###### Abstract  
Estabell-reinforced bio-based epoxy composites show enhanced thermal conductivity, hardness, and density, optimized via response surface methodology. FT-IR and microscopy confirm seashell powder as a chemically inert bio-filler. This scalable approach valorizes tidal seashell waste, supporting circular economy goals and enabling sustainable, lightweight materials for construction, marine, and automotive applications. Tidal seashell waste represents an abundant, underutilized marine resource that poses environmental disposal challenges but offers potential as a sustainable bio-filler in epoxy composites. This study investigates its incorporation into bio-based epoxy systems to reduce reliance on non-renewable materials and promote circular economy objectives. Processed seashell powder was blended into epoxy formulations, and response surface methodology was applied to optimize filler loading and resin composition. Comprehensive characterization included tensile strength, impact resistance, hardness, density, and thermal conductivity testing, along with microscopy analysis to evaluate filler dispersion and interfacial bonding. The optimized composites demonstrated improved hardness, density, and thermal stability while maintaining acceptable tensile and impact strength. Microscopy confirmed uniform filler distribution at optimal loadings but revealed agglomeration and void formation at higher contents, which can reduce interfacial bonding efficiency. These findings highlight the feasibility of valorizing marine waste as a reinforcing filler in sustainable composite production, supporting environmental goals and offering a scalable approach for the development of durable, lightweight materials suitable for structural, coating, and industrial applications. e acmcopy2020-00-0001-0  
lightweight nature, high strength, corrosion resistance, and durability. However, conventional composites often rely on fossil fuel-derived polymers and fillers, raising significant environmental sustainability concerns. In response, bio-composites produced from renewable and natural sources have emerged as more sustainable alternatives, particularly those reinforced with naturally sourced polymers and fillers [1; 2; 3; 4]. Among these natural waste sources, seashell residues represent a significant global environmental challenge. Improperly managed, they contribute to solid waste accumulation, unpleasant odors, and potential health hazards. Disposal is logistically complex and costly, with substantial production volumes reported worldwide: approximately 300,000 tonnes of oyster shells annually in China, over 160,000 tonnes in Taiwan [5; 6], around 320,000 tonnes in South Korea (with only 30% reused) [7], and additional large-scale outputs in Galicia, Spain [8], and Peru [9]. In Europe, seashell residues are classified as special waste, incurring disposal fees of up to 0.25 \(\upmu\) per kilogram, thus imposing considerable costs on producers [10]. Utilizing seashell waste as a reinforcing filler in bio-composites offers dual benefits: addressing waste management challenges and improving material properties. Previous studies have demonstrated that seashell-derived bio-fillers can enhance the mechanical, thermal, and acoustic performance of polymer matrices while supporting sustainability goals. For example, [PERSON] et al. reported improved mechanical and acoustical properties in polyurethane foams [11], while [PERSON] et al. observed notable gains in mechanical strength and thermal performance in epoxy systems incorporating mollusk shell powders [12]. [PERSON] et al. developed bio-epoxy composites with fish scale and seashell fillers, assessing structural properties across various loadings [13]. [PERSON] et al. reinforced 3D-printed polylactic acid with calcined seashell powder, achieving enhanced mechanical strength and thermal stability [14]. [PERSON] et al. utilized finely ground seashells in ABS matrices to improve flame retardancy and mechanical performance [15]. [PERSON] et al.