Peroxide curing with precipitated silica.A study of peroxide peroxide (pərŏk`sīd), chemical compound containing two oxygen atoms, each of which is bonded to the other and to a radical or some element other than oxygen; e.g. curing of silica silica or silicon dioxide, chemical compound, SiO2. It is insoluble in water, slightly soluble in alkalies, and soluble in dilute hydrofluoric acid. Pure silica is colorless to white. filled elastomer elastomer (ĭlăs`təmər), substance having to some extent the elastic properties of natural rubber. The term is sometimes used technically to distinguish synthetic rubbers and rubberlike plastics from natural rubber. compounds affords an opportunity to explore silica reinforcing mechanisms free from the constraints and ambiguities present in zinc oxide zinc oxide, chemical compound, ZnO, that is nearly insoluble in water but soluble in acids or alkalies. It occurs as white hexagonal crystals or a white powder commonly known as zinc white. activated sulfur cure systems. Mechanical properties of rubber compounds are largely the result of the combined influence of filler-polymer bond strengths and the type and number of sulfur crosslinks. These two factors determine the balance between the viscous viscous /vis·cous/ (vis´kus) sticky or gummy; having a high degree of viscosity. vis·cous adj. 1. Having relatively high resistance to flow. 2. Viscid. and elastic responses to deforming forces. Carbon black reinforcement operates principally through polymer bonding; 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, influence on crosslinking is relatively minor. In contrast to this, precipitated silica has (because of its reaction with soluble zinc) a profound, and usually degrading TO DEGRADE, DEGRADING. To, sink or lower a person in the estimation of the public. 2. As a man's character is of great importance to him, and it is his interest to retain the good opinion of all mankind, when he is a witness, he cannot be compelled to disclose , effect on crosslinking. Thus, in many compounding situations it is not possible to ascertain the true reinforcing function of silica fillers. Comparisons with carbon black or among silicas of varying surface area are frequently problematic and complicated. This silica compounding dilemma has existed ever since the introduction of fine particle reinforcing silica some 50 years ago. A recent, proposed solution to the problem is the use of a zinc-free cure system (ref. 1) in which the exclusion of soluble zinc species prevents the silica-zinc reaction from occurring. Another approach, described later, is a replacement of sulfur by carbon-to-carbon crosslinks produced by peroxide 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. . Peroxide systems provide a means to make silica-black comparisons on an equal crosslink basis, and to evaluate silicas of varying surface area, free from cure effects. Natural rubber Carbon blacks and fine particle precipitated silicas are the only fillers capable of producing the highest level of reinforcement (i.e., tear strength and abrasion abrasion /abra·sion/ (ah-bra´zhun) 1. a rubbing or scraping off through unusual or abnormal action; see also planing. 2. a rubbed or scraped area on skin or mucous membrane. resistance) in rubber compounds. Because the use and production of blacks outweigh out·weigh tr.v. out·weighed, out·weigh·ing, out·weighs 1. To weigh more than. 2. To be more significant than; exceed in value or importance: The benefits outweigh the risks. that of silicas by some thirty fold, silica characterization is frequently obtained through comparison with carbon black of similar reinforcing potential - in compounds of matching hardness. The latter constraint is critical, since hardness is a principal influence on the mechanical properties of elastomer compounds. The results of such a comparison in sulfur cured natural rubber (table 1), based on a 20 phr replacement of HAF imp. 1. Hove. by a silica of 150 BET surface area, show that silica has produced typical reductions in rheometer rhe·om·e·ter n. An instrument for measuring the flow of viscous liquids, such as blood. crosslinking and in high strain modulus See modulo. M300. Although hardness and dynamic modulus Dynamic modulus is the ratio of stress to strain under vibratory conditions (calculated from data obtained from either free or forced vibration tests, in shear, compression, or elongation). It is a property of viscoelasticity materials. (E') are similar, the large loss in crosslinks indicates widely disparate states of cure and precludes a meaningful analysis of other properties. Table 1 - silica and black in natural rubber sulfur cure system HAF N330 40 20 Silica 150 BET -- 20 ODR cure rate 150 [degrees] C, T90 19 20 ODR crosslinks, dN-m 47 37 Durometer 55 52 M300 modulus, MPa 9.8 6.0 Elongation, % 630 715 Pendulum rebound, % at 23 [degrees] C 72.9 72.4 at 100 [degrees] C 81.7 80.5 DMA at 90 [degrees] C; 1 Hz; 15% E", MPa 0.67 0.46 E' 4.7 4.20 Tangent delta 0.142 0.109 Acceleration (8811): sulfur - 2.5; MOR MOR abbr. middle-of-the-road MOR adj abbr (MUS) (= middle-of-the-road) → para el gran público MOR adj abbr (Mus) (= - 1.2; TBTD TBTD Tibetan Book of The Dead - 0.2; ZnO - 3. Can this situation and the attendant questions of crosslink disparity dis·par·i·ty n. pl. dis·par·i·ties 1. The condition or fact of being unequal, as in age, rank, or degree; difference: "narrow the economic disparities among regions and industries" be resolved when peroxide curing forms the basis for a comparison between the two fillers? Comparisons carded out at 30 phr filler content (table 2) indicate that the peroxide system is indeed effective in providing an equal crosslink basis for comparing silica and black reinforcement. Two major areas of contrast emerge. High strain (300%) extension modulus is drastically lower with silica, and compression set is more than twice that of the ISAF ISAF International Security Assistance Force (UN program) ISAF International Sailing Federation ISAF International Shark Attack File ISAF Israeli Air Force ISAF Information Security Awareness Forum black compound. In sulfur systems, large set values generally reflect a break-up and decrease in chain length of polysulfide pol·y·sul·fide n. A sulfide compound containing at least two sulfur atoms per molecule. crosslinks. Since this mechanism is obviously not taking place with peroxide formed carbon-carbon bonds A carbon-carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond – a bond composed of two electrons, one from each of the two atoms. , the explanation must be found in filler interactions, that is, the balance between filler-polymer bonding and filler-filler agglomeration ag·glom·er·a·tion n. 1. The act or process of gathering into a mass. 2. A confused or jumbled mass: . Table 2 - silica and black in natural rubber peroxide cure system ISAF N121 30 -- Silica 150 BET -- 30 ODR cure rate 160 [degrees] C, T90 32 31 ODR crosslinks, dN-m 58 59 Durometer 50 56 M300 modulus, Mpa 15.0 7.3 Elongation, % 310 445 Pendulum rebound, % at 23 [degrees] C 72.4 70.3 at 100 [degrees] C 83.4 82.6 Compression set, % 10 24 Formulation (1015): DCP DCP - definitional constraint programming - 2.4; ODPA ODPA on Demand Platform Authentication ODPA on Demand Port Activation - 1; paraffinic oil - 3. The noted loss in 300% modulus provides familiar evidence of weak filler-polymer bonding, and the silica tendency to promote hardness (six durometer points here) is an indication of hydrogen bonded hydrogen bond n. A chemical bond in which a hydrogen atom of one molecule is attracted to an electronegative atom, especially a nitrogen, oxygen, or fluorine atom, usually of another molecule. filler-filler attachment. Both phenomena represent cases of potential instability, which leads to the breaking and reformation Reformation, religious revolution that took place in Western Europe in the 16th cent. It arose from objections to doctrines and practices in the medieval church (see Roman Catholic Church) and ultimately led to the freedom of dissent (see Protestantism). of silica bonds. These structural changes produce high compression set values. Slightly lower resilience resilience (r  ·zilˑ·yens),n in the silica compound, as measured by pendulum rebound, can be attributed to its higher durometer. A second peroxide cure silica-black comparison with lower silica content (table 3) demonstrates that, at equal durometer as well as equal crosslinks, there is no significant difference in dynamic properties imparted by silica or black. Table 3 - silica and black in peroxice cured NR at equal durometer and crosslinks Silica 150BET -- 15 HAF N330 40 25 MDR crosslinks, dN-m 20 21 MDR cure rate, 160 [degrees] C, T50 minutes 3.7 3.5 Mooney viscosity, ML100 44 52 Durometer 56 55 M300 modulus, MPa 18 15 Tensile 24 23 Elongation, % 365 385 MG trouser tear, kN/m 2.1 2.7 Pico abrasion index 58 58 Pendulum rebound (Z), % 66 67 Dynamic modulus at 90 [degrees] C (DMA, 1Hz; 15%) E', MPa 2.0 2.2 E" 0.20 0.22 Tangent delta 0.102 0.104 Formula (3959): NR - 100; oil - 5; ODPA - 1; stearic acid stearic acid /ste·a·ric ac·id/ (ste-ar´ik) a saturated 18-carbon fatty acid occurring in most fats and oils, particularly of tropical plants and land animals; used pharmaceutically as a tablet and capsule lubricant and as an emulsifying - 2; DCP - 2.4. At this point it is instructive in·struc·tive adj. Conveying knowledge or information; enlightening. in·struc  tive·ly adv. to return to note the dynamic
properties of the sulfur cure compounds in table 1. The dynamic data
here show that a pronounced reduction in both loss modulus E" and
tangent tangent, in mathematics.1 In geometry, the tangent to a circle or sphere is a straight line that intersects the circle or sphere in one and only one point. delta has occurred with the partial replacement of black by silica. Since no such change in these properties took place in the peroxide cure vulcanizates, an explanation must involve some aspect of the sulfur system and its interaction with silica. The most likely mechanism appears to be the previously noted reaction of soluble zinc with silica surface silanols in which the silica surface has been modified by the attachment of zinc ions. One result of this modification is a reduction in the extent and strength of the silica network structure, which in turn offers less resistance to low frequency deforming forces. The net result is lower energy absorption and consequent lower loss modulus E", and tangent delta. The use of silane silane or silicon hydride Any of a series of inorganic compounds of silicon and hydrogen with covalent bonds and the general chemical formula SinH(2n + 2). coupling agents can be expected to produce similar results, by the same mechanism. Further inquiry directed toward separating filler-polymer from filler-filler agglomeration effects involved the addition of zinc oxide and stearic acid to the peroxide cured 30 phr silica formula. This approach is based on the consequence of the zinc-silica reaction, which modifies the silica surface and promotes the break-up of silica agglomerates before vulcanization and testing. The result should be a reduction in set and an increase in rebound and, in fact, these changes did occur with addition of zinc oxide alone (table 4). When zinc is fully solubilized by added stearic acid, the decline in 300% modulus indicates that silica-polymer bonding has been reduced. We can thus make a provisional conclusion that silica structure effects (agglomeration) are more important than filler-polymer bonding in explaining the differences between black and silica in peroxide cured natural rubber. Table 4 - peroxide cured NR: silica and black soluble zinc effect Zinc oxide -- 3 3 Stearic acid -- -- 2 MDR crosslinks, dN-m 27 29 27 Durometer 58 61 58 M300, MPa 7.60 7.80 6.10 Compression set, 70 hours @ 100 [degrees] C, % 31.4 18.10 17.60 Pendulum rebound (Z), % at 23 [degrees] C 61 69 70 at 100 [degrees] C 69 76 78 Formula (3247): NR - 100; silica 150BET - 30; oil - 3; ODPA - 1; DCP - 2.4. A study of silica surface area effects also benefits from peroxide curing, where relative freedom from sulfur crosslink modification by silica (more pronounced at high surface areas) allows a more fundamental evaluation of reinforcing potential (table 4). Actually, the basic silica property which controls elastomer reinforcement is not surface area, but primary particle size Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. , generally in the 15 to 20 nanometer range. However, practical testing requirements dictate the use of nitrogen adsorption adsorption, adhesion of the molecules of liquids, gases, and dissolved substances to the surfaces of solids, as opposed to absorption, in which the molecules actually enter the absorbing medium (see adhesion and cohesion). BET surface area measurements for silica classification. Small particle or agglomerate agglomerate Large, coarse, angular rock fragments associated with lava flow that are ejected during explosive volcanic eruptions. Although they may appear to resemble sedimentary conglomerates, agglomerates are igneous rocks that consist almost wholly of angular or rounded size equals large surface area. In the subject comparison there appear slight but definite trends to increased hardness, cure rate, crosslinks, compression set and dynamic loss modulus at higher surface areas. The only major effect appears in a substantial rise in Mooney viscosity with increased surface area, quite likely the result of stronger network forces which accompany agglomerate size reduction. This particular study involved only a 30 phr filler content, and therefore cannot be expected to reveal any substantial distinctions in reinforcing properties such as abrasion and tear. At filler contents of 40 and 50 phr, trouser tear, in particular, would increase in proportion to surface area. Semi-reinforcing silicas Evaluation of various surface area grades of silica in peroxide cure systems can be expanded to include the semi-reinforcing types with surface areas below 100 [m.sup.2]/g. An SEM micrograph micrograph /mi·cro·graph/ (-graf) 1. an instrument used to record very minute movements by making a greatly magnified photograph of the minute motions of a diaphragm. 2. (figure 1) of two SR, grades together with a 150 BET reinforcing grade, provides a clear picture of the increase in agglomerate size which accompanies decreased surface area, i.e., increased primary particle size. The large agglomerates of these silicas form a weak filler-polymer reinforcing network which translates to lower tensile tensile, adj having a degree of elasticity; having the ability to be extended or stretched. and tear strengths. More departures from full reinforcing behavior are seen in the low viscosity and high resilience (pendulum rebound) of these compounds (table 6). These properties can be related to the large areas of unfilled rubber seen in the photomicrograph photomicrograph /pho·to·mi·cro·graph/ (fo?to-mi´kro-graf) a photograph of an object as seen through an ordinary light microscope. pho·to·mi·cro·graph n. A photograph made through a microscope. . Although these contribute to increased flow during extrusion, calendering calendering, a finishing process by which paper, plastics, rubber, or textiles are pressed into sheets and smoothed, glazed, polished, or given a moiré or embossed surface. and molding, silica network structure effects are still strong enough to effectively reduce swell and nerve. All of these surface area related processing and property changes take place with little or no change in cure rate or rheometer crosslinking. Table 6 - semi-reinforcing silicas in peroxide cured NR Silica 150 BET 30 -- -- Silica 65 BET -- 30 -- Silica 35 BET -- -- 30 ODR 160 [degrees] C: T90 19 25 24 ODR crosslinks, dN-m 66 64 60 Mooney viscosity, ML100 58 50 56 Durometer 56 52 51 M300, MPa 7.9 8.60 7.80 Tensile 20 18 17 Elongation, % 445 420 390 Pendulum rebound, % at 23 [degrees] C 79.3 84.1 85.3 at 100 [degrees] C 87.2 90.3 90.3 Formula (8868): SMR (Specialized Mobile Radio) The communications services used by police, ambulances, taxicabs, trucks and other delivery vehicles. Throughout the U.S., approximately 3,000 independent operators are licensed by the FCC to offer this service, which provides always-on 60 - 100; par. oil - 3; ODPA - 1; DCP - 2.4. [Figure 1 ILLUSTRATION OMITTED] 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 formula basis for comparison between peroxide and sulfur cure systems in EPDM departs significantly from that used with natural rubber. Major changes include a filler content of 60 phr and the omission of fatty acid fatty acid, any of the organic carboxylic acids present in fats and oils as esters of glycerol. Molecular weights of fatty acids vary over a wide range. The carbon skeleton of any fatty acid is unbranched. Some fatty acids are saturated, i.e. from both sulfur and peroxide compounds. The latter factor provides a soluble zinc-free environment. Under these conditions an equal hardness comparison There are a large number of hardness testing methods available (eg. Vickers, Brinell and Rockwell). Although it is impossible in many cases to give an exact conversion it is possible to give a comparison table. between sulfur and peroxide cures reveals little difference in physical properties, other than compression set (table 7). The relatively large set values, even for peroxide, can, as in the NR discussion, be ex-plained by silica agglomeration, and in the sulfur case also by rearrangement re·ar·range tr.v. re·ar·ranged, re·ar·rang·ing, re·ar·rang·es To change the arrangement of. re of polysulfide chains. The equivalence of 300% modulus and abrasion index indicates that silica-polymer bonding is not involved in the compression set mechanism. Table 7 - peroxide and sulfur cure systems in EPDM 60 phr silica
Peroxide Sulfur(*)
Zinc oxide 1 3
Stearic acid -- --
Zinc dimethacrylate 3 5
Sulfur -- 1.5
ZBDC -- 2
DPTH -- 1
TBBS -- 1
BPDIB 2.8 0
Silane A174 1.5 --
Durometer 23 [degrees] C 78 79
100 [degrees] C 73 76
MDR 160 [degrees] C T50 minutes 8.2 10
MDR crosslinks, dN-m 41 46
Mooney scorch 121 [degrees] C, T5 30+ 10
Compression set,
70 hrs @ 100 [degrees] C, % 44 82
(*) Ciptane 255LD Table 7a - peroxide and sulfur cure systems in EPDM
Peroxide
Stress/strain Orig. Aged(*)
M300, MPa 9.8 --
Tensile 23 17
Elongation, % 505 255
MG trouser tear, kN/m 14
Pico abrasion index 137
Pendulum rebound (Z), %
23 [degrees] C 57
100 [degrees] C 58
DeMattia cut growth
KC to 500% growth 1
Sulfur
Stress/strain Orig. Aged(*)
M300, MPa 9.8 --
Tensile 25 14
Elongation, % 575 110
MG trouser tear, kN/m 13
Pico abrasion index 166
Pendulum rebound (Z), %
23 [degrees] C 58
100 [degrees] C 60
DeMattia cut growth
KC to 500% growth 2
(*) Aged 700 hours at 140 [degrees] C When the peroxide-sulfur comparison is made in the presence of zinc oxide and stearic acid (table 8), several pronounced differences appear. In this case the sulfur compound is inferior in aging, tear, cut growth and abrasion. When stress/strain testing takes place at 100 [degrees] C, the peroxide cure is more effective in retaining both tensile and tear strengths. Table 8 - peroxide and sulfur cure systems in EPDM with zinc oxide and stearic acid
Peroxide
DCP 2.8
EGDMA 5.0
Sulfur --
MDB --
MBTS --
ZBDC --
Stearic acid 2
Zinc oxide 15
ODR cure rate,
155 [degrees] C, T90 20
ODR crosslinks, dN-m 69
Durometer 79
Stress/Strain tested at 23 [degrees] C 100 [degrees] C
M300, MPa 3.3 2.3
Tensile 14 6.7
Elongation, % 690 980
MG trouser tear kN/m 105 60
Aging 700 hours at 150
[degrees] C (reflux):
Durometer 88
Tensile, MPa 10.3
Elongation, % 220
Ross flex cut growth,
aged 240 hours at 100
[degrees] C:
KC to 500% growth 100+
DeMattia cut growth
KC to 500% growth. 9
Pico abrasion index 84
Sulfur-
DCP -
EGDMA --
Sulfur 0.4
MDB 2.0
MBTS 1.5
ZBDC 1.0
Stearic acid 2
Zinc oxide 15
ODR cure rate,
155 [degrees] C, T90 20
ODR crosslinks, dN-m 68
Durometer 75
Stress/Strain tested at 23 [degrees] C 100 [degrees] C
M300, MPa 1.9 1.6
Tensile 14 4.0
Elongation, % 710 970
MG trouser tear kN/m 85 45
Aging 700 hours at 150
[degrees] C (reflux):
Durometer 88
Tensile, MPa 10.9
Elongation, % 130
Ross flex cut growth,
aged 240 hours at 100
[degrees] C:
KC to 500% growth 4
DeMattia cut growth
KC to 500% growth. 2
Pico abrasion index 67
Formula (6634): EPDM346 - 100; Hil-Sil 210 - 55; oil -20; TMQ TMQ Terminal-Port Queueing (Cisco) TMQ Talking Message Queue - 2; Stearic acid - 2; zinc oxide - 15; PEG 3350 - 1. An evaluation of silica and black characteristics in peroxide cured EPDM presents some complications (table 9). At the high filler content of these formulas it is necessary to include more plasticizing materials with silica to maintain hardness equal to that of the black compound. These plasticizers plasticizers mostly triaryl phosphates, such as tricresyl, triphenyl phosphates, which are poisonous. See also triorthocresyl phosphate. appear to be at least partially responsible for significant reductions in viscosity, crosslinking, 300% modulus, heat build-up build·up also build-up n. 1. The act or process of amassing or increasing: a military buildup; a buildup of tension during the strike. 2. and increased elongation elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the planet as measured from the earth. in the silica compound. Trouser tear strength, however, remains at an unusually high level for a peroxide cure. Resilience properties are comparable.
Table 9 - peroxide cured EPDM: silica and black
Silica Black
BPDIB 2.8 2.8
Silica 215 BET 60 --
HAF N330 -- 60
Paraffinic oil 15 --
EPDM 1446A 20 --
Zinc dimethacrylate 3 6
Stearic acid -- --
MDR cure rate,
165 [degrees] C, T50 5.3 5.0
MDR crosslinks, dN-m 28 38
Mooney viscosity, ML100 82 140
Durometer 73 73
M300 modulus, MPa 7.1 21
Tensile 23 24
Elongation, % 600 330
MG trouser tear, kN/m 11 5.3
Pico abrasion index 123 141
Compression set, 35 23
70 hrs. @ 100 [degrees] C
Pendulum rebound (Z), %
at 23 [degrees] C 59 56
at 100 [degrees] C 58 60
Goodrich flexometer, 100
[degrees] 1MPa:
Heat build-up 26 [degrees] C 44 [degrees] C
Transparent EPDM Peroxide curing of EPDM and other polymers allows the attainable with sulfur systems. A formula typical of those sometimes used in footwear constructions is based on a blend of EPDM and EVA Eva to marry winner of singing contest. [Ger. Opera: Wagner, Meistersinger, Westerman, 225–228] See : Prize 1. Eva - A toy ALGOL-like language used in "Formal Specification of Programming Languages: A Panoramic Primer", F.G. ethylene ethylene (ĕth`əlēn') or ethene (ĕth`ēn), H2C=CH2, a gaseous unsaturated hydrocarbon. It is the simplest alkene. vinyl acetate Vinyl acetate, also known as VAM for vinyl acetate monomer, has the chemical formula CH3COOCH=CH2 and is a colorless liquid with a sweet flavor. Systematic names include 1-acetoxyethylene and acetic acid ethenyl ester. (table 10). Comparisons of various grades of precipitated silicas in this formula show the variation in stress/strain properties which is normal for surface area effects, and a very wide range of haze measurements. Luminous lu·mi·nous adj. Emitting light, especially emitting self-generated light. transmittance is fairly uniform MDR MDR, n See multidrug resistance. MDR, n the abbreviation for minimum daily requirement, specifically the Minimum Daily Requirements for Specific Nutrients compiled by the United States Food and Drug Administration. cure rate,for all silicas. An attempt to relate haze to the number of 2 to 20 micron micron: see micrometer. One micrometer, which is one millionth of a meter or approximately 1/25,000 of an inch. The tiny elements that make up a transistor on a chip are measured in micrometers and nanometers. See process technology. sized agglomerates seen in 500X micrographs produced a rather rough correlation (figure 2). Evidently it would be possible to use haze as a measure of 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. , if one defines dispersion in terms of these agglomerate sizes. There is, however, no relation between compound physical properties and haze or dispersion at this level.
Table 10 - peroxide cured EPDM: silica and black
EPDM 1660 60
EVA 150 40
Silica 25
TAC 0.50
DMBPH 2
Property ranges
Luminous transmittance, % 83-89
Haze, % 15-55
Durometer 73-76
M300, MPa 5.9-7.7
Tensile 10-19
Elongation, % 365-525
Pendulum rebound, % 60-63
[Figure 2 ILLUSTRATION OMITTED] NBR NBR Number NBR Nightly Business Report (PBS show) NBR National Business Review (New Zealand weekly business newspaper) NBR National Bureau of Asian Research NBR National Board of Review and XNBR XNBR Carboxylated Nitrile Rubber Similar semi-reinforcing grades of silica and black are compared in peroxide cured NBR (table 11) in formulas which contain zinc and magnesium oxides magnesium oxide: see magnesia. , as well as stearic acid. These materials will react with, and can be expected to have some modifying effect on, the silica. The resulting soluble zinc and magnesium magnesium (măgnē`zēəm, –zhəm), metallic chemical element; symbol Mg; at. no. 12; at. wt. 24.305; m.p. about 648.8°C;; b.p. about 1,090°C;; sp. gr. 1.738 at 20°C;; valence +2. attachment to the silica reduces silica-polymer bonding and leads to somewhat lower values of 100% modulus, tensile and abrasion index. Since ODR ODR Online Dispute Resolution ODR On-Demand Routing ODR One-Definition Rule (C++) ODR Octal Data Rate (high speed memory interface transfers 8 bits of data per clock cycle) ODR Office of Dispute Resolution crosslinks are slightly higher with silica, these property reductions are evidently independent of crosslinking effects, and refer only to silica surface modification. Table 11 - peroxide cured NBR: silica and black Silica 60 BET 50 50 -- Silane A174 (methacryloxy) -- 1 -- FEF N550 -- -- 50 ODR cure rate, 155 [degrees] C, T90 10.5 10.5 11.8 ODR crosslinks, dN-m 79 80 70 Compression set, 70 hrs. @ 150 [degrees] C, % 32 27 32 Mooney viscosity, ML100 52 48 54 Durometer 70 72 69 M100 modulus, MPa 3.4 5.0 5.70 Original S/S Tensile, MPa 14 19 21 Elongation, % 385 265 270 Aged 330 hrs. @ 135 [degrees] C Tensile 18 18 16 Elongation 80 70 40 Durometer 86 85 89 Pico abrasion index 68 165 147 Fuel B immersion, 48 hrs. @ 23 [degrees] C %volume increase 30.6 29.0 28.6 Formula (8635): NBR 40-65- 100; G62- 10; TMQ- 1.5; ODPA - 1.5; MgO - 5; ZnO - 5; stearic acid - 2; PEG - 1; SR350 - 5; DCP - 1.6. Counteractive coun·ter·act tr.v. coun·ter·act·ed, coun·ter·act·ing, coun·ter·acts To oppose and mitigate the effects of by contrary action; check. coun surface modification by the addition of silane A174 (methacryloxy-) removes the discrepancies between the black and silica compounds, and produces an unexpectedly high abrasion index, substantially greater than was obtained from either vinyl or mercapto silanes. With or without silane coupling, heat resistance with silica is markedly superior to that of the FEF FEF forced expiratory flow. FEF abbr. forced expiratory flow FEF forced expiratory flow rate. compound. A comparison of peroxide and sulfur cure systems in carboxylated nitrile nitrile: see rubber. raises as many questions as it answers. In the example under examination here (table 12) hardness is comparable but higher crosslinks with peroxide have an obvious influence on 100% modulus, elongation and trouser tear strength. Since scorch safety is frequently a problem with XNBR, the peroxide improvement together with somewhat lower viscosity is noteworthy. Difference in pico indices at the high level characteristics of any XNBR compound offer small basis for making meaningful conclusions. As in many similar situations, the major reservation with the peroxide compound concerns the low level of elongation and tear strength, particularly after heat aging. In respect to percent retained elongation there is little to choose between the peroxide and sulfur systems. Table 12 - peroxide curing of carboxylated nitrile 50 phr silica
Peroxide Sulfur
BPDIB 1.2 --
Sulfur -- 1.5
MBTS -- 1.5
Zinc oxide 3 3
Durometer 84 83
ODR Crosslinks @
20'/160 [degrees] C 125 97
Compression set,
70 hrs./100 [degrees] C 29 58
Mooney scorch
121 [degrees] C, T5' 11.9 4.6
Mooney viscosity, ML100 88 110
M100 modulus, MPa 7.9 4.1
Tensile 22 21
Elongation, % 300 470
Elongation aged 70 hrs. 150 200
/121 [degrees] C 4.9 7.0
CG trouser tear, kN/m 905 420
Formula (6263): XNBR221 - 100; Hi-Sil 210 - 25; Hi-Sil 532 - 25; DOP DOP In currencies, this is the abbreviation for the Dominican Republic Peso. Notes: The currency market, also known as the Foreign Exchange market, is the largest financial market in the world, with a daily average volume of over US $1 trillion. - 5; stearic acid - 2; MgO - 1. Summary The use of a peroxide cure system in natural rubber and other elastomers offers a valuable means of investigating the reinforcement potential of precipitated silica, free from the modifications produced by the zinc-silica reaction. Exclusion of soluble zinc also makes it possible to distinguish between the filler structure and filler-polymer aspects of silica reinforcement, and provides an explanation of the reduction in tangent delta (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. ) achieved by the replacement of carbon black by precipitated silica. Table 5 - silica types in natural rubber peroxide cure
Surface area, BET 135 150 190
MDR 160 [degrees] C, T50 4.2 3.7 3.5
MDR crosslinks, dN-m 26 27 29
Viscosity, ML100 60 69 74
Durometer: at 23 [degrees] C 55 58 58
at 100 [degrees] C 54 57 58
M300 modulus, MP 8.3 7.6 7.8
Elongation, % 455 500 495
Tensile 22 25 25
Aged 700 hours at 80 [degrees] C
Tensile 1.7 2.0 2.1
Compression set,
70 hours at 100 [degrees]C, % 25.1 31.4 33.0.
Dynamic properties
Pendulum rebound (Z), %:
at 23 [degrees] C 63 61 62
at 100 [degrees] C 71 69 70
DMA dynamic modulus, 1Hz, MPa
E' -40 [degrees] C 390 440 460
20 [degrees] C 10 16 17
30 [degrees] C 5.0 7.1 7.8
60 [degrees] C 4.9 6.70 7.3
E" 60 [degrees] C 1.19 1.28 1.11
Tan Delta 60 [degrees] C 0.242 0.191 0.151
Surface area, BET 215 250
MDR 160 [degrees] C, T50 3.1 2.7
MDR crosslinks, dN-m 30 31
Viscosity, ML100 85 124
Durometer: at 23 [degrees] C 58 61
at 100 [degrees] C 58 61
M300 modulus, MP 7.7 9.1
Elongation, % 500 470
Tensile 25 24
Aged 700 hours at 80 [degrees] C
Tensile 3.3 4.7
Compression set,
70 hours at 100 [degrees]C, % 33.1 37.5
Dynamic properties
Pendulum rebound (Z), %:
at 23 [degrees] C 62 60
at 100 [degrees] C 69 69
DMA dynamic modulus, 1Hz, MPa
E' -40 [degrees] C 225 140
20 [degrees] C 15 24
30 [degrees] C 8.1 10.4
60 [degrees] C 7.7 9.7
E" 60 [degrees] C 1.12 1.28
Tan Delta 60 [degrees] C 0.146 0.132
Reference (1.) N.L. Hewitt, Rubber World, Sept. 1992. |
|
||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion