Bull. Spec. CORESTA Congress, Lisbon, 2000, p. 196, T6
The characterization of cigarette paper using transient thermography
Philip Morris USA, R&D Operations Center, Richmond, VA, USA
Porosity, resistance to airflow, thickness, and basis weight, are important characteristics of cigarette paper. Variations in microstructure and composition, which contribute to differences in airflow impedance and porosity, typically manifest themselves as variations in the heat transport behavior of paper. Methods capable of assessing these characteristics rapidly and nondestructively may provide significant benefits in the development and manufacturing of paper products. This work describes the use of transient thermography to characterize the heterogeneity and anisotropy of cigarette paper. The technique utilizes a broad band pulsed excitation source to initiate low level thermal gradients within the paper. The resulting heat flow is then monitored using a high-speed, high sensitivity infrared camera. The detailed behavior of the transient temperature field depends on the boundary conditions and the local values of specific heat, thermal conductivity, and density. Cigarette papers typically exhibit detectable spatial variations of these effective bulk properties. These variations may arise from fiber size distribution, fiber orientation, additives, detailed microstructure, and moisture content. Differences in thermal responses among regions within a given specimen are a direct result of these local characteristics in conjunction with variations in local thickness and basis weight. Analysis of the associated thermal transients provides a basis for the investigation of paper design and variations inherent in the paper manufacturing process. Transient thermography has several advantages. It is non-contact, requires only minimal heating of the paper material, and has high spatial resolution. In addition, it is rapid and has the potential for on-line, real-time monitoring of paper processes. Experimental results are discussed in the context of the paper construction and conventional test methods such as air permeability, opacity, and basis weight.