Microstructure–sealing performance linkage of metallocene linear low density polyethylene and low density polyethylene blends

Abstract

The microstructure–sealing performance linkages of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) blends using thermo-rheological tools are discussed. The effect of molecular architecture in metallocene catalyzed LLDPE (mLLDPE), Ziegler–Natta catalyzed LLDPE (ZN-LLDPE) on the miscibility, and rheological behavior of the blends with LDPE is shown. Even though the macro parameters like density, melt flow rate of the LLDPEs are comparable, subtle differences in the microstructure manifested by comonomer type and its distribution across molecular weight affects the sealing performance of the LLDPE/LDPE blends. For LLDPE matrix, tailor-made comonomer distribution affording thinner lamellas (viz., thickness <11.8 nm) is more critical to sealing process than having total higher comonomer content. For LLDPE/LDPE blends, the thicker lamellae of main chain polymer of LDPE co-crystallize with homo-polyethylene like fraction of LLDPE. The co-crystallization of LLDPE and LDPE helps to achieve hot tack sealing at lower percentage of molten polymer and it appears to be the dominating factor over diffusion of polymer chains across the melt interface to achieve sealing.