Melt Fracture, Wall Slip, and Flow-Induced Fractionation of Bimodal Polyethylenes

摘要

The melt fracture and wall slip behaviors of bimodal polyethylene (PE) resins are compared with those of unimodal PE resins. The apparent wall slip is estimated by comparing the flow curves obtained by capillary rheology measurements with the linear viscoelastic data. It is confirmed that the higher content of small chains could cause more wall slip. The unimodal resin with broader molecular weight distribution (MWD) and the bimodal resin with higher content of low molecular weight (MW) component have matte surface roughness on the extrudates at lower stress. It is proposed that the flow-induced fractionation leading to the small chains being more concentrated on the die wall interface could cause the wall slip and unusual melt fracture behaviors in the capillary extrusion.