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Searching for Suitable Polymers and Processing Conditions
A set of commercial polyethylenes (three LDPE and three LLDPE) was rheological characterized and processed in a laboratory double bubble extrusion line with the purpose of investigating: i) whether their relative processability could be predicted in the laboratory and ii) the effect of operating and machine variables on processability. Oscillatory shear and extensional measurements were able to differentiate the various materials, who also behaved quite differently upon processing. Those with a stronger shear thinning behaviour, higher elasticity and higher melt strength were the most suited to the process. Bubble stability and thickness uniformity were assumed as the main requirements for processability. The former was estimated by monitoring the time required to stabilize the bubble and examining any variation/oscillation in size/shape. Bubble stability depends on the interaction between various parameters, the most relevant being those related with the film cooling stage, namely the axial position of the air rings, the air flow rate and air velocity. The study was preceded by an assessment of the performance of the re-heating oven and die/calibration/centring, as these parameters could also narrow the practical operating window.
From O. S. Carneiro 1 | J. A. Covas 1 | C. Domingues 1
1IPC/I3N – Institute for Polymers and Composites, Department of Polymer Engineering, University of Minho, Guimarães, Portugal
(Received 14.07.2011; accepted 08.12.2011)
Appeared in International Polymer Processing 2012/03, Page 348-357
DOI: 10.3139/217.2538
Direct link: http://www.polymer-process.com/IPP2538
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Bi-axially Oriented Blown Film Technology [818 KB]
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