Mechanism of gross melt fracture elimination in the extrusion of polyethylenes in the presence of boron nitride

The mechanism by which the addition of a small amount of boron nitride into a polyethylene eliminates gross melt fracture is elucidated. Simple elongational viscosity measurements at high rates revealed that the presence of boron nitride decreases the extensional viscosity of polyethylenes. The extensional rates at which these effects are present were found to be about the same with those at which gross melt fracture is obtained (calculated from Cogswells analysis). Thus, it can be argued that the well dispersed boron nitride particles decrease extensional stresses that are responsible for gross melt fracture and/or their presence dissipate the release of energy resulting from isolated rupture or slip planes within the melt originating at the entrance to the capillary.