Understanding organic peroxides to obtain optimal crosslinking performance.Of the seven different classes of organic peroxides (ref. 1), the two most commonly used for crosslinking elastomers are the dialkyl and peroxyketal peroxides. These two classes of organic peroxides are stable at room temperature and are offered commercially in pure and diluted forms. The diluted or "extended" forms of these peroxides are generally preferred by the rubber industry, as they are safer and easier to handle. The extended forms are dispersed on an inert carrier such as calcium carbonate calcium carbonate, CaCO3, white chemical compound that is the most common nonsiliceous mineral. It occurs in two crystal forms: calcite, which is hexagonal, and aragonite, which is rhombohedral. or clay, or they are compounded by the manufacturer in a 40% assay polymer masterbatch. Definitions to key abbreviations used in this article can be found in table I. Refer to tables 1-3 for chemical names, structures and half-life information. Software for calculating organic peroxide time-temperature halt-life data for both compounding and crosslinking profiles is available. The dialkyl and peroxyketal peroxides suited for crosslinking possess either one or two oxygen-oxygen bonds, designed to break apart thermally, to produce free radicals for the curing reaction. We will now discuss the benefits of the two different classes of peroxide for crosslinking applications. Dialkyl peroxides The dialkyl peroxides are the most widely used, as they are cost-efficient for most crosslinking applications. In particular, the most efficient dialkyl peroxides are the solid, aromatic types, such as dicumyl peroxide (DCP DCP - definitional constraint programming or DCP-40KE) and m/p-di(t-butylperoxy) diisopropylbenzene (VC-R or 802-40KE) (table 2). DCP-40KE is an efficient crosslinking peroxide that does not have any bloom issues. However, DCP-40KE produces acetophenone as a decomposition decomposition /de·com·po·si·tion/ (de-kom?pah-zish´un) the separation of compound bodies into their constituent principles. de·com·po·si·tion n. 1. product. Acetophenone is a liquid at room temperature and exhibits an undesirable odor for certain automotive and industrial applications. The benefit of DCP is that it is more thermally active, i.e., has a lower hall-life temperature and will decompose de·com·pose v. de·com·posed, de·com·pos·ing, de·com·pos·es v.tr. 1. To separate into components or basic elements. 2. To cause to rot. v.intr. 1. at a faster rate for a given temperature, compared to m/p-di(t-butylperoxy)-diisopropylbenzene (802-40KE or VC-R). 802-40KE is equal in efficiency to DCP-40KE on a molar molar /mo·lar/ (mo´lar) 1. pertaining to a mole of a substance. 2. a measure of the concentration of a solute, expressed as the number of moles of solute per liter of solution. Symbol M, , or mol/L. basis and is more efficient on a weight basis. As 802-40KE is more thermally stable than DCR DCR Department of Conservation and Recreation DCR Decrease DCR Digital Cable Ready (television) DCR Dark Crisis (Yu-Gi-Oh! cards) DCR Debt Coverage Ratio DCR Dacryocystorhinostomy it must be used at higher crosslinking temperatures. The benefit of the solid 802-40KE peroxide is its increased scorch time protection during compounding. 802-40KE produces solid decomposition by-products that are higher in molecular weight and thus exhibit a milder aromatic odor. However, these decomposition by-products are polar solids that migrate to the rubber surface to create a crystalline bloom. Thus 802-40KE may be unacceptable for certain applications where bloom cannot be tolerated, e.g., OEM (Original Equipment Manufacturer) The rebranding of equipment and selling it. The term initially referred to the company that made the products (the "original" manufacturer), but eventually became widely used to refer to the organization that buys the products and automotive gaskets and seals. An important liquid aliphatic aliphatic /al·i·phat·ic/ (al?i-fat´ik) pertaining to any member of one of the two major groups of organic compounds, those with a straight or branched chain structure. al·i·phat·ic adj. dialkyl peroxide listed in table 2, is 2,5-dimethyl-2,5-di(t-butylperoxy)hexane hexane /hex·ane/ (hek´san) a saturated hydrogen obtained by distillation from petroleum. hex·ane n. (DBPH). The liquid DBPH peroxide is also available as a free flowing powder dispersed on calcium carbonate (DBPH-50). In table 4, we compare the crosslinking efficiency of DCP 40KE, 802-40KE and DBPH-50, for crosslinking a general purpose 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 . DCP and 802 provide equivalent molar crosslinking performance, based on the 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. (ref. 3) results; however, nearly 1.7 times more moles Moles Definition A mole (nevus) is a pigmented (colored) spot on the outer layer of the skin (epidermis). Description Moles can be round, oval, flat, or raised. They can occur singly or in clusters on any part of the body. of DBPH-50 peroxide are required. DBPH-50 is less efficient on a molar basis due to the energies of the free radicals generated upon decomposition. The DCP peroxide produces all high-energy radicals of 104.9 kcal/mole; whereas the liquid, aliphatic DBPH produced some 99.9 kcal/mole radicals. Free-radical energies in excess of 101 kcal/mole are necessary (ref. 4) for efficient crosslinking by a hydrogen-abstraction mechanism. These free-radical energies are based on hydrogen bond 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. dissociation dissociation, in chemistry, separation of a substance into atoms or ions. Thermal dissociation occurs at high temperatures. For example, hydrogen molecules (H2 energy data. It is important to note that DBPH-50 exhibits good crosslinking efficiency on a weight basis compared to DCP-40KE and 802-40KE. The best peroxide for crosslinking efficiency, where peroxide thermal stability, no odor and no bloom are required, is 2,5-dimethyl-2,5-di(t-butylperoxy) hexane (DBPH or DBPH-50). DBPH offers the unique benefit of virtually no odor and no bloom, due to the nature of its decomposition by-products. DBPH has earned limited FDA FDA abbr. Food and Drug Administration FDA, n.pr See Food and Drug Administration. FDA, n.pr the abbreviation for the Food and Drug Administration. approval (ref. 5) for indirect food contact and is a popular curative curative /cur·a·tive/ (kur´ah-tiv) tending to overcome disease and promote recovery. cu·ra·tive adj. 1. Serving or tending to cure. 2. for EPDM, EPM EPM equine protozoal myeloencephalitis. , HNBR HNBR Hydrogenated Acrylonitrile-Butadiene Rubber , VMQ VMQ Virtual Memory Query and FKM FKM Fluoroelastomer FKM Fogarty Klein Monroe (Houston, Texas) FKM Field Kitchen, Modular applications. The other liquid dialkyl peroxide listed in table 2 is 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, typically extended on calcium carbonate (130-XL). However, the 130-XL peroxide is not commonly used by the rubber industry. Its significantly higher half-life reduces productivity for most 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. applications. It is generally used for crosslinking higher melting thermoplastics, e.g., ultra high molecular weight polyethylene (UMWPE) and high density polyethylene High-density polyethylene (HDPE) is a polyethylene thermoplastic made from petroleum. It takes 1.75 kilograms of petroleum (in terms of energy and raw materials) to make one kilogram of HDPE. (HDPE HDPE abbr. high-density polyethylene ). In table 5, we provide the bond strengths for crosslinking with peroxides versus sulfur cure. Conventional peroxides, and blends of peroxide with acrylic, methacrylic, allylic al·lyl n. The univalent, unsaturated organic radical C3H5. [Latin allium, garlic + -yl (so called because it was first obtained from garlic). and bismaleimide coagents, all result in carbon-carbon (C-C C-C Carbon-Carbon C-C Carotid-Cavernous (relating to the carotid artery and the sinuses) ) higher bond strengths, compared to the lower energy sulfur-sulfur (S-S S-S Surface-to-Surface S-S Space to Space ) bonds for sulfur 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. . The difference in bond strength explains why peroxides generally have better heat aging, higher hardness and modulus, but reduced 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. , tear strength and flex fatigue. Figure 1 shows an example of C-C bond energy performance. The EPDM was heated at 180[degrees]C in a rubber process analyzer (ref. 6) under zero shear conditions until completely cured; then a fixed 28% strain was applied for one hour. The S' (elastic modulus elastic modulus or elastic constant In materials science and physical metallurgy, any of various numbers that quantify the response of a material to elastic or springy deflection. ) line for the sulfur cure drops off with time compared to the 802-40KE peroxide, and blends of 802-40KE with SR-351(ref. 7) (trimethyolpropane triacrylate). We interpret this "drop off' to the greater flexibility and mobility of the S-S bonds, which can break and re-form. In summary, this example teaches that both peroxide, and blends of peroxide with an acrylic coagent, will produce strong carbon-carbon (C-C) bonds. The various stress relaxation Stress relaxation describes how polymers relieve stress under constant strain. Because they are viscoelastic, polymers behave in a nonlinear, non-Hookean fashion.[1] curves for the peroxide and the peroxide-coagent blends run in parallel to each other, regardless of the initial state of cure. Thus, a blend of peroxide and coagent is a viable means to obtain desired C-C bond crosslinking while trying to minimize effects of bloom. This is particularly useful when curing with 802-40KE. By reducing the amount of this peroxide in a rubber formulation, the amount of bloom can be reduced or possibly eliminated. [FIGURE 1 OMITTED] Peroxyketal peroxides The peroxyketal peroxides possess several unique benefits over the dialkyl type. The peroxyketals provide significantly faster crosslinking rates, up to ten times faster than a dialkyl peroxide at equivalent cure temperatures. In addition, these peroxides are all aliphatic liquids that produce low odor with no bloom. Two very useful peroxyketals for crosslinking elastomers are listed in table 3. These are (231-XL) 1,1-di(tbutylperoxy)-3,3,5-trimethylcyclohexane and (230-XL) nbutyl-4,4-di-(t-butylperoxy)valerate. Based on the postulated pos·tu·late tr.v. pos·tu·lat·ed, pos·tu·lat·ing, pos·tu·lates 1. To make claim for; demand. 2. To assume or assert the truth, reality, or necessity of, especially as a basis of an argument. 3. decomposition mechanisms, some of the free radicals generated by these peroxyketals are low in energy (99.9 kcal/mole) and are thus less efficient compared to the dialkyl peroxides. Therefore, the peroxyketals can greatly benefit from the use of coagents to improve cost-performance. In table 6, we compare DCP-40KE, 802-40KE and 231-XL (a peroxyketal - 40% on Ca[CO.sub.3]) in a fast cure EPDM (70% ethylene ethylene (ĕth`əlēn') or ethene (ĕth`ēn), H2C=CH2, a gaseous unsaturated hydrocarbon. It is the simplest alkene. , 9-11% diene Dienes are hydrocarbons which contain two double bonds. Dienes are intermediate between alkenes and polyenes. Classes Dienes can be divided into three classes:
Thus, peroxyketals provide the benefits of improved productivity along with the elimination of aromatic odors Odors anosmia Medicine. the absence of the sense of smell; olfactory anesthesia. Also called anosphrasia. — anosmic, adj. halitosis bad breath; an unpleasant odor emanating from the mouth. and bloom. Another benefit can be lower energy costs and reduced heat aging of parts by allowing the same cure cycle time, but at significantly reduced crosslinking process temperatures. In figure 2, we provide additional data comparing the dialkyls (DCP-40KE, 802-40KE and DBPH-50) to a peroxyketal (231-XL) in 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. (polyethylene 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. ). The peroxides were compared on an equal molar basis and the same ranking of cure efficiency was found: DCP = 802 > DBPH > 231 (based on the [M.sub.H] values). [FIGURE 2 OMITTED] Peroxyketal peroxides and coagents Although the lower energy radicals produced by peroxyketals are not suited for crosslinking by hydrogen abstraction, they are reactive with various monomeric monomeric /mono·mer·ic/ (mon?o-mer´ik) 1. pertaining to, composed of, or affecting a single segment. 2. in genetics, determined by a gene or genes at a single locus. coagents. In table 7, we show the tremendous benefit of using blends of coagents, e.g., triallyl cyanurate (TAC 1. TAC - Translator Assembler-Compiler. For Philco 2000. 2. TAC - Terminal Access Controller. ) with a peroxyketal (230-XL). With one part of TAC, 230-XL was used equal molar to 802-40KE for crosslinking EVA and achieved a higher state of cure based on the [M.sub.H] values. Furthermore, we reaped the benefit of a three-fold improvement in productivity based on the [T.sub.C90] value of 5.3 minutes versus 17 minutes for the 802-40KE. From this simple example, it is clear that a peroxyketal-coagent blend provides many benefits, including improved productivity, reduced cycle time, better cost-performance, no bloom and low odor, at equivalent to better crosslinking performance. Peroxides and metallic coagents Sartomer has developed several metallic coagents. One in particular is well suited for the crosslinking of elastomers. In table 8, we provide the structure for zinc dimethacrylate (ZnDMA). Earlier, we discussed the benefits of peroxides with conventional coagents that generate carbon-carbon crosslinks. However, as described in a recent seminar, Sartomer postulated another type of crosslinked bond when using ZnDMA. This ionic type a kind of heavy-faced type (as that of the following line). See also: Ionic bond created by the ZnDMA is intermediate in strength between a sulfur cure and a peroxide cure. The bond strength information can be found in table 5 and a pictograph pictograph - pictogram of the crosslinking mechanism in table 8. To study this effect, we conducted a series of cures in EPDM (70% ethylene, 9-11+% diene) comparing a sulfur cure to DCP-40KE, 802-40KE and 231-XL peroxides with and without the ZnDMA coagent. The level of peroxide was adjusted to provide equivalent crosslinking for all the formulations, with respect to the sulfur cure control. The amount of ZnDMA was kept at a constant five parts as shown in table 9. Initial crosslinking evaluations were conducted using a moving die rheometer rhe·om·e·ter n. An instrument for measuring the flow of viscous liquids, such as blood. to confirm equivalent state of cure for all formulations. In figure 3, we show a graph of stress relaxation obtained from an RPA RPA Remote Patron Authentication RPA Rural Payments Agency (UK Department of Environment, Food and Rural Affairs) RPA Replication Protein A RPA RNAse Protection Assay RPA Regional Plan Association RPA Random-Phase Approximation . In that graph of torque versus time, we compare the three peroxides, which were adjusted in concentration to obtain equivalent state of cure attained by the sulfur control. Fully cured elastomer samples were subjected to the stress relaxation test consisting of a 42% applied strain (3[degrees] arc) at 180[degrees]C for nearly one hour. The decay in the elastic modulus, S', is recorded versus time. All three peroxides provided nearly equivalent performance, as expected. Due to the elastic nature of the sulfur-sulfur bonds, there was the expected drop-off in torque (or modulus) for the sulfur vulcanization control. We then examined the effect of reducing the peroxide concentration and used blends of peroxide with the metallic coagent ZnDMA. Again, the peroxide concentration was adjusted to maintain the equivalent state of cure based on MDR data. In table 10, we show a stress relaxation example comparing DCP and a blend of DCP and ZnDMA, to the sulfur control. The stress relaxation data in figure 4 confirm that the blend of DCP and ZnDMA provides a more flexible crosslinked bond, with a bond-strength intermediate between a conventional peroxide cure and a sulfur cure. In addition, we did not observe any reversion reversion: see atavism. for the peroxide-metallic coagent blends during our MDR evaluations. However, reversion was noted for the sulfur cure. [FIGURE 4 OMITTED] This blend of peroxide and metallic coagent provides improved flexibility without sacrificing thermal stability. Figure 5 (ref. 8) illustrates the dramatic increased flex-fatigue resistance, provided by a blend of dicumyl peroxide and ZnDMA, for a crosslinked EPDM. [FIGURE 5 OMITTED] Figure 6 (ref. 9) shows the significantly higher tear strength for SR-634, a proprietary scorch retarded ZnDMA formulation used in combination with dicumyl peroxide. The tear strength for the DCP-ZnDMA blend is much higher than the sulfur control. [FIGURE 6 OMITTED] So, in summary, we believe it is possible to customize needed performance by the use of peroxide-coagent blends of this nature. The use of peroxide and metallic coagents appears to alter the final crosslinked network, providing increased flexibility and tear strength performance. DBPH-50-HP for APA (All Points Addressable) Refers to an array (bitmapped screen, matrix, etc.) in which all bits or cells can be individually manipulated. APA - Application Portability Architecture type FKM elastomers DBPH-50-HP is a proprietary "HP" or high performance peroxide formulation based on the peroxide 2,5-dimethyl-2,5di(t-butylperoxy)hexane. The novel DBPH-50-HP peroxide formulation has the capability of providing increased scorch time (ref. 10) in EPDM, EPM, VMQ, FKM, and more recently in the new APA (advanced polymer architecture) fluoroelastomers, marketed by DuPont Dow Elastomers. The new VTR (VideoTape Recorder) A videotape recording and playback machine. VTR may refer to consumer MiniDV and DV recorders or to professional machines such as Betacam, DVCPRO and DVCAM. grades of fluoroelastomer have a unique cure site monomer monomer (mŏn`əmər): see polymer. monomer Molecule of any of a class of mostly organic compounds that can react with other molecules of the same or other compounds to form very large molecules (polymers). system (ref. 11) that provides improved processability, faster cure rates, low mold fouling and improved hot-demolding properties. These new fluoroelastomers were designed to be more efficiently cured with peroxides compared to the grades previously developed. Figure 7 provides a VTR 8600 carbon black based formulation and MDR rheographs, where the crosslinking performance of DBPH-50, 130-XL and the novel DBPH-50-HP were compared (ref. 12). The results show that DBHP-50-HP provided superior scorch time protection that surpasses 130-XL, a peroxide with a significantly higher half-life stability compared to DBPH. [FIGURE 7 OMITTED] This unexpectedly higher scorch time data compared to 130-XL are further supported by a significantly greater mold filling capability for high performance DBPH-50-HP compared to the other two peroxides (ref. 13). Thus, DBPH-50-HP provides the benefit of good crosslinking performance, with enhanced scorch time safety, based on rheometer and actual mold filling tests. Lastly, DuPont Dow (ref. 14) found that DBPH-50-HP provided a lower percent compression set, when tested at 200[degrees]C for 22 hours, versus DBPH-50 and 130-XL type peroxides. Thus, the HP cure system helps the manufacturer better utilize the full engineering capabilities of this new fluoroelastomer. In summary, DBPH-50-HP provides the best combination of scorch protection, improved mold flow and final physical properties for this new grade of fluoroelastomer developed by DuPont Dow Elastomers. Summary In this article, we have described the two major classes of organic peroxides used for the crosslinking of various elastomers. These are the dialkyl and peroxyketal type peroxides. Several examples were given for crosslinking EPDM and EVA. By reviewing the decomposition mechanism, the type and energies of the free radicals produced, and the half-life of the various peroxides, we come to a better understanding of the crosslinking reaction. With this understanding, one can better tailor the crosslinking reaction speed and efficiency by making proper choices when selecting an organic peroxide. In addition, there are ways to further modify the crosslink network by the use of peroxide-coagent blends to achieve desired improvements in productivity, solving problems associated with odor, bloom, scorch time, mold flow issues, flex-fatigue and hot tear strength. Lastly, we reviewed recent data on a high performance peroxide, DBPH-50-HR for crosslinking a new grade of FKM elastomer.
Table 1--abbreviations
Abbreviation Chemical name/description
DBPH 2,5-dimethyl-2,5-di(t-butylperoxy)hexane
DBPH-50 2,5-dimethyl-2,5-di(t-butylperoxy)hexane; 45-48% on
CaC[0.sub.3]
DBPH-50-HP 2,5-dimethyl-2,5-di(t-butylperoxy)hexane; 45% on
CaC[0.sub.3] containing high performance proprietary
additives
DCP Dicumyl peroxide
DCP-40KE Dicumyl peroxide 40% on clay
EPDM Poly(ethylene-propylene-diene) terpolymer
EPM Poly(ethylene-propylene) copolymer
EVA Poly(ethylene vinyl acetate)
FKM Fluoroelastomer
MDR Moving die rheometer
RPA Rubber process analyzer
SR 351 Trimethylol propane triacrylate
TAC Triallyl cyanurate
TMQ Polymerized 1,2-dihydro-2,2,4-trimethylquinone (an
antioxidant)
VC-R m/p-di(t-butylperoxy)diisopropylbenzene
VMQ Silicone elastomer
ZnDMA Zinc dimethacrylate
130-XL 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3; 40% on
calcium carbonate
230-XL n-butyl-4,4-di-(t-butylperoxy)valerate; 40% on calcium
carbonate
231-XL 1,1-Di(t-butylperoxy)-3,3,5-trimethylcyclohexane; 40%
on CaC[0.sub.3]
802-40KE m/p-di(t-butylperoxy)diisopropylbenzene; 40% on clay
Table 4--cure performance of various dialkyl
type peroxides in a general purpose EPDM
elastomer
Formulation
Ingredient Phr
EPDM 100
N-990 40
N-550 25
Sunpar 2280 10
ZnO 5
40% peroxide See below
Peroxide type DCP-40KE 802-40KE DBPH-50
Phr 7.0 4.3 5.5
Moles of peroxide groups 0.0102 0.0104 0.0170
Crosslinking in an MDR 2000E at 180[degrees]C, 1[degrees] arc
MH (dN-m) 14.60 15.66 16.05
ML (dN-m) 3.06 3.00 3.00
[T.sub.S 0.4] (seconds) 18.6 22.2 22.8
[T.sub.C90] (minutes) 2.93 5.36 6.32
Mooney viscosity and scorch time at 135[degrees]C
Mooney viscosity 44.1 43.1 43.1
t5 (minutes) 7.8 15.2 16.2
Notes
DCP 40KE = dicumyl peroxide (40% on clay)
802 40KE = K,K'-di(t-butylperoxy)diisopropylbenzene (40% on clay)
DBPH-50 = 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (45% on
CaC[0.sub.3])
Molecular weight information
DCP 40KE = 270.37 g/mole; 802 40KE = 338.48 g/mole:
DBPH-50 = 290.44 g/mole
Table 5--crosslink bond strength
Crosslink system Bond Bond strength (kJ)
Peroxide C-C 350
Peroxide and coagent C-C 350
Peroxide and m. coagent 0-[M.sup.++]-[O.sup.-] (intermediate
~294/300)
Low sulfur C-S 285
Std. Sulfur S-S 155-270
Table 6--comparing the crosslinking
performance of two dialkyl type peroxides to
a peroxyketal type peroxide (231-XL)
Formulation
Ingredient Phr
EPDM 100 100
N330 50 50
Paraffinic oil 10 10
Zinc oxide 5 5
Zinc stearate 2
TMQ 2
Peroxide See below
Crosslinking EPDM (70 ethylene, high diene)
DCP-40KE 5 -- --
802-40KE -- 3.13 --
231-XL -- -- 9.4
Peroxide (moles) 1 1 3.4
Moving die rheometer at 180[degrees]C, 1[degrees] arc
[M.sub.H]-[M.sub.L](in.-lbs.) 24.2 23.7 23.3
[T.sub.s1](min.) 0.36 0.44 0.22
[T.sub.c50](min.) 1.20 2.04 0.37
[T.sub.c90](min.) 3.25 5.96 0.58
Molecular weight information: DCP-40KE = 270.37 g/mole;
802-40KE = 338.48 g/mole; 231-XL = 334.45 g/mole
Table 7--blends of peroxides and coagents to
produce desired carbon-carbon bond type
croslinks
Crosslinking EVA using 230-XL and SR 507
802-40KE 2.5 -- --
230-XL -- 4.5 3.0
TAC (SR 507) -- -- 1.0
Crosslinking ODR at 330[degrees]F (165.5[degrees]C), 3[degrees] arc
[M.sub.H] (in.-lbs.) 62 51 79
[M.sub.L] (in.-lbs.) 10 11 11
[T.sub.S2] (minutes) 2.4 1.5 1.6
[T.sub.c90] (minutes) 17 5.4 5.3
Table 9--crosslinking EPDM using peroxides alone and
in blends versus a sulfur cure
EPDM 100 100 100 100 100 100 100
N 330 50 50 50 50 50 50 50
Paraffinic 10 10 10 10 10 10 10
Zinc oxide 5 5 5 5 5 5 5
Zinc 2 2 2 2 2 2 2
TMQ 2 2 2 2 2 2 2
Sulfur 0.5 0 0 0 0 0 0
Sulfads 0.5 0 0 0 0 0 0
Unads 1.5 0 0 0 0 0 0
B. Zimate 4
DCP-40KE 0 5 3.5 0 0 0 0
ZnDMA (SR 0 0 5 0 5 0 5
802 40KE 0 0 0 3.13 2.19 0 0
231-XL40 0 0 0 0 0 9.40 6.58
Crosslinking at 180[degrees]C, 1 degree arc moving die
MH 27.69 27.43 27.66 26.81 27.22 27.32 27.11
ML 4.21 3.26 3.00 3.13 2.99 3.98 4.44
MH-ML 23.48 24.17 24.66 23.68 24.23 23.34 22.67
TS1 0.48 0.36 0.34 0.44 0.405 0.22 0.19
TS2 0.61 0.42 0.39 0.57 0.50 0.24 0.21
TC50 1.24 1.20 1.11 2.04 1.89 0.37 0.32
TC90 1.76 3.24 3.10 5.96 5.87 0.58 0.53
S' max 27.69 27.43 27.66 26.81 27.22 27.32 27.11
S" max 2.73 2.33 3.31 2.39 3.26 2.36 3.45
Tan D max 0.098 0.085 0.120 0.089 0.120 0.086 0.127
S' fin 24.68 27.14 27.49 26.63 26.81 26.37 25.23
S" fin 5.71 2.42 3.34 2.47 3.39 2.44 3.52
Tan D fin 0.231 0.089 0.122 0.093 0.126 0.092 0.140
Table 10--use of dicumyl peroxide and zinc
dimethacrylate to provide a blend of covalent
and ionic crosslinks
Crosslinking EPDM
Example of [O.sup.-]-[M.sup.++]-[O.sup.-] bond with peroxide and
coagent
Sulfur 0.5 0 0
Sulfads 0.5 0 0
Unads 1.5 0 0
B. Zimate 4 0 0
Luperox DC40KEP 0 5 3.5
ZnDMA (SR708) 0 0 5
Crosslinking at 180[degrees]C, 1 degree arc moving die rheometer
MH 27.69 27.43 27.66
MH-ML 23.48 24.17 24.66
TC90 1.76 3.24 3.10
Above samples were fully cured at 180[degrees]C in the rubber
process analyzer, then subjected to a 3[degrees] arc (42% strain)
at 180[degrees]C for one hour (see figure 4).
References (1.) Sanchez, J. and Myers, T.N., "Organic peroxides," Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, Volume 18, (1996)pp. 203-310 (2.) Technical publication and computer diskette The official name for the floppy disk. See floppy disk. diskette - floppy disk , "Half-life peroxide selection based on half-life," Atofina Chemicals, Inc. (3.) Moving die rheometer manufactured by Alpha Technologies, Inc. (4.) Palys, L.H., Callais, P.A., Novits, F. and Moskal, M.G., "Selection and use of organic peroxides for crosslinking," presented at a meeting of the Rubber Division, ACS (Asynchronous Communications Server) See network access server. , May 5-8, 1998. (5.) Atofina Chemicals, "Indirect food additives food additives, substances added to foods by manufacturers to prevent spoilage or to enhance appearance, taste, texture, or nutritive value. By quantity, the most common food additives are flavorings, which include spices, vinegar, synthetic flavors, and, in the summary," Bulletin. (6.) Alpha Technologies, Inc. (7.) A commercial product of the Sartomer Company, Inc. (8.) Richard Costin and Walter Nagel, Sartomer bulletin and technical paper, "Selecting acrylic type coagents for hose and belt applications." (9.) Sartomer bulletin "Use of acrylate Noun 1. acrylate - a salt or ester of propenoic acid propenoate salt - a compound formed by replacing hydrogen in an acid by a metal (or a radical that acts like a metal) and polybutadiene coagents as reactive plasticizers plasticizers mostly triaryl phosphates, such as tricresyl, triphenyl phosphates, which are poisonous. See also triorthocresyl phosphate. ." (10.) Palys, L.H., Callais, P.A., Novits, M.F. and Moskal, M.G., "New peroxide formulations for crosslinking chlorinated chlorinated /chlo·ri·nat·ed/ (klor´i-nat?ed) treated or charged with chlorine. chlorinated charged with chlorine. chlorinated acids some, e.g. polyethylene, silicone, fluoroelastomer and polyethylene co-and terpolymer ter·pol·y·mer n. A polymer that consists of three distinct monomers. [Latin ter, thrice; see trei- in Indo-European roots + polymer.] type elastomers," presented at a meeting of the Rubber Division, ACS, May, 1997. (11.) Stevens, R.D. and Lyons, D.F., "New improved processing HFP-peroxide cured types of Viton," presented at a meeting of the Rubber Division, ACS, October, 2001. (12.) MDR rheograph data provided courtesy of Ronald Stevens and Eric Thomas Eric Thomas may refer to:
(13.) Spider Flow mold data provided courtesy of Ronald Stevens, DuPont Dow Elastomers. (14.) Viton VTR 8600, 200[degrees]C percent compression set data provided courtesy of Ronald Stevens, DuPont Dow Elastomers. |
|
||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion