A novel iron ion cross-linking strategy dramatically improves the strength and flame retardant of degradable foams from rice straw fibers

Abstract

Biodegradable natural cellulose-based foams have received increasing attention in the area of logistical transport, construction, healthcare, and chemicals, whereas the flammability and poor mechanical behaviors of foams restricted its application. Herein, a clean production route was proposed to fabricate biodegradable rice straw fiber foam containing ammonium polyphosphate (APP), phytic acid (PA), and iron ions through simple foam molding technology. The introduction of PA and APP as flame retardants acted as an acid source to form phosphorus-containing carbon layers on the surface of the fiber to achieve flame retardant effect. Moreover, the incorporation of iron ions for cross-linking resulted in the formation of Fe³⁺-APP/PA complexes on fibers, which further improved the mechanical properties and flame retardant of the foams. Compared with pristine LCF, compressive strength of LCF/APP-PA/Fe³⁺ was improved by 254.6% and 107.9% in XY and Z directions, respectively. The total heat release and smoke release of LCF/APP-PA/Fe³⁺ were reduced by 27.1% and 27.4%, respectively. Moreover, the optimized LCF/APP-PA/Fe³⁺ possessed well flame retardancy metrics, which can be directly reflected from the self-extinguishing of flame after removing alcohol lamp. This work presented a novel and versatile green approach to improve the strength and flame retardant properties of renewable wood fiber foams. Fiber foams with properties such as lightweight, high strength, flame retardant, and thermal insulation have promising applications in logistics and transport, construction, healthcare, and chemicals.