Silica Production of Silica Natural Rubber (NR) Precipitated Silica Filled NR Composite In Situ Precipitation of Silica Filled Composite from Centrifuged Latex Determination of Silica Content in Sample Properties Conclusion

1. IN SITU PRECIPITATION
FOR
PREPARATION OF
NR-SILICA COMPOSITES
Syed Mohammed Sajl
Semester 7
B Tech – Polymer Science &
Engineering

2. INDRODUCTION
1. Silica
2. Production of Silica
3. Natural Rubber (NR)
4. Precipitated Silica Filled NR Composite
5. In Situ Precipitation of Silica Filled
Composite from Centrifuged Latex
6. Determination of Silica Content in Sample
7. Properties
8. Conclusion
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3. 1. SILICA
• Silica is a crystalline compound.
• There are two types of silica i.e., Natural
Silica and Synthetic Silica.
• Natural Silica is non-reinforcing and has
been used as a filler.
• The synthetic ones are reinforcing and
their particle sizes as small as the carbon
black besides an extremely reactive
surface.
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4. 2. PRODUCTION OF SILICA
• Acidification of alkali silicate solutions
under controlled conditions Produces
precipitated silica.
Na2SiO3 + HCl  2NaCl + H20 + Si02
• Precipitated silica is silicon dioxide
containing about 10-14% water.
• Particle size is in the range 1-40 nm.
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5. • Natural rubber (NR) is cis
1,4polyisoprene.
• Rubber is separated from the latex by
coagulation usually by acidification.
• The coagulum is then processed into
different marketable forms.
3. NATURAL RUBBER (NR)
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6. • The molecular weight of polymer ranges from
200,000 to 600,000.
• Latex contains more than 90% of the
Hydrocarbon, cis-I,4- polyisoprene, naturally
occurring resins, proteins, sugars etc.
• Natural rubber is a versatile and adaptable
material.
• An ammonia solution can be used to prevent
the coagulation of raw latex while it is being
transported from its collection site.
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7. 4. PRECIPITATED SILICA FILLED
NATURAL RUBBER COMPOSITES
• Precipitated Silica, is one of the most promising
alternatives to carbon black.
• Silica reduces the rolling resistance and hence
fuel consumption, in case of tyres.
• The silica enables the production of high-
performance tyres with low rolling resistance.
• The main characteristic - particle size-surface area
• Silica has hydroxyl groups - filler agglomeration
• Commercial nano silica is good but difficult to
incorporate
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8. SEM Photographs of the Tear
Fractured Surfaces of Rubber
Compounds
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9. 10/6/2013 Elective Seminar 9
Rubber
Rubber
Rubber
Rubber
OSi
O
OSi
O
OSi
O
OSi
O
OSi
O
OSi
O
OSi
O
O
O
OSi
O
Figure: Natural Rubber –
Silica Composite

10. • The problem in silica is the difficulty in incorporation, as
Silica is hydrophilic and rubber is hydrophobic in nature.
• The rubber-silica interaction can be improved by using
silane coupling agents.
• The most widely used compound is silica is Bis (3-
triethoxy silyl propyl) tetra sulphide (TESPT) or Si 69.
• The production of precipitated silica starts with the
reaction of an alkaline silicate solution with a mineral
acid.
• Sulfuric acid and sodium silicate solutions are added
simultaneously with agitation to water. Precipitation is
carried out under alkaline conditions.
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11. 5. IN SITU PRECIPITATION OF SILICA
FILLED COMPOSITES FROM
CENTRIFUGED LATEX
• Latex filtered and Stabilized.
• Mixed with 60% Sodium Silicate
• Ammonium Chloride Solution added.
• 2% Acetic Acid added to Coagulate the latex.
• The coagulum is washed with water
• It is then Dried at 70 C for 48hrs
Na2SiO3 + 2 NH4Cl 2 NaCl + 2 NH3 + H2SiO3
H2SiO3 H2O + SiO2
• Ammonia evolved is analyzed -- confirms the
occurrence of the reaction
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12. In Situ Precipitation – Schematic
Representation
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Filter Centrifuged
Latex
keeping the
Mixture for 24 hours
Stabilized with Non-
ionic Stabilizer
Add Sodium Silicate
and stirred for one hour.
Silica was precipitated
by drop wise addition
Latex was coagulated
as crumbs by the
addition of 2% Acetic
Acid.
Crumbs were
washed with water till
the washings were
neutral
It is dried in an air oven
at 70C for 48 hours
Precipitation was repeated with varying
amounts of Sodium Silicate to prepare
Natural Rubber Silica Composites
drop wise addition
of saturated solution of
Ammonium Chloride.

13. 6. DETERMINATION OF SILICA
CONTENT IN THE SAMPLE
• The silica content of the dried coagulum
samples is determined by igniting a known
weight of the sample in a previously
weighed silica crucible in a muffle furnace.
• The temperature of the furnace is kept at
550 C for five hours time.
• It is then cooled.
• From the weight of the ash the loading of
silica and the loss of the silica was
calculated.
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14. Silica Content during the
Precipitation in Concentrated Latex
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SAMPLE SILICA CONTENT EXPECTED
(phr)
SILICA CONTENT DETERMINED
(phr)
M-1 1.002 1.002
M-2 2.004 2.001
M-3 3.007 3.002
M-4 4.009 4.000
M-5 5.012 5.003
M-10 10.024 10.015
M-20 20.048 19.942
M-30 30.072 28.017
M-40 40.096 36.524
M-50 50.120 42.258
• The percentage moisture content of all samples was found to be less than
0.01%

15. 7. PROPERTIES OF COMPOSITES PREPARED
FROM THE SILICA MIXES OF DIFFERENT
COMPOSITIONS
• Tensile strength of the composites increases with
the rise of in situ precipitated silica content.
• Tear strength increases proportionally with increase
in silica up to 20 phr,above 20 phr it shows very
small change.
• The reduced stress values increased with increase
in concentration of silica.
• Hardness increases as the silica content increases.
• Resilience decline with increase in silica content.
• Abrasion resistance improves with the in situ silica
content.
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16. Variation of Tensile Strength with
Concentration of Silica
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10
15
20
25
30
35
0 10 20 30 40
TensileStrength(MPa)
Concentration of Silica (phr)

17. Variation of Elongation at Break with
Concentration of Silica
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0
400
800
1200
0 10 20 30 40 50
ElongationatBreak(%)
Concentration of Silica (phr)

18. Variation of Tear Strength with
Concentration of Silica
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0
20
40
60
80
0 10 20 30 40 50
TearStrength(N/mm)
Concentration of Silica (phr)

19. Variation of Reduced Stress with
Concentration of Silica
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0.0000
0.0100
0.0200
0.0300
0.0400
0.0500
0 10 20 30 40 50
ReducedStress
Silica Content (phr)

20. 8. CONCLUSION
• Silica can be incorporated in NR Latex by In-situ
precipitation procedure to prepare rubber
composites.
• The vulcanizates prepared by this novel technique
show superior mechanical properties compared to
those prepared from conventional silica.
• The latex precipitated silica is found to have better
rubber- filler interaction compared to commercial
silica
• Enhanced rubber- filler interaction
• Improved tensile and tear strength
• Improved tensile modulus10/6/2013 Elective Seminar 20

21. • Silica of any desired concentration can be
incorporated in to the dry rubber directly or indirectly.
• Ageing resistance and permeability showed
improved values.
• This method is simple and cost reducing.
• Improved filler distribution
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22. 10/6/2013 Elective Seminar 22
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23. 10/6/2013 Elective Seminar 23