ABSTRACT
The impact modification of poly(methylmethacrylate) (PMMA) by the mechanical blending of a low-molecular-weight matrix with preformed particles can only be achieved by a process involving shear deformation, such as extrusion or injection molding. To maintain good optical properties, the rubbery domains in modified PMMA should be smaller than the wavelength of visible light, and/or the refractive index of the secondary phase should match that of the matrix. The most obvious distinctions between the 3L-particle-modified PMMAs and the 2L-particle-modified PMMAs lie in the nature of the particle cavitation. The crazes then propagate in the matrix perpendicular to the principal stress axis by the usual mechanism of growth at constant stress in the craze fibrils, as in unmodified PMMA. Widespread crazing has been also been reported elsewhere to occur at crack tips in notched specimens of particle-modified PMMA, where the local triaxiality and strain rates are generally much higher than in simple tension.
