Bridging the Modulus Gap between LLDPE and HDPE

Abstract

Developing blown film resins for the production of films that exhibit the toughness properties of linear low density polyethylene (LLDPE) with the stiffness and tensile characteristics of high density polyethylene (HDPE) has historically been difficult to achieve for both resin producers and film converters. Resin producers have attempted to push the density higher for LLDPE film resins and lower for HDPE film resins. Separately, film producers are continuously searching for the same hybrid film through blending low (LDPE), linear low (LLDPE), medium (MDPE) and high-density (HDPE) polyethylenes. Producing successful film blends for heavy-duty applications with densities over 0.918 g/cm3 usually results in a high performance LLDPE film resin being blended with low levels of a MDPE or HDPE. As the level of MDPE or HDPE increases, loss of critical toughness properties such as machine direction tear (MD tear) and dart impact strength is observed. There now exists a novel method of producing films that possess a full density range between 0.918 g/cm3 and 0.938 g/cm3. This approach is based on the utilization of a new family of high molecular weight medium density polyethylene (HMW-MDPE) film resins. By blending an HMW-MDPE with a resin density of 0.938 g/cm3 with high performance LLDPE film resins, films can be fabricated over a wide range of densities without the loss of tear and impact properties. These blends can be produced at thin or thick gauges on either high stalk or conventional blown film equipment.