Filled rubbers elastomers

This behavior provides evidence of the fading memory property of the material. Therefore, the entire strain (and temperature) history must affect the constimtive behavior of filled rubber elastomers. While the strain-rate sensitivity and the failure time dependency are recognized and well-documented in the case of other materials such metals, the incorporation of history-dependent properties of elastomers requires further clarification. 

Goettler LA, Cole WF (2001) Short fiber-filled rubber composites. In Bhowmick AK, Stephens HL (eds) Handbook of elastomers, 2nd edn. Marcel Dekker, New York... 

Improvement of the mechanical properties of elastomers is usually reached by their reinforcement with fillers. Traditionally, carbon black, silica, metal oxides, some salts and rigid polymers are used. The elastic modulus, tensile strength, and swelling resistence are well increased by such reinforcement. A new approach is based on block copolymerization yielding thermoelastoplastics, i.e. block copolymers with soft (rubbery) and hard (plastic) blocks. The mutual feature of filled rubbers and the thermoelastoplastics is their heterogeneous structure u0). 

An important feature of filled elastomers is the stress softening whereby an elastomer exhibits lower tensile properties at extensions less than those previously applied. As a result of this effect, a hysteresis loop on the stress-strain curve is observed. This effect is irreversible it is not connected with relaxation processes but the internal structure changes during stress softening. The reinforcement results from the polymer-filler interaction which include both physical and chemical bonds. Thus, deforma-tional properties and strength of filled rubbers are closely connected with the polymer-particle interactions and the ability of these bonds to become reformed under stress. 

PE-PEP diblock were similar to each other at high PE content (50-90%). This was because the mechanical properties were determined predominantly by the behaviour of the more continuous PE phase. For lower PE contents (7-29%) there were major differences in the mechanical properties of polymers with different architectures, all of which formed a cubic-packed sphere phase. PE-PEP-PE triblocks were found to be thermoplastic elastomers, whereas PEP-PE-PEP triblocks behaved like particulate filled rubber.The difference was proposed to result from bridging of PE domains across spheres in PE-PEP-PE triblocks, which acted as physical cross-links due to anchorage of the PE blocks in the semicrystalline domains. No such arrangement is possible for the PEP-PE-PEP or PE-PEP copolymers (Mohajer et al. 1982). 

In composite, multicomponent systems, 2H NMR is particularly suited to investigate interfacial properties. This is illustrated in filled rubbers, semicrystalline and thermoplastic elastomers, based on copolymers (Section 15.5). 

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]. 

Solid state NMR offers several advantages for the investigation of filled rubbers since molecular properties of elastomer chains can be measured selectively by NMR e>q)eriments. The method is very sensitive to the molecular scale heterogeneity in a sample. The network structure which is composed of chemical, physical and topological junctions can also be andyzed by NMR relaxation experiments [11,12,14,15],... 

Diamine salts of fatty acids are used as multifunctional additives in natural rubber compounds filled with carbon black.They affect the elastomer-carbon black interface. With an increased concentration of multifunctional additive, the concentration of bound rubber decreases but dispersion of carbon black is improved. In silica filled rubber, multifunctional additive also improves the dispersion of silica, but in addition, it decreases the negative influence of silica filler on vulcanization rate. 

There exists as yet no rigorous extension of the statistical theory of rubber elasticity to a filled elastomer. Nevertheless, many attempts have been made to apply the theory to data on filled rubbers, usually with the objective of obtaining at least an approximate estimate of the number of filler-rubber attachments. These attempts have been discussed in earlier reviews (17, 126) and will not be considered here in full detail. We only restate briefly some of the experimental and theoretical difficulties inherent in this approach. 

Figure 10.65. Dependence of tensile strength of the filled crosslinked elastomer of natural rubber on the swelling ratio in different plasticizers 1 DMP 2 DBF 3 DOP 4 DBS 5 vaseline oil. [Data from Dogad-kin B A, Fedukin D L, Gul V E, Colloid J., XIX, 217, 1957.1...

IV. The Mix A Nanocomposite of Elastomer and Filler V. Mechanical Properties of Filled Rubbers... 

According to the theories on reinforcement of polymer melts and elastomers by particulate fillers, " the initial modulus of a filled rubber composite is given by diflerent contributions. Figure 2.8 reports the dependence of the shear complex modulus on the strain amplitude. 

When an uncured but well dispersed filled rubber is subjected to solvent extraction, not all of the elastomer is recovered. The portion of rubber that is not extracted is called the bound rubber. The bound rubber layer results from a complex combination of physical adsorption, chemi-adsorption and mechanical interlocking. The surface activity of carbon black is related to the bound rubber. Wolff et alP have investigated the existence of the bound rubber layer and studied its characteristics. They measured the bound rubber layer for SBR filled with carbon black using NMR and the thickness of the bound rubber... 

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