Research Journal of Recent Sciences ________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 357-360 (2012)
Res.J.Recent Sci.

Short Communication

Preparation and Studies of Nitrile Rubber Nanocomposites with
Silane Modified Silica Nanoparticles
Das Chayan and Kapgate Bharat P.
Department of Chemistry, Visvesvaraya National Institute of Technology, Nagpur, INDIA

Available online at, www.isca.in
(Received 31th October 2011, revised 9th January 2012, accepted 28th January 2012)

Abstract
Rubber silica nanocomposites are prepared by mixing nitrile rubber (NBR) with surface modified silica nano particles. Silica nano
particles are synthesized by sol-gel method that involves hydrolysis followed by condensation of tetraethyl orthosilicate (TEOS).
Surface modification of silica particles is done with the treatment of silane coupling agent viz. 3-mercaptopropyltrimethoxysilane.
Presence of silane coupling agent in silica is revealed by IR studies. Thermogravimetric analysis is done to find out silica content
in the composites and to study the thermal properties. Stress strain studies are found to be useful to assess the improvement of the
mechanical properties of the composites.
Keywords: sol-gel, surface modification, rubber - silica nanocomposite.

Introduction
Synthesis of nano silica has gained much attention due to its
superior properties and most widely being used as filler in
rubber, paint, adhesive, functional fibre, plastic etc 1-4. Stober
and co-workers reported a simple synthesis process of
spherical and monodispersed silica nanoparticles via sol-gel
method5. The synthesis takes place in two steps viz.
hydrolysis and condensation of silicon alkoxides in a mixture
of alcohol and water6. Ammonia is used as a catalyst.
Hydrolysis: Si–(OR)4 + H2O → Si–(OH)4 + 4R–OH,
Condensation: 2Si–(OH)4 → 2(Si–O–Si) + 4H2O
One of the important application of silica is it’s use as a filler
in rubber matrix for reinforcement. Nano silica has more
prominent reinforcing effect over commercial micro silica
owing to it’s better dispersion capability in rubber matrix.
However, they have tendency to form agglomerate due to
high surface energy and ability to form inter particle
hydrogen bonding via the hydroxyl (silanol) groups present
on the surface7-8. This results in strong filler-filler
interactions which is not favorable for effective
reinforcement.
This problem can be overcome via surface modification of
the silica particles. Silane coupling agents are the most used
type of modifier agents9-11. Organo-modification of
nanosilica surface with organosilanes can efficiently improve
its compatibility with organic matrix and also increase the
degree of dispersion. As a result, thermal and mechanical
properties of the composite are improved.
In this work, the effect of surface modified silica on the
thermal and mechanical properties of the nitrile rubber
(NBR) has been studied. Silica nano particles are synthesized
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by sol-gel method followed by surface modification with the
treatment of γ–mercptopropyltrimethoxysilane (γ-MPS).
Silica rubber composites are then prepared by mixing the
surface modified silica with nitrile rubber (NBR) along with
other additives followed by vulcanization. Amount of γ-MPS
is varied in composites 2 and 3 as 2% and 3% respectively.
Composite 1 is prepared with unmodified silica particles i.e.
γ-MPS is not used in this case. Thermogravimetric analysis
and stress-strain studies are carried out for all three
composites. Thermal and mechanical properties of
composites 2 and 3 are compared with composite 1 to see the
effect of surface modification of silica particles on the
properties of the rubber composites.

Material and Methods
Acrylonitrile rubber (NBR) KNB-35L was used as a raw
rubber. Tetraethyl orthosilicate (TEOS) 98% was purchased
from Acros Organics. γ-MPS (γ–mercpto propyltri
methoxysilane) 99% was purchased from Aldrich.THF and
Ammonia were purchased from Merck. Toulene and Ethanol
were purchased from Fischer Scientific. Sulfur, Zinc oxide
(ZnO), Stearic acid, Mercaptobenzothiazoledisulfide
(MBTS), and polyethylene glycol (PEG) were purchased
from Sara Polymer Pvt. Ltd.
Preparation of silica nanoparticles by sol-gel method:
Silica nanoparticles were synthesized by sol gel process by
the reaction of ethanol (8 mole), water (3 mole) and TEOS
(0.5 mole) as reported in literature12. 25% ammonia (0.08
mole) was used as catalyst. A thermal treatment at 150°C for
2 h was given to the silica particles to remove physisorbed
water. Surface modification of the silica particles were
carried out following a reported procedure by refluxing silica
and γ–mercptopropyltrimethoxysilane (γ-MPS) in toluene at
110°C for 3h followed by washing and drying13.
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Research Journal of Recent Sciences _____________________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 357-360 (2012)
Res.J.Recent Sci.
Preparation of rubber composite: On a two roll open
mixing mill, silica and cross linking ingredients were mixed
with rubber (Compounding formulation is given in table 1).
Then vulcanization was done by heat pressing at 140°C for
10 min. in a mold to obtain rubber composites in the form of
a thin sheet of thickness ca. 1 mm.
Table - 1
Compounding formula of rubber vulcanizates
Ingredients (phr)a
1
2
3
NBR
100
100
100
Nanosilica
6
5
5
Silane coupling agentb
0
2%
3%
Zinc oxide
4
4
4
Stearic acid
1
1
1
MBTSc
1
1
1
Sulphur
1.5
1.5
1.5
Polyethylene glycol
0.5
0.5
0.5
Characterizations: FT-IR spectra of the silica nanoparticles
were obtained using a Perkin- Elmer FT-IR
spectrophotometer. Thermogravimetric analyses (TGA) were
done using a Perkin Elmer Thermal Analyzer. The sample
was placed in a alumina pan and heated in the temperature
range 30-8000C under air and the heating rate was 100 C/min.
Tensile tests of cured samples were carried out using
Zwick1456 (model 1456, Z010, Ulm Germany) with
crosshead speed 200 mm/min (ISO 527).

Thermogravimetry: The results of thermogravimetric
analysis of the rubber composites are given in Table- 2 and
figure - 2. The amounts of combined silica in the composites
are determined from residual weight percentage. Nature of
the curve is similar for all the composites 1-3. First weight
loss observed at the temperature range 3500C to 4900C is due
to degradation of the rubber component. The next weight
loss at the temperature range 5200C to 6400C is due to the
decomposition of carbonaceous residue 14. The onset
temperature of composites 2 and 3 containing surface
modified silica increases little compared to that of 1. The
temperature at maximum weight loss (T max) is determined
from the peaks obtained in Derivative Thermogravimetry
(DTG)15. It is observed that the value is higher for the
composites containing surface modified silica particles
indicating greater thermal stability for them over that of
composite containing unmodified silica. The value of T max is
highest for composite 2.
Table - 2
Thermogravimetric analysis
Silica
Onset
Temp. at Max.
Sample
content
temp. (0C)
Wt. loss. (0C)
a
(phr)
1
6
406
423
2
5
411
457
3
5
410
432

Results and Discussion
FTIR: FTIR spectra of the silica nanoparticles are shown in
figure - 1. Presence of silane coupling agent, γ-MPS is
evident from the vibrational peaks around ~2900 cm-1 and
1400 cm-1. These are the characteristic peaks for
organosilanes that corresponds to the Si-CH2 stretching and
bending mode respectively13. The rest of the peaks are
assigned to the silanol (~3450 cm-1, ~ 1100 cm-1, and ~950
cm -1) and siloxane groups (~1200 cm-1 to 1100 cm-1 and
~467 cm-1).
Figure - 2
Thermogravimetric analysis of rubber composites

Figure - 1
FT-IR Spectra of silica nanoparticles

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Mechanical Properties: Mechanical properties of the
composites 1-3 are tabulated in table 3. Hardness values are
found to be around 45 and that is less for rubber composites
containing modified silica. Stress-train studies shows that
50%, 100%, 200% and 300% modulus are comparable for
both type of composites containing unmodified (1) and
modified silica nano particles (2 and 3). But tensile strength
values are higher for the surface modified silica rubber nano
composites compared to that of unmodified silica rubber
nano composite. Also, it is increased significantly from 2 to
3 with increase in silane coupling agent, γ-MPS. Elongation
at break is also increased for composites 2 and 3 compared to
that for 1. The value is more for composite 2 that contains

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Research Journal of Recent Sciences _____________________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 357-360 (2012)
Res.J.Recent Sci.
lesser γ-MPS this time. This result is in accordance with the
observation in the previous section where higher thermal
stability of the composite 2 in comparison to the others was
noted. These results suggest that better silica reinforcement
in the rubber matrix has been achieved due to surface
modification of silica nano particles with silane coupling
agent, γ-MPS16.
Table - 3
Mechanical properties of rubber composites
Mechanical Properties
1
2
3
σ50% (MPa)
0.62 0.64
0.61
σ100% (MPa)
0.81 0.78
0.79
σ200% (MPa)
1.00 0.91
0.96
σ300% (MPa)
1.17 1.04
1.12
Tensile Strength (MPa)
2.68 3.46
4.58
Elongation at break (%)
567 765
683
Hardness (Shore A)
46.0 41.0
43.9

Conclusion
Nitrile rubber - silica nanocomposites are prepared with
surface modified silica nanoparticles and their thermal and
mechanical properties are studied. Presence of silane
coupling agents in silica nano particles is detected from FTIR
studies. Improvement in mechanical properties is observed
from Stress-strain studies. It shows higher tensile strength
and elongation at break for the rubber composites containing
surface modified silica particles compared to that containing
silica particle without surface modification. This is in
accordance with the thermogravimetric analysis where
similar improvement in thermal stability is also observed.
Hence, better reinforcement in the rubber matrix by using
surface modified silica nanoparticles can be concluded.
Further studies in this area are underway where some
modification in synthetic technique will be taken care of and
comparison of properties, including dynamic mechanical
analysis, will be done with unfilled rubber composite.

Acknowledgement
Mr. Kapgate thanks VNIT for fellowship. Help and support
received from Dr. A. Das, Mr. D. Basu and Dr. S. S. Umare
are gratefully acknowledged.

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