Extruder Screws for Lldpe Blown Film

After the introduction of linear low density polyethylene (LLDPE) resins into the United States market about 4 years ago, it soon became obvious that most screws designed for conventional low density polyethylene (LDPE) extrusion could not economically process LLDPE in blown film applications. LDPE screws, when used for LLDPE extrusion, require more torque than is available from most blown film extruder drives, and tend to deliver melt temperatures much higher than desired for film blowing. This is due to the different shear rheology of LLDPE as austrated in Fig. 1. Figure 1 shows that LLDPE is substantially more viscous in shear than is LDPE; furthermore, LLDPE ex- hibits a significantly lower shear sensitivity than LDPE.