Reduced loadings of nano- and micro-ZnO in natural rubber latex foam: Effects on cushioning and antifungal properties for fresh mango packaging

The development of sustainable cushioning materials is essential for the protection of packaged fruits during handling and storage while minimizing environmental impact. This study investigated the influence of zinc oxide (ZnO) particle size (nano vs micro) and reduced loading level on the performance of natural rubber latex foam (NRLF), processed via microwave-assisted vulcanization. Nano-ZnO (70 ± 10 nm) and micro-ZnO (300 ± 60 nm) were incorporated at 0.5–4.2 parts per hundred rubber (phr). Nano-ZnO enhanced foam morphology, yielding smaller and more uniform cells, higher compressive strength (30.5 ± 1.7 kPa at 1.5 phr), and improved energy absorption. Notably, NRLF with 1.5 phr nano-ZnO exhibited significant antifungal activity against Colletotrichum acutatum, the causative agent of mango anthracnose, achieving inhibition zones up to 36 mm—surpassing micro-ZnO at higher loadings. These enhancements are attributed to better ZnO dispersion, increased crosslink density, and greater surface-mediated reactive oxygen species (ROS) generation. These results highlight the potential of nano-ZnO foam formulation, offering a dual-function, eco-friendly alternative to synthetic foams, supporting shelf-life extension and mechanical protection in fresh mango packaging.