Effect of branch distribution on rheology of LLDPE during early stages of crystallization

ABSTRACT: For a series of semicrystalline ethylene-R-olefin copolymers (linear low-density polyethylene, LLDPE) produced by metallocene and Ziegler-Natta polymerization, the effect of the copolymer composition on the morphology and the evolution of linear viscoelastic properties during isothermal crystallization was studied. The purpose of this study is to explore the extreme sensitivity of rheology and processing to small variations in molecular detail in LLDPE. The metallocene LLDPE sample contains fewer branched units (2.6 mol % C-6) than the Ziegler-Natta copolymer (3.8 mol % C-6), but still, it melts at lower temperatures than the more branched Ziegler-Natta LLDPE analogue. Physical gelation as observed by rheology occurs over a broader temperature region for the metallocene LLDPE than for the Ziegler-Natta copolymer. DSC and rheological observations indicate that the solidification behavior in LLDPEs is determined more by the composition distribution than by the overall content of branched units. A HDPE was included in the study for comparison purposes

Interfacial tension reduction in PBT/PE/clay nanocomposite

We investigated the effect of organically modified nanoclay (organoclay) on immiscible polymer blends [polybutylene terephthalate (PBT)/polyethylene (PE)] with a special focus on the role of clay as a compatibilizer. When organoclay (Nanofil 919; Sud-Chemie, Inc.) is added to the blend, the clay first locates at the interface and then selectively locates in the PBT phase due to its affinity with PBT. This results in effective size reduction and narrowed size distribution of the dispersed phase. However, with a small amount of organoclay, it is observed that the clay locates at the interface regardless of its affinity for a specific component to minimize the chemical potential. The interfacial tension change of the blend with the addition of organoclay was quantitatively predicted from extensional force measurement. When the blend is subjected to an extension, the interfacial tension functions as a resistance against drop deformation. When we added organoclay to the blend, the extensional force was significantly reduced, which means that the contribution of the interfacial tension to the total force is reduced. For a 10/90 PBT/PE blend, the interfacial tension was reduced from 5.76 to 0.14 cN m(-1) when 1 wt% of organoclay was added. This interfacial tension reduction arises from the localization of the organoclay at the interface and its nonhomogeneous distribution along the interface, suppressing the coalescence between the droplets, which is a role of a compatibilizer. Conclusively, the immiscible polymer blends can be compatibilized with organoclay. The organoclay changes the blend morphology by interfacial tension reduction due to the localization of the organoclay at the interface and by the viscosity ratio change due to the selective localization by its affinity to a specific component in the blend