In Situ Precipitation for Preparation of NR Silica Composites

IN SITU PRECIPITATION FOR

PREPARATION OF NR-SILICA COMPOSITES

Syed Mohammed SajlSemester 7

B Tech – Polymer Science & Engineering

INDRODUCTION

1. Silica2. Production of Silica3. Natural Rubber (NR)4. Precipitated Silica Filled NR Composite5. In Situ Precipitation of Silica Filled

Composite from Centrifuged Latex 6. Determination of Silica Content in Sample7. Properties8. Conclusion

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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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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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• 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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• 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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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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SEM Photographs of the Tear Fractured Surfaces of Rubber

Compounds

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Rubber

Rubber

Rubber

RubberOSi

O

OSi

O

OSi

O

OSi

O

OSi

O

OSi

O

OSi

O

OO

OSi

O

Figure: Natural Rubber – Silica

Composite

• 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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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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In Situ Precipitation – Schematic Representation

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Filter Centrifuged Latex

keeping theMixture 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 additionof saturated solution

of Ammonium Chloride.

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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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%

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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Variation of Tensile Strength with Concentration of Silica

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0 5 10 15 20 25 30 35 40 4510

15

20

25

30

35

Concentration of Silica (phr)

Tensi

le S

trength

(M

Pa)

Variation of Elongation at Break with Concentration of Silica

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0 5 10 15 20 25 30 35 40 450

400

800

1200

Concentration of Silica (phr)

Elo

ngati

on a

t B

reak (

%)

Variation of Tear Strength with Concentration of Silica

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0 5 10 15 20 25 30 35 40 450

20

40

60

80

Concentration of Silica (phr)

Tear

Str

ength

( N

/mm

)

Variation of Reduced Stress with Concentration of Silica

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0 5 10 15 20 25 30 35 40 450.0000

0.0100

0.0200

0.0300

0.0400

0.0500

Silica Content (phr)

Reduce

d S

tress

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 modulus04/11/2023 Elective Seminar 20

• 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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