Interparticle ligament

Fig. 13.39 The toughness jump in Izod fracture energy in rubber-particle-modified HDPE blends at an interparticle ligament thickness of A = 0.6 pm, twice the thickness of crystallized layers on rubber particles (from Bartczak et al. (1999a) courtesy of Elsevier).

In practice, much of the literature still reports notched Izod numbers, but these can be deceptive, especially for materials close to a ductile-brittle transition. Better indicators of real toughness are obtained when samples of different thickness are considered. As one adds more rubber to a plastic, a critical concentration is often found where the toughness increases dramatically. In some cases, e.g., polymers that are capable of shear yielding, this correlates better with the interparticle distance or "ligament thickness" than with any other variable. 

The selection of the dominant deformation mechanism in the matrix depends not only on the properties of this matrix material but also on the test temperature, strain rate, as well as the size, shape, and internal morphology of the rubber particles (BucknaU 1977, 1997, 2000 Michler 2005 Michler and Balta-Calleja 2012 Michler and Starke 1996). The properties of the matrix material, defined by its chemical structure and composition, determine not rally the type of the local yield zones and plastic deformation mechanisms active but also the critical parameters for toughening. In amorphous polymers which tend to form fibrillated crazes upon deformation, the particle diameter, D, is of primary importance. Several authors postulated that in some other amorphous and semiciystalline polymers with the dominant formation of dUatational shear bands or extensive shear yielding, the other critical parameter can be the interparticle distance (ID) (the thickness of the matrix ligaments between particles) rather than the particle diameter. 

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