Improving the rheology of linear low-density polyethylene (LLDPE) and processability of blown film extrusion using a new binary processing aid

To improve the processability of LLDPE, a binary processing aid composed of polyethylene glycol (PEG) and hydrocalumite was designed. Hydrocalumite containing HPO32- was successfully synthesized with co-precipitation of calcium and aluminum hydroxide in the presence of phosphorous acid. Scanning Electron Microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, Thermogravimetric analyses (TGA) and Ion chromatography were utilized for the characterization of the synthesized hydrocalumite. SEM images showed the layered structure. Ion Chromatography demonstrated the molar ratio of Ca2+/Al3+ was 2:1.3 as an interlayer ion. The influence of PEG/hydrocalumite with the different ratios as a processing aid on the rheological properties of LLDPE was investigated by capillary rheometry. The results obtained showed that PEG/hydrocalumite processing aid with a ratio of 1:3 exhibited the best effect on the reduction of critical stress due to the best coverage of the extruder surface. The measurement of processing parameters in the blown film extruder revealed that hydrocalumite interacted with metallic oxides, created a slippery film layer on the die wall. This leads to a decrease in the die pressure and power consumption by 11% and 21%, respectively. SEM analysis confirmed a delay in Sharkskin instability at a higher shear rate.