Thermomechanical behavior of metallocene ethylene-α-olefin copolymers

Abstract

The thermal, dynamic mechanical and stress–strain properties of a set of commercial LLDPEs prepared by metallocene catalysts were studied and compared with two LLDPEs obtained with traditional Ziegler–Natta catalysts. The type and amount of comonomer strongly affects the degree of crystallinity and branching, resulting in different material morphology and macroscopic thermomechanical behavior. Within each set of ethylene-α-olefin copolymers a gradual decrease in the percentage crystallinity and position and intensity of β- and γ-transition is observed, with respect to the comonomer content. In addition, the studied materials are characterized by the absence of an α-transition. This behavior is attributed to the high comonomer content (5–24)%. Tensile behavior changes from the typical necking, cold drawing and strain hardening to the uniform elastomeric deformation, as the comonomer content increases. The experimental methods used, in combination with scanning electron microscopy, lead to converged results, while tensile testing proved to be sensitive to the crystallite size and distribution.