The Basic Rubber Compound
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Transcript of The Basic Rubber Compound
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The Basic
Rubber
Compound
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Introduction
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Introduction
First development ( Goodyear and Hancock)
Rubber compound is a mixture of a number ofdifferent ingredients
Raw gum elastomer as adhesive
Significant swelling capacity of raw gum.
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The basic compound formula
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Raw
Materials
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Raw gum elastomer
The key ingredient in rubber industry
Many of the properties of the final product dependupon it
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Sulfur
Widely use cross-linking agent.
Results: 1) More dimensional stable
2) Less heat-sensitivity
3) Less swelling4) Less sticking
Cheap, rubber-makers sulfur (particle sizevariation), oil coated.
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Sulfur Rubber-makers sulfur
suitable for vulcanizing rubber
It has a low ash content
Low acidity
Sufficiently fine for adequate dispersion andreaction
High sulfur level- bloom
Blooming occurs if an additive dissolves totally in
the polymer at the processing temperature but is
only partially soluble at ambient temperature
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Sulfur
Highly amorphous form of sulfur, known as insolublesulfur, is available to reduce this problem.
Dispersion in the compound can be more difficult
NO affect on products performance
Aesthetically displeasing
In the uncured compound, bloom can reduce tack
needed in building operations such as
plying up uncured sheets of rubber to obtain thicker sheets
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Zinc oxide and stearic acid
Zinc oxide + stearic acid zinc stearate
Together with sulfur & accelerator, constitute the cure
system for the formulation and speed up the rate at
which sulfur vulcanization occurs
With this curing system, it can be reduced time from
several hours to few minutes
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Accelerators
speeds up the rate of vulcanization
Grouped into several chemical classes
delayed action accelerator (sulfenamides)
short induction accelerator (dithiocarbamate)
o slow cure accelerator (guanidines)
o Fast cure accelerator (thiurams and
dithiocarbamate)
sulfur donor accelerator (TMTD, DTDM)
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Other cross-linking systems
Peroxides
Electron beam curing Miscellaneous
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Peroxides
suitable for curing rubber they do not need unsaturated bonds
Not as popular as sulfur
In the basic rubber compound formulation, thezinc oxide, stearic acid, sulfur and accelerator canall be replaced by a single material, the peroxide
Contact with oxygen (air) should be avoided
during vulcanization These compounds can interact with the peroxide
in peroxide cure systems and thus interferewith cure
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Peroxides
Advantages
improvement in heat aging resistance ofvulcanizate thus lifetime can be extended
upper processing temperature limits can be
pushed up a little
Disadvantages
Reduced mechanical properties
Post curing is sometimes undertaken for peroxide
cured vulcanizates, to complete the cure and
remove unwanted byproducts
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Peroxides
Coagents
cross-link density of a peroxide cured
compound can be increased by addition of
chemicals called coagents
e.g., methacrylates
This results in a higher state of cure with
improvements in properties such as
compression set
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Electron beam curing
not widely used throughout the industry
process has found a place in partially cross-
linking components of tires
radiation dosage:
about four Megarads for partial cross-linking
much higher doses for fully vulcanizing even thin
rubber sections
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Antioxidants, age resistors
and anti-degradants
Many vulcanizates become brittle when they
aged
Aging can be caused by the presence of
oxygen, accelerated by heat
Antioxidants are designed to slow down this
process and can act as free radical
scavengers
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Antioxidants, age resistors
and anti-degradants
many antioxidants are available
Selection criteria:
light colored compounds
where the product comes into contact with a
surface that can not tolerate a stain
volatility
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Antioxidants, age resistors
and anti-degradants
Antiozonants,such as p-phenylene diamines,
provide protection against ozone, and are
often added to a compound
This chemical group also has very good
antioxidant activity
Antidegradant
An antidegradant is a compounding material usedto retard deterioration caused by oxidation,
ozone, light or combinations of these