Thermal Conductivity and Degradation Kinetics of Copper Nanoparticle-Reinforced Polypropylene Composites: Towards Thermally Enhanced Active Food Packaging

Abstract

This study investigates the thermal conductivity and degradation kinetics of copper nanoparticle (Cu NP) reinforced polypropylene (PP) composites as potential materials for thermally enhanced food-packaging applications. Cu NP–PP nanocomposites were prepared by twin-screw extrusion at 0, 1, 2, 5, and 10 wt% Cu NP. Thermal conductivity (λ) was measured using the transient hot-wire method (ASTM D5930; n = 5 specimens per composition), while thermal stability was characterised by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC; n = 3 per composition). Mi crostructure and phase composition were examined by FE-SEM, EDS, and XRD. Cu NP incorporation raised lambda from 0.18 +/- 0.02 W/m/K (pure PP) to 0.47 +/- 0.05 W/m/K at 10 wt% — a 2.6-fold enhancement consistent with percolation network formation (phi_c ~0.004, t = 1.87). Multi-rate Kissinger kinetic analysis of TGA data (four heating rates: 5, 10, 15, 20 C/min) yielded apparent activation energy (Ea) increasing from 168 +/- 4 kJ/mol to 189 +/- 5 kJ/mol, corroborated by Ozawa-Flynn-Wall (OFW) isoconversional analysis, and accompanied by a 17 C rise in onset degradation temperature. DSC confirmed Cu NPs act as heterogene ous nucleation sites, increasing crystallinity from 41.7 +/- 0.8 % to 50.2 +/- 1.2 % and crystallisation tempera ture by 7 C. The principal novelty of this work is the quantitative percolation threshold determination (phi_c, t) and formal multi-rate Kissinger kinetic analysis for the Cu NP-PP system, providing physical pa rameters absent from prior studies. Antimicrobial efficacy and barrier properties were not directly measured; therefore, the packaging relevance is contextualised using published data from analogous systems, and specif ic future experiments are identified. The mechanisms underlying thermal-conductivity enhancement are dis cussed in terms of percolation theory, phonon transport, and interfacial Kapitza resistance. Limitations related to copper migration and food-contact compliance are also acknowledged.