Rubber-toughened polymers deformation mechanisms

Bucknall CB (2000) Deformation mechanisms in rubber-toughened polymers. In Paul DR and Bucknall CB (eds) Polymer Blends, Vol 2. Wiley, New York p 83... 

Kuboky and co-workers [40] used transmission electron microscopy (TEM) to study block and white crazes in high impact polystyrene (PS). They examined the mechanism of block craze formation and found that the rubber molecules were not necessarily diffused into the entire crazes. The length of the block crazes varied before they turned to white and in some cases only white crazes were generated from the rubber particles. TEM should thus be used with caution in examining stained rubber-toughened polymers to ensure that all crazes, including the white crazes, were considered for evaluation of the extent of the deformation behaviour [41]. 

Mechanical Properties and Deformation Micromechanics of Rubber-Toughened Acrylic Polymers... 

It is well known that the main mechanisms of inelastic deformation are shear yielding and multiple crazing in the rigid matrix phase, as well as cavitation in the soft dispersed phase in rubber-toughened plastics and multiphase polymers [42]. Eor many years, these mechanisms have been studied using microscopy techniques. 

As one might intuitively expect, the incorporation of rubber particles within the matrix of brittle plastics enormously improves their impact resistance. Indeed, the impact resistance imparted by the rubber is the principal reason for its incorporation (Rosen, 1967) in rubber-plastic blends and grafts. Toughening in such polymers is also observed under other loading conditions, such as simple low-rate stress-strain deformation and fatigue. It is believed that several deformation mechanisms are important in all such cases, though their relative importance may depend on the polymer and on the nature of the loading. 

Rubber toughening is the most often used method of improving the impact resistance of polymers (Bucknall 1977). The impact modified materials are usually the blends of a rigid matrix polymer with an elastomer. The composition of the constituents, their miscibility, and the morphology influence the deformation and failure mechanism in the blend. Particle size of the elastomer, its dispersion, and its adhesion with matrix are also the important factors determining the toughness. 

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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