Elastic modulus control composites

Elastic Modulus. The third key issue relates to improvements required in the elastic modulus of these ceramic fibers. Studies indicate that modulus improvements will depend on careful control of composition and increases in fiber density (24). Earlier discussions in this chapter summarized the low densities of these ceramic fibers relative to their crystalline counterparts, as well as the existence of considerable pore volume. 

It has been reported (5) that the elastic modulus of ABS resins prepared by either mass or emulsion polymerization can be represented by a single relationship with the dispersed phase volume fraction. This is in agreement with the theory that the modulus of a blend with dispersed spherical particles depends only on the volume fraction and the modulus ratio of particles to matrix phase. Since the modulus of rubber is almost 1000 times smaller than the modulus of the matrix SAN, the rubber particle volume fraction alone is the most important parameter controlling modulus values of ABS resins. Even for rubber particles containing a high occlusion level, as in ABS produced by mass polymerization, the modulus of the composite particle still remains imchanged from pure rubber, suggesting a unique relationship between modulus and dispersed phase volume fraction. Also, the modulus of a material is a small strain elastic property and is independent of particle size in ABS. The effects of rubber content on modulus and on tensile... 

The combination of monomers to form copolymers can be compared with the mixing of metals to form solid solutions, which is the basis of alloy formation. The chemical engineer by small variations in copolymer composition can synthesize polymers with subtly different properties. The properties which are controlled by changes in copolymer composition include elastic modulus, toughness, melt viscosity, and thermal stability (l.N.ll). We return to this subject again in Chapters 4 and 5. Copolymers are also polymerized with block or graft structures (see Fig. l.S) for specific purposes (1.N.12). 

Plants utilize their ability to control the local composition and the microfibril orientation within the cell walls to accommodate differential strains within their composite architecture. This is evidenced for example by changes in the microfibril orientation in trees depending on the specific function of the tissue,as well as in the graded change in elastic modulus... 

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