The research is part of an effort to develop innovative technologies to reduce toxicant levels in smoke. This is an essential part of a research programme that seeks to reduce toxicant exposure in smokers and then determine whether this has any impact on the risk of developing smoking-related diseases.
A novel, synthetic active carbon was found to be twice as effective at adsorbing certain vapour phase compounds from cigarette smoke as standard carbon filter material in laboratory tests. The carbon, is a spherical high performance adsorbent with an internal nanostructure that has been optimised to produce a highly efficient material for the selective filtration of volatile cigarette smoke toxicants. The carbon used in one cigarette filter has an internal volume equivalent to one drop of water and a huge internal surface area equivalent to 1/3rd the area of a tennis court.
Standard carbon used in tobacco industry is typically derived from coconut shells. The new carbon has a bimodal pore size distribution with micropores (<2 nm in diameter) to trap the smoke toxicants and larger (3-80 nm pore diameter) ‘transport’ pores that are especially useful when the flow rate is high (such as those encountered during smoking).
“The smoke is moving very fast,” explains Chuan Liu, a principal scientist at British American Tobacco. “The larger transport pores guide the toxicant molecules into the smaller pores where they become trapped. Getting them in there without the transport pores would be a bit like trying to park a car at right angles whilst driving at speed,” he said.
Tests using 60mg (equivalent to 1/70th of a teaspoon of sugar) of carbon in the cigarette filter can improve the filtration efficiency of certain smoke toxicants by as much as 60 per cent compared to the existing coconut-shell derived carbon used. Even under intensive machine smoking, improvements are observed, for example a 50 per cent reduction in benzene and a 15 per cent reduction in formaldehyde levels.
The second technology is a polystyrene based ion-exchange resin that is typically used for water filtration. The material, supplied by Mitsubishi Chemical Corporation is normally supplied in bead form in a wet environment. To make it suitable for use in a cigarette filtration application, it is necessary to remove the water and dry the material to ca 15 per cent or less moisture.
Aldehydes and hydrogen cyanide in the smoke were found to stick to the resin. Aldehydes are formed when polysaccharides in the leaf are burned and hydrogen cyanide formed when nitrogenous compounds are burned. Tests using 60 mg of the resin beads gave reductions in smoke formaldehyde greater than 50 per cent, and substantial removal of HCN (>50 per cent) and acetaldehyde (~40 per cent) were also observed.
Chris Proctor, Chief Scientific Officer at British American Tobacco, cautions, however, that: “Even if you can reduce the levels of a significant number of toxicants in tobacco smoke, there is no guarantee that this will result in reduced exposure in people or result in a reduction in health risks.” This is why scientists at British American Tobacco are testing prototype cigarettes made using this highly activated carbon in clinical studies in Germany to determine whether reductions in toxicant levels seen in smoking machine tests translate to reduced exposure levels in smokers.