Experimental characterization of miscanthus-starch composites for building thermal insulation: Physical, hygro-thermal and mechanical properties

Faced with growing environmental problems and high-energy consumption in the building sector, the development of sustainable building materials has become crucial. Since the 1990s, plant biomass has been used to manufacture bio-sourced insulation materials. Due to its rapid growth and good thermal properties, miscanthus is an eco-friendly alternative to mineral or oil-based synthetic insulation. This article presents the properties of miscanthus aggregates and a miscanthus-based composite material, studied for its hygro-thermal and mechanical properties. The optimal composite composition is studied using potato starch as binder. Different mass ratios of starch with respect to miscanthus are tested: 10%, 15%, 20%, 30%, and 40%. Experimental tests are conducted on the aggregates first then on the composite to evaluate material properties under various conditions. Samples are characterized in terms of apparent and absolute densities, compressive strength, and hygro-thermal properties (thermal conductivity, moisture buffering value, vapor permeability and sorption isotherm). It was found that using 20% starch by weight provided the optimal balance, resulting in a composite with high mechanical strength and effective hygro-thermal properties. Notably, the material achieved a thermal conductivity of 0.053 W/(m·K) at 15% relative humidity—comparable to other organic insulation materials.