A Comparative Study between the Physical properties of Natural Rubber/Carbon Black blend and Natural Rubber/non Carbon Black blend

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Natural Rubber has been continuously developed due to its advantages such as good combination of strength and damping property. The addition of Carbon Back (CB) in Natural Rubber is very important to enhance the strength of the natural rubber. We have studied the relative effect of CB on Natural Rubber against a non black rubber, keeping all other parameters constant. This experiment gives us an idea about how reinforced a NR/CB blend can be as compared to a NR/non CB blend.[1]The effects of carbon blacks on vulcanization and mechanical properties of filled and non filled Natural Rubber (NR) are investigated. Curing kinetics is studied by Rheometer and the results indicate that the curing characteristics are influenced by combination of surface area of carbon black and sulphur content on the filler surface, because the former one enhances the physical cross-linking and the latter one introduces the additional chemical cross-linking. Both the degree of cross-linking and cure rate increase with increasing surface area and sulphur content, whereas the optimum cure time and scorch time decrease. The reinforcing nature of the carbon black is assessed from mechanical measurements. It is suggested that the surface area of carbon blacks strongly affects the physical properties of NR/carbon black composites.
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  International Journal for Research in Engineering Application & Management (IJREAM) ISSN : 2454-9150  Vol-04, Issue-02, May 2018 177 | IJREAMV04I02038144   DOI : 10.18231/2454-9150.2018.0143   © 2018, IJREAM All Rights Reserved.   A Comparative Study between the Physical properties of Natural Rubber/Carbon Black blend and Natural Rubber/non Carbon Black blend Sayan Basak    B.Tech, Department of Polymer Science and Technology, University of Calcutta, India.   Abstract - Natural Rubber has been continuously developed due to its advantages such as good combination of strength and damping property. The addition of Carbon Back (CB) in Natural Rubber is very important to enhance the strength of the natural rubber. We have studied the relative effect of CB on Natural Rubber against a non black rubber, keeping all other parameters constant. This experiment gives us an idea about how reinforced a NR/CB blend can be as compared to a NR/non CB blend.[1]The effects of carbon blacks on vulcanization and mechanical properties of filled and non filled Natural Rubber (NR) are investigated. Curing kinetics is studied by Rheometer and the results indicate that the curing characteristics are influenced by combination of surface area of carbon black and sulphur content on the filler surface, because the former one enhances the physical cross-linking and the latter one introduces the additional chemical cross-linking. Both the degree of cross-linking and cure rate increase with increasing surface area and sulphur content, whereas the optimum cure time and scorch time decrease. The reinforcing nature of the carbon black is assessed from mechanical measurements. It is suggested that the surface area of carbon blacks strongly affects the physical properties of NR/carbon black composites. Keywords - Natural Rubber, Carbon Black, Physical Properties, Reinforcing, Filler. I.   I NTRODUCTION    Natural Rubber produced by  Heva    Brasiliensis  whose chemical structure is cis 1, 4- poly isoprene, possesses excellent physical properties of a general purpose rubber. Presently, conventional Carbon Black (N110, N220, N330, etc.) is used because of its outstanding reinforcing filler.  NR  –   CB vulcanizates are characterized by high mechanical stress, remarkable resilience, excellent elasticity, good low heat build up and good dynamic  properties. In this experiment, we have focused on these characteristic  phenomenons with respect to a non CB filled natural Rubber. The properties of CB compounds depend on several factors such as carbon loading and the particle sizes, which include the particle-particle interaction. II.   M ATERIALS NEEDED   Compound A Compound B With CB (with Carbon) Without CB (without Carbon) Name Phr Name Phr 1. Natural Rubber 100 1. Natural Rubber 100 2 ZnO 5 2. ZnO 5 3. Stearic Acid 2 3. Stearic Acid N110 2 4. Carbon Black  N110 20 4. Carbon Black - 5. Accelerator (MBTS) 1.2 5. Accelerator (MBTS) 1.2 6. Sulphur 2.5 6. Sulphur 2.5 Total 130.7 Total 110.7 a)   Compounding and Processing b)   Two Roll Mill  International Journal for Research in Engineering Application & Management (IJREAM) ISSN : 2454-9150  Vol-04, Issue-02, May 2018 178 | IJREAMV04I02038144   DOI : 10.18231/2454-9150.2018.0143   © 2018, IJREAM All Rights Reserved.  Two Roll Mills usually consists of two hollow cast iron rolls, cylindrical in shape, having provisions for passing cold water or steam through the rolls. There are gears attached with the motor which are either of different sizes or of different teeth with some size so s to give a differential speed to the front roll as compared to the back roll. We used the friction ratio of 1.15: 1.00 Other specifications for the mixing mill are provided below: i)   Roll Size (dia X length) = 6 X 12 ii)   Approx. batch weight = (0.9  –   1.8) kg iii)   Drive (H.P.) = 7.5 iv)   The mixing time for each of the compounds for batch A and batch B are given below: Compound A Compound B Name Time (Min) Name Time (Min) 1. Natural Rubber 3 1. Natural Rubber 3 2. ZnO 2 2. ZnO 2 3. Stearic acid 2 3. Stearic acid 2 4. C-Black (N110) 4 4. C-Black (N110) - 5. Accelerator 2 5. Accelerator 2 6. Sulphur 2 6. Sulphur 2 Total 15 Total 11 c)   Rheological Test with moving die Rheometer The moving die Rheometer measures the change in the stiffness of a rubber sample. The sample is compressed  betweens two heated plates and by an applied oscillating force. The degree of vulcanization determines the cure characteristics of the sample as it is heated and compressed. Specifications for the Moving Die Rheometer: i)   Standard  –   complies with ASTM D 5289 ii)   Oscillation frequency : 10  –   300 cpm iii)   Oscillation amplitude : + 0.5 o  ~ 3 0  iv)   Temperature range : 160 0  C v)   Torque range : 0 Elasticity S‟ –   1  –   200 lb-in vi)   Viscosity : S‟ –   0.3  –   200 lb-in vii)   Power : 1Q, 220 V, + 10%, 50 Hz + 3 Hz, 10 A The graph for both the compounds A and B are attached- Fig 1- Rheograph for NR CB Blend Fig 2- Rheograph for NR/ non CB Blend The reading from the graph is as follows: Parameter NR/CB blend NR/Non CB blend 1. T c  50 2.85 minutes   3.72 minutes 2. T c 90 6.17 minutes 19.60 minutes 3. S‟ ML  1.3 lb in 0.0 lb in 4. S” ML  1.1 lb in 0.1 lb in 5. S‟ T min  1.12 minutes 1.93 minutes  International Journal for Research in Engineering Application & Management (IJREAM) ISSN : 2454-9150  Vol-04, Issue-02, May 2018 179 | IJREAMV04I02038144   DOI : 10.18231/2454-9150.2018.0143   © 2018, IJREAM All Rights Reserved.  6. S‟ T min  9.23 minutes 66.57 minutes For our compression molding, e had increased a 10 o C in the temperature as a result of which the cutting time become half of that being specified by the Rheometer. For Δ T = T 2    –   T 1  (T 2  is the final temperature and T 1  is the initial temperature) Where Δ T = 10, T 2    –   T 1  = 10 It follows that the ratio between K  2  (at T 2 ) and K  1 (at T 1 ) will equal to 2 owing to doubling of the rate constant. K  2 /K  1  = 2 Employing Arrhenius equation, K  2 /K  1 = {Ae ( -Ea/RT2 } / {Ae ( -Ea/RT1 ) = e [ - E a/R(1/T 2  –   1/T 1 )] = 2 Or, K  2 / K  1 =  exp (- Ea/R  –    Δ  1/T) = 2 . . . Δ 1/ T = (1/T 2  –   1/T 1 ) = {(T 1 /T 1 T2) - (T 2 /T 1 T2)} = (- ΔT/T 1 T 2 ) Once we are holding Δ 1/ T = - 10/T 1 T 2 Substituting this into the Arrhenius equation, Exp (-Ea/R -10/ T 1 T2) = 2 Or, 10Ea/R T 1 T2 = ln2 Or, T 1 T 2 = 10 Ea/Rln2 Writing in terms T 1, T 1  (T 1 +10) = 10 Ea/R.lr2 Or, T 12  + 10T 1 -  (10Ea/R.lr2) = 0 Solving the quadratic equation, we have, T 1 = Ea X 8.3 X 10 -3 K T 2 = {(Ea X 8.32 X 10 -3 ) + 10} K T 1    –   T 2 = 10 K d)   Compression Molding The Rubber compression molding process begins with a  piece of uncrushed rubber which has been preformed to a control weight and shape. As the mould is closed, the material is compressed between the plates causing the compound to flow to fills the cavity. The material is held in the mould under high pressure and elevated temperature to activate the cure system in the rubber compounds. III.   P ROPERTY T ESTS AND THE R  ESULTS   i)   Rheological Test The lowest torque value recorded or the graph is called ML. It measures the stiffness of an uncured rubber at a given temperature. From the graph we see that ML  NR/CB ˃  ML  NR/nonCB  This clearly gives us an indication that the strength of  NR/CB blend even at uncured stage is much higher than that of NR/non CB blend [2] TS 2  is the time from the beginning of the test to the time the torque has increased 2 units above ML value. It is measured in time units and provides information about scorch time or at which point the owing actually starts. As the curing progresses, the torque increases further. The slope depends on the compound and the system. That is why we see the slope of NR/CB blend is a bit higher than that of NR/Non CB blend. After some time the torque attains a maximum value and plateaus out. The highest torque recorded on the graph, is called the Moment Highest (MH). Time from the start of the test point to the point where 90% of the MH value is reached is called its T c 90. It is a measure of the curing time of the system. From our results, (T c 90 for NR/CB blend) / (T c 90 for NR/non CB blend) = 6.17/19.60 = 1/3 (approx) The cure time and the cure rate become faster because of the Carbon Black Content. The crosslink density also increases and the reversion resistance is improved in the material as a NR/CB blend. The cure time is faster since it is widely evidenced the CB would automatically perform  better as a physical cross linker in the rubber material as a result of the rubber molecules being absorbed into the block surfaces during compounding. b) Tensile Test   Referring to the chart C1 and both of the compared graphs we got from the Tensile Test, it is evident that the tensile stress of the NR/CB blend was much more higher than that of NR/Non CB blend proving the amount of reinforcement. The tensile strength in MPa recorded for NR/CB blend was 18.41 which that of NR/Non CB blend were 4.462. Beside that there was a great difference in the Young‟s Modulus that was recorded for both the samples (5.5: 1.0, NR/CB:  NR/Non CB) The relationship between the tensile stress and percentage of elongation was plotted. Based on the graph, it was showed that the tensile stresses were continuously increasing as the percentage of elongation was increased for  both the compounds. [3] The stiffness recorded for CB/NR  blend was 2769.32 (NM) and that for unfilled NR was 652.352, indicating a great deficiency in the reinforcement. While the CB filled NR, it was found that the materials displayed the small elastic behaviour, where the low stress level was produced at high strain. On the other hand it was  International Journal for Research in Engineering Application & Management (IJREAM) ISSN : 2454-9150  Vol-04, Issue-02, May 2018 180 | IJREAMV04I02038144   DOI : 10.18231/2454-9150.2018.0143   © 2018, IJREAM All Rights Reserved.  also found that the CB filled NR exhibited thicker line rather than the unfilled NR line in which refers to the noise level of NR compound under the tensile force. The noise level resulted from the effect of molecular interaction  between the mature and filler particles in respond to the force applied during tensile test, where the fillers acted as the strain amplifier, which strongly influenced the flow  behaviour and its mechanical properties. Furthermore, the high modules value exhibited by the CB filled NR compound compressed showed that the stiffness of the material increased due to the addition of the CB. K = EA/L, where, K is the stiffness, E is the Young‟s Modulus  A is the area and L is the length The tensile stress 6 = F/A, = Force/Area Or, A = KL/E (by substituting the value of A) Or, 6 = FE/KL Or, 6 α K  -1 (FE/KL) Or, 1/6 α K  -1 (KL/FE) This concedes the problem in the stress versus strain curve whereby the tensile decreased since the stiffness increased resulting from the Reinforcement effect. c) Shore Hardness The shore hardness for both the filled and unfilled NR was measured with a SHOR E  –   A device. The following data‟s  were observed-  NR/CB blend -63 shore hardness  NR/Non CB blend-58 shore hardness IV.   RESULTS    –    TENSILE   TESTING    –    C1 CB/NR Gauge length (mm) Width (mm) Thickness (mm) Total elongation at max. force Tensile strength (MPa) Elongation at fracture Stiffness (Nm) Proper-ties and their values 25 4.63 2.05 724.97 18.411 181.463 2679.32 Young‟s modulus Load on Break on Stress at Break (NM) Extension at  break Strain at  break Ring stiffness Load at 100% modules 6.812 0.1744 18.341 181.463 7.251 0.0000262 0.01567 Stress at 100% modules Extension at 100% modules 1.6541 25 NR/ Non CB Gauge length (mm) Width (mm) Thickness (mm) Total elongation at max. force Tensile strength (MPa) Elongation at friction Stiffness (Nm) Proper-ties and their values 25 4.49 1.93 652.192 4.462 168.088 652.334 Young‟s modulus Load on Break on Stress at Break (NM) Extension at  break Strain at  break Ring stiffness (MPa) Load at 100% modules 1.396 0.0399 4.415 168.12 6.728 0.000006467 Stress at 100% modules Extension at 100% modules 0.7615 0.25
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