Multifunctional carboxymethyl cellulose/soybean extract composite with rambutan peappel polyphenols for exceptional UV-protective biodegradable packaging

Biodegradable packaging with exceptional UV protection addresses a critical need for photosensitive products. This study developed a ternary composite system based on citric acid-crosslinked carboxymethyl cellulose (CMC)/aqueous soybean extract (ASE) matrices (CMC/ASE ratios: 100/0–25/75) fortified with rambutan peel extract (RPE, 10 wt%) as natural UV-blocking agent. The CMC/ASE blend provided the structural matrix, while RPE imparted exceptional photostability. The films were characterized to evaluate their physicochemical structure (FTIR, WAXD, SEM), optical properties (UV-Vis spectroscopy, colorimetry), mechanical performance (tensile testing), and surface wettability (water contact angle). In addition, the biodegradation behavior was assessed, and the functional performance was validated using vitamin C tablets. FTIR confirmed RPE integration with enhanced aromatic C C absorption at 1600–1650 cm⁻¹ . Remarkably, all RPE-containing films achieved an identical and exceptional level of UV protection (UPF 141.5, blocking 99.3% of total UV including, 99.8% of UVB and 99.0% of UVA) independent of the CMC/ASE composition, while maintaining 70–85% visible transparency. This composition-independent performance, observed at the fixed 10 wt% RPE loading used here, enables the CMC/ASE ratio to be tuned for other film properties without compromising photostability. The Non-RPE films showed minimal protection (UPF 1.2–1.4). Functional testing showed that the RPE-containing films preserved 74.3% of vitamin C after 7 days of UV exposure, compared with 55.2% for the controls. The biodegradation rate was composition-dependent (68–92% weight loss in 28 days), increasing with ASE content. This study reports the integration of ASE and RPE into a citric acid-crosslinked CMC matrix, demonstrating that agricultural-waste-derived polyphenols can impart pharmaceutical-grade UV shielding to fully biodegradable polysaccharide films. Consequently, these functionalized materials offer an eco-friendly and high-performance alternative to conventional petrochemical-based protective packaging.