Filter of an aerosol-generating article having a novel filter material

Abstract

There is provided an aerosol-generating article (10)(100)(310) comprising: an aerosol-generating substrate (12)(114)(312); and a filter (18)(122)(314) axially aligned with the aerosol-generating substrate, the filter (18)(122)(314) comprising at least one filter segment (126)(318) of filter material, the filter material comprising a plurality of fibres, the plurality of fibres comprising a polyhydroxyalkanoate compound, wherein the fibres provide a total external surface area of from 0.12 square metres per gram to 0.28 square metres per gram. The at least one filter segment comprises at least 20% by weight of the polyhydroxyalkanoate compound.

Description

[0001] The present invention relates to a filter for an aerosol-generating article and an aerosol-generating article comprising said filter.

[0002] Conventional aerosol-generating articles such as filter cigarettes typically comprise a cylindrical rod of shredded tobacco filler surrounded by a paper wrapper and a cylindrical filter axially aligned with the wrapped tobacco rod and most often in end-to-end relationship. The cylindrical filter typically comprises one or more filter segments of fibrous filter material such as a tow of cellulose acetate defined by a paper filter segment wrapper. Conventionally, the wrapped tobacco rod and the filter are joined by a tipping wrapper tape which is typically made of an opaque paper material which defines the entire length of the filter and an adjacent portion of the wrapped tobacco rod.

[0003] Aerosol-generating articles in which an aerosol-generating substrate such as a tobacco-containing substrate is heated rather than burned are also known in the art. Typically in such articles, an aerosol is generated by transferring heat from a heat source to a physically separated aerosol-generating substrate or material.

[0004] By way of example, aerosol-generating articles in which an aerosol is generated by electrical heating of an aerosol-generating substrate have been proposed. Many prior art documents disclose aerosol-generating devices for consuming aerosol-generating articles. Such devices include, for example, electrically heated aerosol-generating devices in which an aerosol is generated by transferring heat from one or more electrical heater elements of the aerosol-generating device to an aerosol-generating substrate of a heated aerosol-generating article. As another example, aerosol-generating articles are also known in which an aerosol is generated by transferring heat from a combustible fuel element or heat source to an aerosol-generating substrate. The combustible fuel element or heat source may be positioned in contact with, within, around or downstream of the aerosol-generating substrate.

[0005] During use of one such aerosol-generating article, volatile compounds are released from the aerosol-generating substrate by heat transfer and entrained in the air drawn through the aerosol-generating article. When the released compounds cool, the compounds condense to form an aerosol.

[0006] Typically, aerosol-generating articles of the type may include a mouthpiece comprising a porous filter material such as cellulose acetate. In some known aerosol-generating articles, a hollow tubular section formed of a filter material such as cellulose acetate is provided at a position between the aerosol-generating substrate and the mouth end of the article to impart structural strength to the article.

[0007] The most commonly used filter material, cellulose acetate, provides a relatively high filtration efficiency and a cellulose acetate tow filter provides effective filtration of mainstream smoke generated from an aerosol - forming substrate. However, it has also been found that cellulose acetate provides a relatively high level of absorption and capture of water from mainstream smoke. The mainstream smoke delivered to the consumer thus has a significantly reduced moisture content and may in some cases be considered undesirably "dry". This can have an adverse effect on the overall smoking experience.

[0008] Cellulose acetate and many other commonly used filter materials are not highly biodegradable. However, alternative dispersible or degradable materials often fail to provide acceptable filtration efficiency and consumer smoking experience. In addition, many known dispersible and degradable materials are not suitable for existing manufacturing processes and require significant modification of existing methods and equipment to make their use commercially viable.

[0009] There is a desire to provide a new and improved aerosol - generating article that has enhanced biodegradability compared to known articles that include conventional filter materials such as cellulose acetate. In particular, there is a desire to provide such a new aerosol - generating article that provides an improved smoking experience to the consumer. For example, there is a desire to provide an aerosol - generating article that can reduce the "dry" smoke effect that is common in articles that include cellulose acetate as a filter material, as described above. There is also a desire to provide such an aerosol - generating article in which the draw resistance (RTD) of the filter material segment can be adjusted to obtain an overall acceptable RTD for the article. In addition, there is a desire to provide such an aerosol - generating article that can be effectively produced by an automated high - speed manufacturing process without significant modification of existing equipment.

[0010] The present disclosure relates to an aerosol - generating article for generating an inhalable aerosol upon heating or combustion. The aerosol - generating article may include a strip of an aerosol - forming substrate and a filter segment axially aligned with the strip. The filter segment may include a filter material formed from a plurality of fibers, the plurality of fibers comprising a polyhydroxyalkanoate (PHA) compound. The fibers comprising the PHA compound may provide a total external surface area of from 0.12 square meters per gram to about 0.28 square meters per gram within the filter segment.

[0011] In addition, the present disclosure relates to a filter for an aerosol - generating article. The filter may include at least one filter segment of a filter material. The filter segment may include a filter material formed from a plurality of fibers, the plurality of fibers comprising a polyhydroxyalkanoate (PHA) compound. The fibers comprising the PHA compound may provide a total external surface area of from 0.12 square meters per gram to about 0.28 square meters per gram within the filter segment.

[0012] According to the present invention, there is provided an aerosol-generating article comprising an aerosol-generating substrate and a filter axially aligned with the aerosol-generating substrate, the filter comprising at least one filter segment of filter material, the filter material comprising a plurality of fibres, the plurality of fibres comprising a polyhydroxyalkanoate (PHA) compound. The fibres comprising the polyhydroxyalkanoate compound provide a total external surface area of from about 0.12 square metres per gram to about 0.28 square metres per gram within the filter segment.

[0013] According to the present invention, there is also provided a filter comprising at least one filter segment of filter material, the filter material comprising a plurality of fibres, the plurality of fibres comprising a polyhydroxyalkanoate (PHA) compound. The fibres comprising the polyhydroxyalkanoate compound provide a total external surface area of from about 0.12 square metres per gram to about 0.28 square metres per gram within the filter segment.

[0014] The term "aerosol-generating article" is used herein in the context of the present invention to describe an article in which an aerosol-generating substrate is heated or combusted to produce an aerosol and deliver the aerosol to a consumer. As used herein, the term "aerosol-generating substrate" denotes a substrate capable of releasing volatile compounds upon heating or combustion to generate an aerosol.

[0015] When a user applies a flame to one end of a cigarette and draws air through the other end, a conventional cigarette will be lit. The local heat provided by the flame and the oxygen in the air drawn through the cigarette causes the end of the cigarette to be ignited, and the resulting combustion generates inhalable smoke. In contrast, in a heated aerosol-generating article, an aerosol is generated by heating a flavour-generating substrate such as a tobacco-based substrate or a substrate containing an aerosol former and a flavourant. Known heated aerosol-generating articles include, for example, electrically heated aerosol-generating articles and aerosol-generating articles in which an aerosol is generated by heat transfer from a combustible fuel element or heat source to a physically separate aerosol-forming material.

[0016] The filter of the present invention can be used as a filter for a mouthpiece in a heated aerosol-generating article in which an aerosol-generating substrate is heated to generate an aerosol without combusting the substrate. However, the filter of the present invention is also suitable for use as a filter for a combustible smoking article in which an aerosol-generating substrate is combusted during use to generate smoke.

[0017] As used herein, the term "aerosol - forming substrate" describes a substrate that is capable of releasing volatile compounds upon heating (including combustion), which volatile compounds can form an aerosol. The aerosol formed from the aerosol - forming substrate can be visible or invisible and can include vapors (e.g., fine particulate matter in the gaseous state, which is usually liquid or solid at room temperature) as well as liquid droplets of gas and condensed vapors. As used herein, the term "aerosol" encompasses the aerosol produced when the substrate in a heated aerosol - generating article is heated and the smoke produced when the substrate in a combustible smoking article is burned.

[0018] As defined above, the present invention provides a filter for an aerosol - generating article, the filter comprising at least one filter segment, the filter segment comprising a filter material formed from a plurality of fibers, the plurality of fibers comprising a PHA compound and having a total external surface area of from 0.12 m² / g to 0.28 m² / g within the filter segment. The PHA - containing fibers are hereinafter referred to as "PHA fibers". A filter segment comprising a plurality of PHA - containing fibers is hereinafter referred to as a "PHA filter segment".

[0019] PHA is a polyhydroxyester of 3 -, 4 -, 5 - and 6 - hydroxyalkanoic acids, which is produced by a variety of bacterial species under nutrient - limiting conditions with an excess of carbon and exists as discrete cytoplasmic inclusions within bacterial cells. PHA molecules typically consist of from 600 to 35,000 (R) - hydroxy fatty acid monomer units. Depending on the total number of carbon atoms within the PHA monomer, PHA can be classified as short - chain - length PHA (scl - PHA; 3 to 5 carbon atoms), medium - chain - length PHA (mcl - PHA; 6 to 14 carbon atoms) or long - chain - length PHA (lcl - PHA; 15 or more carbon atoms).

[0020] Compared to fibers of other filter materials such as cellulose acetate of equal weight, PHA fibers have lower hydrophilicity. Thus, in the aerosol - generating article of the present invention, it has been found that the tendency of the filter segment to absorb water / vapor from the aerosol generated from the aerosol - forming substrate during use is significantly reduced. As a result, the water content in the aerosol can be advantageously maintained at a higher level. This directly addresses the "dry smoke" problem often encountered with conventional smoking articles and provides an improved smoking experience for consumers.

[0021] Since PHA fibers have a much higher level of biodegradability compared to fibers of other filter materials such as cellulose acetate, the articles according to the present invention are more biodegradable overall. At the same time, since PHA fibers are obtained through a natural fermentation process, the aerosol - generating articles according to the present invention also provide improved sustainability for the production process.

[0022] Filters formed from PHA fibers have also been found to provide good filter hardness, which can be further enhanced by packaging the filter segment with a hard mouthpiece segment.

[0023] According to the present invention, the PHA filter segment is formed from PHA fibers that are arranged to provide a total external surface area of from 0.12 m² / g to 0.28 m² / g.

[0024] The total external surface area of the PHA fibers within the PHA filter segment is thus at least about 0.12 m² / g. Preferably, the total external surface area of the PHA fibers within the PHA filter segment is at least about 0.13 m² / g, more preferably at least about 0.14 m² / g, and even more preferably at least about 0.15 m² / g.

[0025] Additionally, the total external surface area of the PHA fibers within the PHA filter segment is not greater than about 0.28 m² / g. Preferably, the total external surface area of the PHA fibers within the PHA filter segment is not greater than about 0.27 m² / g, more preferably not greater than about 0.26 m² / g, and even more preferably not greater than about 0.25 m² / g.

[0026] This defined range of total external surface area has been found to provide an optimal balance between controlling and reducing the water absorption level of the PHA filter segment while maintaining an acceptable draw resistance (RTD) level of the PHA filter segment. The PHA filter segment of the present invention is thus highly versatile as it is suitable for use both in combustible smoking articles and in heated aerosol generation articles. This enables the use of the same manufacturing equipment and techniques for the manufacture of filter segments for various types of aerosol generation articles since the same filter material is suitable for multiple uses. Thus, the manufacture of the filter segment can be carried out in a more efficient manner.

[0027] The RTD level provided by the PHA filter segment can be low enough such that the PHA filter segment can be used in heated aerosol generation articles where a relatively low RTD level is preferred. The level of RTD is also low enough such that a relatively long PHA filter segment can be provided without adversely affecting the overall RTD, such as in combustible smoking articles.

[0028] Most of the external surfaces of the PHA fibers within the PHA filter segment are typically exposed and will thus come into contact with the aerosol as the aerosol generated by the aerosol - generating substrate passes through the PHA filter segment during use. Thus, the total external surface area of the PHA fibers will affect the filtration of the aerosol as the aerosol passes through the PHA filter segment. Subsequently, the sensory properties of the aerosol can thus be controlled by varying the total external surface area of the PHA fibers.

[0029] For example, by increasing the total external surface area within a defined range, it may be possible to control the absorption and retention of certain aerosol components such as water. This can advantageously improve the sensory properties of the aerosol delivered to the consumer from the aerosol-generating substrate. As discussed above, selecting the total external surface area of the PHA fibers within a defined range enables the provision of a PHA filter segment that can reduce the water absorption level of the filter segment compared to a corresponding cellulose acetate tow segment. This may be beneficial for combustible smoking articles where it is desired to reduce the absorption of water from the mainstream smoke to reduce the "dry smoke" effect. This may also be beneficial for heated aerosol-generating articles where the aerosol-generating substrate is heated during use to generate an aerosol. For example, in cases where the aerosol-generating substrate is heated at a relatively low temperature, or where a high water content aerosol is desired, it may be advantageous to have a reduced water adsorption level provided by the PHA filter segment.

[0030] Advantageously, the water absorption level provided by the PHA filter segment of the present invention enables an acceptable smoking experience to be provided for most different types of aerosol-generating articles.

[0031] The total external surface area of the PHA fibers within the PHA filter segment can be varied within a defined range by controlling at least one of the cross-sectional dimensions, cross-sectional shape, and number of the PHA fibers.

[0032] The PHA fibers can have a substantially circular cross-section. In such an embodiment, the total external surface area of the PHA fibers within the filter segment is preferably between about 0.12 square meters per gram and about 0.16 square meters per gram.

[0033] The PHA fibers can have a Y-shaped cross-section. In such an embodiment, the total external surface area of the PHA fibers within the filter segment is preferably between about 0.21 square meters per gram and about 0.28 square meters per gram.

[0034] Preferably, the PHA fibers have a monofilament denier (dpf) of about 3.2 to about 5.0. The monofilament denier, corresponding to the average denier of each individual PHA fiber within the filter, is the weight in grams of a single fiber or filament having a length of 9000 meters. In the present invention, the value of the dpf thus gives an indication of the thickness of each individual PHA fiber within the filter segment. The monofilament denier is expressed in denier, where 1 denier corresponds to 1 gram / 9000 meters. The dpf of a filter or filter segment can be readily determined based on measurements of the weight and length of a representative fiber sample from the filter or filter segment.

[0035] The monofilament denier (dpf) of the PHA fibers is thus preferably at least about 3.2. Preferably, the dpf is at least about 3.3, more preferably at least about 3.4, more preferably at least about 3.5, more preferably at least about 3.6, more preferably at least about 3.7.

[0036] The denier per filament (dpf) of the PHA fibers is preferably no greater than about 5.0. Preferably, the dpf is no greater than about 4.9, more preferably no greater than about 4.8, more preferably no greater than about 4.7, more preferably no greater than about 4.6, and more preferably no greater than about 4.5.

[0037] In some embodiments, the denier per filament can be between about 3.3 and about 4.9, or between about 3.4 and about 4.8, or between about 3.5 and about 4.7, or between about 3.6 and about 4.6, or between about 3.7 and about 4.5.

[0038] In other embodiments, the denier per filament can be between about 3.2 and about 4.2, or between about 3.2 and about 4.0, or between about 3.2 and about 3.8, or between about 3.2 and about 3.6, or be about 3.4.

[0039] In other embodiments, the denier per filament can be between about 4.0 and about 5.0, or between about 4.2 and about 5.0, or between about 4.4 and about 5.0.

[0040] Preferably, the total denier of the filter material including the PHA fibers is between about 20,000 and about 50,000, more preferably between about 25,000 and about 40,000, and more preferably between about 30,000 and about 40,000. The "total denier" of the filter material defines the total weight in grams of 9000 meters of the combined fibers forming the filter material. The total denier of the filter segment thus corresponds to the denier per filament multiplied by the total number of fibers in the filter segment.

[0041] The PHA fibers provided within the filter of the aerosol - generating article according to the present invention can be formed from any suitable PHA compound, including PHA polymers or copolymers. Suitable PHA compounds include, but are not limited to: polyhydroxypropionate, polyhydroxyvalerate, polyhydroxybutyrate, polyhydroxyhexanoate, and polyhydroxyoctanoate. In a particularly preferred embodiment, the PHA compound is poly(3 - hydroxybutyrate).

[0042] The PHA filter segment preferably contains at least about 5 wt% of PHA fibers, more preferably at least about 10 wt% of PHA fibers, more preferably at least about 20 wt% of PHA fibers, more preferably at least about 30 wt% of PHA fibers, more preferably at least about 40 wt% of PHA fibers, more preferably at least about 50 wt% of PHA fibers, more preferably at least about 60 wt% of PHA fibers, more preferably at least about 70 wt% of PHA fibers, more preferably at least about 80 wt% of PHA fibers, more preferably at least about 90 wt% of PHA fibers, and more preferably at least about 95 wt% of PHA fibers.

[0043] The remainder of the fibers within the PHA filter segment can comprise any suitable material. Suitable fiber materials will be known to the person skilled in the art and include but are not limited to polylactic acid (PLA) and cellulose acetate.

[0044] The PHA filter segment is thus formed from a relatively high content of PHA fibers. This provides enhanced biodegradability of the filter and the aerosol-generating article as a whole. As previously mentioned, it has been found that it is technically challenging to form a filter segment with a high proportion of degradable polymer that provides acceptable filtration properties. However, the inventors have surprisingly found that a filter segment incorporating a relatively high PHA fiber content can be produced that provides a desired level of filtration properties such as filtration efficiency and draw resistance.

[0045] The PHA fibers of the filter according to the invention can be produced using any suitable method. Suitable techniques for manufacturing PHA fibers will be known to the person skilled in the art and include but are not limited to melt spinning, gel spinning, and electrospinning. Preferably, the PHA fibers are produced by melt spinning. Melt spinning is often considered the most economical spinning process as it does not require the recovery or evaporation of solvents, in stark contrast to solution spinning. Additionally, the spinning rate using melt spinning is typically quite high, which is advantageous in terms of overall productivity and manufacturing efficiency.

[0046] The PHA fibers can optionally be crimped in the same manner as the cellulose acetate fibers in existing filter segments.

[0047] The PHA filter segment can be formed from a fibrous filter material consisting only of PHA fibers. However, in certain preferred embodiments of the present invention, the PHA fibers can be combined with fibers of one or more additional biodegradable polymers to form the filter segment. For example, the filter segment preferably comprises at least about 5 wt% of at least one biodegradable polymer selected from the group consisting of: starch, polybutylene succinate (PBS), poly(butylene adipate-co-terephthalate) (PBAT), thermoplastic starch and thermoplastic starch blends (TPS), polycaprolactone (PCL), polyglycolic acid (PGA), polyvinyl alcohol (PVOH / PVA), viscose, regenerated cellulose, polysaccharides, cellulose acetate with a degree of substitution (DS) less than 2.1, polyamides, protein-based biopolymers, chitosan-chitin-based biopolymers, and combinations thereof. The inventors have found that including one or more of these components in the blend of fibrous materials from which the filter segment is formed also helps to enhance the biodegradability of the filter segment and the aerosol-generating article as a whole.

[0048] In a preferred embodiment, the PHA filter segment comprises at least about 10% by weight of one such additional biodegradable polymer. More preferably, the PHA filter segment comprises at least about 11%, or at least 12% by weight, or at least 13% by weight, or at least 14% by weight of the additional biodegradable polymer. Even more preferably, the PHA filter segment comprises at least about 15% by weight of one such additional biodegradable polymer.

[0049] The inventors have found that including one or more of these components in the blend of fibrous materials from which the filter segment is formed also helps to enhance the biodegradability of the filter segment and the aerosol generating article as a whole.

[0050] Additionally, while it has previously been found to be technically challenging to manufacture PHA-containing filaments or fibers using existing techniques and equipment, the inventors have surprisingly found that when PHA is incorporated into the blend as described above, filaments or fibers incorporating a high content of PHA can be produced because this makes it easier to form filaments by spinning techniques.

[0051] In a particularly preferred embodiment, the at least one biodegradable polymer is one or more of PBAT, PCL, and PBS. Without wishing to be bound by theory, the inventors have found that the use of one or more of these selected biodegradable polymers will help to improve the mechanical, thermal, and morphological properties of the polymer blend. In particular, it has been found that the combined use of PBAT and PBS provides particularly well-balanced mechanical properties, especially with respect to tensile strength and elongation.

[0052] PHA fibers can be formed from PHA compounds alone or can be formed in combination with one or more other polymers such as polylactic acid (PLA). PHA fibers are thus formed from a polymer blend comprising PHA compounds.

[0053] The PHA filter segment preferably comprises at least about 5% by weight of PHA compounds, more preferably at least about 10% by weight of PHA compounds, more preferably at least about 20% by weight of PHA compounds, more preferably at least about 30% by weight of PHA compounds, more preferably at least about 40% by weight of PHA compounds, more preferably at least about 50% by weight of PHA compounds, more preferably at least about 60% by weight of PHA compounds, more preferably at least about 70% by weight of PHA compounds, more preferably at least about 80% by weight of PHA compounds, more preferably at least about 90% by weight of PHA compounds, more preferably at least about 95% by weight of PHA compounds.

[0054] The PHA filter segment of the aerosol-generating article according to the present invention preferably further comprises an additive for reducing certain smoke components in the aerosol generated from the aerosol-generating substrate. For example, the PHA filter segment preferably further comprises an additive for reducing phenol and phenol derivatives. Suitable additives will be known to the person skilled in the art and include, but are not limited to: polyethylene glycol (PEG), triacetin, triethyl citrate, cellulose acetate flakes or combinations thereof.

[0055] Preferably, the filter segment comprises from about 3% to about 15% by weight of the additive, more preferably from about 5% to about 9% by weight of the additive.

[0056] In certain preferred embodiments of the present invention, the PHA filter segment comprises polyethylene glycol, such as PEG 400. The combination of PHA fibers with an additive such as PEG for reducing phenolic compounds from the aerosol generated from the aerosol-generating substrate has been found to be particularly effective. PHA fibers generally provide good filtration efficiency for undesirable smoke components, but are less effective in removing phenolic compounds. By introducing a compound that will specifically reduce the level of phenolic compounds in the aerosol generated from the aerosol-generating substrate, the filtration capacity of the filter comprising PHA fibers according to the present invention can be further optimized. This in turn will improve the sensory properties of the aerosol delivered to the consumer.

[0057] In a particularly preferred embodiment, based on the total weight of the filter material, the PHA filter segment further comprises at least about 5% by weight of polyethylene glycol. Preferably, based on the total weight of the filter material, the filter segment comprises no more than 10% by weight of polyethylene glycol.

[0058] In other preferred embodiments of the present invention, the PHA filter segment further comprises a mixture of cellulose acetate and triacetin. Preferably, the mixture comprises at least 90% by weight of triacetin and at most 10% by weight of cellulose acetate. The mixture can be formed by adding cellulose acetate flakes to triacetin to form a solution. The solution can then be sprayed onto the PHA fibers in the PHA filter segment. This combination has been found to advantageously replicate the combined effect of triacetin and cellulose acetate fibers in the filter of a conventional cigarette.

[0059] As mentioned above, it has been found that due to the lower affinity of PHA fibers for water, PHA fibers absorb less water from the aerosol generated from the aerosol-generating substrate than an equal amount of cellulose acetate fibers. As demonstrated in the examples below, the amount of water absorbed by the PHA filter segment is significantly lower than the amount of water absorbed by a comparative filter segment formed from an equal weight of cellulose acetate fibers.

[0060] For example, when exposed to water in liquid form, the PHA filter segment of the present invention preferably absorbs less than half the amount of water absorbed by a corresponding filter segment formed from cellulose acetate fibers under the same conditions.

[0061] Compared to cellulose acetate, the reduced water absorption by PHA fibers in the filters of the present invention results in a higher water content in the aerosol delivered from the aerosol-generating article during use.

[0062] For example, the amount of water in the aerosol collected during smoking of a combustible smoking article comprising a filter with PHA fibers according to the present invention is at least 10% higher and preferably at least 15% higher than the amount of water in the aerosol collected during smoking of a corresponding combustible smoking article with a filter segment of cellulose acetate tow under the same conditions.

[0063] An aerosol-generating article comprising a filter containing a PHA filter segment is thus able to deliver an aerosol with a higher moisture level, which is more sensorially acceptable to the consumer. In particular, the "dry smoke" effect that may be experienced during smoking of an aerosol-generating article with a conventional cellulose acetate filter can be advantageously reduced.

[0064] The PHA filter segment of the aerosol-generating article according to the present invention can be advantageously adjusted to provide a desired level of draw resistance (RTD). For some aerosol-generating articles, such as heated aerosol-generating articles having an aerosol-generating substrate that generates an aerosol by heating rather than combustion, it may be desirable to provide a relatively low RTD for the PHA filter segment. This may be the case when a relatively low filtration efficiency is desired. Alternatively, in cases where a relatively long filter or mouthpiece is required, for example, if the aerosol-generating substrate is relatively short, a low RTD may be needed. For example, a low RTD can be achieved by using PHA fibers having a dpf value within the upper part of a defined range, which have a relatively large size.

[0065] For alternative aerosol-generating articles, such as combustible articles, it may be more preferable to provide a higher RTD for the PHA filter segment to increase the filtration efficiency.

[0066] Preferably, in the aerosol - generating article according to the present invention, for a 27 - millimeter filter segment, the RTD of the PHA filter segment is at least about 30 millimeters of water column. More preferably, for a 27 - millimeter filter segment, the RTD of the PHA filter segment is at least about 35 millimeters of water column, and even more preferably at least about 40 millimeters of water column. Even more preferably, in the aerosol - generating article according to the present invention, for a 27 - millimeter filter segment, the RTD of the PHA filter segment is at least about 45 millimeters of water column, and even more preferably at least about 50 millimeters of water column. For a 27 - millimeter filter segment, the RTD of the PHA filter segment is preferably not more than about 150 millimeters of water column, more preferably not more than 125 millimeters of water column, and even more preferably not more than about 100 millimeters of water column. For example, for a 27 - millimeter filter segment, the RTD of the PHA filter segment can be between about 30 millimeters of water column and about 150 millimeters of water column, or between about 35 millimeters of water column and about 150 millimeters of water column, or between about 40 millimeters of water column and about 125 millimeters of water column, or between about 45 millimeters of water column and about 100 millimeters of water column, or between about 50 millimeters of water column and about 100 millimeters of water column.

[0067] In certain preferred embodiments of the present invention, the PHA filter segment has an RTD of at least about 60 millimeters of water column (based on the length of the PHA filter segment in the article). More preferably, the RTD of the PHA filter segment is at least about 65 millimeters of water column, and even more preferably at least about 70 millimeters of water column. Even more preferably, in the aerosol - generating article according to the present invention, the RTD of the PHA filter segment is at least about 75 millimeters of water column, and even more preferably at least about 80 millimeters of water column. The RTD of the PHA filter segment (based on the length of the PHA filter segment in the article) is preferably not more than about 120 millimeters of water column, more preferably not more than about 110 millimeters of water column, and even more preferably not more than about 100 millimeters of water column. For example, the RTD of the PHA filter segment can be between about 60 millimeters of water column and about 120 millimeters of water column, or between about 65 millimeters of water column and about 120 millimeters of water column, or between about 70 millimeters of water column and about 110 millimeters of water column, or between about 75 millimeters of water column and about 110 millimeters of water column, or between about 80 millimeters of water column and about 100 millimeters of water column, or be about 90 millimeters of water column. Such ranges may be particularly suitable for combustible smoking articles.

[0068] In other preferred embodiments of the present invention, the PHA filter segment has an RTD (based on the length of the PHA filter segment in the article) of at least about 10 millimeters of water column. More preferably, the RTD of the PHA filter segment is at least about 12 millimeters of water column, even more preferably at least about 15 millimeters of water column. Even more preferably, in an aerosol-generating article according to the present invention, the RTD of the PHA filter segment is at least about 18 millimeters of water column, more preferably at least about 20 millimeters of water column. The RTD (based on the length of the PHA filter segment in the article) of the PHA filter segment preferably does not exceed about 40 millimeters of water column, more preferably does not exceed about 35 millimeters of water column, even more preferably does not exceed about 30 millimeters of water column. For example, the RTD of the PHA filter segment can be between about 10 millimeters of water column and about 40 millimeters of water column, or between about 12 millimeters of water column and about 40 millimeters of water column, or between about 15 millimeters of water column and about 35 millimeters of water column, or between about 20 millimeters of water column and about 30 millimeters of water column, or be about 27 millimeters of water column. Such ranges may be particularly suitable for heated aerosol-generating articles in which the aerosol-generating substrate is heated rather than burned to produce an aerosol.

[0069] "Draw resistance" means the static pressure difference between the two ends of a sample when air flows across the sample under steady conditions with a volume flow rate of 17.5 milliliters per second at the output end. The RTD of the sample can be measured using the method described in ISO standard 6565:2002.

[0070] It has also been found that the PHA filter segment of an aerosol-generating article according to the present invention provides good stability in terms of RTD, which means that high variability of the RTD can be advantageously avoided. For example, within a sample of 20 aerosol-generating articles according to the present invention, the standard deviation from the target RTD is typically between 2% and 10%, more preferably between 2% and 5%.

[0071] Preferably, the PHA filter segment of an aerosol-generating article according to the present invention has an average radial hardness of at least 80%, more preferably at least 85%. The PHA filter segment can thus provide a desired level of filter hardness, comparable to that provided by conventional cellulose acetate tow filters. If desired, the radial hardness of the PHA filter segment can be further increased by packaging it with a hard filter segment, for example, a filter segment packaging with a basis weight of at least about 80 grams per square meter (gsm), or at least about 100 gsm, or at least about 110 gsm.

[0072] As used herein, the term "radial hardness" refers to the compression resistance in a direction transverse to the longitudinal axis. The radial hardness of an aerosol-generating article around a filter can be determined by applying a load to the article at a position across the filter transverse to the longitudinal axis of the article and measuring the average (mean) indentation diameter of the article. The radial hardness is given by the following formula:

[0073]

[0074] where D S is the original (non-indentation) diameter, and D d is the indentation diameter after applying a set load for a set duration. The harder the material, the closer the hardness is to 100%.

[0075] To determine the hardness of a part of an aerosol article, such as a filter, the aerosol-generating articles should be aligned parallel in a plane, and the same part of each aerosol-generating article to be tested should be subjected to a set load for a set duration. This test is performed using a known DD60A densitometer device (manufactured by Heinr. Borgwaldt GmbH, Germany and commercially available), which is equipped with a measuring head for aerosol-generating articles (such as cigarettes) and an aerosol-generating article container.

[0076] Two load-applying cylindrical rods are used to apply the load, which extend across the diameter of all aerosol-generating articles simultaneously. According to the standard test method of this instrument, the test should be performed such that twenty contact points occur between the aerosol-generating article and the load-applying cylindrical rods. In some cases, the filter to be tested may be long enough such that only ten aerosol-generating articles are needed to form twenty contact points, where each smoking article contacts two load-applying rods (since they are long enough to extend between these rods). In other cases, if the filter is too short to achieve this, then twenty aerosol-generating articles should be used to form twenty contact points, where each aerosol-generating article contacts only one of the load-applying rods, as discussed further below.

[0077] Two additional fixed cylindrical rods are located under the aerosol-generating articles to support the aerosol-generating articles and counteract the load applied by each of these load-applying cylindrical rods.

[0078] For the standard operating procedure for such a device, a total load of 2 kg is applied for a duration of 20 seconds. After 20 seconds have elapsed (and while the load is still applied to the smoking article), the indentation in the load-applying cylindrical rod is determined and then used to calculate the hardness according to the above formula. The temperature is maintained in the region of 22 degrees Celsius ± 2 degrees. The above test is referred to as the DD60A test. The standard way to measure the filter hardness is when the aerosol-generating article has not been consumed. Additional information regarding the measurement of the average radial hardness can be found, for example, in U.S. Patent Application Publication No. 2016 / 0128378.

[0079] As described above, compared to conventional cellulose acetate filters, using PHA fibers to produce the filter segment of the aerosol-generating article according to the present invention will advantageously provide improved biodegradability.

[0080] Preferably, when measured by the test method described in ISO 14851 "Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium - Method for measuring the oxygen demand in a closed respirometer (2005)", the biodegradability of the PHA filter segment in an aqueous medium is at least about 45%, more preferably at least about 50%, and most preferably at least about 55%.

[0081] Under the same test conditions, the cellulose acetate filter segment shows a biodegradability of approximately 30%. Thus, it can be seen that using PHA fibers instead of cellulose acetate fibers to form the filter segment can significantly improve the biodegradability of the filter segment.

[0082] The size of the PHA filter segment can vary depending on the type of aerosol-generating article into which it is introduced.

[0083] Preferably, the PHA filter segment has a length of at least about 4 mm, more preferably at least about 5 mm, more preferably at least about 7 mm, and most preferably at least about 10 mm.

[0084] Preferably, the PHA filter segment has a length less than or equal to about 30 mm, less than or equal to about 27 mm, more preferably less than or equal to about 25 mm, and most preferably less than or equal to about 20 mm.

[0085] For example, the length of the PHA filter segment is preferably between about 5 millimeters and about 30 millimeters, more preferably between about 10 millimeters and about 30 millimeters, even more preferably between about 15 millimeters and about 30 millimeters, and most preferably between about 20 millimeters and about 30 millimeters. Alternatively, in such an embodiment, the length of the PHA filter segment can be from about 4 millimeters to about 27 millimeters, preferably from about 5 millimeters to about 27 millimeters, more preferably from about 10 millimeters to about 27 millimeters, even more preferably from about 15 millimeters to about 27 millimeters, and most preferably from about 20 millimeters to about 27 millimeters. Or alternatively, in such an embodiment, the length of the PHA filter segment can be from about 4 millimeters to about 25 millimeters, preferably from about 5 millimeters to about 25 millimeters, more preferably from about 10 millimeters to about 25 millimeters, even more preferably from about 15 millimeters to about 30 millimeters, and most preferably from about 20 millimeters to about 25 millimeters.

[0086] For embodiments of the present invention in which the aerosol-generating article is in the form of a combustible smoking article, as described in more detail below, the length of the PHA filter segment is preferably between about 20 millimeters and about 30 millimeters, more preferably between about 25 millimeters and about 30 millimeters, and most preferably about 27 millimeters.

[0087] For an alternative embodiment of the present invention in which the aerosol-generating article is in the form of a heated aerosol-generating article having an aerosol-generating substrate intended to be heated by means of an electric heating means or an integrated heat source, as described in more detail below, the length of the PHA filter segment is preferably between about 5 millimeters and about 15 millimeters, more preferably between about 5 millimeters and about 10 millimeters, and most preferably about 7 millimeters.

[0088] The PHA filter segment preferably has an outer diameter approximately equal to the outer diameter of the aerosol-generating article. Preferably, the filter segment has an outer diameter of at least 5 millimeters. The PHA filter segment can have an outer diameter of from about 5 millimeters to about 12 millimeters, such as from about 5 millimeters to about 10 millimeters or from about 6 millimeters to about 8 millimeters. In a preferred embodiment, the PHA filter segment has an outer diameter within 10% of 7.2 millimeters.

[0089] The shape of the PHA filter segment can also vary according to the desired configuration of the aerosol-generating article. In certain embodiments, the PHA filter segment can be in the form of a solid cylindrical filter tip segment of fibrous filter material comprising PHA fibers. Such a filter segment will thus provide a configuration similar to that of a conventional cellulose acetate tow filter tip segment.

[0090] In an alternative embodiment, the PHA filter segment can be in the form of a hollow tube segment. The hollow tube segment has a larger exposed surface area than a cylindrical filter tip segment of equivalent diameter, which will further improve the biodegradation of the PHA filter segment.

[0091] The hollow tube section preferably has a wall thickness of at least about 0.3 mm. More preferably, the hollow tube section has a wall thickness of at least about 0.4 mm. Even more preferably, the hollow tube section has a wall thickness of at least about 0.5 mm.

[0092] Preferably, the hollow tube section has a wall thickness less than or equal to about 1.9 mm. More preferably, the hollow tube section has a wall thickness less than or equal to about 1.5 mm. Even more preferably, the hollow tube section has a wall thickness less than or equal to about 1.2 mm. Particularly preferably, the hollow tube section has a wall thickness less than or equal to about 0.9 mm.

[0093] In some embodiments, the hollow tube section can generally have a length of at least about 4 mm. Preferably, the length of the hollow tube section is at least about 5 mm. More preferably, the length of the hollow tube section is at least about 7 mm. Even more preferably, the length of the hollow tube section is at least about 10 mm.

[0094] In the case where the PHA filter section is in the form of a hollow tube section, in addition to PHA fibers, the filter material can also contain some cellulose acetate. For example, the hollow tube section can contain about 5% to about 15% cellulose acetate by weight. Without wishing to be bound by theory, it should be understood that a certain amount of cellulose acetate in the hollow tube section can impart the desired filtration properties and mechanical properties to the hollow tube section, as well as facilitate the manufacture of the hollow tube section.

[0095] The filter of the aerosol - generating article according to the present invention can be a single - stage filter consisting only of the PHA filter section. Alternatively, the filter of the aerosol - generating article according to the present invention can further include one or more additional filter sections formed of a filter material, which can be provided upstream or downstream of the PHA filter section as described above. For example, the PHA filter section can be combined with one or more axially - aligned filter tip sections formed of a fibrous filter material, which may or may not include PHA fibers. Alternatively or additionally, the PHA filter section can be combined with one or more tubular elements, such as a hollow acetate tube or a cardboard tube. For example, in certain embodiments, the filter can include a support element in the form of a hollow acetate tube. Alternatively or additionally, the PHA filter section can be combined with an aerosol cooling element.

[0096] Preferably, the additional filter section is formed of a material that is not cellulose acetate. Particularly preferably, the additional filter section includes PHA fibers, which can optionally be held in the desired shape by means of a suitable binder such as PVA. Preferably, each of the additional filter sections contains at least about 25% by weight of a PHA compound, more preferably at least about 50% by weight of a PHA compound.

[0097] The filter of the aerosol-generating article according to the present invention may optionally comprise a flavorant. Various different means may be used to introduce the flavorant, which will be known to the person skilled in the art. For example, the flavorant may be introduced in the form of a capsule, which may be provided in the PHA filter segment or in another filter segment.

[0098] Preferably, the filter of the aerosol-generating article according to the present invention comprises a capsule within the PHA filter segment, wherein the capsule contains an additive for altering the aerosol generated by the aerosol-generating substrate during use. Preferably, the additive is a flavorant. Using PHA fibers with a dpf value in the range of 3.2 to 5.0 means that the PHA fibers can have a relatively large cross-section. This in turn means an increase in the amount of available space between individual fibers compared to filters formed from fibers with a lower dpf value. The PHA filter segment formed from PHA fibers with a dpf within this range is thus particularly suitable for introducing capsules. The capsules can be easily introduced into the PHA filter segment during manufacture. In addition, the capsules will be effectively retained in the desired axial position within the PHA filter segment.

[0099] The filter of the aerosol-generating article according to the present invention is preferably defined by an outer wrapper, for example, the mouthpiece wrapper defining the filter segment, the downstream end of the aerosol-generating substrate, and any additional components that may be provided therebetween. As described in WO-A-2017 / 162838, the mouthpiece wrapper may include a removable mouthpiece wrapper portion. This enables at least a portion of the mouthpiece wrapper to be removed before discarding the aerosol-generating article. Removal of the mouthpiece wrapper will expose the underlying filter segment and can thus advantageously accelerate the biodegradation rate of the filter material.

[0100] As defined above, the aerosol-generating article according to the present invention further comprises an aerosol-generating substrate, which is preferably in the form of a strip of aerosol-generating substrate. Preferably, the aerosol-generating substrate is a strip of tobacco material.

[0101] The aerosol-generating substrate may have a length of from about 5 millimeters to about 100 millimeters. Preferably, the aerosol-generating substrate has a length of at least about 5 millimeters, more preferably at least about 7 millimeters. Additionally, or alternatively, the aerosol-generating substrate preferably has a length of less than about 80 millimeters, more preferably less than about 65 millimeters, even more preferably less than about 50 millimeters. In a particularly preferred embodiment, the aerosol-generating substrate has a length of less than about 35 millimeters, more preferably less than 25 millimeters, even more preferably less than about 20 millimeters. In one embodiment, the aerosol-generating substrate may have a length of about 10 millimeters. In a preferred embodiment, the aerosol-generating substrate has a length of about 12 millimeters.

[0102] In some embodiments, the aerosol-generating article according to the present invention is a filter cigarette or other combustible smoking article, wherein the aerosol-generating matrix comprises tobacco material that is combusted to form a smoke. In any such embodiment, the aerosol-generating matrix may comprise a tobacco rod. The tobacco rod may comprise one or more of cut filler and reconstituted tobacco.

[0103] For embodiments in which the aerosol-generating article is in the form of a combustible smoking article, the aerosol-generating matrix, which is typically a tobacco rod, preferably has a length of from about 10 mm to about 100 mm, more preferably a total length of from about 30 mm to about 70 mm. The tobacco rod may comprise one or more of cut filler and reconstituted tobacco.

[0104] As discussed above, the filter of the present invention comprising a PHA segment may also be applied to heated aerosol-generating articles in which tobacco material is heated rather than combusted to form an aerosol. In one type of heated aerosol-generating article, the tobacco material is heated by one or more electrical heating elements to produce an aerosol. In another type of heated aerosol-generating article, an aerosol is produced by transferring heat from a combustible or chemical heat source to physically separated tobacco material, which may be located within, around, or downstream of the heat source. The present invention also encompasses aerosol-generating articles in which a nicotine-containing aerosol is generated from tobacco material, a tobacco extract, or other nicotine source, for example, by a chemical reaction, without combustion and in some cases without heating.

[0105] For embodiments in which the aerosol-generating article is in the form of a heated aerosol-generating article in which the aerosol-generating matrix is intended to be heated to form an aerosol, the aerosol-generating matrix preferably has a length of from about 5 mm to about 40 mm, more preferably from about 9 mm to about 15 mm.

[0106] For such embodiments in which the aerosol-generating article is in the form of a heated aerosol-generating article, the aerosol-generating matrix is preferably formed from homogenized tobacco material, which is formed by the agglomeration of tobacco particles. The aerosol-generating matrix may comprise one or more sheets of homogenized tobacco material. The one or more sheets may be textured. As used herein, the term "textured sheet" means a sheet that has been curled, embossed, debossed, perforated, or otherwise deformed. Alternatively, the aerosol-generating matrix may comprise a plurality of strips or laminae of homogenized tobacco material. The strips or laminae may be substantially aligned with each other in the longitudinal direction or may be randomly oriented.

[0107] The homogenized tobacco material for use in the aerosol-generating matrix may have a tobacco content of at least about 40% by weight, more preferably at least about 60% by weight, more preferably at least about 70% by weight, and most preferably at least about 90% by weight, based on dry weight.

[0108] The homogenized tobacco material for use in an aerosol - generating substrate may comprise one or more intrinsic binders that are endogenous to tobacco, one or more extrinsic binders that are exogenous to tobacco, or a combination thereof to assist in agglomerating particulate tobacco. Alternatively or additionally, the homogenized tobacco material for use in an aerosol - generating substrate may comprise other additives, including but not limited to tobacco and non - tobacco fibers, aerosol - forming agents, humectants, plasticizers, flavorants, fillers, aqueous and non - aqueous solvents, and combinations thereof.

[0109] Extrinsic binders suitable for inclusion in the homogenized tobacco material for use in an aerosol - generating substrate are known in the art and include but are not limited to: gums such as guar gum, xanthan gum, gum arabic, and locust bean gum; cellulose binders such as hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, and ethyl cellulose; polysaccharides such as starch; organic acids such as alginic acid; conjugate base salts of organic acids such as sodium alginate; agar and pectin; and combinations thereof.

[0110] Non - tobacco fibers suitable for inclusion in the homogenized tobacco material for use in an aerosol - generating substrate are known in the art and include but are not limited to: cellulose fibers; softwood fibers; hardwood fibers; jute fibers; and combinations thereof. Prior to inclusion in the homogenized tobacco material for use in an aerosol - generating substrate, the non - tobacco fibers may be treated by suitable methods known in the art, including but not limited to: mechanical pulping; refining; chemical pulping; bleaching; sulfate pulping; and combinations thereof.

[0111] An aerosol - generating substrate for a heated aerosol - generating article typically includes an “aerosol - forming agent”, i.e., a compound or mixture of compounds that will promote aerosol formation during use and preferably substantially resist thermal degradation at the operating temperature of the aerosol - generating article. Examples of suitable aerosol - forming agents include: polyols such as propylene glycol, triethylene glycol, 1,3 - butanediol, and glycerol; esters of polyols such as glycerol monoacetate, glycerol diacetate, or glycerol triacetate; and aliphatic esters of mono -, di -, or poly - carboxylic acids such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Preferred aerosol - forming agents are polyols or mixtures thereof such as propylene glycol, triethylene glycol, 1,3 - butanediol, and most preferably glycerol.

[0112] Preferably, the aerosol - forming substrate comprises at least 10% by weight of an aerosol - forming agent, more preferably at least 12% by weight of an aerosol - forming agent, and even more preferably at least about 15% by weight of an aerosol - forming agent. Alternatively or additionally, the aerosol - forming substrate preferably comprises no more than 30% by weight of an aerosol - forming agent, more preferably no more than about 25% by weight of an aerosol - forming agent, and even more preferably no more than about 20% by weight of an aerosol - forming agent. For example, the aerosol - forming substrate may comprise from about 10% to about 30% by weight of an aerosol - forming agent, or from about 12% to about 25% by weight of an aerosol - forming agent, or from about 15% to about 20% by weight of an aerosol - forming agent. In a particularly preferred embodiment, the aerosol - forming substrate comprises about 18% by weight of an aerosol - forming agent.

[0113] The aerosol - generating article according to the present invention may also include one or more additional components between the filter and the aerosol - forming substrate. For example, the aerosol - generating article may further include one or more of the following: a support element, an aerosol - cooling element, and a transfer element. The construction of such components will be known to those skilled in the art.

[0114] For example, in certain preferred embodiments of the present invention, the aerosol - generating article is arranged in a linear sequence to include: an aerosol - forming substrate, a support element immediately downstream of the aerosol - forming substrate, an aerosol - cooling element located immediately downstream of the support element, and a mouthpiece including a PHA filter section at the downstream end of the filter.

[0115] In other preferred embodiments of the present invention, the aerosol - generating article is arranged in a linear sequence to include: an aerosol - forming substrate, a transfer element, an aerosol - cooling element, a spacer element, and a mouthpiece filter.

[0116] In certain preferred embodiments of the present invention, the aerosol - generating article further includes a combustible heat source at the upstream end of the aerosol - generating article, which is in contact with the upstream end of the aerosol - forming substrate. For example, the aerosol - generating article may include a carbonaceous heat source at the upstream end for heating the aerosol - forming substrate during use to generate an aerosol. Suitable carbonaceous heat sources will be known to those skilled in the art.

[0117] The present invention will now be further described with reference to the accompanying drawings, in which:

[0118] Figure 1 A schematic longitudinal cross - sectional view of an aerosol - generating article according to a first embodiment of the present invention, which is to be used with an aerosol - generating device including a heater element, is shown;

[0119] Figure 2 A schematic longitudinal cross - sectional view of an aerosol - generating article according to a second embodiment of the present invention, which includes an integral heat source, is shown; and

[0120] Figure 3 shows a schematic longitudinal cross - sectional view of an aerosol - generating article according to a third embodiment of the present invention; and

[0121] Figure 4 shows a schematic longitudinal cross - sectional view of an aerosol - generating system that includes an electrically - operated aerosol - generating device and Figure 1 the aerosol - generating article shown in [[ ]].

[0122] Figure 1 The aerosol - generating article 10 shown in [[ ]] includes a strip 12 of an aerosol - generating substrate, a support element 14 provided as a hollow tubular element, a cooling element 16, and a mouth - end filter section 18. These four elements are arranged in sequence and axially aligned and are defined by a substrate wrapper 20 to form the aerosol - generating article 10. The aerosol - generating article 10 has a mouth - end 22 and a distal end 24 located at the end of the article opposite the mouth - end 22. Figure 1 The aerosol - generating article 10 shown in [[ ]] is particularly suitable for use with an electrically - operated aerosol - generating device that includes a heater for heating the strip of the aerosol - generating substrate.

[0123] In use, air is drawn by the user from the distal end 24 through the aerosol - generating article to the mouth - end 22. The distal end 24 of the aerosol - generating article can also be described as the upstream end of the aerosol - generating article 10, while the mouth - end 22 of the aerosol - generating article 10 can also be described as the downstream end of the aerosol - generating article 10. The elements of the aerosol - generating article 10 located between the mouth - end 22 and the distal end 24 can be described as upstream of the mouth - end 22, or alternatively as downstream of the distal end 24.

[0124] The aerosol - generating substrate 12 is located at the extreme distal or upstream end of the aerosol - generating article 10. In the Figure 1 embodiment schematically shown in [[ ]], the aerosol - generating substrate 12 includes an aggregated sheet of crimped homogenized tobacco material defined by a wrapper. The crimped sheet of homogenized tobacco material contains glycerol as an aerosol - forming agent.

[0125] The support element 14 is located immediately downstream of the aerosol - generating substrate 12 and adjacent to the aerosol - generating substrate 12. In Figure 1In the embodiment shown, the support element is a hollow tube formed from a fibrous filter material. The support element 14 positions the aerosol - forming substrate 12 at the distal end 24 of the aerosol - generating article 10 such that it can be penetrated by the heating element of the aerosol - generating device. In fact, the support element 14 is used to prevent the aerosol - forming substrate 16 from being forced towards the aerosol - cooling element 16 within the aerosol - generating article 10 when the heating element of the aerosol - generating device is inserted into the aerosol - forming substrate 12. The support element 14 also serves as a spacer to separate the aerosol - cooling element 16 of the aerosol - generating article 10 from the aerosol - forming substrate 12.

[0126] The aerosol - cooling element 16 is located immediately downstream of the support element 14 and abuts the support element 16. In use, the volatile substances released from the aerosol - forming substrate 12 travel along the aerosol - cooling element 16 towards the mouth end 22 of the aerosol - generating article 10. The volatile substances can be cooled within the aerosol - cooling element 16 to form an aerosol inhaled by the user. In Figure 1 In the embodiment schematically shown, the aerosol - cooling element includes a tubular element 20. The crimped and aggregated polylactic acid sheets define a plurality of longitudinal channels extending along the length of the aerosol - cooling element 40.

[0127] The filter segment 18 is located immediately downstream of the aerosol - cooling element 16 and abuts the aerosol - cooling element 16. In Figure 1 In the embodiment schematically shown, the filter segment 18 includes a single cylindrical filter tip segment of fibrous filter material formed from multiple PHA fibers, where the multiple PHA fibers have a denier per filament of approximately 3.4 and a total denier of approximately 34,000. The PHA fibers have a circular cross - sectional shape and are substantially longitudinally aligned with each other along the length of the filter segment. The total external surface area of the PHA fibers is equivalent to approximately 0.16 square meters per gram. The PHA fibers have been formed and crimped by a melt - spinning process. The filter tip segment of the fibrous filter material is defined by a filter tip wrapper (not shown).

[0128] Figure 2 The aerosol - generating article 100 shown includes a combustible heat source 112, a strip 114 of aerosol - forming substrate, a transfer element 116, an aerosol - cooling element 118, a spacer element 120, and a mouthpiece filter segment 122. These elements are arranged in sequence and axially aligned and are defined by a substrate wrapper to form the aerosol - generating article 100.

[0129] The combustible heat source 112 includes a substantially cylindrical carbonaceous material having a length of approximately 10 millimeters. The combustible heat source 112 is a blind heat source. In other words, the combustible heat source 112 does not include any air channels extending through it.

[0130] The strip 114 of the aerosol - forming substrate is arranged at the proximal end of the combustible heat source 112. The aerosol - forming substrate 114 includes a substantially cylindrical rod of tobacco material 124 defined by a filter tip segment wrapper 126.

[0131] The non - combustible, substantially air - impermeable first barrier 128 is arranged between the proximal end of the combustible heat source 112 and the distal end of the aerosol - forming substrate 114. The first barrier 128 includes an aluminum foil disc. The first barrier 128 also forms a heat - conducting member between the combustible heat source 112 and the aerosol - forming substrate 114 to conduct heat from the proximal face of the combustible heat source 112 to the distal face of the aerosol - forming substrate 114.

[0132] The heat - conducting element 130 defines the proximal part of the combustible heat source 112 and the distal part of the aerosol - forming substrate 114. The heat - conducting element 130 includes an aluminum foil tube. The heat - conducting element 130 is in direct contact with the proximal part of the combustible heat source 112 and the filter tip segment wrapper 126 of the aerosol - forming substrate 114.

[0133] The mouthpiece filter 122 includes a single cylindrical filter tip segment 126 of fibrous filter material formed from multiple PHA fibers, where the multiple PHA fibers have a denier per filament of approximately 3.4 and a total denier of approximately 34,000. The PHA fibers have a circular cross - sectional shape and are substantially longitudinally aligned with each other along the length of the filter segment. The exposed surface area of the PHA fibers is equivalent to approximately 0.16 square meters per gram. The PHA fibers have been formed and crimped through a melt - spinning process. The filter tip segment of the fibrous filter material is defined by a filter tip segment wrapper (not shown).

[0134] Figure 3 The aerosol - generating article 310 shown in the figure is a combustible smoking article that includes an aerosol - forming substrate 312 and a filter 314 arranged coaxially with each other. The aerosol - forming substrate 312 includes a tobacco rod defined by an outer wrapper (not shown). The mouthpiece wrapper 316 defines both the filter 314 and the end of the aerosol - forming substrate 312 and attaches the filter 314 to the aerosol - forming substrate 312.

[0135] The filter 314 includes a single cylindrical filter tip segment 318 of fibrous filter material formed from PHA fibers, where the PHA fibers have a denier per filament of approximately 3.4 and a total denier of approximately 34,000. The PHA fibers have a circular cross - sectional shape and are substantially longitudinally aligned with each other along the length of the filter segment. The total outer surface area of the PHA fibers is equivalent to approximately 0.16 square meters per gram. The PHA fibers have been formed and crimped through a melt - spinning process. The filter tip segment of the fibrous filter material is defined by a filter tip segment wrapper (not shown).

[0136] Figure 4shows a part of an electrically operated aerosol generating system 200 that uses a heater blade 210 to heat Figure 1 the strip 12 of the aerosol - forming substrate of the aerosol - forming article 10 shown in Figure 4 . The heater blade 210 is mounted in an aerosol - forming article chamber within the housing of the electrically operated aerosol - generating device 212. The aerosol - generating device 212 defines a plurality of air holes 214 to allow air to flow to the aerosol - forming article 10, as Figure 4 indicated by the arrows in

[0137] Comparative example

[0138] The PHA filter segment according to the present invention is prepared from PHA fibers, and the parameters are shown in Table 1 below. The PHA fibers are formed using a melt - spinning method, and then the fibers are crimped and formed into a filter segment using standard filter manufacturing equipment. For comparison purposes, a conventional cellulose acetate (CA) tow filter segment was prepared, which has a similar denier per filament (dpf) and total denier value.

[0139] Table 1: Parameters of PHA filter segment and cellulose acetate filter segment

[0140] Parameter PHA filter section CA filter section Denier per filament 3.2 3 Total denier 27000 27000 Filter section weight (mg) 406.76 409.76 <![CDATA[External surface area (m 2 / g)]]> 0.161 0.329

[0141] In a first test, the water absorption of the PHA filter segment and the CA filter segment according to the present invention when exposed to water was compared. For each filter segment, the filter tip packaging was removed and the filter segment was attached to the probe of a force tensiometer (KRUSS force tensiometer, model K100). The filter segment was moved downward by the probe towards a container of water and automatically stopped when the filter segment contacted the water. The filter segment was kept in contact with the water for 300 seconds so that the filter material could absorb water, and then the filter segment was weighed to determine the amount of water absorbed during the test. For each of the PHA filter segment and the CA filter segment, this test was repeated three times and the average value of water absorption was calculated, as shown in Table 2 below:

[0142] Table 2: Water absorption of PHA filter segment and CA filter segment after exposure to water

[0143]

[0144] The amount of water absorbed by the PHA filter segment according to the present invention during the test was thus less than 40% of the amount of water absorbed by the CA filter segment. This test thus confirmed that the water affinity of the PHA filter segment according to the present invention is significantly reduced compared to a conventional CA filter segment.

[0145] In a second test, the water absorption of the PHA filter segment and the CA filter segment according to the present invention upon exposure to moisture was compared. For each filter segment, the filter tip segment packaging was removed, the fibers forming the filter segment were placed in a Petri dish, and exposed to air at 22 degrees Celsius and 50% relative humidity for 70 hours. This was carried out in a vapor sorption analyzer (ProUmid SPSx-1μ). For each filter segment, the weight of the fibers was measured at the start of the test, and the weight change over time due to the absorption of water vapor by the fibers was measured. For each of the PHA filter segment and the CA filter segment, the mass percentage difference (%dm) value of the sample was calculated, which represents the increase in the sample weight as a percentage of the initial weight. The %dm values of each sample at the end of the 70-hour test are shown in Table 3 below:

[0146] Table 3: Water absorption of PHA filter segment and CA filter segment after exposure to moisture

[0147]

[0148] The results confirmed that the amount of water vapor absorbed by the cellulose acetate fibers during the 70-hour test was more than 50 times greater than that absorbed by the PHA fibers. During the test, very little water vapor was absorbed by the PHA fibers. This further confirmed that the water affinity of the PHA filter segment according to the present invention was significantly reduced compared to a conventional CA filter segment.

[0149] In a third test, the water absorption from the mainstream smoke of the PHA filter segment according to the present invention and a conventional CA filter segment was compared. For each filter segment, a combustible tobacco rod was combined with a single segment of the filter material forming the filter Figure 3 to prepare a conventional smoking article as described above. Then each smoking article was smoked in a smoking machine under ISO conditions (puff volume 35 ml; puff duration 2 seconds every 60 seconds) as set forth in ISO 3308:2000, and the resulting smoke was analyzed. For each filter segment, the amount of water in the mainstream smoke collected during the smoking test was measured, as shown in Table 4:

[0150] Table 4: Water in the mainstream smoke generated during the smoking test under ISO conditions

[0151] PHA filter section CA filter section Water (mg / cigarette product) 0.82 0.68

[0152] This confirmed that when smoking under the same conditions, the mainstream smoke generated by the smoking article incorporating the PHA filter segment had a water content approximately 20% higher than that from the smoking article including the CA filter segment. This confirmed that the PHA filter segment absorbed less water from the mainstream smoke, thus reducing the potential problem of drying the smoke as described above.

Claims

1. A heated aerosol - generating article, the aerosol - generating article comprising: An aerosol - generating substrate; A filter axially aligned with the aerosol - generating substrate, the filter comprising at least one filter segment of filter material formed from multiple fibers, the multiple fibers comprising a polyhydroxyalkanoate compound, wherein the fibers provide a total external surface area of from 0.12 square meters per gram to 0.28 square meters per gram within the filter segment and wherein the at least one filter segment comprises at least 20% by weight of the polyhydroxyalkanoate compound.

2. The heated aerosol - generating article according to claim 1, wherein the multiple fibers comprising the polyhydroxyalkanoate compound have a circular cross - sectional shape and provide a total external surface area of from 0.12 square meters per gram to 0.16 square meters per gram within the filter segment.

3. The heated aerosol - generating article according to claim 1, wherein the multiple fibers comprising the polyhydroxyalkanoate compound have a Y - shaped cross - sectional shape and provide a total external surface area of from 0.21 square meters per gram to 0.28 square meters per gram within the filter segment.

4. The heated aerosol - generating article according to claim 1 or 2, wherein the fibers comprising the polyhydroxyalkanoate compound have a monofilament denier (dpf) of from 3.2 to 5.

0.

5. The heated aerosol - generating article according to claim 1 or 2, wherein the total denier of the fibers comprising the polyhydroxyalkanoate compound is between 25,000 and 40,000.

6. The heated aerosol - generating article according to claim 1 or 2, wherein the filter material further comprises multiple fibers of at least one additional biodegradable polymer.

7. The heated aerosol - generating article according to claim 1 or 2, wherein the draw - through resistance (RTD) of the filter segment comprising the multiple fibers comprising the polyhydroxyalkanoate compound is between 10 millimeters of water column and 40 millimeters of water column.

8. The heated aerosol - generating article according to claim 1 or 2, wherein when tested according to ISO 14851, the filter segment comprising the multiple fibers comprising the polyhydroxyalkanoate compound has at least 50% biodegradability in an aqueous medium.

9. The heated aerosol - generating article according to claim 1 or 2, wherein the filter segment comprising the multiple fibers comprising the polyhydroxyalkanoate compound further comprises at least 5% by weight of polyethylene glycol.

10. The heated aerosol - generating article according to claim 1 or 2, wherein the filter segment comprising the multiple fibers comprising the polyhydroxyalkanoate compound has an average radial hardness of at least 80%.

11. The heated aerosol - generating article according to claim 1 or 2, wherein the filter segment comprising the multiple fibers comprising the polyhydroxyalkanoate compound is defined by a wrapper having a basis weight of at least 100 grams per square meter (gsm).

12. The heated aerosol-generating article according to claim 1 or 2, wherein the filter section comprising the plurality of fibers comprising the polyhydroxyalkanoate compound is in the form of a hollow tubular element.

13. The heated aerosol-generating article according to claim 1 or 2, wherein the aerosol-generating substrate is a tobacco rod having a length of 5 mm to 15 mm.

14. A filter for a heated aerosol-generating article, the filter comprising at least one filter section of filter material formed from a plurality of fibers comprising a polyhydroxyalkanoate compound, wherein the fibers provide a total external surface area of from 0.12 m² / g to 0.28 m² / g within the filter section and wherein the at least one filter section comprises at least 20% by weight of the polyhydroxyalkanoate compound.

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