Enhanced Thermal, Mechanical, and Barrier Properties of Packaging Grade Linear Low-Density Polyethylene (LLDPE) Nanocomposites With Commercial Graphene Nanoplatelets

In this work, the rheological, thermal, mechanical, and barrier properties of nanocomposites based on metallocene-based linear low-density polyethylene (mLLDPE) and a commercial graphene nanoplatelet (GNP) prepared by melt mixing extrusion were investigated. This type of LLDPE is important in the production of flexible packaging films for food, and the addition of GNP may improve barrier and mechanical properties. This particular GNP presents approximately 5% volatile substances (impurity, water, or functional groups) and a mixed morphology composed of crystalline leaves surrounded by an amorphous material, with a predominance of spot defects of vacancy 16 nm distant. At ideal concentrations, this GNP acted as a processing aid, decreasing torque and pressure during processing. The increase of GNP in the nanocomposites increases the complex viscosity and torque. Excellent dispersion of the nanofiller in the polymer matrix was attained. This GNP acts as a nucleating agent in LLDPE, increasing the degree of crystallinity and crystallization temperature, showing a higher crystallinity for lower GNP concentrations. The growth of two types of crystals was observed, and the presence of GNP increased the formation of smaller crystals. Although the crystalline melting temperature and crystallization enthalpy did not change significantly in relation to the neat polymer, the melting enthalpy increases with GNP concentration. The addition of the GNP increases the barrier properties to oxygen and water vapor and the thermal stability of the nanocomposites. The introduction of the GNP also increases Young's modulus but decreases elongation and stress at break in comparison to the neat LLDPE.