Upcycling sunflower pith as a sustainable bio-aggregate for circular insulation systems: A thermal, acoustic, and fire performance assessment

Upcycling agricultural residues into building insulation provides a critical pathway to lower embodied carbon and advance circular construction. In this study, the use of sunflower pith as a sustainable bio-aggregate is explored through the evaluation of its performance as loose-fill insulation and as the core of bio-based panels bound with starch or sodium alginate. Thermal properties were assessed at both aggregate and panel scales, alongside an examination of the mechanical, acoustic, and fire behaviour of the finished boards. The results indicate that competitive thermal performance does not require intensive purification: less refined pith demonstrated only a marginal increase in thermal conductivity compared to high-purity fractions. With thermal conductivities near 0.04 W m -1 K -1 , these panels perform similarly to conventional insulators while exhibiting more favourable fire response and competitive acoustic absorption. Furthermore, preliminary integration into rendered External Thermal Insulation Composite Systems (ETICS) suggests that the system can provide effective protection against water ingress and fire under the tested conditions. These findings highlight the potential of sunflower pith for building insulation, with promising prospects for next-generation circular building materials, although further research is required to confirm its suitability for full-scale façade applications.