Dual-functional LDPE and PP films with SiO₂-microbubble hybrid structures for thermal resistance and intelligent food spoilage detection

We report a novel multifunctional, high-performance polymer nanocomposite featuring a smart sensing capability for spoiled food fumes and superior thermal insulating properties. The SiO₂ nanoparticle-incorporated foamed LDPE/PE matrix reduced thermal conductivity by 20% relative to the classical Maxwell–Eucken prediction, while the parallel-branch thermal-network model more accurately captured the multiphase heat-transfer behaviour involving the polymer matrix, gas-filled pores, nanoparticles and interfacial regions. This thermal barrier performance, validated using differential scanning calorimetry (DSC), nanoindentation and thermogravimetric analysis (TGA), is attributed to engineered thermal tortuosity of 1.28 in the mechanically strong nanocomposite, a marked improvement over the 1.08 typically found in standard polymer foam. By strategically decorating the polymer-air interface with the nanoparticles directs heat through a path 18% more complex than a simple random dispersion. When integrated with a porphyrin-doped PVA chemochromic film, the dual layered systems provided a real time visual indicator of seafood spoilage via fume triggered pH shifts. This work introduces a scalable Sense-and-Shield smart packaging film with a novel stacked architecture that decouples thermal insulation from optically clear, leach-resistant colorimetric spoilage sensing in humid food environments.