Effects of Polyester Mixing on Smoldering Spread Through Cotton Wad

In this study, the effects of physical deformation and thermal absorption of polyester on cotton smoldering are examined. Polyester fibers or polyester granules are mixed with cotton fibers to form a wad, and the smoldering spread through it is observed macroscopically and microscopically to investigate the suppression effects of polyester mixing. For polyester fibers, two types having different thicknesses are used. It is found that the suppression effect is the highest for thin polyester fibers, and the lowest for polyester granules when the mixing ratio is the same. From microscopic observation, it is seen that polyester fibers shrink more than granular ones. Such shrinkage causes additional movements of adjacent cotton fibers, which may hinder the progress of combustion. In contrast to polyester fibers, polyester granules seem to have minor influence on the movement of cotton fibers. It is also seen that the melted fibrous polyester has a larger contact area with unburnt cotton fibers than melted granular one, which may influence the pyrolysis of the cotton. In investigation of interval of mixed polyester in cotton wad calculated at rough estimate, hereafter referred to as the “polyester interval”, it is found that the smoldering suppression effect increases as the mixing ratio is large or the polyester interval is shortened. This also suggests that both the amount and the polyester interval may be related to thermal absorption. These results indicate that the smoldering suppression by polyester may be affected by both its physical deformation and thermal absorption.