CRB 30204 RUBBER
TECHNOLOGY – CHAPTER 2
Dr. SK Ong
Chapter Outline

Rubber Additives
 Compounding
ingredient
 Vulcanization systems
 Rubber reinforcement theories
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Raw Rubber Processing
Testing: Viscosity/Plasticity
Raw rubber
Mastication
Tool: Two-roll mill or internal mixer
Compounding
Testing: Scorch & Cure Characteristic
Rubber compound
Shaping
Vulcanization
Testing: Tensile Test, Tear Strength,
Compression Set, Abrasion,
Resilience, Hardness, Ageing etc
Tool: Calendering, spreading,
extruding, compression moulding,
transfer moulding, injection
moulding
Final product
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Viscosity Test – Mooney Viscometer
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Equipment: Mooney Viscometer
Properties measured: viscosity of raw rubber
(incoming rubber bale)
Unit : Mooney units
Standards: IS0 289, ASTM D 1646, BS 903: Part
A58, DIN 53523-3
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How Mooney Viscometer Works?
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A knurled knob (rotor) rotates (at 2 revolutions/min) in
a closed heated cavity (like a mold), filled with uncured
rubber.
Shearing action will develops btwn compound & rotor
when the rotor rotate
This results in torque (resistance of the rubber to the
turning rotor)
Mooney units is directly relate to torque
The higher the number, the higher the viscosity (higher
resistance of the rubber against the rotor rotation)
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Schematic Diagram of Mooney Viscometer
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Mooney Viscosity Results
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Wallace Plastimeter



Measures the plasticity or viscosity of cylindrically
cut unvulcanized rubbers which is under a constant
compressive force btwn 2 parallel plates
Very simple & crude methods for measuring flow of
rubber
Disadvantages: operate at extremely low shear
rate range (0.0025 to 1 s-1)
Wallace Plastimeter (Cont’)

Determine the Plasticity Retention Index (PRI) of raw
natural rubbers (ASTM D 3194)
 PRI
is a measure of the resistance of raw NR to
oxidation.
 Oxidation effect is assessed by measuring the plasticity
before ageing (P0) and after ageing for 30mins in the
Wallace - MRPRA ageing oven at 140°C (P30)
Wallace Plastimeter (Cont’)
Tackiness (Rubber)

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Tackiness: ability of an uncured rubber compound to
stick to itself or another compound in short dwell time
with moderate applied pressure
Important property when a rubber product was built by
laying one calendered/extruded rubber ply on top of
another
Uncured layers must hv good tackiness prior to curing
Tackiness can be deteriorate due to blooming of
additives like sulfur, accelerators, waxes etc (tackifier
can be added to improve this property)
Tool: Tel-Tak Tackmeter (no ATSM/ISO test std)
Mastication


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Entangled rubber chains are ‘torn apart’ at weakest
bond
Free radicals will recombine or add to a double
bond in another rubber chain w/o O2 present.
(rubber chain not permanently broken)
With O2 present, peroxy radical formed.
(permanent breakdown of rubber chain)
Tool: Two-roll mill, internal mixer, injection molding
etc
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Compounding/Mixing

Obj:
 Obtain
uniform blend with good dispersion of each
ingredient
 Produce consistent batches which are uniform in
viscosity & degree of dispersion.


Main tools: Two-roll mill or internal mixer
Main constituents: Rubber, antioxidant, accelerator,
vulcanizing agent(s), activator, reinforcing
agents/filler, processing aids, extender/diluents &
pigments.
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Main Compounding Ingredients
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Rubber or blends of rubbers
Vulcanizing agent(s)
Accelerators of vulcanization
Activators of accelerators
Reinforcing agents or filler (carbon black, mineral filler)
Processing aids (peptisers, plasticizers, dispersing aids)
Extenders or diluents (extending oils, cheap inert
mineral fillers)
Pigments or colouring materials
Antidegradants
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Example
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Accelerators


Majority contains nitrogen or sulphur atoms
Classified in term of cure rates or chemical structure
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Classification of Accelerators
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Classification of Accelerators (cont.)
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More Information on Selected Accelerators
Accelerators
Characteristics
Dithiocarbamates Example: Zinc dibutyl dithiocarbamate (ZDBC).
Very scorchy & very fast curing. Useful in low temperature
(down to 100oC) vulcanization and in elastomers with low
levels of unsaturation such as EPDM. Note that as
temperature reduces scorch increases & cure rate
decreases.
Thiurams
Example: Tetramethylthiuram disulfide (TMTD).
Somewhat less scorchy than dithiocarbamates & fast
curing. TMTD is less scorchy in the absence of sulfur. In this
case its function would be that of a cross-linking agent
rather than an accelerator. Tetramethylthiuram
monosulfide (TMTM) gives good compression set.
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More Information on Selected Accelerators
Accelerators
Characteristics
Thiazoles
eg: Mercaptobenzothiazole (MBT).
Moderate cure rate & scorch giving a low modulus
vulcanizate.
Guanidines
eg: Diphenyl guanidine (DPG).
Scorchy & slow curing. Most often used in combination
with other accelerators.
Sulfenamides
eg: N-cyclohexyl-2-benzothiazolseu lfenamide (CBS).
Long scorch with medium to fast cure. It would be a good
choice when mixing compounds containing reinforcing
furnace blacks which generate more heat.
The sulfenamide N,N-dicyclohexyl-2-benzothiazyl
sulfenamide (DCBS) gives longer scorch & slower curing.
DCBS gives excellent adhesion when bonding brass
20
coated steel to rubber, Dr.
egOng
in SK
tire production.
Examples of Accelerators & Its Structure
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Examples of Accelerators & Its Structure
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Vulcanization characteristics by various
accelerators and combinations.
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Various Accelerators & Its Cure Time
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Activator
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
Increase vulcanization rate by activating the accelerator
Types of activators
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Inorganic compounds, mainly metal oxides e.g. Zinc oxide 3-5 p.h.r.
Organic acids, high molecular weight monobasic fatty acids e.g. stearic
acid 1-3 p.h.r.
Alkaline substances, mainly amines e.g. diethanolamine 2 p.h.r. used in
silica-filled compounds, and compounds with acidic ingredients)
Normally ZnO & stearic acid are used together or zinc stearate to
replace both
Zinc oxide reacts with stearic acid to form zinc stearate
Together w/accelerator they speed up the rate at which sulfur
vulcanization occurs.
With sulfur alone, the curing process might take hours. With this
curing system, it can be reduced to minutes.
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Vulcanizing Agents – Sulfur
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It reacts chemically with the raw gum elastomer forming
cross-links between the polymer chains, resulting in a
more dimensionally stable and less heat-sensitive
product.
Elastomers need to hv unsaturated bonds
Its cost is relatively low but its function is essential.
Grade for rubber application: cyclic sulfur in fine
rhombic crystal shape (S8) /amorphous sulfur
At high sulfur level in a compound, it can slowly bloom
to the surface.
Sulfur donor like TMTD/TETD can be use also
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Chemistry of Sulfur Vulcanization

Refer to Handouts
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Sulfur Vulcanization System
Cure systems
(phr)
Accelerator (phr)
Conventional
2.0 - 3.5
1.0 - 0.4
EV
0.3 - 0.8
6.0 - 2.5
Semi-EV
1.0 - 1.7
2.5 - 1.0
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Sulphur Vulcanizing System

EV system:
 Mainly
monosulphide cross-link
 Little modification except on pendant grps

CV system:
 Mainly
di-,poly- & cyclic sulphide cross-link
 Sulphide cross-link easily decompose & causing main
chain modification
Note: C-C bond: strong; C-S bond: medium strong: S-S bond: weak; S-Sx-S
bond: weak
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Vulcanizing Agents – Peroxide
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Most common organic peroxide: dicumyl peroxide
(DCP)
Elastomer do not need unsaturated bonds
Major curative for silicone rubber
Note: not recommended for some elastomers such as
IIR or CIIR
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Chemistry of Peroxide Curing

Peroxide decomposition:
abstraction of a hydrogen atom from
an allylic position on the polymer
addition of the peroxide-derived radical
to a double bond of the polymer molecule

Crosslinking of 2 polymeric free radicals
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Chemistry of Peroxide Curing (Cont.)

Or addition of polymeric free radicals to double
bonds
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Cares When Using Peroxide
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
Reason: to avoid unwanted interaction with
peroxide
Example
 Antioxidant
selection
 Contact with oxygen (air) should be avoided during
vulcanization (such as in hot air ovens or autoclave
curing).
 Some ingredients, which are not part of the cure
system, which are common in sulfur systems can interact
with the peroxide in peroxide cure systems and thus
interfere with cure.
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Peroxides Cure
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Vulcanizate hv good resistance towards oxidative
ageing & reversion due to stable C-C x/link
Compression set is also improved
Tensile strength, tear strength, and fatigue (dynamic
deformation such as constant flexing) life are
reduced.
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Peroxides Cure
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Post cure (continued cure outside of the mold) is
sometimes undertaken with peroxide cured
vulcanizates, to complete the cure and remove
unwanted byproducts.
x/link density of a peroxide cured compound can
be increased by addition of chemicals called
coagents, of which methacrylates are a good
example.
This results in a higher state of cure with
improvements in properties such as compression set
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Dynamic Vulcanization
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For thermoplastic elastomer (TPE)
Vulcanizing or x/linking of one polymer during its
molten-state mixing with another polymer or with other
polymers.
The polymers are first thoroughly mixed and then,
during further mixing, one of the polymers will x/linked,
whereas the remaining other polymeric material
remains uncrosslinked.
The process produces a dispersion of x/linked polymer
in a matrix or continuous phase of uncrosslinked
polymer.
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Filler

Function of fillers:
Reinforcement effect, i.e. to increase mechanical properties
(eg, TS & resistance to tearing) in the vulcanizate & to
increase stiffness
 Compound cost reduction
 Might be for coloring purpose


Types of filler
Reinforcing filler (Carbon black & silica):
To improve the mechanical properties of the filled rubber
vulcanizate
 Non-reinforcing filler (Clay, Calcium carbonate etc)
Stiffer & harder filled rubber vulcanizate will be obtained

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Particle Size vs. Reinforcement
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Size>5000 nm: non-reinforcing
Size btwn 1000 – 5000 nm: weak reinforcing but
with high loading, reinforcement can be obtain
Size< 1000 nm: Reinforcing
Size< 100 nm: True reinforcing
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Carbon Black
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Hv various type with different physical & chemical
properties
Multiple size, surface area, structure & surface
activities
Its surface has functional grps like phenolic, ketones,
carboxylic, lactones etc. these functional grps will
be responsible in interacting with the rubber
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Structure, Aggregation &
Agglomeration
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Structure refers to degree of aggregation, a low
structure means there are 30 particles/aggregate
while high structure hv 200 particle/aggregate
Aggregate hv tendency to agglomerate during
processing; these agglomerates are called
secondary aggregate
Bonds btwn aggregates are weak vs. those bond of
primary aggregate
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CB Aggregates
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Reinforcing

Filler-rubber interaction depends on:
 External
factor: total surface area of the filler which
are in contact with rubber
 Internal factor: surface activities & chemical properties
 Geometry factor: filler’s structure & filler porosity
(minor factor)
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Surface Area
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The smaller the particle size the bigger the surface
area
Bigger surface area results in higher interaction
btwn filler & rubber
As 

d 2
1 3
d e
6

6
de
As = surface area; d = diameter & e = filler
density
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Surface Activities & Chemical
Properties
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Chemical properties of a filler depends on the
presence of functional grps which hv oxygen
Polar rubber hv better affinity to polar filler
Reinforcement factor
= surface area x surface activity
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Chemical Functions on CB Surface
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Structure
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Primary structure refers to degree of aggregation
Secondary structure refers to agglomeration of
aggregates; agglomeration is a result of Van der
Waals forces
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Structure
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CB loading & Selected Properties
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Carbon Black Classification
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Following ASTM D 1765
1st alphabet refer top rate of vulcanization; N refer
to normal rate & S is slow rate
1st digit after the alphabet refers to particle size;
smaller the number, smaller size.
2nd & 3rd digit after the 1st digit don’t hv special
meaning
5 major reinforcing CB are N110, N220, N330,
N341 & N550
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ASTM Grades ofCB
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ASTM Grades of CB
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Silica
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More expensive vs. CB but yet performance similar as
CB
Special performance: improvement in tear strength,
reduction in heat buildup, & increase in compound
adhesion in multicomponent products such as tires
Preparation method of silica: fume silica & precipitate
silica
Fume Silica: smallest filler size (7–15 nm); obtained
from high temp rxtn btwn silicon tetrachloride and
water vapor
Precipitate silica: better reinforcing performance &
reinforcing factor determine via particle size.
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Silica (cont.)

Important properties of silica in reinforcement:
 Ultimate
particle size
 Extent of hydration

Others important physical properties: pH, chemical
composition & oil absorption
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Characteristic of Silica Filled
Vulcanizates vs CB Filled Vulcanizates
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No change in modulus as much as CB
Abrasion resistance is good
TS is good
Much better tear strength
Used when non-black reinforcement required; eg
shoe sole, non black side wall tire or good tear
resistance needed
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Physical Properties of Silica
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Silica is an amorphous, consists of silicon and
oxygen arranged in a tetrahedral structure of a 3D lattice
Particle size ranges from 1–30 nm & surface area
from 20–300m2/g.
There is no long-range crystal order, only shortrange ordered domains in a random arrangement
with neighbouring domains
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Chemical Properties of Silica
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Surface silanol concentration (silanol groups —Si—
O—H) influence the degree of surface hydration
Surface acidity is controlled by hydroxyl grps on the
surface & is intermediate btwn those of P—OH &
B—OH.
This intrinsic acidity can influence peroxide
vulcanization, although in sulphur curing, there is no
significant effect
Rubber–filler interaction is affected by these sites
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Chemical Properties of Silica (cont.)
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Surface hydration caused by water vapour
absorption is affected by [surface silanol]
High levels of hydration can adversely affect final
compound physical properties
Silicas are hydroscopic & thus require dry storage
conditions
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Silica loading in SBR: 50phr
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Types of Silanols
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Isolated
Geminal (2 —OH grps on the same silicon atom)
Vicinal (on adjacent silicon atoms)
Siloxane bridge
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Silica Grps
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Problems with Silica Filler
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Increase in viscosity during compounding; especially
high surface area one
Deactivation of accelerator system  longer cure
time
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Solutions
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Using combination of 2 or more accelerators eg one
from thiazole or sulfenamide & the other one from
guaidine, tiurams or ditiocarbamate
Use glycol activator (eg polyethylene glycol or
diethylene glycol)  to prevent rxtn btwn moisture
Using EV system
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Silane Coupling Agent
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Function: to improve the affinity btwn rubber and
silica
Silane coupling agent: bifunctional compounds which
react with silica surface & sulphur containing grps in
vulcanized rubber
Results: increased in modulus, resilience, abrasion
resistance but decrement in tear strength
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Silane Coupling Agent (cont.)
:
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Other Fillers – Clay

Commonly used white filler, due to:
 Low
cost
 Reinforcing efficiency is btwn low to medium
 Ease of processing especially for extrusion &
calendering

Grades of China clays:
 Soft
clays
 Hard clays
 Calcined clays
 Treated clays
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China Clays

Soft clays:
 Particle
size > 2 nm
 Often used at high loading for low-cost compounds

Hard clays
 Particle
sizes < 2 nm
 Higher TS, tear resistance & abrasion resistance are
obtainable by using the hard clays vs. soft clays.
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China Clays (cont.)

Calcined clays:
 Obtained
from hard clays in which the combined water
has been removed
 Give higher hardness, TS & electrical resistivity vs. hard
clays

Treated clays:
 Hard
clays which have been chemically treated offer
better filler reinforcement than the untreated clays
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Other Fillers
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
Calcium carbonate is used as a low-cost filler in rubber
products for static applications such as carpet underlay.
Calcium carbonates grades:
Ground limestone
 Whiting
 Precipitated whiting
 Treated whiting


Titanium dioxide finds extensive use in white products
such as white tire sidewalls where appearance is
important
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Effect of Particle Size on Hardness of
Vulcanizates
Carbon black type
Average particle Parts of filler per point increase in hardness
ASTM
Code
size (nm)
CR
IIR
NR
SBR
N 220
ISAF
28
1.3
1.5
1.7
2.0
N 330
HAF
32
1.5
1.7
1.9
2.3
N 660
GPF
70
2.0
2.2
2.5
3.0
N 990
MT
300
3.3
3.7
4.2
5.0
Hydrated silica
20
1.5
1.6
2.0
1.6
Calcium silicate
25
2.2
1.9
3.0
3.3
Hard clay
2 X 103
4.5
5.9
5.0
4.9
Soft clay
10 X 103
5.0
9.1
7.7
5.6
Whiting
12 X 103
5.0Dr. Ong SK 9.1
6.4
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8.4
Non black
Factors Contributes to Modulus of
CB Filled Vulcanizates
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Pure gum: directly proportional to x/link density; 
x/link denstiy, modulus
Filler-rubber bonds: physical and/or chemical
interaction btwn filler & rubber increase apparent
x/link density of the system
Structure: at moderate filler loading, high structure
fillers formed 3-D network through the rubber
matrix; filler network can increase modulus up to
2% (due to Van der Waals-London attraction. At
abt 10% strain, 90% of the network broke down
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Factors Contributes to Modulus of
CB Filled Vulcanizates (cont.)

Strain amplification (hydrodynamic effect(
 When
rubber filled with CB/silica, an equivalent
volume fraction of rubber is replaced with rigid non
deforming filler.
 When deformed, filler does not undergo deformation
 So the microscopic strains experienced by rubber chains
is greater than the macroscopic strains
 This is called strain amplifications
 it depends on filler loading & filler type
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X/link Density
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
x/lonk density=degree of x/link= how many x/link
formed
Method to determine x/link density:
 Swelling
– Flory Rehners
 Physical method – Mooney Rivlin
 Rheocurve (indirect)


Both method hv pros & cons, selection depends…
For research purpose, both method hv to be
included for consistency of results
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Swelling Method – Flory Rehners
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

Need to hv c value (solubility parameters)
Takes long time as need to wait until equilibrium of
swelling achieve
Method: Vulcanized rubber immersed in a solvent
until equilibrium weight reached
For a given solvent, higher x/link density lower
swelling
For a given degree of x/link, more powerful solvent
give higher degree of swelling
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Flory-Rehner Eq.


2 

 1 ln1  vr   vr  cvr

x/link density,v  
1
Vs 
1/ 3

v

vr


r
2


Vs=molar volume of the solvent
vr=volume fraction of rubber in the swollen gel
c= interaction constant, for NR usually is 0.4 in good
solvent (determine the cohesive energy density of
solvent & polymer & the swollen gel)
Note: Effectiveness depends on obtaining good estimation of c
At high cure state, further increase in cure only results in small changes in
volume fraction of rubber (poor accuracy)
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Mooney Rivlin Method




Carried out based on stress-strain measurement of
the samples
Must hv ‘straight line’
Intercept at y-axis must be +ve
Takes long measurement time since low x/head
speed is used
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Mooney-Rivlin Eq.


f
Reduced stress, F 
   2  2C1  2C2 1
A
*
= extension ratio
C1, C2=elastic constants
f=force
A=cross sectional area of the specimen
f/A=nominal stress
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Kinetic Theory of Elasticity & x/link
Density
  RTvph   2 
= extension ratio
v ph =number of physical crosslinks per cm3
R=gas constant
T= absolute temp
Physical x/link density can be calculated from elastic
constant C1 (intercept of f/A (- -2) vs. -1 where ph =
2C1/RT
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Plot of f/A (- -2) vs.
-1 for a range of NR
vulcanizates. Sulfur
content increases from 3
to 4%, with time of
vulcanization & other
quantities as variables
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Smallwood-Guth-Gold Eq

E f  Eo 1 2.5 14.12

Ef = modulus of filled rubber
Eo = modulus of rubber matrix
 = volume fraction of the filler
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Rheocurve


Tmax – Tmin: measure moduli (M100, M300)
Tmax – Tmin lower, M100 lower
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Reinforcing Efficiency

Measurement:
 Rheometer
(Tmax – Tmin)
 Tensile modulus
 Modified Guth-Smallwood eq.
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Processing aids (peptisers,
plasticizers, dispersing aids)


Function: to aid (help) processing
Types:
Processing aids
 Plasticizer
 Factice
 Low molecular weight polyethylene/Wax
 Fatty acids
 Superior processing rubber (SP rubber)
 Reground crumb
 Reclaimed rubber

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Plasticizer

Types of plasticizers:
 The
chemical plasticizers (peptiser)
 The physical plasticizers (softeners & extenders)


Peptiser was used to ease NR mol. chain break
down (Added to the rubber at the start of
mastication)
Physical plasticizer don’t react chemically with the
rubbers but function by modifying the physical
characteristics of either compounded rubber/
finished vulcanizate
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Eg of Peptizer
Producer
Trade name Chemical name
Anchor
Chemical
Pepton 22
Pepton 65
Bayer
Renacit IV
Renacit VII
Min. operative
temp. (oC)
115
Di (benzamidophenyl)disulphide
Zinc-2-benzamido- 65
thiophenate
Zinc salt of
70
pentachlorothiophe
nol
Pentachlorothiophen 70
ol with activating
dispersing
additives.
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Plasticizer –Softeners/Extenders


Petroleum oils are the most commonly used physical
plasticisers for processing
Types of petroleum oils used as processing aids and
extenders are classified under three headings:
 Paraffinic
 Napthenic
 Aromatic
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Factice




Types of factice: white factice & brown factice
Function: to facilitate processing by improving the
incorporation & dispersion of powders & reduce
power consumption
Presence of 5-30 phr of factice may be used to
control die swell, improve surface quality & prevent
distortion of shape during open steam vulcanization
Large loadings of factice e.g. 100 -150 phr are
used in very soft compounds such as pencil erasers
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Low MW PE/Wax

Functions:
 As
processing aid
 As release agent to prevent sticking together of rubber
compounds
 As lubricant to help could flow & extrusion & prevent
blocking in dies
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Fatty Acid

Function:
 As
a plasticizer
 Aids dispersion of CB and other fillers
 Minimizes any tendency for sticking to the mill rolls

Eg: stearic acid & is commonly used btwn 1-2 phr
for sulfur vulcanization system
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Superior Processing Rubber

Function:
 Controlling
"nerve" during mixing processes
 Improving shaping operations
 Ensuring dimensional stability of rubber compounds

E.g. PA 80 which consists of 80% vulcanised and
20% unvulcanised NR & PA57 which consists
essentially of 70 parts of PA80 with 30 parts of a
non-staining processing oil.
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Crumb



Function: to remove air  reduce blisters in rubber
products
Can be obtained either by cryogenic grinding using
liquid nitrogen or buffing process such as tyre
buffings
Crumb can be used at a level of 5-20 phr
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Reclaimed Rubber

Function:
 To
reduce compound cost
 To improve processing such as reducing shrinkage, &
swell & increasing calendaring & extrusion rates

Obtained from treatment of vulcanized scraps by
the application of heat & chemical agents, i.e. from
devulcanization or depolymerization
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Degradation of Unsaturated
Rubber
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Antidegradants



Function: to extend the service life of vulcanized
elastomer by protecting them from oxygen, ozone,
light, heat, and flex fatigue
Why?...due to the unsaturated backbones
Types:
 Staining
antioxidant & antiozonant
 Non-staining antioxidant & antiozonant
 Antiozonant
 Waxes
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Antioxidant

A/O react with
 Oxygen
to prevent oxidation of vulcanized rubber
 Free radicals that degrade vulcanized rubber


2 main classes of staining: polymerized
dihydroquinolines & diphenylamines
Non staining hv 4 grps: phosphites, hindered
phenols, hindered bisphenols & hydroquinones
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Eg of Non Staining Antioxidant
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Eg of Staining Antioxidant
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Antiozonant





2 classes: staining & non-staining antiozonants
Non-staining types are less powerful & less versatile
vs to the staining types
Most common antiozonant: para-Phenylenediamines
(PPDs)
General structure:
Also improve resistance to fatigue, oxygen, heat,
and metal ions
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Waxes



Used to improve rubber ozone protection primarily
under static conditions.
Hv 2 categories: Microcrystalline wax & paraffin wax
Microcrystalline wax:
 Tm:
in the region of 55 to 100°C
 Extracted from residual heavy lube stock of refined
petroleum

Paraffin wax:
 Tm:
in the region 35 to 75°C
 Obtained from the light lube distillate of crude oil
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Selection Criteria of Antidegradant –
1. Discoloration & Staining


In general, phenolic antioxidants tend to be
nondiscoloring and amines are discoloring.
Thus for elastomers containing CB, more active
amine antioxidants are preferred as discoloration is
not important.
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Selection Criteria of Antidegradant –
2. Volatility



As a rule, the higher the MW of the antioxidant, the
less volatile it will be
Hindered phenols tend to be highly volatile
compared with amines of equivalent molecular
weight
Correct addition of antioxidants in the compound
mix cycle is critical if loss of material is to be
avoided
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Selection Criteria of Antidegradant –
3. Solubility




Low solubility of an antidegradant  material to
bloom to the surface  loss of protection
Therefore, solubility of antidegradants, particularly
antiozonants, controls their effectiveness.
The materials must be soluble up to 2.0 phr, must be
able to migrate to the surface
Must not be soluble in water or other solvents such
as hydraulic fluid so as to prevent extraction of the
protectant from the rubber.
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Selection Criteria of Antidegradant –
4. Chemical Stability

Antidegradant stability against heat, light, oxygen,
& solvents is required for durability
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Selection Criteria of Antidegradant –
5. Concentration


Most antidegradants have an optimum
concentration for max effectiveness after which the
material solubility becomes a limiting factor.
para-Phenylenediamines: good oxidation resistance
at a loading of 0.5 – 1.0 phr & antiozonant at the
range 2.0 – 5.0phr. Above 5.0 phr paraphenylenediamines tend to bloom
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Selection Criteria of Antidegradant –
6. Environment, Health, & Safety

For ease of handling & avoidance of dust &
inhalation, antidegradants should be dust free while
free flowing.
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Principal Theories of Antiozonant
Mechanisms

Scavenger theory




Postulates that the antiozonant competes with the rubber for
ozone.
Ozonized antiozonant forms a protective film on the
surface of the vulcanized rubber, preventing further
attack
3rd mechanism postulated is that the antiozonants react
with elastomer ozonide fragments, relinking them and
essentially restoring the polymer chain
4th theorized mechanism suggests that Criege
zwitterions are formed from the ozonide produced.
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Some Common Antidegradant
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