Experimental and numerical characterization of cardboard–date palm fiber–polystyrene composites: Thermal assessment and techno-economic analysis

Improving the energy efficiency of buildings and thermal comfort are significant challenges, both socially and in terms of regulations. Enhancing the thermal performance of building envelopes using bio-based recycled insulation materials is a relevant solution. However, there is currently a lack of standardised thermal and durability data for composites combining cardboard, date palm fibers, and polystyrene, which limits their acceptance in building applications. This study focuses on the thermal, mechanical, and hydric characterization of a new insulation material composed of recycled components, with the aim of its application in the building sector. The materials are composed of 80 % cardboard and 20 % fibers, with the addition of 2 %, 4 %, and 6 % polystyrene. Thermal performance was evaluated using two methods: the high-insulation house and the Hot Disk device, which allows for precise measurements. An experimental setup was used to simulate humid conditions and evaluate capillary absorption. Compression tests on cylindrical samples revealed good mechanical strength, particularly in radially oriented layers. The results show that the apparent density of the composites ranges from 213 to 264 kg·m⁻³ , thermal conductivity from 0.085 to 0.104 W·m⁻¹ ·K⁻¹ , water absorption from 217 % to 297 %, and compressive strength from 0.8 to 3.3 MPa. The optimal thickness is between 0.11 and 0.19 m, resulting in savings of between 60.70 $.m⁻² and 61.65 $.m⁻² on energy costs, with a return on investment of between 1.73 and 1.85 years. Although the composites achieve thermal conductivity values within the insulation range, their high susceptibility to moisture requires careful management at the design stage. Installation should therefore be limited to interior dry environments or protected façades, with the use of vapour control layers or ventilated rainscreens, and should avoid direct ground contact or exposure to driving rain without adequate protection. Overall, the study demonstrates that these recycled composites are cost-effective alternatives for improving building energy efficiency.