The thermal performance of banded paper cigarettes
This talk describes preliminary investigations characterizing the differences in the thermal smoldering behavior of banded and non-banded cigarettes. Both free smolder and smolder during contact with combustible substrates will be described. The ability of Philip Morris banded paper to reduce the relative ignition propensity* of cigarettes results from the manner in which the heat generation from the cigarette is modulated during smoldering combustion. As the cigarette's combustion zone enters a low permeability band, the coal temperature is lowered due to the reduction in oxygen diffusion. If the oxygen restriction is sufficient, the temperature falls below the threshold required to sustain combustion and the cigarette is extinguished. If the coal continues to burn through the band, the coal temperature increases to an equilibrium temperature determined by the permeability of the base cigarette paper. When a cigarette is placed on a substrate, such as that used in the NIST methods, heat is naturally transferred to the substrate material. From the perspective of the cigarette, the added heat sink acts in concert with the band to reduce the coal temperature. From the reference of the substrate materials, the cigarette presents heat flux with a unique spatial and temporal variation. The distribution of resulting thermal field and the partial pressure of oxygen determines whether or not the substrate materials transition to smoldering or flaming combustion.* Test Methods for Quantifying the Propensity of Cigarettes to Ignite Soft Furnishings, U.S. Department of Commerce Technology Administration, National Institute of Standards and Technology, NIST special publications 851, August 1993.