Valorization of Coconut Coir Waste into a Sponge-Structured Carrier for Natural Rubber-Based Oxygen Scavenger: A Sustainable Alternative to Powder-Based Sachets

This study presents the development and evaluation of an eco-friendly, metal-free oxygen scavenging sachet utilizing a sustainable coconut coir-based sponge as the carrier. The sponge was impregnated with a natural rubber (NR) matrix catalyzed by food-grade magnesium stearate (MgSt), forming a biodegradable and food-safe active packaging component. Optimization of the NR concentration (1–5%) identified 3% as ideal for multilayer formation and effective oxygen absorption. Sponge sizes ranging from 1 × 1 cm to 5 × 5 cm were assessed, with 4 × 4 cm demonstrating the best balance between matrix loading and scavenging capacity. The optimized sachet, using a 4 × 4 cm sponge (1 g), exhibited an oxygen absorption capacity of 207.2 ± 5.95 cc/g within 8 h and maintained stable performance across a range of temperatures (15–37 °C) and relative humidity levels (30–90%). Characterisation via SEM confirmed multilayer film formation, while FT-IR and NMR validated chemical interactions. Kinetic analysis showed first-order scavenging behaviour, with higher temperatures accelerating reaction rates. The sachet was further tested in real food packaging (khoa product), where it effectively extended shelf life by delaying microbial and oxidative spoilage. These findings support the application of natural rubber-based, sponge-supported systems as sustainable alternatives in active food packaging.