SynopsisA relationship has been found for OSA (olefin-acrylonitrile-styrene) polymers between normalized Izod impact strength ( A I / N ) or yield stress (A,oy/N) with mean particle radius. These normalized functions (which analytically include radius and rubbery phase volume) are representative of the toughening effect of a single particle with respect to the styrene-acrylonitrile (SAN) rigid matrix. A I / N and Aay/N increase exponentially as a function of the radius. This approach, for Izod, was also applied to HIPS and toughened nylon reported in the literature and similar results were obtained. In the case of nylon, however, the A I / N values are split in two different curves related to the tough-brittle transition described in that literature. Refemng to OSA, three samples (with the largest radii more than 0.22 pm) fail in a brittle manner and do not fit the curve of A I / N : they fit, however, that of Aay/N. Further work must be done in order to investigate a decisive role either of interfacial adhesion (eventual lack for these three materials) or of tough-brittle transition mentioned before for shear-yielding deforming materials. In fact, OSA has behavior intermediate between that of nylon and HIPS which deforms by crazing.

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