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Ind. Eng. Chem. Res. 2010, 49, 5012–5017
Ionic Liquids as Vulcanization Accelerators Juliusz Pernak,*,† Filip Walkiewicz,† Magdalena Maciejewska,‡ and Marian Zaborski‡ Poznan UniVersity of Technology, pl. M. Sklodowskiej Curie 2, 60-965 Poznan, and Technical UniVersity of Lodz, Institute of Polymer and Dye Technology, Poland
The synthesis, physical properties, and antimicrobial activity of imidazolium, benzalkonium, and phosphonium ionic liquids with 2-mercaptobenzothiazolate has been studied. Synthesized ionic liquids were used as acceleration agents in the vulcanization of rubber. Use of synthesized salts allows to reduce amount of 2-mercaptobenzothiazole, which is commonly used in vulcanization but is an allergenic agent. We obtain in our research shorter vulcanization time, no loss of mechanical properties of rubber, and reduction of the allergen from 56 to 87% in comparison with the vulcanization without ILs. 1. Introduction Ionic liquids (ILs) are defined generally as salts with melting points below 100 °C.1-4 The definition of ILs clearly differs them from well-known molten salts. Research on ILs has been one of the most rapidly growing fields in chemistry and industry in the past years. This is mainly due to the many unique properties of ionic liquids. They are able to solvate a large variety of organic compounds, both polar and nonpolar, and show potentially “environmentally-friendly” characteristics (e.g., negligible vapor pressure and flammability). Accordingly, ILs are nonvolatile compounds, thus decreasing the chance for fugitive emissions. Their chemical and physical properties can be tuned for a range of potential applications by varying the cations and anions. Antielectrostatic properties of ILs have been also recognized.5 It was recently demonstrated that with low vacuum and very high temperature ILs could be distilled, but under such conditions, some of them are unstable.6 In the past few years ILs have been employed not only as solvents for various types of polymerization,7 but they have also been used to dissolve polymers (cellulose,8,9 silk fibroin,10 starch11), to add functionality to them, and to create new polymer composites. ILs have also shown great potential in becoming ecofriendly, as they are free of both arsenic and pentachlorophenol, and effective wood preservatives.12,13 Applications of ILs as solvents for polymerization processes, as components of polymeric matrixes (such as polymer gels), as templates for porous polymers, and as novel electrolytes for electrochemical polymerizations have been reviewed.14-17 In this paper, we described use of novel ILs with 2-mercaptobenzothiazolate anion as accelerators for vulcanization process. 2. Experimental Part Materials. Acrylonitrile butadiene rubber NBR (EUROPREN N3960) was obtained from Bayer. Benzalkonium chloride and tetradecyl(trihexyl)phposphonium chloride and 2-mercaptobenzothiazole were obtained from Sigma Aldrich and used without further purification. 1-Alkyl-3-methylimidazolium bromides were obtained by a procedure described earlier.18 All solvents were used as obtained without further purification. 1-Butyl-3methylimidazolium salts as bromide-[C4mim][Br] (7), * To whom correspondence should be addressed. Tel.: +48 61 665 3682. E-mail:
[email protected]. † Poznan University of Technology. ‡ Technical University of Lodz.
chloride-[C4mim][Cl] (8), hexafluorophosphate-[C4mim][PF6] (9), and tetrafluoroborate-[C4mim][BF4] (10) were obtained from Fluka. Synthesis of 2-Mercaptobenzothiazolate Ionic Liquids. A 0.001 mol portion of 2-mercaptobenzothiazole and 0.001 mol of benzalkonium chloride or 1-alkyl-3-methylimidazolium bromide or tetradecyl(trihexyl)phosphonium chloride and a stechiometric amount of potassium hydroxide were dissolved in methanol. The mixtures were stirred at room temperature (rt) for 1 h and then inorganic solid was filtered off. After evaporation of methanol, the product was extracted with anhydrous acetone. Potassium chloride or bromide was filtered and acetone was evaporated. Obtained product was dried in vacuum at 80 °C overnight. Benzalkonium 2-Mercaptobenzothiazolate 1-[BA][2MBT], Solid. 1H NMR (300 MHz, DMSO-d6) δ ppm 0.86 (t, J ) 6,7 Hz, 3H), 1.24 (m, 20H), 1.75 (m, 2H), 2.99 (s, 6H), 3.27 (t, J ) 6.5 Hz, 2H), 4.6 (s, 2H), 6.92 (t, J ) 8 Hz, 1H), 7.08 (t, J ) 8.3 Hz, 1H), 7.25 (d, J ) 8.5 Hz, 1H), 7.39 (d, J ) 8.7 Hz, 1H), 7.39 (m, 3H), 7.56 (m, 2H); 13C NMR (75 MHz, DMSOd6) δ ppm 13.9, 21.9, 22.1, 25.8, 28.5, 28.7, 28.8, 29.0, 31.3, 49.0, 63.5, 66.2, 116.6, 119.0, 120.4, 124.2, 128.1, 128.8, 130.1, 132.9, 136.7, 155.2, 184.9. 1-Butyl-3-Methylimidazolium 2-Mercaptobenzothiazolate 2-[C4mim][2MBT], Liquid. 1H NMR (DMSO-d6) δ ppm 0.86 (t, J ) 6.9 Hz, 3H), 1.24 (m, 2H), 1.74 (m, 2H), 3.85 (s, 3H), 4.15 (t, J ) 7.2 Hz, 2H), 6.98 (t, J ) 7.2 Hz, 1H), 7.14 (t, J ) 7.1 Hz, H), 7.27 (d, J ) 8.1 Hz, H), 7.44 (d, J ) 7.2 Hz, H), 7.70 (s, 1 H), 7.77 (s, 1H), 9.21 (s, 1H); 13C NMR (75 MHz, DMSO-d6) δ ppm 13.3, 18.8, 31.4, 35.8, 48.6, 116.2, 119.6, 121.1, 122.3, 123.6, 124.8, 135.7, 136.6,153.2,192.2. Elemental analysis calc. (%) for C15H19N3S2 (305.46): C 58.98, H 6.27, N 13.76. Found: C 58.84, H 6.41, N 13.52. 1-Hexyl-3-Methylimidazolium 2-Mercaptobenzothiazolate 3-[C6mim][2MBT], Liquid. 1H NMR (DMSO-d6) δ ppm 0.82 (t, J ) 7.0 Hz, 3H), 1.15 (m, 6H), 1.71 (m, 2H), 3.87 (s, 3H), 4.16 (t, J ) 7.2 Hz, 2H), 7.01 (t, J ) 5.9 Hz, 1H), 6.96 (t, J ) 7.5 Hz, 1H), 7.11 (t, J ) 8.0 Hz, 1H), 7.28 (d, J ) 8.0 Hz, 1H), 7.45 (d, J ) 7.4 Hz, 1H), 7.73 (s, 1H), 7.81 (s, 1H), 9.27 (s, 1H); 13C NMR (75 MHz, DMSO-d6) δ ppm 13.7, 21.5, 27.6, 29.1, 35.7, 38.9, 48.7, 116.2, 119.5, 120.9, 122.2, 123.6, 124.6, 135.7, 136.5, 153.8, 191.5. Elemental analysis calc. (%) for C17H23N3S2 (333.51): C 61.22, H 6.95, N 12.60. Found: C 60.94, H 6.68, N 12.38. 3-Methyl-1-Octylimidazolium 2-Mercaptobenzothiazolate 4-[C8mim][2MBT], Liquid. 1H NMR (DMSO-d6) δ ppm 0.82
10.1021/ie100151n 2010 American Chemical Society Published on Web 04/23/2010
Ind. Eng. Chem. Res., Vol. 49, No. 10, 2010
(t, J ) 7.0 Hz, 3H), 1.24 (m, 10H), 1.72 (m, 2H), 3.86 (s, 3H), 4.16 (t, J ) 7.2 Hz, 2H), 7.04 (t, J ) 5.9 Hz, 1H), 6.91 (t, J ) 7.5 Hz, H), 7.15 (t, J ) 8.0 Hz, 1H), 7.22 (d, J ) 8.0 Hz, 1H), 7.46 (d, J ) 7.4 Hz, 1H), 7.73 (s, 1H), 7.79 (s, 1H), 9.23 (s, 1H); 13C NMR (75 MHz, DMSO-d6) δ ppm 13.8, 21.5, 27.6, 28.9, 29.1, 31.7, 35.7, 38.9, 48.7, 116.2, 119.5, 120.9, 122.2, 123.6, 124.6, 135.7, 136.5, 153.8, 191.5. Elemental analysis calc. (%) for C19H27N3S2 (361.57): C 63.11, H 7.53, N 11.62. Found: C 63.05, H 7.22, N 11.29. 1-Dodecyl-3-Methylimidazolium 2-Mercaptobenzothiazolate 5-[C12mim][2MBT], Liquid. 1H NMR (DMSO-d6) δ ppm 0.82 (t, J ) 7.0 Hz, 3H), 1.25 (m, 18H), 1.72 (m, 2H), 3.86 (s, 3H), 4.16 (t, J ) 7.2 Hz, 2H), 7.04 (t, J ) 5.9 Hz, 1H), 6.91 (t, J ) 7.5 Hz, H), 7.15 (t, J ) 8.0 Hz, 1H), 7.22 (d, J ) 8.0 Hz, 1H), 7.46 (d, J ) 7.4 Hz, 1H), 7.73 (s, 1H), 7.79 (s, 1H), 9.23 (s, 1H); 13C NMR (75 MHz, DMSO-d6) δ ppm 14.8, 22.5, 26.1, 28.7, 29.0, 29.1, 29.2, 29.3, 29.6, 29.9, 31.6, 35.9, 48.7, 116.3, 119.7, 120.8, 122.2, 123.7, 124.6, 135.9, 136.4, 153.7, 191.6. Elemental analysis calc. (%) for C23H35N3S2 (417.67): C 66.14, H 8.45, N 10.06. Found: C 65.96, H 8.21, N 10.32. Tetradecyl(trihexyl)phosphonium 2-Mercaptobenzothiazolate 6-[P66614][2MBT], Liquid. 1H NMR (DMSO-d6) δ ppm 0.84 (m, 12H), 1.2 (m, 48H), 2.2 (m, 8H), 6.92 (t, J ) 8 Hz, 1H); 7.1 (t, J ) 8.3 Hz, 1H), 7.27 (d, J ) 8.5 Hz, 1H), 7.43 (d, J ) 8.7 Hz, 1H); 13C NMR (75 MHz, DMSO-d6) δ ppm 13.8, 13.9, 17.2 (d, JC,P ) 47 Hz, CH2), 17.9 (d, JC,P ) 47 Hz, 3 CH2), 20.6 (d, JC,P ) 4 Hz, 4 CH2), 21.8, 22.1, 28.1, 28.7 (d, JC,P ) 4.6 Hz, CH2), 28.9, 29.1, 29.7 (d, JC,P ) 15 Hz, 3 CH2), 29.9, 30.4, 31.3, 115.8, 119.5, 121.1, 124.7, 135.2, 152.3, 185.8. Elemental analysis calc. (%) for C39H72NPS2 (650.1): C 72.05, H 11.16, N 2.15. Found: C 71.98, H 10.95, N 1.84. Thermal Analysis. Melting points and other thermal transitions of the ILs were determined by DSC, with a Mettler Toledo Stare TGA/DSC1 (Leicester, UK) unit, under nitrogen. Samples between 5 and 15 mg were placed in aluminum pans and were heated from 25-110 °C at the heating rate of 10 °C min-1 and cooling with intracooler at cooling rate of 10 °C min-1 to -100 °C. Thermogravimetrical analysis was performed on Mettler Toledo Stare TGA/DSC1 unit (Leicester, UK) under nitrogen. Samples between 2 and 10 mg were placed in aluminum pans and were heated from 30 to 500 °C at the heating rate of 10 °C min-1. Antimicrobial Activity. The antimicrobial activity was determined by the tube dilution method and described earlier.19 The lowest concentration of compound at which there was no visible growth (turbidity) was taken as the MIC. The lowest concentration of compound supporting no colony formation was defined as the MBC. The following microorganisms were used: Micrococcus luteus NCTC 7743, Staphylococcus aureus NCTC 4163, Staphylococcus epidermidis ATCC 49134, Enterococcus faecium ATCC 49474, Moraxella catarrhalis ATCC 25238, Escherichia coli ATCC 25922, Bacillus subtilis ATCC 6633, Candida albicans ATCC 10231, and Rhodothorula rubra (Demml 1889, Lodder 1934). Standard strains were supplied by the National Collection of Type Cultures (NCTC) London and American Type Culture Collection (ATCC). Rhodothorula rubra was obtained from the Department of Pharmaceutical Bacteriology, University of Medical Sciences, Poznan. Preparation and Characterization of Rubber Compounds. Rubber compounds with general formulations given in Table 1 were prepared using a laboratory two-roll mill. Each of the samples contained NBR, sulfur, zinc oxide, stearic acid, and accelerator (synthesized ILs or 2-mercaptobenzothiazole) and
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Table 1. Compound Formulation of Different Rubbers ingredient
with ionic liquid
without ionic liquid
a
100 5
100 5 2 2 2
NBR ZnO MBTb sulfur stearic acid ionic liquid
2 2 2c
a Acrylonitrile-butadiene elastomer. b 2-Mercaptobenzothiazole. the case of [C12mim][2MBT] and [P66614][2MBT], 1 phr was added.
c
In
Scheme 1. Prepared ILs
were cured at 160 °C until they developed a 90% increase of torque (measured using an oscillating disk rheometer produced by ZACH METALCHEM). The rubber compounds with 1-butyl-3-methylimidazolium bromide 7, chloride 8, hexafluorophosphate 9, and tetrafluoroborate 10 were also prepared. The tensile properties of vulcanizates were determined according to ISO-37 with a universal machine ZWICK 1435. The cross-link density of vulcanizates was determined by equilibrium swelling in toluene, based on the Flory-Rehner equation20 using the Huggins parameter of elastomer-solvent interaction µ ) 0.381 + 0.671Vr [eq 1]. ln(1 - Vr) + Vr + µVr2 νe ) Vr Vo Vr1/3 2
(
)
(1)
where: νe - cross-link density, Vr - volume fraction of elastomer in swollen gel, Vo - molar volume of solvent [mol/cm3]. Thermal and UV Degradation of Vulcanizates. The thermal degradation of vulcanizates were performed in the temperature 70 °C for 120 h. The UV degradation of vulcanizates was carried out for 120 h using UV 2000 (Atlas) machine in two alternating segments: a day segment (irradiation 0.7 W/m2, temperature 60 °C, time 8 h) and night segment (without UV radiation, temperature 50 °C, time 4 h). 3. Results and Discussion We prepared six ILs based on 1,3-dialkylimidazolium, benzalkonium (where R ) C12H25 60% and C14H29 40%) and phosphonium cations combined with the 2-mercaptobenzothiazolate anion (Scheme 1). All of these salts were synthesized via anion-exchange reaction. Potassium chloride or bromide as a byproduct was successfully removed from an anhydrous acetone solution. The products were dried in vacuum at 80 °C for 24 h and stored over P4O10. The water content, determined by Karl Fischer measurements, was found to be less than 400 ppm. The obtained ILs were characterized by 1H and 13C NMR spectroscopy and elemental analysis CHN. Characteristic shifts for CdS bonds
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Table 2. Prepared ILs with 2-Mercaptobenzothiazolate
1 2 3 4 5 6
IL
yield [%]
X2MBTa
[BA][2MBT] [C4mim][2MBT] [C6mim][2MBT] [C8mim][2MBT] [C12mim][2MBT] [P66614][2MBT]
92 87 94 93 82 96
0.35 0.54 0.5 0.46 0.4 0.23
a
e
Tgb [°C]
Tcc [°C]
Tmd [°C] 77
-35.8 -35.3 -42.7
22 -7.75
46.8 34.7
-65.3
Tonset5%e [°C]
Tonset50% [°C]
175 210 227 225 214 330
210 250 268 268 252 365
b
Rass ratio of anion. Glass transition temp determined by DSC. c Crystallization temp determined by DSC. d Melting point determined by DSC. Decomposition temp determined from onset to 5 wt % mass loss. f Decomposition temp determined from onset to 50% mass loss.
Table 3. MIC and MBC Valuesa of Imidazolium 2-Mercaptobenzothiazolates and Their Precursors [C10mim][ Cl]b organism M. luteus S. aureus S. epidermidis E. feacium M. catarhalis E. coli B. subtilis C. albicans R. Rubra a
MIC
MBC
40 40
643 664
321
1287
[C10mim][2MBT] MIC
MBC
21 80 80 1283 320 80 159 159 41
20 1283 642 1283 642 159 1283 642 642
[C12mim][Cl]b MIC
MBC
18 36
36 145
73
73
[C12mim][2MBT] MIC
MBC
4.8 9.6 4.8 19 2.4 9.6 38 9.6 9.6
9.6 148 9.6 19 19 19 38 74 74
In micromolar. b Reference 22.
Table 4. Kinetics of Vulcanization
d
IL
Gmaxa [dNm]
Gminb [dNm]
∆Gc [dNm]
Goptd [dNm]
tvule [min]
tpf [s]
1 2 3 4 5 6 7 8 9 10 2MBT-Hg
129.4 147.1 135.7 151.3 132.7 143.7 54.2 50.7 63.7 71.2 137.0
26.7 26.2 26.8 26.8 19.1 19.1 21.2 21.1 18.4 26.3 21.7
102.7 120.9 108.9 124.5 113.6 124.6 33.0 29.6 45.3 44.9 115.3
119.1 135.0 124.8 138.8 121.3 131.2 50.9 47.7 59.2 66.7 125.5
25 45 45 50 50 50 40 45 40 40 90
62 44 46 44 62 94 60 64 73 76 130
a Maximal torque during vulcanization. b Minimal torque during vulcanization. c Increment of torque in the rubber compound during vulcanization. Optimal torque during vulcanization. e Optimal vulcanization time. f Scorch time. g 2-Mercaptobenzothiazole, standard.
were observed at about 180 ppm in the 13C NMR spectra prove that negative charge is localized on the nitrogen atom in the anion. Synthesized ILs were liquid at room temperature (salts 2, 3, and 6) with high viscosities. The physicochemical properties of all prepared compounds are presented in Table 2. As shown in Table 2 thermal stability increases in the order ammonium [BA][2MBT] > imidazolium [Cxmim][2MBT] > phosphonium [P66614][2MBT] from 175 to over 300 °C. For imidazolium salts with hexyl and octyl group 2 and 3 and for phosphonium 6 only glass transition were observed. The reduction of amount of 2-MBT to level 0.23 as in case phosphonium IL 6 or at least 0.56 is important for application of final product, because 2-mercaptobenzothiazole is known as an allergenic agent.21 As shown in Table 3, obtained salts are biocidal active against fungi C. albicans and R. Rubra, as well as gramm positive and negative bacteria. Imidazolium IL with dodecyl substituent [C12mim][2MBT] (5) is more effective then halide precursor. Results for kinetics of vulcanization are summarized in Table 4. Application of synthesized ILs resulted in a considerably shorter vulcanization time of rubber compounds in comparison with the conventional 2-mercaptobenzothiazole system. It confirmed that prepared ILs act as catalysts of interface reactions and can be applied as vulcanization accelerators. Unfortunately, ILs caused the reduction of scorch time. This might have an
adverse impact on the processing or storage of rubber compounds, due to the risk of scorching. However, some vulcanizing retarders could be applied to avoid the scorching. The values of torque increment as well as Gmax and Gmin being comparable with the standard rubber compound, confirmed that ILs act as effective accelerating agents. The dispersion of cross-linking system components (ZnO, sulfur, and accelerator) is very important for the activation of sulfur vulcanization. It is known that sulfur and accelerator diffuse inside the elastomer matrix and are adsorbed on the zinc oxide surface during vulcanization. Therefore, higher activity of synthesized ILs in vulcanization process was probably due to more homogeneous dispersion of cross-linking agents in elastomer. This was confirmed by SEM images of NBR vulcanizates (Figures 1-5). Considering the standard vulcanizate with MBT, zinc oxide particles (Figure 1) were not homogeneously distributed in the elastomer matrix. They created microsized agglomerates (about 10 µm in size). The agglomeration of zinc oxide particles caused their surface area to decrease, followed by a reduction of the interface between the zinc oxide, sulfur, and accelerator. As a result, the efficiency of elastomer cross-linking decreased. In the case of vulcanizates with prepared ILs, more homogeneous dispersion of cross-linking agents’ particles was observed (Figures 2-5). Zinc oxide formed small agglomerates about 1-2 µm in size, which were quite homogeneously distributed in the elastomer. Apart form accelerating action, ILs acted as dispersing agents
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Figure 1. SEM image of NBR vulcanizate containing 2-mercaptobenzotiazole (standard). Figure 3. SEM image of NBR vulcanizate containing ILs[C4mim][2MBT] (2).
Figure 2. SEM image of NBR vulcanizate containing ILs[BA][2MBT] (1).
preventing zinc oxide particles from agglomeration. Homogeneous dispersion of ZnO particles provided better contact between the activator and other components of the cross-linking system, resulting in higher efficiency of vulcanization. It is worth noting that commercially available 1-butyl-3methylimidazolium bromide (7), chloride (9), hexafluorophosphate (9), and tetrafluoroborate (10) exhibited lower activity in the vulcanization process compared to 2-mercaptobenzothiazolate ILs. Gmax, Gopt, and ∆G values of rubber compounds cross-linked with salts 7-10 were considerably lower than for elastomer containing synthesized ILs or standard accelerator 2-mercaptobenzothiazole (Table 4). The optimal vulcanization time for rubber compounds containing bromide (7), chloride (8), and commercially available ILs (9 and 10) was shorter compared with the standard, similarly to elastomers cross-linked with prepared ILs. The reduction of scorch time was also observed.
Figure 4. SEM image of NBR vulcanizate containing ILs[C12mim][2MBT] (5).
Mechanical properties of vulcanized rubber were tested on a Zwick 1435 apparatus. The results are summarized in Tables 5-7. Application of ILs increased the cross-link density of acrylonitrile-butadiene elastomer (NBR) vulcanizates due to the catalytic effect on the efficiency of the interface cross-linking reactions. However, vulcanizates containing conventional imidazolium ILs (9 and 10) exhibited considerably lower crosslinking density comparing with the standard or elastomer cured with prepared ILs. This confirmed that the activity of ILs in curing process highly depends on the presence of the 2-mercaptobenzothiazolate anion. Rubber vulcanized with [BA][2MBT] (1) and [C4mim][2MBT] (2) revealed higher tensile strength compared with standard vulcanizate containing 2-mercaptobeznothiazole. The lower tensile strength and elongation at break of vulcanizates
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NBR vulcanizates with ILs revealed higher thermal resistance in comparison with conventionally cross-linked rubber. However, ILs did not protect the rubber from UV degradation. The modulus increase at 100 and 200% elongation and considerable decrease of elongation at break confirmed that UV irradiation caused the further cross-linking of rubber. As a result, the crosslinking density of vulcanizates increased and their tensile strength deteriorated. It is important to note that reduction of amounts of the 2-mercaptothiazole (compared of use the pure 2-MBT and prepared ILs) in the vulcanization system generally does not influence the mechanical properties of the obtained rubber. 4. Conclusions
Figure 5. SEM image of NBR vulcanizate containing ILs[P66614][2MBT] (6).
with other synthesized or conventional ILs likely resulted from their high cross-linking density. The tensile strength of vulcanizates containing conventional 1-butyl-3-methylimidazolium salts was lower than for elastomer vulcanized with 2-mercaptobenzothiazolate ILs.
In this paper we described six novel ILs with 2-mercaptobenzothiazolate anion. The synthesis, physical properties, and antimicrobial activity of imidazolium, benzalkonium, and phosphonium ILs were reported. As shown, synthesized salts can be used as rubber vulcanization accelerators. Use of these compounds reduces the vulcanization time, which is important due to economical aspects and makes rubber more stable against thermal degradation. Moreover, applied ILs enable the reduction of the amount of 2-mercaptobenzothiazole in vulcanizates. It is very significant achievement from an environmental point of view. Additionally, the final products of vulcanization with ILs contain less of the allergenic agent, what makes the finished goods user-friendly.
Table 5. Mechanical Properties of Rubber Vulcanized with ILs IL
υea (×10-5) [mol/cm3]
SE 100%b [MPa]
SE 200%c [MPa]
SE 300%d [MPa]
TSe [MPa]
EBf [%]
1 2 3 4 5 6 7 8 9 10 2MBT-Hg
10.18 10.33 10.44 10.38 9.94 10.32 9.20 9.74 9.96 10.90 10.13
1.14 1.31 1.24 1.29 1.27 1.47 1.15 1.05 1.11 1.22 1.21
1.59 1.87 1.79 1.87 1.74 2.33 1.58 1.25 1.56 1.73 1.74
2.00 2.56 2.55 2.63 2.30 3.64 2.02 1.39 2.09 2.35 2.27
14.2 11.6 9.2 6.4 15.0 6.5 7.2 3.3 5.2 4.5 10.5
643 491 453 435 539 382 617 675 536 458 651
a Cross-linking density calculated on the basis of swelling in toluene. b Stress at 100% of elongation. c Stress at 200% of elongation. d Stress at 300% of elongation. e Tensile strength. f Elongation at break. g Standard.
Table 6. Mechanical Properties of Rubber Vulcanized with ILs after Thermal Degradation (70 °C, 120 h)
a
IL
SE 100%a [MPa]
SE 200%b [MPa]
SE 300%c [MPa]
TSd [MPa]
EBe [%]
1 2 3 4 5 6 2MBT-Hf
1.23 1.41 1.37 1.40 1.34 1.53 1.22
1.74 2.07 2.01 2.03 1.85 2.40 1.70
2.30 2.84 2.90 2.97 2.57 4.13 2.19
10.0 9.3 7.5 4.8 7.6 4.5 4.6
517 395 363 350 460 311 485
Stress at 100% of elongation. b Stress at 200% of elongation. c Stress at 300% of elongation. d Tensile strength. e Elongation at break. f Standard.
Table 7. Mechanical Properties of Rubber Vulcanized with ILs after UV Degradation (120 h)
a
IL
SE 100%a [MPa]
SE 200%b [MPa]
SE 300%c [MPa]
TSd [MPa]
EBe [%]
1 2 3 4 5 6 2MBT-Hf
1.30 1.58 1.59 1.54 1.53 1.70 1.40
1.75 2.10 2.09 2.01 2.10 1.80
2.18
2.3 2.3 2.2 2.1 2.5 2.1 2.4
315 236 225 216 259 177 341
b
c
2.31
Stress at 100% of elongation. Stress at 200% of elongation. Stress at 300% of elongation. d Tensile strength. e Elongation at break. f Standard.
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ReceiVed for reView January 22, 2010 ReVised manuscript receiVed March 25, 2010 Accepted April 16, 2010 IE100151N
