Physical properties of peroxide cured HXNBR based compounds.Improving the mechanical properties and heat resistance of existing classes of robber materials to meet the increasing demands of modern engineering applications is a constant challenge. Hydrogenated nitrile nitrile: see rubber. butadiene butadiene (by  t'ədī`ēn), colorless, gaseous hydrocarbon. There are two structural isomers of butadiene; they differ in the location of the two carbon-carbon double bonds in the robber (HNBR HNBR Hydrogenated Acrylonitrile-Butadiene Rubber ) is a high performance 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. that was
developed specifically to meet these increasingly stringent demands.
Introducing a carboxylic acid carboxylic acid: see carboxyl group. carboxylic acid Any organic compound with the general chemical formula −COOH in which a carbon (C) atom is bonded to an oxygen (O) atom by a double bond to make a carbonyl group (−C=O; see group attached to the backbone through and through; thoroughly; entirely. - Lord Lytton. See also: Backbone of HNBR to form HXNBR is expected to further improve HNBR's superior mechanical strength, adhesion properties 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. Reference to a carboxyl carboxyl /car·box·yl/ (kahr-bok´sil) the monovalent radical —COOH, occurring in those organic acids termed carboxylic acids. car·box·yl n. elastomer can be found as early as 1933 in a French patent, while the earliest carboxyl nitrile elastomer mention is in a patent published in 1946. Since the commercial introduction of carboxylated nitrile rubber Nitrile rubber, or Buna-N,is a synthetic rubber copolymer of acrylonitrile (ACN) and butadiene. Some trade names are: Nipol, Krynac and Europrene. in 1955, it has been widely known in the industry that derivative XNBR XNBR Carboxylated Nitrile Rubber compounds could present excellent tensile and tear strength, as well as good abrasion resistance. The prospect of aggregating these mechanical properties with the chemical and thermal advantages produced by hydrogenation hydrogenation (hīdrôj`ənā'shən, hī'drəjənā`shən), chemical reaction of a substance with molecular hydrogen, usually in the presence of a catalyst. has driven a significant body of research ever since the commercial development of hydrogenated nitrilebutadiene robber in the mid-1980s. Hydrogenated carboxylated nitrile butadiene robber (HXNBR) is formed by polymerizing a conjugated conjugated adj. Conjugate. estrogens, conjugated Warning - Hazardous drug! C.E.S. diene Dienes are hydrocarbons which contain two double bonds. Dienes are intermediate between alkenes and polyenes. Classes Dienes can be divided into three classes:
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. carboxylic acid such as acrylic or methacrylic acid methacrylic acid /meth·a·cryl·ic ac·id/ (meth?ah-kril´ik) an organic acid that polymerizes easily to form a ceramic-like mass. Its esters, methyl and polymethyl methacrylate, are used in the manufacture of acrylic resins and plastics. to produce a polymer with a C=C backbone and a random or statistical 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). distribution. However, selective hydrogenation of the C=C double bonds without other side reactions proved problematic (ref. 1). Earlier attempts to circumvent this problem by carboxylating a partially saturated hydrogenated nitrile rubber (XHNBR) have proven unsatisfactory. The approach involved polymerizing a conjugated diene and an unsaturated nitrile followed by hydrogenating the product. In a second post-polymerization reaction, the HNBR product is carboxylated with a carboxylic acid such as maleic acid maleic acid (məlē`ĭk): see fumaric acid. to produce carboxylated hydrogenated nitrile-butadiene rubber (XHNBR). XHNBR differs from HXNBR in a couple of important respects. First, the carboxylic acid requires a C=C double bond in the HNBR as a reaction site. Hence, the degree of saturation Degree of saturation is a physical property of soil indicating a degree of saturation of pores in a soil. It is defined as a ratio of total volume of water (liquid phase content) and total volume of voids (liquid and gas phase): in HNBR must be carefully controlled to ensure the presence of an adequate number of reaction sites. The resulting sites are double bonds in the polymer backbone from the 1,4-addition, most likely in trans configuration. However, because the available reactive sites are unevenly distributed throughout the polymer chain, it is very difficult to control either the level or distribution of the acid in the polymer (ref. 2). A second consequence of the XHNBR two post-polymerization reaction process is a significant increase in production costs over the single post-polymerization reaction required to produce HXNBR. To counter the problems inherent in the earlier XHNBR process, Bayer has developed a method for selectively hydrogenating a carboxylated nitrile rubber so that only hydrogenation of the C=C double bonds occurs. The resulting product, known as Therban XT VPKA 8889 (XT), is an HXNBR terpolymer ter·pol·y·mer n. A polymer that consists of three distinct monomers. [Latin ter, thrice; see trei- in Indo-European roots + polymer.] that is substantially flee from carboxyl group carboxyl group (kärbŏk`sĭl), in chemistry, functional group that consists of a carbon atom joined to an oxygen atom by a double bond and to a hydroxyl group, OH, by a single bond. hydrogenation (ref. 3). With only one post-polymerization reaction required to hydrogenate hydrogenate to cause to combine with hydrogen; to reduce with hydrogen. the XNBR, the process is both less expensive and more highly controllable than the process used to make XHNBR. Bayer utilizes very selective catalysis catalysis Modification (usually acceleration) of a chemical reaction rate by addition of a catalyst, which combines with the reactants but is ultimately regenerated so that its amount remains unchanged and the chemical equilibrium of the conditions of the reaction is not in the polymerization polymerization Any process in which monomers combine chemically to produce a polymer. The monomer molecules—which in the polymer usually number from at least 100 to many thousands—may or may not all be the same. process to randomize ran·dom·ize tr.v. ran·dom·ized, ran·dom·iz·ing, ran·dom·iz·es To make random in arrangement, especially in order to control the variables in an experiment. the distribution of the carboxyl reaction sites, which in turn governs both the levels and distribution of the acid throughout the polymer chain. Performance characteristics Typical characteristics of XT include a polymer Mooney of 77 (ML 1+4 @ 100 [degrees] C), 33% ACN ACN Accenture (stock symbol) ACN Accenture ACN Australian Company Number ACN Automatic Collision Notification (US DOT) ACN Acetonitrile ACN Anglican Communion Network content and 3.5% residual 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. . Both existing sulfur and peroxide cure systems can be used, however optimal scorch safety is achieved with zinc peroxide Zinc peroxide (ZnO2) is a chemical compound used as a bleaching and curing agent. Perhaps its most important use is to promote cross-linking in carboxylated nitrile rubber and other elastomers. as activator, instead of ZnO (ref. 4). Ionic crosslinks can be generated on the carboxylic acid sites in the presence of multivalent multivalent /mul·ti·va·lent/ (-val´ent) 1. having the power of combining with three or more univalent atoms. 2. active against several strains of an organism. metal ions. Other bifunctional bi·func·tion·al adj. 1. Having two functions: bifunctional neurons. 2. Chemistry Having or involving two functional groups or binding sites: chemicals that can react with carboxylic acid can also be used as crosslink agents. Because of the presence of carboxylic acid groups in HNBR polymer chains, XT vulcanizates have very unique physical properties. As we might expect, the strength and abrasion performance characteristics of the XNBR feedstock are conveyed to XT vulcanizates. However, a main objective is also to migrate the high temperature performance properties, characteristic of hydrogenated nitrile-butadiene rubber to compounds created with this polymer. Table 1 presents the formulations used for this investigation. A regular grade of HNBR and a XNBR polymer are used for comparison with HXNBR. The most obvious difference between HXNBR and XNBR is the level of C=C in the polymer chain. We would expect that the physical properties of HXNBR will be superior to XNBR because the conversion of butadiene units into ethylene units should result in a more rugged polymer. Also, because residual saturation is low in the HXNBR (below 5%), an improved heat aging resistance is expected. Effects of temperature on physical properties The three compounds were tested at different strains for 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 , 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. at break and modulus at 23, 100, 125, 150 and 170 [degrees] C. As Table 2 demonstrates, the XT (HXNBR) based compound presents a very different property profile from the other two. Due mainly to the presence of additional ionic crosslinks, when the samples were tested at room temperature both carboxylated polymers demonstrated both a higher modulus and higher tensile strength than HNBR. However, the HXNBR based compound yields a superior elongation at break than the XNBR based compound. The HXNBR based compound also exhibits the best tensile strength at high testing temperatures. Table 2 shows that, overall, the XT based compound has the best physical properties at testing temperatures as high as 170 [degrees] C. Hot tear strength Table 3 and Figure 1 show that, compared to XNBR and HNBR, the HXNBR compound possesses excellent tear strength at all temperatures in both die B and die C tear tests. At 100 to 170 [degrees] C, for example, XT's die B tear strength remains in the 30-40 kN/m range, while the die B tear for XNBR and HNBR are only between 10-20 kN/m. The HXNBR die C tear strength is also significantly higher than that of the HNBR and XNBR based compound in the 23-170 [degrees] C temperature range. [FIGURE 1 OMITTED] As we would expect, because the distributed polymer structure includes a small percentage of carboxylic acid, the low temperature flexibility of the HXNBR compound is not as great as regular HNBR. This is demonstrated in the TR test results expressed in table 4. However, the low temperature test results of HXNBR compounds are comparable to XNBR. Abrasion resistance As we noted at the outset, it is well known that the introduction of carboxylic acid groups into a nitrile-butadiene polymer improves abrasion resistance (ref. 5). This effect is also shown in our Pico abrasion tests on compounds produced with a peroxide cure system. The Pico abrasive index of HXNBR is compared with two HNBR with 34% and 28% ACN, respectively. It is clear that HXNBR had much better Pico abrasion resistance than regular HNBR (figure 2). This unique property of HXNBR indicates that this polymer has very important potential in applications such as rubber rolls and shaft seals. [FIGURE 2 OMITTED] One anticipated special property of XT (HXNBR) is improved adhesion to other materials, including natural fibers, fabrics, metals and plastics. It displays particularly good adhesion when the substrate to which it is applied also bears polar groups. Of particular interest is the fact that superior adhesion is maintained even at elevated temperatures. Whereas HNBR and XNBR also demonstrate good adhesion at room temperature, it declines as the temperature increases. The adhesion of HXNBR, XNBR and HNBR compounds to a nylon fabric was tested at both room temperature and 125 [degrees] C. The results of this test for HNBR, XNBR and HXNBR, respectively, can be seen in figure 3. HXNBR both surpasses the other two polymers at room temperature, maintaining its advantage at high temperature. [FIGURE 3 OMITTED] XT (HXNBR) for processibility XT must be processed with somewhat more care than most other synthetic rubber synthetic rubber: see rubber. compounds due to the presence of the carboxyl groups and the fact that it has excellent high temperature adhesion properties. Not unlike XNBR recipes, XT requires lower mixing temperatures with a drop at <150 [degrees] C recommended. To prevent stickiness, a processing aid such as 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 or low molecular weight polyethylene can be used (ref. 6). It is also important to add metal curatives at the second stage of the mix (Zn[O.sub.2] delivers better scorch safety than ZnO). Compounds utilizing white fillers must be carefully monitored to prevent scorching scorch v. scorched, scorch·ing, scorch·es v.tr. 1. To burn superficially so as to discolor or damage the texture of. See Synonyms at burn1. 2. , however succinic anhydride/phthalic anhydride anhydride (ănhī`drīd, –drĭd) [Gr.,=without water], chemical compound formed by removing water, H2O, from another compound; the anhydride can also react with water to form the original compound. can improve scorch safety in both sulfur and peroxide cure systems. Aging characteristics of HXNBR The reader may be aware that carboxylated nitrile-butadiene rubber has generally poor aging properties due to the presence of both the C=C and carboxyl groups when compared to both regular and hydrogenated 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 . Similarly, an HNBR grade has better aging resistance when compared to HXNBR. However, XT has significantly superior aging properties than either NBR or XNBR, as illustrated in figure 4. [FIGURE 4 OMITTED] Blends As the data illustrate in figure 5, significant performance advantages can be realized by blending HNBR XT and HNBR with ZDA. The result is a higher modulus and tensile strength than exhibited by either product alone. [FIGURE 5 OMITTED] Blending also improves the low temperature properties of the compound. Furthermore, the Pico abrasion resistance can be as much as doubled by blending as little as 25 phr XT into the recipe. As we observe in figure 6, a compound of 100% XT without ZDA ([diamond] line) has a characteristic peak at about 60-80 [degrees] C. This is thought to be associated with the breaking of ionic bonds. This peak is largely absent from the curves for the blends that include ZDA. [FIGURE 6 OMITTED] Summary and conclusions As figure 7 illustrates, peroxide cured XT based compounds present unusually high tear strength at high temperature when compared with regular HNBR, giving this polymer significant potential in applications where resistance to hot tear is required. [FIGURE 7 OMITTED] These compounds also have higher tear tensile strength and higher elongation at break at high temperature than either regular HNBR and XNBR based compounds. Compared to HNBR and XNBR, XT has excellent adhesion to nylon fabrics that are used in the belt industry. There is a lack of temperature dependence in the XT adhesion properties, giving it particularly dramatic high temperature performance. XT's abrasion resistance is much better than regular HNBR and considerably better than XNBR throughout our temperature test range. XT's higher Tg is apparent as the peak tan delta shifts to the right (compare blue line and red line). Blended compounds with up to 40 phr XT have a tan delta peak at about the same temperature as the peak for HNBR/ZDA. This means that the blend has a significantly better low temperature flexibility than we would expect for a blend of XT/ZDA. One possible explanation could be that the crosslinking nature of the XT portion in the blend is altered in the presence of ZDA. In summary, our data indicate that XT (HXNBR) is an excellent material choice for applications such as oil well specialties where a high modulus, high strength polymer is required to hold up against high pressure decompression decompression /de·com·pres·sion/ (de?kom-presh´un) removal of pressure, especially from deep-sea divers and caisson workers to prevent bends, and from persons ascending to great heights. explosion. This product also promises significant performance advantages for applications requiring adhesion to metals, plastics, natural and synthetic fibers. In addition, the excellent Pico abrasion resistance of XT also makes it a good choice for applications that need this type of performance. XT can be easily blended with regular HNBR. In the presence ZDA, the blend of XT with regular HNBR shows excellent mechanical properties, enhanced adhesion and Pico abrasion resistance, as well as good low temperature properties. While more data and experience are required to further investigate the potentials for blending HXNBR with HNBR and other elastomers in order to further improve the performance of this new specialty Therban grade, early data are very encouraging.
Table 1 - formulation of HNBR, XNBR and HXNBR based
compounds
Compound 99SF 57 58 59 60 61 62
Carbon black, N660 1A 50 50 50 50 50 50
Therban XT 1A 100 100
XNBR 1A 100 100
HNBR 1A 100 100
Naugard 445 1B 1 1 1 1 1 1
Plasthall TOTM 1B 5 5 5 5 5 5
Stearic acid 1B 1 1 1 1 1 1
Diak #7 2A 1.5 1.5 1.5 1.5 1.5 1.5
Struktol ZP 1014 2A 7 7 7
Vulcup 40KE 2A 7.5 7.5 7.5 7.5 7.5 7.5
Vulkanox ZMB-2/C5
(ZMMBI) 2A 0.4 0.4 0.4 0.4 0.4 0.4
Zinc oxide 2A 3 3 3
Total 169.4 173.4 169.4 173.4 169.4 173.4
Table 2 - comparative tensile strength and
elongation at break
Compound HNBR XNBR HXNBR
Test temperature ([degrees] C) 23 23 23
Hardness durom. A2 inst. (pts.) 67 84 81
Ultimate tensile (MPa) 23.63 25.66 29.3
Ultimate elongation (%) 223 138 231
Test temperature ([degrees] C) 100 100 100
Hardness durom. A2 inst. (pts.) 65 74 67
Ultimate tensile (MPa) 8.47 15.32 17.96
Ultimate elongation (%) 109 116 329
Test temperature ([degrees] C) 125 125 125
Hardness durom. A2 inst. (pts.) 65 76 66
Ultimate tensile (MPa) 6.73 11.36 15.32
Ultimate elongation (%) 95 100 288
Test temperature ([degrees] C) 150 150 150
Hardness durom. A2 inst. (pts.) 65 66 67
Ultimate tensile (MPa) 6.46 10.03 13.21
Ultimate elongation (%) 87 89 257
Test temperature ([degrees] C) 170 170 170
Hardness durom. A2 inst. (pts.) 67 72 72
Ultimate tensile (MPa) 4.64 7.54 10.51
Table 3 - comparative tear strength of HXNBR, XNBR and
HNBR compounds
HNBR+Zn HNBR+Zn
Die B (kN/m) HNBR+ZnO [O.sup.2] XNBR+ZnO [O.sup.2]
23 [degrees] C 46.95 40.69 50.73 43.74
100 [degrees] C 16.26 15.09 23.51 21.41
125 [degrees] C 18.08 12.2 20.18 18.3
150 [degrees] C 9.25 17.49 19.25 18.1
170 [degrees] C 11.02 10.54 16.43 14.44
Die C (kN/m)
23 [degrees] C 32.46 34.45 23.51 20.42
100 [degrees] C 11.25 11.03 10.77 7.23
125 [degrees] C 8.85 7.9 9.18 6.44
150 [degrees] C 4.57 5.5 6.79 5.12
170 [degrees] C 4.23 4.56 6.69 4.62
HNBR+Zn
Die B (kN/m) HXNBR+ZnO [O.sup.2]
23 [degrees] C 85.45 62.18
100 [degrees] C 39.76 31.65
125 [degrees] C 31.63 25.01
150 [degrees] C 38.56 27.52
170 [degrees] C 30.61 27.34
Die C (kN/m)
23 [degrees] C 32.28 28.09
100 [degrees] C 21.74 20.37
125 [degrees] C 19.77 16.86
150 [degrees] C 16.22 14.11
170 [degrees] C 12.97 13.04
Table 4 - temperature retraction comparison
HNBR XNBR HXNBR
Cure time (min.) 20 20 20
Cure temperature ([degrees] C) 170 170 170
Initial elongation (%) 50% 50% 50%
TR 10 ([degrees] C) -22 -14 -14
TR 30 ([degrees] C) -19 -8 -8
TR 50 ([degrees] C) -16 -1 -2
TR 70 ([degrees] C) -13 5 3
Temp. retraction TR10-TR70 9 19 17
Table 5 - adhesion test results at different
temperatures
Compound HNBR XNBR HXNBR
Cure time (min.) 40 40 40
Cure temperature ([degrees] C) 160 160 160
Test temperature ([degrees] C) 23 23 23
Adhesion to Nylon Nylon Nylon
Adhesion strength (kNm) 2.92 3.62 4.97
Cure time (min.) 40 40 40
Cure temperature ([degrees] C) 160 160 160
Test temperature ([degrees] C) 125 125 125
Adhesion to Nylon Nylon Nylon
Table 6 - test recipe formulations
XNBR 100
NBR 100
HNBR 100
HXNBR 100
Zinc oxide 3 3
Maglite D 3
Naugard 445 1.5 1.5 1.5 1.5
Carbon black, N660 50 50 50 50
TOTM 5 5 5 5
DIAK #7 1.5 1.5 1.5 1.5
Zinc peroxide (50%) 7 7
Table 7 - HXNBR/HNBR with ZDA blending
Formulations:
HNBR 100 75 60 0
ZDA content 80 60 48 0
Plasticizer 20 15 12 0
Therban XT 0 25 40 100
N330 30 30 30 30
Struktol ZP 1014 7 7 7 7
Vulcup 40KE 6 6 6 6
Table 8 - recipe formulation
Therban A 3407 100
Therban XT VP KA 8889 100
Armeen 18D 0.5 0.5
Naugard 445 1.5 1.5
Carbon black, N660 Sterling-V 50 50
Plasthall TOTM 5 5
Diak #7 1.5 1.5
Struktol ZP 1014 7 7
Vulcup 40KE 7.5 7.5
References (1.) S. Bhattacharjee, A.K. Bhowmick and B.N Avasthi, Makromol. Chem., 193, 659 (1992). (2.) Markownikow's rule: In the ionic addition of hydrogen halides to a C=C double bond, the halogen halogen (hăl`əjĕn) [Gr.,=salt-bearing], any of the chemically active elements found in Group 17 of the periodic table; the name applies especially to fluorine (symbol F), chlorine (Cl), bromine (Br), and iodine (I). attaches itself to the carbon atom Noun 1. carbon atom - an atom of carbon atom - (physics and chemistry) the smallest component of an element having the chemical properties of the element bearing the least number of hydrogen atoms. (3.) The products of hydrogenation of carboxyl groups include aldehyde aldehyde (ăl`dəhīd) [alcohol + New Lat. dehydrogenatus=dehydrogenated], any of a class of organic compounds that contain the carbonyl group, and in which the carbonyl group is bonded to at least one hydrogen; the general , gem diol diol an organic compound containing two hydroxy groups, a dihydric alcohol. Called also glycol. and hydroxyl groups. (4.) Other cure systems are possible. (5.) Stearic acid should be used to reduce stickiness and accelerate cure in black filled compounds. |
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