Leak-Based Method for the Measurement of Air Permeability of Papers

Abstract

Summary The air permeability of cigarette paper is currently assessed according to the international standard ISO 2965 by applying a constant pressure difference of 1 kPa between the two faces of a sample and by measuring the corresponding airflow. Lower Ignition Propensity regulations have led tobacco manufacturers to use specific cigarette papers with narrow bands of low air permeability and diffusion capacity to achieve regulatory compliance. The international standard ISO 2965 was revised in 2009 to take into account the specific geometry and characteristics of the bands and to include suitable narrow measuring heads. The consequence was a significant reduction of the measured airflow levels with banded papers and a need for equipment covering specifically low airflow ranges. The well-known pressure-airflow relationship across cigarette paper enables the development of an alternative method to ISO 2965 which does not require direct airflow measurement, and therefore airflow meters which are costly parts of the current measuring devices. The alternative method is based on the measurement of the change of the pressure over time after an initial pressure difference was applied between the two faces of the paper. The consecutive analysis of the pressure difference profile, impacted by the leak across the paper, enables the derivation of the air permeability. The related theoretical aspects were developed for both viscous and inertial airflows, and experimental investigations were conducted with banded and conventional cigarette papers as well as a permeability calibration standard. Results obtained with the proposed method showed good consistency with ISO 2965 measurements and a lower repeatability, demonstrating that a leak-based method could be a simple and reliable alternative.