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Paper plays an important role in the chemistry of cigarette smoke

The main physical function of cigarette paper is simply to keep the tobacco in the form of a tube, down which smoke can be drawn.

Cigarette manufacturing is a high-speed process which puts certain demands on the mechanical properties of the cigarette paper.  The structure of the cigarette paper also affects the combustion mechanisms that occur during both smouldering and puffing.  This, in turn, can significantly affect the smoke chemistry and other performance characteristics of the cigarette.

Paper science

The principal ingredient of cigarette paper is cellulose fibre, derived mainly from either wood pulp or flax.  It usually also contains about 20% to 30% calcium carbonate as filler pigment and usually up to about 2% of burn additives - salts like potassium or sodium citrate that affect the burn rate of the paper.

The combination of the filler and the burn additives gives a white, coherent paper ash after the paper is burnt. 

Fibre processing during paper manufacture gives the paper its inherent or natural porosity - influencing the burn rate of the cigarette and consequently the mainstream and sidestream smoke yields. 

In addition, burn additives that promote faster burning may result in lower machine measured mainstream ‘tar’ yields of the cigarette by reducing the puff number.  ‘Tar’ yield per puff is not increased by burn additives.

The scanning electron micrograph (SEM) images below show a typical structure of the cigarette paper[1].
3 scanning electron micrographs (SEMs) showing a typical structure of the cigarette paper   

Air permeability and natural porosity are the two parameters used to describe and characterise the porous structure of cigarette paper. 

Permeability is measured using an internationally defined standard, e.g., CORESTA Method No. 40[2] whilst porosity is usually measured by a technique called mercury porosimetry.

Porosity is more closely associated with the diffusion capacity of the cigarette paper than air permeability. This is due to the physics that controls air flow through pores of different sizes[3]

Electrical or laser perforation is sometimes introduced to further enhance the permeability of the cigarette paper and to offer increased air dilution during smoking.  In contrast to natural permeability, electrical perforation has a minor effect on oxygen diffusion through the paper and consequently does not change the burn rate of the cigarette paper. 

The phenomenon becomes more complex as the porosity (and permeability) of the paper changes when the paper is being heated during smoking. 

Effects of cigarette paper on smoke chemistry

A number of systematic evaluations on the effects of cigarette paper variables on a range of paper properties and cigarette smoke yields have been carried out[4,5].

Below is a box-plot of a statistically based central composite design involving three cigarette paper parameters, the amount of fibre, amount of filler and the permeability.

10134_figure90v2

The study found that all three parameters could have an impact on smoke chemistry.  Data analysis indicated that it is possible to predict the effect of paper physical characteristics on machine measured mainstream smoke yields of tar, nicotine and CO within the experimental space, for a given blend.

Lower ignition propensity cigarette papers

Several countries (including Canada and Australia) have introduced regulations requiring cigarettes to pass a test for ignition propensity, and there are a variety of scientific challenges in developing and assessing such products.

Additional alginate, starch or cellulose fibre may be applied to the surface of cigarette paper as bands to reduce its air porosity or permeability.  This technique is widely used to control a cigarette’s ability to self-extinguish during the ‘ignition propensity’ tests (ASTM 2187-04 Standard Test Method for Measuring the Ignition Strength of Cigarettes).

Both the bands applied and the test geometry (e.g., the number of layers of filter paper substrate) have been found to affect the way cigarettes smoulder[6,7]

Thermal infrared camera images reveal the unique way a smouldering cigarette burns on a 10-layer Whatman No.2 filter paper substrate[6,7].

 

10109_figure91

   4 infrared photographs of how a smoulding cigarette burns on a 10-layer Whatman No 2 filter paper substrate
  

These infrared images show a progressively upward bending of the smouldering coal and the curved paper char lines. 

This is caused by the lower region of the smouldering cigarette (the “coal”) losing heat to the substrate and therefore burning at a lower temperature - visible in the images.  A physical gap is created between the coal and the substrate allowing the natural air flow - or buoyancy - around the periphery of the coal. 

These images provide detailed insights into the interaction between a burning cigarette and a cellulose substrate as set out in the ASTM 2187-04 test method.


  1. Branton, P., Baker, R. R. (2002). Methods for the structural characterisation of cigarette paper. Oral presentation made at the 56th Tobacco Science Research Conference, Lexington, Kentucky, USA, September 29-October 2, 2002. PDF: PDF: Methods for the structural... - PDF: Methods for the structural... (491 kb) Opens new window
  2. CORESTA (1994). CORESTA recommended method No. 40: Determination of air permeability of materials used as cigarette papers, filter plug wrap and filter joining paper including materials having an oriented permeable zone. Opens new window
  3. Baker, R. R. (1989). The viscous and inertial flow of air through perforated papers. Beiträge zur Tabakforschung International. 14 (5): 253-260.
  4. Case, P. D., Astl, G. (2003). Systematic studies on cigarette paper. The influence of filler, fibre and natural permability on paper properties and mainstream ISO yields. Paper presented at the 57th Tobacco Science Research Conference, Norfolk, Virginia, USA, September 21-24, 2003.  PDF: PDF: Systematic studies on cigarette paper... - PDF: Systematic studies on cigarette paper... (245 kb) Opens new window
  5. Case, P. D., Astl, G. (2003). Systematic studies on cigarette paper. The influence of filler, fibre and natural permeability on paper properties and mainstream ISO yields. Oral presentation made at the CORESTA Joint Meeting of the Smoke Science and Product Technology Study Groups, Freiburg, Germany, September 7-11, 2003.  PDF: PDF: Systematic studies on cigarette… - PDF: Systematic studies on cigarette… (272 kb) Opens new window
  6. Liu, C. (2005). A smouldering cigarette on 10-layer Whatman filter paper substrate: temperature distribution. Paper presented at the CORESTA Joint Meeting of the Smoke Science and Product Technology Study Groups, Stratford-upon-Avon, UK, September 4-8, 2005.  PDF: PDF: A smouldering cigarette on… - PDF: A smouldering cigarette on… (393 kb) Opens new window
  7. Liu, C. (2005). The ASTM2187- 02b Standard Method on Testing Cigarette’s Ignition Propensity: Temperature Distribution. Poster presented at the British Combustion Institute Spring Meeting on Fire Research, London, April, 2005.  PDF: PDF: The ASTM2187-02b standard method… - PDF: The ASTM2187-02b standard method… (1,386 kb) Opens new window
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