Cross-linking of excellent flame retardancy pulp-ammonium polyphosphate foam with biodegradable, recyclable properties

Large-scale use of petroleum-based plastic foams has caused serious environmental problems. Biodegradable and renewable plant resources have become ideal alternative materials. However, the inherent low mechanical strength and flammability of plant-based foams have prevented their widespread use. In this paper, pulp foams (PUPs) were prepared by cross-linking pulp fibers with ammonium polyphosphate (APP) in a novel and simple method. The resulting foam exhibits ultralow density (12.4 mg cm⁻³), good mechanical properties, high flame retardancy, and recyclable, degradable performance. In the compression experiment, the compressive strength of PUP (15%) foam increased by 175% at 80% strain. Besides, PUP (15%) retains its woven structure well after vertical and horizontal combustion tests. It is expected that this work will provide new insights into the production of flame-retardant foams, which have a high potential to replace flammable and non-degradable petroleum-based foams.