Model rubber

Tsai et al. have also used RAIR to investigate reactions occurring between rubber compounds and plasma polymerized acetylene primers deposited onto steel substrates [12J. Because of the complexities involved in using actual rubber formulations, RAIR was used to examine primed steel substrates after reaction with a model rubber compound consisting of squalene (100 parts per hundred or phr), zinc oxide (10 phr), carbon black (10 phr), sulfur (5 phr), stearic acid (2 phr). 

When a plasma polymerized acetylene film on a steel substrate was reacted with the squalene-containing model rubber compound at 155°C for 15 min, a new band assigned to zinc stearate appeared near 1539 cm in the RAIR spectra... 

Fig. 13. RAIR spectra of model rubber compound reacted with plasma polymerized acetylene films on steel substrates for (A) 0, (B) 15, (C) 0 and (D) 45 min. Adapted by permission of Gordon and Breach Science Publishers from Ref. [12].

Many applications of XPS to problems in adhesion science have been reported in the literature. One interesting example is provided by the work of Tsai et al. on the use of XPS to investigate reactions between model rubber compound and plasma polymerized acetylene films that was discussed above [22,23], Consideration of that system permits some interesting comparisons to be made regarding the type of information that can be obtained from RAIR and XPS. 

Fig. 39. Auger depth protile obtained from a plasma-polymerized film on a polished steel substrate after the film was reacted with a model rubber compound for 65 min. Reproduced by permission of Gordon and Breach Science Publishers from Ref [45].

The Auger depth profile obtained from a plasma polymerized acetylene film that was reacted with the same model rubber compound referred to earlier for 65 min is shown in Fig. 39 [45]. The sulfur profile is especially interesting, demonstrating a peak very near the surface, another peak just below the surface, and a third peak near the interface between the primer film and the substrate. Interestingly, the peak at the surface seems to be related to a peak in the zinc concentration while the peak just below the surface seems to be related to a peak in the cobalt concentration. These observations probably indicate the formation of zinc and cobalt complexes that are responsible for the insertion of polysulfidic pendant groups into the model rubber compound and the plasma polymer. Since zinc is located on the surface while cobalt is somewhat below the surface, it is likely that the cobalt complexes were formed first and zinc complexes were mostly formed in the later stages of the reaction, after the cobalt had been consumed. 

Positive SIMS spectra obtained from plasma polymerized acetylene films on polished steel substrates after reaction with the model rubber compound for times between zero and 65 min are shown in Fig. 44. The positive spectrum obtained after zero reaction time was characteristic of an as-deposited film of plasma polymerized acetylene. However, as reaction time increased, new peaks appeared in the positive SIMS spectrum, including m/z = 59, 64, and 182. The peaks at 59 and 64 were attributed to Co+ and Zn, respectively, while the peak at 182 was assigned to NH,J(C6Hn)2, a fragment from the DCBS accelerator. The peak at 59 was much stronger than that at 64 for a reaction time of 15 min. However,... 

Negative SIMS spectra obtained from plasma polymerized acetylene films on polished steel substrates as a function of reaction time with the model rubber compound are shown in Fig. 45. The most important changes observed in the... 

The theory proposed for equilibrium swelling and diffusion is based on the assun tlon that the hydrophilic impurities are present in particulate form and are dispersed throughout the rubber. The precise nature of this impurity in natural rubber is not known so it was decided to make a model rubber by adding 0.17. of a hydrophilic Impurity (sodium chloride) to a solution polymerised synthetic rubber (cis-polyisoprene) Ich is chemically the same as natural rubber. Using this model rubber it is possible to check the theory more precisely since both the nature and concentration of the hydrophilic lgq>urlty in the model rubber are known. It is proposed that the water diffuses through the rubber and forms droplets of solution inside the rubber where there are particles of the hydrophilic impurity thereby causing a non-uniform distribution of water in the rubber. The... 

A model rubber was made from cis-polyisoprene, a synthetic rubber which is chemically similar to natural rubber, to which had been added a small amount of hydrophilic impurity. This was 0.17. of sodium chloride in most of the experiments but 1% of an animal protein (bovine albumen) was also used for one set of experiments and this gave similar results to those obtained when sodium chloride was used, demonstrating that the phenomenon is not a feature of one type of impurity only. Since the cis-polyisoprene used was solution polymerized it was relatively free from hydrophilic impurities before mixing. The desired amount of sodium chloride was dissolved in water to form a concentrated solution. This solution was added to the rubber on a heated mill, the water then evaporated producing a fine dispersion of... 

Figure 1. Absorption of water by (a) natural rubber, (b) model rubber, and (c)...

Table I Equilibrium concentration of water in model rubber immersed in sodium chloride solutions...

Figure 3. Concentration dependence of the diffusion coefficient of water in model rubber using samples ( ) initially dry arui (O) initially containing water. Line calculated using Equation 9 with s a = 1.8 X 10 and Ci — 0.1%.

These act as sites for droplets of solution. The impurities in natural rubber have not been identified but experiments with a model rubber have shown that the nature of the impurity, providing that it is hydrophilic, is not critical. No evidence has been found of Internal rupturing of the rubber by the formation of water droplets. 

Gregg J., E. C., Jr. and Lattimer, R. R, Polybutadiene vulcanization. Chemical structures from sulfur-donor vulcanization of an accurate model. Rubber Chem. Technol, 57, 1056, 1984. 

In most applications, the structure is considered as having linear behavior, but nonlinearity of several types can be found nonlinear deformation models (rubber, etc.), nonlinear geometry (large deformations), plasticity (nonlinearity between strain and stress above the yield point), etc. Nonlinear structural analysis must almost inevitably be performed by numerical methods. 

The above picture is further supported by studies of dynamic mechanical spectroscopy. Thus Matsuo et al. (1970f>) measured E and E" as a function of temperature for a number of compositions, and compared the results to Takayanagi s mechanical model rubber-plastic phase continuity (Takayanagi et al, 1963) (see Section 2.6.4) results are shown in Figure 8.24. 

RAIR spectra indicated that there was little reaction between a similar model rubber compound containing squalane, the saturated analog of squalene, and the plasma polymerized acetylene primer. It was concluded that an important product was formed by reaction of components of the curing system with squalene and that product reacted with the plasma polymer film, eventually leading to crosslinking between squalene and the film [13]. This reaction product was not formed in the presence of squalane. 

Interaction of Silica Particles in a Model Rubber System The Role of Silane Surface Treatments... 

Spectral Correlation Charts for Model Rubber Compounds... 

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