Synthesis of Nanosilica & Preparation of Natural Rubber Nanocomposites

Synthesis of Nanosilica &
Preparation of Natural Rubber
Nanocomposites
Binu Narayanan, Syam Das,
Varun K P & Syed Mohammed
Sajl
Semester 6
B Tech – PS & E
Tuesday, August 20, 2013 1B Tech PS & E - Minor Project

Introduction
• The potential applications of Nanomaterials in
various fields have caught the attention of
academic and industrial research world in the last
decade.
• Nanotechnology is emerging to revolutionize the
world we live in with radical breakthrough in areas
such as materials and manufacturing, electronics,
medicine and healthcare, environment and energy,
chemical and pharmaceutical, biotechnology and
agriculture, computation and information
technology etc.

• The uniqueness of nanoparticles is that
their properties can be selectively
controlled by controlling the size,
morphology and composition of
constituents.
• Despite the current interest nanoparticles
are not a new phenomenon, with scientists
being aware of colloids and sols, for more
than 100 years.
Tuesday, August 20, 2013 B Tech PS & E - Minor Project 3

Silica
• Silica is a crystalline compound occurring
abundantly as quartz, sand and many other
minerals and is used to manufacture a variety of
materials, especially glass and concrete.
• Natural silica is non-reinforcing and has been
used as a filler, only to reduce the cost.
• Important natural varieties are silica
(amorphous), silica (crystalline), silica
diatomaceous (fossil origin) and silica
(microcrystalline).

• Types of synthetic silica are precipitated,
pyrogenic, aerogels and hydrogels.
• Of these varieties, precipitated silica and
pyrogenic (fumed) silica are being used for
elastomer reinforcement.

Production and Characterization of
Silica
• Acidification of alkali silicate solutions under
controlled conditions produces precipitated silica.
Na2SiO3 + HCl→ 2NaCl + H2O + SiO2
………………… (1.1)
• Colloidal pyrogenic silica is produced by reaction
of silicon tetrachloride at high temperatures with
water.
SiCl4 + 2H2O → SiO2 + 4HCl
.….…………………………… (1.2)
• The reaction products are quenched immediately
after coming out of the burner.Tuesday, August 20, 2013 7B Tech PS & E - Minor Project

• Precipitated silica is silicon dioxide
containing about 10-14% water, with
particle size in the range 1-40 nm. They
are reinforcing fillers giving composites of
high tensile strength, tear resistance,
abrasion resistance and hardness.
• It is being used in the manufacture of
translucent and colored products, shoe
soling, tyres and other mechanical rubber
goods. Fumed or pyrogenic silica is silicon
dioxide containing less than 2% combined
water.

Figure: Structure of silica: (a) A unit structure of silica containing
SiO4 unit in which one silicon is surrounded by four oxygen
atoms in a tetrahedral geometry. (b) The expanded structure
showing the coordination of oxygen atom between two silicon
atoms.

Figure: Structure of Amorphous Silica (SiO2)

Experimental
Setup

a. Reactor
The experiments were carried out using a reactor of 500ml
capacity. After optimizing the concentration, laboratory scale
synthesize was done using a 3000ml Borosil beaker as the
reactor.
b. Stirring and heating
A mechanical stirrer provided with three leaf blade was used
for stirring the slurry. The speed of the stirrer was varied from
30 rpm to 150 rpm depending on the concentration of the
slurry and the optimum was 50-60 rpm. Heating was done
using a hot plate which was set constant at 70 0C.
EXPERIMENTAL SETUP

c. Filtration
Vacuum filtration was done using a Buchner funnel, suction
flask, tubing and a vacuum pump.
d. Drying
Hot air oven with a temperature setting adjustable to 300 0C was
used. The cake obtained after filtration was scrapped out and
spread out evenly on a glass plate using a glass rod. Glass plate
was then placed in the oven and dried for the required time at
100 0C.
e. Calcination
A muffle furnace with a temperature range of 50 0C to 1200 0C
was used for calcinations. The dried sample was ground into fine
powder and then kept in the muffle furnace at 600 0C for 6 hrs.
During this time the organic part will go and we get fine silica
powder.Tuesday, August 20, 2013 B Tech PS & E - Minor Project 13

SYNTHESIS OF NANOSILICA
• Silica was prepared from sodium silicate and HCI using
5%Polyethyleneglycol as the medium.
• This was then intimately mixed with stoichiometric amount of
1N HCI required for the preparation of silica in the reacting
vessel.
• 10% sodium silicate solution prepared in distilled water was
then added drop wise to the above stirring mixture at a
temperature of 60 0C.
• The pH of the mixture was maintained between 1and 2 to get
nanosize silica.
• If HCI is added into the sodium silicate solution it is difficult to
maintain the pH in the range 1-2 and there is a chance of
gelation causing an increase in size of the particles and
stirring also became difficult.Tuesday, August 20, 2013 14B Tech PS & E - Minor Project

• After the addition of sodium silicate the
reaction mixture was stirred continuously
for a period of 2hours and the temperature
was maintained at 70 0C.
• This enables the uniform distribution of the
medium in the reaction mixture, so that it
could act as a matrix to collect the formed
particles.
• It also enabled the conversion of silicic
acid, formed by the reaction between HCI
and sodium silicate, into silica.

• The acid plays a catalytic role in enhancing
the co-condensation of silicon oxides within
the dispersing agent's matrix.
• It is expected that the addition of the above
dispersing agent would produce silica in the
nanoscale.
• The interaction between the hydroxyl groups
of dispersing medium and the hydroxyl
groups of silica would results in co-
condensation.
• Hydrogen bonding between the polymer and
the developing polysilicate network leads to
system homogeneity.

Na2SiO3 + 2HCl→ H2SiO3 + 2NaCl …………
(2.1)
H2SiO3 → SiO2 + H2O
.….………………………… (2.2)
• After completion of reaction, the resultant
slurry was kept at room temperature for 24
hours.
• It was then filtered by vacuum filtration. After
completely emptying out the solution into the
funnel, the washing was started with distilled
water.
• The washings continued until all the sodiumTuesday, August 20, 2013 B Tech PS & E - Minor Project 17

• The cake obtained after washing was
scraped out using a scrapper and spread
evenly on a glass plate of dimension 20
cm x 20 cm.
• This was then placed in a hot air oven at a
temperature of 70 0C for 24 hrs.
• The cake thus obtained was then ground
to obtain fine powder. After complete
drying it was calcined in a muffle furnace
at 600 0C for 3 hours to get fine silica
powder.

X-RAY DIFFRACTION (XRD)
• X-Ray is an important tool to identify the crystalline
nature, purity and size of materials.
• The X-Ray diffraction patterns of the silica and modified
silica samples are shown.
• Strong broad peak observed around 22-23 is the
characteristic of amorphous Si02.
• This shows that the synthesized silica, commercial silica
and modified silica are in an amorphous state.
• The full width at half maximum (FWHM) is used to
determine the average particle size (Cs) of the silica
samples using the Scherrer formula.

Figure: X-Ray Diffraction Set-up

Figure: Schematic Representation of X-Ray Diffraction

Figure: XRD of Nanosilica

PREPARATION OF NATURAL
RUBBER–NANOSILICA
COMPOSITES
• The mixing was done as per ASTM D-3184
(1989) on a two roll laboratory size mixing mill
(150 mm 300 mm).
• After complete mixing, the stock was sheeted
out at a fixed nip gap.
• The samples were kept for 24 hours for
maturation.
• The sheets were vulcanized in the hydraulic
press at 150 0C and 200 kg/cm2 pressure to
their optimum cure time, as determined using a
Rubber Process Analyzer (RPA – 2000, AlphaTuesday, August 20, 2013 23B Tech PS & E - Minor Project

Table: Recipe for Preparation of Nanocomposites
Ingredients Dosage (in phr)
Natural Rubber 100
Zinc Oxide 5
Stearic Acid 2
6 PPD (Para
Phenyline Diamene)
1
CBS 0.6
TMTD – (Tetra Methyl
Thiuram Disulphide)
0.2
Sulphur 2.5
Nano Silica (in
various
concentrations)
0, 0.5, 1.0, 2.5, 5

Figure: Variation of Cure Time with Silica loading
0 1 2 3 4 5
4.0
4.5
5.0
Curetime(min)
Nano filler loading(Phr)

• The Cure Time increases with silica
content for.
• Cure Time increases by the addition of 0.5
to 5 phr nanosilica in the gum mix, this
indicates that the nanosilica-accelerator
interaction is present.
• With increasing silica content, however,
the cure time increases.
• This may be attributed to the slight acidic
nature of Silica. Generally acids retard the
cure reaction.

Figure: Variation of Differential Torque and Scorch Time with
Silica loading
0 1 2 3 4 5
1.5
2.0
2.5
3.0
3.5
4.0
scorch time
Dmax-Dmin

• The differential torque i.e., the difference
between the minimum and maximum torques
developed during cure is found to be higher
with filler loading for nanosilica compounds.
• The differential torque increased by the
addition of nanosilica in the gum compound.
• The differential torque is a measure of the
extent of the cross link formation and the filler
–matrix interaction.
• The values for the nanosilica compounds
indicate that it has higher cross link density
and higher filler- matrix interaction than gum.

Mechanical Properties

Figure: Variation of tensile strength and tear strength with silica
loading
0 1 2 3 4 5
10
15
20
25
30
35
40
45
50
55
Tensile strength(N/mm
2
)
Tear strength (N/mm)

• The figure shows the variation of tensile
strength with silica loading.
• The tensile strength increases up to 1 phr
and drops beyond 1 phr for the
nanocomposites.
• It shows the better reinforcing efficiency of
the nanosilica resulting from the higher
surface area and better interaction of
nanosilica with the matrix.
• The higher tear strength value of nanosilica
compound is due to better interaction of
nanosilica with the matrix.
• 17% increase in Tensile Strength and 16%
increase in Tear Strength with 1 phr
Nanosilica.

Figure: Variation of Elongation at Break and 300% Modulus with silica
loading
0 2 4 6
800
900
1000
1100
1200
1300
Elongation at break%
300% modulus(N/mm
2
)
1.0
1.5
2.0
2.5
3.0

• The smaller particle size of the nanosilica
helps it better arrest or deviate the tear
cracks, resulting in higher tear resistance.
• Elongation at break decreased with higher
filler loading.
• Modulus at 300% increased with filler
loading.
• It indicates a more restrained matrix,
resulting from better chances of filler –
matrix interaction, in the case of nanosilica
compounds.

Figure: Variation of hardness with silica loading
0 1 2 3 4 5
25
30
35
40
45
Hardness(shoreA)
• The hardness increases with filler loading for nanosilica compound
again indicating better efficiency of the nanofillers.

Conclusions

Conclusions
• Under controlled conditions nanosilica can be
successfully prepared by a precipitation route.
• Poly ethylene glycol solution can be used for the
preparation of inorganic particles.
• The particle size of the silica can be controlled by using
the precipitation medium and its concentration.
• Nanosilica prepared by this method has a particle size
less than 20 nm which is lower than that of the
commercially available silica.
• The particle size of silica was found to be 15 nm from the
XRD results XRD results show that the synthesized silica
is predominantly amorphous in nature.

• Nanosilica is effective reinforcing filler in natural
rubber compound.
• Differential torque, scorch time and cure time
increase with silica loading for nanosilica
compounds.
• Filler-matrix interaction is better for nanosilica
when compared with reported properties of silica
filled NR in literature.
• The introduction of the nanosilica in the rubber
compound improves the tensile strength,
modulus and tear strength and hardness
properties are also good for the nanosilica
compounds.

References

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