JP7583804B2 - Aerosol-generating article filters having novel filtering materials - Google Patents

Description

The present invention relates to a filter for an aerosol-generating article, and to an aerosol-generating article that includes a 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, most often in end-to-end relationship, with the rolled tobacco rod. The cylindrical filter typically comprises one or more plugs of fibrous filtering material, such as cellulose acetate tow, surrounded by a paper plug wrap. Conventionally, the rolled tobacco rod and filter are joined by a band of tipping wrapper, usually formed from an opaque paper material, that surrounds the entire length of the filter and adjacent portions of the rolled 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 heat transfer from a heat source to a physically separate aerosol-generating substrate or material.

As an example, aerosol-generating articles have been proposed, in which the aerosol is generated by electrical heating of an aerosol-generating substrate. Numerous prior art documents disclose aerosol-generating devices for consuming aerosol-generating articles. Such devices include, for example, electrically heated aerosol-generating devices, in which the aerosol is generated by heat transfer from one or more electric heater elements of the aerosol-generating device to the aerosol-generating substrate of the heated aerosol-generating article. As another example, aerosol-generating articles are also known in which the aerosol is generated by heat transfer from a combustible fuel element or heat source to the aerosol-generating substrate. The combustible fuel element or heat source may be located in contact with the aerosol-generating substrate, within the aerosol-generating substrate, around the aerosol-generating substrate, 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 are entrained in air drawn through the aerosol-generating article. As the released compounds cool, they condense to form an aerosol.

Typically, an aerosol-generating article of the type described may include a mouthpiece comprising a porous filtration 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.

Cellulose acetate, the most commonly used filtration material, can provide relatively high filtration efficiency, and cellulose acetate tow filters provide effective filtration of mainstream smoke generated from an aerosol-generating substrate. However, cellulose acetate has also been found to absorb and trap relatively high levels of water from the mainstream smoke. As a result, the mainstream smoke delivered to the consumer has a significantly reduced moisture content and, under certain conditions, may be perceived as undesirably "dry". This can have a negative impact on the overall smoking experience.

Cellulose acetate and many other commonly used filtration materials are not highly biodegradable. However, alternative dispersible or degradable materials often fail to provide acceptable filtration efficiency and smoking experience to consumers. Furthermore, many known dispersible and degradable materials are not suitable for use in existing manufacturing processes and would require overly significant modifications of existing methods and equipment to make their use commercially viable.

It would be desirable to provide new and improved aerosol-generating articles with enhanced biodegradable properties compared to known articles containing conventional filtration materials such as cellulose acetate. In particular, it would be particularly desirable to provide novel aerosol-generating articles that can provide consumers with an acceptable smoking experience, for example, by reducing the "dry" smoke effect often found in articles containing cellulose acetate as a filtration material, as described above. It would be desirable to provide one such aerosol-generating article in which the resistance to draw (RTD) of the filtration material segments can be adjusted to achieve an acceptable RTD for the article as a whole. It would further be desirable to provide such an aerosol-generating article that can be efficiently manufactured in an automated and high-speed manufacturing process without requiring major modifications to existing equipment.

The present disclosure relates to an aerosol-generating article for producing an inhalable aerosol upon heating and burning. The aerosol-generating article may include a rod of an aerosol-generating substrate and a filter segment axially aligned with the rod. The filter segment may include a filtration material formed from a plurality of fibers including a polyhydroxyalkanoic acid (PHA) compound. The fibers of the PHA compound may have a denier per fiber (dpf) of 1.5 to 3.2.

The present disclosure further relates to a filter for an aerosol-generating article. The filter may include at least one filter segment of a filtration material. The filter segment may include a filtration material formed from a plurality of fibers including a polyhydroxyalkanoic acid (PHA) compound. The fibers of the PHA compound may have a denier per fiber (dpf) of 1.5 to 3.2.

In accordance with 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 a filtration material comprising a plurality of fibers comprising a polyhydroxyalkanoic acid (PHA) compound. The fibers have a denier per fiber (dpf) of about 1.5 to about 3.2.

The present invention further provides a filter comprising at least one filter segment of a filtration material comprising a plurality of fibers comprising a polyhydroxyalkanoic acid (PHA) compound. The fibers have a denier per filament (dpf) of about 1.5 to about 3.2.

The term "aerosol-generating article" is used herein with respect to the present invention to describe an article in which an aerosol-generating substrate is heated or combusted to generate an aerosol for delivery to a consumer. As used herein, the term "aerosol-generating substrate" refers to a substrate that has the ability to generate an aerosol by releasing volatile compounds upon heating or combustion.

A conventional cigarette is lit when a user applies a flame to one end of the cigarette and draws air through the other end. Localized heat provided by the flame and oxygen from the air drawn through the cigarette ignite the end of the cigarette, and the resulting combustion produces inhalable smoke. In contrast, in heated aerosol-generating articles, the aerosol is generated by heating a flavor-generating substrate, such as, for example, a tobacco-derived substrate or a substrate containing an aerosol former and a flavorant. Known heated aerosol-generating articles include, for example, electrically heated aerosol-generating articles and aerosol-generating articles in which the aerosol is generated by heat transfer from a combustible fuel element or heat source to a physically separated aerosol-forming material.

The filter of the invention finds particular application in conventional smoking articles in which an aerosol-generating substrate is combusted during use to produce smoke. However, the filter of the invention is also suitable for use as a filter or mouthpiece in a heated aerosol-generating article having an aerosol-generating substrate that is heated by suitable means during use, as described above.

As used herein, the term "aerosol-generating substrate" describes a substrate capable of releasing volatile compounds that can form an aerosol when heated (including combusted). The aerosol generated from an aerosol-generating substrate may be visible or invisible and may include vapor (e.g., gaseous fine particles of a substance that is normally liquid or solid at room temperature), as well as gas and liquid droplets of condensed vapor. As used herein, the term "aerosol" encompasses aerosols generated upon heating of a substrate in a heated aerosol-generating article, and smoke generated upon combustion of a substrate 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 plurality of fibers of a PHA compound having a denier per fiber in the range of about 1.5 to 3.2. The fibers comprising the PHA compound are hereinafter referred to as "PHA fibers." The filter segment comprising a plurality of PHA fibers is hereinafter referred to as "PHA filter segment."

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

PHA fibers are less hydrophilic than fibers of other filtration materials, such as cellulose acetate, of comparable weight. Thus, in the aerosol-generating articles of the present invention, the filter segments have been found to have a significantly lower tendency to absorb water/vapor from the aerosol generated from the aerosol-generating substrate during use. As a result, the level of water in the aerosol can be advantageously maintained at a higher level. This directly addresses the "dry smoke" problem commonly encountered with conventional smoking articles, providing the consumer with an improved smoking experience.

Since PHA fibers have a much higher level of biodegradability compared to fibers of other filtration materials such as cellulose acetate, the article according to the invention has a higher overall biodegradability. At the same time, since the PHA fibers are obtained by a natural fermentation process, the aerosol-generating article according to the invention also offers improved sustainability for the manufacturing process.

The low range dpf also advantageously reduces the overall weight of the filter segment, further significantly improving the biodegradability of the aerosol-generating article.

In accordance with the present invention, the filter segments are formed of PHA fibers having a relatively low denier per filament (dpf) of about 1.5 to about 3.2. However, the PHA fibers may be formed to provide a relatively high resistance to withdrawal (RTD), which may be desirable for a particular filter design. For example, in combustible smoking articles where relatively high filtration efficiency is preferred, a high value of RTD may be desirable. Alternatively, it may be desirable where relatively short filter segments are preferred.

Filters formed with PHA fibers have also been found to provide good filter hardness, which can be further enhanced by surrounding the filter segments with a stiff plug wrap.

The denier per filament, which corresponds to the average denier of the individual PHA fibers in the filter, is about 1.5 to about 3.2. The term "denier per filament" (dpf) corresponds to the weight in grams of a single fiber or filament having a length of 9000 meters. Thus, in the present invention, the value of dpf indicates the thickness of each of the individual PHA fibers in the filter segment. Denier per filament is expressed in units of denier, with 1 denier corresponding to 1 gram per 9000 meters. PHA Filters

Thus, it is preferred that the denier per filament (dpf) of the PHA fiber is at least about 1.5. Preferably, the dpf is at least about 1.6, more preferably at least about 1.7, more preferably at least about 1.8, more preferably at least about 1.9, more preferably at least about 2.0.

The denier per filament (dpf) of the PHA fibers is additionally about 3.2 or less. Preferably, the dpf is about 3.1 or less, more preferably about 3.0 or less, more preferably about 2.9 or less, more preferably about 2.8 or less, more preferably about 2.7 or less.

In some embodiments, the denier per filament may be from about 1.6 to about 3.1, or from about 1.7 to about 3.0, or from about 1.8 to about 2.9, or from about 1.9 to about 2.8, or from about 2.0 to about 2.7.

In other embodiments, the denier per filament may be from about 1.5 to about 2.0, or from about 1.5 to about 1.9, or from about 1.5 to about 1.8.

In other embodiments, the denier per single fiber may be about 2.0 to about 3.2, or about 2.2 to about 3.0, or about 2.4 to about 3.0, or about 2.6 to about 2.8. Preferably, the total denier of the filtration material including the PHA fibers is about 20,000 to about 50,000, more preferably about 25,000 to about 40,000. The "total denier" of the filtration material defines the total weight in grams of 9000 meters of the combined fibers that form the filtration material. Thus, the total denier of a filter segment is equal to the denier per single fiber multiplied by the total number of fibers in the filter segment.

The transverse cross-sectional shape of the PHA fibers can be varied, for example, to control the external surface area of the fibers within the filter. By controlling the external surface area of the PHA fibers, the total surface area of the PHA fibers exposed to the aerosol as it passes through the filter segment can also be controlled. This, in turn, will in part control the filtration characteristics of the PHA fibers, such as, for example, the amount of water absorbed by the fibers.

The total external surface area of the PHA fibers in the filter segment is preferably from about 0.15 square meters/gram to about 0.55 square meters/gram, more preferably from about 0.2 square meters/gram to about 0.5 square meters/gram, and more preferably from about 0.25 square meters/gram to about 0.45 square meters/gram.

The PHA fibers may have a substantially round cross-section. In such embodiments, the total exterior surface area of the PHA fibers within the filter segment is preferably from about 0.15 square meters per gram to about 0.30 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 from about 0.25 square meters per gram to about 0.55 square meters per gram.

The PHA fibers provided in the filter of the aerosol-generating article according to the present invention may be formed of any suitable PHA compound, including a PHA polymer or copolymer. 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).

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

The remaining fibers in the PHA filter segment may comprise any suitable material. Suitable fibrous materials are known to those skilled in the art and include, but are not limited to, polylactic acid (PLA) and cellulose acetate.

Thus, the PHA filter segments are formed with a relatively high level of PHA fibers. This enhances the biodegradability of the filter and the overall aerosol-generating article. As discussed above, it has previously been found to be technically difficult to form filter segments with a high percentage of degradable polymer that provide acceptable filtration properties. However, the inventors have surprisingly found that it is possible to produce filter segments that incorporate relatively high levels of PHA fibers and provide desirable levels of filtration properties such as filtration efficiency and resistance to withdrawal.

The PHA fibers of the filters according to the invention may be manufactured using any suitable method. Suitable techniques for the manufacture of PHA fibers are known to those 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 opposed to solution spinning, since there is no need to recover or evaporate the solvent. Furthermore, the spinning speeds with melt spinning are 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 the existing filter segments.

The PHA filter segment may be formed from a fibrous filtration material formed solely of PHA fibers. However, in certain preferred embodiments of the present invention, the PHA fibers may be combined with a plurality of fibers of an additional biodegradable polymer to form the filter segment. For example, the filter segment preferably comprises at least about 5 weight percent of at least one biodegradable polymer selected from the group consisting of starch, polybutylene succinate (PBS), polybutyrate adipate terephthalate (PBAT), thermoplastic starch and thermoplastic starch blends (TPS), polycaprolactone (PCL), polyglycolide (PGA), polyvinyl alcohol (PVOH/PVA), viscose, regenerated cellulose, polysaccharides, cellulose acetate having a degree of substitution (DS) of less than 2.1, polyamides, protein-based biopolymers, chitosan-chitin-based biopolymers, and combinations thereof.

In preferred embodiments, the PHA filter segment comprises at least about 10 weight percent of one of these additional biodegradable polymers. More preferably, the PHA filter segment comprises at least about 11 weight percent, or at least 12 weight percent, or at least 13 weight percent, or at least 14 weight percent of the additional biodegradable polymer. Even more preferably, the PHA filter segment comprises at least about 15 weight percent of one of these additional biodegradable polymers.

The inventors have discovered that including one or more of these components in the blend from which the fibrous material of the filter segments is formed further contributes to enhanced biodegradability of the filter segments and the aerosol-generating article as a whole.

Furthermore, while it has previously been found to be technically difficult to produce PHA-containing filaments or fibers using existing techniques and equipment, the inventors have surprisingly discovered that when PHAs are combined in a blend as described above, they are easier to form into filaments by spinning techniques, and therefore filaments or fibers can be produced that incorporate high levels of PHA.

In a particularly preferred embodiment, the at least one biodegradable polymer is one or more of PBAT, PCL and PBS. Without intending to be bound by theory, the inventors have discovered that the use of one or more of these selected biodegradable polymers contributes to improved mechanical, thermal and morphological properties of the polymer blend. In particular, the combined use of PBAT and PBS has been found to provide particularly balanced mechanical properties, particularly with respect to tensile strength and elongation.

PHA fibers may be formed with PHA compounds alone or in combination with one or more other polymers, such as polylactic acid (PLA). Thus, PHA fibers are formed from a blend of polymers that includes the PHA compound.

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

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 the reduction of phenol and phenol derivatives. Suitable additives are well known to those skilled in the art and include, but are not limited to, polyethylene glycol (PEG), triacetin, triethyl citrate, cellulose acetate flakes, or combinations thereof.

The filter segments preferably contain from about 3 weight percent to about 15 weight percent of the additive, and more preferably from about 5 weight percent to about 9 weight percent of the additive.

In certain preferred embodiments of the present invention, the PHA filter segments comprise a polyethylene glycol, such as PEG 400. The combination of PHA fibers with an additive, such as PEG, for the reduction of 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 constituents, but are less effective at removing phenolic compounds. It is possible to further optimize the filtration capacity of a filter according to the present invention comprising PHA fibers by incorporating a compound that specifically reduces the level of phenolic compounds in the aerosol generated from the aerosol-generating substrate. This improves the sensory properties of the aerosol delivered to the consumer.

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

In another preferred embodiment of the invention, the PHA filter segment further comprises a mixture of cellulose acetate and triacetin. Preferably, the mixture comprises at least 90 weight percent triacetin and up to 10 weight percent cellulose acetate. The mixture may be formed by adding cellulose acetate flakes to triacetin to form a solution. The solution may 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 conventional cigarette filters.

As discussed above, PHA fibers have been found to absorb less water from an aerosol generated from an aerosol-generating substrate than an equivalent amount of cellulose acetate fibers due to the lower affinity of the PHA fibers for water. As shown in the examples below, the amount of water absorbed by a PHA filter segment is significantly lower than the amount of water absorbed by a comparative filter segment formed of an equivalent weight of cellulose acetate fibers.

For example, when exposed to water in liquid form, the PHA filter segments of the present invention preferably absorb less than half the amount of water that would be absorbed under the same conditions by an equivalent filter segment formed from cellulose acetate fibers.

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

For example, the amount of moisture in the aerosol collected during smoking of a combustible smoking article containing a filter according to the present invention using PHA fibers under ISO conditions was at least 10 percent higher, preferably at least 15 percent higher, than the amount of moisture in the aerosol collected during smoking of a comparable combustible smoking article having a filter segment of cellulose acetate tow under the same conditions.

Aerosol-generating articles including filters containing PHA filter segments can therefore deliver aerosols with higher moisture levels, which are more perceptually acceptable to consumers. In particular, the "dry smoke" effect that may be experienced during smoking of aerosol-generating articles using conventional cellulose acetate filters may be advantageously reduced.

The PHA filter segments of the aerosol-generating articles according to the invention may be adapted to provide a desired level of resistance to draw (RTD). Advantageously, the PHA fibers may be arranged to provide a relatively high RTD to the PHA filter segment. Thus, the PHA filter segments are particularly suitable for use in filters of combustible smoking articles, where a relatively high RTD is typically desirable. Alternatively, the PHA filter segments may be particularly suitable for aerosol-generating articles, where a relatively short mouthpiece or filter is preferred, since an acceptable RTD may still be provided.

Preferably, in an aerosol-generating article according to the invention, the RTD of the PHA filter segment for a 27 millimeter filter segment is at least about 25 millimeters _H2O . More preferably, the RTD of the PHA filter segment for a 27 millimeter filter segment is at least about 50 millimeters _H2O , more preferably at least about 100 millimeters _H2O . Even more preferably, in an aerosol-generating article according to the invention, the RTD of the PHA filter segment for a 27 millimeter filter segment is at least about 150 millimeters _H2O , more preferably at least about 180 millimeters _H2O . The RTD of the PHA filter segment for a 27 millimeter filter segment is preferably no greater than about 300 millimeters _H2O , more preferably no greater than 250 millimeters _H2O . For example, the RTD of the PHA filter segment for a 27 millimeter filter segment can be from about 25 millimeters _H2O to about 300 millimeters _H2O , or from about 50 millimeters _H2O to about 300 millimeters _H2O , or from about 100 millimeters _H2O to about 250 millimeters _H2O , or from about 150 millimeters _H2O to about 250 millimeters _H2O , or from about 180 millimeters _H2O to about 250 millimeters _H2O , or about 200 millimeters _H2O .

Preferably, in an aerosol-generating article according to the invention, the RTD of the PHA filter segment (based on the length of the PHA filter segment in the article) is at least about 25 millimeters H ₂ O. More preferably, the RTD of the PHA filter segment is at least about 50 millimeters H ₂ O, more preferably at least about 100 millimeters H ₂ O. Even more preferably, in an aerosol-generating article according to the invention, the RTD of the PHA filter segment is at least about 150 millimeters H ₂ O, more preferably at least about 180 millimeters H ₂ O. The RTD of the PHA filter segment (based on the length of the PHA filter segment in the article) is preferably no greater than about 300 millimeters H ₂ O, more preferably no greater than 250 millimeters H ₂ O. For example, the RTD of the PHA filter segment can be from about 25 millimeters _H2O to about 300 millimeters _H2O , or from about 50 millimeters _H2O to about 300 millimeters _H2O , or from about 100 millimeters _H2O to about 250 millimeters _H2O , or from about 150 millimeters _H2O to about 250 millimeters _H2O , or from about 180 millimeters _H2O to about 250 millimeters _H2O , or about 200 millimeters _H2O .

Preferably, in an aerosol-generating article according to the invention, the RTD of the PHA filter segment (based on the length of the PHA filter segment in the article) is at least about 20 millimeters H ₂ O. More preferably, the RTD of the PHA filter segment is at least about 22 millimeters H ₂ O, more preferably at least about 25 millimeters H ₂ O. Even more preferably, in an aerosol-generating article according to the invention, the RTD of the PHA filter segment is at least about 28 millimeters H ₂ O, more preferably at least about 30 millimeters H ₂ O. The RTD of the PHA filter segment (based on the length of the PHA filter segment in the article) is preferably no greater than about 45 millimeters H ₂ O, more preferably no greater than 40 millimeters H ₂ O. For example, the RTD of the PHA filter segment can be from about 20 millimeters _H2O to about 45 millimeters _H2O , or from about 22 millimeters _H2O to about 45 millimeters _H2O , or from about 25 millimeters _H2O to about 40 millimeters _H2O , or from about 28 millimeters _H2O to about 40 millimeters _H2O , or from about 30 millimeters _H2O to about 40 millimeters _H2O , or about 37 millimeters _H2O .

"Resistance to withdrawal" refers to the static pressure difference between the two ends of the sample when air flows through it under steady conditions with a volumetric 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.

The PHA filter segments of the aerosol-generating articles according to the invention have additionally been found to provide good stability in RTD, meaning that high variability in RTD can be advantageously avoided. For example, within 20 samples of an aerosol-generating article according to the invention, there will typically be a standard deviation from the target RTD of 2 percent to 10 percent, more preferably 2 percent to 5 percent.

Preferably, the PHA filter segments of the aerosol-generating articles according to the invention have an average radial hardness of at least 80 percent, more preferably at least 85 percent. Thus, the PHA filter segments can 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 segments can be further increased by surrounding the PHA filter segments with a stiff plug wrap, such as a plug wrap having 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.

式中Ｄ_Sは元の（押し下げられていない）直径であり、Ｄ_dは設定継続時間にわたり、設定された負荷をかけた後の押し下げられた直径である。材料が硬いほど硬度は１００％に近づく。 The term "radial hardness" as used herein refers to resistance to compression 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 across the article at the location of the filter in a direction transverse to the longitudinal axis of the article and measuring the average (mean) depressed diameter of the article. Radial hardness is given by:

where _Ds is the original (undepressed) diameter and _Dd is the depressed diameter after a set load is applied for a set duration. The harder the material, the closer the hardness will be to 100%.

To determine the hardness 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 being tested should be subjected to a set load for a set duration. This test is performed using a well-known DD60A Densimeter instrument (manufactured and sold by Heinr. Borgwaldt GmbH, Germany), which is fitted with a measuring head for an aerosol-generating article such as a cigarette, and with an aerosol-generating article container.

Loading is applied using two loading cylindrical rods that extend across the diameter of all aerosol-generating articles at once. Standard test methods for this instrument should ensure that testing is performed such that twenty points of contact are created between the aerosol-generating articles and the loading cylindrical rods. In some cases, the filter being tested may be long enough that only ten aerosol-generating articles are needed to create twenty points of contact, with each smoking article contacting both loading rods (because they are long enough to extend between the rods). In other cases, where the filter is too short to achieve this, twenty aerosol-generating articles should be used to create twenty points of contact, with each aerosol-generating article contacting only one of the loading rods, as discussed further below.

Two additional fixed cylindrical rods are positioned below the aerosol-generating article to support the aerosol-generating article and counter the loads exerted by each of the load-applying cylindrical rods.

For standard operating procedures for such devices, an overall load of 2 kg is applied for 20 seconds. After the 20 seconds have elapsed (and the load is still applied to the smoking article), the depression on the load application cylindrical rod is determined and then used to calculate the hardness from the above equation. The temperature is kept within the range of 22 degrees Celsius ± 2 degrees Celsius. The above test is referred to as the DD60A test. The standard method of measuring filter hardness is when the aerosol-generating article has not yet been consumed. Additional information regarding the measurement of average radial hardness can be found, for example, in U.S. Published Patent Application Publication No. 2016/0128378.

As discussed above, the use of PHA fibers to fabricate filter segments of aerosol-generating articles according to the present invention advantageously provides improved biodegradability compared to conventional cellulose acetate filters.

Preferably, the PHA filter segments have a biodegradability in aqueous media of at least about 45 percent, more preferably at least about 50 percent, and most preferably at least about 55 percent, as measured according to the test method described in ISO 14851 Determination of the ultimate aerobic biodegradability of plastic materials in aqueous media - Method by measurement of oxygen demand in a closed respirometer (2005).

Under the same test conditions, cellulose acetate filter segments exhibit approximately 30 percent biodegradability. Therefore, it is believed that using PHA fibers instead of cellulose acetate fibers to form filter segments will result in a significant improvement in the biodegradability of the filter segments.

The size of the PHA filter segment can vary depending on the type of aerosol-generating article in which it is incorporated.

Preferably, the PHA filter segment has 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 segment has a length of about 30 millimeters or less, about 27 millimeters or less, more preferably about 25 millimeters or less, and most preferably about 20 millimeters or less.

For example, the length of the PHA filter segment is preferably about 5 millimeters to about 30 millimeters, more preferably about 10 millimeters to about 30 millimeters, even more preferably about 15 millimeters to about 30 millimeters, and most preferably about 20 millimeters to about 30 millimeters. Alternatively, in such embodiments, the length of the PHA filter segment may be 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. As a further alternative, in such embodiments, the length of the PHA filter segment may be about 4 millimeters to about 25 millimeters, preferably about 5 millimeters to about 25 millimeters, more preferably about 10 millimeters to about 25 millimeters, even more preferably about 15 millimeters to about 30 millimeters, and most preferably about 20 millimeters to about 25 millimeters.

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 from about 20 millimeters to about 30 millimeters, more preferably from about 25 millimeters to about 30 millimeters, and most preferably about 27 millimeters.

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 that is intended to be heated by electrical heating means or an integral heat source, as described in more detail below, the length of the PHA filter segment is preferably from about 5 millimeters to about 15 millimeters, more preferably from about 5 millimeters to about 10 millimeters, and most preferably about 7 millimeters.

The PHA filter segment preferably has an outer diameter approximately equal to the outer diameter of the aerosol-generating article. The filter segment preferably has an outer diameter of at least 5 millimeters. The PHA filter segment may have an outer diameter of about 5 millimeters to about 12 millimeters, for example, 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 to within 10 percent of 7.2 millimeters.

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

In an alternative embodiment, the PHA filter segment may be in the form of a hollow tube segment. A hollow tube segment has a larger exposed surface area than a cylindrical plug of comparable diameter, which may further improve the biodegradability of the PHA filter segment.

The hollow tube segments preferably have a wall thickness of at least about 0.3 millimeters. More preferably, the hollow tube segments have 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.

The hollow tube segments preferably have a wall thickness of about 1.9 millimeters or less. More preferably, the hollow tube segments have a wall thickness of about 1.5 millimeters or less. Even more preferably, the hollow tube segments have a wall thickness of about 1.2 millimeters or less. It is especially preferred that the hollow tube segments have a wall thickness of about 0.9 millimeters or less.

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

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

The filter of the aerosol-generating article according to the invention may be a single segment filter consisting of only a PHA filter segment. Alternatively, the filter of the aerosol-generating article according to the invention may further comprise one or more additional filter segments formed from a filtering material, which may be provided upstream or downstream of the PHA filter segment as described above. For example, the PHA filter segment may be combined with one or more axially aligned filter plugs formed from a fibrous filtering material, which may or may not include PHA fibers. Alternatively or additionally, the PHA filter segment 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 additional filter segments are formed from a material other than cellulose acetate. Particularly preferably, the additional filter segments comprise PHA fibers, which may optionally be held in a desired shape by a suitable adhesive such as PVA. Preferably, each of the additional filter segments comprises at least about 25 weight percent PHA compound, and more preferably at least about 50 weight percent PHA compound.

The filter of the aerosol-generating article according to the present invention may optionally include a flavoring agent. The flavoring agent may be incorporated using a variety of different means that will be known to those skilled in the art. For example, the flavoring agent may be incorporated in the form of a capsule that may be provided in the PHA filter segment or in an additional filter segment.

The filter of the aerosol-generating article according to the invention is preferably surrounded by an outer wrapper, e.g. a tipping wrapper, which surrounds the filter segment, the downstream end of the aerosol-generating substrate, and any additional components that may be provided therebetween. The tipping wrapper may comprise a removable tipping wrapper portion, as described in WO-A-2017/162838, which allows at least a portion of the tipping wrapper to be removed before the aerosol-generating article is discarded. Removal of the tipping wrapper exposes the underlying filter segment and may therefore advantageously increase 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, which is 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 about 5 millimeters to about 100 mm. Preferably, the aerosol-generating substrate has a length of at least about 5 millimeters, and 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, and 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, and even more preferably less than about 20 millimeters. In one embodiment, the aerosol-generating substrate may have a length of about 10 millimeters. In one preferred embodiment, the aerosol-generating substrate has a length of about 12 millimeters.

As discussed above, the filters of the present invention comprising PHA segments find particular application in combustible smoking articles due to the potential to provide relatively high levels of RTD for PHA segments having a defined range of dpf. In a preferred embodiment, the aerosol-generating article according to the present invention is therefore a filtered cigarette or other smoking article having an aerosol-generating substrate therein, comprising tobacco material that combusts to form smoke. Thus, in any of the above-described embodiments, the aerosol-generating substrate may comprise a tobacco rod. The tobacco rod may comprise one or more cut fillers and reconstituted tobacco.

For embodiments in which the aerosol-generating article is in the form of a combustible smoking article, the aerosol-generating substrate is typically a tobacco rod, preferably having a length of from about 10 millimeters to about 100 millimeters, more preferably having a total length of from about 30 millimeters to about 70 millimeters.

Alternatively, an aerosol-generating article according to the invention may be an article in which the tobacco material therein is heated to form an aerosol, rather than combusted. In one type of heated aerosol-generating article, the tobacco material is heated by one or more electrical heating elements to generate the aerosol. In another type of heated aerosol-generating article, the aerosol is generated by the transfer of 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 invention further encompasses aerosol-generating articles in which a nicotine-containing aerosol is generated from tobacco material, tobacco extract, or other nicotine source without combustion, and in some cases without heating, e.g., by a chemical reaction.

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

For those 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 homogenized tobacco material formed from an agglomeration of tobacco particles. The aerosol-generating substrate may comprise one or more of an assembly of sheets of homogenized tobacco material. One or more of the sheets may be textured. As used herein, the term "textured sheet" means a sheet that is crimped, embossed, debossed, perforated, or otherwise deformed. Alternatively, the aerosol-generating substrate may comprise a plurality of strips or strands of homogenized tobacco material. The strips or strands may be substantially aligned with one another in the longitudinal direction, or may be randomly oriented.

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

The homogenized tobacco material for use in the aerosol-generating substrate may include one or more intrinsic binders that are tobacco intrinsic binders, one or more extrinsic binders that are tobacco extrinsic binders, or combinations thereof to aid in the aggregation of particulate tobacco. Alternatively, or in addition, the homogenized tobacco material for use in the aerosol-generating substrate may include other additives, including, but not limited to, tobacco and non-tobacco fibers, aerosol formers, humectants, plasticizers, flavorants, fillers, aqueous and non-aqueous solvents, and combinations thereof.

Suitable exogenous binders for inclusion in homogenized tobacco materials for use in aerosol-generating substrates are well known in the art and include, but are not limited to, gums (e.g., guar gum, xanthan gum, gum arabic, locust bean gum, etc.), cellulosic binders (e.g., hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, etc.), polysaccharides (e.g., starch, organic acids such as alginic acid, conjugate base salts of organic acids such as sodium alginate, agar, pectin, etc.), and combinations thereof.

Non-tobacco fibers suitable for inclusion in homogenized tobacco material for use in an aerosol-generating substrate are well 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 homogenized tobacco material for use in an aerosol-generating substrate, the non-tobacco fibers may be treated by any suitable process known in the art, including, but not limited to, mechanical pulping, refining, chemical pulping, bleaching, sulfate pulping, and combinations thereof.

Aerosol-generating substrates for heated aerosol-generating articles typically include an "aerosol former", i.e., a compound or mixture of compounds that facilitates the formation of an aerosol during use and that is preferably substantially resistant to thermal decomposition at the use temperature of the aerosol-generating article. Examples of suitable aerosol formers include polyhydric alcohols (such as propylene glycol, triethylene glycol, 1,3-butanediol, glycerin, etc.), esters of polyhydric alcohols (such as glycerol monoacetate, diacetate or triacetate), and aliphatic esters of mono-, di- or polycarboxylic acids (such as dimethyl dodecanedioate, dimethyl tetradecanedioate, etc.). Preferred aerosol formers are polyhydric alcohols or mixtures thereof (such as propylene glycol, triethylene glycol, 1,3-butanediol, and most preferably glycerin).

The aerosol-generating substrate preferably comprises at least about 10 weight percent aerosol formers, more preferably at least about 12 weight percent aerosol formers, and even more preferably at least about 15 weight percent aerosol formers. Alternatively or additionally, the aerosol-generating substrate preferably comprises no more than 30 weight percent aerosol formers, more preferably no more than about 25 weight percent aerosol formers, and even more preferably no more than about 20 weight percent aerosol formers. For example, the aerosol-generating substrate may comprise from about 10 weight percent to about 30 weight percent aerosol formers, or from about 12 weight percent to about 25 weight percent aerosol formers, or from about 15 weight percent to about 20 weight percent aerosol formers. In a particularly preferred embodiment, the aerosol-generating substrate comprises about 18 weight percent aerosol formers.

The aerosol-generating article according to the present invention may further comprise one or more additional 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 moving element. The structure of such components will be well known to those skilled in the art.

For example, in certain preferred embodiments of the present invention, the aerosol-generating article includes, in a linear, continuous arrangement, an aerosol-generating substrate, a support element immediately downstream of the aerosol-generating substrate, an aerosol-cooling element immediately downstream of the support element, and a mouthpiece including a PHA filter segment at the downstream end of the filter.

In another preferred embodiment of the present invention, the aerosol-generating article includes, in a linear, continuous arrangement, an aerosol-generating substrate, a moving 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 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 during use to generate an aerosol. Suitable carbonaceous heat sources will be known to those skilled in the art.

The invention will now be further described with reference to the drawings.

FIG. 1 shows a schematic longitudinal cross-section of an aerosol-generating article according to a first embodiment of the invention for use in an aerosol-generating device comprising a heater element. FIG. 2 shows a schematic longitudinal cross-sectional view of an aerosol-generating article according to a second embodiment of the invention, which includes an integral heat source. FIG. 3 shows a schematic longitudinal cross-section of an aerosol-generating article according to a third embodiment of the invention. FIG. 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 FIG.

The aerosol-generating article 10 shown in FIG. 1 comprises a rod of aerosol-generating substrate 12, a support element 14 provided as a hollow tubular element, a cooling element 16, and an oral end filter segment 18. These four elements are arranged in continuous and coaxial alignment and surrounded by a substrate wrapper 20 to form the aerosol-generating article 10. The aerosol-generating article 10 has an oral end 22 and a distal end 24 located at the opposite end of the article relative to the oral end 22. The aerosol-generating article 10 shown in FIG. 1 is particularly suitable for use in an electrically operated aerosol generating device that includes a heater for heating the rod of aerosol-generating substrate.

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

The aerosol-generating substrate 12 is located at the farthest distal or upstream end of the aerosol-generating article 10. In the embodiment illustrated in FIG. 1, the aerosol-generating substrate 12 comprises an assembly of a crimped homogenized tobacco material sheet surrounded by a wrapper. The crimped sheet of homogenized tobacco material includes glycerin as an aerosol former.

The support element 14 is located immediately downstream of the aerosol-generating substrate 12 and abuts against the aerosol-generating substrate 12. In the embodiment shown in FIG. 1, the support element is a hollow tube formed from a fibrous filter material. The support element 14 positions the aerosol-generating substrate 12 at the farthest distal end 24 of the aerosol-generating article 10 so that it can be penetrated by the heating element of the aerosol-generating device. In effect, the support element 14 serves to prevent the aerosol-generating substrate 12 from being pushed downstream in the aerosol-generating article 10 toward the aerosol-cooling element 16 when the heating element of the aerosol-generating device is inserted into the aerosol-generating 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-generating substrate 12.

The aerosol cooling element 16 is located immediately downstream of and adjacent to the support element 14. In use, volatile material emitted from the aerosol-generating substrate 12 passes along the aerosol cooling element 16 toward the mouth end 22 of the aerosol-generating article 10. The volatile material may be cooled within the aerosol cooling element 16 to form an aerosol that is inhaled by the user. In the embodiment shown in FIG. 1, the aerosol cooling element includes a tubular element 20. An assembly of crimped sheets of polylactic acid defines a plurality of longitudinal channels that extend along the length of the aerosol cooling element 40.

The filter segment 18 is located immediately downstream of and adjacent to the aerosol cooling element 16. In the embodiment shown in FIG. 1, the filter segment 18 comprises a single cylindrical plug of fibrous filtration material formed from a plurality of PHA fibers having a denier per filament of about 3 and a total denier of about 27,000. The PHA fibers have a circular cross-sectional shape and are substantially longitudinally aligned with one another along the length of the filter segment. The total exterior surface area of the PHA fibers corresponds to about 0.16 square meters per gram. The PHA fibers are formed by a melt spinning process and are crimped. The plug of fibrous filtration material is surrounded by a plug wrap (not shown).

The aerosol-generating article 100 shown in FIG. 2 includes a combustible heat source 112, a rod of aerosol-generating substrate 114, a moving element 116, an aerosol cooling element 118, a spacer element 120, and a mouthpiece filter segment 122. These elements are arranged in a continuous, coaxial alignment and surrounded by a substrate wrapper to form the aerosol-generating article 100.

The combustible heat source 112 comprises a substantially annular cylindrical body of 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 therethrough.

A rod of aerosol-generating substrate 114 is disposed at the proximal end of the combustible heat source 112. The aerosol-forming substrate 114 comprises a substantially annular cylindrical plug 124 of tobacco material surrounded by a filter plug wrap 126.

A non-flammable, substantially impermeable first barrier 128 is disposed 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 for conducting heat from the proximal surface of the combustible heat source 112 to the distal surface of the aerosol-generating substrate 114.

The thermally conductive element 130 surrounds the proximal portion of the combustible heat source 112 and the distal portion of the aerosol-generating substrate 114. The thermally conductive element 130 comprises an aluminum foil tube. The thermally conductive element 130 is in direct contact with the proximal portion of the combustible heat source 112 and the filter plug wrap 126 of the aerosol-generating substrate 114.

The mouthpiece filter 122 comprises a single cylindrical plug 126 of fibrous filtration material formed from a plurality of PHA fibers having a denier per filament of about 3 and a total denier of about 27,000. The PHA fibers have a circular cross-sectional shape and are substantially longitudinally aligned with one another along the length of the filter segment. The total exterior surface area of the PHA fibers corresponds to about 0.16 square meters per gram. The PHA fibers are formed by a melt spinning process and are crimped. The plug of fibrous filtration material is surrounded by a plug wrap (not shown).

The aerosol-generating article 310 shown in FIG. 3 is a combustible smoking article that includes an aerosol-generating substrate 312 and a filter 314 arranged in a coaxial arrangement with respect to one another. The aerosol-generating substrate 312 includes a tobacco rod surrounded by an outer wrapper (not shown). A tipping wrapper 316 surrounds both the filter 314 and the ends of the aerosol-generating substrate 312 and attaches the filter 314 to the aerosol-generating substrate 312.

The filter 314 comprises a single cylindrical plug 318 of fibrous filtration material formed from PHA fibers having a denier per filament of about 3 and a total denier of about 27,000. The PHA fibers have a circular cross-sectional shape and are substantially longitudinally aligned with one another along the length of the filter segment. The total exposed surface area of the PHA fibers corresponds to about 0.16 square meters per gram. The PHA fibers are formed by a melt spinning process and are crimped. The plug of fibrous filtration material is surrounded by a plug wrap (not shown).

Figure 4 shows a portion of an electrically operated aerosol generating system 200 utilizing a heater blade 210 to heat the rod of the aerosol-generating substrate 12 of the aerosol-generating article 10 shown in Figure 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 number of air holes 214 for allowing air to flow to the aerosol-generating article 10, as illustrated by the arrows in Figure 4. The aerosol generating device 212 includes a power source and electronic components, which are not shown in Figure 4.

Comparative Example PHA filter segments according to the present invention are prepared from PHA fibers with the parameters shown in Table 1 below. The PHA fibers are formed using a melt spinning process, after which the fibers are crimped and formed into filter segments using standard filter manufacturing equipment. For comparison purposes, conventional cellulose acetate (CA) tow filter segments are prepared with similar values of denier per filament (dpf) and total denier.

The first test compares the water absorption of PHA filter segments according to the present invention and CA filter segments upon exposure to water. For each filter segment, the plug wrap is removed and the filter segment is attached to the probe of a force tensiometer (KRUSS force tensiometer, model K100). The filter segment is moved downwards by the probe into a container of water, automatically stopping when the filter segment contacts the water. The filter segment is held in contact with the water for 300 seconds to allow the filter material to absorb the water, and then the filter segment is weighed to determine the amount of water absorbed during the test period. For each of the PHA and CA filter segments, this test was repeated three times and the average water absorption was calculated, as shown in Table 2 below.

Thus, the amount of water absorbed by the PHA filter segment according to the present invention during the test was less than 40 percent of the amount of water absorbed by the CA filter segment. Thus, this test shows that the PHA filter segment according to the present invention has a significantly lower affinity for water compared to the conventional CA filter segment.

The second test compares the water absorption of PHA filter segments according to the invention and CA filter segments upon exposure to moisture. For each filter segment, the plug wrap is removed and the fibers forming the filter segment are placed in a Petri dish and exposed to air at 22° C. and 50 percent relative humidity for 70 hours. This is performed with a vapor sorption analyzer (ProUmid SPSx-1μ). For each filter segment, the fibers are weighed at the start of the test and the change in weight over time due to the fibers absorbing water vapor is measured. For each of the PHA and CA filter segments, a percentage difference in the mass of the samples (% dm) value is calculated, expressing the increase in the weight of the sample as a percentage of its original weight. The % dm values for each sample at the end of the 70-hour test are shown in Table 3 below:

The results show that the amount of water vapor absorbed by the cellulose acetate fibers during the 70 hour test was more than 50 times greater than the amount of water vapor absorbed by the PHA fibers. The PHA fibers absorbed very little water vapor during the test. This further indicates that the PHA filter segments according to the present invention have a significantly lower affinity for water compared to conventional CA filter segments.

In the third test, the water absorption from mainstream smoke by the PHA filter segment according to the present invention and the conventional CA filter segment is compared. For each of the filter segments, a conventional smoking article is prepared as described above with reference to FIG. 3, using a combustible tobacco rod and a single segment of filtering material forming a filter. Each of the smoking articles is then smoked in a cigarette smoker under ISO conditions described in ISO 3308:2000 (puff volume 35 ml, puff duration 2 seconds every 60 seconds), and an analysis of the resulting smoke is performed. For each of the filter segments, the amount of water in the mainstream smoke collected during the smoking test is measured, as shown in Table 4:

This indicates that, when smoked under comparable conditions, smoking articles incorporating PHA filter segments produce mainstream smoke having a moisture content that is about 20 percent higher than the moisture content of mainstream smoke from smoking articles containing CA filter segments. This indicates that the PHA filter segments do not absorb as much water from the mainstream smoke as the CA filter segments, thereby reducing the potential dry smoke problem discussed above.

Claims (12)

1. 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 a filtration material formed from a plurality of fibers comprising a polyhydroxyalkanoic acid compound, the fibers having a denier per fiber (dpf) of 1.5 to 2.7, a total denier of the fibers being 25,000 to 40,000, and the at least one filter segment comprising at least 20 weight percent of the polyhydroxyalkanoic acid compound. The aerosol-generating article of claim 1, wherein the plurality of fibers comprising the polyhydroxyalkanoic acid compound have a circular cross-sectional shape and provide a total exterior surface area within the filter segment of 0.15 square meters/gram to 0.3 square meters/gram. The aerosol-generating article of claim 1, wherein the plurality of fibers comprising the polyhydroxyalkanoic acid compound have a Y-shaped cross-sectional shape and provide a total exterior surface area within the filter segment of 0.3 square meters/gram to 0.55 square meters/gram. The aerosol-generating article according to any one of claims 1 to 3, wherein the filtering material further comprises a plurality of fibers of at least one additional biodegradable polymer. 5. The aerosol-generating article of claim 1, wherein the filter segment comprising the plurality of fibers comprising the polyhydroxyalkanoic acid compound has a resistance to draw (RTD) of from 150 millimeters _H2O to about 250 millimeters _H2O . The aerosol-generating article according to any one of claims 1 to 5, wherein the filter segment comprising the plurality of fibers containing the polyhydroxyalkanoic acid compound is at least 50 percent biodegradable in an aqueous medium when tested according to ISO 14851. The aerosol-generating article according to any one of claims 1 to 6, wherein the filter segment comprising the plurality of fibers containing the polyhydroxyalkanoic acid compound further comprises at least 5 weight percent polyethylene glycol. The aerosol-generating article according to any one of claims 1 to 7, wherein the filter segment comprising the plurality of fibers containing the polyhydroxyalkanoic acid compound has an average radial hardness of at least 80 percent. The aerosol-generating article of any one of claims 1 to 8, wherein the filter segment comprising the plurality of fibers containing the polyhydroxyalkanoic acid compound is surrounded by a wrapper having a basis weight of at least 100 grams per square meter (gsm). The aerosol-generating article according to any one of claims 1 to 9, wherein the filter segment comprising the plurality of fibers containing the polyhydroxyalkanoic acid compound is in the form of a hollow tubular element. The aerosol-generating article according to any one of claims 1 to 10, wherein the aerosol-generating substrate is a tobacco rod having a length of at least 30 millimeters. A filter for an aerosol-generating article, the filter comprising at least one filter segment of a filtration material formed from a plurality of fibers comprising a polyhydroxyalkanoic acid compound, the fibers having a denier per fiber (dpf) of 1.5 denier to 2.7 denier, the total denier of the fibers being 25,000 to 40,000, and the at least one filter segment comprising at least 20 weight percent of the polyhydroxyalkanoic acid compound.

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