Small angle X-ray scattering investigation of deformation in PMMA toughened with core-shell particles

Tensile deformation of PMMA toughened with core-shell particles has been in vestigated by ill situ small angle X-ray scattering (SAXS). Each core-shell particle consisted of a PMMA core surrounded by a rubber shell, encased in a thin PMMA outer layer. Toughened PMMA (RTPMMA) specimens containing low and high particle concentrations were compared. The samples were tested und er uniaxial tension at strain rates of 0.5 and 5.0 mm min(-1), at room temp erature (20 degreesC). The SAXS pattern of each undeformed RTPMMA specimen consisted of circular concentric fringes which correspond to the form facto r of the core-shell particles. Highly localised failure within the particle s was observed when low particle concentration samples were deformed beyond the yield point. This localised failure occurred at the poles of the parti cles at, or adjacent to. the: core/shell interface. As the sample was stret ched further, the failure was then seen to extend either side of the poles around, or alongside, the interface. In contrast, when the particle concent ration was high, the particles stretched considerably without failing. No e vidence for crazing was seen in the SAXS patterns obtained from these RTPMM A samples tested under the conditions used. Crazing was therefore not consi dered to be a major deformation mechanism.