Polypropylene Linear viscoelastic behavior

LDPE, and with polypropylene, PP, was studied In steady state shear, dynamic shear and uniaxial extenslonal fields. Interrelations between diverse rheological functions are discussed In terms of the linear viscoelastic behavior and Its modification by phase separation Into complex morphology. One of the more Important observations Is the difference In elongational flow behavior of LLDPE/PP blends from that of the other blends the strain hardening (Important for e.g. fllm blowing and wire coating) occurs In the latter ones but not In the former. 

In 1981, Bernstein and Zapas [10] extended the work of Ericksen [11] (which describes the discontinuous deformations of solid elastic bars) to viscoelastic materials which obey the Bernstein, Kearsley, and Zapas (BKZ) theory [12]. As in the case of Ericksen s work, the Bernstein and Zapas treatment cannot predict a priori when the material will exhibit the phenomenon of necking, but it does give an explanation for the formation of the neck, which depends on the stretch history. Most recently we have obtained experimental data, using a variety of stress and strain histories, on isotactic polypropylene, the mechanical behavior of which can be described fairly well by the BKZ theory [13]. In most cases the experiments were carried out up to and beyond the point of necking until fracture occurred. In what follows we present these results and also some results obtained on several different linear polyethylenes. 

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