Hybrid blends of similar ethylene 1-octene copolymers

Two binary blends of FA + FM and SF + FM comprising ethylene 1-octene copolymers (EOC), one component prepared by Ziegler-Natta and another by metallocene catalysts were investigated in terms of the thermal, viscoelastic, rheological, mechanical, and morphological properties. The big difference between the Ziegler-Natta and metallocene catalyzed EOCs is the distribution and the length of the side chain branching. Each component in FA + FM has similar melt index (MI), density, and comonomer content, while that of the second pair (SF + FM) has similar MI and density, but differs in comonomer content. Both the melt and solution blended materials exhibit two distinct melting and crystallization peaks, implying that the constituents exclude one another during crystallization. A single beta relaxation shifted to lower temperature with the content of metallocene EOC, indicates miscibility in the amorphous region, while the gamma transition is observed in the same position within experimental error. Rheological observations suggest the FA + FM to be miscible, but not SF + FM, implying that the difference in the distribution and the length of the side chain branching influences the melt properties of the EOC blends regardless of the similarity in the density and MI. In addition, no dependency of comonomer contents and the difference in the side chain branching on the mechanical properties is observed. Morphological studies observed from the slow cooled specimens show large spherulitic diameter and ring space for the Ziegler-Natta EOC. In particular, grass like spherulitic sheaf structure is dominated in the blend by the addition of metallocene EOCs. Hence the properties of the hybrid blends consisting of similar MI and density are influenced by not only the distribution of the comonomer, but also the length of the side chain branching. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.