Mechanical and Oil Resistance Characteristics of Rubber Blends

ELASTOMERE UND KUNSTSTOFFE ELASTOMERS AND PLASTICS

NBR · CR · PVC · Rubber blends · Mechanical and Oil Resistance Vulcanizing system · Oil resistance Different rubber blends based on nitrile butadiene rubber, NBR (N3980–39% Characteristics of Rubber acrylonitrile) have been prepared to get a product with high oil resistant and good mechanical properties. The Blends Based on Nitrile obtained mixes included NBR, chloroprene rubber (CR) and polyvinyl chlo- 1 ride (PVC). The ratio of each component Butadiene Rubber (NBR, CR and PVC) as binary or ternary blend system has been varied and the corresponding vulcanizing systems have been carefully selected. It has been found that the type of rubber and the composition of blends markedly affect their oil resistance. In contrast, the type of crosslinks and crosslinking Blending of polymers has gained much in- (NR). The elastomeric composite has excel- density slightly affect the oil resistance terest, since about 3-4 decades ago, due to lent compatibility between two rubbers of of the corresponding vulcanizates. the fact that, it can be used to produce new different polarity when properly com- polymeric materials, i.e, compositions with pounded and processed. Anmin, et al. [12] specific properties suitable for certain spe- prepared hydrogenated nitrile rubber Mechanische Eigenschaften und cial application. Nitrile rubber (NBR) is wide- (HNBR)/clay nanocomposites using conven- Ölbeständigkeit von NBR ly used in many applications like oil seals, tional two-roll mill mixing technique. They Verschnitten gaskets, etc. The performance of NBR can found that adding organoclay in HNBR be improved by blending with various poly- elastomer greatly improves material ther- NBR · CR · PVC · Kautschukverschnitte · mers [1-4]. The interaction of polymeric ma- mal stability and aging performance in dif- Vulkanisationssysteme · terials with different solvents or liquids is a ferent medium at elevated temperature. Ölbeständigkeit problem from both the academic and tech- Severe, et al. [13] produced dynamic vul- Verschnitte aus NBR und CR bzw. PVC nological points of view. In the literature, canizates from HNBR and three different wurden hergestellt um eine hohe there is a noticeable shortage of reports oil resistant elastomers. These are CR, EIR, Ölbeständigkeit und gute mechanische dealing with the influence of oils on the me- and carboxylated nitrile rubber (XNBR). Eigenschaften zu erzielen. Das Ver- chanical and the properties of polar diene They concluded that the dynamically vul- schnittverhältnis wurde variert und das rubbers, e.g., the chloroprene and the nitrile canized blends held up better under oil ag- Vernetzungssystem angepasst. Es rubbers. The vulcanizates based on these ing than under air aging. Sulekha and wurde gefunden, dass die Konstitution rubbers swelled in oils only to a limited de- Joseph [14] studied the efficiency and per- des Polymeren und das Verschnittver- hältnis die Ölbeständigkeit maßgeblich gree, although the aforementioned publica- manence of polymer hound antioxidants beeinflussen. Im Gegensatz hierzu tions show that even limited swelling may like polyisobutylene bound paraphenylen- haben die Art der Vernetzung und die cause hazardous changes of rubber parts ediamine (PIB-PD) and chlorinated paraffin Vernetzungsdicht eine untergeordnete performance [5-7]. wax bound paraphenylene diamine (CPW- Wirkung. Magryta Jacek, et al. [8] showed that even a PD) in NBR vulcanizates. The vulcanizates small degree of swelling of the vulcanizates showed improved aging resistance in com- causes decrease of their mechanical prop- parison to vulcanizates containing conven- erties and considerable changes of the dy- tional antioxidant. The liquid polymer namic characteristics of CR and NBR. Patil bound antioxidants reduce the amount of and Coolbaugh [9] summarized some of the plasticizer required for compounding. The advantages and limitations of commercial elastomers with special emphasis on their oil-resistant character Oyama, et al. [10] re- late invented an oil-resistant rubber composition having excellent solvent crack resistance comprising a partially hydrogenat- Authors ed unsaturated nitrile/conjugated diene A.M.Omran, A.M.Youssef, copolymer rubber and a liquid unsaturated M.M.Ahmed, and E.M.Abdel-Bary, nitrile/conjugated diene copolymer. Telang R.T.L.Hellipolis Cairo, (Egypt) and Manjanath [11] made the rubber composite from a unique blend of nitrile rubber, Corresponding author: polychloroprene (neoprene), epoxidised Prof. E.M.Abdel-Bary German University in Cairo natural rubber (EIR) and natural rubber New Cairo City, Egypt Tel. +20 |2| 185665479 1 Paper given at IRC 2009, Nuremberg, june 29. to E-mail: july 02.,2009 [email protected]

KGK · Mai 2010 197 ELASTOMERE UND KUNSTSTOFFE ELASTOMERS AND PLASTICS

present work is aiming to study the charac- 1 Formulations of NBR and CR with different vulcanizing systems. teristics of NBR belnded with polychloro- MIXTURE CODE MN1 MN2 MN3 MN4 MN5 MN6 MN7 MN8 MC1 MC2 prene (CR) or polyvinylchloride ( PVC). Thus, NBR 100 100 100 100 100 100 100 100 - - the properties of the corresponding rubber CR ------100 100 mixes and vulcanites as well as the effects St. Acid 1 1 1 1 1 1 1 1 1 1 of blend compositions on their oil and fuel Zn O 5 5 5 5 5 5 5 5 5 5 resistant are evaluated. ZA 4010 1 1 1 1 1 1 1 1 1 1 Mg O ------4 4 Experimental C.B.(GPF) 45 45 45 45 45 45 45 45 45 45 DBP 5 5 5 5 5 5 5 5 5 5 Materials The basic materials used in this work are: CBS 0.7 ------Acrylonitrile butadiene rubber (NBR, MBT - - - - 1 - - - - - N3980 – 39% acrylonitrile, Mooney Viscos- MBTS - 1 0.5 - 1 - - - - - ity (ML-4 (100oC): 80, EINE CHEM, ITALY), DOTG - - - - - 1 1 - - - Chloroprene rubber (CR, Mooney Viscosity TMTD - - 0.7 2 2.5 3 3 - - - (ML-4 (100oC): 75-90, Bayer, Germany), Poly- S 2.5 2.5 2.5 0.5 - 0.5 - - - - vinyl Chloride (PVC, K-Value 70, SABIC mar- ETU ------2 3 keting ltd. An afﬁliate of SABIC, KSA), Zinc DCP ------3 - - Oxide (ZnO, Bayer, Germany), Magnesium Oxide (MgO, Bayer, Germany), sulphur (S, 2 Formulations of NBR and CR with different blend ratios.

Dammam, KSA), tetramethylthiuram disul- BLEND CODE B1 B2 B3 B4 B5 B6 B7 phide (TMTD, Bayer, Germany), ethylene NBR 100 90 70 50 30 10 - thiourea of 2-mercapto imidazole (ETU, CR - 10 30 50 70 90 100 Bayer, Germany), 2-mercaptobenzthiazol St. Acid 1 1 1 1 1 1 1 (MBT, Bayer, Germany), dibenzothiazyl di- Zn O 5 5 5 5 5 5 5 sulphide (MBTS, Bayer, Germany), N-cy- ZA 4010 1 1 1 1 1 1 1 clohexyl-1,2-benzothiazyl sulphenamide Mg O - 0.4 1.2 2 2.8 3.6 4 (CBS, Bayer, Germany), diortho-tolyl guani- C.B.(GPF) 45 45 45 45 45 45 45 dine (DOTG, Bayer, Germany), dicumyl per- DBP 5 5 5 5 5 5 5 oxide (DCP, TAIpel, Taiwan). MBTS 0.5 0.45 0.35 0.25 0.15 0.05 - TMTD 0.7 0.63 0.49 0.35 0.21 0.07 - Recipes S 2.5 2.25 1.75 1.25 0.75 0.25 - Basic formulations used for choose the vul- ETU - 0.2 0.6 1 1.4 1.8 2 canizing system for NBR and CR mixtures, and those for determining the best blend Formulations of NBR with different ratios of PVC compositions of NBR/CR and NBR/PVC 3 BLEND CODE B B B B B B B blends are shown in Table 1. 11 22 33 44 55 66 77 NBR 100 100 100 100 100 100 100 Techniques and methods PVC 0 10 30 50 70 90 100 St. Acid 1 1 1 1 1 1 1 Mixing and compounding Zn O 5 5 5 5 5 5 5 Mixing of NBR and CR mixtures were car- ZA 4010 1 1 1 1 1 1 1 ried out on a laboratory open two roll mill C.B.(GPF) 45 45 45 45 45 45 45 (400mm. diameters and 600mm. working DBP 5 6.7 10.2 13.6 17 20.5 22.2 length). The gear friction of the mill is 1:1.4. MBTS 0.5 0.5 0.5 0.5 0.5 0.5 0.5 The hollow rolls were cooled by using ﬂush- TMTD 0.7 0.7 0.7 0.7 0.7 0.7 0.7 ing water in order to regulate the tempera- S 2.5 2.5 2.5 2.5 2.5 2.5 2.5 ture not exceeding 60 oC during the different stages of mixing according to ASTM

D-15-627. The rubber mixes obtained were ing Disc Rheometer (ODR) model 4308 from R[ MC90 ML tC90 tL ](2) sheeted and left for a period of at least 6 hrs Zwick, Germany. The measured parameters before testing. are: ML – minimum torque, MH – maximum Where – tL is the time of ML.

The addition of ingredients during mixing torque, tS2 – time to 2 units of torque in- These measurements were accomplished was carried following the same order and crease above minimum, MC90 – torque at according to ASTM D-2084. conditions of mixing. The used rubber for- 90% of full torque development, where mulations are given in Tables1-3. Preparation of the test samples

MC90 ML [ MH ML ¸90100] (1) The rubber mixes were compression mold- Rheology measurements ed at 150o2˚C, using an electrically heated

The cure characteristics of rubber com- In addition tC90 was measured – equivalent hydraulic press at their optimum cure time pounds were carried out using an Oscillat- to optimum cure time, the cure rate: derived from rheological measurements.

198 KGK · Mai 2010 1 2

1 Rheometric characteristics of NBR/CR blends 2 Physico-mechanical properties of the different NBR/CR blends

3 4

3 Equilibrium swelling percent % in engine and hydraulic oils of the 4 Equilibrium swelling percent % in Diesel and gasoline of the different NBR/CR blends different NBR/CR blends

The applied hydraulic force during vulcani- Physico-mechanical properties of the Swelling of the test samples zation attained 50 Kgf/cm2. Dumbbell test samples The equilibrium swelling was carried out ac- shaped tensile strength was punched from The mechanical properties were deter- cording to ASTM D-471. The swelling was the compression moulded sheet along the mined using the tensile testing machine performed by immersing the specimens in mill grain direction using C-type dumbbell type Zwick 1445 according to ASTM D-412. engine oil Type (50), hydraulic oil Type (37), specimens, according to ASTM D-412. All tests were carried out at room tempera- and toluene at room temperature 25 o2˚C, ture (25 o2˚C). for 24 hours. The variation of apparent per-

4 The overall properties of different NBR and CR mixes and vulcanizates.

MIXTURE CODE MN1 MN2 MN3 MN4 MN5 MN6 MN7 MN8 MC1 MC2

TS2 3.4 4.6 3.7 4.3 11.6 1.9 2.9 3.3 1.8 0.4

TC90 21 15 7 9 17.5 9.5 22 21.5 15.5 14

Properties R [1/min] 0.197 0.18 0.876 0.573 0.155 0.42 0.074 0.066 0.225 0.23 Rheometric Tensile Strength 163 187 136 148 142 122 172 178 223 238 Modulus 100% 31 28 34 21 13 24 16 31 39 34 Modulus 200% 61 52 68 37 18 45 25 66 87 74 Elongation % 459 603 379 701 1478 505 1213 411 425 496 Permanent Set % 3 4 3 5 25 0 21 2 1 4 Properties Hardness ‘A’ 68 68 71 62 55 64 57 67 69 68 Physico-mechanical Physico-mechanical Resilience % 19 18 22 22 20 22 21 20 35 43 Engine oil(50) %0.8 0 0 0.4 0 0.3 0 0 0.2 0.6 Hydraulic oil(37) 0.2 0.6 0 0 0 0 0 0.4 1.5 2.4 Diesel 1.7 2 1 2 1.7 1.9 1.5 1.8 15.3 22.8 Gasoline 13.4 11.2 11.1 11.9 13.2 11 11.9 11.4 43.6 47.2 Toluene 64.6 63.3 55.5 57.1 75.8 59.7 73.3 51.1 108.9 113 Crosslinking Density 10-4 43.17 43.74 47.85 46.99 38.95 45.58 39.75 50.78 24.17 23.68

KGK · Mai 2010 199 ELASTOMERE UND KUNSTSTOFFE ELASTOMERS AND PLASTICS

5 6

5 Equilibrium swelling percent % in Toluene of the different 6 Crosslinking density of the different NBR/CR blends NBR/CR blends

centage of change in mass was calculated. Thus, the optimum properties of NBR for- been prepared, as shown in Table 3. The

It is expressed as the percentage of the mulations were found for the mixture MN3, properties of both mixes and vulcanizates original mass [15-16]. where the vulcanizing system used was: have been evaluated. The proper vulcaniz- S2.5phr TMTD 0.7 phr MBTS 0.5 phr. ing system calculated according the weight Equilibrium swelling percent% Also, for obtaining optimum properties of fraction of each type in the blends has been

[ WWo Wo]¸100 (3) CR mixtures, the vulcanizing system should selectes. The obtained results for the differ-

be: ETU 2phr for the mixture MC1 formula- ent rubber blends are given in Table4, and where Wo – the initial mass before swelling tion Besides, the mixtures MN3-MN7 for in Figures1-6. and W – the mass after equilibrium swell- NBR formulations had excellent hydraulic From Figure 1 it can be concluded that the ing. oil resistance. optimum cure time increases with increasing CR concentration in the blend up to NBR/CR Results and discussion Effect of the compositions of NBR/CR (1:1), after which it tends to level off. This blends on rubber vulcanizates: increase in the optimum cure time is due Effect of vulcanization system on the Blending of two or more polymers for prop- to the lower rate of crosslinking of CR in properties of NBR and CR vulcanizates erty improvement and economic advan- presence of sulphur, compared with that of Table1shows the four different vulcanizing tage has gained considerable importance. A NBR. Figure2shows that increasing the CR systems, which were selected to vulcanize large number of polymer blends has been content leads to an increase in tensile NBR and also the two different systems, proposed for commercial purpose [17-18]. strength, while chang in modulud is less re- which were selected to vulcanize the CR Polymer blends are versatile polymeric ma- markable. Figure3shows that the oil resist- rubber under investigation. The effects of terials, the properties of which can be tai- ant in engine oil decreases with increasing different vulcanizing systems are given in lored accordingly [19-20]. Effect of blend CR concentration in the blend. This because Table5. compositions of NBR/CR in the ratios has CR itself is less oil resistant than NBR due to

5 Overall properties of NBR and CR with different blend ratios.

BLEND CODE B1 B2 B3 B4 B5 B6 B7

TS2 3.7 1.6 1.3 1.2 1.2 1.2 1.8

TC90 7 12 13.2 15 16.3 17.6 15.5

Properties R [1/min] 0.876 0.54 0.645 0.376 0.324 0.257 0.225 Rheometric Tensile Strength 136 142 147 176 185 193 223 Modulus 100% 34 40 46 49 43 38 39 Modulus 200% 68 84 90 96 92 81 87 Elongation % 379 324 304 355 364 411 425 Permanent Set 3 2 2 2 2 2 1

Properties % Hardness ‘A’ 71 73 74 78 75 72 69 Physico-mechanical Physico-mechanical Resilience % 22 16 17 25 25 32 35 Engine oil(50) %0 0 0 0 0 0.13 0.22 Hydraulic oil(37) 0 0.02 0.08 0.26 0.52 0.66 1.52 Diesel 1 1.2 1.8 3.8 7.3 8.4 15.3 Gasoline 11.1 13.7 22.6 29 34 41.5 43.6 Toluene 55.5 58.4 70.4 74.5 87.4 105.4 108.9 Crosslinking Density 10-4 47.85 45.01 37.65 34.47 29.64 25.24 24.17

200 KGK · Mai 2010 tensile strength is due to PVC as thermo- 7 7 Effect of PVC plastic material. In this case, elogation at content on the mechanical break is higher in absence of PVC and it de- properties creases with increasing PVC concentration. The relationship is linear and given in Fig- ure 8. This linearity indicates ,again, the compatibility of NBR with PVC. Figure9shows the effect of PVC concentration on the resistance of the blend to diesel and gasoline. From this figure it can be seen that PVC has practically no effect on the degree of swelling in diesel fuel and the swelling percent does not exceed 1 % for all blend composition. However it decreases in case of gasoline from about 11 % for NBR the difference in polarity, CN is more elec- On the other hand the principal attributes of alone to about 5% when 50% of PVC was tron withdrawing than Cl. the PVC toward the NBR is improved chemi- added. In case of toluene, the swelling de- Figure 4shows that the degree of swelling in cal resistance of NBR, thermal ageing, tear crease from 55% to about 40%, as shown in gasoline increases with increasing CR con- resistance, and abrasion resistance in appli- Figure10. It is intersting to observe that the centration in the blend. Thus, the blend be- cations like feed hose covers, gaskets, con- decrease in swelling starts markedly at 10 % comes less resistant to gasoline and diesel veyor belt covers, printing roll covers, etc [21]. PVC followed by slight decrease with in- with increases concentration of CR. The Effect of blend compositions of NBR/PVC in creasing PVC concentration. maximum swelling in diesel attaind 15% for the ratios has been prepared. The mixes and Calculation of the degree of crosslinking CR, while for NBR is about 2 %. The other vulcanizates properties have been evaluated. from swelling data in tolune showed that blends lie between these values and gov- The concentrations of PVC in the NBR matrix the crosslinking density decreases with in- erned by the equation given on the figure. are varied as following: 0, 10, 30, 50, 70, 90, creasing PVC concenteration. This decrease Figures 5 and 6 show that the degree of and 100phr, as shown in Table6 and Figures7. in the crosslinking density and at the same swelling in toluene increases with increas- Figure 11 shows that a linear relationship time decrease in the equilibrium degree of ing CR concentration in the blend and con- exists between Modulus 100% and blend swelling in toluene is due to the presence of sequently, the caculated crosslinking den- composition. This indicates that PVC and PVC, which did not contribute to the creation sity decreases. This again indicates that CR NBR are compatible at all blend ratios. The of crosslinks and only act as a filler, as shown in the blend is undercured. Thus, the opti- empirical equation governing this relation- in Figure 11. Thus, the equilibrium swelling mum concentrations of NBR and CR in the ship is given on the figure. In case of modu- in toluene decreases, and at the same time blend will determined according to the re- lus 200% the linearity exists until 50 % PVC the apparent crosslinking density decreaes quired properties. concentration and deviates from linearity. as PVC restrict the swelling in toluene. In conrast , pracically no effect on tensile Effect of the compositions of NBR/PVC strength has been found. This indicates that Conclusion blends on rubber vulcanizates at lower concentration of PVC , the tensile From the obtained results, as shown in Ta- One of the commercially important and mis- strength is mainly due to crosslinking of ble6, and Figures7-11, the following conclu- cible polymer blends is that of NBR and PVC. NBR. However at high concentration, the sions can be derived:

6 Overall properties of NBR with different ratios of PVC

BLEND CODE B11 B22 B33 B44 B55 B66 B77

TS2 3.7 3 2.6 2.8 2.8 3.1 3.2

TC90 7 8.5 9.6 10.2 11.4 10 9

Properties R [1/min] 0.876 0.85 0.638 0.52 0.473 0.63 0.59 Rheometric Tensile Strength 136 138 139 146 153 146 143 Modulus 100% 34 43 63 82 113 122 131 Modulus 200% 68 89 120 143 _ _ _ Elongation % 379 316 243 209 165 150 135 Permanent Set 3 2 3 4 5 6 6

Properties % Hardness ‘A’ 71 74 79 83 87 89 90 Physico-mechanical Physico-mechanical Resilience % 22 15 15 15 14 14 14 Engine oil(50) %0 0 0 0 0 0 0 Hydraulic oil(37) 0 0 0 0 0 0 0 Diesel 1 0.8 0.6 0.6 0.5 0.3 0.2 Gasoline 11.1 6.4 5.7 5.4 5 4.6 4.5 Toluene 55.5 46.9 44.4 41.3 40.5 39.6 38.5 Crosslinking Density 10-4 47.85 51.43 49.06 47.88 45.39 43.32 42.96

KGK · Mai 2010 201 ELASTOMERE UND KUNSTSTOFFE ELASTOMERS AND PLASTICS

8 9

8 Elongation at break of the different NBR/PVC blends 9 Equilibrium swelling percent % in diesel and gasoline of the NBR/PVC blends

10 11

10 Equilibrium swelling percent % in Toluene of the different NBR/ 11 Crosslinking density of the different NBR/PVC blends PVC blends

1 The presence of CR in the blend impaired References their swelling resistance. [1] J.Oravec Y.Oishi H.Hirahara., K.Mori., Polym. composites in Air, Water and Oil at Elevated 2 The optimum cure time increases with Int. 32 (1993) 303. Temperature”, no.051, 2007. increasing CR concentration in the blend [2] S.George., K.T.Varughese., S.Thomas Polymer [13] Severe G., White J. L., J. Appl. Polym. Sci., 95 up to 1:1 increasing the CR content leads 41 (2000) 579. (2005) 2. to an increase in tensile strength, while [3] E. M. El-Nesr A. M. Ali and E. M. Abdel-Bary, [14] B. Sulekha and P.Joseph., Internatl. J. Polym. chang in modulud is less remarkable J.Elastomers and Plastics, 35 (2003) 209. Mater. 54 (2005 333 . [4] E.M.Abdel-Bary W. von Soden and F. M Helaly, [15] M.T.Ramesan, A.Rosamma and N.V.Khanh, Re- 3 Increasing the PVC content leads to an Polymer Adv. Technol. 11 (2000)1. active & Functional Polymers 62 (2005) 41. increase in modulus (100%) and modulus [5] M. Gajewski,. Polimery–Tworzywa Wielkocza [16] D.K.Setua; C.Soman, A.K.Bhowmick, and (200 %) and decrease in elongation at steczkowe, 19 (1974) 244. G.N.Mathur, Polym. Eng. Sci., 42 (2002) 1. break. [6]J.J.C.Busﬁeld, C.Deeprasertkul, A.G Thomas, [17] M. T Ramesan., T. K. Manoj., R. Alex and B. Kuri- 4 All NBR/PVC blends had excellent engine Polymer, 41 (2000) 9219. okose, Mater J.. Sci., 37 (2003) 109. and hydraulic oils resisatance and the [7] W.M Rzymski,., J.Jentzsch, Plast und Kautchuk, [18] B.Pinel and F., Boutaud, Nucl. Instrum.Methods more desired characteristics of vulcani- 37 (1990) 48. Phys. Res.,Sect. B – Interactions with Materials [8] J.Magryta, C.Debek, D.Debek, J.Appl. Polym. and Atoms, 151 (1999) 471,. zates with respect to fuel and oil resistant Sci., 99 (2006) 2010. [19] J.K.Kim and R.P., Burford, Rubber Chem. Tech- can be achevied with PVC concenteration [9] O. P.Abhimanyu T. S., Coolbaugh “Elastomers: nol., 71 (1998) 1028. not more than 30phr. Rubber Chem. Technol. 78 (2005) 516. [20] J.R Dunn,., D.C Coulthard,., H.A.Pﬁsterer,. Rub- [10] U.S Patent 4421884, (1983) M.Oyama. ber Chem. Technol., 51 (1978) 389. [11] U.S Patent 6756106 (2004) .M.R.Telang. [21] A. Mousa, U. S., Ishiaku Z. A I.. Mohd, Polymer [12] A.Huang, X.Wang, D.Jia, Y.Li, “Thermal Stability Bulletin 53 (2005) 203. and Aging Characteristics of HNBR/Clay Nano-

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