Miscellaneous Toughening Agents

Liquid-crystalline polymers (LCP) can be used in thermoset systems as initially miscible modifiers that phase-separate during cure. [Pg.412]

Functionalized LCP may be used as comonomers in thermoset formulations. Upon cure, liquid-crystalline thermosets (LCT) are obtained, with a morphology characterized by the presence of liquid-crystalline dispersed domains. [Pg.412]

Examples of these formulations are systems based on a difunctional LC epoxy monomer (diglycidyl ether of 4-4 -dihydroxy-Q -methylstilbene), cured with methylene dianiline (Ortiz et ai, 1997). The generation of liquid-crystalline microdomains (smectic or nematic) in the final material required their phase-separation before polymerization or at low conversions. This could be controlled through the initial cure temperature. Values of Gjo, (kJm ) were 0.68 (isotropic), 0.75 (nematic), and 1.62 (smectic). The large improvement produced by the smectic microdomains was attributed to an extensive plastic deformation. [Pg.413]

Sue et al. (1997) reported results for the same LC epoxy monomer cured with various hardeners. Kjc values could be increased up to 1.89 MPam. Observations of fracture surfaces indicated that crack bridging, crack branching, and crack deflection were the main toughening mechanisms. [Pg.413]

The use of liquid reactive rubbers to toughen thermosets leads to a decrease of both T — g and the Young s modulus (see Fig. 13.7). Thermoplastics can be added to these formulations to improve thermal and mechanical properties. [Pg.413]

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