Academia.eduAcademia.edu

Figure 9 – uploaded by MD Mahbubur Rahman

See full PDFdownloadDownload figure
Figure 9. Storage modulus E’ of NBR-34 vulcanizates with 15 phr various plasticizers as a function of temperature. Table 2. Dynamic mechanical analysis (DMA) analysis of NBR-34 vulcanizates with various plasticizers

Figure 9 Storage modulus E’ of NBR-34 vulcanizates with 15 phr various plasticizers as a function of temperature. Table 2. Dynamic mechanical analysis (DMA) analysis of NBR-34 vulcanizates with various plasticizers

Related Figures (17)

1 6PPD, N-(1,3-dimethylbutyl)-N’—phenyl-p—phenylenediamine; ? CBS, N-cyclohexyl-benzothiazole-2-sulfonamide Table 1. Composition and time of addition during mixing. NBR with 34% ACN and 18% ACN were named NBR-34 and NBR-18 accordingly. The formulation of the materials, which is reported in Table 1, differs mainly in the NBR type, plasticizer types, and contents, whereas the other mixing ingredients were kept almost unchanged.
1 6PPD, N-(1,3-dimethylbutyl)-N’—phenyl-p—phenylenediamine; ? CBS, N-cyclohexyl-benzothiazole-2-sulfonamide Table 1. Composition and time of addition during mixing. NBR with 34% ACN and 18% ACN were named NBR-34 and NBR-18 accordingly. The formulation of the materials, which is reported in Table 1, differs mainly in the NBR type, plasticizer types, and contents, whereas the other mixing ingredients were kept almost unchanged.
Figure 1. Vulcanization curves of various plasticized NBR compounds. The cure characteristics were examined by using a moving disc rheometer, and the curing curves acquired from NBR-34 compounds with 15 phr of different plasticizers areshown exemplarily in Figure 1. It was clearly evident that, due to the dilution effects [20] of the plasticizers, the maximum torque Mjqx values decreased when the plasticizers were simply added. Minay is reduced gradually up to 5phr, and a significant reduction has occurred at 15 phr. Minimum torque M,,i; is comparable, independent of the type of plasticizer, as is shown in Figure 1 for NBR-34. Figure 2 gives the torque differences (AM = Minax — Minin) of NBR vulcanizate as a function of plasticizer content. The lower AM indicates one of the possible reasons for the low degree of crosslinking of compounds with a higher loading of plasticizers [4,11,29]. AM for plasticizer-loaded
Figure 1. Vulcanization curves of various plasticized NBR compounds. The cure characteristics were examined by using a moving disc rheometer, and the curing curves acquired from NBR-34 compounds with 15 phr of different plasticizers areshown exemplarily in Figure 1. It was clearly evident that, due to the dilution effects [20] of the plasticizers, the maximum torque Mjqx values decreased when the plasticizers were simply added. Minay is reduced gradually up to 5phr, and a significant reduction has occurred at 15 phr. Minimum torque M,,i; is comparable, independent of the type of plasticizer, as is shown in Figure 1 for NBR-34. Figure 2 gives the torque differences (AM = Minax — Minin) of NBR vulcanizate as a function of plasticizer content. The lower AM indicates one of the possible reasons for the low degree of crosslinking of compounds with a higher loading of plasticizers [4,11,29]. AM for plasticizer-loaded
Figure 2. Torque differences during curing of plasticized NBR compounds based on NBR-34 anc NBR-18 as a function of plasticizer content. NBR-18 is comparatively more significant than for NBR-34, as shown in Figure 2. A large number of unsaturated bonds in NBR-18 due to the butadiene monomer could be responsible for the higher degree of crosslinking [30].
Figure 2. Torque differences during curing of plasticized NBR compounds based on NBR-34 anc NBR-18 as a function of plasticizer content. NBR-18 is comparatively more significant than for NBR-34, as shown in Figure 2. A large number of unsaturated bonds in NBR-18 due to the butadiene monomer could be responsible for the higher degree of crosslinking [30].
Figure 3. Vulcanization time as a function of plasticizer content for the investigated NBR compounds. The vulcanization time of NBR compounds is shown in Figure 3. The NBR-34 vulcanizates clearly showed a lower curing time compared to the NBR-18 as well as lower difference in torque values (see Figure 2). For NBR-34, the addition of plasticizer changes the vulcanization time, and there is minimal difference between the four plasticizers. TDAE- and Mesamoll®-loaded NBR-18 showed increased cure time. However, EECO decreases the vulcanization time of NBR-18. The optimum conversion of epoxidation of bio-based plasticizers is about 90% [31]. As a result, bio-based plasticizers contain 10% fatty acid ester. The acid value of EECO is about 2.32 mg of KOH/mg, whereas the acid value of EESO is about 0.68 KOH/mg [7]. The higher acid value corresponds to the higher free fatty acid. The fatty acid acts as a co-activator during the formulation of NBR compounds [32].
Figure 3. Vulcanization time as a function of plasticizer content for the investigated NBR compounds. The vulcanization time of NBR compounds is shown in Figure 3. The NBR-34 vulcanizates clearly showed a lower curing time compared to the NBR-18 as well as lower difference in torque values (see Figure 2). For NBR-34, the addition of plasticizer changes the vulcanization time, and there is minimal difference between the four plasticizers. TDAE- and Mesamoll®-loaded NBR-18 showed increased cure time. However, EECO decreases the vulcanization time of NBR-18. The optimum conversion of epoxidation of bio-based plasticizers is about 90% [31]. As a result, bio-based plasticizers contain 10% fatty acid ester. The acid value of EECO is about 2.32 mg of KOH/mg, whereas the acid value of EESO is about 0.68 KOH/mg [7]. The higher acid value corresponds to the higher free fatty acid. The fatty acid acts as a co-activator during the formulation of NBR compounds [32].
Figure 4. Variation of tensile strength with plasticizer content for NBR vulcanizates. reported in [4]. However, our own examinations of the macro-dispersion index gave no correlation with the tensile strength values for increasing amount of plasticizer. The tensile strength of bio-based plasticized NBR-34 is slightly higher compared to NBR-18. One possible reason for this is the higher polarity of NBR-34 due to higher content of ACN compared to NBR-18 [33]. The conventional plasticizers do not contain any OH groups, and therefore, compatibility with a polar polymer-like NBR [14] is restricted, leading to a lower tensile strength.
Figure 4. Variation of tensile strength with plasticizer content for NBR vulcanizates. reported in [4]. However, our own examinations of the macro-dispersion index gave no correlation with the tensile strength values for increasing amount of plasticizer. The tensile strength of bio-based plasticized NBR-34 is slightly higher compared to NBR-18. One possible reason for this is the higher polarity of NBR-34 due to higher content of ACN compared to NBR-18 [33]. The conventional plasticizers do not contain any OH groups, and therefore, compatibility with a polar polymer-like NBR [14] is restricted, leading to a lower tensile strength.
Figure 5. Variation of strain at the break with plasticizer content for NBR vulcanizates.
Figure 5. Variation of strain at the break with plasticizer content for NBR vulcanizates.
Figure 6. Dependence of tear strength on plasticizer content for NBR vulcanizates. The tear strength values (see Figure 6) show a significant increase in the case of bio-based plasticizers, especially at higher plasticizer loading. In the case of TDAE and Mesamoll®, the tear strength remains almost constant at around 8 N/mm. In contrast, the bio-based plasticized NBR compounds showed an increase of up to 9 to 11 N/mm at 15 phr loading range. Tearing of NBR vulcanizate occurs due to the propagation of cracks initiated at the stress concentration point through the wearing of rubber molecules at the NBR-carbon black interfaces [10]. The micro-plasticization of the interfaces using an effective plasticizer can hinder the propagation of cracks [36]. The tear strength is not much influenced by increasing amount of conventional plasticizers.
Figure 6. Dependence of tear strength on plasticizer content for NBR vulcanizates. The tear strength values (see Figure 6) show a significant increase in the case of bio-based plasticizers, especially at higher plasticizer loading. In the case of TDAE and Mesamoll®, the tear strength remains almost constant at around 8 N/mm. In contrast, the bio-based plasticized NBR compounds showed an increase of up to 9 to 11 N/mm at 15 phr loading range. Tearing of NBR vulcanizate occurs due to the propagation of cracks initiated at the stress concentration point through the wearing of rubber molecules at the NBR-carbon black interfaces [10]. The micro-plasticization of the interfaces using an effective plasticizer can hinder the propagation of cracks [36]. The tear strength is not much influenced by increasing amount of conventional plasticizers.
Figure 7. Shore A hardness values as a function of plasticizer content for NBR vulcanizates.
Figure 7. Shore A hardness values as a function of plasticizer content for NBR vulcanizates.
Figure 8. Compression set (CS)values as a function of plasticizer content for NBR vulcanizates. Figure 8 shows the CS values of different oil content of two NBR vulcanizates. Both types of NBR with bio-based plasticizers have a higher CS, which increases with oil content. The use of Mesamoll® and TDAE results in a more or less unchanged CS. A previous study [4] proved that in a rubber vulcanizate with low oil content, the filler dispersion was poor, but at higher oil content, the plasticizing effect and segmental mobility were pronounced, leading to higher CS values [4]. In a previous study [11], compression set values correlated to the hardness values. The highest CS was found for the material with the lowest hardness. Here, the same effect could be found. A low CS value represents a better recovery behavior after load release. However, the bio-based plasticizers show a maximum CS value of ~12%; this is still a low value compared to the threshold, which is ~40% for a gasket [37].
Figure 8. Compression set (CS)values as a function of plasticizer content for NBR vulcanizates. Figure 8 shows the CS values of different oil content of two NBR vulcanizates. Both types of NBR with bio-based plasticizers have a higher CS, which increases with oil content. The use of Mesamoll® and TDAE results in a more or less unchanged CS. A previous study [4] proved that in a rubber vulcanizate with low oil content, the filler dispersion was poor, but at higher oil content, the plasticizing effect and segmental mobility were pronounced, leading to higher CS values [4]. In a previous study [11], compression set values correlated to the hardness values. The highest CS was found for the material with the lowest hardness. Here, the same effect could be found. A low CS value represents a better recovery behavior after load release. However, the bio-based plasticizers show a maximum CS value of ~12%; this is still a low value compared to the threshold, which is ~40% for a gasket [37].
Figure 10. Loss modulus E” of NBR-34 vulcanizates with 15 phr various plasticizers as a function of temperature.
Figure 10. Loss modulus E” of NBR-34 vulcanizates with 15 phr various plasticizers as a function of temperature.
Figure 11. Mechanical loss factor tan 6 of NBR-34 vulcanizates with 15 phr various plasticizers as a function of temperature. plasticizers have higher values of tan 6 compared to NBR/TDAE or NBR/Mesamoll®. According to previous studies [38,39], the values of tan 6 and E’ predicts rubber performance. The maximum of tan 5 of the compounds is shifted to lower values in the case of the bio-based plasticizers EESO and EECO as well as the synthetic plasticizer Mesamoll®. This is due to the lower Tg values of these plasticizers. For practical application, a lower T, can be of importance, because molecular mobility starts at lower temperatures. This means, the flexibility of the material is given in a larger temperature range. Further, because of the viscoelasticity, a mechanical material loading with higher frequencies can lead to a shift of Tg to higher temperatures. Therefore, materials with basically lower Tg are advantageous. The heights of the tan 6 peak are not strongly different for the different plasticizers This means, the energy loss in the network is comparable.
Figure 11. Mechanical loss factor tan 6 of NBR-34 vulcanizates with 15 phr various plasticizers as a function of temperature. plasticizers have higher values of tan 6 compared to NBR/TDAE or NBR/Mesamoll®. According to previous studies [38,39], the values of tan 6 and E’ predicts rubber performance. The maximum of tan 5 of the compounds is shifted to lower values in the case of the bio-based plasticizers EESO and EECO as well as the synthetic plasticizer Mesamoll®. This is due to the lower Tg values of these plasticizers. For practical application, a lower T, can be of importance, because molecular mobility starts at lower temperatures. This means, the flexibility of the material is given in a larger temperature range. Further, because of the viscoelasticity, a mechanical material loading with higher frequencies can lead to a shift of Tg to higher temperatures. Therefore, materials with basically lower Tg are advantageous. The heights of the tan 6 peak are not strongly different for the different plasticizers This means, the energy loss in the network is comparable.
Table 3. Results of TGA of NBR-34 vulcanizates with various plasticizers. Polarized microscopy olasticizers that influenced he optical pictures of the was performed as a helpful tool for better understanding the extent of the the dispersion within CB-reinforced NBR vulcanizates. Figure 13 shows investigated cross section areas of plasticized NBR vulcanizates. Here Figure 13a shows a higher number of agglomerates compared to Figure 13b, but the size of agglomerates s smaller. A previous study [43] stated that the plasticizer decreases the shear stress between the CE occluded by the polymer c hain. When the polymer is mixed, the polymer molecules have to slip over 2ach other, which is the reason for more agglomerates remaining [15]. Here, the optical observation fo! Vesamoll®- and EESO-load [DAE. TDAE-loaded NBR ed NBR vulcanizates indicate a more homogeneous appearance compared tc vulcanizate is depicted in Figure 13c. When the plasticizers were not well lispersed among the matrix, then the number of agglomerates decreased. This phenomenon is callec untiplasticization [14]. Figure 13d shows TDAE coagulates within the polymer matrix inhomogeneousl} rear the edge.
Table 3. Results of TGA of NBR-34 vulcanizates with various plasticizers. Polarized microscopy olasticizers that influenced he optical pictures of the was performed as a helpful tool for better understanding the extent of the the dispersion within CB-reinforced NBR vulcanizates. Figure 13 shows investigated cross section areas of plasticized NBR vulcanizates. Here Figure 13a shows a higher number of agglomerates compared to Figure 13b, but the size of agglomerates s smaller. A previous study [43] stated that the plasticizer decreases the shear stress between the CE occluded by the polymer c hain. When the polymer is mixed, the polymer molecules have to slip over 2ach other, which is the reason for more agglomerates remaining [15]. Here, the optical observation fo! Vesamoll®- and EESO-load [DAE. TDAE-loaded NBR ed NBR vulcanizates indicate a more homogeneous appearance compared tc vulcanizate is depicted in Figure 13c. When the plasticizers were not well lispersed among the matrix, then the number of agglomerates decreased. This phenomenon is callec untiplasticization [14]. Figure 13d shows TDAE coagulates within the polymer matrix inhomogeneousl} rear the edge.
Figure 12. TGA thermograms of NBR-34 vulcanizates with various plasticizers.
Figure 12. TGA thermograms of NBR-34 vulcanizates with various plasticizers.
Figure 13. Cross-sectional view of different vulcanized rubber samples; (a) NBR-34 vulcanizate with 15 phr EESO, (b) NBR-34 vulcanizate with 15 phr Mesamoll®, (c) NBR-34 vulcanizate with 15 phr TDAE (middle of the samples), (d) NBR-34 vulcanizate with 15 phr TDAE (circles mark oil). Figure 13. Cross-sectional view of different vulcanized rubber samples; (a) NBR-34 vulcanizate with
Figure 13. Cross-sectional view of different vulcanized rubber samples; (a) NBR-34 vulcanizate with 15 phr EESO, (b) NBR-34 vulcanizate with 15 phr Mesamoll®, (c) NBR-34 vulcanizate with 15 phr TDAE (middle of the samples), (d) NBR-34 vulcanizate with 15 phr TDAE (circles mark oil). Figure 13. Cross-sectional view of different vulcanized rubber samples; (a) NBR-34 vulcanizate with
Figure 14. Dependence of tensile strength on aging temperature for NBR-34 vulcanizate with various plasticizers.
Figure 14. Dependence of tensile strength on aging temperature for NBR-34 vulcanizate with various plasticizers.
Figure 15. Shore A hardness as a function of aging temperature for NBR-34 vulcanizates with various plasticizers.
Figure 15. Shore A hardness as a function of aging temperature for NBR-34 vulcanizates with various plasticizers.
Figure 16. Compression set as a function of aging temperature for NBR-34 vulcanizates with various plasticizers.
Figure 16. Compression set as a function of aging temperature for NBR-34 vulcanizates with various plasticizers.
Related topics:
EngineeringMaterials ScienceMedicine
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved