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Comparison of the elongational behavior of various polyolefins in uniaxial and equibiaxial flows

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Abstract

For processing operations with a pronounced elongational component, it was found that the uniformity of extruded items is improved by the presence of strain hardening usually measured in uniaxial elongation. Many processing operations such as foaming, film blowing, and blow molding are dominated by biaxial deformations, however, and therefore, the question arises how strain hardening in uniaxial and biaxial deformation compares. Besides a linear and long-chain branched PP, one classical LDPE, an HDPE pipe extrusion grade with a bimodal MMD, and a LCB-mPE were also characterized. For the measurements in uniaxial elongation the Münstedt tensile rheometer (MTR) and the ARES-EVF were used, while the lubricated flow method was applied for equibiaxial deformation. It was found that the strain hardening in uniaxial elongation is more pronounced. The dependence of strain hardening on strain rate is qualitatively the same in both modes. In the range of strain rates, the chosen long-chain branched LDPE and PP exhibit a strain hardening, which is approximately independent of the elongational rates applied, whereas for the HDPE it becomes smaller with increasing rate.

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Notes

  1. The opposite effect is called strain softening and is usually observed in multi-phase melts such as immiscible blends or filled systems (especially in fiber filled materials).

  2. It was made from one part of the stabilized (0.5 wt% Irgafos 38, 0.5 wt% Irganox 38) sample D5 (see Piel et al. 2006 for synthesis conditions; highly long-chain branched) and seven parts of the commercial sample C3 (Stadler et al. 2006b; linear), which is already sufficiently stable. The blending time was 15 min. Data of this sample were previously published as E7 by Stadler et al. (2007a, b).

  3. The kinematic viscosity of 100,000 cSt (at 25 °C) is equivalent to about 102 Pa s.

  4. For the LDPE, Schwetz et al. (2002) found a zero shear-rate viscosity η 0 of 866,000 Pa s at 150 °C, while for the two other PEs no value for this quantity could be obtained as the maximum relaxation times are too long to reach the terminal regime within the time of thermal stability. These samples are found to lie distinctly above the η 0–M w correlation for linear HDPE (Stadler et al. 2006b), which is typical of a slightly branched PE (Shroff and Mavridis 1999; Wood-Adams 2001; Gabriel et al. 2002; Gabriel and Münstedt 2002; Malmberg et al. 2002; Münstedt et al. 2003; Piel et al. 2006; Stadler et al. 2006a, c).

  5. This different behavior can be understood when considering that the stretching of the molecules is different in uniaxial and equibiaxial elongation according to the MSF-theory (Wagner et al. 2003).

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Acknowledgement

F. Stadler would like to thank the Bavarian Research Foundation (BFS), which sponsored his stay at the Yamagata University, and the German Research Foundation (DFG) for the general financial support of his research on long-chain branched polyethylenes. The contributions of Mr. Takahiro Kinumura (Yamagata University) for the help with the equibiaxial measurements and Dr. J. Kaschta and Mrs. I. Herzer (University Erlangen) for the SEC-MALLS are also gratefully acknowledged. We would also like to thank Prof. J. Takimoto (Yamagata University) and Mr. D. Möller (University Erlangen) for discussions. Additional thanks go to Prof. Dr. W. Kaminsky and Dr. C. Piel (University Hamburg) for providing the high molecular blend partner of the LCB-mPE.

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Author notes

  1. J. Stange

    Present address: Bayer Materials Science, 47812, Krefeld-Uerdingen, Germany

  2. F. J. Stadler

    Present address: Unité de Physique et de Chimie des Hauts Polymères, Université Catholique de Louvain, Croix du Sud 1, 1348, Louvain-la-Neuve, Belgium

Authors and Affiliations

  1. Institute of Polymer Materials, Department of Materials Science, Friedrich-Alexander-University Erlangen-Nürnberg, Martensstrasse 7, 91058, Erlangen, Germany

    F. J. Stadler, J. Stange & H. Münstedt

  2. Department of Polymer Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata, 992-8510, Japan

    A. Nishioka & K. Koyama

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  1. F. J. Stadler
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  5. H. Münstedt
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Correspondence to H. Münstedt.

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Stadler, F.J., Nishioka, A., Stange, J. et al. Comparison of the elongational behavior of various polyolefins in uniaxial and equibiaxial flows. Rheol Acta 46, 1003–1012 (2007). https://doi.org/10.1007/s00397-007-0190-y

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  • DOI: https://doi.org/10.1007/s00397-007-0190-y

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