Investigation of correlation between rheological properties of rubber compounds based on natural rubber/styrene-butadiene rubber with their thermal behaviors
Motiee et al. International Journal of Industrial Chemistry 2013, 4:16
http://www.industchem.com/content/4/1/16
RESEARCH
Open Access
Investigation of correlation between rheological
properties of rubber compounds based on
natural rubber/styrene-butadiene rubber with
their thermal behaviors
Fereshteh Motiee*, Saeed Taghvaei-Ganjali and Mercedeh Malekzadeh
Abstract
Background: Rubber compounds are widely used in many applications because of the properties they exhibit. The
physical and mechanical properties of these blends are sensitive to small variations in the amount of the individual
polymers used. Thermogravimetry is currently gaining wide acceptance as a method for compositional analysis of
vulcanizates. Knowledge of the relationship among thermal behavior of rubber compounds with their rheological
properties is important for the assessment of the optimum process conditions to produce materials that have
required properties. The correlation of rheological properties of rubber compounds based on natural rubber/
styrene-butadiene rubber with their thermal behavior has been assessed using thermogravimetry analysis.
Thermogravimetric method permits the analysis to be completed in a short time and requires only a small sample.
Results: Thermogravimetry derivative profile (DTG) of the uncured blends and their rheological properties were
investigated. Differential derivative curves of uncured vulcanizate showed that the degradation of styrene-butadiene
rubber takes place at a higher temperature than that of natural rubber. According to DTG curves, two useful factors
were demonstrated. These factors were
ratio of natural rubber/styrene-butadiene rubber and a
the peak height
h =hNR100
,’
which
could be correlated with the rheological properties of
new factor called ‘normalized factor hSBRNRx =h
SBR100
100x
the blends.
Conclusions: The result showed that the rheological nature of samples had acceptable correlation with the factors
obtained by thermal analysis method. In other words, in this work a simple and reproducible experimental method
was developed to efficiently predict the rheological properties of rubber blends.
Keywords: Natural rubber, Styrene-butadiene rubber, Thermal properties, Rheological properties
Background
Thermogravimetry (TGA) and derivative thermogravimetry
(DTG) methods have emerged as powerful thermoanalytical techniques to monitor physical and chemical
changes in both natural and synthetic materials. TG-DTG
analysis allows the analysis to be completed in a short time
with small amount of sample [1-3].
A standard tire formulation for trucks as well as cars
is a physical blend of natural rubber/styrene-butadiene
rubber (NR/SBR) or natural rubber/butadiene rubber
* Correspondence:
Department of Chemistry, Islamic Azad University, Tehran, Iran
(NR/BR) blends. Natural rubber and styrene/butadiene
rubber have been blended for a long time for many purposes such as lowering the compound cost [4,5]. A lot of
studies have demonstrated the physico-mechanical properties of such blends [6,7].
The rheological and physico-mechanical properties of
NR, BR, and SBR blends are sensitive to small variations
in the amounts of individual polymers used. Thermogravimetric analysis has been employed extensively to identify the elastomeric compounds especially NR/BR, NR/
SBR, and NR/SBR/BR blends. Specifically, differential thermal gravimetric analysis (DTG) has a considerable value
for estimating the basic composition of vulcanizates [8-15].
© 2013 Motiee et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction
in any medium, provided the original work is properly cited.
Motiee et al. International Journal of Industrial Chemistry 2013, 4:16
http://www.industchem.com/content/4/1/16
Page 2 of 8
Table 1 Formulation of tire tread based on NR/SBR blend
Value (phr)
Company
NRa
Components
(STR 20/BN)
0-100
Thaihua, Bangkok, Thailand
SBRb
(Cis-1220)
100-0
Arak Petrochemical, Tehran, Iran
Carbon black
(N-330)
50
Pars Tire, Tehran, Iran
IPPDc
(Pilfex 13)
1.5
Nocil Ltd., Mumbai, India
Rio waxd
(Anti lux 65X)
2
Rhein Chemie, Mannheim, Germany
e
TMQ
(Antioxidant RD)
1
Nanjing, Jiangsu, China
Stearic acid
(PLMAC 1600)
4
Acidchem., Penang, Malaysia, Malaysia
ZnO
-
4
Shekohie, Qom, Iran
S
-
1.1
Tesduck, Tehran, Iran
OBTSf
(Vulcacit/MOZ)
0.8
LG/Lanxess, Zwijndrecht, Belgium
a
Natural rubber; bstyrene-butadiene rubber; cN-isopropyl-N0-phenyl-paraphenylenediamine; dblend of selected paraffins and microwaxes; e2,2,4-trimethy-1,
2-dihydroquinoline;fN-oxydiethylene-2-benzothiazole sulfonamide. phr, parts per hundred rubber.
The DTG curves of samples are used as ‘fingerprints’
in the identification of many single elastomer or blends,
finding that the peak height of the DTG curves is
dependent on the amount of each elastomer in the
blends [16].
Taghvaei et al. analyzed the correlation of DTG peak
height ratio with rheological and physico-mechanical
properties of vulcanizate NR-BR blend and weight percent of BR, using thermogravimetric analysis [17]. We
have recently investigated the correlation of the factor
obtained by TG-DTG curve (hNR/hBR) and aging time of
selected NR/BR blend (60/40). The results have shown
that the relationship between hNR/hBR of blends and
aging time has been fitted to a polynomial equation type,
with acceptable regration [18].
Understanding and predicting of rheological and physicomechanical properties of rubber compounds are really a
great challenge. In this work, the samples of tire treads
formulation were made of NR-SBR blends of known
composition. The relationship between peak height
ratio with their rheological properties and weight
percent SBR of vulcanized NR-SBR blends were
studied using thermogravimetric analysis. In addition,
the correlation of normalized factor with their rheological properties and weight percent of samples were
studied using thermogravimetric analysis as well.
The most important advantages of these techniques
are its easiness in use and its availability over a wide
range of experimental conditions when compared with
other rubber testing methods.
Methods
Materials
The material specifications and the recipe that is used
for preparing the vulcanizate tire tread samples are given
in Table 1. The major end use of this formulation is in
tire for passenger trucks and cars.
Apparatus
The compounds were prepared by a two-roll mill (6 × 18
in.; Wellshayang, Tainan, Taiwan). The mixing roller to
speed ratio was 1.2:1.0 and the roller distance was 10 mm,
which was gradually shortened to 5 mm. The molding
conditions of rubber blends were determined from data
Table 2 The rheological properties of NR/SBR blends
SBR (%)
TS2 (s)
TC90 (s)
MH (kg/cm)
ML (kg/cm)
CRI (s−1)
0
205
422
5.51
1.10
17.824
20
246
4 (...truncated)
