Interfacial self-adhesion of polyethylene blends: the role of long chain branching and extensional rheology

The interfacial self-adhesion strength of polyethylene (PE) binary blends in temperatures higher than the melting point was investigated in relation to their components’ structures and elongational rheological properties. Four binary blends were prepared from the combination of a conventional polyethylene; LDPE or Ziegler-Natta LLDPE, with a metallocene catalyzed ethylene α-olefin copolymer; linear (Linear-m) or long chain branched (LCB-m). Interfacial adhesion was carried out by bringing two films into intimate contact under slight pressure and heat for 0.5 s. Adhesion strength was then measured by peeling immediately after sealing while the adherents were still in the molten state. Blending metallocene in 20, 40, and 60 wt% compositions with conventional PEs enhanced the self-adhesion. However, the adhesion strength of the blends containing 60 wt% metallocene resins was significantly lower than the adhesion strength of neat metallocene resins. This was interpreted to be due to the formation of a segregated layer of highly branched short chains of LDPE or Zn-LLDPE at the surface of films. The increase in adhesion strength of LDPE/Linear-m and Zn-LLDPE/Linear-m blends was more than LDPE/LCB-m and Zn-LLDPE/LCB-m blends. This was attributed to the faster reptation of linear chains, hence superior diffusion across the interface compared to LCB containing resin. The higher increase of adhesion strength for all compositions of LDPE blends was observed compared to their Zn-LLDPE counterparts. The temperature range in which the film showed a plateau of its highest adhesion strength was determined for all blend compositions. The results indicated that the temperature window of plateau adhesion strength for LDPE blends were broader than their Zn-LLDPE counterparts. Therefore, this work suggests that the final plateau temperature (T _pf ) can be correlated with the area under stress–strain curve of the extensional rheological measurements, which is called toughness. Then, the higher melt toughness can result in a broader adhesion strength plateau.