carbonblack

7/30/2019 carbonblack

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Co ri ht Jose h Greene 2001

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Carbon Black

Professor Joe Greene

CSU, CHICO


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Carbon Black Reference: Rubber Technology, Chapter 3

Phenomenon of carbon black reinforcement was discovered in early

1900s Physical and chemical attachments are capable of giving reinforcement effects

by increasing the tensile strength and modulus of the rubbery phase

Carbon black and vulcanization generates a 3-D network

Carbon black

Range of physical and chemical attributes

Particle size, surface area, structure, surface activity

Gas-furnace blacks: Thermal black process: 3% of current carbon black

Initially made using gas as the source of carbon and the fuel source

Carbon black had small particles and were acidic

Worked well with natural rubber

Large amounts of air pollution was generated and expensive

Oil furnace black (1943) is the current manufacturing method: 97% of black

Low grade petroleum feedstock was cheaper, less polluting, and flexible process

Higher structure and more alkaline than gas furnace (channel) blacks

Improved significantly the properties of SBR polymers


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Carbon Black Manufacture Manufacture and Morphology

Typical oil furnace reactor, Figure 3.1

Refractory lined tube that can be horizontal or vertical.

Feedstock oil, natural gas, or other fuel, and air are preheated and injectedinto the combustion zone at specific rates for the carbon black

Burning generates a very hot, turbulent atmosphere for cracking the feedstockoil.

90% of the feedstock is based on refinery heavy bottom oils.

Chemical reactions to convert the aromatic feedstock to elemental carbon arenot well understood and complex

Collision of particles in a liquid-like state produces aggregates of sphericalparticles fused together in a random grape-cluster configuration, Fig 3.2

The carbon is formed in aggregates with a distribution of sizes

Water quench is used to rapidly reduce the temperature and terminate thereaction.

The smoke exiting the reactor is a mixture of carbon black aggregates,combustion gases, and moist air.

The smoke preheats the feedstock and air, and generates steam for plant use.

Fluffy black and gases (tail gas) are separated by filtration, and the loose blackis pulverized to a 325 mesh and then pelletized


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Carbon Black Manufacture Manufacture and Morphology

Wet-pelleting process is used

A rotating, pin-studded shaft mixes the loose black with water and binder toproduce small beads or pellets.

Wet pellets are fed into a rotary drier heated by combustion of thetailgas from the earlier step in the process.

Steam that is generated is removed and replaced with air that oxidizes thecarbon black, which influences the chemical properties of the carbon blackand, in turn, the cure rate and properties of the vulcanizates.

The pelleted black is screened for uniformity and passed overmagnetic separators to remove metallic contamination that mayhave gotten in the product stream.

Finished product is packaged and shipped

Furnace black categories Reinforcing: hard, tread. Have a smaller particle size and lower yields and

more expensive than semi-reinforcing.

Semi-reinforcing: soft, carcass.


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Carbon Black Properties Physical and Chemical Properties

Particle size can be measured by electron micrographs, Figure 3.3

Average diameter is 19 to 95 nm (nanometers or 10-9 m)

Particles are measured manually or with image analysis software

Particle size can be measured by tint strength test (ASTM D3265) Carbon black sample is mixed with zinc oxide and a soybean oil epoxide to

produce a black or gray paste.

Paste is spread to produce a suitable surface for measuring the reflectance ofthe mixture with a photoelectric reflectance meter.

Reflectance is compared to the reflectance of paste containing theIndustry Tint Reference Black (ITRB) prepared in the same manner.

Tint test is affected by the structure as well as the particle size of the

black.

For a given particle size, the higher structure blacks have a lowertinting strengths.

Average particle size can be estimated from statistical equationsthat relate tint strength and structure to particle size as measured

from electron micrographs.


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Carbon Black Surface Area Surface Area

Very important in carbon black because it defines how much

surface is available for interactions with other materials present ina rubber compound.

Small particle-size black will have higher surface area, but the texture ornature of the surface area can also influence the surface area.

BET method (ASTM D3037) to determine surface area

Adsorption of a gas, usually nitrogen, on the surface. Surface area can be measured from electron micrographs

Standard rubber grade black (nitrogen surface area of less than 130 m2/g)are nonporous

Non-specialty furnace blacks give good inverse correlation between nitrogen

surface area and the particle size measurements. Specialty furnace blacks require a devolatilization step to remove residual

oils present on the surface of the blacks

Volume of void space between aggregates per unit weight ofcarbon black increases with the number of particles per aggregate

Non-spherical particles pack differently from spheres


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Carbon Black Chemical Properties Chemical Properties

Chemical nature of a carbon black is variable

Evidence for the presence on the surface of at least four oxygen containinggroups, carboxyl, phenol, quinone, and lactone.

Elastomers are polar in nature, neoprene or nitrile rubber Will react more strongly with fillers with dipoles, OH, COOH, or Cl

Chemical surface groups affect the rate of cure with manyvulcanization systems

Physical adsorption activity of the filler surface is of much greater overallimportance for the mechanical properties of the general-purpose rubbersthan the chemical nature.

Oxygen content influences the cure rate Increased oxygen gives longer scorch period, a slower rate of cure, and a

lower modulus at optimum cure.

Amount of oxidation during the pellet drying operation can affect the curerate and modulus of rubber compounds.

Carbon blacks are generally electrically conductive because of thehighly conjugated bonding scheme in crystalline regions


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Carbon Black Nomenclature Nomenclature

First digit following the letter indicates the particle size range

Lower numbers for smaller particle-size blacks

Last two digits are arbitrarily assigned by ASTM

Table 3.1

Properties

ASTM D1765

ASTM Old Name

N110 SAF (Super-abrasion furnace)N220 ISAF (Intermediate Super-abrasion furnace)

N330 HAF (High abrasion furnace)

N358 SPF (Super processing furnace)

N660 GPF (General-purpose furnace)

N762 SRF (Semireinforcing furnace)


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Carbon Black Properties Properties

High surface area and high structure carbon blacks are associated with increased

reinforcement Particle size affects abrasion resistance, heat build-up (resilience), tensile strength,

and tear strength.

Structure has more of an effect on modulus, hardness, and extrudate swell.

Four carbon blacks are shown to demonstrate the effects of varying surface area,structure, and black loadings on various compound properties.

Structure Differences

N339 vs N356

N650 vs N660

Both pairs have

Equivalent surface N2 surface area Large differences in structure from

DBP absorption and void volume data

N339 and N356 vs N650 and N660 shows large difference insurface area

Nitrogen

Surface

area m2/g

DBP

Absorption

cc/100g

Void

Volume

cc/100g

Tint

Strength,

%ITRB

N339 98.9 118.4 69.2 108.8

N356 100.1 160.2 77.7 103.2

N650 38.8 123.7 57.4 52.7

N660 39.3 89.7 44.5 59.2


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Carbon Black Properties Three compound recipes based upon different

polymers enable the observation of changes incarbon black effects from one polymer to another

Table 3.3

Figures 4 through 12

Mechanical properties for Different concentrations (loading

levels) of carbon black

EPDM Compound

EPDM 100 phr

Naphthenic oil 12Zinc oxide 5

Stearic acid 1

Processing aid 2

Sulfur 1.5

MBT 0.5

TMTD 3

Carbon black 0 to 80phr

SBR Compound

SBR-1500 100 phr

Aromatic oil 5Zinc oxide 3

Stearic acid 1.5

Sulfur 1.75

CBS 0.85

DPG 0.28

Carbon black 0 to 80phr

NR Compound

Natural Rubber 100 phr

Highly aromatic oil 15

Zinc oxide 5

Stearic acid 2.5

Antioxidant 2

Antiozonant 2

Sulfur 1.5

CBS 1.6Carbon black 0 to 80phr


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Carbon Black Properties Compound Property Group 1

Viscosity, modulus, hardness, extrudate swell

Measures the degree of stiffening that carbon contributes

High structure and an increase in the amount of carbon black surfaceavailable for attachment to the polymer result in the rubber compound to bemore viscous and less elastic

Viscosity, modulus, hardness, extrudate swell, Figures 3.4, 3.5,3.6

Increases with increased amount of carbon black for all three recipes, SBR,EPDM, and NR

The N356 carbon black (highest N2 surface area) had the highest viscosity,modulus at 200% elongation, and hardness; and the least amount of extrudateswell.

The higher the N2 surface area the higher the viscosity, modulus at 200%elongation, and hardness; and the lower amount of extrudate swell.

The N660 carbon black (lowest N2 surface area and lowest void volume) hadthe lowest viscosity, modulus at 200% elongation, and hardness; and the mostamount of extrudate swell.


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Abrasion resistance, tear strength, and tensile strength

Measures the resistance to failure under several types of stress

Strength related properties enhanced by carbon black surface area andincreased black loading up to a limiting value that is dependent on the

packing characteristics (morphology) of the carbon black aggregates.

High structure and an increase in the amount of carbon black surface available

for attachment to the polymer in the rubber compound. Asblack loading in increased to maximum level, the carbon aggregates are no

longer adequately separated by polymer which weakens the rubber composite

Abrasion Resistance, Figures 3.8a, 3.8b, 3.8c

Abrasion resistance is most affected by surface area and loading

Lower surface area GPF blacks (N650 and N660) contribute smallimprovements in abrasion, regardless of carbon black loadings

Higher surface area HAF blacks (N339 and N356) contribute betterimprovements in abrasion, depending on carbon black loadings.

Higher structure N356 black reach maximum abrasion resistance at lowerloadings than N339, but N339 ultimately gives higher abrasion resistance


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Tear-strength, Figures 3.9a and 3.9b

As carbon black is increased, the tear strength increases up to a peak, thendecreases after that.

Structure causes a shift in the strength curve to the left (lower limiting valuefor strength because of the effect of higher structure on packing)

Tensile strength, Fig 3.10a

Unfilled EPDM rubber compound has very low tensile strength.

Tensile strength is increased dramatically as carbon black is added until amaximum tensile strength is attained.

Higher surface area HAF blacks give improved tensile strength compared toGPF blacks, but not significantly difference due to structure.

NR compound has inherently higher tensile strength in the unfilled naturalrubber due to its crystallizing ability.

Carbon black causes less of a change in NR

Tensile strength reaches a maximum at relatively low carbon black loadings (2-40 phr) and shows a decreasing tendency as the black loading is increased.

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