1. CRB 30204 RUBBER TECHNOLOGY – CHAPTER 2
8/16/2012
CRB RUBBER TECHNOLOGY – CHAPTER 2
Dr. SK Ong

2. Chapter Outline Rubber Additives Compounding ingredient
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Chapter Outline
Rubber Additives
Compounding ingredient
Vulcanization systems
Rubber reinforcement theories
Dr. Ong SK

3. Raw Rubber Processing Raw rubber Mastication Compounding
Testing: Viscosity/Plasticity
Raw rubber
Mastication
Tool: Two-roll mill or internal mixer
Compounding
Testing: Scorch & Cure Characteristic
Rubber compound
Shaping
Tool: Calendering, spreading, extruding, compression moulding, transfer moulding, injection moulding
Vulcanization
Testing: Tensile Test, Tear Strength, Compression Set, Abrasion, Resilience, Hardness, Ageing etc
Final product
Dr. Ong SK

4. Viscosity Test – Mooney Viscometer
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Viscosity Test – Mooney Viscometer
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
Dr. Ong SK

5. How Mooney Viscometer Works?
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How Mooney Viscometer Works?
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)
Dr. Ong SK

6. Schematic Diagram of Mooney Viscometer
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Schematic Diagram of Mooney Viscometer
Dr. Ong SK

7. Mooney Viscosity Results
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Mooney Viscosity Results
Dr. Ong SK

8. 8/16/2012
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 ( to 1 s-1)

9. Wallace Plastimeter (Cont’)
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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)

10. Wallace Plastimeter (Cont’)
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Wallace Plastimeter (Cont’)

11. 8/16/2012
Tackiness (Rubber)
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)

12. Mastication 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
Dr. Ong SK

13. Compounding/Mixing Obj: Main tools: Two-roll mill or internal mixer
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.
Dr. Ong SK

14. Main Compounding Ingredients
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Main Compounding Ingredients
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
Dr. Ong SK

15. 8/16/2012
Example
Dr. Ong SK

16. Accelerators Majority contains nitrogen or sulphur atoms
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Accelerators
Majority contains nitrogen or sulphur atoms
Classified in term of cure rates or chemical structure
Dr. Ong SK

17. Classification of Accelerators
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Classification of Accelerators
Dr. Ong SK

18. Classification of Accelerators (cont.)
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Classification of Accelerators (cont.)
Dr. Ong SK

19. More Information on Selected Accelerators
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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.
Dr. Ong SK

20. More Information on Selected Accelerators
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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 coated steel to rubber, eg in tire production.
Dr. Ong SK

21. Examples of Accelerators & Its Structure
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Examples of Accelerators & Its Structure
Dr. Ong SK

22. Examples of Accelerators & Its Structure
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Examples of Accelerators & Its Structure
Dr. Ong SK

23. 8/16/2012
Vulcanization characteristics by various accelerators and combinations.
Dr. Ong SK

24. Various Accelerators & Its Cure Time
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Various Accelerators & Its Cure Time
Dr. Ong SK

25. Activator Increase vulcanization rate by activating the accelerator
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Activator
Increase vulcanization rate by activating the accelerator
Types of activators
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.
Dr. Ong SK

26. Vulcanizing Agents – Sulfur
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Vulcanizing Agents – Sulfur
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
Dr. Ong SK

27. Chemistry of Sulfur Vulcanization
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Chemistry of Sulfur Vulcanization
Refer to Handouts
Dr. Ong SK

28. Sulfur Vulcanization System
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Sulfur Vulcanization System
Cure systems
(phr)
Accelerator (phr)
Conventional EV
Semi-EV
Dr. Ong SK

29. 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
Dr. Ong SK

30. 8/16/2012
Dr. Ong SK

31. Vulcanizing Agents – Peroxide
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Vulcanizing Agents – Peroxide
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
Dr. Ong SK

32. Chemistry of Peroxide Curing
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Chemistry of Peroxide Curing
Peroxide decomposition:
Crosslinking of 2 polymeric free radicals
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
Dr. Ong SK

33. Chemistry of Peroxide Curing (Cont.)
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Chemistry of Peroxide Curing (Cont.)
Or addition of polymeric free radicals to double bonds
Dr. Ong SK

34. Cares When Using Peroxide
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Cares When Using Peroxide
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.
Dr. Ong SK

35. 8/16/2012
Peroxides Cure
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.
Dr. Ong SK

36. 8/16/2012
Peroxides Cure
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
Dr. Ong SK

37. Dynamic Vulcanization
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Dynamic Vulcanization
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.
Dr. Ong SK

38. Filler Function of fillers: Types of filler
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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
Dr. Ong SK

39. Particle Size vs. Reinforcement
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Particle Size vs. Reinforcement
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
Dr. Ong SK

40. 8/16/2012
Carbon Black
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
Dr. Ong SK

41. 8/16/2012
Dr. Ong SK

42. Structure, Aggregation & Agglomeration
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Structure, Aggregation & Agglomeration
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
Dr. Ong SK

43. 8/16/2012
CB Aggregates
Dr. Ong SK

44. Reinforcing Filler-rubber interaction depends on:
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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)
Dr. Ong SK

45. Surface Area The smaller the particle size the bigger the surface area
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Surface Area
The smaller the particle size the bigger the surface area
Bigger surface area results in higher interaction btwn filler & rubber
As = surface area; d = diameter & e = filler density
Dr. Ong SK

46. Surface Activities & Chemical Properties
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Surface Activities & Chemical Properties
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
Dr. Ong SK

47. Chemical Functions on CB Surface
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Chemical Functions on CB Surface
Dr. Ong SK

48. Structure Primary structure refers to degree of aggregation
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Structure
Primary structure refers to degree of aggregation
Secondary structure refers to agglomeration of aggregates; agglomeration is a result of Van der Waals forces
Dr. Ong SK

49. 8/16/2012
Structure
Dr. Ong SK

50. 8/16/2012
Dr. Ong SK

51. CB loading & Selected Properties
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CB loading & Selected Properties
Dr. Ong SK

52. Carbon Black Classification
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Carbon Black Classification
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
Dr. Ong SK

53. 8/16/2012
ASTM Grades ofCB
Dr. Ong SK

54. 8/16/2012
ASTM Grades of CB
Dr. Ong SK

55. Silica More expensive vs. CB but yet performance similar as CB
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Silica
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.
Dr. Ong SK

56. Silica (cont.) Important properties of silica in reinforcement:
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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
Dr. Ong SK

57. Characteristic of Silica Filled Vulcanizates vs CB Filled Vulcanizates
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Characteristic of Silica Filled Vulcanizates vs CB Filled Vulcanizates
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
Dr. Ong SK

58. Physical Properties of Silica
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Physical Properties of Silica
Silica is an amorphous, consists of silicon and oxygen arranged in a tetrahedral structure of a 3- D lattice
Particle size ranges from 1–30 nm & surface area from 20–300m2/g.
There is no long-range crystal order, only short- range ordered domains in a random arrangement with neighbouring domains
Dr. Ong SK

59. Chemical Properties of Silica
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Chemical Properties of Silica
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
Dr. Ong SK

60. Chemical Properties of Silica (cont.)
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Chemical Properties of Silica (cont.)
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
Dr. Ong SK

61. Silica loading in SBR: 50phr
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Silica loading in SBR: 50phr
Dr. Ong SK

62. Types of Silanols Isolated
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Types of Silanols
Isolated
Geminal (2 —OH grps on the same silicon atom)
Vicinal (on adjacent silicon atoms)
Siloxane bridge
Dr. Ong SK

63. 8/16/2012
Silica Grps
Dr. Ong SK

64. Problems with Silica Filler
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Problems with Silica Filler
Increase in viscosity during compounding; especially high surface area one
Deactivation of accelerator system  longer cure time
Dr. Ong SK

65. 8/16/2012
Solutions
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
Dr. Ong SK

66. 8/16/2012
Silane Coupling Agent
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
Dr. Ong SK

67. Silane Coupling Agent (cont.)
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Silane Coupling Agent (cont.) :
Dr. Ong SK

68. 8/16/2012
Dr. Ong SK

69. 8/16/2012
Dr. Ong SK

70. 8/16/2012
Dr. Ong SK

71. 8/16/2012
Dr. Ong SK

72. Other Fillers – Clay Commonly used white filler, due to:
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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
Dr. Ong SK

73. China Clays Soft clays: Hard clays Particle size > 2 nm
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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.
Dr. Ong SK

74. China Clays (cont.) Calcined clays: Treated 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
Dr. Ong SK

75. 8/16/2012
Other Fillers
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
Dr. Ong SK

76. Effect of Particle Size on Hardness of Vulcanizates
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Effect of Particle Size on Hardness of Vulcanizates
Carbon black type
Average particle size (nm)
Parts of filler per point increase in hardness
ASTM
Code CR
IIR NR
SBR
N 220
ISAF 28
1.3
1.5
1.7
2.0
N 330
HAF 32
1.9
2.3
N 660
GPF 70
2.2
2.5
3.0
N 990 MT
300
3.3
3.7
4.2
5.0
Non black
Hydrated silica 20
1.6
Calcium silicate 25
Hard clay
2 X 103
4.5
5.9
4.9
Soft clay
10 X 103
9.1
7.7
5.6
Whiting
12 X 103
6.4
8.4
Dr. Ong SK

77. Factors Contributes to Modulus of CB Filled Vulcanizates
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Factors Contributes to Modulus of CB Filled Vulcanizates
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
Dr. Ong SK

78. Factors Contributes to Modulus of CB Filled Vulcanizates (cont.)
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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
Dr. Ong SK

79. X/link Density x/lonk density=degree of x/link= how many x/link formed
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X/link Density
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
Dr. Ong SK

80. Swelling Method – Flory Rehners
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Swelling Method – Flory Rehners
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
Dr. Ong SK

81. Flory-Rehner Eq. Vs=molar volume of the solvent
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Flory-Rehner Eq.
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)
Dr. Ong SK

82. 8/16/2012
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
Dr. Ong SK

83. Mooney-Rivlin Eq. l= extension ratio C1, C2=elastic constants f=force
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Mooney-Rivlin Eq.
l= extension ratio
C1, C2=elastic constants
f=force
A=cross sectional area of the specimen
f/A=nominal stress
Dr. Ong SK

84. Kinetic Theory of Elasticity & x/link Density
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Kinetic Theory of Elasticity & x/link Density
l= extension ratio
=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 (l- l-2) vs. l-1 where ph = 2C1/RT
Dr. Ong SK

85. Plot of f/A (l- l-2) vs. l-1 for a range of NR vulcanizates. Sulfur
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Plot of f/A (l- l-2) vs. l-1 for a range of NR vulcanizates. Sulfur
content increases from 3 to 4%, with time of vulcanization & other quantities as variables
Dr. Ong SK

86. Smallwood-Guth-Gold Eq
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Smallwood-Guth-Gold Eq
Ef = modulus of filled rubber
Eo = modulus of rubber matrix
 = volume fraction of the filler
Dr. Ong SK

87. Rheocurve Tmax – Tmin: measure moduli (M100, M300)
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Rheocurve
Tmax – Tmin: measure moduli (M100, M300)
Tmax – Tmin lower, M100 lower
Dr. Ong SK

88. Reinforcing Efficiency
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Reinforcing Efficiency
Measurement:
Rheometer (Tmax – Tmin)
Tensile modulus
Modified Guth-Smallwood eq.
Dr. Ong SK

89. Processing aids (peptisers, plasticizers, dispersing aids)
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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
Dr. Ong SK

90. Plasticizer Types of plasticizers:
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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
Dr. Ong SK

91. Eg of Peptizer Producer Trade name Chemical name
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Eg of Peptizer
Producer
Trade name
Chemical name
Min. operative temp. (oC)
Anchor Chemical
Pepton 22
Di (benzamido-phenyl)disulphide
115
Pepton 65
Zinc-2-benzamido-thiophenate 65
Bayer
Renacit IV
Zinc salt of pentachlorothiophenol 70
Renacit VII
Pentachlorothiophenol with activating dispersing additives.
Dr. Ong SK

92. Plasticizer –Softeners/Extenders
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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
Dr. Ong SK

93. Factice Types of factice: white factice & brown factice
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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 phr are used in very soft compounds such as pencil erasers
Dr. Ong SK

94. Low MW PE/Wax Functions: As processing aid
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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
Dr. Ong SK

95. 8/16/2012
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
Dr. Ong SK

96. Superior Processing Rubber
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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.
Dr. Ong SK

97. Crumb Function: to remove air  reduce blisters in rubber products
8/16/2012
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
Dr. Ong SK

98. Reclaimed Rubber Function:
8/16/2012
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
Dr. Ong SK

99. Degradation of Unsaturated Rubber
8/16/2012
Degradation of Unsaturated Rubber
Dr. Ong SK

100. 8/16/2012
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
Dr. Ong SK

101. Antioxidant A/O react with
8/16/2012
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
Dr. Ong SK

102. Eg of Non Staining Antioxidant
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Eg of Non Staining Antioxidant
Dr. Ong SK

103. Eg of Staining Antioxidant
8/16/2012
Eg of Staining Antioxidant
Dr. Ong SK

104. Antiozonant 2 classes: staining & non-staining antiozonants
8/16/2012
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
Dr. Ong SK

105. 8/16/2012
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
Dr. Ong SK

106. 8/16/2012
Dr. Ong SK

107. Selection Criteria of Antidegradant – 1. Discoloration & Staining
8/16/2012
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.
Dr. Ong SK

108. Selection Criteria of Antidegradant – 2. Volatility
8/16/2012
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
Dr. Ong SK

109. Selection Criteria of Antidegradant – 3. Solubility
8/16/2012
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.
Dr. Ong SK

110. Selection Criteria of Antidegradant – 4. Chemical Stability
8/16/2012
Selection Criteria of Antidegradant – 4. Chemical Stability
Antidegradant stability against heat, light, oxygen, & solvents is required for durability
Dr. Ong SK

111. Selection Criteria of Antidegradant – 5. Concentration
8/16/2012
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 para- phenylenediamines tend to bloom
Dr. Ong SK

112. Selection Criteria of Antidegradant – 6. Environment, Health, & Safety
8/16/2012
Selection Criteria of Antidegradant – 6. Environment, Health, & Safety
For ease of handling & avoidance of dust & inhalation, antidegradants should be dust free while free flowing.
Dr. Ong SK

113. Principal Theories of Antiozonant Mechanisms
8/16/2012
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.
Dr. Ong SK

114. Some Common Antidegradant
8/16/2012
Some Common Antidegradant
Dr. Ong SK