Many polymers can be processed using simultaneous stretching techniques. One of the most widespread technique is that of the 'bubble' where biaxial orientation can be imparted simultaneously in both the machine and transverse directions of the film. There are various types of bubble process in industrial use, and the specific process used depends on the material itself,a nd the property requirements. This article concentrates on films of two of the most extensively used polymers - polypropylene and low desntiy polyethylene - and considers how the polymer structure and the way it is processed can influence the finished film properties.
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