Filler-elastomer bonds

In the last part of the paper, filler-elastomer chemical interactions which are able to take place through surface functional groups or surface reactive hydrogens are studied. The effect exerted by the created filler-elastomer bonds in the reinforcement process is then discussed. 

In this connection, Fig. 2 provides a qualitative illustration for interpreting modulus change of an elastomer upon filler blending 9). A hydrodynamic or strain amplification effect, the existence of filler-elastomer bonds, and the structure of carbon black 10) all play a part in this modulus increase. 

It appears, beyond all doubt, that filler-elastomer interactions result in the formation of chemical bonds between the polymer and the solid surface, which are due to a reaction of the macromolecule either with the surface chemical groups or with the surface hydrogen atoms. Is, however, the formation of covalent filler elastomer bonds a prerequisite for reinforcement to occur ... 

The filler-elastomer chemical interactions take place through its surface functional groups and hydrogen atoms. Coupling agents improve polymer-filler adhesion. From the point of view of dynamic-mechanical properties for low strains, the filler-elastomer bonds have a positive effect in the reinforcement process. 

Predictions of the mechanical response of filled elastomers are further aggravated by the phenomenon of strain dilatation. As soon as dilatation commences, the tensile stress lag behind elongation, the degree of dilatation for a given composite being roughly a measure for the deviation from the expected mechanical response. Dilatation increases with particle size and volume fraction of filler—it decreases somewhat if the filler is bonded to the matrix. Farris (16,17) showed that dilatation can account well for the mechanical behavior of solid propellants and his equation ... 

Graphitized carbon blacks, thus undoubtly display reinforcing abilities which become obvious when considering the tensile strength of the unfilled vulcanizate. It follows that the formation of a filler-elastomer chemical bond is not a requirement for reinforcement to occur. It strongly participates, however, in its effectiveness, and determines the good mechanical properties connected with rubber reinforce-... 

The use of additives to make the surface of precipitated silica less hydrophilic and more rubberphilic facilitates incorporation, dispersion, and more intimate filler-elastomer contact during compoimding. This provides an improvement in rubber physical properties, as would be expected from a high surface area, high oil absorption filler. However, reinforcement comparable to that obtained with carbon black requires a polymer-filler bonding mechanism comparable to that provided at the carbon... 

Zinc salt of maleated EPDM rubber in the presence of stearic acid and zinc stearate behaves as a thermoplastic elastomer, which can be reinforced by the incorporation of precipitated silica filler. It is believed that besides the dispersive type of forces operative in the interaction between the backbone chains and the filler particles, the ionic domains in the polymer interact strongly with the polar sites on the filler surface through formation of hydrogen bonded structures. 

Lower-density E-plastomers have found alternate use in cast film processes to make elastic film laminates with good breathability which contain laminates of liquid impermeable extensible polymeric films with extensible-thermoplastic-polymer-fiber nonwovens and nonwoven webs of polyethylene-elastomer fibers as the intermediate layers. The development relates to a breathable film including an E-plastomer and filler that contributes to pore formation after fabrication and distension of the film. The method and extent of distension is designed to produce a breathable film by stretching the film to form micropores by separation of the film of the E-plastomer from the particulate solids. This film is useful for manufacture of absorbent personal-care articles, such as disposable diapers and sanitary napkins and medical garments. In detail, these constructions comprise a liquid impermeable extensible film comprising polyolefins. The outer layer contains extensible-thermoplastic-polymer-fiber nonwovens, and an elastic intermediate layer contains nonwoven webs of fiber E-plastomers. The intermediate layer is bonded to the film layer and the outer... 

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. 

A practical means of assessing the stability of the formed bond has been suggested by Sircar and Voet22), who, for various carbon blacks and elastomers, plotted the unextractable amount of rubber from the filler as a function of the temperature of extraction for a variety or solvents. They observed the experimental points related to a given polymer-filler blend to be falling linearly, and the extrapolation to zerografting ratio provided the so-called solvolysis temperature Tm, which appears to be independent of the solvent used. Tm represents the temperature theoretically required to eliminate all bonds between carbon blacks and elastomer and is, therefore,... 

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