Paper filters – the influence of different paper compositions and paper properties on filtration efficiency and pressure drop
Smoke yields, smoke composition and the taste of a cigarette can be modified by changing different parts of the cigarette, especially the different filter design. Cellulose acetate is currently the most common material for cigarette filters, but also other materials, such as paper, are available with different filtration properties. The overall filtration efficiency is usually controlled by the filter material as well as the pressure drop. Paper filters tend to have higher filtration efficiency than cellulose acetate filters at the same pressure drop.
This study investigates the impact of the fibre type and paper properties, especially air permeability and thickness, on pressure drop and filtration efficiency. In a first step papers with different fibre types and paper properties were produced. Then filters were manufactured from the papers and cigarettes were produced using these filters. The filtration efficiency for tar or nicotine in % was determined by measuring nicotine or the retained particular phase of tar on the cambridge filter pad divided by the total nicotine or particular phase for NFDPM (cambridge filter pad and cigarette filter).
It was found that at constant filter rod weight different fiber types can increase the pressure drop of a filter by 50 mmWG. As a consequence lower paper consumption is needed at the same pressure drop. Additionally also the filtration efficiencies for tar and nicotine could be influenced by different fibre types. The filtration efficiency could be reduced by approx. 5%. Looking at different paper properties by keeping the fibre type constant, the influence of air permeability and thickness of the paper was investigated. The results show that at the same filter rod weight, air permeability and thickness could vary the pressure drop in a range from 200 – 500 mmWG. As a consequence by varying the paper properties it is possible to adjust the pressure drop and consequently the filtration efficiency for tar and nicotine from 30 up to 60%.
In summary it can be concluded that the fibre type and paper properties such as thickness and air permeability have an influence on pressure drop and filtration efficiency and thereby allow to fine-tune the design of paper filters.