Influence Of Oxygen Concentration On The Flammability Characteristics Of Fire-Retardant Cellulose

The flammability characteristics of pure and fire retardant-treated cellulose were tested by controlled-atmosphere cone calorimeter at a heat flux of 50kW·m^-2 and a gas flow rate of 24L·s(-1) under the oxygen-controlled atmosphere of 12%, 15%, 18% and 21% oxygen concentration respectively. The fire retardants used were boric acid, guanylurea phosphate (GUP), and FRW (containing boric acid and guanylurea phosphate). The characteristics of heat releasing, mass change, dense smoke and poisonous gases releasing of pure and fire retardant-treated cellulose were summarized by comprehensive analysis of the parameter obtained from the cone test. Also the effect of oxygen concentration on the burning of the samples was investigated systemically.It indicates that all the combustion process of the samples can be divided into three stages generally: initial smoldering stage, flaming stage and after-glowing stage. The changes regularity of samples on heat release rate (HRR), mass loss rate (MLR), rate of smoke release (RSR) and rate of CO₂ production (Pco₂) appeared isochronous, for all of these parameter come to its peaks at the time when flaming combustion was the most acutely. And that nearly all the mass loss, heat release, smoke release and CO₂ production occured in flaming stage. It is comparatively complex in CO release, owing to the influence of oxygen concentration and fire-retardant treatment. As a whole, CO releasing mainly occurs in after-glowing, which attributed to the partial oxidation of wood charcoal.All the fire-retardant treatment suppressed the flaming combustion of cellulose effectively, decreased the heat release rate, total heat released, peak and average mass loss rates, shorten the ignition time(except the boric acid treated sample ), while increased CO and residue yield in all the oxygen concentrations. The fire retardants enhanced the release rate and total release of dense smoke and CO when the oxygen concentration of combustion atmosphere is 12%, 15% and 18%, whenas, in the air atmosphere, fire-retardant treatment remarkably inhibited the releasing of dense smoke and CO during the flaming combustion.For fire retardant-treated samples, with the decrease of oxygen concentration, gaseous combustion process became mild, the release rate and total release of heat and CO₂ gradually reduced, while that of dense smoke and CO increased, mass loss rate became slow but char yield enhanced. For pure samples, release rate, total release of dense smoke and CO as well as the ability of smoke production gradually decreased along with the decreasing oxygen concentration between 15% and 21%, opposite to the treated samples, which mainly resulted from acutely burning in high oxygen concentration for pure samples; when the oxygen concentration decreased to 12%, all of this parameters increased rapidly because of the incomplete combustion of pyrolytic product.