Valorization of harmful algal blooms into sustainable polymer composites for a circular economy

The simultaneous increase in harmful Sargassum blooms and the high carbon footprint of the polymer industry necessitate sustainable material solutions. This study presents a circular economy approach for valorizing Sargassum biomass into a multifunctional inorganic ash filler for recycled polypropylene (rPP) composites. Sargassum biomass was calcined to produce mineral-rich ash and surface-modified using a silane coupling agent to improve compatibility with the rPP matrix. Composites containing untreated and silane-treated ash at different filler loadings were fabricated and evaluated for mechanical, thermal, flame-retardant, and environmental performance. The composite containing 10 wt% silane-treated ash exhibited optimal mechanical properties, achieving a 21.4% increase in tensile strength and a 22.2% increase in flexural strength compared to neat rPP. Heat Deflection Temperature increased from 95 to 110 °C, while the Limiting Oxygen Index increased from 17.5 to 23.5% at 15 wt% ash loading, indicating improved flame retardancy. Life Cycle Assessment showed that Sargassum-derived ash exhibited an approximately 88% lower estimated Global Warming Potential than commercial talc filler. These findings demonstrate the potential of Sargassum ash as a sustainable multifunctional filler supporting circular economy and environmental sustainability goals.