Design of EPDM for blends with NR/BR for tire sidewalls: Influence of molecular structure and carbon black distribution on properties.Ever since the development of EPDM rubber EPDM rubber (ethylene propylene diene monomer rubber) is an elastomer which is characterized by wide range of applications. EPDM rubber is used in vibrators and seals; glass-run channel; radiator, garden and appliance hose; tubing; washers; belts; and electrical insulation. , its use in tires has been a major challenge. In the early days of its existence, the 1960s, this rubber was considered an ozone-resistant alternative for SBR SBR - Spectral Band Replication rubber for whole tires. Indeed, complete tires were built based on EPDM EPDM Ethylene-Propylene-Diene-Monomer EPDM Enterprise Product Data Management EPDM Ethylene Propylene Dimonomer (industrial/commercial piping/plumbing components) EPDM Engineering Product Data Management . The penetration of EPDM in this application has never happened because of insufficient performance - mainly wear resistance, cut growth and rolling resistance Rolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when an object such as a ball or tire rolls. It is caused by the deformation of the wheel or tire or the deformation of the ground. . On top of that, the absence of tack was experienced as a major problem in tire building, although by proper selection of polymer variables this could be overcome to a large extent (ref. 1). Later, attention was focused on the application of EPDM rubber in blends with NR, SBR and BR, mainly with the intention to improve the ozone resistance of the latter, to avoid the use of antiozonants or waxes. This pertains in particular to that part of a tire which is in continuous direct contact with the outside air and subject to large dynamic deformations - the sidewall side·wall n. 1. A wall that forms the side of something. 2. A side surface of an automobile tire, between the edge of the tread and the wheel rim. Noun 1. . It is a common experience that about 30-40 phr EPDM is required in conventional tire sidewall compounds in order to `repair' for the loss of ozone-resistance by the omission omission n. 1) failure to perform an act agreed to, where there is a duty to an individual or the public to act (including omitting to take care) or is required by law. Such an omission may give rise to a lawsuit in the same way as a negligent or improper act. of the antiozonants (ref. 2). The inclusion of EPDM, in its turn, creates another problem - the fatigue fatigue, in engineering fatigue, in engineering, microscopic cracking of materials, especially metals, after repeated applications of stress. Fissures may be formed within pieces of metal during their manufacture when, while cooling from the molten state, and cut growth resistance of the tire. This is commonly blamed on the low unsaturation un·sat·u·rat·ed adj. 1. Of or relating to an organic compound, especially a fatty acid, containing one or more double or triple bonds between the carbon atoms. 2. Capable of dissolving more of a solute at a given temperature. level of the EPDM, compared to NR or BR, so that in the blend, either the EPDM is under-cured or the highly unsaturated unsaturated /un·sat·u·rat·ed/ (un-sach´ur-at?ed) 1. not holding all of a solute which can be held in solution by the solvent. 2. denoting compounds in which two or more atoms are united by double or triple bonds. rubber components are over-cured. Traditionally, solutions out of this dilemma have been sought in selecting EPDM grades which have a high level of unsaturation (ethylidene-nor-bornene content, most commonly) and a molecular weight as high as possible, as reflected by a very high Mooney viscosity. The resulting problems with mixing were then corrected by blending the polymer with extender See Media Center Extender, bus extender and DOS extender. oil (ref. 3). Extensive work has been done in the past to overcome this cure-incompatibility by the selection of proper curatives, with little success (ref. 4). Further, the selection of the high Mooney viscosity EPDM grade creates again another problem - the mixing of all components. A poor dispersion dispersion, in chemistry dispersion, in chemistry, mixture in which fine particles of one substance are scattered throughout another substance. A dispersion is classed as a suspension, colloid, or solution. of the EPDM in the other rubber components negatively influences the beneficial effects of the EPDM in the first place. Considerations not commonly taken along in finding ways out of this vicious circle vi·cious circle n. A condition in which a disorder or disease gives rise to another that subsequently affects the first. are that the addition of EPDM to NR and/or BR creates phases with intrinsic intrinsic /in·trin·sic/ (in-trin´sik) situated entirely within or pertaining exclusively to a part. in·trin·sic adj. 1. Of or relating to the essential nature of a thing. 2. polarity (1) The direction of charged particles, which may determine the binary status of a bit. (2) In micrographics, the change in the light to dark relationship of an image when copies are made. and viscosity differences. This has a strong effect on carbon black distribution, because it is well known that most carbon black tends to end up in the NR/BR phase and little, if any, in the EPDM phase (ref. 5). Consequently, the EPDM phase behaves as if being non-reinforced. Similarly, curatives tend to migrate to the more polar NR/BR phase, which makes the EPDM even more under-cured than it already is. It is a challenging job to find a way out of this endless list of problems. The purpose of this article is to step away from the traditional approach of seeking solutions via a high unsaturation and high molecular weight of the EPDM. We will determine which molecular parameters of EPDM govern the fatigue and cut growth resistance in tire sidewall blends. This is done on straight compounds containing blends of the various rubbers, as well as on compounds in which the majority of the carbon black has been masterbatched first into the EPDM before this is mixed with the other polymers. This is done in order to enhance the carbon black level of the EPDM phase in the blend. The ultimate aim is then to find a new way out of this long challenging problem. Experimental Materials A series of commercial EPDM grades was taken along in this study, as given in table 1 with their molecular composition and structural characteristics. An experimental grade was added to this list, corresponding to the common perception of an EPDM grade suited for tire-sidewall applications - high unsaturation and very high molecular weight, as represented by a Mooney viscosity ML(1+4) 150 [degrees] C of 75, even though the polymer is extended with 50 phr paraffinic oil. Table 1 - compositional and structural characteristics of EPDM polymer samples EPDM A B C D E Ethylene content [wt %] 46 53 53 66 65 Propylene content [wt %] 47 41 40 27 28 ENB content [wt %] 5 5 5 5 5 DCPD content [wt %] 2 2 2 2 2 Oil content [phr] Polymer Mooney ML(1+4) at 125 [degrees] C 34 45 64 32 47 ML(1+4) at 150 [degrees] C Mn x [10.sup.3] 37 47 36 38 42 Mw x [10.sup.3] 217 160 214 142 172 Mz x [10.sup.3] 900 450 680 350 470 Mw/Mn 6 4 6 4 4 EPDM F G H I Exp. Ethylene content [wt %] 65 51 50 49 67 Propylene content [wt %] 28 38 38 40 26 ENB content [wt %] 5 9 9 9 9 DCPD content [wt %] 2 2 2 2 Oil content [phr] 50 Polymer Mooney ML(1+4) at 125 [degrees] C 63 35 45 61 ML(1+4) at 150 [degrees] C 75 Mn x [10.sup.3] 37 39 38 33 200 Mw x [10.sup.3] 182 140 160 235 450 Mz x [10.sup.3] 530 420 500 790 1,000 Mw/Mn 5 4 4 7 2.3 Compound recipes A compound recipe was used consisting of a blend of NR, BR and EPDM, as given in table 2, typical for tire sidewall purposes. For the experimental grade, an adjustment needed to be made in the recipe to correct for the 50 phr oil extension. Unfortunately, this resulted in an additional paraffinic oil level in that recipe of 17.5 phr. vs. de 8.75 phr in the standard recipe. It needs to be anticipated that this may give rise to certain systematic differences.
Table 2 - NR/BR/EPDM recipes for tire sidewalls
Straight recipes
Ingredients (phr) Rec. 1 Rec. 2
EPDM A-1 35.00
EPDM experimental 52.50
NR TSR 20 30.00 30.00
BR 1207 35.00 35.00
ZnO (UM) 3.00 3.00
Stearic acid 1.00 1.00
Carbon black N-550 50.00 50.00
Par. oil Sunpar 2280 8.75 --
Na. oil Sunthene 4240 12.00 12.00
DPG-80 0.20 0.20
TBBS 0.70 0.70
S-80% 1.50 1.50
Total phr 177.15 185.90
Masterbatch recipes
Ingredients (phr) Rec. 3 Rec. 4 Rec. 5
EPDM B, C, E, F 100.00
EPDM experimental 150.00
NR TSR 20 46.20
BR 1207 53.80
ZnO (UM) 3.00 3.00 3.00
Stearic acid 1.00 1.00 1.00
Carbon black N-550 100.00 100.00 23.10
Par. oil Sunpar 2280 25.00
Na. oil Sunthene 4240 12.00 12.00 12.00
DPG-80 0.20 0.20 0.20
TBBS 0.70 0.70 0.70
S-80% 1.50 1.50 1.50
Total phr 243.40 268.40 141.50
Rec. 6 Rec. 7
Compounds
Rec. 4 (EPDM Exp.) 96.95
Rec. 5 (NR/BR) 91.97 91.97
Rec. 3 (EPDM B, C, E, E) 88.20
Total phr 180.17 188.92
As a reference compound, a third recipe was used representing a commercial NR/BR compound used for tire sidewalls, which was kindly disclosed for the purpose of this study, but cannot be mentioned here for proprietary reasons. Mixing The mixing procedure of straight compound recipes I and II consisted of two steps. First, the compounds were mixed without curatives in a Werner and Pfleiderer GK2 tangential tan·gen·tial also tan·gen·tal adj. 1. Of, relating to, or moving along or in the direction of a tangent. 2. Merely touching or slightly connected. 3. internal mixer mixer, either of two electronic devices in which two or more signals are combined. In the type of mixer used in radio receivers, radar receivers, and similar systems, a signal is translated upward or downward in frequency. : batch weight approx. 3 kg.: * Step 1: 0-30 seconds: load bale bale 1. a package of wool in a wool pack weighing 150-250 lb depending largely on whether it is greasy or scoured. 2. a compressed bundle of hay, either about 100 lb tied with wire or twine, or large, round, untied bales, as big as a small hay stack and referred to as 'big bales'. polymers and masticate mas·ti·cate v. To chew food. mas  ti·ca tion n. or
disintegrate dis·in·te·grate v. dis·in·te·grat·ed, dis·in·te·grat·ing, dis·in·te·grates v.intr. 1. To become reduced to components, fragments, or particles. 2. till; * Step 2: 30-40 seconds: addition of the other ingredients; * Step 3: 40~350 seconds: further mixing till 160 [degrees] C and dump on two-roll mill for addition of curatives according to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. ISO (1) See ISO speed. (2) (International Organization for Standardization, Geneva, Switzerland, www.iso.ch) An organization that sets international standards, founded in 1946. The U.S. member body is ANSI. 4097 [2] procedure. Second, vulcanization vulcanization (vŭl'kənəzā`shən), treatment of rubber to give it certain qualities, e.g., strength, elasticity, and resistance to solvents, and to render it impervious to moderate heat and cold. ingredients were added on an open mill. For the EPDM carbon black masterbatch recipes, three mixing stages were used. During a first mixing step, the individual EPDM and NR/BR masterbatches were mixed in a so-called Y-mixing procedure. The EPDM masterbatch contained 70% of the overall loading of carbon black in the final compound. Then, after conditioning for one day, a short two minutes remix re·mix tr.v. re·mixed, re·mix·ing, re·mix·es To recombine (audio tracks or channels from a recording) to produce a new or modified audio recording: stage followed of the EPDM and NR/BR masterbatches using the internal mixer. Next, the compounds were dumped dump v. dumped, dump·ing, dumps v.tr. 1. To release or throw down in a large mass. 2. a. on an open mill for addition of the vulcanization ingredients. Vulcanization The compounds were vulcanized vul·ca·nize tr.v. vul·ca·nized, vul·ca·niz·ing, vul·ca·niz·es To improve the strength, resiliency, and freedom from stickiness and odor of (rubber, for example) by combining with sulfur or other additives in the presence of heat by pressing them between preheated metal plates with 2 and 6 mm spacers in a press for a period of t'90 + 10% minutes at 160 [degrees] C. This corresponds to the average time needed to reach 90% vulcanization + 10% time as determined by an oscillating os·cil·late intr.v. os·cil·lat·ed, os·cil·lat·ing, os·cil·lates 1. To swing back and forth with a steady, uninterrupted rhythm. 2. disc rheometer rhe·om·e·ter n. An instrument for measuring the flow of viscous liquids, such as blood. . Specimens were mechanically cut out of the square vulcanized plates. Testing Characterization tests In computer programming, a characterization test is a means to describe (characterize) the actual behavior of an existing piece of software, and therefore protect existing behavior of legacy code against unentended changes via automated testing. were done according to established ISO standards This is a list of ISO standards that are discussed in Wikipedia articles. For a list of all the more than 16,000 ISO standards (as of 2007), see the ISO Catalogue. About 300 of the standards produced by ISO and IEC's Joint Technical Committee 1 (JTC1) have been made freely/publicly where possible. Mooney measurements on the compounds were performed according to ISO 289-1985, using a temperature of 100 [degrees] C. Results are given as ML (1+4) 100 [degrees] C. Vulcanization characteristics were measured with an oscillating disc rheometer according to ISO 3417-1977, at a temperature of 160 [degrees] C and with 3 [degrees] amplitude amplitude (ăm`plĭt  d'), in physics, maximum displacement from a zero value or rest position. of oscillation OscillationAny effect that varies in a back-and-forth or reciprocating manner. Examples of oscillation include the variations of pressure in a sound wave and the fluctuations in a mathematical function whose value repeatedly alternates above and below some . Tensile tensile, adj having a degree of elasticity; having the ability to be extended or stretched. stress-strain properties were measured according to ISO 37-1977, using Type 2 test pieces. Tear strength measurements were done on Delft Delft (dĕlft), city (1994 pop. 91,941), South Holland prov., W Netherlands. It has varied industries and is noted for its ceramics (china, tiles, and pottery) known as delftware. Founded in the 11th cent. test pieces according to ISO 816-1983 and on angle nicked (ISO 34 B(b)) and angle un-nicked (ISO 34 B(a)). Rebound rebound (rē´bownd), n/v 1. a recovery from illness. n 2. an outbreak of fresh reflex activity after withdrawal of a stimulus rebound adjective resilience resilience (r  ·zilˑ·yens),n was measured according to ISO 4662-1978, using a Schob pendulum. Compression set measurements were performed according to ISO 815-1972 at two different conditions, namely 70 h. at 23 [degrees] C with 25% compression and 22 h. at 70 [degrees] C with 25% compression. Results Straight mixes The results of the straight (non-masterbatched) mixes of the various EPDM polymers are compared in table 3 for the compound Mooney and cure properties, and table 4 for the vulcanized properties. All are compared to the NR/BR reference compound.
Table 3 - compound Mooney viscosity and cure properties of NR/BR/EPDM
compounds (straight mixing)
EPDM A B C D E
Mooney ML (1+4)
100 [degrees] C
ML [MU] 43 47 51 48 50
Slope [-] 0.508 0.494 0.476 0.515 0.516
Rheometer, 3 [degrees]
arc, 160 [degrees] C
ML [N.m] 1.2 1.2 1.4 1.3 1.4
ts2 [min.] 5.5 5.9 5.6 5.5 5.5
t'c(90) [min.] 9.5 10.1 9.3 9.5 9.5
MH [N.m] 5.3 5.5 5.8 5.8 5.8
EPDM F G H I NR/BR
Mooney ML (1+4)
100 [degrees] C
ML [MU] 54 42 46 50
Slope [-] 0.482 0.518 0.499 0.482
Rheometer, 3 [degrees]
arc, 160 [degrees] C
ML [N.m] 1.5 1.2 1.3 1.4 1.7
ts2 [min.] 5.4 5.5 5.8 5.6 5.1
t'c(90)[min.] 9.2 9.6 10.0 9.8 10.2
MH [N.m] 6.2 5.6 5.6 6.0 6.6
Table 4 - physical properties of NR/BR/EPDM compounds (straight mixing)
EPDM A B C D E
Hardness [A] 53 54 54 58 57
Tensile strength dumb-bell 2 [MPa] 9.3 10.4 9.8 10.6 11.4
M100 [MPa] 1.7 1.7 1.8 2.0 1.8
M300 [MPa] 6.7 6.4 6.5 7.3 6.7
Elongation [%] 410 477 447 439 526
Tear strength/Delft/SLT [N] 33 32 30 55 51
Tear strength angle unnicked [kN/m] 24 25 33 34 32
Tear strength angle nicked [kN/m] 12 12 26 22 25
Compression set ISO type B
22 hours at -25
[degrees] C [%] 54 54 57 71 72
70 hours at 23 [degrees] C [%] 13 14 14 25 23
22 hours at 70 [degrees] C [%] 22 24 24 22 23
Resilience (Schob) [%] 58 58 59 59 59
Monsanto Tel-Tack 2-7 hrs. [Ounce] 21 22 18 16 15
EPDM F G H I NR/BR
Hardness 59 54 55 56 55
Tensile strength dumb-bell 2 13.2 10.5 10.7 11.2 17.1
M100 2.0 1.8 1.7 1.8 1.5
M300 7.4 7.0 6.6 7.0 6.6
Elongation 555 432 481 465 631
Tear strength/Delft/SLT 78 34 30 35 81
Tear strength angle unnicked 38 25 26 28 40
Tear strength angle nicked 36 12 15 13 52
Compression set ISO type B
22 hours at -25
[degrees] C 70 46 51 45 93
70 hours at 23 [degrees] C 26 14 14 15 8
22 hours at 70 [degrees] C 25 23 24 25 20
Resilience(Schob) 60 58 58 59 58
Monsanto Tel-Tack 2-7 hrs. 12 21 20 18 34
The results of the physical properties (table 4) have been statistically evaluated using Statgraphics multiple regression Multiple regression The estimated relationship between a dependent variable and more than one explanatory variable. software. Only models and those experimental parameters with a significance level [is greater than] 95% (p-value p-value, n in statistics, the probability that a random variable will be found to have a value equal to or greater than the observed value by chance alone. This value provides an objective basis from which to assess the relative change in the data. [is less than] 0.05) and a students t-value [is greater than] 4 were validated val·i·date tr.v. val·i·dat·ed, val·i·dat·ing, val·i·dates 1. To declare or make legally valid. 2. To mark with an indication of official sanction. 3. . The results of these statistical regression Noun 1. statistical regression - the relation between selected values of x and observed values of y (from which the most probable value of y can be predicted for any value of x) regression toward the mean, simple regression, regression analyses are depicted de·pict tr.v. de·pict·ed, de·pict·ing, de·picts 1. To represent in a picture or sculpture. 2. To represent in words; describe. See Synonyms at represent. in figures 1-6 for hardness, tear strength Delft, tear strength angle nicked/un-nicked, rebound resilience and Monsanto TEL TEL Telephone TEL Telegram TEL Telugu (langauge) TEL Terrorist Exclusion List TEL Technology-Enhanced Learning TEL Transporter-Erector-Launcher TEL Tetra-Ethyl Lead TEL Team Deutsche Telekom tack. Depicted are the observed values of the pertinent PERTINENT, evidence. Those facts which tend to prove the allegations of the party offering them, are called pertinent; those which have no such tendency are called impertinent, 8 Toull. n. 22. By pertinent is also meant that which belongs. Willes, 319. properties against the ones predicted on the basis of the linear regression Linear regression A statistical technique for fitting a straight line to a set of data points. . Only these molecular parameters are taken along in the prediction, which show significance in the correlation and therefore are significantly contributing to the property. These parameters are listed under the figures. Because the other parameters may still play, be it an insignificant role in the property involved, the correlation between the observed and predicted values is usually subject to some scatter scat·ter v. 1. To cause to separate and go in different directions. 2. To separate and go in different directions; disperse. 3. To deflect radiation or particles. n. , en-larged by the fact that the range of the plots is usually only very small. Further, two populations of data are commonly observed, related to two series of polymers, one with high and another with low ethylene ethylene (ĕth`əlēn') or ethene (ĕth`ēn), H2C=CH2, a gaseous unsaturated hydrocarbon. It is the simplest alkene. content (table 1).
Figure 1 - multivariate analysis of the hardness
Predicted
Independent variable Coefficient Std. t- Sign. level
error value (p-value)
Constant 42.5 2.8 15.1 0.000
Ethylene content 0.237 0.050 4.69 0.002
Figure 2 - multivariate analysis of tear strength delft
Predicted
Independent variable Coefficient Std. t- Sign. level
error value (p-value)
Constant -57.2 24.64 -2.32 0.053
Ethylene content 1.795 0.44 4.06 0.005
Figure 3 - multivariate analysis of tear strength
angle un-nicked
Predicted
Independent variable Coefficient Std. t- Sign. level
error value (p-value)
Constant -7.44 5.46 -1.36 0.22
Ethylene content 0.522 0.09 5.80 0.001
Polymer Mooney 0.169 0.05 3.16 0.019
Figure 4 - multivariate analysis of tear strength
angle nicked
Predicted
Independent variable Coefficient Std. t- Sign. level
error value (p-value)
Constant -41.62 11.62 -3.58 0.012
Ethylene content 0.828 0.19 4.32 0.005
Polymer Mooney 0.319 0.114 2.80 0.031
Figure 5 - multivariate analysis of the rebound resilience
Predicted
Independent variable Coefficient Std. t- Sign. level
error value (p-value)
Constant 51.91 0.977 53.15 0.000
Ethylene content 0.091 0.014 6.62 0.001
Polymer Mooney 0.37 0.080 4.56 0.004
Figure 6 - multivariate analysis of the Monsanto
Tel-tack after 2-7 hours (average value)
Predicted
Independent variable Coefficient Std. t- Sign. level
error value (p-value)
Constant 48.79 4.19 11.65 0.000
Ethylene content -0.445 0.058 -7.60 0.0003
Mw/Mn -1.268 0.345 -3.68 0.0104
The data obtained for the straight mixes, as seen in table 4, deviate considerably from the values obtained for the commercial NR/BR tire sidewall compound, as indicated with NR/BR in this table. For all polymers, the properties which closely relate to tear, like tensile strength tensile strength Ratio of the maximum load a material can support without fracture when being stretched to the original area of a cross section of the material. When stresses less than the tensile strength are removed, a material completely or partially returns to its , the various tear strength tests, etc., are way below the values obtained for the NR/BR compound. Compression sets for the EPDM-containing compounds are equal at 70 [degrees] C, somewhat worse at room temperature and much better at -25 [degrees] C than the NR/BR compound. The latter obviously because of the occurrence of crystallinity Crystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. In a gas, the relative positions of the atoms or molecules are completely random. in the NR phase at these low temperatures. Resilience is comparable to the NR/BR mix. Tack is about 2/3 of the NR/BR mixes for amorphous Unorganized or vague. A lack of structure. For example, the amorphous state of a spot on a rewritable optical disc means that the laser beam will not be reflected from it, which is in contrast to a crystalline state which will reflect light. See crystalline. EPDM grades; 1/2 for crystalline Like a crystal. It implies a uniform structure of molecules in all dimensions. For example, phase change technology, widely used for rewritable optical discs, uses crystalline spots (bits) to reflect the laser beam. Amorphous, non-crystalline bits do not reflect light. grades. As to the molecular parameters that significantly influence the various properties, figures 1-6 show that it is primarily the ethylene content of EPDM which controls the particular property. Only in the case of the angle nicked/un-nicked tear strength tests is the molecular weight of the polymers, as given by the Mooney viscosity, is also involved. In the cases of the resilience and tack, it is only the ethylene content and the molecular weight distribution of the EPDM which contribute significantly. Overall, the surprising result is that the unsaturation level of the EPDM grade does not show up in either one of the properties investigated. This already puts considerable doubt on the common assumption that apart from a high molecular weight, a high unsaturation is also needed for EPDM grades to be blended with NR and BR. Masterbatching The much lower properties of the straight compounds compared with the NR/BR reference led us to investigate whether this could be due, at least partially, to improper
Tables 5 and 6 show data for the masterbatched compounds, to be compared with the data in tables 3 and 4, respectively. Tables 5 and 6 also contain the data obtained on an experimental grade, supposed to be "the ultimate choice" based on common perception: High molecular weight; high ethylene content; high unsaturation level. We limited the number of other EPDM grades to only those which had shown some promise in the first series of experiments. Given the limited number of EPDM grades, a statistical regression was therefore not considered useful. Table 5 - compound Mooney and cure properties of NR/BR/EPDM compounds (masterbatches) EPDM B C E F Exp. NR/BR Mooney ML (1+4) 100 [degrees] C ML [MU] 43 46 45 47 62 Slope [-] 0.520 0.524 0.541 0.529 0.531 Rheometer, 3 [degrees] arc, 160 [degrees] C ML [N.m] 1.2 1.2 1.2 1.3 1.6 1.7 ts2 [min.] 6.5 6.3 6.2 6.2 2.2 5.1 t'c(90) [min.] 10.6 10.4 10.3 10.5 13.0 10.2 MH [N.m] 4.6 4.7 4.7 5.1 5.4 6.6 Table 6 - physical properties of NR/BR/EPDM compounds (masterbatches) EPDM B C E Hardness [A] 48 48 53 Tensile strength dumbbell 2 [MPa] 9.9 10.1 10.7 M100 [MPa] 1.2 1.2 1.4 M300 [MPa] 3.4 3.4 4.3 Elongation [%] 692 713 673 Tear strength/Delft/SLT [N] 40 48 56 Tear strength angle unnicked [kN/m] 25 26 33 Tear strength angle nicked [kN/m] 18 19 25 Compression setm ISO type B 22 hours at -25 [degrees] C [%] 64 63 76 70 hours at 23 [degrees] C [%] 15 14 25 22 hours at 70 [degrees] C [%] 29 28 30 Resilience (Schob) [%] 55 56 57 Monsanto Tel-Tack 2-7 hrs. [Ounce] 24 24 22 EPDM F Exp. NR/BR Hardness 57 53 55 Tensile strength dumbbell 2 13.0 17.4 17.1 M100 1.5 1.3 1.5 M300 5.1 4.6 6.6 Elongation 700 753 631 Tear strength/Delft/SLT 81 37 81 Tear strength angle unnicked 37 37 40 Tear strength angle nicked 35 33 52 Compression setm ISO type B 22 hours at -25 [degrees] C 74 69 93 70 hours at 23 [degrees] C 28 16 8 22 hours at 70 [degrees] C 33 27 20 Resilience (Schob) 58 58 58 Monsanto Tel-Tack 2-7 hrs. 19 18 34 It is surprising to see how the properties related to tear strength are improved compared to the straight mixes. The compound based on grade F nearly matches the NR/BR compound. Only the angle nicked tear strength is still somewhat lower. However, the values of the angle nicked tear strength of the NR/BR compound are misleading, as the samples studied showed heavy branching during tearing tear·ing n. Epiphora. . Normally, the nicked samples should have a lower tear strength than the un-nicked samples. Of extreme significance for the NR/BR/EPDM blends is that the ratio of nicked/un-nicked is markedly improved by the carbon black masterbatching procedure, indicating a much better carbon black distribution over the individual phases. Compression sets look a little bit worse; resilience and tack are unchanged compared to straight blends. Surprisingly, the experimental polymer supposed to be the best possible choice performs the worst of all. These differences brought about by the masterbatching operation clearly show the importance of carbon black distribution in blends of EPDM with rubbers like NR and BR. It further shows that a quite common EPDM grade like grade F is much more fit for use than the exotic grades often quoted for these applications. This polymer has a medium level ENB unsaturation and a relatively low Mooney viscosity. It strengthens the fact that people tend to overlook the importance of carbon black and accelerator accelerator: see particle accelerator. (1) A key combination such as Alt-G or Ctrl-Shift H that is used to activate a task. (2) An incubator that expects to develop the company considerably faster than normal. See incubator. distribution over the different rubber phases in the blends. Conclusions The physical properties, and especially the tear and tensile strength of vulcanizates based on NR/BR/EPDM blends, have been studied as a function of the EPDM's structural parameters. Contrary to what is commonly assumed, these experiments show that the ethylene content of EPDM is dominant over molecular weight and unsaturation level with respect to optimal tear and tensile properties. The crosslinking efficiency of the EPDM in the NR/BR blend is commonly known to be a function of molecular weight and unsaturation level. Therefore, it can be stated that the influence of the filler fill·er 1 n. One that fills, as: a. Something added to augment weight or size or fill space. b. A composition, especially a semisolid that hardens on drying, used to fill pores, cracks, or holes in wood, plaster, distribution plays a much more important role than the degree of crosslinking. Finally, the present study suggests that the carbon black distribution over the individual NR/BR and EPDM phases are controlled by the EPDM structural parameters. References (1.) C.A. van Gunst, H.J.G. Paulen and E. Wolters, Kautschuk Gummi Kunststoffe 28, 714 (1975). (2.) W.H. Waddell, Rubber Chem. Techn. 71, 590 (1998). (3.) European Patent 0232463 to Polysar Ltd. (4.) W. von Hellens, "Effect of EPDM characteristics on cure state and co-vulcanization in NR/EPDM blends," ACS (Asynchronous Communications Server) See network access server. Rubber Div. 142nd meeting, Nov. 1992, paper 23. (5.) R.H Schuster, "Fullstofftransfer in kautschuk- verschnitten," Freudenberg Germany, September 24-25, 1996. |
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