Elastomer-Filler Systems

In Section 4.4 we saw that the thermoplastic elastomers behave as self-reinforcing systems. Earlier in this chapter, we examined silica- and 

As with simple vulcanizates, the tensile strength of reinforced materials 

It is of interest to compare the mechanical behavior of these model reinforced elastomers with the thermoplastic elastomers discussed in the 

The major conclusion obtained in both of these investigations is that neither primary chemical bonding nor strong secondary physical forces are required for simple reinforcement. It is expected that these results will discomfit those workers whose main theme centers on strong filler interactions, although the latter obviously do play an important role. 

In a unique experiment, Tschoegl (Tschoegl, 1971a,ft Lim and Tschoegl, 1969) recently showed that in model reinforced systems where little or no 

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The principles of compounding were reviewed earlier in this text and cover the fundamental characteristics of polymers, filler systems, and the basics of vulcanization in the context of compound development for tire applications. A compound formulation consists of four basic components the polymer network, the filler or particulate reinforcing system, the stabilizer system, and the vulcanization system (Figure 14.21). In addition a series of secondary materials such as resins, processing oils, and short fiber reinforcements may be included in a formula (Duddey, 2004 Rodgers and Waddell, 2004 Long, 1985). Elastomers used in radial tires are basically of four types ... 

The study of the fracture process of the elastomer-based systems containing fillers evidenced that the weakest zone is the interface elastomer-particle [1191]. The fracture occurs by the destruction of the existing bonds in the contact area, especially of the adhesive bonds. In means that the material structuration by reinforcement is intensified by the increase of adhesive forces. Therefore, using black carbon as reinforcing agent, the maximal effect is achieved whenever the elastomer is in highly elastic state [1192]. Consequently, it results that the reinforcement sensibly depends on temperature [464]. 

Styrene analysis is usually a simple and reliable method. Analogous to DSC analysis, however, the resin content has to be determined by incineration to obtain a quantitative statement for fiber reinforced or filled resin systems. Quantitative analysis becomes difficult when non-reactive components and components not separable by incineration (e.g., elastomer fillers or polymer fibers) are present. Moreover, when a large number of components is involved, complicated chromatograms with peak overlapping will make analysis difficult. 

Pliskin I and Tbkita N (1972) Bound rubber in elastomers analysis of elastomer-filler interaction and its effect on viscosity and modulus of composite systems, J Appl Polym Sci 16 473-492. 

The proper choice of elastomer, cure system and filler will ensure that the desired properties are obtained from a rubber product. Antidegradants are used to prevent these properties from changing during service. The primary degradant effects are oxidation and ozone attack. 

Acid-Base Behavior. The relative acidity-basicity of the filler, generally determined by measuring the pH value of a slurry of a specific mass of filler in 100 mL of deionized water, can influence the behavior of a filler in some systems. For example, the curing behavior of some elastomers is sensitive to the pH value of carbon black. 

Polymer systems have been classified according to glass-transition temperature (T), melting poiat (T ), and polymer molecular weight (12) as elastomers, plastics, and fibers. Fillers play an important role as reinforcement for elastomers. They are used extensively ia all subclasses of plastics, ie, geaeral-purpose, specialty, and engineering plastics (qv). Fillets are not, however, a significant factor ia fibers (qv). 

Elastomers, plastics, fabrics, wood and metals can be joined with themselves and with each other using nitrile rubber/epoxy resin blends cured with amines and/or acidic agents. Ethylene-propylene vulcanizates can also be joined using blends of carboxylated nitrile rubber, epoxy resin and a reactive metal filler (copper, nickel, cobalt). However, one of the largest areas of use of nitrile rubber modified epoxy systems is in the printed circuit board area [12]. 

Thermoplastic polymers, such as poly(styrene) may be filled with soft elastomeric particles in order to improve their impact resistance. The elastomer of choice is usually butadiene-styrene, and the presence of common chemical groups in the matrix and the filler leads to improved adhesion between them. In a typical filled system, the presence of elastomeric particles at a level of 50% by volume improves the impact strength of a brittle glassy polymer by a factor of between 5 and 10. 

The study of the mechanical properties of filled elastomer systems is a chaUenging and exciting topic for both fundamental science and industrial application. It is known that the addition of hard particulates to a soft elastomer matrix results in properties that do not follow a straightforward mle of mixtures. Research efforts in this area have shown that the properties of filled elastomers are influenced by the nature of both the filler and the matrix, as well as the interactions between them. Several articles have reviewed the influence of fiUers hke sihca and carbon black on the reinforcement of elastomers.In general, the strucmre-property relationships developed for filled elastomers have evolved into the foUowing major areas FiUer structure, hydrodynamic reinforcement, and interactions between fiUers and elastomers. 

Lussier [71] has given an overview of Uniroyal Chemical s approach to the analysis of compounded elastomers (Scheme 2.2). Uncured compounds are first extracted with ethanol to remove oils for subsequent analysis, whereas cured compounds are best extracted with ETA (ethanol/toluene azeotrope). Uncured compounds are then dissolved in a low-boiling solvent (chloroform, toluene), and filler and CB are removed by filtration. When the compound is cured, extended treatment in o-dichlorobenzene (ODCB) (b.p. 180 °C) will usually suffice to dissolve enough polymer to allow its separation from filler and CB via hot filtration. Polymer identification was based on IR spectroscopy (key role), CB analysis followed ASTM D 297, filler analysis (after direct ashing at 550-600 °C in air) by means of IR, AAS and XRD. Antioxidant analysis proceeded by IR examination of the nonpolymer ethanol or ETA organic extracts. For unknown AO systems (preparative) TLC was used with IR, NMR or MS identification. Alternatively GC-MS was applied directly to the preparative TLC eluent. 

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