Influence of Mineral Fillers on the Processing of LLDPE Films, 1997 Polymers, Laminations & Coatings Conference Proceedings

Mineral fillers affect the processing rate and stability of polyethylene blown films. Calcium carbonate addition increases throughput, and gives greater stability to linear polyethylenes. To understand this mechanism, we studied thermal characteristics and melt rheology for a range of filled linear low density polyethylenes (LLDPE). Masterbatches were prepared with various calcium carbonate grades, talc and calcined clay. Laboratory-scale blown films were produced, and temperature changes were monitored along the bubble. Mineral distribution within the film was assessed with optical and electron microscopy. Rheological properties of the diluted masterbatches were evaluated over four decades of shear rate.

Mineral fillers increased cooling rates, and improved bubble stability. Coarser grades of calcium carbonates gave the greatest improvement, whereas fine grades and talc had little effect. Micrographs revealed the level of interparticular contact and alignment of anisotropic particles, that gave rise to the differences observed. Filler type and loading did not significantly influence the shear rheology of the compounds, at shear rates associated with film extrusion.