Rubber-modified glassy amorphous polymers prepared via chemically induced phase separation. 3. Influence of the strain rate on the microscopic deformation mechanism

mode of microscopic deformation during impact testing of a 80/20 PMMA/rubbe r blend has been examined by in situ small-angle X-ray scattering using syn chrotron radiation. As discussed previously, the blend studied possesses an extremely small dispersed rubber phase prepared via chemically induced pha se separation and responds as ductile during tensile deformation but suffer s from brittle failure under impact conditions. In part 2, it was shown tha t the ductile behavior is accompanied by cavitation which relieves the tria xial stress state and, subsequently, promotes shear yielding. The present s tudy demonstrates that increasing the strain rate leads to an enhancement o f the nucleation of voids combined with a decreasing tendency for void orie ntation upon tensile deformation. By the introduction of a notch, the defor mation rate is enhanced even further, and the mode of microscopic deformati on transforms to crazing, which explains the poor macroscopic impact toughn ess. Precavitation of the samples, however, restores the toughness, even un der impact conditions.