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Optimization of O-ring formulation containing of natural rubber on swelling behavior.


In 2012, the Thailand's government supportive measure through the tax rebate for the first-time car buyer's program another positive factor supporting automotive market growth. From this program, it makes car circulation increase and increasing demand of energy in the transportation sector. It is causing rapid depletion of fossil fuel reserve and high consumption of fossil fuel in automobile engine also causes environmental pollution. These facts have encouraged researchers to look for alternative fuels [1]. At the present, there is an advocation to use gasohol as a renewable energy instead of gasoline such as E-10, E-20 and E-85 which contain 10%, 20% and 85% of ethanol, respectively. More drivers choose to use alternative energy instead. However, gasohol damages an engine by deterioration the seal, oil hose and swelling of the gasket.

Nowadays, many researchers have been focused on enhancing properties of O-ring materials for a specific application by using blending technique. Natural rubber is obtained from the milky white fluid known as latex which found in a tropical rubber tree. It has been widely studied and reported because of its properties in tire application. It also exhibits outstanding properties such as good mechanical properties, high tear strength, high tensile strength and high flexibility. On the other hand, it swells significantly when immersed in organic solvents such as benzene at high temperatures and sometimes shows poor fatigue resistance [2]. Formulation of rubber O-ring, blending technique with filler is used to improvement. It has been already reported that the blending of natural rubber with the other synthetic rubber. These blends exhibited lower of cure characteristics, solvent resistance properties and good mechanical properties [3,4,5]. Chlorosulfonated polyethylene rubber (CSM) or hypalon (trademark name) exhibited for resistance to chemicals, ultraviolet, organic solvent and temperature. This rubber has additional used such as in sheath materials, coatings and adhesives [6]. The different in polarity of natural rubber and chlorosulfonated polyethylene rubber caused effective of blending material in rubber matrix. From this problem, one such useful method is fill epoxidized natural rubber as a compatibilizer. Epoxidized natural rubber (ENR) is a chemically modified form of the cis-1,4-polyisoprene rubber. It was utilized as compatibilizing agent to improve the blends properties. The incorporation of ENR into the rubber blends has improved process ability, stiffness, resilience and also shows excellent solvent resistance [7,8,9,10]. The compound with ENR-50 as compatibilizer was higher improvement level of tensile, aging and solvent resistant properties than ENR-25 on NR/NBR blend [4]. Filler such as clay, talcum and rice husk ash have been used as rubber filler. Natural zeolite has been utilized as filler in rubber blend on solvent resistance properties [11,12,13,14]. However, natural zeolite was not found to use as filler in NR/CSM blend.

From the gasohol resistance properties of chlorosulfonated polyethylene rubber and natural zeolite, it is interested to compare the effect of them on the gasohol resistance properties. Therefore, the purpose of this research is to investigate the optimization of formulation of natural rubber blend with chlorosulfonated polyethylene rubber by using natural zeolite as filler and epoxidized natural rubber (ENR-50) as compatibilizer in order to produce the polymer material (rubber O-ring) which shows the gasohol on swelling behavior.


A. Material and chemicals:

Natural rubber was obtained from Chon Samut Supply Co., Ltd, Thailand and chlorosulfonated polyethylene rubber (Hypalon 40) was supplied from Jiangxi Hongrun Chemical Co., Ltd., China. Epoxidized natural rubber (ENR-50) was supplied from Muangmai Guthrie Co., Ltd, Thailand. Natural zeolite (250 mesh) was obtained from Gatt Intertrade, Thailand. All chemicals for rubber compounding were commercial grade obtained from Sunny World Chemicals Co., Ltd. including zinc oxide (ZnO), stearic acid, sulfur, tetramethylthiuram disulfide (TMTD), N-cyclohexyl-2-benzothiazole sulphenamide (CBS). Gasohol fuel including E-85 which contain 85% of ethanol respectively was supplied from PTT Public Company Limited.

B. Mixing and vulcanization procedures:

Prepare all chemicals and raw materials which use in the formulation as shown in Table 1. Mixing of all raw materials and chemicals were carried out on laboratory size two-roll mill at room temperature. Box-Behnken design with three variables (ratio of NR/CSM, natural zeolite composition, ENR-50 composition)was used in these experiments (Table 2). The range of these conditions was ratio of NR/CSM blend as 50/50-10/90, composition of natural zeolite as 30-90 phr. and composition of ENR-50 as 0-10 phr. The optimum condition was determined using microsoft excel software and regression analysis method. The compounds were carried out in Moving Die Rheometer (MDR;TECHPRO, rheotech MD+) thatmachine to find scorch time, cure time and torque value. The compounds were compression molded by using a compression mold. After molded the compounds were tested the mechanical properties, and gasohol resistance.

C. Testing:

Gasohol resistance:

The gasohol resistance tests were performed in accordance with ASTM D471. Square test specimens of 2 cm x 2 cm x 2 mm were weighed accurately by using an electrical balance before immersing into gasohol (E-85) at room temperature. The specimen was removed from the gasohol and weighed again after removing surface fluids by blotting with filter paper. The percentage of swelling was calculated according to the equation (1)

swelling (%) = ([[W.sub.1] - [W.sub.0]]/[W.sub.0]) x 100 (1)

Where [W.sub.1] and [W.sub.0] represent the weight of the specimens after and prior to immersion into gasohol.

Tensile strength:

Dumbbell shaped (Die C) samples were punched form the compression-molded slap. Tensile tests were performed according to ASTM D412 using the universal testing machine (NSTRON 3366). They were examined at a cross-head speed of 500 mm/min with load cell of 500 N.


The hardness measurements of the samples were carried out using a Shore A type manual Shore A hardness tester (WALLACE) according to ASTM D2240. It was done by five measurements on each side of a 6 mm thick plate obtained by compression molding.

Compression set:

The test specimens were placed between the plates of the compression device according to ASTM D395. Then, the assembled compression device was placed in an oven at 100[degrees]C for 24 h. After completion, the test specimens were removed and allowed to cool for 30 min and the final thickness of the sample was measured for the determination of compression set according to the equation (2)

Compression set (%) = ([t.sub.0] - [t.sub.i] / [t.sub.0] - [t.sub.n]) x 100 (2)

Where [t.sub.0] and [t.sub.i] represent the breadth of the specimens before and after test and [t.sub.n] as the breadth of the space bar.


A. Cure characteristics:

The effect of content of NR in the NR/CSM blend on cure characteristic was investigated by MDR at 160[degrees]C. The cure characteristics of NR/CSM blends including scorch time, cure time and different torque values of NR/CSM blend were shown in Fig. 2-4.

The scorch time of NR/CSM blend with natural zeolite 60 phr and ENR-50 5 phr is viewed in Fig. 2.It was found that the scorch time slightly decreased with increasing the natural rubber content from 0-100 phr. The curing rate index of CSM is lower than the curing rate index of NR (K. Pal, 2009). The curing rate index decreased with increasing content of CSM in NR/CSM blend.

From Fig. 3, it showed that the cure time of NR/CSM blend decreased with increasing the natural rubber content from 0-100 phr. It can be seen that the cure time increased with the increasing of CSM loading in the rubber compounds. The viscosity of CSM is lower than the viscosity of NR. The lower viscosity components lead to form a continuous phase which is more or less the curing process. In addition, it may due to the activation of double bond that causes the rate of cross-linking in the blend increase (M. Gordana, 2013).

In addition, the results from Fig. 4, it showed that increasing content of NR from 0 to 100 phr in NR/CSM blend decreased different torque values ([M.sub.H]-[M.sub.L]). It indicated that the different torque values ([M.sub.H]-[M.sub.L]) increased with the increasing of CSM loading in the rubber compounds. It is known that the torque difference ([M.sub.H]-[M.sub.L]) shows the shear dynamic modulus which is indirectly related to the crosslink density of the compound. Therefore, it can be concluded that incorporation of CSM loading in the rubber matrix produced a better crosslink density (T. Siriyong, 2007).

B. Gasohol resistance:

The results of gasohol resistance which shows in percentage of swelling at different condition is demonstrated in Fig. 5-7, ratios of NR/CSM (50/50, 30/70 and 10/90 phr), ENR-50 compositions (0, 5 and 10 phr) and natural zeolites (30, 60 and 90 phr) could affect the percentage of swelling. The effect of three independent variables were predicted by the following second-order model equation (3)

Y = 25.749 - 0.152[X.sub.1] + 0.198[X.sub.1] - 0.539[X.sub.1] + 0.016[X.sup.2.sub.1] + 0.212[X.sup.2.sub.2] + 0.005[X.sup.2.sub.3] - 0.019[X.sub.1][X.sub.2] + 0.001[X.sub.1][X.sub.3] - 0.020[X.sub.2][X.sub.3] (3)

Where the percentage of swelling in term of Y, ratio of NR/CSM as [X.sub.1], natural zeolite composition as [X.sub.2] and ENR-50 composition as [X.sub.3]. The coefficient of determination ([R.sup.2]) was 0.9329 which indicated a good agreement between the experimental and predicted values of the swelling. The value of adjusted [R.sup.2] was 0.87 which suggested that the total variation of 87% for the swelling was attributed to the independent variables. The lowest percentage of swelling found in experiment data (Table 3) was 5.13% at ratio of NR/CSM blend30/70, natural zeolite composition 60 phr and ENR-50 5 phr.

It can be seen from Fig. 5, the effect of natural zeolite composition and ratio of NR/CSM blend on percentage of swelling at constant ENR-50 composition (5 phr). The result demonstrated that swelling behavior (%) slightly decreased with increasing of ratio of NR/CSM blend from 50/50 to 30/70 phr and increased with increasing from 30/70 to 10/90 phr. In addition, that swelling behavior (%) decreased with increasing of natural zeolite composition from 30 to 60 phr. Then, it increased with increasing from 60 to 90 phr. Due to natural zeolite performs high adsorption capacity in the process of the material vulcanization which reduces of swelling degree in the hydrocarbon media. The internal porosity of the natural zeolite also creates adsorption forces as well as an adsorption-surface area. Thus, the higher amount of gasohol adsorbed by the natural zeolite indicates the higher micropore volume [17].

The effect of natural zeolite composition and ENR-50 composition on percentage of swelling at constant ratio of NR/CSM blend (30/70) is shown in Fig. 6. It demonstrated that swelling behavior(%) decreased with increasing of natural zeolite composition from 30 to 60 phr and it increased with increasing from 60 to 90 phr. In addition, that swelling (%) slightly decreased with increasing of ENR-50 composition blend from 0 to 5phr and it increased with increasing from 5 to 10phr. In addition, ENR is a modified chemically of natural rubber into polar molecule, so increasing ENR in rubber blend was result in increasing polarlity of the rubber blend. The incorporation of ENR into the rubber blends has improved process ability and also shows excellent oil resistance(N.Z. Noriman, 2010). From reported of Lopttananon, N. studied effect of epoxidized natural rubber as a compatibilizer on properties of natural rubber/carboxylated nitrile rubber blends. The blends compatibilized with ENR-50 showed the higher improvement level of tensile properties, aging properties and solvent resistant properties when compared with ENR-25 [4].

From Fig.7, the result demonstrated that the percentage of swelling decreased with increasing the composition of ENR from 0 to 5phrand it increased with increasing from 5 to 10 phr. In addition, that swelling(%) slightly decreased with increasing of ratio of NR/CSM blend from 50/50 to 30/70phr and it increased with increasing from 30/70 to 10/90 phr. Chlorosulfonated polyethylene rubber (CSM) is a special purposed elastomer and it also exhibits for resistance to alcohol which contains in gasohol. The polarity of the chlorine group in CSM should be resistant to non-polar chemicals such as alcohol. However, from the chemical structures of NR and CSM show different in polarity which result in blend process ability. The compatibilizer as ENR also reduces phase size and solvent resistance (M. Phiriyawirut, 2013).

The mechanical properties of NR/CSM blend at the lowest percentage of swelling compared with other reported in terms of tensile strength, hardness and compression set shown in Table 4.

From the Table 4, the mechanical properties including compression set and swelling were better than other reported and O-ring from the company. On the other hand, the tensile strength was lower than other reported and O-ring from the company. Because of the further loaded natural zeolite could stiffen rubber by replacing the polymer with rigid. However from the O-ring handbook, in dynamic applications a minimum of 1,000 psi (7 MPa) is normally necessary to assure good strength characteristics required for long-term seal ability and wear resistance in moving systems.


The percentage of swelling in gasohol (E-85) was found decreased with increasing natural zeolite. However, adding the natural zeolite more than 60phr leaded to increase of the percentage of swelling. It has been found that ENR-50 could be used to improve gasohol resistance in NR/CSM blend. The optimum composition of natural zeolite, ENR-50, ratio of NR/CSM blend were 60 phr, 5 phr and 30/70, respectively. In addition, this condition showed good mechanical properties including tensile strength, hardness and compression set.


Article history:

Received 28 February 2014

Received in revised form 25 May 2014

Accepted 6 June 2014

Available online 20 June 2014


The financial support from Thailand Research Fund (TRF) based on Research and Researcher for industry: MAG is gratefully acknowledged. The author would like to acknowledge the facility support from department of chemical engineering, Faculty of engineering, Mahidol University, Chon Samut Supply Co., Ltd, Samutprakarn, Thailand and Sunny World Chemical Co., Ltd, Bangkok, Thailand.


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Theerawat Manavanich, M.N. Esthiaghi, and Nuttawan Yoswathana

Department of Chemical engineering, Faculty of Engineering, Mahidol University, Nakhonpathom, Thailand

Corresponding Author: Nuttawan Yoswathana, Department of Chemical Engineering, Faculty of Engineering, Mahidol University, Nakhonpathom, Thailand. E-mail:

Table 1: The formulation use in the preparation of a rubber blends
compound using natural zeolite as filler

Ingredient        Sulphur system

NR/CSM            variable
ZnO               6
Strearic acid     0.5
Sulphur           1.5
TMTD              1.0
CBS               0.5
ENR-50            variable
Natural zeolite   variable

Table 2: Factors and codes values of rubber blends compound which use
natural zeolite as filler

Variables                     Codes          Ranges and levels

                                          -1      0       1

Ratio of NR/CSM blend (phr)   [X.sub.1]   50/50   30/70   10/90
Natural zeolite               [X.sub.2]   30      60      90
  composition (phr)
composition of ENR-           [X.sub.3]   0       5       10

Table 3: Factor values and the response of box-behnken design

Run        [X.sub.1]         [X.sub.2](natural of   [X.sub.3](ENR-50
         (ratio NR/CSM)      zeolite composition)     composition)

1           -1(50/50)               -1(0)                0(60)
2           -1(50/50)               1(10)                0(60)
3           1(10/90)                -1(0)                0(60)
4           1(10/90)                1(10)                0(60)
5           -1(50/50)                0(5)                -1(30)
6           -1(50/50)                0(5)                1(90)
7           1(10/90)                 0(5)                -1(30)
8           1(10/90)                 0(5)                1(90)
9           0(30/70)                -1(0)                -1(30)
10          0(30/70)                -1(0)                1(90)
11          0(30/70)                1(10)                -1(30)
12          0(30/70)                1(10)                1(90)
13          0(30/70)                 0(5)                0(60)
14          0(30/70)                 0(5)                0(60)
15          0(30/70)                 0(5)                0(60)

Run         [T.sub.s]             [T.sub.c]
              (min)                 (min)

1      1.98 [+ or -] 0.05     5.02 [+ or -] 0.09
2      1.16 [+ or -] 0.02     2.32 [+ or -] 0.03
3      2.76                   65.86
4      2.23 [+ or -] 0.04     5.64 [+ or -] 0.09
5      1.53 [+ or -] 0.06     3.76 [+ or -] 0.21
6      1.52 [+ or -] 0.01     3.05 [+ or -] 0.14
7      3.51 [+ or -] 0.11     9.63 [+ or -] 0.24
8      2.02 [+ or -] 0.06     63.10 [+ or -] 1.90
9      3.14 [+ or -] 0.18     10.78 [+ or -] 0.76
10     1.42 [+ or -] 0.02     3.17 [+ or -] 0 .07
11     2.48 [+ or -] 0.01     6.79 [+ or -] 0.22
12     1.34 [+ or -] 0.08     2.68 [+ or -] 0.13
13     1.74 [+ or -] 0.04     4.40 [+ or -] 0.23
14     1.72 [+ or -] 0.03     3.83 [+ or -] 0.07
15     1.75 [+ or -] 0.02     4.05 [+ or -] 0.19

Run        [M.sub.H]-              Swelling
        [M.sub.L] (dN.m)             (%)

1      5.25 [+ or -] 0.05           12.02
2      10.34 [+ or -] 0.02          8.99
3      13.25 [+ or -] 0.10          17.38
4      6.91 [+ or -] 0.01           6.42
5      7.40 [+ or -] 0.01           10.08
6      7.72 [+ or -] 0.06           11.11
7      4.82 [+ or -] 0.01           9.08
8      11.38[+ or -] 0.52           11.76
9      5.05 [+ or -] 50.11          11.02
10     11.15 [+ or -] 0.12          17.99
11     5.30 [+ or -] 0.01           18.45
12     11.97 [+ or -] 0.01          13.25
13     7.56 [+ or -] 0.01           5.13
14     8.33 [+ or -] 0.02           5.47
15     7.81 [+ or -] 0.02           5.15

Table 4: The Mechanical properties of a rubber blends

Sample                      Tensile          Hardness
                            strength (MPa)

NR/CSM/ENR-                 8.0 [+           68.2 [+
  50/natural zeolite        or -] 0.1        or -] 0.4

NR/NBR/natural zeolite      9.40             --

O-Ring from the company     17.5 [+          78.1 [+
                            or -] 0.7        or -] 0.6

Sample                      Compression      Swelling
                            set              (%)

NR/CSM/ENR-                 36.0 [+          5.13
  50/natural zeolite        or -] 1.2

NR/NBR/natural zeolite      31.54            15.83

O-Ring from the company     24.9 [+          10.7
                            or -] 0.7

* From reported of S. Tutchawan at NR/NBR/natural zeolite (20/80/60)
immersed in biodesel.
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Author:Manavanich, Theerawat; Esthiaghi, M.N.; Yoswathana, Nuttawan
Publication:Advances in Environmental Biology
Article Type:Report
Date:Jun 5, 2014
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