Effect of Long-chain Branching on the Foaming of Polypropylene with Azodicarbonamide

Abstract

In this article the influence of long-chain branching on the foaming behavior of polypropylene (PP) is investigated. Different branching contents are achieved by blending a linear PP (L-PP) and a long-chain branched PP (LCB-PP). Whereas, the L-PP does not exhibit any strain hardening in laboratory stretching experiments, blends with amounts of the LCB-PP higher than 2 wt% already show a pronounced strain-hardening behavior. The strain hardening increased with a growing amount of the long-chain branched PP. A laboratory scale foaming apparatus based on a capillary rheometer is developed for the foaming experiments. In foaming tests with azodicarbonamide as chemical blowing agent, a significant improvement of the foaming behavior with respect to a higher expansion ratio, a lower amount of connected cells, and a more homogeneous cell size distribution is found with increasing content of the LCB-PP up to a concentration of 50 wt%. At this concentration, the foaming behavior of the LCB-PP is reached. The results demonstrate that low amounts of long-chain branching can significantly improve the optimal foaming process of PPs with a chemical blowing agent, and that additions of the linear material up to 50 wt% to the LCB-PP do not have any influence on the favorable foaming performance of the long-chain branched PP.

Keywords

linear polypropylene branded polypropylene blends extensional rheology chemical blowing agent cellular structure

Get full access to this article

View all access options for this article.

References

Leaversuch, R. D. (1996). Resins ‘96 , Modern Plastics International, 7(1): 50-51 .

Park, C. B. and Cheung, L. K. (1997). A Study of Cell Nucleation in the Extrusion of Polypropylene Foams , Polymer Engineering and Science, 37(1): 1-17 .

Kurzbeck, S. , Oster, F. , Münstedt, H. , Ngyuen, T. Q. and Gensler, R. (1999). Rheological Properties of Two Polypropylenes with Different Molecular Structure , Journal of Rheology, 43(2): 359-374 .

Phillips, E. M. , McHugh, K. E. , Ogale, K. and Bradley, M. B. (1992). Polypropylen mit hoher Schmelzestabilität , Kunststoffe, 82(8): 671-676 .

Naguib, H. E. , Park, C. B. , Panzer, U. and Reichelt, N. (2002). Strategies for Achieving Ultra Low-density Polypropylene Foams , Polymer Engineering and Science, 42(7): 1481-1492 .

Park, C. B. , Cheung, L. K. and Song, S.-W. (1998). The Effect of Talc on Cell Nucleation in Extrusion Foam Processing of Polypropylene with CO2 and Isopentane , Cellular Polymers, 17(4): 221-251 .

Park, C. B. , Behravesh, A. H. and Venter, R. D. (1998). Low Density Microcellular Foam Processing in Extrusion using CO2 , Polymer Engineering and Science, 38(11): 1812-1823 .

Naguib, H. E. , Park, C. B. and Reichelt, N. (2003). Fundamental Foaming Mechanisms Governing the Volume Expansion of Extruded Polypropylene Foams , Journal of Applied Polymer Science, 91: 2661-2668 .

Michaeli, W. , Lorenz, J. , van Hoorn, R. and Schumacher, H. (2004). Assessment of the Foamability of Polymers on the Basis of their Biaxial Stress/Strain Behaviour, Blowing Agents and Foaming Processes 2004 , Conference Proceedings, Rapra Technology Ltd.

10.

Spitael, P. and Macosko, C. W. (2004). Strain Hardening in Polypropylenes and its Role in Extrusion Foaming , Polymer Engineering and Science, 44(11): 2090-2100 .

11.

Reichelt, N. , Stadlbauer, M. , Folland, R. , Park, C. B. and Wang, J. (2003). PP-blends with Tailored Foamability and Mechanical Properties , Cellular Polymers, 22(5): 315-328 .

12.

Gabriel, C. and Münstedt, H. (2002). Influence of Long-chain Branches in Polyethylenes on Linear Viscoelastic Flow Properties in Shear , Rheologica. Acta, 41(3): 232-244 .

13.

Münstedt, H. , Kurzbeck, S. and Egersdörfer, L. (1998). Influence of Molecular Structure on Rheological Properties of Polyethylenes , Part II: Elongational Behavior, Rheologica Acta., 37(1): 21-29 .

14.

Hachmann, P. and Meissner, J. (2003). Rheometer for Equibiaxial and Planar Elongations of Polymer Melts , Journal of Rheology, 47(4): 989-1010 .

15.

Takahashi, M. , Isaki, T. , Tagikawa, T. and Masuda, T. (1993). Measurement of Biaxial and Uniaxial Extensional Flow Behavior of Polymer Melts at Constant Strain Rates , Journal of Rheology, 37(5): 827-846 .

16.

Stange, J. , Uhl, C. and Münstedt, H. (2005). Rheological Behavior of Blends from a Linear and a Long-chain Branched Polypropylene , Journal of Rheology, 49(5): 1059-1079 .

17.

Sugimoto, M. , Masubuchi, Y. , Takimoto, J. and Koyama, K. (2001). Melt Rheology of Polypropylene containing Small Amounts of High-Molecular-weight Chain. Uniaxial and Biaxial Extensional Flow , Macromolecules, 34: 6056-6063 .

18.

Gendron, R. and Daigneault, L. E. (2000). Rheology of Thermoplastic Foam Extrusion Process, In: Lee, S.-T. (ed.), Foam Extrusion, Technomic Publishing Co., Ltd, Lancester .

19.

Heindl, M. (2004). Einfluss von Dehnströhmungen auf die Morphologieausbildung in Polymerblends, Dissertation, University of Erlangen-Nürnberg, Erlangen, Germany.

20.

Lee, S.-T. (2000). Foam Extrusion, Technomic Publishing Co., Ltd, Lancester .