The effect of cure system on NR bonding.Rubber compounders often create their formulations with a whole range of requirements in mind and then determine how to bond the resulting formulation formulation /for·mu·la·tion/ (for?mu-la´shun) the act or product of formulating. American Law Institute Formulation later, generally as an afterthought af·ter·thought n. An idea, response, or explanation that occurs to one after an event or decision. afterthought Noun 1. . Even if one considers the impact of bonding early in the project, there is often not good data available about the effect of different formulation ingredients on bond integrity. Much of the information available comes from observation and actual production experience, usually obtained without adequate controls. It is hard to find published experimental data on something as fundamental as the effect of accelerators and sulfur sulfur or sulphur (sŭl`fər), nonmetallic chemical element; symbol S; at. no. 16; at. wt. 32.06; m.p. 112.8°C; (rhombic), 119.0°C; (monoclinic), about 120°C; (amorphous); b.p. 444.674°C;; sp. gr. at 20°C;, 2. levels in the cure system. The rubber industry is full of examples of "facts" that everyone knows to be true and which are so widely accepted that it seems a waste of time to question them. However, it is often difficult to find studies or data to support these well-known well-known adj. 1. Widely known; familiar or famous: a well-known performer. 2. Fully known: well-known facts. truisms. This general knowledge base tells us that higher sulfur levels give better bonds and that retarders hurt bonds, but are these generalizations true for all adhesive adhesive, substance capable of sticking to surfaces of other substances and bonding them to one another. The term adhesive cement is sometimes used in place of adhesive, especially when referring to a synthetic adhesive. systems and with all accelerators in different specimen SPECIMEN. A sample; a part of something by which the other may be known. 2. The act of congress of July 4, 1836, section 6, requires the inventor or discoverer of an invention or discovery to accompany his petition and specification for a patent with specimens geometries? Much literature has been published on bonding rubber to metal and testing rubber to metal bonds (refs. 1-7). ASTM ASTM abbr. American Society for Testing and Materials D429 evolved as an official bond testing methodology over the years, beginning with Method A which uses a simple flat bond surface geometry geometry [Gr.,=earth measuring], branch of mathematics concerned with the properties of and relationships between points, lines, planes, and figures and with generalizations of these concepts. to put the bond into tensile stress tensile stress See under axial stress. . It was followed by Method B which was developed as a peel type test in order to better serve in those instances where rubber-metal bonds were more likely to fail in that mode rather than due to simple tension (ref. 8). Method B had the distinct advantage of being quick, easy and inexpensive. After some years of use, D429 had Method C added, which employs a conical conical /con·i·cal/ (kon´i-k'l) cone-shaped. con·i·cal or con·ic adj. Of, relating to, or shaped like a cone. shape in order to create maximum stress along the rubber-metal bond line when a tensile tensile, adj having a degree of elasticity; having the ability to be extended or stretched. force is exerted on the assembly. More recently, Methods D and E were added for testing post 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. bonds. Presently, another method (ref. 9; proposed as Method F) for 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 bonds is under consideration, which involves a smaller convex Convex Curved, as in the shape of the outside of a circle. Usually referring to the price/required yield relationship for option-free bonds. specimen sometimes referred to as the buffer buffer, solution that can keep its relative acidity or alkalinity constant, i.e., keep its pH constant, despite the addition of strong acids or strong bases. specimen. The buffer specimen is essentially a small rubber isolation mount and the geometry is much more characteristic of many actual parts than any of the other test specimens. It is highly 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. since part testing has long been considered to be the final test for bond integrity. A previous paper (ref. 9) showed that different bond test methods yield results that do not always correlate closely in terms of bond strength or mode of failure. Some of these contrasting results reflect substantial differences in the manner in which the rubber-to-metal bond is stressed, making them more meaningful for some actual applications of bonded parts and less meaningful for others, depending on how the bond is stressed in such applications (e.g., shearing shearing In textile manufacturing, the cutting of the raised nap of a pile fabric to a uniform height to enhance appearance. Shearing machines operate much like rotary lawn mowers, and the amount of shearing depends on the desired height of the nap or pile. versus tension versus peeling). The study also showed that the appearance of the failed bond surface does not have a positive correlation Noun 1. positive correlation - a correlation in which large values of one variable are associated with large values of the other and small with small; the correlation coefficient is between 0 and +1 direct correlation with bond strength, and the use of visual standards in preference to force to failure measurements is inappropriate in evaluating bond quality. Furthermore, the test specimen geometry impacts the ability to discriminate dis·crim·i·nate v. dis·crim·i·nat·ed, dis·crim·i·nat·ing, dis·crim·i·nates v.intr. 1. a. between the bond strength of different formulations and adhesive systems and the Method F buffer had the most consistent ability to discriminate differences in responses. This article continues the bond investigations by concentrating on the influence of sulfur 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. choices in natural rubber. To determine the effect of sulfur, two levels were chosen. The lower level of 0.7 phr was chosen as being representative of an efficient vulcanization (EV) cure system and 2.1 phr was chosen for the higher level as being representative of a more conventional sulfur system. The lower level of sulfur is soluble soluble /sol·u·ble/ (sol´u-b'l) susceptible of being dissolved. sol·u·ble adj. Capable of being dissolved, especially easily dissolved. in a NR formulation and shows up not only in EV cure systems, but also in soluble cure systems. Four different accelerators were chosen as part of the main design with the levels of each being adjusted such that the modulus See modulo. and hardness properties were as similar as possible between the high and low sulfur compounds. We felt that this would also keep the crosslink densities relatively similar, although crosslink density was not explicitly measured. The main accelerators used were N-cyclohexyl-2-benzothiazylsulfenamide (CBTS CBTS Computer Based Training System CBTS Computer Based Training Squadron CBTS Can't Be Too Sure ), tetramethylthiuram disulfide tetramethylthiuram disulfide relatively nontoxic acaricide. Experimentally rams show testicular degeneration, hen birds lay soft-shelled eggs and eggs with other abnormalities. Called also thiram. (TMTD TMTD tetramethylthiuram disulfide. ), zinc zinc, metallic chemical element; symbol Zn; at. no. 30; at. wt. 65.38; m.p. 419.58°C;; b.p. 907°C;; sp. gr. 7.133 at 25°C;; valence +2. Zinc is a lustrous bluish-white metal. It is found in Group 12 of the periodic table. dimethyldithiocarbamate (ZDMDC) and dibenzothiazyl disulfide di·sul·fide n. A chemical compound containing two sulfur atoms combined with other elements or radicals. Also called bisulfide. (MBTS MBTS 2-Mercaptobenzothiazyl Disulfide MBTS Missile Bit Test Set MBTS Missile Bench Test Set ). The four accelerators were chosen to represent four major accelerator classes: sulfenamides, thiurams, dithiocarbamates dithiocarbamates fungal seed dressing unlikely to be poisonous for animals. and thiazoles. Obviously, dithiocarbamates would be unlikely to be used as the primary accelerator in most NR formulations due to scorch concerns, but knowledge of their impact on bonding is considered useful in making an informed decision about their influence in a formulation. In addition to the eight runs in the designed experiment, several out-of-design compounds were compared to the compounds within the design. These out-of-design compounds include the guanidine guanidine /gua·ni·dine/ (gwah´ni-den) the compound NHdbondC(NH2)2, a strong base found in the urine as a result of protein metabolism and used in the laboratory as a protein denaturant. accelerator Di-o-tolylguanidine (DOTG), a dicumyl 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. cure system (DCP DCP - definitional constraint programming ) and a pre-vulcanization inhibitor inhibitor /in·hib·i·tor/ (in-hib´i-tor) 1. any substance that interferes with a chemical reaction, growth, or other biologic activity. 2. or retarder retarder, n a chemical added to a substance to slow a chemical reaction, prolong the set of the material, and provide more working time. (PVI See Present Value Index. ). Four different adhesives were chosen to be sure that more general conclusions could be drawn that were not limited to a single adhesive system. Experimental The two test methods used for comparison were ASTM D 429 Method B and the proposed Method F buffer specimens. A generic natural rubber (NR) formulation was chosen for the study (table 1) with all compounds being approximately 45 to 50 durometer Du`rom´e`ter n. 1. An instrument for measuring the degree of hardness; especially, an instrument for testing the relative hardness of steel rails and the like. . This hardness was chosen because it has been reported that soft rubber compounds ([is less than] 50 durometer) are more difficult to bond than harder ones (ref. 10). Therefore, if there is an effect on adhesion adhesion /ad·he·sion/ (ad-he´zhun) 1. the property of remaining in close proximity. 2. the stable joining of parts to one another, which may occur abnormally. 3. , this would help to elucidate e·lu·ci·date v. e·lu·ci·dat·ed, e·lu·ci·dat·ing, e·lu·ci·dates v.tr. To make clear or plain, especially by explanation; clarify. v.intr. To give an explanation that serves to clarify. it. Two solvent-based and two aqueous aqueous /aque·ous/ (a´kwe-us) 1. watery; prepared with water. 2. see under humor. a·que·ous adj. adhesive systems were chosen, all four systems employing both a primer prim·er n. A segment of DNA or RNA that is complementary to a given DNA sequence and that is needed to initiate replication by DNA polymerase. and a cover coat. The two solvent-based adhesives and the two aqueous adhesives were selected such that they are each based on different chemistries. The solvent-based selections were Chemlok 205/220 and Chemlok 205/252X, while the aqueous based selections were Chemlok 8007/8560 and Chemlok 8007/8210. Table 1 - rubber formulations and physical properties Compound identity 1 2 3 Ingredient Natural rubber CV60 100.0 100.0 100.0 Zinc oxide 5.0 5.0 5.0 Stearic acid 2.0 2.0 2.0 IPPD 1.0 1.0 1.0 TMQ 1.0 1.0 1.0 N762 carbon black 40.0 40.0 40.0 Light napthenic process oil 5.0 5.0 5.0 Sulfur 0.7 2.1 0.7 CBTS 2.5 0.5 TMTD 1.5 ZDMDC MBTS PVI DOTG Dicumyl peroxide 40% active Cure time at 153 [degrees] C (minutes) 10 10 7 Compound identity 4 5 6 Ingredient Natural rubber CV60 100.0 100.0 100.0 Zinc oxide 5.0 5.0 5.0 Stearic acid 2.0 2.0 2.0 IPPD 1.0 1.0 1.0 TMQ 1.0 1.0 1.0 N762 carbon black 40.0 40.0 40.0 Light napthenic process oil 5.0 5.0 50.0 Sulfur 2.1 0.7 2.1 CBTS TMTD 0.4 ZDMDC 5.0 0.5 MBTS PVI DOTG Dicumyl peroxide 40% active Cure time at 153 [degrees] C (minutes) 7 15 7 Compound identity 7 8 9 Ingredient Natural rubber CV60 100.0 100.0 100.0 Zinc oxide 5.0 5.0 5.0 Stearic acid 2.0 2.0 2.0 IPPD 1.0 1.0 1.0 TMQ 1.0 1.0 1.0 N762 carbon black 40.0 40.0 400.0 Light napthenic process oil 5.0 5.0 5.0 Sulfur 0.7 21.0 0.7 CBTS TMTD 1.7 ZDMDC MBTS 3.5 1.0 PVI 0.6 DOTG Dicumyl peroxide 40% active Cure time at 153 [degrees] C (minutes) 10 10 7 Compound identity 10 11 Ingredient Natural rubber CV60 100.0 100.0 Zinc oxide 5.0 5.0 Stearic acid 2.0 2.0 IPPD 1.0 TMQ 1.0 1.0 N762 carbon black 40.0 40.0 Light napthenic process oil 5.0 5.0 Sulfur 2.1 CBTS TMTD ZDMDC MBTS PVI DOTG 1.0 Dicumyl peroxide 40% active 6.0 Cure time at 153 [degrees] C (minutes) 20 25 Commercially available materials were used in compounding the formulations used in this study (table 2). A masterbatch using ingredients shown in table 3 was mixed in a 50 liter liter, abbr. l, unit of volume in the metric system, defined since 1964 as equal to 0.001 cubic meters, or 1 cubic decimeter. A cube that has each of its edges equal to 10 centimeters has a volume of 1 liter. The liter is equal to 1.057 liquid quarts, 0. 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. . Table 2 - chemical abbreviations and sources IPPD N-isopropyl-N'-phenyl-p-phenylenediamine TMQ Polymerized 2,2,4-trimethyl-1,2-dihydroquinoline CBTS N-cyclohexyl-2-benzothiazylsulfenamides TMTD Tetramethylthiuram disulfide ZDMDC Zinc dimethyldithiocarbamate MBTS Dibenzothiazyl disulfide PVI N-(cyctohexylthio)phthalimide DOTG Di-o-tolylguanidine DCP Dicumyl peroxide 40% active IPPD Flexzone 3C TMQ Flectol H CBTS Santocure pellets TMTD Perkacit TMTD ZDMDC Methyl zimate MBTS Perkacit MBTS PVI Santogard PVI DOTG Akrochem DOTG DCP Dicup 40C Table 3 Natural rubber CV60 100.0 Zinc oxide 5.0 Stearic acid 2.0 IPPD 1.0 TMQ 1.0 N762 carbon black 40.0 Light napthenic process oil 5.0 Sulfur 0.7 The following mix procedure was used: 0 seconds - load polymer; 30 seconds for 75 [degrees] C - load 1/2 black and chemicals; 85 [degrees] C - load 1/2 black and oil; 100 [degrees] C - sweep; 110 [degrees] C - sweep; 120 [degrees] C - dump Additional sulfur (for the high sulfur compounds) and final accelerator addition was performed on a 15 x 30 cm. two-roll mill. The only exception to this was peroxide-cured compound 11. It had both the sulfur and the IPPD IPPD Integrated Product and Process Development IPPD Intellectual Property Policy Directorate (Canada) IPPD Integrated Product and Process Design IPPD Intradermal Purified Protein Derivative (tuberculin skin test) eliminated to prevent interference with the peroxide cure system. Compound 11 was mixed in a BR 1600 lab internal mixer using the same procedure and finished on a 15 x 30 cm. two-roll mill. Testing (tables 4 and 5) was performed per the test methods: Hardness - ASTM D 2240; tensile, 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. and modulus - ASTM D 412 method A; tear die C - ASTM D 624; compression set - ASTM D 395 method B; heat aging - ASTM D 573; dynamic analysis - ASTM D 2231 (double lap shear shear: see strength of materials. Shear A straining action wherein applied forces produce a sliding or skewing type of deformation. ); adhesion - ASTM D 429 method B and F (proposed). Table 4 - physical properties of the formulations Properties 1 2 3 4 Rheometer @ 153 [degrees] C (MDR) Low torque S'(N-m) 1.77 1.89 1.89 1.89 High torque S'(N-m) 9.58 10.67 8.98 10.86 Tc90(minutes) 6.78 7.90 2.46 3.15 Mooney scorch @ 153 [degrees] C Low torque 24.7 26.8 28.0 27.8 Time to 10 pt. rise (minutes) 5.1 4.3 2.4 3.0 Physical properties Hardness (Shore A) 48 47 52 50 Tensile (mPa) 27.6 25.8 26.7 24.2 Elongation (%) 555 560 535 515 100% modulus (mPa) 1.7 1.9 1.8 2.1 Tear die C (kN/m) 81.3 50.6 53.2 46.8 Compression set 22 hrs. at 100 [degrees] C (%) 34.3 42.2 18.2 25.4 Oven aged: 70 hrs at 100 [degrees] C Hardness (Shore A) 56 54 56 53 Tensile (mPa) 22.4 13.4 21.0 8.1 Elongation (%) 450 340 400 225 Hardness change (points) 56 54 56 53 Tensile change (%) -18.9 -47.9 -21.5 -66.6 Elongation change (%) -18.9 -39.3 -25.2 -56.3 Double lap shear moduli G' 10/10(mPa) 1.034 1.076 1.062 1.097 Tan delta 10/10 (G"/G') 0.108 0.095 0.100 0.093 25% static modulus (mPa) 0.876 0.890 0.883 0.910 Properties 5 6 7 8 Rheometer @ 153 [degrees] C (MDR) Low torque S'(N-m) 1.84 1.63 1.89 1.91 High torque S'(N-m) 5.96 9.80 8.97 9.45 Tc90(minutes) 12.59 3.93 6.55 6.69 Mooney scorch @ 153 [degrees] C Low torque 28.0 24.3 27.3 28.2 Time to 10 pt. rise (minutes) 2.5 1.8 3.7 3.1 Physical properties Hardness (Shore A) 44 48 51 48 Tensile (mPa) 21.7 26.1 26.9 25.8 Elongation (%) 585 615 570 565 100% modulus (mPa) 1.1 1.4 1.7 1.8 Tear die C (kN/m) 27.3 50.4 49.2 44.7 Compression set 22 hrs. at 100 [degrees] C (%) 36.4 31.0 29.7 37.1 Oven aged: 70 hrs at 100 [degrees] C Hardness (Shore A) 40 51 54 58 Tensile (mPa) 11.9 16.8 19.7 15.0 Elongation (%) 495 445 415 315 Hardness change (points) 40 51 54 58 Tensile change (%) -45.1 -35.9 -26.6 -41.8 Elongation change (%) -15.4 -27.6 -27.2 -44.2 Double lap shear moduli G' 10/10(mPa) 0.834 0.943 0.972 1.014 Tan delta 10/10 (G"/G') 0.127 0.105 0.101 0.102 25% static modulus (mPa) 0.621 0.744 0.841 0.828 Properties 9 10 11 Rheometer @ 153 [degrees] C (MDR) Low torque S'(N-m) 1.85 1.83 1.20 High torque S'(N-m) 8.93 9.70 6.64 Tc90(minutes) 3.47 14.72 22.05 Mooney scorch @ 153 [degrees] C Low torque 27.0 27.8 18.5 Time to 10 pt. rise (minutes) 2.9 2.2 2.8 Physical properties Hardness (Shore A) 52 48 45 Tensile (mPa) 25.4 24.1 17.4 Elongation (%) 515 530 435 100% modulus (mPa) 1.9 1.8 1.3 Tear die C (kN/m) 64.8 56.9 36.1 Compression set 22 hrs. at 100 [degrees] C (%) 19.3 60.9 12.3 Oven aged: 70 hrs at 100 [degrees] C Hardness (Shore A) 56 54 46 Tensile (mPa) 17.8 10.3 15.6 Elongation (%) 355 310 485 Hardness change (points) 56 54 46 Tensile change (%) -29.9 -57.3 -10.7 Elongation change (%) -31.1 -41.5 11.5 Double lap shear moduli G' 10/10(mPa) 1.117 1.069 0.800 Tan delta 10/10 (G"/G') 0.098 0.105 0.101 25% static modulus (mPa) 0.952 0.876 0.655 Table 5 - bond test results Adhesion testing 1 2 3 4 Method B 45 degrees (kN/m) Chemlok 205/220 7.8 7.9 7.7 7.8 Chemlok 205/252X 6.4 7.1 6.3 6.7 Chemlok 8007/8210 6.9 7.4 6.7 6.2 Chemlok 8007/8560 7.0 7.3 6.5 6.8 Buffer specimens (kN) Chemlok 205/220 1.946 2.826 2.687 2.934 Chemlok205/252X 2.783 3.559 1.619 2.034 Chemlok8007/8210 3.296 3.142 1.907 2.400 Chemlok8007/8560 2.210 1.887 1.386 1.593 Buffer specimens (% rubber) Chemlok 205/220 70 80 75 90 Chemlok205/252X 90 100 100 95 Chemlok8007/8210 100 90 100 100 Chemlok8007/8560 100 100 95 100 Adhesion testing 5 6 7 8 Method B 45 degrees (kN/m) Chemlok 205/220 4.9 7.2 6.8 8.2 Chemlok 205/252X 5.3 6.8 6.1 8.2 Chemlok 8007/8210 5.9 6.3 6.5 8.1 Chemlok 8007/8560 5.5 6.6 6.0 7.9 Buffer specimens (kN) Chemlok 205/220 2.289 2.945 3.340 4.048 Chemlok205/252X 2.708 2.292 2.705 2.304 Chemlok8007/8210 2.608 2.482 2.627 2.897 Chemlok8007/8560 2.027 1.799 2.092 2.072 Buffer specimens (% rubber) Chemlok 205/220 90 85 90 95 Chemlok205/252X 100 100 100 100 Chemlok8007/8210 100 100 100 100 Chemlok8007/8560 100 100 100 100 Adhesion testing 9 10 11 Method B 45 degrees (kN/m) Chemlok 205/220 9.3 7.8 5.9 Chemlok 205/252X 7.5 7.7 6.1 Chemlok 8007/8210 7.2 7.8 6.5 Chemlok 8007/8560 7.3 7.9 6.3 Buffer specimens (kN) Chemlok 205/220 2.856 2.244 3.282 Chemlok205/252X 2.217 3.745 2.566 Chemlok8007/8210 2.024 1.810 2.691 Chemlok8007/8560 1.639 2.185 1.810 Buffer specimens (% rubber) Chemlok 205/220 90 70 100 Chemlok205/252X 100 100 100 Chemlok8007/8210 100 100 100 Chemlok8007/8560 100 100 100 Method B peel tests were chosen because they are commonly used throughout the industry. The method F buffer test was also chosen because it is representative of the geometry of many actual parts. Method B specimens were molded mold 1 n. 1. A hollow form or matrix for shaping a fluid or plastic substance. 2. A frame or model around or on which something is formed or shaped. 3. Something that is made in or shaped on a mold. at 153 [degrees] C and the Method B peel test was run at the allowed 45 [degrees] angle instead of the standard 90 [degrees] angle. 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. the ASTM procedure, "Experience indicates a lower force is obtained for the 45 [degrees] than for the 90 [degrees] angle, and also a break significantly closer to the bond surface." Method F buffer specimens were cured at 153 [degrees] C to the cure times in table 1 plus five minutes. The metal parts were 1020 cold rolled steel which were phosphatized prior to adhesive and primer application. Results and discussion One question which seems logical to ask is whether there is any correlation between the peel results and the buffer results. Figure 1 shows no correlation between the results of the C205/ C220 adhesion testing. Similarly, if the data for all four adhesive systems is grouped together, there is still no correlation between the two within the confines con·fine v. con·fined, con·fin·ing, con·fines v.tr. 1. To keep within bounds; restrict: Please confine your remarks to the issues at hand. See Synonyms at limit. of the experimental space. As a further step, we can ask whether adhesion is a function of either tear resistance or of modulus. Because different adhesive systems may give different results, these correlations were performed only within specific adhesive systems. Figures 2 and 3 plot the buffer results tot C205/C220 as a function of tear die C and of 25% static shear modulus shear modulus See under modulus of elasticity. . Again, no correlation is observed. On the other hand, the same analysis performed for the Method B peel test (figures 4 and 5) shows a significant correlation with both tear and modulus. The relative effect of modulus and tear die C on the method B peel results is minimized because the properties of the compounds used in the study were all relatively similar. [Figures 1-5 ILLUSTRATION OMITTED] The scorch times for the four main accelerator families fall in the expected progression, with dithiocarbamate being the scorchiest followed by thiuram, thiazole thi·a·zole n. 1. A colorless or pale yellow liquid, C3H3NS, containing a five-member ring composed of a nitrogen atom, a sulfur atom, and three carbon atoms, used in making dyes and fungicides. 2. and sulfenamide in order. Other than scorch times and cure times, the rest of the physical properties (table 4) are relatively similar with the exception of the low sulfur cured dithiocarbamate (compound 5) and the peroxide cure (compound 11). The durometer and static modulus values (figure 6) for the low sulfur dithiocarbamate cure (compound 5) and the peroxide cure system (compound 11) are lower than the rest of the compounds. A plus sign next to the accelerator in the graph indicates it is the high sulfur cured variant variant /var·i·ant/ (var´e-ant) 1. something that differs in some characteristic from the class to which it belongs. 2. exhibiting such variation. var·i·ant adj. . This illustrates the difficulty of using dithiocarbamates in low sulfur cures. The compression set and the elongation values for the dithiocarbamate cure system are not out of line with the rest of the compounds, so we concluded that this compound is not technically undercured. The peroxide cured compound is as tightly cured as we dared to go without dropping elongation values unacceptably low, and the extremely low compression set attests to the stability of this cure system. [Figure 6 ILLUSTRATION OMITTED] The first eight compounds (compounds 1-8) form a designed experiment with sulfur at two levels with each of four different accelerators. Figure 7 shows a combination graph for the Method B peel specimens in which the different cure systems are shown (the + denotes higher level of sulfur with the 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. ) and the four cover-coat adhesives are identified. The C205/220 system gives the highest bond strength seven times out of the first eight systems, which appears to be meaningful. The other adhesive systems flip back and forth, and there does not appear to be any general trend among them. However, the high sulfur/thiazole cure system (compound 8) gives consistently higher peel strength with all four adhesive systems. The dithiocarbamate/low sulfur cure (compound 5) gives the lowest peel strength and also is the only system where the C205/220 goes from being highest to being lowest, which may indicate an interaction. [Figure 7 ILLUSTRATION OMITTED] For the buffer specimens (figure 8), we see the C8007/ 8560 fairly consistently produces the lowest bond strengths, and C205/220 is the highest five times out of eight. However, table 5 shows that C8007/8560 produced surface appearance of 100% rubber in almost all cases (one case was 95%), while C205/220 did not give 100% rubber results with any of the sulfur cures. This demonstrates the problem with using visual criteria for evaluation of bond quality when the pub values are extremely high. In some cases, the break values for the C205/220 system are twice as high as for the C8007/8560 system. This study reconfirms that the appearance of the failed bond surface does not have a positive correlation with bond strength. There appears to be no difference between solvent-based system C205/252X and aqueous system C8007/8210. [Figure 8 ILLUSTRATION OMITTED] The low sulfur variants (compounds 1, 3, 5 and 7) represent EV cure systems in natural rubber. It has been reported that rubber to metal bonding may be difficult with EV cure systems (ref. 11), or that lower free sulfur content detracts from rubber to metal bond strength (ref. 12). Figures 7 and 8 show that these generalizations are inaccurate. Across the range of accelerators studied, there is a greater effect on adhesion based on the choice of adhesive system than on the choice of sulfur level or accelerator type. The lack of a consistent trend may indicate interactions between certain adhesives with either accelerator type or sulfur level. It has also been reported in literature that delayed-action delayed-action adj [bomb etc] → de acción retardada delayed-action adj → à retardement delayed-action delay adj ( accelerator systems are preferred for good bonding because they allow optimum contact between cement cement, binding material used in construction and engineering, often called hydraulic cement, typically made by heating a mixture of limestone and clay until it almost fuses and then grinding it to a fine powder. and rubber surface before the onset of vulcanization (ref. 13). The shortest and longest scorch times are in compounds 6 and 1 (table 4) at 1.8 minutes and 5.1 minutes, respectively. Comparison of the adhesion values for those stocks (figures 7 and 8) indicates the bond is not compromised under these conditions with the scorchier stock. A comparison of compound 9 with compound 3 leads us to conclude that PVI (even at relatively high levels) is not necessarily damaging to bond strength (figures 7 and 8). Compound 10, containing a high sulfur cure and a guanidine accelerator, shows the guanidines to be easily bondable, although it suggests that C8007/8210 is not the best choice. There appears to be an interaction when compared to the other three adhesive systems relative to the results obtained for the other accelerators. The high compression set value for the guanidine accelerator suggests it is not a particularly effective choice as a primary accelerator. Compound 11 (peroxide cure) shows that the results for both the buffer test and the Method B peel test are in line with the results obtained for the sulfur cured compounds. Thus we conclude that peroxide is not necessarily more difficult to bond than the accelerated sulfur cure systems. While one can find cases where the high sulfur cure system gives higher results than the low sulfur system, it is clear that there is no general trend, and one cannot generalize generalize /gen·er·al·ize/ (-iz) 1. to spread throughout the body, as when local disease becomes systemic. 2. to form a general principle; to reason inductively. that high sulfur cures are easier to bond than low sulfur cures in natural rubber. Conclusions There is no correlation between the adhesion results obtained using Method B peels and the buffer specimens, i.e., geometry affects the adhesion test results. The Method B peel test shows a strong correlation with both tear and modulus; the buffer test shows no correlation. Buffer pull results were generally highest for C205/220, which did not give 100% rubber retention on any of the sulfur cures. This demonstrates the problem with using visual criteria for evaluating bond quality when the pull values are extremely high. There appears to be no difference between solvent-based system C205/252X and aqueous system 8007/8210. There is no absolute trend to suggest that high-sulfur cures are easier to bond than low-sulfur cures in natural rubber. Peroxide cured natural rubber is not necessarily more difficult to bond than the general range of sulfur-cured natural rubber. The use of PVI in relatively high levels does not inhibit inhibit /in·hib·it/ (in-hib´it) to retard, arrest, or restrain. in·hib·it v. 1. To hold back; restrain. 2. bonding of the thiuram and sulfur cured NR used in this study. This study reconfirms that the visual appearance of the failed bond surface does not have a positive correlation with bond strength. The choice of the adhesive system has a greater impact on bond strength than the choice of the cure system. References (1.) Alstadt, D.M., Rubber World, 133, 221 (1955). (2.) Alstadt, D.M., and Coleman Cole·man , Cy Originally Seymour Kauffman. Born 1929. American composer and theatrical producer whose best known Broadway productions include Sweet Charity (1966) and The Will Rogers Follies (1991). , E.W., Jr., U.S. Patent 2,905,585, to Lord Corporation (September 1959). (3.) Buchan, S., Rubber to Metal Bonding, Palmerton, New York New York, state, United States New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of , 1959. (4.) DeCrease, W.M., Rubber Age, 87, 1,013-1,019 (1960). (5.) Jazenski, P.J., and Manino, L.G., U.S. Patent 4,119,587, to Lord Corporation (October 1978). (6.) Elliot, D.J., Developments in Rubber Technology, Vol. 1, Applied Science, London, 1979, pp. 1-44. (7.) Weih, M.A., Siverling, C.E. and Sexsmith, F.H., Rubber World, 1955, 29-35 (August 1986). (8.) Annual Book of ASTM Standards 1996, Vol. 9.01 (9), ASTM Publications, Philadelphia, 1996, pp. 59-72. (9.) Del Vecchio Del Vecchio is a surname, and may refer to:
(10.) Hofmann, Werner, ed., Rubber Technology Handbook
This article is about reference works. For the subnotebook computer, see .
(11.) Malaysian Rubber Producers' Research Association, Natural Rubber Formulary formulary /for·mu·lary/ (for´mu-lar?e) a collection of recipes, formulas, and prescriptions. National Formulary see under N. for·mu·lar·y n. and Property Index, Imprint of Luton Ltd., England, 1984, p. 16. (12.) Roberts, A.D., ed., Natural Rubber Science and Technology, Oxford University Press, Oxford, 1988, p. 181. (13.) Blow, C.M., and Hepburn, C. ed., Rubber Technology and Manufacture, Butterworth Scientific, London, 1982, pp. 466-467. |
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