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      Novel Processing Additives for Rotational Molding of Polyethylene

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          Abstract

          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.

          Most cited references30

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          Gas solubility, diffusivity and permeability in poly(ethylene oxide)

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            Bubble dissolution in molten polymers and its role in rotational molding

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              Powder-shape analysis and sintering behavior of high-density polyethylene powders for rotational molding

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                Author and article information

                Journal
                ipp
                International Polymer Processing
                Carl Hanser Verlag
                0930-777X
                2195-8602
                2009
                : 24
                : 5
                : 452-462
                Affiliations
                1 LRT-7, University of the Federal Armed Forces, Munich, Germany
                2 Polymerphysik, Technical University Berlin, Germany
                Author notes
                Mail address: Oleg Kulikov, LRT-7, UniBw Munich, 85577 Neubiberg, Germany. E-mail: oleg@ 123456kulikow.de
                Article
                IPP2296
                10.3139/217.2296
                df1f20c1-3fc3-4b54-8b83-e2973619c167
                © 2009, Carl Hanser Verlag, Munich
                History
                : 28 May 2009
                : 24 August 2009
                Page count
                References: 45, Pages: 11
                Categories
                Regular Contributed Articles

                Polymer science,Materials technology,Materials characterization,General engineering,Polymer chemistry

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