Highly Filled Elastomers

The mechanical properties of highly filled elastomers have led to their use as solid propellants in rocketry. Composite propellants consist of elastomers highly filled with inorganic oxidiser. Mixing is effected in an uncrosslinked state in which the polymer still has a low MW and the consistency of a viscous fluid. The compounded mixture is cast or extruded into the desired shape and hardened by polymerisation 

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Figure 10. Dewetting behavior in a highly filled elastomer.

Figure 1. The stress-strain dilatational behavior of three highly filled elastomers...

The hypothesis of Scott [S5] that highly filled elastomers exhibited yield values was confirmed by Zakharenko and his coworkers [Zl] as well as... 

An obvious prerequisite to the understanding of the behavior of highly filled elastomers is an understanding of the behavior of the elastomer itself. However, any reasonably complete study encompasses too wide a variety of topics and techniques to permit a successful resolution by any individual research group, hence a cooperative effort is indicated. In the poljrmer field, such cooperative efforts have been stimulated in the past merely by the availability of a suitable pol3rmer for study. 

Sharma (90) has examined the fracture behavior of aluminum-filled elastomers using the biaxial hollow cylinder test mentioned earlier (Figure 26). Biaxial tension and tension-compression tests showed considerable stress-induced anisotropy, and comparison of fracture data with various failure theories showed no generally applicable criterion at the strain rates and stress ratios studied. Sharma and Lim (91) conducted fracture studies of an unfilled binder material for five uniaxial and biaxial stress fields at four values of stress rate. Fracture behavior was characterized by a failure envelope obtained by plotting the octahedral shear stress against octahedral shear strain at fracture. This material exhibited neo-Hookean behavior in uniaxial tension, but it is highly unlikely that such behavior would carry over into filled systems. 

Fig. 11). It is, therefore, highly probable that the bulky filler particles impose geometrical hindrances (entropy constraints) for the chain dynamics at the time scale of the NMR experiment (of the order of 1 ms). This effect may be compared with the effect of transient chain entanglements on chain dynamics in polymer melts. It should be remarked that the entanglements density estimated for PDMS melts by NMR is close to its value fi om mechanical experiments [38]. Therefore, it can be assimied that topological hindrances from the filler particles can also be of importance in the stress-strain behavior of filled elastomers. 

Figure 3. The stress-strain dilatational behavior of a 63.5 vol % filled elastomer at a series of hydrostatic pressures at a high strain rate...

Poly(ester-imide) elastomers have been prepared, and contain the reaction product of trimellitic anhydride with polyoxyalkylene diamines like polypropylene oxide diamine. Having excellent tensile strength they are used for making automobile parts [251], or when highly filled they are a suitable replacement for ceramics [252]. 

Position Dependence. In polymers with heterogeneous structures— for example, semicrystalline polymers and filled elastomers— the transport process is complicated by the generally impermeable dispersed phase. Not only does the crystallite or filler particle create a larger path for the diffusing molecule to traverse, but also the presence of a high area interface within the polymer changes the nature of the continuous phase from that of the pure homogeneous state. These effects are related by the expression (4) ... 

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