NANOCOMPOSITE FROM NATURAL RUBBER LATEX AND ORGANOCLAY
BY DISPERSION DESTABILISATION
Nguyen Quang Duy, Nguyen Ngoc Bich
Rubber Research Institute of Vietnam
ABSTRACT
An organically modified clay (organoclay) and natural rubber latex were used to prepare a
nanocomposite from natural rubber using dispersion destabilisation method. As a reinforcing
filler, the organoclay showed better reinforcement efficiency than precipitated silica. The
optimum rate of organoclay incorporation was 4 parts per hundred rubber. XRD and TEM
observations of the nanocomposite showed both, intercalation and exfoliation of the
organoclay in the nanocomposite.
Keywords: Natural rubber, organoclay, nanocomposite, dispersion destabilisation.
INTRODUCTION
Reinforcement of natural rubber with organoclays may result in products having better
properties such as improved tensile strength, heat resistance, ageing resistance and
impermeability. Because of this, considerable interest in forming nanocomposites on natural
rubber using organoclays have been increased recently.
The incorporation of organoclays in a polymer matrix can generally be done by melt
intercalation or emulsion polymerisation. Those approaches may require additional chemicals
and/or equipment and therefore additional costs. In some cases, other drawbacks of the above
approaches may include low efficiency in intercalation and difficulty in controlling
exfoliation.
Perhaps the dispersion destabilisation method for producing a masterbatch from natural
rubber latex and a clay mineral was firstly developed in the 1950’s (Giger and Liponski,
1957). However, the application of this method has been limited at a certain level. Briefly, in
this method an aqueous dispersion of the clay mineral and another dispersion of natural
rubber latex were mixed, and then the dispersion mixture was destabilised using a coagulant.
The coagulum was then sheeted and dried, thus the masterbatch was formed.
A number of recent studies on rubber nanocomposites (Zhang et al., 2000; Wang et al., 2000;
Siby Varghese and Karger-Kocsis, 2003; Valadares et al., 2006) have revealed the potential of
dispersion destabilisation in compounding nanocomposites from natural rubber and
organoclays. This tendency suggests a simple, economical and environmentally friendly
method for the production of natural rubber nanocomposites, for which preliminary results
from this study may provide another illustration.
MATERIALS AND METHODS
Latex and organoclay
HA latex concentrate having a Dried Rubber Content (DRC) of approximately 61% was
obtained from Bo La factory (Phuoc Hoa Rubber Company, Binh Duong Province, Vietnam).
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The organoclay used in this study was Nanofil® 8, (Süd-Chemie, Germany) with
distearyldimethylammonium chloride (DSDMAC) as the modifying agent.
Compounding
The main rubber compound was prepared using the following formula:
-Natural rubber: 100.0 (parts by dry weight)
-Zinc oxide: 5.0
-Sulphur: 2.5
-Accelerator DM (Dibenzothiazole disulphide): 1.5
-Santol D: 0.5
-Antioxidant D (N-phenyl-2-naphthylamine): 1.0
-Stearic acid: 2.0
The content of organoclay incorporated in the rubber compound varied from 0 phr (parts per
hundred of rubber) to 7 phr, with an increment of 0.5 phr. For a comparison, precipitated
silica was incorporated in different treatments in which its content varied from 5 phr to 40
phr, with an increment of 5 phr.
Preparation of nanocomposite
Nanofil® 8 was put into a beaker with about 20 mL distilled water and stirred with a glass rod
in about 15 minutes. The dispersion was then put into another beaker containing HA latex
concentrate. The dispersion mixture was then agitated in about 2 hours using a 100 W stirrer
having a propeller being 60 mm in diameter and having a rotation speed of about 350 rpm.
After being let to stand for about 1 hour, the mixture was coagulated using acetic acid at a
coagulation pH of about 5.5 ph units. The coagulum was then washed and sheeted on a roll
mill, and then dried in an oven at 105 oC in 2 hours 30 minutes.
Compounding was affected on a roll mill. Vulcanisation of the compound was carried out in a
hydraulic press at 145  5 oC at a pressure of 8 kg/cm2 in approximately 5 minutes. The final
product was a sheet having a thickness of about 2 mm. Every batch weighed approximately
100 g.
Testing
Tensile properties of the samples were measured on a bench testing machine (Quasar 10,
Cesar Galdabini SpA, Italy). X-ray diffraction (XRD) measurements were carried out in a
Siemens D5000 (Germany) diffractometer with Cu-K X-ray radiation ( = 0.154 nm). The
diffractogram was scanned in the 2θ range from 0.3o to 10o at a step of 0.01o and a step time
of 0.8 s. Transmission electron microscopic (TEM) observations were carried out with a
JEOL JEM 1010 (Japan) transmission electron microscope.
RESULTS AND DISCUSSIONS
Effect of organoclay on tensile properties
Table 1 shows values of tensile properties of the nanocomposite with different contents of
organoclay incorporated. In general, there was a positive correlation between tensile values
and the quantity of organoclay in the nanocomposite. Optimum values of tensile properties
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were obtained at 4 phr organoclay. However, at a rate of higher than 4 phr, organoclay
brought about no better tensile properties.
Table 1. Effect of organoclay content on tensile properties
Organoclay content (phr)
Tensile strength (MPa)
M300 modulus (MPa)
Elongation at break (%)
0
1
2
3
4
5
6
7
19.08
2.46
593
21.45
2.69
598
22.39
2.78
595
23.86
3.0
615
24.97
3.04
647
19.98
2.99
596
18.94
2.87
590
17.89
2.74
582
Measurements of tensile properties of the nanocomposite with different contents of silica are
shown in Table 2. It could be seen that as a reinforcing filler, precipitated silica generally
gave an equivalent elongation, but a lower modulus and a lower tensile strength in
comparison with those given by organoclay.
Table 2. Effect of silica content on tensile properties
Silicate content (phr)
Tensile strength (MPa)
M300 modulus (MPa)
Elongation at break (%)
0
19.08
2.46
593
5
19.92
2.57
689
10
20
30
40
18.6
2.32
660
16.56
2.28
593
15.8
2.21
590
12.57
1.55
575
Intercalation of organoclay
Figures 1, 2 and 3 show respectively the XRD patterns of the organoclay, the nanocomposite
with 4 phr organoclay, and the nanocomposite with 7 phr organoclay. The XRD pattern of the
organoclay (Figure 1) revealed 2 diffraction peaks at 2θ = 0.9o and 1.5o corresponding to d =
100.30 nm and 59.44 nm. When the organoclay was incorporated in the rubber matrix at a rate
of 4 phr, in the pattern 3 peaks at 2θ = 0.84o, 1.52o and 2.11o corresponding to d = 105.08 nm,
58.68 nm and 41.76 nm are shown (Figure 2). This may indicate the intercalation of the
organoclay to some extent. When the rate of organoclay incorporated in rubber was 7 phr,
there are 5 diffraction peaks in the pattern (Figure 3), of which the first 3 peaks were similar
to those observed with 4 phr organoclay, and 2 more peaks at 2θ = 4.13o and 6.2o
corresponding to d = 21.49 nm and 14.24 nm. Although this might be a sign of better
intercalation of the organoclay, it was assumed that there was some aggregation of the clay
layers at the rate of 7 phr, for TEM micrographs as well as tensile analyses supported this
assumption.
Figure 1. XRD pattern of the organoclay
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Figure 2. XRD pattern of the nanocomposite with 4 phr organoclay
Figure 3. XRD pattern of the nanocomposite with 7 phr organoclay
Morphology of the nanocomposite
TEM micrographs of the nanocomposite with different rate of organoclay incorporation are
shown in Figure 4, Figure 5 and Figure 6.
Figure 4. TEM micrograph of the nanocomposite with 1 phr organoclay
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Figure 5. TEM micrograph of the nanocomposite with 4 phr organoclay
Figure 6. TEM micrograph of the nanocomposite with 7 phr organoclay
It can be seen from the TEM micrographs that at a rate of 1 phr (Figure 4), there could be a
low intercalation rate following a direction. An exfoliation might be indicated when the rate
of incorporation was 4 phr (Figure 5) and following different directions. At 7 phr
incorporation of the organoclay, the separation of clay layers seemed less efficient in
comparison with those obtained with lower rates of incorporation.
CONCLUSIONS
Nanocomposite from natural rubber latex and organoclay could be prepared using dispersion
destabilisation method. With Nanofil® 8, (Süd-Chemie, Germany), the optimum rate of
organoclay incorporation was 4 phr. As a filler, the organoclay showed better reinforcement
efficiency than precipitated silica. XRD and TEM observations of the nanocomposite showed
both, intercalation and exfoliation of the organoclay in the nanocomposite.
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