"The Influence of Shear Thinning on Elongation Hardening of Long-Chain Branched Polypropylene"
, in American Institute of Physics: AIP Conference Proceedings , XVth Int. Congr. on Rheology, Vol. 1027, Seite(n) 354, 8-2008, ISBN: 978-0-7354-0550-9
The Influence of Shear Thinning on Elongation Hardening of Long-Chain Branched Polypropylene
Sprache des Titels:
AIP Conference Proceedings , XVth Int. Congr. on Rheology
Long-chain branched polypropylenes show pronounced strain hardening in elongation. This property,
important for various applications is strongly reduced by shear applied to the melt before elongation. In this work the
influence of shear history on the rheological properties of blends from a linear (L-PP) and a long-chain branched (LCBPP)
polypropylene was studied in detail. Shear thinning is produced in a cone-plate device and the annealing of it is
recorded by the storage modulus, G'(ff)), immediately after applying the shear deformation. In the case of L-PP this
recovery function is simple exponential, whereas additional relaxation processes are found with the presence of LCB-PP
in the blend. In order to investigate the elongational behaviour after various shear histories the sheared sample is removed
from the cone-plate system, compressed into a flat sheet and quenched very fast to ensure residual shear thinning.
Constant elongation rate experiments have been performed using a uniaxial extensional rheometer, the SER universal
testing platform where the tensile stress growth coefficient, ;;*(?,4), is recorded. Shear thinning reduces elongation
hardening reversible. The annealing of this reduction depends on the shear history and the degree of long chain