Synergistic optimization of plant-based natural insulation materials with starch and waste-expanded polystyrene composite binders: Advancing thermo-acoustic efficiency for sustainable building envelopes

Developing sustainable binders and recycling waste materials are key to achieving carbon–neutral building materials. This study optimizes a composite binder using waste-expanded polystyrene (EPS) and cornstarch for bio-based insulation, enhancing thermal and acoustic performance while improving resource efficiency. A Doehlert experimental design optimized the fiber-to-binder (F/B) ratio (40–100 %) and EPS-to-starch (E/S) ratio (0–100 %), also assessing fiber length (short vs. long). For short fibers, the optimal formulation (F/B = 96.74 %, E/S = 27.34 %) achieved a density of 210.9 kg/m³ and thermal conductivity of 0.087 W/m·K. Long fibers (F/B = 89.72 %, E/S = 50 %) resulted in 144.2 kg/m³ and 0.068 W/m·K, meeting DIN 4108–2 standards. Acoustic tests showed strong absorption (49.5 % at 1600 Hz) and a transmission loss of 31.85 dB. This study highlights the potential of combining natural and recycled materials to develop high-performance bio-based insulation for thermal and acoustic applications.