Impact-energy-dissipating processes, rubber

In Fig. 10.1, the relations of the values and tpj, (Xcr 9im) adduced for HDPE samples within the range of 7 = 293 -s- 353 K. As one can see, the increase of any from the indicated structural components results to T j growth, but the relation 1 1 was obtained only for (5 + This relation of complete energy dissipation is typical for rubbers, which is both devitrificated loosely packed matrix with fraction cpj and mechanically disordered crystallites part with fraction x - Hence, the indicated structural components of deformed state define energy dissipation in HDPE, but not amorphous phase itself, the part of which (clusters) does not participated at all in impact energy dissipation process [3]. 

According to more recent theories, the toughness of high impact polystyrene is caused by flow and energy dissipation processes in the continuous polystyrene phase. The rubber particles act as initiating elements. Considerable differences in the thermal expansion coefficients and in the moduli of the polystyrene phase on the one hand and of the rubber particles on the other lead to an inhomogeneous stress distribution in impact polystyrene. Stress maxima create zones of lower density, called crazes (3), in which the polystyrene molecules are extended parallel to the direction of stress. Macroscopi-cally craze formation appears as whitening the flow processes result in irreversible deformation (cold flow). 

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