Mechanisms of Toughening in Nanostructured Polymer Blends

Abstract Often, fillers are added to polymers in order to improve stiffness and inadvertently reduce toughness. This is not unexpected, as it is almost impossible to have a stiff material and still retain considerable level of toughness, especially in a poorly dispersed system. However, if the particles are well dispersed, it is quite possible to have a “win-win” situation, whereby the process will simultaneously improve toughness and stiffness. Fillers can be well dispersed and on a micro-scale agglomerate. If they are well dispersed, they will be well attached to the matrix and will remain so, even at large deformations. Of course agglomerated fillers will be prone to debonding, causing an internal fracture, leading to the formation of voids and hence, eventual deformation. However, brittle polymers can be toughened, significantly, by the addition of miscible amorphous polymers and/or a thermoplastic elastomer. In this chapter, the various mechanisms suitable for toughening nanostructured polymer blends will be succinctly reviewed. The interparticle distance and the interfacial adhesion of the filler to the polymer account for the extent of toughening achievable in the system. By far, toughening (with particulate fillers) immiscible blends has been more successful with semicrystalline than with amorphous polymers. Quite obviously, the toughening mechanism synonymous to conventional polymer blends is expected to be different from the mechanisms based on the nanophase-separated structures, since the latter represents a specific morphology-toughness correlation. This is because; toughness modification in polymer blends results in a specific toughness-morphology correlation and this is even more so, when nano-additives are factored into the system.