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 6B Tech – PS & E

Tuesday, April 11, 2023 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. Tuesday, April 11, 2023 2B Tech PS & E - Minor Project

• 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, April 11, 2023 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. • Pyrogenic silica is too active and expensive.


• 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. ReactorThe 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 heatingA 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. Tuesday, April 11, 2023 B Tech PS & E - Minor Project 12

EXPERIMENTAL SETUP

c. FiltrationVacuum filtration was done using a Buchner funnel, suction flask, tubing and a vacuum pump.

d. DryingHot 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. CalcinationA 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, April 11, 2023 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.


• 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 sodium chloride was removed.


• 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, Alpha Technologies).



Table: Recipe for Preparation of Nanocomposites

Ingredients Dosage (in phr)

Natural Rubber 100Zinc Oxide 5

Stearic Acid 26 PPD (Para Phenyline Diamene)

1

CBS 0.6TMTD – (Tetra

Methyl Thiuram Disulphide)

0.2

Sulphur 2.5Nano 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

Cur

e tim

e (m

in)

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 51.5

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 4 510

15

20

25

30

35

40

45

50

55


Tensile strength(N/mm2) 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 6800

900

1000

1100

1200

1300 Elongation at break%

300% modulus(N/mm2)


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 4 525

30

35

40

45

Hard

ness(s

ho

re A

)


• 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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synthesis of nanosilica & preparation of natural rubber nanocomposites

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precipitated silica

natural silica

silica amorphous

preparation of silica

silica crystalline

silica microcrystalline

unit structure of silica

pyrogenic fumed silica