Critical insights into ethylene-1-alkene copolymers and long-chain branched polyethylene microstructure on thermo-rheological and sealing behavior of multicomponent systems

The microstructure-property relationships in multicomponent ethylene-1-alkene copolymers with different branching in the microstructures are demonstrated. The metallocene catalyzed linear low density polyethylene (mLLDPE), was miscible with both autoclave grade low density polyethylene (LDPE-A) and/or tubular grade low density polyethylene (LDPE-T). For these multicomponent systems, the rheological response was distinctly differentiating and sensitive to the microstructure of LDPE, at higher shear regimes. The thicker lamellae of LDPE-T and/or LDPE-A might co-crystallize if there is a high density polyethylene-like fraction present in the mLLDPE. Even though the macro parameters like density and melt index (MI) of the investigated multicomponent systems are comparable, the subtle differences in the microstructure manifested by type and distribution of comonomer and/or branching affected the sealing performance. Both high comonomer content and comonomer distribution in the mLLDPE matrix affording a higher fraction of material melting below 120°C were found to be critical for the heat sealing. The fraction of material melting at lower temperatures, attributed to the tertiary branches present in the hyper-branched microstructure of LDPE-A, participate in the sealing process, and lower the sealing temperature. It was evident that mLLDPE with asymmetric distribution of lamellae is more sensitive to the microstructure of the LDPE used.