Bioplastic films from Sargassum oligocystum and Eucheuma spinosum seaweeds: Preparation, thermal degradation, and kinetics analysis

• Bioplastic films were synthesized from seaweeds via alginate-based extraction. • Analyses confirmed polysaccharide purity and amorphous character. • S. oligocystum films had higher thermal stability and Ea than E. spinosum films. • Kinetics showed nucleation-controlled, distinct degradation pathways. • Seaweed bioplastics show promise as scalable, sustainable packaging materials. In the framework of a circular economy, bioplastics derived from renewable natural resources are gaining attention as sustainable alternatives to conventional plastics. This study reports the synthesis of bioplastic films from brown seaweed ( Sargassum oligocystum ) and red seaweed ( Eucheuma spinosum ) via alginate extraction, followed by structural and thermal characterization. Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry results confirmed that Sargassum oligocystum -based bioplastic exhibited properties comparable to the commercial sodium alginate-derived bioplastic. Additionally, thermogravimetric analysis results revealed that Sargassum oligocystum decomposed in a single step near 220°C, whereas Eucheuma spinosum degraded in two steps at ≈ 280°C and 330°C. The corresponding bioplastic films showed decomposition at ≈ 225 °C ( Sargassum oligocystum ) and 250°C ( Eucheuma spinosum ). Kinetic studies indicated nucleation-controlled thermal degradation, with activation energies of 20.0 to 26.8 kJ/mol for Eucheuma spinosum and 43.8 to 49.5 kJ/mol for Sargassum oligocystum bioplastics. These findings demonstrate the potential of seaweed-derived bioplastics as renewable, thermally stable materials and provide insights into their degradation mechanisms for future material optimization and practical applications.