Most common carrier resin in calcium carbonate filler masterbatches used for PE films, shopping and garbage bags as well as many others polyolefin products is LLDPE. A typical melt flow index (MFI or MFR) of a carrier resin ranges from 10 to 20 MI. Some master batches actually show higher MFI. Lower MFIs (1 to 2 MI) are also available though.
CaCO3 makers' tests showed that using a carrier with close to the same viscosity as the base resin in the PP bag – 0.7 MI HDPE or 0.9 to 1.5 MI LLDPE – improves physical properties of the final product.
Matching molecular weights of carrier and PE film resins makes it possible to use the highest filler loadings.