Current Requirements for the Processing of Polyolefins

Developments by the polyolefin manufacturers in recent years have significantly changed the demands placed on plants processing these products. The new demands are due partly to greatly increased reactor throughputs. 

Polymerization plants are now planned with throughputs of up to 70 t/h for polypropylene (PP) and over 100 t/h for different types of polyethylene (PE), and many licensors would like to process and pelletize these volumes to specification with just one processing plant. In addition to intake, melting, and homogenization of the raw materials, there is a need for discharge parts, conveying systems, and post-treatment units of an appropriate size. 

In addition, in recent years the products themselves have become much more complex and therefore more difficult to process. One example is the bimodal polyolefins, which have excellent mechanical properties and processability at the same time. These properties are achieved by the manufacture of extremely broad to multimodal molecular weight distributions in appropriately equipped reactors [1]. 

The demands placed on an optimized compounding system for these products are therefore complex and, at times, contradictory [3, 4]  

Conventional machine systems try to meet these conflicting demands by the separate optimization of screw geometries in the individual functional zones. However, the shear rate is similar in every zone, because the screw speed is always the same, and the self-wiping 

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