The pore size distribution of naturally porous cigarette papers and its relation to air permeability and diffusion capacity – Part 1
In the tobacco industry it is well known that porosity is one of the most significant physical properties of cigarette paper. There are indirect as well as direct methods to characterise this parameter. Measurement of the diffusion capacity and the air permeability are indirect methods, where gases are transferred through the paper by concentration or pressure differences. By using mercury porosimetry the porosity is measured directly via the pore volume of the paper.
The aim of this study is to analyse the pore size distributions resulting from mercury porosimetry of eight different cigarette papers with different air permeability, fibre furnish, filler contents and burn additive contents. The pore size distribution has been measured before and after heating the papers to 230 °C for 30 minutes in the presence of air.
For a qualitative analysis, the pore size distributions have been divided into three sections according to the pore radius: 0.04-0.8 µm (section 1), 0.8-3 µm (section 2) and 3-30 µm (section 3). By comparing the pore size distributions for the unheated paper samples with different permeability, it was found that papers with low air permeability show higher pore volumes in section 1, while papers with high permeability show higher pore volumes in section 2. Variation of the filler content causes changes in the pore volume only in sections 1 and 3. As expected the influence of the burn additive content on the pore size distribution is rather small in all sections. By heating the papers before the analysis by Mercury Porosimetry the overall pore volume increases compared to the unheated papers.
The results show how the pore size distribution of cigarette paper can be influenced by various tools available to the cigarette paper manufacturer such as the paper composition and paper properties.