Rotational Foam Molding of Metallocene Catalyzed Polyethylene: CBA Screening and Process Characteristics

Abstract

The objective of this work is to investigate the effects of different chemical blowing agents (CBAs) and processing conditions on the cellular structure of foamed metallocene polyethylene and characterize an appropriate blowing agent. An experimental study was conducted to produce metallocene polyethylene foams in dry-blending-based rotational foam molding. The critical processing parameters that optimize the foam structure have been identified through modifications of the molding conditions. The physical properties and cellular structure of the final foamed parts were also examined. The foaming performance of exothermic and endothermic CBAs was studied. It was revealed that selecting a suitable CBA is crucial as the foam structure depends significantly on the properties of the blowing agent. Exothermic blowing agents resulted in greater foam density reduction and exhibited a wider processing window compared to endothermic blowing agents. It was found that a balance between different properties of the blowing agent is required to achieve control over the foam structure.

Keywords

foam rotational molding metallocene polyethylene chemical blowing agent.

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References

Throne, J.L. ( 1996). Thermoplastic Foams, USA, Sherwood Publishers.

Crawford, R.J. and Throne, J.L. ( 2002). Rotational Molding Technology, Norwich, New York, William Andrew Publishing.

Throne, J.L. The Foaming Mechanism in Rotational Molding, Proc. SPE/ANTEC, 2000: 46: 1304.

Liu, G. , Park, C.B. and Lefas, J.A. Production of Low-Density LLDPE Foams in Rotational Molding, Polym. Eng. Sci., 1998: 38: 1997-2009.

Liu, S.-J. and Tsai, C. An Experimental Study of Foamed Polyethylene in Rotational Molding, Polym. Eng. Sci., 1999 : 39: 1776-1786.

Pop-Iliev, R. and Park, C.B. Formulating Foamable Resins for Achieving a Given Volume Expansion Ratio in Rotational Foam Molding, Proc. SPE/ANTEC, 2001: 47: 1598.

Heck III, R.L. A Review of Commercially Used Chemical Foaming Agents for Thermoplastic Foams, J. Vinyl Additive Technol. , 1998: 4: 113-116.

Cary, R. , Dobson, S. and Ball, E. ( 1999). Azodicarbonamide, Concise International Chemical Assessment Documents, Geneva, World Health Organization, 1999.

Klempner, D. and Sendijarevic, V. ( 2004). Handbook of Polymeric Foams and Foam Technology, 2nd edn, Munich, Hanser Publishers.

10.

Pontiff, T. ( 2000). Foaming Agents for Foam Extrusion, In: Lee, S.T. (ed.), Foam Extrusion: Principles and Practice, New York, Technomic Publishing Co. Inc.

11.

Archer, E. , Harkin-Jones, E. , Kearns, M.P. and Fatnes, A. Processing Characteristics and Mechanical Properties of Metallocene Catalyzed Linear Low-Density Polyethylene Foams for Rotational Molding, Polym. Eng. Sci., 2004: 44: 638-647.

12.

Keating, M.Y. and Lee, I.H. Glass Transition, Crystallinity, Resin Stiffness, and Branch Distribution in Metallocene and Ziegler-Natta ethylene 1-Olefins, J. Macromol. Sci. Phys., 1999: 38: 379-401.

13.

Fatnes, A.M. , Melaaen, I.S. , Almquist, V. and Follestad, A. ( 2000). Production and Use of Metallocene-based Polyethylene in Rotational Molding, Metallocene-Based Polyolefins, Wiley, New York, pp. 543-555.

14.

Annechini, D. , Takacs, E. and Vlachopoulos , J. Some New Results on Rotational Molding of Metallocene Polyethylenes, Proc. SPE/ANTEC, 2001: 47: 1291.

15.

Takacs, E. , Kontopoulou, M. , Annechini, D. and Vlachopoulos, J. An Investigation of the Rotomoldability of New Generation Polyethylene, Proc. SPE/ANTEC, 2000: 46: 1331.

16.

Jandel Scientific Software ( 1996). SigmaScan Pro 3.0, Image Measurement Software.