Clarifying the effects of comonomer distribution between short and long chains on physical and mechanical properties of ethylenic copolymers

Abstract

In this paper, two Zigler‐Natta catalysts (ZNCs) were used to synthesize a commercially available linear low‐density polyethylene (LLDPE), widely used in the packaging industry, on an industrial scale. The catalysts differ only in their ability to distribute comonomers between short and long chains. Both catalysts were fully characterized in the first section, and two similar ethylene/1‐butene copolymers were made using them. Afterward, the produced copolymers were fully characterized using different techniques; namely, differential scanning calorimetry (DSC), successive self‐nucleation and annealing (SSA), oxygen induction time (OIT), melt flow index (MFI), rheometric mechanical spectroscopy (RMS), and a wide range of mechanical experiments. It was revealed that while the presence of comonomers in short chains can reduce their resistance against oxidation (by more than 30%) and can cause a dramatic change in friction coefficients (by more than 20%), some of the other main mechanical properties of the made copolymers were independent of comonomer distribution between long and short chains. In addition, it was shown that ethylenic copolymers' strain hardening modulus (SHM) takes advantage of the homogenous distribution.

Splitting for strength: Manipulating polymerization reactor split ratios to control mechanical and rheological properties in bimodal polyethylene resins

“…The role of HMW chains in creating tie molecules is emphasized, with higher MW chains participating in more lamellae and generating more tie molecules, thereby enhancing the SHM of the alloy. 17,18 These findings emphasize the multifaceted nature of the relationship between molecular characteristics and mechanical properties in BiPE resins, providing valuable insights for applications requiring a balance between short-term and long-term mechanical performance.…”

“…However, the study reveals a contrary trend, attributing the modest drop in impact resistance to the rise in tie molecules due to the increased MW of HMW chains. This phenomenon prevents created crazes from spreading and evolving into cracks, contributing to the overall impact resistance of the samples 17,18 …”

“…This phenomenon prevents created crazes from spreading and evolving into cracks, contributing to the overall impact resistance of the samples. 17,18 In addition, the focus on long-term mechanical properties, particularly the SHM and SCG resistance, sheds light on the resilience of the synthesized samples. As expected, the SHM of samples 1-5 shows a substantial increase with the rise in the MW of HMW chains.…”