rubber seminar_ 1012

8/8/2019 Rubber Seminar_ 1012

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Alejandro Moreno

Ty Van Tran


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Definition of Rubber

History and source of Rubber Properties and Classification of Rubber

Natural Rubber

Synthetic Rubber

Elastomer and elasticity

Vulcanization

Manufacture


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Elastomer = Rubber

Material has the remarkable ability to substantially

return to its original shape after being stretched

considerably.


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0 B.C Aztecs and Mayas Shoe soles, play balls, coated fabrics

18th century EU Rubber

1823 Macintosh Naphtha

1830 Thomas Hancock 1st internal mixing machine

1841 Charles Goodyear Vulcanization process

1843 Hancock Vulcan = the god of fire

1889 John Dunlop 1st pneumatic tire for bicycles

1904 Carbon black Increasing mechanical properties

1910

Motor car Uses and price of NR exploded


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1870s Polyisoprene Europe, in labs

WW I Polybutadiene, Russia, in commercial

1930s Neoprene, Buna-S US and Germany

WW 2GRS copolymer of

butadiene and styreneUS

1960 SNR Shell, Goodyear

2005 58% of rubber is synthetic


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1

2

3

4


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High elasticity

Low Tg Sensitive to oxygen, ozone, light

Not oil resistant

Resistant to inorganic chemicals

Unsuitable for use with organic liquids


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Synthetic rubberNatural rubber

Synthetic natural rubber (SNR)

Butyl Rubber (BR)

Chloroprene Rubber (Neoprene)

Nitrile Rubber (NBR)

Styrene-Butadiene Rubber (SBR)

Thermoplastic elastomers


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C

C C

C

C

H

H

H

H

H

H

H

H

H

H

Hevea Rubber

(cis-polyisoprenene)

Natural rubber

M = 200,000 - 500,000

Proteins, sugars, fatty acids

Potassium, manganese,

phosphorus, copper and iron

Hevea Brasiliensis

Latex

30 40% wt. dry rubber


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Tg = -72oC

Need to be cross-linked to obtain

the high elasticity

Be cross-linked by sulfur, sulfur

donor systems, peroxides, isocyanate

cures and radiation

Easily blended with various fillers

and elastomers


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Transportation Industrial Consumer Hygiene and

medical


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Polyisoprene

Ziegler-Natta catalyst

More uniform and lighter in color than NR

Less of a tendency to crystallize

Application:

Used interchangeably with NR

Used in blends with PB, and SBR


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Monomer: butadiene

The cis 1,4 and 1,2 vinyl

contents govern the

performance of polymers

Lower cost

C C

C CH

H H

H

H

H

H

Appli ti s:

I l i it t r l r, :

Reduce eat uild-up

I pr es t eabrasi resistance, and

t e fricti n n ice f inter tires

I pr eabrasi nand l temperature

flexibilit


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Randomcopol mer,

st rene

Requires reater

reinforcement

ower resilience t an R

Application :

Blend with NR and PB: Tire

production

Conveyor belts, molded rubber

goods,

Carpet backing


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NBRNitrile Butadiene Rubber

Copolymer of butadiene and acrylonitrile

More expensive than SBR or BR

CRChloroprene rubber (neoprene)

Thermal stability

Non-flammable


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A class of copolymers or a physical mix of polymers which consist

both thermoplastic and elastomeric properties

The crosslink in TP polymers: a weaker dipole or hydrogen bond or

takes place in one of the phases of the material

More easily processed: extrusion and injection molding

Be used where conventional elastomers cannot provide the range

of physical properties needed in the product


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Physical Characteristics:

Amorphous Material Generally T > Tg.

Thermodynamic Equilibrium

Dont crystalize

Regarded as liquids

One huge macromolecule


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I Thermoplastic T < Tg

II Elastomer T > Tg


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Retraction force of

Elastomers is dominated

by entropy

Ideal Elastomer


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Main Hypothesis: Micro scale the

deformation is proportional than at

Macro scale

Second Hypothesis: All the chains in

the elastomer network have the samemolar Mass

Third Hypothesis: The material is

incompressible

Elastic modulus depend on the

temperature, density and Ms which is

the mass of chains between two cross

linked points.


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Vulcanized Rubber

Unvulcanized Rubber


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A process which increases

the retractile force and

reduces the amount of

permanent deformationremaining after removal of

the deforming force

Increases elasticity while

decreases plasticity

How?

Crosslinked molecular

networks


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Rubber becomes

essentially insoluble.

Hysteresis is a

measure of

deformation energy

that is not stored but

that is converted to

heat.

These properties are

not functions only of

crosslink density.


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IMPORTANT CHARACTERISTICS

Time elapsed before crosslinking starts Sufficient scorch resistance!

Rate of crosslink formation Fast!

The extent of crosslinking at the end of the process Controlled


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Vulcanization by sulfur without accelerator is no longer of

much commercial significance , but its chemistry has been the

object of much research and study.

A concentration of 8 parts per 100 parts of rubber (phr) requires 5

hours at 140C.

The addition of zinc oxide reduced the time to 3 hours.

The use of accelerators in concentrations as low as 0.5phr has

since reduced the time to asshort as 1 to 3 minutes.


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Accelerated-sulfur

vulcanization is the most

widely used method.

Rapid crosslinking

Good delayed action

required for processing

before the formation of the

vulcanized network.

It is used to vulcanize

natural rubber, synthetic

isoprene rubber, styrene-

butadiene rubber, nitrile

rubber, etc.


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VULCANIZATION BY THE ACTION OF METAL OXIDES

Chlorobutadiene

VULCANIZATION BY THE ACTION OF ORGANIC PEROXIDES

Elastomers

DYNAMIC VULCANIZATION

Vulcanization 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 is obliged to become crosslinked, whereas the

remaining other polymeric material remains uncross.


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Mills Internal Mixing Machines


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Extruders Calenders


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MOLD.- At least two pieces of material,

which when fitted together from a cavity,

resembling the shape of the product.

Mold dimensions are around 1.5 % greater

than required.

Molding is the most important process

during rubber manufacturing.


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Transfer Molding

utocla e curing

Transfer Molding

Compression Molding


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rubber seminar_ 1012

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