Toughness improvement of LLDPE/PP blend by incorporation of GTR waste

Abstract

In this work, the viability of obtaining a completed recycled composite with improved toughness by the addition of ground tire rubber (GTR) waste to a linear low-density polyethylene (LLDPE)/polypropylene (PP) blend is explored. The idea of maintaining additional processing steps as low as possible, thus reducing costs, prevailed. Thus, no treatment was performed on GTR particles, and direct blending was applied. Materials were evaluated by means of mechanical and fracture behavior, in relation to their microstructure and composition. Despite of different particle content and size incorporated, no changes in crystalline structure of LLDPE and PP were observed. Tensile behavior of composites became more ductile than the LLDPE/PP blend—decrease in stiffness around 30% and increase in elongation at break up to 280%—which is directly related to the elastomeric nature of rubber particles. However, there was no clear trend between tensile parameters and particles’ sizes and percentages added. On the other side, fracture tests were very sensitive to changes induced by GTR. Even though there was no adhesion expected between thermoplastic matrix and GTR, the toughness initiation parameter increased with the content of particles added, indicating that interaction occurred between composites constituents. A large improvement in toughness—between 85 and 110%—was obtained when a homogeneous 3D network of GTR particles with no agglomerated structures was achieved. The synergistic effects of GTR particle debonding and cavitation-detachment of PP nodules, with subsequent void growth, were the main mechanisms of toughness improvement.