UBC Theses and Dissertations
The role of surface energy of boron nitride on gross melt fracture elimination of polymers Seth, Manish
Experiments were carried out to measure the surface energy of boron nitride (BN) powders. A reliable procedure has been developed for measurement of surface energy of powders using the capillary rise technique based on Washburn's equation. It is measured by finding the contact angle from liquid penetration experiments with polar and non-polar liquids. Both the dispersive and non-dispersive components of surface energy are determined. The results of the surface energy of BN powders has been found to correlate well with the critical shear rate for the onset of melt fracture, indicating the importance of surface energy in the procedure of selecting an effective processing aid. In addition, experiments were carried out in both an Instron capillary rheometer equipped with a special annular die (Nokia Maillefer wire coating cross-head) and a parallel-plate rheometer to investigate the effect of a new processing additive (boron nitride powder in combination with a fluoroelastomer) on the rheology and processability of molten polymers. Metallocene polyethylenes with and without boron nitride (BN) and fluoroelastomer are tested in extrusion. First, it is demonstrated that BN is a superior processing aid compared to conventional fluoropolymer ones. Secondly, it is found that the combination of BN powders with a small amount of a fluoroelastomer improves even further the processability of molten polymers. They can essentially be processed at higher shear rates without exhibiting gross melt fracture. DSC and TGA experiments using polymer specimens with and without BN were also carried out to investigate the mechanism by which gross melt fracture is being eliminated in the presence of boron nitride.
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