AEROSOL-FORMING SUBSTRATE WITH EXPANDED GRAPHITE

Abstract

An aerosol-forming substrate for use in a heated aerosol-generating article comprises expanded graphite particles. Expanded graphite particles have high thermal conductivity and low density and may improve efficiency of aerosol delivery from the substrate.

Claims

1. An aerosol-forming substrate for use in a heated aerosol-generating article, the aerosol-forming substrate comprising expanded graphite particles.

2. An aerosol-forming substrate according to claim 1 in which the aerosol-forming substrate has a thermal conductivity of at least 0.12 W/(mK).

3. An aerosol-generating article according to claim 1 in which the expanded graphite particles make up at least 1 wt. % of the aerosol-forming substrate.

4. An aerosol-forming substrate according to claim 1 comprising, on a dry weight basis: between 1 and 90 wt. % expanded graphite particles; between 7 and 60 wt. % of an aerosol former; between 2 and 20 wt. % of fibres; and between 2 and 10 wt. % of a binder.

5. An aerosol-forming substrate according to claim 1, comprising between 1 and 15 wt. % expanded graphite particles.

6. An aerosol-forming substrate according to claim 1, wherein the expanded graphite particles have a particle size distribution having a volume D10 particle size between 1 and 20 microns.

7. An aerosol-forming substrate according to claim 1, wherein the expanded graphite particles have a particle size distribution having a volume D90 particle size between 50 and 300 microns.

8. An aerosol-forming substrate according to claim 1, wherein the expanded graphite particles are substantially homogeneously distributed throughout the aerosol-forming substrate.

9. An aerosol-forming substrate according to claim 1, wherein the aerosol-forming substrate is a tobacco-free aerosol-forming substrate.

10. An aerosol-forming substrate according to claim 1 comprising tobacco particles.

11. A method of forming an aerosol-forming substrate according to claim 1, the method comprising: forming a slurry comprising expanded graphite particles, an aerosol former, fibres, and a binder; casting and drying the slurry to form the aerosol-forming substrate or a precursor to the aerosol-forming substrate.

12. A method according to claim 11, wherein forming the slurry comprises: forming a first mixture comprising: the aerosol former; the fibres; water; optionally, an acid; and optionally, nicotine, forming a second mixture comprising: the expanded graphite particles; and the binder, and adding the second mixture to the first mixture to form a combined mixture.

13. An aerosol-generating article comprising an aerosol-forming substrate according to claim 1.

14. An aerosol-generating article according to claim 13 comprising a plurality of elements, including the aerosol-forming substrate, assembled within a wrapper.

15. An aerosol-generating system comprising an aerosol-generating article according to claim 13 and an electrical aerosol-generating device for heating the aerosol-forming substrate.

Description

[0324] Examples will now be further described with reference to the figures in which:

[0325] FIG. 1 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating article;

[0326] FIG. 2 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating system comprising a first aerosol-generating device;

[0327] FIG. 3 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating system comprising a second aerosol-generating device;

[0328] FIG. 4 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating article;

[0329] FIG. 5 is a bar chart showing the yield of nicotine from the aerosol-generating article of the first embodiment when used in the aerosol-generating device of FIG. 2 compared to two alternative aerosol-generating articles;

[0330] FIG. 6 is a bar chart showing the yield of glycerine from the aerosol-generating article of the first embodiment when used in the aerosol-generating device of FIG. 2 compared to two alternative aerosol-generating articles;

[0331] FIG. 7 is a bar chart showing the delivery efficiency of nicotine and glycerine from the aerosol-generating article of the first embodiment when used in the aerosol-generating device of FIG. 2 compared to two alternative aerosol-generating articles;

[0332] FIG. 8 is a bar chart showing the yield of nicotine from the aerosol-generating article of the first embodiment when used in the aerosol-generating device of FIG. 3 compared to two alternative aerosol-generating articles;

[0333] FIG. 9 is a bar chart showing the yield of glycerine from the aerosol-generating article of the first embodiment when used in the aerosol-generating device of FIG. 3 compared to two alternative aerosol-generating articles;

[0334] FIG. 10 is a bar chart showing the delivery efficiency of nicotine and glycerine from the aerosol-generating article of the first embodiment when used in the aerosol-generating device of FIG. 3 compared to two alternative aerosol-generating articles.

[0335] FIG. 1 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating article 10. The aerosol-generating article 10 comprises a rod 12 of aerosol-forming substrate and a downstream section 14 at a location downstream of the rod 12 of aerosol-forming substrate. Further, the aerosol-generating article 10 comprises an upstream section 16 at a location upstream of the rod 12 of aerosol-forming substrate. Thus, the aerosol-generating article 10 extends from an upstream or distal end 18 to a downstream or proximal or mouth end 20.

[0336] The aerosol-generating article has an overall length of about 45 millimetres.

[0337] The downstream section 14 comprises a support element 22 located immediately downstream of the rod 12 of aerosol-forming substrate, the support element 22 being in longitudinal alignment with the rod 12. In the embodiment of FIG. 1, the upstream end of the support element 22 abuts the downstream end of the rod 12 of aerosol-generating substrate. In addition, the downstream section 14 comprises an aerosol-cooling element 24 located immediately downstream of the support element 22, the aerosol-cooling element 24 being in longitudinal alignment with the rod 12 and the support element 22. In the embodiment of FIG. 1, the upstream end of the aerosol-cooling element 24 abuts the downstream end of the support element 22.

[0338] As will become apparent from the following description, the support element 22 and the aerosol-cooling element 24 together define an intermediate hollow section 50 of the aerosol-generating article 10. As a whole, the intermediate hollow section 50 does not substantially contribute to the overall RTD of the aerosol-generating article. An RTD of the intermediate hollow section 26 as a whole is substantially 0 millimetres H.sub.2O.

[0339] The support element 22 comprises a first hollow tubular segment 26. The first hollow tubular segment 26 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The first hollow tubular segment 26 defines an internal cavity 28 that extends all the way from an upstream end 30 of the first hollow tubular segment to a downstream end 32 of the first hollow tubular segment 20. The internal cavity 28 is substantially empty, and so substantially unrestricted airflow is enabled along the internal cavity 28. The first hollow tubular segment 26and, as a consequence, the support element 22does not substantially contribute to the overall RTD of the aerosol-generating article 10. In more detail, the RTD of the first hollow tubular segment 26 (which is essentially the RTD of the support element 22) is substantially 0 millimetres H.sub.2O.

[0340] The first hollow tubular segment 26 has a length of about 8 millimetres, an external diameter of about 7.25 millimetres, and an internal diameter (DFTS) of about 1.9 millimetres. Thus, a thickness of a peripheral wall of the first hollow tubular segment 26 is about 2.67 millimetres.

[0341] The aerosol-cooling element 24 comprises a second hollow tubular segment 34. The second hollow tubular segment 34 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The second hollow tubular segment 34 defines an internal cavity 36 that extends all the way from an upstream end 38 of the second hollow tubular segment to a downstream end 40 of the second hollow tubular segment 34. The internal cavity 36 is substantially empty, and so substantially unrestricted airflow is enabled along the internal cavity 36. The second hollow tubular segment 28and, as a consequence, the aerosol-cooling element 24does not substantially contribute to the overall RTD of the aerosol-generating article 10. In more detail, the RTD of the second hollow tubular segment 34 (which is essentially the RTD of the aerosol-cooling element 24) is substantially 0 millimetres H.sub.2O.

[0342] The second hollow tubular segment 34 has a length of about 8 millimetres, an external diameter of about 7.25 millimetres, and an internal diameter (DsTs) of about 3.25 millimetres. Thus, a thickness of a peripheral wall of the second hollow tubular segment 34 is about 2 millimetres. Thus, a ratio between the internal diameter (DFTS) of the first hollow tubular segment 26 and the internal diameter (DsTs) of the second hollow tubular segment 34 is about 0.75.

[0343] The aerosol-generating article 10 comprises a ventilation zone 60 provided at a location along the second hollow tubular segment 34. In more detail, the ventilation zone is provided at about 2 millimetres from the upstream end of the second hollow tubular segment 34. In this embodiment, the ventilation zone 60 comprises a circumferential row of perforations through a paper wrapper 70 and a ventilation level of the aerosol-generating article 10 is about 25 percent.

[0344] In the embodiment of FIG. 1, the downstream section 14 further comprises a mouthpiece element 42 at a location downstream of the intermediate hollow section 50. In more detail, the mouthpiece element 42 is positioned immediately downstream of the aerosol-cooling element 24. As shown in the drawing of FIG. 1, an upstream end of the mouthpiece element 42 abuts the downstream end 40 of the aerosol-cooling element 24.

[0345] The mouthpiece element 42 is provided in the form of a cylindrical plug of low-density cellulose acetate.

[0346] The mouthpiece element 42 has a length of about 12 millimetres and an external diameter of about 7.25 millimetres. The RTD of the mouthpiece element 42 is about 12 millimetres H.sub.2O. The ratio of the length of the mouthpiece element 42 to the length of the intermediate hollow section 50 is approximately 0.6.

[0347] The rod 12 of aerosol-forming substrate has an external diameter of about 7.25 millimetres and a length of about 12 millimetres.

[0348] The upstream section 16 comprises an upstream element 46 located immediately upstream of the rod 12 of aerosol-forming substrate, the upstream element 46 being in longitudinal alignment with the rod 12. In the embodiment of FIG. 1, the downstream end of the upstream element 46 abuts the upstream end of the rod 12 of aerosol-forming substrate. The upstream element 46 is provided in the form of a cylindrical plug of cellulose acetate. The upstream element 46 has a length of about 5 millimetres. The RTD of the upstream element 46 is about 30 millimetres H.sub.2O.

[0349] The upstream element 46, rod 12 of aerosol-forming substrate, support element 22, aerosol-cooling element 24, and mouthpiece element 42 are circumscribed by the paper wrapper 70.

[0350] The rod 12 of aerosol-forming substrate comprises an aerosol-forming material and thermally conductive particles 44. The aerosol-forming material comprises a reconstituted and gathered sheet comprising tobacco material and glycerine. The thermally conductive particles 44 are carbon particles, specifically expanded graphite particles, having a particle size distribution with a D10 particle size of 6.6 microns, a D50 particle size of 20 microns, and a D90 particle size of 56 microns. Each of the expanded graphite particles has a particle size greater than 2 microns and less than 100 microns. The expanded graphite particles have a volume mean particle size of around 35 microns. Each of the expanded graphite particles is substantially spherical in shape.

[0351] The expanded graphite particles have a density of less than 1000 kilograms per metre cubed. The aerosol-forming substrate, including the aerosol-forming material and the thermally conductive particles 44, have a combined density of around 760 kilograms per metre cubed. The expanded graphite particles make up approximately 4.6% of the aerosol-forming substrate by weight. Glycerine makes up approximately 1.7% of the aerosol-forming substrate by weight.

[0352] The rod 12 of aerosol-forming substrate is formed by a process including the following steps: [0353] pre-mixing a binder, guar gum, with an aerosol-former, glycerine, to form a first pre-mixture; [0354] pre-mixing finely shredded tobacco material and a powder consisting of the expanded graphite particles 44 and having a bulk density of around 0.065 grams per centimetre cubed, to form a second pre-mixture; [0355] mixing the first and second pre-mixtures with water to form a slurry; [0356] homogenising the slurry using a high-shear mixer; [0357] casting the slurry onto a conveyor belt; [0358] controlling a thickness of the slurry and drying the slurry to form a large sheet of aerosol-forming substrate; and [0359] gathering and cutting the large sheet of aerosol-forming substrate to form the rod 12 of aerosol-forming substrate.

[0360] After forming the rod 12 of aerosol-forming substrate, the aerosol-generating article 10 is assembled by positioning the various components of the article 10 and wrapping the components in the wrapper 70.

[0361] FIG. 2 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating system 100. The system 100 comprises an aerosol-generating device 102 and the aerosol-generating article 10 of FIG. 1.

[0362] The aerosol-generating device 102 comprises a battery 104, a controller 106, a heating blade 108 coupled to the battery, and a puff-detection mechanism (not shown). The controller 106 is coupled to the battery 104, the heating blade 108 and the puff-detection mechanism.

[0363] The aerosol-generating device 102 further comprises a housing 110 defining a substantially cylindrical cavity for receiving a portion of the article 10. The heating blade 108 is positioned centrally within the cavity and extends longitudinally from a base of the cavity.

[0364] In this embodiment, the heating blade 108 comprises a substrate and an electrically resistive track located on the substrate. The battery 104 is coupled to the heating blade 108 so as to be able to pass a current through the electrically resistive track and heat the electrically resistive track and heating blade 108 to an operational temperature.

[0365] In use, a user inserts the article 10 into the cavity, causing the heating blade 108 to penetrate the upstream element 46 and rod 12 of aerosol-forming substrate of the article 10. FIG. 3 shows the article 10 inserted into the cavity of the device 102.

[0366] Then, the user puffs on the downstream end of the article 10. This causes air to flow through an air inlet (not shown) of the device 102, then through the article 10, from the upstream end 18 to the downstream end 20, and into the mouth of the user.

[0367] The user puffing on the article 10 causes air to flow through the air inlet of the device. The puff-detection mechanism detects that the air flow rate through the air inlet has increased to greater than a non-zero threshold flow rate. The puff-detection mechanism sends a signal to the controller 106 accordingly. The controller 106 then controls the battery 104 so as to pass a current through the electrically resistive track and heat up the heating blade 108. This heats up the rod 12 of aerosol-forming substrate, which is in contact with the heating blade 108.

[0368] The expanded graphite particles 44 have a significantly higher thermal conductivity than the surrounding aerosol-forming material. As such, these particles may act as local hot-spots and provide a more even temperature throughout the aerosol-forming substrate, particularly in a radial direction from the heating blade 108 where, with prior art substrates, there would be a significant temperature gradient. This may result in a greater proportion of the aerosol-forming substrate reaching a sufficiently high temperature to release volatile compounds, and thus a higher usage efficiency of the aerosol-forming substrate.

[0369] Heating of the aerosol-forming substrate cause the aerosol-forming substrate to release volatile compounds. These compounds are entrained by the air flowing from the upstream end 18 of the article 10 towards the downstream end 20 of the article 10. The compounds cool and condense to form an aerosol as they pass through the internal cavities 28, 36 of the support element and the aerosol-cooling element. The aerosol then passes through the mouthpiece element 42, which may filter out unwanted particles entrained in the air flow, and into the mouth of the user.

[0370] When the user stops inhaling on the article 10, the air flow rate through the air inlet of the device decreases to less than the non-zero threshold flow rate. This is detected by the puff-detection mechanism. The puff-detection mechanism sends a signal to the controller 106 accordingly. The controller 106 then controls the battery 104 so as to reduce the current being passed through the electrically resistive track to zero.

[0371] After a number of puffs on the article 10, the user may choose to replace the article 10 with a fresh article.

[0372] FIG. 3 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating system 200. The system 200 comprises an aerosol-generating device 202 and the aerosol-generating article 11 of FIG. 1.

[0373] The aerosol-generating device 202 comprises a battery 204, a controller 206, an inductor coil 208, and a puff-detection mechanism (not shown). The controller 206 is coupled to the battery 204, the inductor coil 208 and the puff-detection mechanism.

[0374] The aerosol-generating device 202 further comprises a housing 210 defining a substantially cylindrical cavity for receiving a portion of the article 10. The inductor coil 208 spirals around the cavity.

[0375] The battery 204 is coupled to the inductor coil 208 so as to be able to pass an alternating current through the inductor coil 208.

[0376] In use, a user inserts the article 11 into the cavity. FIG. 3 shows the article 10 inserted into the cavity of the device 202.

[0377] Then, the user puffs on the downstream end of the article 10. This causes air to flow through an air inlet (not shown) of the device 202, then through the article 10, from the upstream end 18 to the downstream end 20, and into the mouth of the user.

[0378] The user puffing on the article 10 causes air to flow through the air inlet of the device. The puff-detection mechanism detects that the air flow rate through the air inlet has increased to greater than a non-zero threshold flow rate. The puff-detection mechanism sends a signal to the controller 206 accordingly. The controller 206 then controls the battery 204 so as to pass an alternating current through the inductor coil 208. This causes the inductor coil 208 to generate a fluctuating electromagnetic field. The rod 13 of aerosol-forming substrate is located within this fluctuating electromagnetic field and expanded graphite, the material of the particles 44, is a susceptor material. Thus, the fluctuating electromagnetic field causes eddy currents in the particles 44. This causes the particles 44 to heat up, thereby also heating nearby aerosol-forming material.

[0379] Heating of the aerosol-forming material cause the aerosol-forming material to release volatile compounds. These compounds are entrained by the air flowing from the upstream end 18 of the article 10 towards the downstream end 20 of the article 10. The compounds cool and condense to form an aerosol as they pass through the internal cavities 28, 36 of the support element and the aerosol-cooling element. The aerosol then passes through the mouthpiece element 42, which may filter out unwanted particles entrained in the air flow, and into the mouth of the user.

[0380] When the user stops inhaling on the article 10, the air flow rate through the air inlet of the device decreases to less than the non-zero threshold flow rate. This is detected by the puff-detection mechanism. The puff-detection mechanism sends a signal to the controller 206 accordingly. The controller 206 then controls the battery 204 so as to reduce the current being passed through the electrically resistive track to zero.

[0381] After a number of puffs on the article 11, the user may choose to replace the article 11 with a fresh article.

[0382] FIG. 4 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating article 510. This second embodiment is identical to the first embodiment of FIG. 1 except that the rod 12 of aerosol-forming substrate has been replaced by an alternative rod 512 of aerosol-forming substrate. Identical reference numerals have been used for identical components in the embodiments of FIGS. 1 and 3.

[0383] The rod 512 of aerosol-forming substrate of the second embodiment of FIG. 4 is identical to the rod 12 of aerosol-forming substrate of the first embodiment of FIG. 1 except that the rod 512 of aerosol-forming substrate of the third embodiment of FIG. 4 additionally includes an elongate susceptor element 580.

[0384] The susceptor element 580 is arranged substantially longitudinally within the rod 512 of aerosol-forming substrate so as to be approximately parallel with a longitudinal axis of the rod 512 of aerosol-forming substrate. As shown in the drawing of FIG. 4, the susceptor element 580 is positioned in a radially central position within the rod and extends along the longitudinal axis of the rod 12.

[0385] The susceptor element 580 extends all the way from an upstream end to a downstream end of the rod 512 of aerosol-forming substrate. As such, the susceptor element 580 has substantially the same length as the rod 512 of aerosol-forming substrate.

[0386] In the embodiment of FIG. 4, the susceptor element 580 is provided in the form of a strip of a ferromagnetic steel and has a length of about 12 millimetres, a thickness of about 60 micrometres, and a width of about 4 millimetres.

[0387] The aerosol-generating article 510 of FIG. 4 may be used with the aerosol-generating device 202 of FIG. 3 in the same way as the aerosol-generating article 10 of FIG. 1. Notably, the inclusion of the susceptor element 580 means that the article 510 may be inductively heated. In the example shown in FIG. 4, both the expanded graphite particles and the susceptor element 580 are inductively heatable. So, both the susceptor element 580 and the expanded graphite particles 44 contribute to heating during use.

[0388] The rods of aerosol-forming substrate 12,512 of aerosol-generating articles 10,510 can be described as being thermally enhanced due to the inclusion of 4.6% expanded graphite particles by weight. It has been found by the inventors that such aerosol-generating articles according to the disclosure have an increased yield and delivery efficiency of nicotine and glycerine when compared to aerosol-generating articles comprising rods of aerosol-forming substrate that do not comprise expanded graphite particles.

[0389] The inventors measured the yield of nicotine and glycerine from an aerosol-generating article 602 that does not comprise any thermally conductive particles, an aerosol-generating article 604 in which 4.6% of the tobacco of the aerosol-generating article 602 has been replaced with graphite particles, and an aerosol-generating article 606 in which 4.6% of the tobacco of the aerosol-generating article 602 has been replaced with expanded graphite particles. In other words, the aerosol-generating article 606 is an aerosol-generating article according to the present disclosure and may be the aerosol-generating article shown in FIG. 1.

[0390] FIGS. 5 to 7 show results when aerosol-generating articles 602 to 606 are used with a resistive aerosol-generating device (such as the device shown in FIG. 2).

[0391] FIG. 5 is a bar chart 600 showing the yield of nicotine per aerosol-generating article on the Y axis. The yield is measured in microgram per article and is the total yield achieved during a usage session. On the X axis are bars for each of aerosol-generating article 602 to 606. The yield of nicotine from the aerosol-generating article 602 that does not comprise any thermally conductive particles is 1150 microgram per article. The yield of nicotine from the aerosol-generating article 604 that comprises 4.6% graphite particles by weight is 1190 microgram per article. The yield of nicotine from the aerosol-generating article 606 that comprises 4.6% expanded graphite particles by weight is 1125 microgram per article.

[0392] FIG. 6 is a bar chart 700 showing the yield of glycerine per aerosol-generating article on the Y axis. The yield is measured in microgram per article and is the total yield achieved during a usage session. On the X axis are bars for each of aerosol-generating article 602 to 606. The yield of glycerine from the aerosol-generating article 602 that does not comprise any thermally conductive particles is 3640 microgram per article. The yield of glycerine from the aerosol-generating article 604 that comprises 4.6% graphite particles by weight is 4150 microgram per article. The yield of glycerine from the aerosol-generating article 606 that comprises 4.6% expanded graphite particles by weight is 4540 microgram per article.

[0393] FIG. 7 is a bar chart 800 showing the delivery efficiency of nicotine and glycerine for each of the aerosol-generating articles 602 to 608 during a usage session. The efficiency is shown on the Y axis and is a percentage. In particular, the efficiency is the percentage of that total initial nicotine or glycerine contained in the aerosol-generating article that is delivered to the user or a smoking machine throughout a usage session of that article. The bars 802 representing nicotine delivery efficiency have a diagonal hatching. The bars 804 representing glycerine delivery efficiency have a vertical dashed hatching.

[0394] The efficiency of nicotine delivery from the aerosol-generating article 602 that does not comprise any thermally conductive particles is 29%. The efficiency of nicotine delivery from the aerosol-generating article 604 that comprises 4.6% graphite particles by weight is 31.5%. The efficiency of nicotine delivery from the aerosol-generating article 606 that comprises 4.6% expanded graphite particles by weight is 35.4%.

[0395] The efficiency of glycerine delivery from the aerosol-generating article 602 that does not comprise any thermally conductive particles is 9.3%. The efficiency of glycerine delivery from the aerosol-generating article 604 that comprises 4.6% graphite particles by weight is 10.6%. The efficiency of nicotine delivery from the aerosol-generating article 606 that comprises 4.6% expanded graphite particles by weight is 12.1%.

[0396] FIGS. 8 to 10 show the results when aerosol-generating articles 602 to 606 are used with an inductive aerosol-generating device (such as the device shown in FIG. 3).

[0397] FIG. 8 is a bar chart 900 showing the yield of nicotine per aerosol-generating article on the Y axis. The yield is measured in microgram per article and is the total yield achieved during a usage session. On the X axis are bars for each of aerosol-generating article 602 to 606. The yield of nicotine from the aerosol-generating article 602 that does not comprise any thermally conductive particles is 790 microgram per article. The yield of nicotine from the aerosol-generating article 604 that comprises 4.6% graphite particles by weight is 886 microgram per article. The yield of nicotine from the aerosol-generating article 606 that comprises 4.6% expanded graphite particles by weight is 1197 microgram per article.

[0398] FIG. 9 is a bar chart 1000 showing the yield of glycerine per aerosol-generating article on the Y axis. The yield is measured in microgram per article and is the total yield achieved during a usage session. On the X axis are bars for each of aerosol-generating article 602 to 606. The yield of glycerine from the aerosol-generating article 602 that does not comprise any thermally conductive particles is 3100 microgram per article. The yield of glycerine from the aerosol-generating article 604 that comprises 4.6% graphite particles by weight is 3840 microgram per article. The yield of glycerine from the aerosol-generating article 606 that comprises 4.6% expanded graphite particles by weight is 4800 microgram per article.

[0399] FIG. 10 is a bar chart 1100 showing the delivery efficiency of nicotine and glycerine for each of the aerosol-generating articles 602 to 608 during a usage session. The efficiency is shown on the Y axis and is a percentage. In particular, the efficiency is the percentage of that total initial nicotine or glycerine contained in the aerosol-generating article that is delivered to the user or a smoking machine throughout a usage session of that article. The bars 1102 representing nicotine delivery efficiency have a diagonal hatching. The bars 1104 representing glycerine delivery efficiency have a vertical dashed hatching.

[0400] The efficiency of nicotine delivery from the aerosol-generating article 602 that does not comprise any thermally conductive particles is 19.1%. The efficiency of nicotine delivery from the aerosol-generating article 604 that comprises 4.6% graphite particles by weight is 23.8%. The efficiency of nicotine delivery from the aerosol-generating article 606 that comprises 4.6% expanded graphite particles by weight is 31.4%.

[0401] The efficiency of glycerine delivery from the aerosol-generating article 602 that does not comprise any thermally conductive particles is 7.6%. The efficiency of glycerine delivery from the aerosol-generating article 604 that comprises 4.6% graphite particles by weight is 9.9%. The efficiency of nicotine delivery from the aerosol-generating article 606 that comprises 4.6% expanded graphite particles by weight is 12.1%.

[0402] So, the bar charts of FIGS. 5, 6, 8 and 9 demonstrate that both nicotine and glycerine yield is increased when an aerosol-forming substrate is thermally enhanced by replacing a small portion of tobacco with expanded graphite and that the yield increase is greater when particles of expanded graphite are used to thermally enhance the substrate, rather than particles of graphite. An increase is achieved regardless of whether an aerosol is generated as a result of resistive or inductive heating of the substrate.

[0403] Similarly, the bar chart of FIG. 7 demonstrates that both nicotine and glycerine delivery efficiency is increased when an aerosol-forming substrate is thermally enhanced by replacing a small portion of tobacco with expanded graphite, and that the efficiency increase is greater when particles of expanded graphite are used to thermally enhance the substrate, rather than particles of graphite. An increase is achieved regardless of whether an aerosol is generated as a result of resistive or inductive heating of the substrate.

[0404] One specific embodiment aerosol-forming substrate comprising expanded graphite particles has been described above. Of course, the aerosol-forming substrate may differ in other embodiments. For example, the aerosol-forming substrate comprise a different quantity, proportion, size or density of expanded graphite particles to the specific embodiment described above. In any case, the presence of the expanded graphite particles may thermally enhance the substrate. Furthermore, other features of the substrate such as other features of the substrate's chemical composition may differ.

[0405] FIG. 11 shows an alternative embodiment of an aerosol-generating article 1110 comprising a thermally-enhanced aerosol-forming substrate 1112 that includes discrete elements of a first material 1113 and discrete elements of the second material 1114. Each discrete element of the second material 1114 may contact many discrete elements of the first material 1113 and can therefore act as a thermal pathway through the substrate. The proportions of first material and second material may be varied depending on the specific properties of the first material and the second material and on the desired properties of the aerosol-forming substrate 1112. Other than the differences in the substrate itself, the aerosol-generating article 1110 is identical to the aerosol-generating article 10 of FIG. 1 and like features have been numbered accordingly.

[0406] Some specific thermally-enhanced aerosol forming substrates will now be identified as examples. The examples use combinations of three specific materials identified below; Material A, Material B, and Material C.

Material A

[0407] Material A is a standard homogenised tobacco material. Material A comprises tobacco powder, about 4 wt. % cellulose fibres, about 3 wt. % of guar as a binder, and about 15 wt. % glycerine as an aerosol-former.

[0408] Material A is formed by a process including the following steps: [0409] pre-mixing the binder, guar gum, with the aerosol-former, glycerine, to form a first pre-mixture; [0410] pre-mixing the tobacco powder and water to form a second pre-mixture; [0411] mixing the first and second pre-mixtures to form a slurry; [0412] homogenising the slurry using a high-shear mixer; [0413] casting the slurry onto a conveyor belt; [0414] controlling a thickness of the slurry and drying the slurry to form a large sheet of reconstituted, substantially homogeneous, tobacco-containing, aerosol-forming material; and [0415] crimping and shredding the large sheet of reconstituted and substantially homogeneous aerosol-forming material to form cut-filler.

[0416] Material A has a thermal conductivity of 0.12 W/mK.

Material B

[0417] Material B is a homogenised tobacco material with augmented thermal conductivity. Material B comprises tobacco powder, about 5 wt. % expanded graphite particles, about 4 wt. % cellulose fibres, about 3 wt. % of guar as a binder, and about 15 wt. % glycerine as an aerosol-former.

[0418] The expanded graphite particles have a particle size distribution with a D10 particle size of 6.6 microns, a D50 particle size of 20 microns, and a D90 particle size of 56 microns. Each of the expanded graphite particles has a particle size greater than 2 microns and less than 100 microns. The expanded graphite particles have a volume mean particle size of around 35 microns. Each of the expanded graphite particles is substantially spherical in shape. The expanded graphite particles have a density of less than 1000 kilograms per metre cubed.

[0419] Material B is formed by a process including the following steps: [0420] pre-mixing the binder, guar gum, with the aerosol-former, glycerine, to form a first pre-mixture; [0421] pre-mixing the tobacco powder, expanded graphite particles, and water to form a second pre-mixture; [0422] mixing the first and second pre-mixtures to form a slurry; [0423] homogenising the slurry using a high-shear mixer; [0424] casting the slurry onto a conveyor belt; [0425] controlling a thickness of the slurry and drying the slurry to form a large sheet of reconstituted, substantially homogeneous, tobacco-containing, aerosol-forming material; and [0426] crimping and shredding the large sheet of reconstituted and substantially homogeneous aerosol-forming material to form cut-filler.

[0427] Material B has a thermal conductivity of at least 10% higher than the thermal conductivity of material A, for example between 0.14 W/mK and 0.25 W/mK. The replacement of 5 wt. % of the tobacco powder with expanded graphite particles reduces the overall tobacco content, and therefore nicotine content, slightly. The thermal conductivity of the material is increased, however. In experiments, adding between 4.5 wt. % and 10 wt. % of expanded graphite particles to a homogenized tobacco material increased thermal conductivity by between 20% and 50%.

Material C

[0428] Material C is a non-tobacco aerosol-forming material with high thermal conductivity. Material C comprises, on a dry weight basis, around 76.1 wt. % expanded graphite particles.

[0429] Material C further comprises around 17.7 wt. % of an aerosol former. In this embodiment, the aerosol former is glycerol, specifically ICOF Europe food grade (>99.5% purity) glycerol.

[0430] Material C further comprises, on a dry weight basis, around 3.9 wt. % of fibres. In this embodiment, the fibres are cellulose fibres, specifically Birch cellulose fibers from Stora Enso OYJ.

[0431] Material C further comprises, on a dry weight basis, around 2.3 wt. % of a binder. In this embodiment, the binder is a guar gum, specifically guar gum from Gumix International Inc.

[0432] Material C may further comprise one or more of nicotine, an acid such as fumaric acid, a botanical such as clove or rosmarinus, water, and a flavourant.

[0433] Material C is formed by the process set out below.

[0434] A slurry is formed using a lab disperser capable of mixing viscous liquids, dispersing powders through liquids, and removing gas from a mixture (for example by applying a vacuum or other suitably low pressure). In this embodiment, a commercially available lab disperser from PC Laborsystem was used.

[0435] To form the slurry, a first mixture is formed by adding to the lab disperser around 7.11 grams of the aerosol former, then around 157.5 grams of water, then around 1.57 grams of the fibres. Then, these first ingredients are mixed at 25 degrees Celsius for 5 minutes at 600-700 rpm to ensure a homogeneous mixture and to hydrate the fibers. Then, a second mixture is formed by manually mixing around 32.95 grams of the thermally conductive particles and around 0.92 grams of the binder. This mixing of the second mixture avoids the formation of lumps in the lab dispersion. Then, the second mixture is added to the first mixture to form a combined mixture. Then, the combined mixture is mixed at 5000 rpm for 4 minutes at 25 degrees Celsius and a first reduced pressure of around 200 mbar. The reduced pressure may help to ensure that the thermally conductive particles are homogeneously dispersed in the mixture and that there is little trapped air and few lumps in the combined mixture. Then, the combined mixture is mixed at 5000 rpm for 20 second minutes at 25 degrees Celsius and a second reduced pressure of around 100 mbar. This second reduced pressure may help to remove any remaining air bubbles. This forms a slurry for casting.

[0436] The slurry is then cast and dried using a suitable apparatus. In this embodiment, a commercially available Labcoater Mathis apparatus is used. This apparatus includes a stainless steel, flat support, and a coma blade for adjusting a thickness of slurry cast onto the flat support.

[0437] The slurry is cast onto the flat support and a gap between the coma blade and the flat support is set at 0.6 millimetres. This ensures that a thickness of the slurry is no more than 0.6 millimetres at any given point.

[0438] The slurry is then dried with hot air between 120 and 140 degrees Celsius for between 2 and 5 minutes. After this drying, a sheet of the aerosol-forming substrate is formed. This sheet has a thickness of around 159 microns, a grammage of around 125.7 grams per metre squared, and a density of around 0.79 kilograms per meter cubed.

[0439] The sheet is then crimped and cut to form Material C. The thermal conductivity of Material C is at least 0.28 W(mK).

[0440] It can be seen that a wide range of different aerosol-forming substrates may be produced simply by combining Material A, B, and C in different proportions.

[0441] Thus, a first exemplary aerosol-forming substrate 12 may comprise a mixture of 60 wt. % of discrete elements of Material A and 40 wt. % of discrete elements of Material B. Both Material A and Material B are homogenized tobacco material, but Material B has augmented thermal conductivity by virtue of the presence of expanded graphite particles. The presence of Material B in the first exemplary aerosol-forming substrate provides discrete elements that have increased thermal conductivity and, as a result, aerosol delivery and nicotine delivery are improved.

[0442] A second exemplary aerosol-forming substrate 12 may comprise a mixture of 70 wt. % of discrete elements of Material A and 30 wt. % of discrete elements of Material C. The presence of Material C in the second exemplary aerosol-forming substrate reduced the overall amount of tobacco in the substrate, but significantly improved the thermal conductivity. Material C also contribute to the generation of aerosol.

[0443] A third exemplary aerosol-forming substrate 12 may comprise a mixture of 80 wt. % of discrete elements of Material B and 20 wt. % of discrete elements of Material C. In this example, the first material is Material B, a homogenized tobacco material with augmented thermal conductivity and the second material is Material C.

[0444] Any of these three exemplary aerosol-forming substrates may be used as the substrate in the aerosol-generating article 10 of FIG. 1 or the substrate in the aerosol-generating article 1110 of FIG. 11.

[0445] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term about. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A?10% of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.