The effect of rubber particle size on toughening behaviour of rubber-modified poly(methyl methacrylate) with different test methods

In order to study the effect of particle size on the toughening behaviour of rubber-toughened poly(methyl methacrylate) (PMMA), a systematic model study has been carried out using core-shell type particles, made up of a poly(n-butyl acrylate) (PBA) core and a PMMA outer shell. Two different fracture tests, i.e. a three-point bending test for the evaluation of the fracture toughness (K-1C) and an impact test were employed to study the toughening behaviour. In the case of the impact test, maximum impact strength was obtained for rubber particles with a 0.25 mu m diameter regardless of the rubber phase contents, and only a modest improvement of the impact strength was obtained for blends containing 0.15 or 2 mu m particles. For the three-point bending test, in contrast, even large particles such as the 2 mu m particles provided a significant enhancement in the fracture toughness. The difference in the toughening behaviour due to particle size may be attributed to the test method dependence associated with a change in the deformation mechanism. In the three-point bending test, the deformation mechanism was found to be multiple crazing, whereas in the impact test, the shear yielding induced by cavitation of the rubber particles is predominant. (C) 1998 Elsevier Science Ltd. All rights reserved.