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

Abstract

Tensile deformation of PMMA toughened with core–shell particles has been investigated by in 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 under uniaxial tension at strain rates of 0.5 and 5.0 mm min-1, at room temperature (20°C). The SAXS pattern of each undeformed RTPMMA specimen consisted of circular concentric fringes which correspond to the form factor of the core–shell particles. Highly localised failure within the particles was observed when low particle concentration samples were deformed beyond the yield point. This localised failure occurred at the poles of the particles at, or adjacent to, the core/shell interface. As the sample was stretched further, the failure was then seen to extend either side of the poles around, or alongside, the interface. In contrast, when the particle concentration was high, the particles stretched considerably without failing. No evidence for crazing was seen in the SAXS patterns obtained from these RTPMMA samples tested under the conditions used. Crazing was therefore not considered to be a major deformation mechanism.