Cellulosic Insulation Material I. Effect of Additives on Some Smolder Characteristics

Abstract

Minimum temperatures for the initiation of smolder in cellulosic insulation materials were measured by the method of Bowes and Townshend (1-D heat flow through a layer on a hot surface). The minimum temperature decreases rather rapidly with layer thickness; a range of about 320°C to 220°C is indicated for layers from 3 to 30 cm thick. Additives (boric acid, elemental sulfur, commercial retardant blend) have a substantially lesser effect; boric acid, the most effective, raises the ignition temperature only about 20°C. Thermal analytical kinetics (DSC) are used, in conjunction with the Bowes and Townshend ignition model, to successfully predict ignition temperatures and to demonstrate that the first overall stage of oxidation of the material is responsible for its ignition characteristics. It is demonstrated that solid reactant consumption, neglected in the model, somewhat distorts the ignition data; oxygen consumption effects are minimal. Boric acid is also the most influential additive on smolder propagation; it doubles the minimum thickness for continued propagation (from 3½ to 6 cm). Additive effects on propagation are determined by their influence on both overall stages of insulation oxidation.