Development and evaluation of sustainable henequen fibre foams for thermal insulation

The increasing demand for sustainable thermal insulation materials stems from environmental concerns associated with conventional petroleum and mineral-based options, which exhibit high toxicity and global warming potential. While bio-based alternatives exist, they often present challenges related to chemically intensive processing, scalability, and cost-effectiveness. This study investigates the production of porous foams from lignocellulosic henequen fibres utilising a simple and scalable mechanical fibrillation process. Two distinct foam formulations were developed: one employing xanthan gum, a natural polysaccharide, as a binder to enhance structural integrity, and the other utilising borax, a natural mineral salt, to cross-link exposed cellulose in the fibrillated fibres. The resulting foams exhibited a highly porous structure with enhanced chemical and mechanical fibre interconnections. The xanthan gum-bound foam exhibited a thermal conductivity of 42 mW/m*K, an apparent density of 21 ${\mathrm{kg/m}}^3$, and a compressive stiffness of 56 kPa. The borax-crosslinked foam achieved a thermal conductivity of 43 mW/m*K, an apparent density of 11.5 ${\mathrm{kg/m}}^3$, and a compressive stiffness of 19 kPa. Notably, both foams demonstrated a limiting oxygen index of 29.5$\text{\%}$, classifying them as self-extinguishing, despite the inherent flammability of the natural fibres. The xanthan gum-bound foam also maintained comparable physical and thermal properties after three recycling cycles. A cradle-to-gate life cycle assessment revealed significant reductions in toxicity and global warming potential compared to conventional insulation materials, specifically rigid polyurethane and glass wool. This research demonstrates the feasibility of utilising a straightforward fibrillation and template-forming process with abundant henequen fibres to produce sustainable insulation foams with good thermo-mechanical performance, improved fire safety, and a diminished environmental footprint.