Boron Improved High Limiting Oxygen Index Polyelectrolyte Treatment for Cotton

The flammability of cotton fabric poses a risk of injury and death, specifically in aerospace applications, where oxygen concentrations are higher than typical atmospheric conditions. In an effort to reduce its flammability in high-oxygen environments, cotton was treated with a 12-bilayer coating consisting of poly(allylamine hydrochloride) (PAH), poly(sodium phosphate) (PSP), and ammonium pentaborate tetrahydrate (APB). With a formulation of 6.5% PAH/8% PSP+5% APB, cotton is rendered self-extinguishing, exhibiting a reduction in peak heat release and fire growth capacity of 72 and 88%, respectively. Moreover, cotton remains self-extinguishing in highly oxygenated environments, having a limiting oxygen index of 35.5%. This layer-by-layer assembled coating operates via an intumescent mechanism that is aided by the formation of borate esters cross-linking the char structure, resulting in reduced gas diffusion and increased thermal stability. This unique, scalable treatment is especially promising for space exploration and could potentially be used in other polymeric materials.