The calcium carbonates used were determined to have mainly the calcite crystal form and partly the aragonite crystal form. The absolute zeta potential values were 5 mV before coating but they increased to 10–15 mV after coating. In other words, the tendency to agglomeration was reduced after coating. The coated calcium carbonates showed a hydrophobic property due to the stearic acid surface treatment.
The results showed that the moisture of the uncoated and coated calcium carbonates had the desired value of less than 0.1%, if dried in contact mode (static bed or stirred) either at 80 °C or 110 °C, while hot air and vacuum drying conditions delivered higher moisture values. Furthermore, it was revealed that stirred contact drying before calcium carbonate coating and stirred contact drying of the matrix polymer and coated calcium carbonate before compounding is a mandatory process to reduce the moisture to the desired values and to avoid macropores, i.e., holes in the films. However, it is not necessary to achieve the targeted moisture level in the LLDPE/coated CaCO3 compounds before film casting.
Using stirred contact drying (high shear mixer) was also found to be superior in terms of easy processing, because drying and coating of the calcium carbonate and drying of the matrix polymer/coated calcium carbonate physical mixtures could be combined. Usage of the high shear mixer was also advantageous in terms of scale-up issues.