Enhancing barrier and shielding properties of multilayered flexible packaging with carbon-based composites

Abstract

Current multilayered flexible packaging solutions for protecting sensitive electronic devices suffer from low reuse and recyclability. It leads to increasing amounts of waste, slow degradation, emissions, and contamination of soil and oceans, among other issues. The lack of recyclability is due to their complex structure. To provide barrier and shielding properties, dissimilar materials, i.e., aluminum and polymer, are joined with adhesive layers. The recycling of this type of structure requires energy and time-consuming approaches. In this context, we proposed redesigning the multilayered structure to create a more sustainable solution using carbon-based composites. Our approach aims to be compatible with industrial use and is based on widely available materials at the industrial scale: a high-density polyethylene (HDPE) matrix with key properties provided by two carbon-based fillers: graphene platelets (G) for a barrier against permeability and multiwalled carbon nanotubes (CNT) for increased electrical conductivity. Methodologically, we took three steps to achieve the proposed composite: First, we investigated the barrier and electrical conductivity effects of G using coextrusion in a semi-industrial scale fabrication process to produce an 8-layer structure. Concentrations lower than 0.5 wt.%, G improved the barrier effect by around 42% for oxygen and water in samples with smoother surfaces. However, no increase in electrical conductivity was found at 1 wt.%. Additionally, layer design - specifically, selective placement of filler in chosen layers - proved to be an important tool for achieving enhanced properties. Second, we focused on improving the electrical properties necessary for achieving shielding properties by investigating single-layer HDPE/CNT films with G as a secondary filler, resulting in a hybrid composite. A transition from an insulative to a more conductive composite was achieved at 6.49 wt.% CNT. Synergism was found for hybrid composites with 99:1 CNT:G ratios at a fixed concentration of 9 wt.% but was highly dependent on the cooling conditions of the sample. At the same filler content, no improvement in barrier properties was found. Third and finally, using a coextrusion technique with a multiplying element, we produced multilayered films with 129 layers of HDPE/CNT, HDPE/G, and HDPE/CNT/G with compositions up to 4.5 wt.% and compared their barrier and shielding properties to singlelayer films. The multilayered structures exhibited an overall improved barrier to water and oxygen. Increased shielding, ranging from 13% to 110% depending on the structure type, and microwave absorption performance properties. The improvements were ascribed to the selective filler placement and increased dielectric properties of the multilayered films. Although we were unable to achieve the commercial values recommended for shielding (10 dB) of sensitive devices with flexible 100 μm thick films, our investigation demonstrated the potential to achieve combined properties in a composite flexible film for packaging applications by adjusting the processing method and layer design.

Date	3 Nov 2023
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Nicole R. Demarquette (Supervisor), Abdellah Ajji (Co-supervisor) & Guilherme Mariz de Oliveira Barra (Co-supervisor)