Natural CaCO₃ improves the moisture resistance and mechanical performance of hemp-starch biocomposites: A multi-objective optimization study

Bio-based insulation materials provide a sustainable alternative for reducing the environmental impact of buildings, but their application can be limited by insufficient mechanical strength and moisture sensitivity. This study investigates hemp-shives/starch composites incorporating natural calcium carbonate (CaCO₃) to improve their mechanical and moisture-related performance. Response Surface Methodology (RSM) based on a Central Composite Design (CCD) was used to optimize the composite formulation. The optimal formulation increased compressive strength by 38% and improved water resistance by 29% compared with the reference material, while maintaining a low thermal conductivity of 0.056 W/m·K. CaCO₃ incorporation reduced capillary water absorption and surface wettability and improved the cohesion of the composite. SEM, mercury intrusion porosimetry, and ultrasonic measurements revealed a reduction in pore volume and a refinement of the pore structure. Hygrothermal characterization further indicated improved moisture buffering and controlled vapor transport. TGA and FTIR analyses supported enhanced thermal stability and interactions between the mineral and bio-based phases. Overall, the results demonstrate that natural CaCO₃ can effectively enhance the mechanical and moisture-related performance of hemp-starch insulation composites while preserving their thermal insulation properties, highlighting their potential for sustainable building applications.