Desenvolvimento de blendas de PEMDL e PEBDL para aplicação em geomembranas

Abstract

Polyethylene geomembranes have technical requirements defined by the GRI GM13 standard, with environmental stress crack resistance (ESCR) being a critical property. The enhancement of this property has been associated with a higher density of tie molecules between adjacent crystalline lamellae, which tends to increase with the content of short-chain branching (SCB) in the polymer. On the other hand, an increase in the SCB contend tends to reduce the degree of crystallinity of the polymer, and the GRI GM13 standard also establishes requirements for density and yield stress, which are favored by a higher degree of crystallinity, consequently, a balance of properties necessary. In this context, the objective of this work was the development of blends of linear medium-density polyethylene (LMDPE) and linear low-density polyethylene (LLDPE), with higher SCB content, for use in geomembranes, with emphasis on ESCR. For this purpose, LMDPE blends with 5, 10, and 15 wt% LLDPE were evaluated, as well as samples of their neat components. After extrusion, the samples were compression-molded into plaques, and density, thermal fractionation, tensile strength, and ESCR tests were conducted. The results indicated good compatibility between the blend components, evidenced by the additive behavior of density and tensile mechanical properties, along with a significant increase in ESCR for LLDPE contents above 10 wt%. Thermal fractionation by DSC suggested predominantly independent crystallization, indicating that co-crystallization, if present, was limited. The incorporation of 10 wt% LLDPE was considered optimal, resulting in ESCR improvement of at least 154% without significant reductions in density or mechanical properties, which are also important requirements for geomembranes.