tetramethylthiuram
disulfide (TMTD)
Fast curing sulfur-
bearing accelerator for
SBR, Nitrile, Butyl and
EPD
Sulfenamides N-cyclohexyl-2-
benzothiazyl-
sulfonamide(CBS)
Safe-processing, delayed
action accelerator for
natural rubber, SBR and
Nitrile
Dithiocarbamates Zinc dimethyl Fast curing accelerator
Xanthates Dibutylxanthogen
disulfide
Fast curing, low
temperatureaccelerator
fornatural rubber and
SBR

19. ACTIVATORS AND
RETARDERS
•Activators-used to activate the accelerator
and improve its effectiveness (ZnO, stearic
acid, litharge, magnesia, and amine)
-attain good crosslink efficiency
•Retarders -used to reduce the scorchness
(phthalic anhydride, salicylic acid and sodium
acetate)

20. ANTIDEGRADANTS
•To retard the deterioration of rubber compounds
initiated by
-oxygen, ozone
-heat, light
-metal catalyst and
-mechanical flexing

21. FILLERS
•Fillers are added to rubber to meet material
property targets example tensile strength and
abrasion resistance
•To reinforce physical properties
•To reduce cost
•Devided into two types(Reinforcing and
Extending)
•Selection of reinforcing filler is the third most
important task in compounding(next to
elastomer and cure system)

22. TYPES OF FILLERS
1)Reinforcing Type:
Carbon Black;(listed in order of increasing
particle size) N220 (ISAF),N330 (HAF),N550
(FEF),N762 (SRF-LM) andN990 (MT)
•Carbon black properties; Particle size, surface
area, particle size distribution, structure
(aggregates), surface activity (chemical functional
groups).
Non-Black;Silica,Zinc Oxide, Magnesium
Carbonate, Aluminum Silicate, Sodium
Aluminosilicate and Magnesium Silicate.

23. CARBON BLACK
•The single most important reinforcing filler in
rubber is carbon black, a colloidal form of carbon
obtained by thermal decomposition of
hydrocarbons (soot)
–It increases tensile strength and resistance to
abrasion and tearing of the final rubber
product
–Carbon black also provides protection from
ultraviolet radiation
–Most rubber parts are black in color because
of their carbon black content

24. NON-BLACK
Silica and Silicate
•Silica increases tear strength, reduces heat buildup,
increases compound adhesion in tires.
•Secondary properties: pH, chemical composition,
and oil absorption
•Advantages of Silica over carbon black in rubber
formations:
•Reduction in heat build-up and improvement
in tear strength, cut, chip, and chucking
resitance.
•When loadings approach 20%, the drop in
abrasion resistance renders the formulation
no longer practical.

25. TYPES OF FILLERS (CONTINUED)
2)Extending Type:
•Calcium Carbonate
•Barium Sulfate
•Aluminum Trihydrate
•Talc

26. PARTICLES SIZE
•Play a major role in the tensile strength
small particle size highest tensile
strength at optimum loading
•Fine fillers is difficult to process (need more
energy for their dispersion into the elastomer)
•Effects Mooney scorch
small particle size the scorch
resistance
reduces

27. PLASTICIZERS,SOFTENERS, AND
TACKIFIERS
•Objective for Using -Aid mixing, Modify
viscosity, Produce tack,Provide flexibility at low
temperature

28. SELECTION OF PLASTICIZERS
•The important criteria are:
1)Compatibility
2)Efficiency
3)Cost
Example:
•Aromatic type oil is not compatibe with NR,
Isoprene, IIR, EPDM
•Paraffinic type oil is not compatible with SBR,
butadiene, NBR, CR

29. OTHER ADDITIVES
Antioxidants-Oxidation of the polymer breaks
down long chain molecules.
•More severe at elevated temperatures
•Primary antioxidants: terminates reactions
(phenolic, amine)
•Secondary antioxidants: neutralizes reactive
materials (phosphite, thioesters)
Antistatic-
•agents attract moisture, causing the surface to be
more reactive, dissipates charges

30. OTHER ADDITIVES
Flame retardants
•Based on combinations of bromine, Cl, antimony,
boron, and phosphorous
•Many emit afire-extinguishing gas when
heated
•Others swell or foam to form a insulating
barrier against heat and flame.
•Alumina trihydrate (ATH) emits water
Heat Stabilizers
•Retard thermal decomposition for PVC
•Based on lead and cadmium in past. 28% Ca
pollution came from plastics
•New developments based on barium-zinc, Ca-
zinc, Mg-Zinc, etc..

31. TO BE CONTINUED
Plasticizers
•Chemical agent added to increase flexibility,
reduce melt temperature, and lower viscosity
•Neutralize Van der Waals’ forces
•Over 500 different plasticizers available
examples: Dioctyl phtalate(DOP), di-2-
ethylhexyl phthalate (carcinogenic in animals)
Anitdegradantuse

32. TO BE CONTINUED
Preservatives
•Protects plastic (PVC and elastomers) against
attacks by insects, rodents, and microorganisms
•Examples Antimicrobials, mildewicides,
fungicides, and rodenticides
Processing Aids
•Antiblockingagents (waxes) prevents sticking
•Emulsifiers lowers surface tension.
•Detergents and wetting agents (viscosity)
•Solvents for molding, painting, or cleaning
•Oils are processing aids can be paraffinic,
napthanic, and aromatic.

33. TO BE CONTINUED
AntidegradantUse
•Discoloration and staining
Phenolic antioxidants are nondiscoloring
Amines (preferred) are discoloring
•Volatility
Higher Mw of the antioxidant, the less volatile it will be
Hindered phenols are highly volatile compared to amines
Correct addition of antioxidants in mix is critical for less loss
•Solubility
Low solubility of antidegradantcauses material to bloom at
surface with loss of protection for the product.
•Chemical Stability
Stable against heat, light, oxygen, and solvents
•Concentration
Most have optimum concentration for max effectiveness.

34. TO BE CONTINUED
Coupling agents-
•Promotors of surface adhesion between
dissimilar materials, e.g., glass and polymers.
Silane and titanate
Curing agents-chemicals that cause crosslinking.
•Inhibitors used to establish shelf life
•Catalyst (hardeners) start reactions. Organic
peroxides used to cross-link elastomers as well
as Benzoyl peroxides and MEK.
•Promoters or accelerators speed reactions up,
e.g., cobalt naphthanate.

35. TO BE CONTINUED
UV Stabilizers
•Plastics susceptible to UV degredation are
Polyolefins, polystyrene, PVC, ABS, polyesters,
and polyurethanes,
•Polymer absorbs light energy and causes
crazing, cracking, chalking, color changes, or
loss of mechanical properties
•UV stabilizers can be carbon black, 2-hydroxy-
benzophenones, 2-hydroxy-phenyl-
benzotrizoles

36. COMPOUND PREPARATION
•Rubber compounds are prepared in internal
mixers.
•Internal mixers generate high shear forces that
disperse the fillers and raw materials into an
uniform, quality compound.
•After mixing it is dropped onto a mill or
extruder or pelletizer.
•Temperatures and times are recorded for each
step in the mix process.
•Heat history, power consumption, etc. are
monitored