Development of Sustainable Packaging with Enhanced Properties: Utilizing Coffee Waste-Derived Plasticizer, Eggshells, and Natural Rubber in PHBV Bioplastic Blends

Introduction: Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a biodegradable bioplastic offering sustainable alternatives to petroleum-based plastics. However, its brittleness and poor processability limit packaging applications. This study enhances PHBV performance by incorporating food waste-derived additives: coffee oil epoxide (COE) as plasticizer and eggshell-derived calcium carbonate (CaCO₃) as reinforcing filler with high-molecular-weight natural rubber (NR). The objective is to improve the thermal, mechanical, and barrier properties of PHBV while maintaining its biodegradability for environmentally friendly packaging applications.

Method: PHBV blends were prepared using twin-screw extruder with varying NR, COE, and CaCO₃ compositions. Films were characterized using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), mechanical tensile testing, and oxygen transmission rate (OTR) analysis. Soil burial biodegradation testing over 117 days assessed environmental impact through weight loss and thickness reduction. Statistical analysis used one-way ANOVA with Tukey's HSD test (p < 0.05).

Results: COE addition improved PHBV/NR flexibility and processability, while CaCO₃ enhanced mechanical strength. SEM showed uniform dispersion without phase separation. DSC results indicated significant melting point decrease from 170.4°C (PHBV) to 166.5°C (PHBV/NR/COE/CaCO₃), and crystallinity reduction from 68.5% to 50.8% with COE and eggshells incorporation, confirming improved flexibility and reduced brittleness. OTR values decreased significantly for COE-containing sheets, indicating enhanced barrier properties. The biodegradation study revealed weight loss of 26.25% for PHBV and 28.85% for PHBV/NR/COE sheets, confirming environmental compatibility. Processing trials indicated that PHBV/NR/COE blends formed well-defined sheets, unlike PHBV/NR blends, which were sticky and difficult to process.

Conclusion: Blending PHBV with waste-derived COE and CaCO₃ plus NR significantly enhanced thermal stability, mechanical strength, and barrier properties without compromising biodegradability. These modified films demonstrate improved flexibility, processability, and environmental performance, making them strong candidates for sustainable food packaging. This study highlights upcycled food waste potential in advancing green polymer solutions and supports industrial scalability.