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Licensed Unlicensed Requires Authentication Published by De Gruyter April 6, 2013

Novel Processing Additives for Rotational Molding of Polyethylene

  • O. Kulikov , K. Hornung and M. Wagner


Over 85% of the articles manufactured via rotational molding employ Polyethylene (PE) resins. PE resins used for rotomolding have usually particle sizes less than about 0.8 mm and used as powders or micro-pellets. During heating in a rotating mold, these particles get fused and merge into one piece. A disadvantage of the rotomolding process is long cycle times that affect not only the production rate but also increase thermal degradation of the polymer due to its long exposure to heat. One of the problems in rotomolding is bubbles of gasses trapped during sintering of the PE powders which reduce mechanical strength of the article produced. We propose to use reacting mixtures of Polyethylene Glycol with citric acid as an additive to rotomolding grades of PE. The additive accelerates sintering of the PE particulates and greatly reduces number of bubbles in the melt but at high concentrations (>0.4 wt.%) it impedes flow of the particles. Fine powders with particles of irregular shape and wide distribution of sizes are characterized by low flowability while micro-pellets of oval shape with smooth surface have too high flowability for rotomolding. To improve cost-efficiency and quality of the rotomolding process we propose to use micro-pellets instead of powders and to fabricate micro-pellets by extrusion at reduced temperatures and cutting the produced strands in conditions of air-cooling. Amazingly, the same processing additives improve extrusion of PE resins and rotomolding of the PE micro-pellets. The additives also adjust flowability of micro-pellets in the direction to optimum. Silica fume, vinyl-silanes and stearates can be ingredients of the additive package. Mechanisms of the observed improvements are discussed.

Mail address: Oleg Kulikov, LRT-7, UniBw Munich, 85577 Neubiberg, Germany. E-mail:


Bauer, P., et al., U.S. Patent 6 048 937 (2000)10.1088/1126-6708/2000/07/048Search in Google Scholar

Beall, G. L.: Rotational Molding Design Materials, Tooling, and Processing, Hanser Publishers, Munich(1998)Search in Google Scholar

Bellehumeur, C. T., Tiang, J. S., “Modeling of Bubble Formation in Rotational Molding”, SPE ANTEC Tech. Papers, 46, 13561359(2000)Search in Google Scholar

Bruins, P. F.: Basic Principles of Rotational Molding, CRC Press, Boca Raton(1971)Search in Google Scholar

Chaudhary, B. I., et al., “Processing Enhancers for Rotational Molding of Polyethylene”, Polym. Eng. Sci., 41, 17311742(2001) DOI: 10.1002/pen.10870Search in Google Scholar

Conway, J. M., “Effects of Moisture in Thermosets on Finished Product Properties”, Modern Plastics, 7, 6468(1973)Search in Google Scholar

Crawford, R. J., Kearns, M., Practical Guide to Rotational Moulding, Rapra Technology, Shawbury(2003)Search in Google Scholar

Crawford, R. J., Throne, J. L., Rotational Moulding Technology, Plastics Design Library, William Andrew Publishing, New York(2002)Search in Google Scholar

Dodge, P. T., et al.: “Rotational Molding”, in Encyclopedia of Polymer Science and Technology, BikalesN.M. (Ed.), Vol. 11, 3rd Edition, John Wiley & Sons, New Jersey(2004)10.1002/0471440264.pst326Search in Google Scholar

Evans, K., “Rotomolding Works Better in a Vacuum”, Plastics Technology, 7, 5657(1998)Search in Google Scholar

Foster, W. E., “Need a Tough Rotomolded Part? Now You Can Rotomold Polycarbonate”, Plastics Technology, 11, 4748(1970)Search in Google Scholar

Gogos, G., “Bubble Removal in Rotational Molding”, SPE ANTEC Tech. Papers, 45, 14331440(1999)Search in Google Scholar

Greco, A., Maffezzoli, A., “Powder-Shape Analysis and Sintering Behavior of High-Density Polyethylene Powders for Rotational Molding”, J. Appl. Polym. Sci., 92, 449460(2004) DOI: 10.1002/app.20012Search in Google Scholar

Gruenschloss, E., “A Powerful Universal Plasticating System for Single-screw-extruders and Injection-moulding Machines”, Int. Polym. Proc., 3, 226234(2003)Search in Google Scholar

HappoldtJr., W. B., et al., U.S. Patent 2 448 799 (1945)10.1136/bmj.2.4421.448Search in Google Scholar

Henwood, N., “Tips for Using Color in Rotomolding, Part 2”, Rototalk, a Newsletter of ARM Int'l SAR Division., 2, 4(2006)Search in Google Scholar

Kallio, K., et al., U.S. Patent Appl. 20010025092 (2001)Search in Google Scholar

Kontopoulou, M., et al., “Polymer Melt Formation and Densification in Rotational Molding”, SPE ANTEC Tech. Papers, 45, 14281432(1999)Search in Google Scholar

Kontopoulou, M., Vlachopoulos, J., “Bubble Dissolution in Molten Polymers and Its Role in Rotational Molding”, Polym., Eng. Sci., 39, 11891198(1999) DOI: 10.1002/pen.11505Search in Google Scholar

Kratel, G., et al., U.S. Patent 3 953 487 (1976)Search in Google Scholar

Kulikov, O., et al., “Chapter 15 Novel processing additives for extrusion of polyolefins” in Advances in polymer processing: macro- to nanoscales, Thomas, S., Weimin, Y., (Ed.), Woodhead Publishing, London(2009)10.1533/9781845696429.3.438Search in Google Scholar

Lin, H., Freeman, B. D., “Gas Solubility, Diffusivity and Permeability in Poly(ethylene oxide)”, J. Membr. Sci., 239, 105117(2004) DOI: 10.1016/j.memsci.2003.08.031Search in Google Scholar

Massey, L. K.: Permeability Properties of Plastics and Elastomers, 2nd Edition, William Andrew, New York(2003)Search in Google Scholar

Maziers, E., U.S. Patent Appl. 20050255264 (2005)Search in Google Scholar

Maziers, E., U.S. Patent Appl. 20080018019 (2008a)Search in Google Scholar

Maziers, E., U.S. Patent Appl. 20080103264 (2008b)Search in Google Scholar

Metz, S. J.: Water Vapor and Gas Transport through Polymeric Membranes, PrintPartners Ipskamp, Enschede(2003)Search in Google Scholar

Nagy, T., White, J. L., “The Effect of Colorants on the Properties of Rotomolded Polyethylene Parts”, Polym. Eng. Sci., 36, 10101018(2004) DOI: 10.1002/pen.10488Search in Google Scholar

Needham, D. G., U.S. Patent 4 668 461 (1987)Search in Google Scholar

Needham, D. G., U.S. Patent 5 530 055 (1996)Search in Google Scholar

Nova Chemicals, Rotational Molding Polyethylene Processing Guide, Alberta, Canada(1999)Search in Google Scholar

Nugent, P., “Chapter 6 Rotational Molding” in Handbook of Plastic Processes, Harper, C.A. (Ed.), Wiley, New Jersey(2006)10.1002/0471786586.ch6Search in Google Scholar

Penfold, J., et al., U.S. Patent 6 048 935 (2000)10.1088/1126-6708/2000/10/048Search in Google Scholar

Pick, L. T., Harkin-Jones, E., Third Polymer Processing Symposium, Belfast, 259268(2004)Search in Google Scholar

Rauwendaal, C.: Polymer Extrusion, Hanser Publishers, Munich(1986)Search in Google Scholar

Sowa, M. W., U.S. Patent 3 974 114 (1976)Search in Google Scholar

Spence, A. G., Crawford, R. J., “The Effect of Processing Variables on the Formation and removal of Bubbles in Rotationally Molded Products”, Polym. Eng. Sci., 36, 9931009(1996a) DOI: 10.1243/PIME_PROC_1996_210_151_02Search in Google Scholar

Spence, A. G., Crawford, R. J., “Removal of Pinholes and Bubbles from Rotationally Molded Products”, Proc. Inst. Mech. Eng. Part B, 210, 521533(1996b) DOI: 10.1002/pen.10487Search in Google Scholar

Swain, R. D., U.S. Patent 6 682 685 (2004)Search in Google Scholar

Uminski, M., Saija, L. M., “Spray Drying of Low-Tg Acrylic Dispersions”, Surf. Coat. Int., 81, 557560(1998) DOI: 10.1007/BF02693083Search in Google Scholar

Wang, W., Kontopoulou, M., “Rotational Molding of TPOs containing Polyolefin Plastomers”, Rotational Molding Newsletter, 7/1, 1115(2007)Search in Google Scholar

Whatcott, R. B.: Development of a Practical Flow Test for Rotational Molding, Brigham Young University, Provo, UT(2008)Search in Google Scholar

Xu, L., Crawford, R. J., “Analysis of the Formation and Removal of Gas Bubbles in Rotationally Moulded Thermoplastics”, J. Mat. Sci., 28, 20672074(1993) DOI: 10.1007/BF00367563Search in Google Scholar

Yokoyama, T.: Fluidity of Powder. Powder Technology Handbook, 2nd Edition, Marcel Dekker, New York(1997)Search in Google Scholar

Zhang, H., Cloud, A., “The Permeability Characteristics of Silicone Rubber”, Proc. Global Advances in Materials and Process Engineering, Dallas, (2006)Search in Google Scholar

Received: 2009-05-28
Accepted: 2009-08-24
Published Online: 2013-04-06
Published in Print: 2009-11-01

© 2009, Carl Hanser Verlag, Munich

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