| Extrusion of polyethylene leads to defects, such as melt fracture and sharkskin roughness when performed at high rates and pressures. Silicones and fluorocarbons are known to act as slippery agents, reducing those defects. Typical silicones and fluorocarbon additives present a number of technology disadvantages. Because of their nature, commercial silicones and fluorocarbons do not mix well with polyethylene. Consequently, they have been used to coat the die of the extruder before the addition of polyethylene. This method is not efficient for large scale production, since it requires frequent interruption of the process to recoat the die. The approach we envision eliminates these problems entirely.;This dissertation describes the synthesis of novel extrusion aids for polyethylene using the precision branching technology developed in the Wagener group. Precisely placed silicones and fluorine branches of various branch lengths between precision long-run polyethylene segments can be synthesized using Acyclic Diene Metathesis (ADMET). The long-run polyethylene segments between branches will allow for better mixing of the extrusion aid additive in the extruder, and equally important, the long run polyethylene units between branches will co-crystallize with polyethylene after exiting the extruder. This represents the first such application in extrusion aid technology. The purpose of this work is to identify successful synthetic methods that will be used to produce extrusion aids in which the branch sizes and distances between branches can be varied. The goal is to find the appropriate polyethylene run length and branch size for optimum performance.;At least three benefits accrue for these research results: 1) the extrusion aid additive will be "locked" into the polymer (via co-crystallization) leading a cleaner processing: 2) lower extrusion pressures will be needed for the same output thus saving energy; 3) less die swell, melt fracture, and sharkskin effects will be observed, resulting in an improved product. Very small amounts of the additive are needed to achieve all positive effects and low molecular weight polymers are enough to lead to positive results. |
