Vulcanizate tests

For rapid determination of the tan 6 at low frequencies and room temperature of the large number of rubber vulcanizates tested, we adapted the Yerzley Oscillograph. This equipment was one of the earliest instruments used for determining the dynamic mechanical properties of rubber vulcanizates. 

Fig. 4.8. Failure envelopes from rubber vulcanizates. (a) Schematic representation of the dependence of tensile stress-strain curves for an amorphous rubber on strain rate and temperature (b) failure points for a resin-cured butyl rubber gum vulcanizate tested at various rates and temperatures, = stress at break, b = elongation at break (c) comparison of vulcanizates (Viton B is a fluoroelastomer). Ab = relative extension at break, Ec = equilibrium modulus. (From Smith, 1962.)...

Fig. 10 G -strain curve of NR/ZDMA vulcanizates, test temperature 60 °C and frequency 1 Hz [58]...

Plasticity Retention Index. The oxidation behavior of natural mbber may affect both the processing characteristics and final vulcanizate performance, and the plasticity retention index (PRI) test can be used to give an indication of both. Natural antioxidants present in natural mbber give some protection and a measure of the efficacy of protection is given by PRI. PRI% = P q j Pq x 100, where Pq is the initial Wallace plasticity and P q is the... 

The important vulcanizate properties demanded by this application, low heat buildup, and low dynamic set have been determined in the Goodrich Flexometer test. The compound containing the antireversion agent exhibits a marked decrease in heat buildup and dynamic permanent set (Figures 14.21 and 14.22). 

The hydrogenation of unsaturated polymers and copolymers in the presence of a catalyst offers a potentially useful method for improving and optimizing the mechanical and chemical resistance properties of diene type polymers and copolymers. Several studies have been published describing results of physical and chemical testing of saturated diene polymers such as polybutadiene and nitrile-butadiene rubber (1-5). These reports indicate that one of the ways to overcome the weaknesses of diene polymers, especially nitrile-butadiene rubber vulcanizate, is by the hydrogenation of carbon-carbon double bonds without the transformation of other functional unsaturation such as nitrile or styrene. 

The influence of ZnCFO concentration (3,0 5,0 7,0 phr) on formation of properties complex of the unfilled rubber mixes and their vulcanizates on the basis of isoprene rubber of the following recipe, phr isoprene rubber - 100,0 sulfur - 1,0 di - (2-benzothiazolyl) -disulfide - 0,6 N, N -diphenylguanidine - 3,0 stearic acid - 1,0, was carried out in comparison with the known activator - zinc oxide (5,0 phr). The analysis of Rheometer data of sulfur vulcanization process of elastomeric compositions at 155°C (fig. 5) shows, that on crosslink density and cure rate, about what the constants of speed in the main period (k2) testify, they surpass the control composition with 5,0 phr of zinc oxide. Improvement of the complex of elastic - strong parameters of rubbers with ZnCFO as at normal test conditions, and after thermal air aging (tab. 1), probably, is caused by influence of the new activator on vulcanization network character. So, the percent part of polysulfide bonds (C-Sx-C) and amount of sulfur atoms appropriating to one crosslink (S atoms/crosslink) in vulcanizates with ZnCFO are decreased, the percent part of disulfide bonds (C-S2-C) is increased (fig. 62). 

In all the above methods, it is necessary to cure specimens of test samples for each of a series of curing times and then perform the desired test on the vulcanizate. However, in the test for continuous measurement of vulcanization complete information could be obtained with saving in time. The mooney viscometer test approaches this objective. However a weakness of the mooney viscometer test is that the test is completed before a measurable modulus value after the scorch point has been obtained. This is because the test sample is destroyed after the induction period is passed due to tearing by continuous rotation of the rotor whether small or large. To overcome this deficiency and to provide a total cure curve for the entire vulcanization cycle, a series of instruments called cure meters was developed. In each of these instruments the stiffness or modulus of the compound was chosen as parameters for vulcanization continuously. The Vulkameter developed by Bayers, Germany was the first of the cure meters developed. 

The simplest check on cure is by a hardness determination which is to be done after the vulcanizate is sufficiently cooled to room temperature and the test is done better after 24 hours of cure. 

The testing procedure of properties of elastomeric vulcanizates after immersion in organic liquids is common for both natural and synthetic rubbers. ASTM D171-66 [7] used for this purpose serves as a method for estimating the comparative ability of rubbers to withstand the effects of liquids by examination of the material after removal from the liquid. However proper testing of the physical properties on swollen rubber poses many problems. 

Conan t F.S, The Firestone Tyre and Rubber Company, Akron Ohio, Physical Testing of Vulcanizates, Rubber Technology Second Edition, 1973 by Maurice Morton, Van Nostrand Reinhold Company, NY. 

Figure 8-8. Stress strain curve for pure gum vulcanizate illustrating the difference in stress between the inside (A) and outside (B) circumference of ring test piece...

Finally, it is instructive to compare the temperature effect on the tensile strength of the SBS and SIS block polymers. As noted previously (Figure 6) the tensile strength of an elastomer vulcanizate can be related to the difference between the test temperature and the Tg of the elastomer, in accordance with the viscoelastic theory of tensile strength. Since the Tg values for polyisoprene ( — 65°C) and polybutadiene ( —95°C) differ... 

Vulcanized rubber was ozonized as follows. Natural rubber was compounded with the ingredients shown in Table III and cured at 141 °C. for 13 minutes. The vulcanizates were cut off from the sheets with JIS No. 1 dumbbell cutter to obtain the specimens for the ozone crack test. The test pieces were exposed to an oxygen atmosphere containing 0.01% ozone under an elongation of 50%, and a time, t0, required for the initial crack formation was measured. 

By fitting experimental data for different deformation modes to these functions, the three network parameters of unfilled polymer networks Gc, Ge, and ne/Te can be determined. The validity of the concept can be tested if the estimated fitting parameters for the different deformation modes are compared. A plausibility criterion for the proposed model is formulated by demanding that all deformation modes can be described by a single set of network parameters. The result of this plausibility test is depicted in Fig. 44, where stress-strain data of an unfilled NR-vulcanizate are shown for the three different deformation modes considered above. Obviously, the material parameters found from the fit to the uniaxial data provide a rather good prediction for the two other modes. The observed deviations are within the range of experimental errors. 

These feedstocks were tested in a number of carbon black furnace reactors employing different geometries and different operating conditions. The experiments were designed to develop data for correlation between feedstock composition, yield, production rate, and properties of carbon black produced. The physical properties of the carbon blacks were measured as were the properties of uncured rubber compounds and vulcanizates in standard test recipes. 

Pullout Tests. The method to determine the adhesion between the dipped cords and the SBR vulcanizate was the tire cord adhesion test (L/,75), Figure 1. Here, two cords are embedded (to a depth of 10 mm) into opposite ends of a rubber block (76 mm x 13 mm x 6.4 mm). Samples are then cured 23 min at 155 °C and allowed to rest 1 day. Bond strengths are determined by clamping the two free cord ends in an Instron and pulling at the rate of 50 mm/min. 

Another important point is the question whether static offsets have an influence on strain amplitude sweeps. Shearing data show that this seems not to be the case as detailed studied in [26] where shear rates do not exceed 100 %.However, different tests with low dynamic amplitudes and for different carbon black filled rubbers show pronounced effects of tensile or compressive pre-strain [ 14,28,29]. Unfortunately, no analysis of the presence of harmonics has been performed. The tests indicate that the storage (low dynamic amplitude) modulus E of all filled vulcanizates decreases with increasing static deformation up to a certain value of stretch ratio A, say A, above which E increases rapidly with further increase of A. The amount of filler in the sample has a marked effect on the rate of initial decrease and on the steady increase in E at higher strain. The initial decrease in E with progressive increase in static strain can be attributed to the disruption of the filler network, whereas the steady increase in E at higher extensions (A 1.2. .. 2.0 depending on temperature, frequency, dynamic strain amplitude) has been explained from the limited extensibility of the elastomer chain [30]. 

Swelling tests on the vulcanizates produced are an alternative option. The mean distance between two crosslinks can be applied to determine the concentration of crosslinks [9]. The reaction can only be studied once the gel point has been reached, since only then does a three-dimensional network form. 

Sion and placed in a-glass chamber at room temperature with constant ozone flow. The ozone concentration was kept at 2.78 mg/1 or 1,400 ppm which is about 10,000 times the ozone concentration in the atmosphere. We also tested samjdes of natural rubber, butyl rubber and EPDM rubber vulcanizates together under the same condition for comparison. Results are summarized in Table 2. 

X parameter, a perfect correlation was not to be expected. From the correlation curve so-established the swelling of experimental vulcanizates could be predicted with reasonable accuracy from the easily determined x parameter. The GC method diould be particularly valuable for testing experimental samples, whenever only small amounts are available. For non-crosslinked materials, the magnitude of the x parameter is a direct indication of the solubility of the polymer in any given solvent. The dividing line between solvents and non-K>lvent of the polymer can be drawn at approximately x = 0.5, the smaller the values of x below this limit, the better the solvent. It is a simple matter to measure the retention characteristics of a series of probes and thus determine a suitable >lvent for any pdymer. It should be noted, however, that the temperature at which tfie GC determination is possible (T>Tg+ 50) may sometimes ermeed the temperature of interest and the dependence of x on temperature may have to be assessed. 

Ozonization of Vulcanizates. Control or unprotected test specimens, containing the ingredients listed in Table II, were prepared on a laboratory rubber mill (S). Corn-... 

Experimental 1x6 inch test specimens of the unprotected and protected vulcanizates were elongated 20% and ozonized for 15 minutes at room temperature, using a stream of ozonized oxygen flowing at 0.10 cubic meter per hour and furnishing approximately 1 X 10 mole of ozone per hour. The test strips were examined visually during ozonization to determine the time required to obtain initial surface cracking. 

Figure 7. Effect of the pyrolysis temperature on physical properties (a) — (g) of rubber vulcanizates (MP test) (a) tensile strength (b) elongation (c) 300% modulus (d) tear strength (e) hardness (f) cut growth (g) abrasion. Test recipe of rubber compounds is the same as in Table III (Q) 15 (A) 20 ( 3>) 30 (ffz) 4 ...

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