Highly Thermal Conductive and Electromagnetic Shielding Polymer Nanocomposites from Waste Masks

Abstract

Over 950 billion (about 3.8 million tons) masks have been consumed in the last four years around the world to protect human beings from COVID-19 and air pollution. However, very few of these used masks are being recycled, with the majority of them being landfilled or incinerated. To address this issue, we propose a repurposing upcycling strategy by converting these polypropylene (PP)-based waste masks to high-performance thermally conductive nanocomposites (PP@G, where G refers to graphene) with exceptional electromagnetic interference shielding property. The PP@G is fabricated by loading tannic acid onto PP fibers via electrostatic self-assembling, followed by mixing with graphene nanoplatelets (GNPs). Because this strategy enables the GNPs to form efficient thermal and electrical conduction pathways along the PP fiber surface, the PP@G shows a high thermal conductivity of 87 W m⁻¹ K⁻¹ and exhibits an electromagnetic interference shielding effectiveness of 88 dB (1100 dB cm^-1), making it potentially applicable for heat dissipation and electromagnetic shielding in advanced electronic devices. Life cycle assessment and techno-economic assessment results show that our repurposing strategy has significant advantages over existing methods in reducing environmental impacts and economic benefits. This strategy offers a facile and promising approach to upcycling/repurposing of fibrous waste plastics.

Keywords: Electromagnetic interference shielding; Life cycle assessment; Mask waste; Repurposing; Thermal conductivity.

Fig. 1

a Estimation of waste masks volumes and reuse data from 2018 to 2023 [4]. b Conventional route for disposing waste masks. c Preparation process of highly thermal conductive nanocomposites with EMI shielding property from waste mask PP. d Schematic illustration of as-prepared PP@G nanocomposites for thermal management and photograph of the PP@G nanocomposites for EMI shielding applications. e Life cycle assessment of 1 kg PP: comparing landfill disposal versus PP@G nanocomposite preparation: Fossil fuel depletion (FFD); Global warming (GW); Carcinogenics (Carc); Acidification (Acid); Ecotoxicity (Ecotox); Smog; Eutrophication (Eutro); Ozone depletion (ODP); Non carcinogenics (Non-carc); Respiratory effects (Resp). f Techno-economic analysis (TEA) of as-prepared low-cost (low GNP contents) and high-performance (high GNP contents) PP@G nanocomposites in the c process

Fig. 2

SEM images of a PP fiber and b PP@TA fiber; c EDS elemental maps of O distribution on PP@TA. d Contact angles of PP fiber and PP@TA. TEM images of e GNPs and f PAE@GNPs. g Raman spectra of GNPs and PAE@GNPs. h Schematic illustration of assembly process of PP@TA and PAE@GNPs. i Zeta potentials of PP fiber, PP@TA, PAE@GNPs in water. j Lateral size distributions of GNPs and diameter distributions of PP fibers. k Photograph and SEM image of PP@GNPs

Fig. 3

a Changes in the in-plane TC of as-prepared PP@G nanocomposites with varying GNP contents. b XRD spectra of as-prepared PP@G nanocomposite as measured on the top surface and cross-section (inset shows directions of incident X-rays). c SEM images of the cross-sections of as-prepared PP@G nanocomposites with low and high GNP content. d 3D nano-CT image of 1 mm long as-prepared PP@G nanocomposite and the corresponding e X–Y and f X–Z edge plane. g Schematic illustration of the interconnected GNPs network that forms efficient phonon/electron transport channels within as-prepared PP@G nanocomposite. h Comparison of in-plane specific TCE between as-prepared PP@G₆₆ nanocomposites and other previously reported filler-filled polymer-based nanocomposites with random and 3D networked nanofiller structures. Comparison of i two GNPs distributions (edge-to-face and face-to-face) and the corresponding j heat flow and k heat flux

Fig. 4

a Schematic illustration of heat transfer from LED lights using PI film or as-prepared PP@G₆₆ film as cooling substrate. b Thermal infrared images of LED lights using as-prepared PP@G₆₆ film and PI film as cooling substrate at different voltages, respectively, and c corresponding temperature changes. d Thermal infrared images of smartphones integrated with as-prepared PP@G₆₆ film and PI film. e Schematic diagram of heat transfer from flexible circuit using steel heat sink or as-prepared PP@G₆₆ heat sink as cooling substrates. f Thermal infrared images of flexible circuit with integrated steel heat sink and as-prepared PP@G₆₆ heat sink at different voltages and g corresponding temperature changes. h Cyclability of flexible circuit with as-prepared PP@G₆₆ heat sink

Fig. 5

a Electrical conductivity of as-prepared PP@G nanocomposites with varying GNP contents; Insets show lighting a LED bulb using as-prepared PP@G nanocomposites with different GNP contents. b EMI SE curves and c SE_T, SE_A, and SE_R values of as-prepared PP@G nanocomposites with different GNP contents in X-band. d EMI SE curves of as-prepared PP@G₆₆ nanocomposites with different thicknesses. e Reflectivity (R), absorptivity (A), and transmittance (T) coefficients of as-prepared PP@G nanocomposites with different GNP contents. f Schematic illustration of EMI shielding mechanism of as-prepared PP@G nanocomposites. g Comparison of EMI SE/t values of as-prepared PP@G nanocomposites with the previously reported materials. h Schematic illustration of the shielding effect of as-prepared PP@G nanocomposites and PP film on the electric field generated by the Tesla coil