Quantitative Evaluation of Flame-Retardant Cotton Finishes by the Limiting-Oxygen Index (LOI) Technique

Abstract

The limiting oxygen index (LOI) technique provides a quantitative measure of reduced ftammability for fabrics over broad ranges of chemical treatment. Several conventional flame-retardant finishes for cellulosics gave linear LOI relationships with phosphorus content when compared at fixed nitrogen/phosphorus ratios. Tris(aziridinyl)phosphine oxide (APO) was an exception. Precise measurement of the role of N in enhancing the flame-retardant effectiveness can be made with this technique. The synergistic interaction of N and P can thus be described and measured. Two chemical systems were examined in depth, and it was possible to describe LOI as simple functions of N and P contents for each system. The synergistic effect did not predominate at a specific N/P ratio. LOI of about 0.26 is associated with a 5-in. char length in the vertical test for several fabrics, a sateen fabric being an exception. Fabric air permeability was found to be a primary factor governing chemical requirements and is probably more important than fabric weight. Other nitrogenous durable-press reactants are less effective than melamines. Complex relationships as functions of nitrogen content were noted at different phosphorus levels.