CN114760867A

CN114760867A - Aerosol-generating article filter with novel filter material

Info

Publication number: CN114760867A
Application number: CN202080083957.0A
Authority: CN
Inventors: S·帕帕基里罗
Original assignee: Philip Morris Products SA
Current assignee: Philip Morris Products SA
Priority date: 2019-12-03
Filing date: 2020-11-30
Publication date: 2022-07-15
Also published as: KR20220109420A; BR112022010060A2; EP4069005A1; US20220408801A1; WO2021110600A1; JP2023505158A

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) in axial alignment with the aerosol-generating substrate, the filter (18) (122) (314) comprising at least one filter segment (126) (318) of filter material comprising a plurality of fibres comprising a polyhydroxyalkanoate compound, wherein the fibres provide a total external surface area of from 0.12 m/g to 0.28 m/g. The at least one filter section comprises at least 20% by weight of polyhydroxyalkanoate compound.

Description

Aerosol-generating article filter with novel filter material

The present invention relates to a filter for an aerosol-generating article and an aerosol-generating article comprising the filter.

Conventional aerosol-generating articles such as filter cigarettes typically comprise a cylindrical rod of tobacco cut filler surrounded by a paper wrapper and a cylindrical filter axially aligned with, most often in end-to-end relationship with, the wrapped tobacco rod. Cylindrical filters typically comprise one or more filter segments of fibrous filter material, such as cellulose acetate tow, defined by a paper filter segment wrapper. Conventionally, the wrapped tobacco rod and the filter are joined by a tipping wrapper band, typically made of an opaque paper material defining the entire length of the filter and an adjacent portion of the wrapped tobacco rod.

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

For example, aerosol-generating articles have been proposed in which an aerosol is generated by electrical heating of an aerosol-generating substrate. A number of 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 electric 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.

During use of one such aerosol-generating article, volatile compounds are released from the aerosol-generating substrate by heat transfer and entrained in air drawn through the aerosol-generating article. As the released compound cools, the compound condenses to form an aerosol.

Typically, aerosol-generating articles of the type described may comprise a mouthpiece comprising a porous filter material, such as cellulose acetate. In some known aerosol-generating articles, a hollow tubular segment formed from a filtration material, such as cellulose acetate, is provided at a location between the aerosol-generating substrate and the mouth end of the article to impart structural strength to the article.

The most commonly used filter material cellulose acetate may provide relatively high filtration efficiency and cellulose acetate tow filters provide efficient filtration of mainstream smoke generated from an aerosol-generating substrate. However, cellulose acetate has also been found to provide relatively high levels of water absorption and capture from mainstream smoke. Mainstream smoke delivered to consumers therefore has a significantly reduced moisture content and may be considered to be undesirably "dry" in some cases. This may adversely affect the overall smoking experience.

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. Furthermore, many known dispersible and degradable materials are not suitable for use in existing manufacturing processes and require significant modification of existing methods and equipment to make their use commercially viable.

It would be desirable to provide a new and improved aerosol-generating article having enhanced biodegradability compared to known articles comprising conventional filter materials such as cellulose acetate. It is particularly desirable to provide a new aerosol-generating article which provides an improved smoking experience to the consumer. For example, it would be desirable to provide an aerosol-generating article capable of reducing the "dry" smoke effect, which is common with articles comprising cellulose acetate as the filter material, as described above. It would also be desirable to provide an aerosol-generating article in which the Resistance To Draw (RTD) of the length of filter material can be adjusted in order to obtain an RTD that is acceptable for the article as a whole. Furthermore, it would be desirable to provide an aerosol-generating article that can be efficiently produced in an automated high-speed manufacturing process without requiring significant modification of existing equipment.

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

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

According to the present invention, there is provided an aerosol-generating article comprising an aerosol-generating substrate and a filter in axial alignment with the aerosol-generating substrate, the filter comprising at least one filter segment of filter material comprising a plurality of fibres comprising a Polyhydroxyalkanoate (PHA) compound. The fibers comprising the polyhydroxyalkanoate compound provide a total external surface area within the filter section of from about 0.12 m/g to about 0.28 m/g.

In accordance with 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 fibers, the plurality of fibers comprising a Polyhydroxyalkanoate (PHA) compound. The fibers comprising the polyhydroxyalkanoate compound provide a total external surface area within the filter section of from about 0.12 m/g to about 0.28 m/g.

The term "aerosol-generating article" is used herein in connection with 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" refers to a substrate capable of releasing volatile compounds upon heating or combustion to generate an aerosol.

A conventional cigarette will light when a user applies a flame to one end of the cigarette and draws air through the other end. The localized heat provided by the flame and the oxygen in the air drawn through the cigarette causes the end of the cigarette to ignite and the resulting combustion produces inhalable smoke. In contrast, in heated aerosol-generating articles, aerosols are generated by heating a flavour-generating substrate, such as a tobacco-based substrate or a substrate containing an aerosol former and a flavour. 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.

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

As used herein, the term "aerosol-generating substrate" describes a substrate capable of releasing volatile compounds which can form an aerosol when heated (including combustion). The aerosol generated by the aerosol-generating substrate may be visible or invisible and may comprise vapour (e.g. fine particulate matter in the gaseous state, which is typically a liquid or solid at room temperature) as well as liquid droplets of gas and condensed vapour. As used herein, the term "aerosol" encompasses aerosols produced when a substrate is heated in a heated aerosol-generating article and smoke produced when a substrate is combusted in a combustible smoking article.

As defined above, the present invention provides a filter for an aerosol-generating article, the filter comprising at least one filter segment comprising a filter material formed from a plurality of fibers comprising a PHA compound, having a total external surface area within the filter segment of from 0.12 m/g to 0.28 m/g. 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".

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

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

The articles according to the invention are more biodegradable overall, due to the far higher level of biodegradability of the PHA fibers compared to fibers of other filtering materials, such as cellulose acetate. At the same time, the aerosol-generating article according to the invention also provides improved sustainability for the production process, since the PHA fibers are obtained by a natural fermentation process.

It has also been found that filters formed with PHA fibers provide good filter stiffness which can be further enhanced by defining the filter segment with stiff filter segment wrappers.

In accordance with the present invention, the PHA filter segments are formed from PHA fibers arranged to provide a total outer surface area of 0.12 m/g to 0.28 m/g.

The total outer surface area of the PHA fibers within the PHA filter section is therefore at least about 0.12 square meters per gram. Preferably, the total external surface area of the PHA fibers within the PHA filter section is at least about 0.13 square meters per gram, more preferably at least about 0.14 square meters per gram, more preferably at least about 0.15 square meters per gram.

Additionally, the total outer surface area of the PHA fibers within the PHA filter section is no greater than about 0.28 square meters per gram. Preferably, the total external surface area of the PHA fibers within the PHA filter section is no greater than about 0.27 square meters per gram, more preferably no greater than about 0.26 square meters per gram, and more preferably no greater than about 0.25 square meters per gram.

This defined range of total external surface area has been found to provide an optimal balance between controlling and reducing the water uptake level of the PHA filter segment while maintaining an acceptable level of Resistance To Draw (RTD) for the PHA filter segment. The PHA filter segment of the present invention is therefore highly versatile in that it is suitable for use in both combustible smoking articles and heated aerosol-generating articles. This enables the manufacture of filter segments for various types of aerosol-generating articles to be carried out using the same manufacturing equipment and techniques, as the same filter material is suitable for use in a variety of applications. Thus, the manufacture of the filter segment can be performed in a more efficient manner.

The RTD levels provided by the PHA filter segments may be sufficiently low such that the PHA filter segments may be used in heated aerosol-generating articles in which relatively low RTD levels are preferred. The level of RTD is also sufficiently low that relatively long PHA filter segments can be provided without adversely affecting the overall RTD, for example in a combustible smoking article.

Most of the outer surface of the PHA fibers within the PHA filter segment is typically exposed and will therefore come into contact with the aerosol as it is generated by the aerosol-generating substrate passing through the PHA filter segment during use. Thus, the total outer surface area of the PHA fibers will affect the filtration of the aerosol as it passes through the PHA filter segment. In turn, the organoleptic properties of the aerosol can thus be controlled by varying the total outer surface area of the PHA fibers.

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 constituents, such as water. This may advantageously improve the sensory properties of the aerosol delivered from the aerosol-generating substrate to the consumer. As discussed above, selecting the total external surface area of the PHA fibers within the defined ranges enables providing PHA filter segments that can reduce the water uptake level of the filter segment as compared to the corresponding cellulose acetate tow segments. This may be beneficial for combustible smoking articles where it is desirable to reduce the absorption of water from mainstream smoke to reduce the "dry smoke" effect. This may also be beneficial for heated aerosol-generating articles in which the aerosol-generating substrate is heated during use to generate an aerosol. For example, 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 provide a reduced level of water adsorption by the PHA filter segment.

Advantageously, the level of water absorption provided by the PHA filter segments of the present invention is such that an acceptable smoking experience can be provided for most different types of aerosol-generating articles.

The total outer 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 size, cross-sectional shape, and number of PHA fibers.

The PHA fibers may have a substantially circular cross-section. In such embodiments, the total external surface area of the PHA fibers within the filter segment is preferably between about 0.12 square meters per gram to about 0.16 square meters per gram.

The PHA fibers may have a Y-shaped cross-section. In such embodiments, the total external surface area of the PHA fibers within the filter segment is preferably between about 0.21 square meters per gram to about 0.28 square meters per gram.

Preferably, the PHA fibers have a denier per filament (dpf) of about 3.2 to about 5.0. The denier per filament, corresponding to the average denier per individual PHA fiber within the filter, is the weight in grams of an individual fiber or filament having a length of 9000 meters. In the present invention, the value of dpf therefore gives an indication of the thickness of each individual PHA fiber within the filter segment. Denier per filament 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.

The PHA fibers therefore preferably have a denier per filament (dpf) of 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.

The PHA fibers preferably have a denier per filament (dpf) of 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, more preferably no greater than about 4.5.

In some embodiments, the denier per filament may 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.

In other embodiments, the denier per filament may 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 about 3.4.

In other embodiments, the denier per filament may 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.

Preferably, the total denier of the filter material including 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 a 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 filament denier times the total number of fibers in the filter segment.

The PHA fibers provided within the filter of the aerosol-generating article according to the present invention may be formed from any suitable PHA compound, including PHA polymers or copolymers. Suitable PHA compounds include, but are not limited to: polyhydroxypropionates, polyhydroxyvalerates, polyhydroxybutyrates, polyhydroxyhexanoates and polyhydroxyoctanoates. In a particularly preferred embodiment, the PHA compound is poly (3-hydroxybutyrate).

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

The remainder of the fibers within the PHA filter segment may comprise any suitable material. Suitable fibrous materials will be known to the skilled person and include, but are not limited to, polylactic acid (PLA) and cellulose acetate.

The PHA filter segments are thus formed from a relatively high content of PHA fibers. This provides for enhanced biodegradability of the filter and aerosol-generating article as a whole. As noted above, it has previously been found that it is technically challenging to form a filter segment having a high proportion of degradable polymers that provides acceptable filtration properties. However, the present inventors have surprisingly found that filter segments incorporating relatively high PHA fiber content can be produced that provide a desired level of filtration properties such as filtration efficiency and resistance to draw.

PHA fibers of filters according to the invention can be produced using any suitable method. Suitable techniques for producing PHA fibers will be known to the skilled artisan 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 because there is no need to recover or evaporate the solvent, in sharp contrast to the case of solution spinning. Furthermore, the spinning rate using melt spinning is generally quite high, which is advantageous in terms of overall productivity and manufacturing efficiency.

The PHA fibers may optionally be crimped in the same manner as the cellulose acetate fibers in existing filter sections.

The PHA filter segments may be formed of fibrous filter material formed of PHA fibers only. However, in certain preferred embodiments of the present invention, the PHA fibers may be combined with a plurality of additional fibers of biodegradable polymer to form a filter segment. For example, the filter segment preferably comprises at least about 5% by weight of at least one biodegradable polymer selected from the group consisting of: starch, polybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT), thermoplastic starch and thermoplastic starch blend (TPS), Polycaprolactone (PCL), Polyglycolide (PGA), polyvinyl alcohol (PVOH/PVA), viscose, regenerated cellulose, polysaccharides, cellulose acetate with a Degree of Substitution (DS) of less than 2.1, polyamides, protein-based biopolymers, chitosan-chitin based biopolymers, and combinations thereof. The present inventors have found that the inclusion of one or more of these ingredients 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.

In preferred embodiments, 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% by weight, or at least 12% by weight, or at least 13% by weight, or at least 14% by weight of additional biodegradable polymer. Even more preferably, the PHA filter segment comprises at least about 15% by weight of one such additional biodegradable polymer.

The present inventors have found that the inclusion of one or more of these ingredients 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.

Additionally, while previously it has been found that making PHA-containing filaments or fibers using existing techniques and equipment is technically challenging, the present inventors have surprisingly found that when combining PHA in a blend as described above, filaments or fibers incorporating high levels of PHA can be produced as this makes it easier to form filaments by spinning techniques.

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 present 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 mixture. In particular, it has been found that the combined use of PBAT and PBS can provide particularly well balanced mechanical properties, especially in terms of tensile strength and elongation.

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.

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

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

Preferably, the filter section 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.

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

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

In other preferred embodiments of the invention, the PHA filter segment further comprises a mixture of cellulose acetate and triacetin. Preferably, the mixture comprises at least 90% by weight triacetin and at most 10% by weight cellulose acetate. The mixture may 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 section. This combination has been found to advantageously replicate the combined effect of triacetin and cellulose acetate fibers in the filter of a conventional cigarette.

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

For example, when exposed to water in liquid form, PHA filter segments of the invention preferably absorb less than half the amount of water that a corresponding filter segment formed of cellulose acetate fibers absorbs under the same conditions.

The reduced water absorption by the PHA fibers in the filter of the present invention results in a higher water content in the aerosol delivered from the aerosol-generating article during use compared to cellulose acetate.

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

Aerosol-generating articles comprising filters comprising PHA filter segments are therefore capable of delivering aerosols with higher moisture levels, which are more organoleptically acceptable to consumers. In particular, the "dry smoke" effect that may be experienced during smoking of an aerosol-generating article having a conventional cellulose acetate filter may advantageously be reduced.

The PHA filter segments of aerosol-generating articles according to the present invention may advantageously be adjusted to provide a desired level of Resistance To Draw (RTD). For some aerosol-generating articles, such as heated aerosol-generating articles having an aerosol-generating substrate that is heated rather than combusted to produce an aerosol, it may be desirable to provide a relatively low RTD for the PHA filter segment. This may be the case when it is desired to provide low filtration efficiency. Alternatively, where a relatively long filter or mouthpiece is required, for example if the aerosol-generating substrate is relatively short, a low RTD may be required. For example, a low RTD, which has a relatively large size, can be achieved by using PHA fibers having a dpf value within the upper portion of the defined range.

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

Preferably, in aerosol-generating articles according to the invention, the RTD of the PHA filter segment is at least about 30 mm H for a 27 mm filter segment₂And (4) an O column. More preferably, for a 27 millimeter filter segment, the RTD of the PHA filter segment is at least about 35 millimeter H₂O column, more preferably at least about 40 mm H₂And (4) an O column. Even more preferably, in the aerosol-generating article according to the invention, the RTD of the PHA filter segment is at least about 45 mm H for a 27 mm filter segment₂O column, more preferably at least about 50 mm H₂And (4) an O column. For a 27 mm filter segment, the RTD of the PHA filter segment preferably does not exceed about 150 mm H₂O column, more preferably not more than 125 mmH₂O columns, more preferably no more than about 100 mm H₂And (4) an O column. For example, for a 27 mm filter segment, the RTD of the PHA filter segment may be at about 30 mm H₂O column to about 150 mm H₂Between O columns, or at about 35 mm H₂O column to about 150 mm H₂Between O columns, or at about 40 mm H₂O column to about 125 mm H₂Between O columns, or at about 45 mm H₂O column to about 100 mm H₂Between O columns, or at about 50 mm H₂O column to about 100 mm H₂Between the O columns.

In certain preferred embodiments of the invention, the PHA filter section has a H of at least about 60 millimeters₂RTD of O column (based on length of PHA filter segment in the article). More preferably, the RTD of the PHA filter section is at least about 65 mm H₂O columns, more preferably at least about 70 mm H₂And (4) an O column. Even more preferably, in aerosol-generating articles according to the invention, the RTD of the PHA filter segment is at least about 75 mm H₂O column, more preferably at least about 80 mm H₂And (4) an O column. The RTD of the PHA filter segment (based on the length of the PHA filter segment in the article) preferably does not exceed about 120 mm H₂O columns, more preferably no more than about 110 mm H₂O column, more preferably no more than about 100 mm H₂And (4) an O column. For example, the RTD of a PHA filter segment may be at about 60 mm H₂O column to about 120 mm H₂Between O columns, or at about 65 mm H₂O column to about 120 mm H₂Between O columns, or at about 70 mm H₂O column to about 110 mm H₂Between O columns, or at about 75 mm H₂O column to about 110 mm H₂Between O columns, or at about 80 mm H₂O column to about 100 mm H₂Between O columns, or about 90 mm H₂And (4) an O column. Such a range may be particularly suitable for combustible smoking articles.

In other preferred embodiments of the invention, the PHA filter section has a H of at least about 10 mm₂RTD of O column (based on length of PHA filter segment in the article). More preferably, the RTD of the PHA filter section is at least about 12 mm H₂O column, more preferably at least about 15 mm H₂And (4) an O column. Even more preferably, in accordance with the present inventionIn the inventive aerosol-generating article, the RTD of the PHA filter segment is at least about 18 mm H₂O column, more preferably at least about 20 mm H₂And (4) an O column. The RTD of the PHA filter segment (based on the length of the PHA filter segment in the article) preferably does not exceed about 40 mm H₂O columns, more preferably no more than about 35 mm H₂O columns, more preferably no more than about 30 mm H₂And (4) an O column. For example, the RTD of a PHA filter segment may be about 10 mm H₂O column to about 40 mm H₂Between O columns, or at about 12 mm H₂O column to about 40 mm H₂Between O columns, or at about 15 mm H₂O column to about 35 mm H₂Between O columns, or at about 20 mm H₂O column to about 30 mm H₂Between O columns, or about 27 mm H₂And (4) an O column. Such a range may be particularly suitable for heated aerosol-generating articles in which the aerosol-generating substrate is heated rather than combusted to produce an aerosol.

"resistance to draw" refers to the static pressure difference between the two ends of the sample as the flow traverses the sample under steady conditions with a volumetric flow rate at the output end of 17.5 ml/sec. The RTD of the samples can be measured using the method set forth in ISO standard 6565: 2002.

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

Preferably, the PHA filter segment of the aerosol-generating article according to the present invention has an average radial stiffness of at least 80%, more preferably at least 85%. The PHA filter segments are thus capable of providing a desired level of filter stiffness that is comparable to that provided by conventional cellulose acetate tow filters. If desired, the radial stiffness of the PHA filter segments can be further increased by defining the PHA filter segments with a stiff filter segment wrap, for example, a filter segment wrap having a basis weight of at least about 80 grams per square meter (gsm), or at least about 100gsm, or at least about 110 gsm.

As used herein, the term "radial stiffness" refers to the resistance to compression in a direction transverse to the longitudinal axis. The radial stiffness of the aerosol-generating article around the filter may be determined by: a load is applied across the article at the location of the filter transverse to the longitudinal axis of the article, and the average (mean) depression diameter of the article is measured. The radial hardness is given by:

wherein D_SIs the original (un-recessed) diameter, and D_dIs the recess diameter after the set load is applied for the set duration. The harder the material, the closer to 100% the hardness.

To determine the stiffness of a portion of an aerosol-generating article, such as a filter, the aerosol-generating articles should be aligned parallel in a plane and the same portion of each aerosol-generating article to be tested should be subjected to a set load for a set duration of time. This test was performed using a known DD60A densitometer device (manufactured and commercially available from heinr bougovor GmbH) equipped with a measuring head for an aerosol-generating article, such as a cigarette, and with an aerosol-generating article container.

The load is applied using two load applying cylindrical rods that 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 rod. In some cases, the filter to be tested may be long enough that only ten aerosol-generating articles are required to form twenty contact points, with each smoking article contacting two load applying rods (as they are long enough to extend between the rods). In other cases, if the filter is too short to achieve this, twenty aerosol-generating articles should be used to form twenty contact points, where each aerosol-generating article contacts only one of the load applying bars, as discussed further below.

Two further fixed cylindrical rods are located beneath the aerosol-generating article to support the aerosol-generating article and to counteract the load applied by each of these load-applying cylindrical rods.

For a standard operating procedure for such a device, a total load of 2kg is applied for a duration of 20 seconds. After 20 seconds have elapsed (and with the load still being applied to the smoking article), the depression in the load applying cylindrical rod is determined and then used to calculate the hardness according to the above equation. The temperature was maintained in the region of 22 degrees celsius ± 2 degrees. The test described above is referred to as the DD60A test. The standard way of measuring the hardness of a filter is when the aerosol-generating article has not been consumed. Additional information regarding the measurement of average radial stiffness can be found, for example, in U.S. published patent application No. 2016/0128378.

As mentioned above, the use of PHA fibres to produce a filter segment of an aerosol-generating article according to the invention will advantageously provide improved biodegradability compared to conventional cellulose acetate filters.

Preferably, the biodegradability of the PHA filter segment in aqueous medium is at least about 45%, more preferably at least about 50%, most preferably at least about 55%, when measured according to the test method described in ISO 14851 "determination of the final aerobic biodegradability of plastic materials in aqueous medium — method of measuring oxygen demand in a closed respirometer (2005)".

Under the same test conditions, the cellulose acetate filter segment showed a biodegradability of about 30%. It can thus be seen that the use of PHA fibers instead of cellulose acetate fibers to form a filter segment can significantly improve the biodegradability of the filter segment.

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

Preferably, the PHA filter segments have a length of at least about 4 millimeters, more preferably at least about 5 millimeters, more preferably at least about 7 millimeters, and most preferably at least about 10 millimeters.

Preferably, the PHA filter segments have a length of less than or equal to about 30 millimeters, a length of less than or equal to about 27 millimeters, more preferably, a length of less than or equal to about 25 millimeters, and most preferably, a length of less than or equal to about 20 millimeters.

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 embodiments, the PHA filter segments may have a length of about 4 millimeters to about 27 millimeters, preferably about 5 millimeters to about 27 millimeters, more preferably about 10 millimeters to about 27 millimeters, even more preferably about 15 millimeters to about 27 millimeters, and most preferably about 20 millimeters to about 27 millimeters. Still alternatively, in such embodiments, the PHA filter segments may have a length of about 4 mm to about 25 mm, preferably about 5 mm to about 25 mm, more preferably about 10 mm to about 25 mm, even more preferably about 15 mm to about 30 mm, most preferably about 20 mm to about 25 mm.

For embodiments of the 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 mm to about 30 mm, more preferably between about 25 mm to about 30 mm, most preferably about 27 mm.

For alternative embodiments of the 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 electrical heating means or an integral heat source, the length of the PHA filter segment is preferably between about 5 mm and about 15 mm, more preferably between about 5 mm and about 10 mm, most preferably about 7 mm, as described in more detail below.

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

The shape of the PHA filter segment may also vary depending on the desired configuration of the aerosol-generating article. In certain embodiments, the PHA filter segments may be in the form of solid cylindrical filter segments of fibrous filter material comprising PHA fibers. Such a filter segment would therefore provide a similar construction to a conventional cellulose acetate tow filter segment.

In alternative embodiments, the PHA filter segments may be in the form of hollow tube segments. The hollow tube segments have a larger exposed surface area than cylindrical filter segments of equivalent diameter, which further improves the biodegradation of the PHA filter segments.

The hollow tube segments preferably have a wall thickness of at least about 0.3 millimeters. More preferably, the hollow tube segment has a wall thickness of at least about 0.4 millimeters. Even more preferably, the hollow tube segments have a wall thickness of at least about 0.5 millimeters.

Preferably, the hollow tube segment has a wall thickness of less than or equal to about 1.9 millimeters. More preferably, the hollow tube segments have a wall thickness of less than or equal to about 1.5 millimeters. Even more preferably, the hollow tube segments have a wall thickness of less than or equal to about 1.2 millimeters. Particularly preferably, the hollow tube section has a wall thickness of less than or equal to about 0.9 mm.

In some embodiments, the hollow tube segments may generally have a length of at least about 4 millimeters. Preferably, the length of the hollow tube segment is at least about 5 mm. More preferably, the length of the hollow tube segment is at least about 7 millimeters. Even more preferably, the length of the hollow tube segment is at least about 10 millimeters.

Where the PHA filter segment is in the form of a hollow tube segment, the filter material may contain some cellulose acetate in addition to the PHA fibers. For example, the hollow tube segment may comprise about 5% to about 15% by weight cellulose acetate. Without wishing to be bound by theory, it is understood that the amount of cellulose acetate in the hollow tube segments may impart desirable filtration and mechanical properties to the hollow tube segments, as well as facilitate manufacture of the hollow tube segments.

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

Preferably, the further filter section is formed from a material other than cellulose acetate. Particularly preferably, the further filter segments comprise PHA fibers, which may optionally be held in a desired shape by means of a suitable binder, such as PVA. Preferably, each of the additional filter segments comprises at least about 25% by weight of PHA compound, more preferably at least about 50% by weight of PHA compound.

The filter of the aerosol-generating article according to the invention may optionally comprise a flavouring agent. The flavoring agent can be introduced using a variety of different means, which will be known to the skilled person. For example, the flavoring may be introduced in the form of capsules, which may be provided in the PHA filter section or in an additional filter section.

Preferably, the filter of the aerosol-generating article according to the invention comprises a capsule within the PHA filter segment, wherein the capsule contains an additive for modifying the aerosol generated by the aerosol-generating substrate during use. Preferably, the additive is a flavoring agent. Using PHA fibers having 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 fibres compared to filters formed from fibres having lower dpf values. PHA filter segments formed from PHA fibers having a dpf in this range are therefore particularly suitable for introduction into capsules. The capsules can be easily introduced into the PHA filter section during manufacture. Furthermore, the capsule will be effectively maintained in the desired axial position within the PHA filter segment.

The filter of the aerosol-generating article according to the invention is preferably defined by an outer wrapper, e.g. a tipping wrapper defining the filter segment, the downstream end of the aerosol-generating substrate and any further components which may be provided therebetween. The tipping wrapper may comprise A removable tipping wrapper portion, as described in WO-A-2017/162838. This enables removal of at least a portion of the tipping package before the aerosol-generating article is discarded. Removal of the tipping wrapper will expose the underlying filter segment and may thus advantageously accelerate the rate of biodegradation of the filter material.

As defined above, the aerosol-generating article according to the invention further comprises an aerosol-generating substrate, preferably in the form of a rod of aerosol-generating substrate. Preferably, the aerosol-generating substrate is a rod of tobacco material.

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

In certain embodiments, the aerosol-generating article according to the invention is a filter cigarette or other combustible smoking article in which the aerosol-generating substrate comprises tobacco material which combusts to form smoke. In any such embodiment, the aerosol-generating substrate may comprise a tobacco rod. The tobacco rod may include one or more of cut filler and reconstituted tobacco.

For embodiments in which the aerosol-generating article is in the form of a combustible smoking article, the aerosol-generating substrate, 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 include one or more of cut filler and reconstituted tobacco.

As discussed above, the filter of the present invention comprising a PHA segment may also be applied in a heated aerosol-generating article in which tobacco material is heated rather than combusted to form an aerosol. In one type of heated aerosol-generating article, tobacco material is heated by one or more electrical heating elements to produce an aerosol. In another type of heated aerosol-generating article, the aerosol is generated by transferring heat from a combustible or chemical heat source to a physically separate 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 a tobacco material, tobacco extract or other nicotine source, e.g., by a chemical reaction, without combustion and in some cases without heating.

For embodiments in which the aerosol-generating article is in the form of a heated aerosol-generating article in which it is desired to heat the aerosol-generating substrate to form an aerosol, the aerosol-generating substrate preferably has a length of from about 5 millimetres to about 40 millimetres, more preferably from about 9 millimetres to about 15 millimetres.

For such embodiments in which the aerosol-generating article is in the form of a heated aerosol-generating article, the aerosol-generating substrate is preferably formed from a homogenized tobacco material formed from agglomeration of tobacco particles. The aerosol-generating substrate 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, gravure, perforated, or otherwise deformed. Alternatively, the aerosol-generating substrate may comprise a plurality of rods or slivers of homogenized tobacco material. The strips or slivers may be substantially aligned with each other in the longitudinal direction, or may be randomly oriented.

The homogenized tobacco material for use in the aerosol-generating substrate may have a tobacco content of at least about 40 weight percent on a dry weight basis, more preferably at least about 60 weight percent on a dry weight basis, more preferably at least about 70 weight percent on a dry weight basis, most preferably at least about 90 weight percent on a dry weight basis.

Homogenized tobacco material for use in aerosol-generating substrates may comprise one or more intrinsic binders that are tobacco endogenous binders, one or more exogenous binders that are tobacco exogenous binders, or a combination thereof to help agglomerate particulate tobacco. Alternatively or additionally, the homogenized tobacco material used in the aerosol-generating substrate may comprise other additives, including but not limited to tobacco and non-tobacco fibres, aerosol-formers, humectants, plasticizers, flavourants, fillers, aqueous and non-aqueous solvents, and combinations thereof.

Foreign binders suitable for inclusion in homogenized tobacco material for use in aerosol-generating substrates 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.

Non-tobacco fibres suitable for inclusion in homogenized tobacco material for use in aerosol-generating substrates 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 the aerosol-generating substrate, the non-tobacco fibres may be treated by suitable methods known in the art, including but not limited to: mechanically pulping; refining; chemical pulping; bleaching; sulfate pulping; and combinations thereof.

Aerosol-generating substrates for heated aerosol-generating articles typically comprise an "aerosol former", i.e. a compound or mixture of compounds which in use will promote aerosol formation and preferably substantially resist thermal degradation at the operating temperature of the aerosol-generating article. Examples of suitable aerosol-forming agents include: polyhydric alcohols such as propylene glycol, triethylene glycol, 1, 3-butanediol and glycerin; esters of polyhydric alcohols, such as monoacetin, diacetin, or triacetin; and aliphatic esters of mono-, di-or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Preferred aerosol formers are polyols or mixtures thereof, such as propylene glycol, triethylene glycol, 1, 3-butylene glycol, and most preferably glycerol.

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

Aerosol-generating articles according to the invention may also comprise one or more further components between the filter and the aerosol-generating substrate. For example, the aerosol-generating article may further comprise one or more of: a support element, an aerosol-cooling element and a transfer element. The construction of such components will be known to the skilled person.

For example, in certain preferred embodiments of the present invention, an aerosol-generating article comprises, in linear order: the aerosol-generating substrate, a support element immediately downstream of the aerosol-generating substrate, an aerosol-cooling element located immediately downstream of the support element, and a mouthpiece comprising a PHA filter segment at a downstream end of the filter.

In other preferred embodiments of the invention, the aerosol-generating article comprises, in linear order: an aerosol-generating substrate, a transfer element, an aerosol-cooling element, a spacer element and a mouthpiece filter.

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

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

figure 1 shows a schematic longitudinal cross-sectional view of an aerosol-generating article according to a first embodiment of the present invention, the article being to be used with an aerosol-generating device comprising a heater element;

figure 2 shows a schematic longitudinal cross-sectional view of an aerosol-generating article according to a second embodiment of the present invention, the article comprising an integral heat source; and

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

figure 4 shows a schematic longitudinal cross-sectional view of an aerosol-generating system comprising an electrically operated aerosol-generating device and the aerosol-generating article shown in figure 1.

The aerosol-generating article 10 shown in figure 1 comprises a rod 12 of aerosol-generating substrate, a support element 14 provided as a hollow tubular element, a cooling element 16 and a mouth end filter segment 18. These four elements are arranged in sequence and axially aligned and defined by the substrate package 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. The aerosol-generating article 10 shown in figure 1 is particularly suitable for use with an electrically operated aerosol-generating device comprising a heater for heating a rod of aerosol-generating substrate.

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

The aerosol-generating substrate 12 is located at the very distal or upstream end of the aerosol-generating article 10. In the embodiment illustrated in figure 1, the aerosol-generating substrate 12 comprises a gathered sheet of crimped homogenized tobacco material defined by a wrapper. The crimped sheet of homogenized tobacco material comprises glycerol as aerosol former.

The support element 14 is located immediately downstream of the aerosol-generating substrate 12 and abuts the aerosol-generating substrate 12. In the embodiment shown in fig. 1, the support element is a hollow tube formed of a fibrous filter material. The support element 14 positions the aerosol-generating substrate 12 at the distal extremity 24 of the aerosol-generating article 10 such that it is penetrable by a heating element of the aerosol-generating device. Indeed, the support element 14 serves to prevent the aerosol-generating substrate 16 from being forced towards the aerosol-cooling element 16 within the aerosol-generating article 10 when a heating element of an aerosol-generating device is inserted into the aerosol-generating substrate 12. The support element 14 also acts as a spacer to separate the aerosol-cooling element 16 of the aerosol-generating article 10 from the aerosol-generating substrate 12.

The aerosol-cooling element 16 is located immediately downstream of the support element 14 and abuts the support element 16. In use, volatile materials released from the aerosol-generating substrate 12 pass along the aerosol-cooling element 16 towards the mouth end 22 of the aerosol-generating article 10. The volatile material may cool within the aerosol-cooling element 16 to form an aerosol for inhalation by a user. In the embodiment illustrated in fig. 1, the aerosol-cooling element comprises a tubular element 20. The crimped and gathered polylactic acid sheet defines a plurality of longitudinal channels extending along the length of the aerosol-cooling element 40.

The filter segment 18 is located immediately downstream of the aerosol-cooling element 16 and abuts the aerosol-cooling element 16. In the embodiment illustrated in fig. 1, the filter segment 18 comprises a single cylindrical filter segment of fibrous filter material formed from a plurality of PHA fibers having a denier per filament of about 3.4 and a total denier of about 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 corresponded to about 0.16 square meters per gram. PHA fibers have been formed and crimped by a melt spinning process. The filter segments of fibrous filter material are defined by a filter segment wrapper (not shown).

The aerosol-generating article 100 shown in figure 2 comprises a combustible heat source 112, a rod 114 of aerosol-generating 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 defined by a substrate wrapper to form the aerosol-generating article 100.

The combustible heat sources 112 comprise substantially cylindrical carbonaceous material having a length of about 10 millimetres. The combustible heat source 112 is a blind heat source. In other words, the combustible heat sources 112 do not include any air channels extending therethrough.

A rod 114 of aerosol-generating substrate is arranged at the proximal end of the combustible heat source 112. The aerosol-generating substrate 114 comprises a substantially cylindrical rod of tobacco material 124 defined by a filter segment wrapper 126.

A 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-generating substrate 114. The first barrier 128 comprises a disk of aluminum foil. The first barrier 128 also forms a thermally conductive member between the combustible heat source 112 and the aerosol-generating substrate 114 to conduct heat from the proximal face of the combustible heat source 112 to the distal face of the aerosol-generating substrate 114.

The heat conducting element 130 defines a proximal portion of the combustible heat source 112 and a distal portion of the aerosol-forming substrate 114. The heat transfer element 130 comprises an aluminum foil tube. The heat conducting element 130 is in direct contact with the proximal portion of the combustible heat source 112 and the filter segment wrapper 126 of the aerosol-generating substrate 114.

The mouthpiece filter 122 comprises a single cylindrical filter segment 126 of fibrous filter material formed from a plurality of PHA fibers having a denier per filament of about 3.4 and a total denier of about 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 about 0.16 square meters per gram. PHA fibers have been formed and crimped by a melt spinning process. The filter segments of fibrous filter material are defined by a filter segment wrapper (not shown).

The aerosol-generating article 310 shown in figure 3 is a combustible smoking article comprising an aerosol-generating substrate 312 and a filter 314 arranged in coaxial alignment with one another. The aerosol-generating substrate 312 comprises a tobacco rod defined by an overwrap (not shown). The tipping wrapper 316 defines both the filter 314 and an end of the aerosol-generating substrate 312 and attaches the filter 314 to the aerosol-generating substrate 312.

The filter 314 comprises a single cylindrical filter segment 318 of fibrous filter material formed of PHA fibers having a denier per filament of about 3.4 and a total denier of about 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 corresponded to about 0.16 square meters per gram. PHA fibers have been formed and crimped by a melt spinning process. The filter segments of fibrous filter material are defined by filter segment wrappers (not shown).

Fig. 4 shows a portion of an electrically operated aerosol-generating system 200 which utilises a heater blade 210 to heat a rod 12 of aerosol-generating substrate of the aerosol-generating article 10 shown in fig. 1. The heater blade 210 is mounted within an aerosol-generating article chamber within the housing of an 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-generating article 10, as illustrated by the arrows in fig. 4. The aerosol-generating device 212 comprises a power supply and electronics not shown in figure 4.

Comparative example

PHA filter segments according to the present invention were produced from PHA fibers with the parameters shown in table 1 below. PHA fibers are formed using a melt spinning process, and then the fibers are crimped and formed into filter segments using standard filter manufacturing equipment. For comparison purposes, conventional Cellulose Acetate (CA) tow filter segments were prepared having similar denier per filament (dpf) and total denier values.

Table 1: parameters of PHA filter segment and cellulose acetate filter segment

Parameter(s)	PHA filter section	CA filter segment
			Denier per filament	3.2	3
Total denier	27000	27000
			Filter segment weight (mg)	406.76	409.76
External surface area (m)²/g)	0.161	0.329

In a first test, the water uptake of exposure of PHA filter segments according to the invention and CA filter segments to water was compared. For each filter segment, the filter segment wrapping is removed and the filter segment is attached to a probe of a tension tensiometer (KRUSS tension tensiometer, model K100). The filter segment is moved by the probe downwardly towards the reservoir of water and automatically stops when the filter segment comes into contact with the water. The filter segment was kept in contact with 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 procedure. This test was repeated three times and the average of water absorption was calculated for each of the PHA and CA filter segments as shown in table 2 below:

table 2: water absorption by PHA and CA filter stages after Water Exposure

The amount of water absorbed by the PHA filter segment according to the present invention during the testing procedure was therefore less than 40% of the amount of water absorbed by the CA filter segment. This test thus demonstrates that the water affinity of the PHA filter segments according to the invention is significantly reduced compared to conventional CA filter segments.

In a second test, the water uptake of exposure of PHA filter segments according to the invention and CA filter segments to moisture was compared. For each filter segment, the filter segment wrapping 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 done in a vapour sorption analyzer (ProUmid SPSx-1. mu.). For each filter segment, the weight of the fibers was measured at the beginning 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 and CA filter stages, a mass percent difference (% dm) value for the sample was calculated, which represents the increase in sample weight as a percentage of the initial weight. The% dm values at the end of the test for 70 hours are shown in table 3 below for each sample:

table 3: water absorption by PHA and CA filter sections after exposure to moisture

The results demonstrate that the amount of water vapor absorbed by the cellulose acetate fibers during the 70 hour test is more than 50 times greater than the amount of water vapor absorbed by the PHA fibers. During the test, the PHA fibers absorbed very little water vapor. This further demonstrates that the water affinity of the PHA filter segments according to the present invention is significantly reduced compared to conventional CA filter segments.

In a third test, the water uptake from mainstream smoke of PHA filter segments according to the invention and conventional CA filter segments were compared. For each filter segment, a conventional smoking article is prepared as described above in connection with fig. 3 using a combustible tobacco rod and a single segment of filter material forming the filter. Each smoking article was then smoked in a smoking machine under ISO conditions (puff volume 35 ml; puff duration of 2 seconds per 60 seconds) as set forth in ISO 3308:2000 and an analysis of the resulting smoke was performed. For each filter segment, the amount of water in the mainstream smoke collected during the smoking test was measured as shown in table 4:

table 4: water in mainstream smoke generated during smoking testing under ISO conditions

	PHA filter section	CA filter segment
			Water (mg/smoking article)	0.82	0.68

This confirms that when smoked under equivalent conditions, the smoking articles incorporating the PHA filter segments produced mainstream smoke with approximately 20% higher water content than mainstream smoke from smoking articles including the CA filter segments. This confirms that the PHA filter segment absorbs less water from the mainstream smoke than the CA filter segment, thereby reducing the potential problems of drying the smoke as described above.

Claims

1. An aerosol-generating article comprising:

an aerosol-generating substrate;

a filter in axial alignment with the aerosol-generating substrate, the filter comprising at least one filter segment of filter material formed from a plurality of fibres comprising a polyhydroxyalkanoate compound, wherein the fibres provide a total external surface area within the filter segment of from 0.12 to 0.28 m/g and wherein the at least one filter segment comprises at least 20% by weight of the polyhydroxyalkanoate compound.

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

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

4. An aerosol-generating article according to any preceding claim, wherein the fibre comprising the polyhydroxyalkanoate compound has a denier per filament (dpf) of from 3.2 to 5.0.

5. An aerosol-generating article according to any preceding claim, wherein the total denier of the fiber comprising the polyhydroxyalkanoate compound is between 25,000 and 40,000.

6. An aerosol-generating article according to any preceding claim, wherein the filter material further comprises a plurality of fibres of at least one further biodegradable polymer.

7. An aerosol-generating article according to any preceding claim, wherein the Resistance To Draw (RTD) of the filter segment comprising the plurality of fibers comprising the polyhydroxyalkanoate compound is at 10 millimeter H₂O column to about 40 mm H₂Between the O columns.

8. An aerosol-generating article according to any preceding claim, wherein the filter segment comprising the plurality of fibres comprising the polyhydroxyalkanoate compound has a biodegradability in aqueous medium of at least 50% when tested according to ISO 14851.

9. An aerosol-generating article according to any preceding claim, wherein the filter section comprising the plurality of fibres comprising the polyhydroxyalkanoate compound further comprises at least 5% by weight of polyethylene glycol.

10. An aerosol-generating article according to any preceding claim, wherein the filter segment comprising the plurality of fibres comprising the polyhydroxyalkanoate compound has an average radial stiffness of at least 80%.

11. An aerosol-generating article according to any preceding claim, wherein the filter section comprising the plurality of fibres comprising the polyhydroxyalkanoate compound is defined by a wrapper having a basis weight of at least 100 grams per square meter (gsm).

12. An aerosol-generating article according to any preceding claim, wherein the filter segment comprising the plurality of fibers comprising the polyhydroxyalkanoate compound is in the form of a hollow tubular element.

13. An aerosol-generating article according to any preceding claim, wherein the aerosol-generating substrate is a tobacco rod having a length of about 5 to 15 millimetres.

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