Filled rubbers

Rubber media appear as porous, flexible rubber sheets and microporous hard rubber sheets. Commercial rubber media have 1100-6400 holes/in. with pore diameters of 0.012-0.004 in. They are manufactured out of soft rubber, hard rubber, flexible hard rubber and soft neoprene. The medium is prepared on a master form, consisting of a heavy fabric belt, surfaced on one side with a layer of rubber filled with small round pits uniformly spaced. These pits are 0.020 in. deep, and the number per unit area and their surface diameter determine the porosity of the sheet. A thin layer of latex is fed to the moving belt by a spreader bar so that... 

Silicone rubber filled with microspheres and reinforced with a plastic honeycomb Polybutadiene-acrylonitrile elastomer modified phenolic resin with a subliming powder... 

On the dusted track the diminished adhesion friction component is clearly apparent for all three rabbers when comparing them with the master curves on the clean track The friction plateau observed for the rubbers filled with 50 pphr black which is typical for tire tread compounds is observed for most rubbers, as shown in Figure 26.5. 

FIGURE 26.4 Master curves on smooth, wavy glass, on a sihcon carbide track dusted with magnesium oxide and on a clean silicon carbide track of three acrylate-butadiene rubber (ABR) compounds as gum rubber, filled with 20 pphr carbon black and 50 pphr, respectively. (From Grosch, K.A., Sliding Friction and Abrasion of Rubbers, PhD thesis, University of London, London 1963.)... 

This method has gained wide acceptance due to its simplicity and environmental friendliness. Research is under way to improve the economy of this method. The most important step is the preparation of ground rubber, since the size and topography of the particles vary with the different techniques of grinding [30]. The characteristics of the ground rubber play a vital role in determining the properties of the ground rubber-filled rubber composites. 

Naskar, A.K., Bhowmick, A.K., and De, S.K., Melt-processable rubber Chlorinated waste tire rubber-filled polyvinyl chloride, J. Appl. Polym. Sci., 84, 622, 2002. 

Fig. 40 WAXD patterns of non-polar rubbers (a) and polar rubbers filled with 20 phr swollen clay (b). All the vulcanized rubbers contain some curing ingredients like organic accelerator, zinc oxide, etc...

Fig. 9.49 The evolution of the interfacial area of a viscous Thiokol rubber in a 26.6-cm parallel-disk mixing chamber with a. — 0.5, with the number of turns. The rubber filled up half the chamber with one-quarter cream color (at the channel block at the left side) and one-quarter black. The numbers on the figure indicate the number of turns from 1/4 to 10. [Reprinted by permission from B. David and Z. Tadmor, Laminar Mixing in Co-rotating Disk Processors, Int. Polym. Process., 3, 38-47 (1988).]...

H NMR transverse magnetisation relaxation experiments have been used to characterise the interactions between NR, isoprene rubber, BR, EPDM and polyethylacrylate rubbers with hydrophilic silica and silicas modified with coupling agents [124-129]. These studies showed that the physical interactions and the structures of the physical networks in rubbers filled with carbon black and rubbers filled with silicas are very similar. In both cases the principal mechanism behind the formation of the bound rubber is physical adsorption of rubber molecules onto the filler surface. 

Composite—A material that contains two or more structurally different components with properties different from that of any individual component. Examples include crosslinked polyester resin reinforced with glass fiber and rubber filled with carbon black. 

The above interpretations of the Mullins effect of stress softening ignore the important results of Haarwood et al. [73, 74], who showed that a plot of stress in second extension vs ratio between strain and pre-strain of natural rubber filled with a variety of carbon blacks yields a single master curve [60, 73]. This demonstrates that stress softening is related to hydrodynamic strain amplification due to the presence of the filler. Based on this observation a micro-mechanical model of stress softening has been developed by referring to hydrodynamic reinforcement of the rubber matrix by rigid filler... 

The presence of filler in the rubber as well as the increase of the surface ability of the Aerosil surface causes an increase in the modulus. The temperature dependence of the modulus is often used to analyze the network density in cured elastomers. According to the simple statistical theory of rubber elasticity, the modulus should increase twice for the double increase of the absolute temperature [35]. This behavior is observed for a cured xmfilled sample as shown in Fig. 15. However, for rubber filled with hydrophilic and hydrophobic Aerosil, the modulus increases by a factor of 1.3 and 1.6, respectively, as a function of temperature in the range of 225-450 K. It appears that less mobile chain units in the adsorption layer do not contribute directly to the rubber modulus, since the fraction of this layer is only a few percent [7, 8, 12, 21]. Since the influence of the secondary structure of fillers and filler-filler interaction is of importance only at moderate strain [43, 47], it is assumed that the change of the modulus with temperature is mainly caused by the properties of the elastomer matrix and the adsorption layer which cause the filler particles to share deformation. Therefore, the moderate decrease of the rubber modulus with increasing temperature, as compared to the value expected from the statistical theory, can be explained by the following reasons a decrease of the density of adsorption junctions as well as their strength, and a decrease of the ability of filler particles to share deformation due to a decrease of elastomer-filler interactions. 

Fig. 17. Temperature dependence of the relative change of (Tj ) (O) and the relative change of tensile strength at break ( ) for silicon rubber filled by hydrophilic (A) and hydrophobic (B) Aerosil [46] die value of is measured for filled PDMS containing 60 vol% of hydrophilic Aerosil (300 m g" ) (336 phr) and hydrophobic Aerosil (60 m g" ) the sample composition is described in the caption to Fig. 15...

Table 4.7. Technical properties of samples based on liquid rubber filled with carbon black 2541...

Silicone elastomers ( silicone rubber ) filled with silica have outstandir properties, and many commonly used products are made of these materials. Silicone rubbers filled with silica exhibit high mechanical strength and high chemical stability, and can be used at temperatures ranging fixnn -50 °Cto+300°C[l]. 

Conceptually, the problems associated with the optimization of specific mechanical properties by variations of structure and morphology are the same in rubber-filled systems, ass-bead filled systems and semicrystalline polymers. When the fracture properties are singled out, our understanding of the relationships between macroscopic failure and local failure is hampered by the limited knowledge of stress transfer in statistically nonhomogeneous structures. The increased use of composites theory and micromechanics to address these problems would appear to be appropriate. 

Keyboard switches are integrated composition of insulate silicone rubber and conductive silicone rubber filled with carbon black. They are commonly called rubber contacts, which serve as an electrical contact and a mechanical spring. Contacts made of silicone rubber were developed in response to demands for more compact size, mass production and for lower cost. 

SBR filled with intercalated montmorillonite had substantially lower toluene uptake compared with the same rubber filled with carbon black (see Figure 15.42). Figure 5.28 shows that the diffusion coefficient of kerosene, which defines penetration rate, decreases when the concentration of carbon black in SBR vulcanizates is increased. Figure 15.33 compares the uptake rate of benzene by unfilled rubber and by silica and carbon black filled rubber. Both fillers reduce the solvent uptake but carbon black is more effective. 

A study of SBR rubber showed a difference in the behavior over the temperature range of 20-70°C between the unfilled rubber and rubber filled with carbon black. T2 changes by a few tens percent for filled rubber in this temperature range and it almost doubles in the unfilled rubber. The increased temperature contributes to the increased molecular mobility but this effect is retarded by the bound segments in the filled rubber. ... 

Figure 7.35. taiiS of natural rubber filled with carbon black and silica vs. interaggregate distance, 833. [Adapted, by permission, from Wang M-J, Wolff S, Tan E-H, Rubb. Chem. Technol., 66, No.2, 1993, 178-95.]... 

Figure 14.8. Conductivity of butyl rubber filled with carbon black vs. temperature. [Data from Nasr G M, Badawy M M, Gwaily S E, Shash N M, Hassan H II, Polym. Degradat. Stabil., 48, No.2, 1995,237-41.]...

Major results. Figure 14.7 shows that the resistivity of aluminum-filled PMMA changes abruptly. Smaller volumes of filler contribute a little to resistivity but, after certain threshold value of filler concentration, further additions have little contribution. A similar relationship was obtained for nickel powder the only difference is in the final value of resistivity, which was lower for nickel due to its higher conductivity. The same conclusions can be obtained from conductivity deteiminations of epoxy resins filled with copper and nickel. Figure 14.8 shows the effect of temperature on the electric conductivity of butyl rubber filled with different grades of carbon black. In both cases, conductivity decreases with temperature, but lamp black is substantially more sensitive to temperature changes. Even more pronounced changes with temperature were detected for the dielectric loss factor and dissipation factor for mineral filled epoxy." ... 

Figure 18.5. Resistivity of neoprene and butyl rubber filled with 40 phr N550 vs. pressure during the cure. [Data from Thompson C M, Allen J C, Rubb. Chem. Technol., 67, No.l, 1994, 107-18.]...

Figure 18.19. Bound rubber vs. mixer rotor speed for natural rubber filled with carbon black. [Adapted, by permission, from Mai lick A, Tripathy D K, De S K, J. Appl. Polym. Sci., 53, No. 11, 1994, 1477-90.]...

Figure 19.29 shows the comparative shielding efficiency data for various materials. Rubber filled with lead oxides comes very close in performance to lead and is superior to concrete and aluminum. Exposure of these shields to radiation causes degradation of mechanical properties (hardness, in particular, is increased) but it does not affect shielding efficiency. 

Figure 6-10. Mooney-Rivlin plots of natural rubber filled with MT carbon black Top set actual data without using the strain amplification factor. Bottom curves after reduction using the strain amplification factor, equation (6-95). [After L. Mullins and N. R. Tobin, J. Appl. Polym. Sci., 9, 2993 (1965), by permission of John Wiley Sons, Inc.]...

The effect of the size of EPDM domains in the PP dominant matrix has been investigated since the initial study of TPV (15-19). It is well known that the size of the rubber domain affects the mechanical properties of both TPE and TPV. Wu (29) suggested that the critical mbber domain size and the critical distance between rubber domains are very important for toughness in rubber-filled nylon. This also appears to be the case of TPV. The typical stress-strain curve for TPV is shown in Fig. 8.17. 

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