Effect of MWD on the amount of polymer process aid required to suppress sharkskinmelt fracture in LLDPE

摘要

At TAPPI-2000 it was reported [1]that different types of High-Performance Hexene Linear Low Density Polyethylene (HPH-LLDPE)behaved differently with respect to the onset of sharkskin melt fracture (SSMF),depending on the breadth of the molecular weight distribution(MWD).The MWD differences weresmall and subtle,but the effect on the on set of melt fracture was significant.The present study is a continuatin of that work,through a comparative investigation under shear rate conditions high enough to induce melt fracture in both narrow and broad-MWD LLDPEs.A fluoropolymer process aid (PPA) was then added in stepwise increments untilmelt fracture was eliminated.It was found that the narrow-MWD resin required more than twice the amount of PPA to eliminate SSMF.