Aerosol-generating article having downstream element comprising novel filtration material with phenol-reducing additive

Abstract

An aerosol-generating article (10)(100)(1000) comprises: an aerosol-generating substrate (12)(112)(1004); a downstream element (42)(150)(1008) provided downstream of the aerosol- generating substrate (12)(112)(1004) and in axial alignment with the aerosol-generating substrate, the downstream element comprising a filtration material comprising a cellulosic filtration material comprising a fibrous material; and an additive coating applied to the fibrous material, the additive coating comprising at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol; wherein the plug element comprises at least 5 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

Description

[0001] AEROSOL-GENERATING ARTICLE HAVING DOWNSTREAM ELEMENT COMPRISING NOVEL FILTRATION MATERIAL WITH PHENOL-REDUCING ADDITIVE

[0002] The present invention relates to an aerosol-generating article having a downstream element formed of a novel filtration material.

[0003] 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 an abutting end-to-end relationship, with the wrapped tobacco rod. The cylindrical filter typically comprises one or more plug elements of a fibrous filtration material, such as cellulose acetate tow, circumscribed by a paper plug wrap. Conventionally, the wrapped tobacco rod and the filter are joined by a band of tipping wrapper, normally formed of an opaque paper material that circumscribes the entire length of the filter and an adjacent portion of the wrapped tobacco rod. In known filter cigarettes, the filter is typically adapted for the removal of particulate and gaseous components of the mainstream smoke.

[0004] A number of aerosol-generating articles in which tobacco is heated rather than combusted have also been proposed in the art. In heated aerosol-generating articles, an aerosol is generated by heating an aerosol-generating substrate, such as tobacco. Known heated aerosol-generating articles include, for example, smoking articles in which an aerosol is generated by electrical heating or by the transfer of heat from a combustible fuel element or heat source to an aerosolgenerating substrate. During smoking, volatile compounds are released from the aerosolgenerating substrate by heat transfer from the heat source and entrained in air drawn through the smoking article. As the released compounds cool they condense to form an aerosol that is inhaled by the consumer. Many known heated aerosol-generating articles comprise one or more elements formed of a fibrous filtration material.

[0005] After an aerosol-generating article has been smoked and discarded, it would generally be desirable for its components - and particularly for any elements formed of fibrous filtration material - to break down as quickly as possible. However, cellulose acetate, the fibrous filtration material most ordinarily used in aerosol-generating articles, is not biodegradable, and can persist in the environment for years. As a result, used cigarette filters formed from cellulose acetate have a tendency to accumulate in the environment, and are among the most commonly retrieved plastic items in beach clean-up activities. Therefore, it would be desirable to provide a more sustainable alternative to cellulose acetate for producing aerosol-generating article components and in particular, filter or mouthpiece components.

[0006] To tackle the environmental impact caused by post-consumption waste of articles containing non-biodegradable plastic, discarded directly into the environment, certain jurisdictions are introducing legislations banning single-use plastic products (SUPs). The term SUPs denotes products made wholly or partly from plastic and that are typically intended to be used just once or for a short period of time before being disposed of. Accordingly, it would be generally desirable to replace single-use plastics in aerosol-generating articles with natural, biodegradable alternatives.

[0007] A wide variety of alternative materials have in fact already been proposed for use as filtration materials for aerosol-generating articles. In order for such alternative filtration materials to provide an acceptable filtration efficiency, an additive may be combined with the filtration material to remove certain undesirable compounds, such as phenols, from the aerosol generated from the substrate. At the same time, use of certain additives in combination with the filtration material may improve the sensorial or organoleptic properties of the smoke or aerosol. However, the migration of such additives within the alternative filtration materials has been found to be problematic and this reduces the effectiveness of the additive.

[0008] Thus, it would be desirable to provide an aerosol-generating article comprising an element formed of a filtration material that can effectively reduce or remove undesirable compounds from the aerosol generated from the substrate (for example, phenols).

[0009] Further, it would be desirable to provide such an aerosol-generating article wherein the element is formed of a filtration material having increased biodegradability, but which provides a filtration efficiency that is comparable to that of a cellulose acetate tow.

[0010] Further, it would be desirable to provide such an aerosol-generating article that gives an acceptable sensory experience to the consumer. In particular, it would be desirable for the component to be formed of a biodegradable filtration material that has very little or no impact on the taste perceived by the consumer during use of the aerosol-generating article, and that generally does not adversely impact the smoking experience.

[0011] In addition, it would be desirable to provide such an aerosol-generating article that can be readily manufactured using existing high-speed techniques and apparatus requiring only minimal modifications.

[0012] Furthermore, it would be desirable for the filtration material to be such that it can be effectively formed into components that provide an acceptable appearance and feeling to the consumer. For example, it would be desirable for the filtration material to be such that it can be effectively formed into components for an aerosol-generating article, which provide a desirable density, firmness and resistance to draw (RTD).

[0013] The present disclosure relates to an aerosol-generating article. The aerosol-generating article may comprise an aerosol-generating substrate. The aerosol-generating article may comprise a downstream element provided downstream of the aerosol-generating substrate and in axial alignment with the aerosol-generating substrate. The downstream element may comprise a plug element comprising a cellulosic filtration material comprising a fibrous material. The downstream element may further comprise an additive coating applied to the fibrous material. The additive coating may be provided over an outer surface of the fibrous material, such as to form a layer containing the additive over at least a portion of the outer surface of the fibrous material. Alternatively, or in addition, the additive coating may impregnate or be absorbed into the fibrous material, such that at least some of the additive is present within the fibres. Thus, when describing downstream elements for use in aerosol-generating articles in accordance with the present disclosure, the term “applied to the fibrous material” means that additive is present on, within, or both on and within the fibres.

[0014] The additive coating may comprise at least one of dipropylene glycol and tripropylene glycol. The plug element may comprise at least 5 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

[0015] According to the present invention there is provided an aerosol-generating article comprising: an aerosol-generating substrate; a downstream element provided downstream of the aerosol-generating substrate and in axial alignment with the aerosol-generating substrate, the downstream element comprising a plug element comprising a cellulosic filtration material comprising a fibrous material; and an additive coating applied to the fibrous material, the additive coating comprising at least one ethoxylated castor oil; wherein the plug element comprises at least 5 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

[0016] As used herein with reference to the invention, the term “aerosol-generating article” is used to describe an article comprising an aerosol-generating substrate that is heated to generate an inhalable aerosol for delivery to a user.

[0017] As used herein with reference to the invention, the term “aerosol-generating substrate” is used to describe a substrate comprising aerosol-generating material that is capable of releasing upon heating (including combustion) volatile compounds that can generate an aerosol.

[0018] As used herein with reference to the invention, the term “aerosol” is used to describe a dispersion of solid particles, or liquid droplets, or a combination of solid particles and liquid droplets, in a gas. The aerosol may be visible or invisible. The aerosol may include vapours of substances that are ordinarily liquid or solid at room temperature as well as solid particles, or liquid droplets, or a combination of solid particles and liquid droplets. As used herein, the term “aerosol” encompasses the aerosol produced upon heating of a substrate in a heated aerosolgenerating article and the smoke produced upon combustion of a substrate in a combustible smoking article.

[0019] As used herein with reference to the invention, the term “aerosol-generating device” is used to describe a device that interacts with the aerosol-generating substrate of the aerosolgenerating article to generate an aerosol. Aerosol-generating articles according to the invention have a proximal end through which, in use, an aerosol exits the aerosol-generating article for delivery to a user. The proximal end of the aerosol-generating article may also be referred to as the downstream end or the mouth end of the aerosol-generating article. In use, a user draws directly or indirectly on the proximal end of the aerosol-generating article in order to inhale an aerosol generated by the aerosol-generating article.

[0020] Aerosol-generating articles according to the invention have a distal end. The distal end is opposite the proximal end. The distal end of the aerosol-generating article may also be referred to as the upstream end of the aerosol-generating article.

[0021] Components of aerosol-generating articles according to the invention may be described as being upstream or downstream of one another based on their relative positions between the proximal end of the aerosol-generating article and the distal end of the aerosol-generating article.

[0022] As used herein with reference to the invention, the term “longitudinal” is used to describe the direction between the upstream end and the downstream end of the aerosol-generating article. During use, air is drawn through the aerosol-generating article in the longitudinal direction.

[0023] As used herein with reference to the invention, the term “length” is used to describe the maximum dimension of the aerosol-generating article or a component of the aerosol-generating article in the longitudinal direction.

[0024] As used herein with reference to the invention, the term “transverse” is used to describe the direction perpendicular to the longitudinal direction. Unless otherwise stated, references to the “cross-section” of the aerosol-generating article or a component of the aerosol-generating article refer to the transverse cross-section.

[0025] As used herein with reference to the invention, the term “width” denotes the maximum dimension of the aerosol-generating article or a component of the aerosol-generating article in a transverse direction. Where the aerosol-generating article has a substantially circular crosssection, the width of the aerosol-generating article corresponds to the diameter of the aerosolgenerating article. Where a component of the aerosol-generating article has a substantially circular cross-section, the width of the component of the aerosol-generating article corresponds to the diameter of the component of the aerosol-generating article.

[0026] As used herein with reference to the invention, the term “rod” is used to denote a generally cylindrical element having a substantially circular, oval or elliptical cross-section.

[0027] As used herein with reference to the invention, the term "hollow tubular element" is used to denote a generally cylindrical element having a lumen along a longitudinal axis thereof. The tubular portion may have a substantially circular, oval or elliptical cross-section. The lumen may have a substantially circular, oval or elliptical cross-section. In particular, the term "hollow tubular element" is used to denote an element defining at least one airflow conduit establishing an uninterrupted fluid communication between an upstream end of the hollow tubular element and a downstream end of the tubular element.

[0028] Unless otherwise specified, the resistance to draw (RTD) of a component or an aerosolgenerating article in accordance with the invention is measured in accordance with ISO 6565- 2015. The RTD refers the pressure required to force air through the full length of a component. The terms “pressure drop” or “draw resistance” of a component or article may also refer to the “resistance to draw”. Such terms generally refer to the measurements in accordance with ISO 6565-2015 and are normally carried out at a volumetric flow rate of about 17.5 millilitres per second at the output or downstream end of the measured component, at a temperature of about 22 degrees Celsius, a pressure of about 101 kPa (about 760 Torr) and a relative humidity of about 60%.

[0029] The aerosol stream generated during use of an aerosol-generating article is a complex mixture of chemicals, including semi-solid particles dispersed in a fluid matrix of vapours and permanent gases. As used herein with reference to the invention, the term "filtration efficiency" is used to describe the ability of an element comprising a filtration material to capture particulate matter contained in such aerosol stream. In practice, the term “filtration efficiency” denotes the fraction of the overall dry particulate matter carried in the aerosol stream that is retained within the element comprising filtration material during use.

[0030] As used herein, the term “phenols” refers to a class of chemical compounds consisting of a hydroxyl group ( — OH) bonded directly to an aromatic hydrocarbon group. The phenol group includes phenol, catechol, m+P cresols, and o-cresol.

[0031] The present invention provides an improved aerosol-generating article including at least one downstream element formed of a filtration material comprising an additive for reducing phenols. The additive comprises at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol in a predetermined amount, which is proportional to the dry weight of cellulosic filtration material in the downstream element.

[0032] Compared with other known additives that present comparable affinity for phenols, an additive in accordance with the present invention has been found to display significantly reduced tendency to migrate within the filtration material. Accordingly, the efficiency of the downstream element in reducing the phenols in the aerosol generated from the aerosol-generating substrate can advantageously be maximised. Further, as will be discussed below, use of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol in combination with one or more other agents has been found to provide an even higher ability to scavenge phenols compared with when the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol is used alone.

[0033] The filtration material can advantageously be formed using a biodegradable fibrous material or cellulosic sheet material as a carrier for the additive. Aerosol-generating articles according to the present invention can therefore advantageously be formed of more sustainable materials, containing a reduced or zero level of single use plastics.

[0034] In particular, aerosol-generating articles according to the invention can use natural fibrous or sheet materials to form elements such as filtration elements, thereby significantly improving the biodegradability of the aerosol-generating article. Several alternative filtration materials with good biodegradability that are suitable for use in aerosol-generating articles according to the present invention will be described below.

[0035] In the additive coating of aerosol-generating articles according to the present invention, the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol is provided for reducing phenols. That is, the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol in the coating additive is capable of capturing or otherwise converting at least some of the phenols and phenol derivatives produced upon heating or burning of the aerosol-generating substrate.

[0036] Dipropylene glycol (CAS Number: 25265-71-8) is a mixture of three isomers, namely 4- oxa-2,6-heptandiol, 2-(2-hydroxy-propoxy)-propan-1-ol, and 2-(2-hydroxy-1-methyl-ethoxy)- propan-1-ol. At room temperature, it is a colourless, nearly odourless liquid with a boiling point of about 230 degrees Celsius. It is miscible in water and soluble in ethanol.

[0037] Tripropylene glycol (CAS Number: 24800-44-0) is similarly a mixture of three isomers. At room temperature, it is a clear, almost colourless with an ether odour with a boiling point of about 270 degrees Celsius. It is miscible in water and soluble in ethanol.

[0038] Tetrapropylene glycol (CAS Number: 25657-08-3 or 24800-25-7) is similarly also a mixture of isomers. At normal temperature and pressure, it is a liquid with a mild sweet odour.

[0039] Dipropylene glycol, tripropylene glycol and tetrapropylene glycol have been found to display outstanding phenol absorption capability combined with a very good compatibility with cellulose. In fact, the affinity for cellulose makes especially dipropylene glycol and tripropylene glycol particularly suitable ideal additives for cellulosic materials and far superior with respect to ester plasticizers previously considered, such as triacetine and triethylcitrate that have shown poor compatibility and high migration.

[0040] Preferably, the coating additive comprises at least 40 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol, more preferably at least 50 percent by weight, based on the total weight of the coating additive.

[0041] Preferably the coating additive comprises up to 80 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol, more preferably up to 70 percent by weight, based on the total weight of the coating additive.

[0042] For example, the coating additive may comprise between 40 percent and 80 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol or between 50 percent and 70 percent by weight, based on the total weight of the coating additive. In some embodiments, the coating additive may further comprise an exogenous polysaccharide.

[0043] The term “polysaccharide” generally identifies a polymeric carbohydrate composed of a long chain of monosaccharide units joined by glycosidic linkages with a general formula of (CeH Osjn, with n typically in the range from 40 to 3000. Polysaccharides, which occur widely in nature, exhibit a molecular structure that can be linear or highly branched, and may be composed by multiple ones of the same monosaccharide unit (homopolysaccharides) or include different monosaccharide units (heteropolysaccharides). Common examples of polysaccharides found in plants include cellulose and starch. Glycogen is an example of a polysaccharide commonly found in most mammalian and nonmammalian cells. Chitin is a polysaccharide found in the exoskeletons of insects, the cell walls of fungi, and certain hard structures in invertebrates and fish.

[0044] As used herein with reference to the present invention, the term “exogenous polysaccharide” is used to denote a polysaccharide incorporated into the additive coating that may be applied to a plug element comprising a cellulosic filtration material which may have a certain endogenous polysaccharide content of its own, such as for example in the case of a plug element comprising paper material. The exogenous polysaccharide is provided in an isolated form and has been extracted and separated from other components of a material (for example, a plant material) from which it has been derived. The exogenous polysaccharide is therefore provided extrinsically from any cellulose or hemicellulose derived from plant material that is present in the pulp from which the cellulosic filtration material - to which the additive coating is applied - is made. In other words, the term “exogenous polysaccharide” refers to a separate and distinct source of polysaccharide to any polysaccharide provided intrinsically within the cellulosic filtration material.

[0045] The at least one exogenous polysaccharide is preferably selected from the group consisting of starch, modified starch, alkenyl succinate starches, pullulan, alginate, and combinations thereof. Suitable types of starch include, but are not limited to, potato starch, rice starch, cassava starch and corn starch.

[0046] The term “starch” is used herein with reference to the present invention to denote a polymeric carbohydrate consisting of multiple glucose units joined by a-(1 -^4)-D glycosidic bonds. In nature, starch is produced in most green plants for energy storage purposes.

[0047] From a chemical viewpoint, starch consists primarily of two types of molecules: amylose and amylopectin. Amylose is characterised by a linear, helical structure, whereas amylopectin is highly branched. Different types of starch typically contain different proportions of amylose and amylopectin. For example, potato starch and corn starch contain amylopectin and amylose in an approximately 3:1 ratio, whereas waxy maize starch is almost entirely formed of amylose. In some embodiments, the at least one exogenous polysaccharide is a modified starch, such as oxidized waxy potato starch or a thin boiled starch or an acetylated starch or an oxidised and lightly acetylated starch.

[0048] Acetylated starch is a form of modified starch, which has been modified to increase the number of acetyl groups. As a result of the increased number of acetyl groups, the use of acetylated starch may improve the capabilities of starch in reducing phenols from the mainstream aerosol.

[0049] Inclusion of an exogenous polysaccharide in the coating additive may have the added benefit that the exogenous polysaccharide acts as a binder for the fibres. With this in mind, an exogenous polysaccharide may be applied at various stages during the manufacturing process, for example in the form of an aqueous solution. The aqueous solution may for example be sprayed onto the fibres. Other suitable techniques will be known to a person of ordinary skill in the art, including but not limited to applying the aqueous solution on a size press where the fibrous material is a non-woven sheet material, such as a paper material.

[0050] In some embodiments, the additive coating further comprises at least one hydrogenated or non-hydrogenated ethoxylated castor oil.

[0051] Ethoxylated castor oils are obtained from the reaction of castor oil with ethylene oxide.

[0052] Castor oil is a vegetable oil pressed from castor beans. At room temperature, it is a colourless or pale yellow liquid, with a boiling point of about 313 degrees Celsius and a density of about 0.96 grams / cubic centimetre. Castor oil includes a mixture of triglycerides including primarily (85-85%) ricinoleates, in combination with oleic acid and linoleic acid as the other significant components.

[0053] The chain length and average molecular weight of ethoxylated castor oils depend on the quantity of ethylene oxide used during the synthesis. The term “molecular weight” is used to denote the sum of the atomic weights of each of the atoms in a given molecule. However, polymer molecules generally present a certain variability in terms of molecular weight, polymer chain length, which may for example depend on the conditions under which polymerisation occurred. There will therefore be a distribution of molecular weights, so the term “average molecular weight” is typically used when describing polymer molecules to account for that degree of variability.

[0054] The “number average molecular weight” is defined as the total weight of polymer divided by the total number of molecules. The “weight average molecular weight” depends not only on the number of molecules present, but also on the weight of each molecule. Since larger molecules in a sample weigh more than smaller molecules, the weight average molecular weight is necessarily skewed to higher values, and is always greater than the number average molecular weight.

[0055] An increase in the number average molecular weight is generally accompanied by an overall increase in density of the polymer. Therefore, depending on their number average molecular weight, some ethoxylated castor oils are liquid at room temperature, while other ethoxylated castor oils may be described as semi-liquid, pastes or wax-like solids. This may have an impact on how easy it is to apply an additive coating comprising an ethoxylated castor oil to a substrate.

[0056] Preferably, in the additive coating of aerosol-generating articles according to the present invention, the at least one ethoxylated castor oil has a number average molecular weight of at least 1080 Dalton, more preferably at least 1200 Dalton, even more preferably at least 1400 Dalton.

[0057] In addition, or as an alternative, in the additive coating of aerosol-generating articles according to the present invention, the at least one ethoxylated castor oil preferably has a number average molecular weight of less than or equal to 3000 Dalton, more preferably less than or equal to 2800 Dalton, even more preferably less than or equal to 2600 Dalton.

[0058] In certain embodiments, the additive coating comprises at least one ethoxylated castor oil having a number average molecular weight from 1080 Dalton to 3000 Dalton, preferably from 1200 Dalton to 3000 Dalton, more preferably from 1400 Dalton to 3000 Dalton. In particularly preferred embodiments, the additive coating comprises at least one ethoxylated castor oil having a number average molecular weight from 1600 Dalton to 3000 Dalton or even from 1800 Dalton to 3000 Dalton.

[0059] In other embodiments, the additive coating comprises at least one ethoxylated castor oil having a number average molecular weight from 1080 Dalton to 2800 Dalton, preferably from 1200 Dalton to 2800 Dalton, more preferably from 1400 Dalton to 2800 Dalton. In particularly preferred embodiments, the additive coating comprises at least one ethoxylated castor oil having a number average molecular weight from 1600 Dalton to 2800 Dalton or even from 1800 Dalton to 2800 Dalton.

[0060] In further embodiments, the additive coating comprises at least one ethoxylated castor oil having a number average molecular weight from 1080 Dalton to 2600 Dalton, preferably from 1200 Dalton to 2600 Dalton, more preferably from 1400 Dalton to 2600 Dalton. In particularly preferred embodiments, the additive coating comprises at least one ethoxylated castor oil having a number average molecular weight from 1600 Dalton to 2600 Dalton or even from 1800 Dalton to 2600 Dalton.

[0061] The inventors have found that ethoxylated castor oils having a number average molecular weight falling in the ranges described above can reliably and consistently be applied onto cellulosic filtration materials intended for use as substrates to manufacture components for use in aerosol-generating articles in accordance with the present invention.

[0062] Preferably, in the additive coating of aerosol-generating articles according to the present invention, the at least one ethoxylated castor oil is obtained by reacting 1 stoichiometric equivalent of castor oil with from 1 to 50 stoichiometric equivalents of ethylene oxide. Different ethoxylated cast oil compounds are labelled PEG-x, wherein x indicates the number of ethylene oxide moieties per moiety of castor oil involved in the reaction (INCI nomenclature).

[0063] More preferably, in the additive coating of aerosol-generating articles according to the present invention, the at least one ethoxylated castor oil is obtained by reacting 1 stoichiometric equivalent of castor oil with from 5 to 45 stoichiometric equivalents of ethylene oxide.

[0064] Even more preferably, in the additive coating of aerosol-generating articles according to the present invention, the at least one ethoxylated castor oil is obtained by reacting 1 stoichiometric equivalent of castor oil with from 10 to 40 stoichiometric equivalents of ethylene oxide.

[0065] Without wishing to be bound by theory, it is hypothesised that higher ethylene oxide to castor oil stoichiometric ratios are associated with a reduced tendency to migration when an ethoxylated castor oil is applied onto a substrate, such as the cellulosic filtration materials of interest in the context of the present disclosure.

[0066] Particularly preferred ethoxylated castor oil compounds for inclusion in the additive coating of aerosol-generating articles according to the present invention comprise PEG-10, PEG-25 and PEG-40.

[0067] As noted briefly above, prior to or after undergoing ethoxylation, castor oil may be hydrogenated. Hydrogenation results into the removal of double bonds present in the ricinoleic or other fatty acid moieties. In other words, hydrogenation at least partially saturates the castor oil molecules.

[0068] As a result, hydrogenated castor oil displays increased stability and melting point, so much so that hydrogenated castor oil is solid at room temperature (melting point: about 80 degrees Celsius).

[0069] Ethoxylated hydrogenated castor oils (also referred to as hydrogenated castor oil ethoxylates) are obtained from the reaction of castor oil with ethylene oxide. Different ethoxylated hydrogenated castor oils are labelled PEG-n-HCO, wherein n indicates the number of ethylene oxide moieties per moiety of hydrogenated castor oil involved in the reaction.

[0070] In some embodiments, the additive coating further comprises a liquid aliphatic polyester oligomer.

[0071] As used herein, the term “liquid” denotes an aliphatic polyester oligomer that is liquid at normal temperature and pressure (that is, a temperature of 20 degrees Celsius and an absolute pressure of 101.325 kPa).

[0072] The at least one aliphatic polyester oligomer has preferably a boiling point of at least 60 degrees Celsius, more preferably a boiling point of at least 70 degrees Celsius, even more preferably a boiling point of at least 80 degrees Celsius.

[0073] The at least one aliphatic polyester oligomer preferably has a viscosity of less than or equal to 20000 cPs at 100 degrees Celsius. Plug elements comprising a cellulosic filtration material comprising a fibrous material and an additive coating including at least one aliphatic polyester oligomer applied to the fibrous material have been observed to maintain a highly desirable degree of flexibility.

[0074] Notable aliphatic polyester oligomers are polyesters obtained from the polycondensation of at least one hydroxy acid or by ring-opening polymerization of their lactone counterpart or by ring opening polymerization of their cyclic oligomers. Other suitable aliphatic polyesters are obtained by the polycondensation of aliphatic diacids and aliphatic diols. Examples of the latter comprise liquid polyesters obtained from the polycondensation of diacids such as oxalic, succinic acid, adipic acid, azelaic acid, sebacid acid and isomers of butanediol, isomers of propanediol, ethanediol. Either polyesters obtained from hydroxyacids, lactones, or diacids and diols, may include an amount of monofunctional monomers in form of aliphatic alcohols or acids to act as chain stoppers.

[0075] In some embodiments, the coating additive may further comprise at least one aliphatic polyester such as a polymer of hexanedioic acid (adipic acid), 1 ,4-butanediol, 1 ,2-propanediol, and dodecanoic acid (Admex 760 supplied by Eastman), or a polymer of hexanedioic acid and 1 ,2-propanediol (PA4 sourced from Condensia Quimica). Another suitable polyester is derived from succinic acid, 1 ,2-propanediol (Hallgreen R-8010 sourced from Hallstar Industrial).

[0076] In some embodiments, the additive coating further comprises a polyadipate plasticiser or a polylactate plasticiser. For example, the polyadipate plasticiser may comprise one or more of poly(ethylene adipate), poly(butylene adipate).

[0077] Suitable polyadipate plasticisers for inclusion in the additive coating in aerosol-generating articles according to the present invention include, for example, AdmexTM available from Eastman, or products in the Glyplast PA series available from Condensia Quimica.

[0078] Suitable polylactate plasticisers for inclusion in the additive coating in aerosol-generating articles according to the present invention include, for example, products in the Glyplast OLA series available from Condensia Quimica.

[0079] In some embodiments, the additive coating further comprises a lactate-based surfactant. Suitable lactate-based surfactants for inclusion inclusion in the additive coating in aerosolgenerating articles according to the present invention include, for example lauryl lactyl lactate (koplactylate), sodium stearoyl lactylate, dermosoft® decalact MB available from Evonik.

[0080] By applying an additive as described above to the cellulosic filtration material of the downstream element, the downstream element is made capable of capturing or otherwise converting at least some of the phenols produced by the aerosol-generating article during use. The inclusion of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol, alone or in combination with one or more of the further agents described above, therefore helps reduce the level of phenols in the mainstream aerosol as it passes through the downstream plug element from the aerosol-generating substrate whilst minimising any undesirable effects on the taste sensation experience by the consumer.

[0081] As described above, in aerosol-generating articles according to the present invention the plug contains at least 5 percent by weight of the at least one of dipropylene glycol and tripropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

[0082] Preferably, the plug contains at least 6 percent by weight of the at least one of dipropylene glycol and tripropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis. More preferably, the plug contains at least 7 percent by weight of the at least one of dipropylene glycol and tripropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis. Even more preferably, the plug contains at least 10 percent by weight of the at least one of dipropylene glycol and tripropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

[0083] In aerosol-generating articles according to the present invention the plug may contain up to 35 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

[0084] Preferably, the plug contains less than or equal to 30 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis. More preferably, the plug contains less than or equal to 25 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis. Even more preferably, the plug contains less than or equal to 20 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

[0085] In certain embodiments, the plug contains from 5 percent to 35 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, preferably from 5 percent to 30 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, more preferably from 5 percent to 25 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, even more preferably from 5 percent to 20 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

[0086] In other embodiments, the plug contains from 6 percent to 35 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, preferably from 6 percent to 30 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, more preferably from 6 percent to 25 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, even more preferably from 6 percent to 20 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

[0087] In other embodiments, the plug contains from 7 percent to 35 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, preferably from 7 percent to 30 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, more preferably from 7 percent to 25 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, even more preferably from 7 percent to 20 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

[0088] In other embodiments, the plug contains from 10 percent to 35 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, preferably from 10 percent to 30 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, more preferably from 10 percent to 25 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis, even more preferably from 10 percent to 20 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

[0089] In embodiments wherein the additive coating comprises a further additive in combination with the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol - in line with the foregoing description - a ratio between the content of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol and the content of the further additive in the additive coating may be up to 90:10. Preferably, a ratio between the content of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol and the content of the further additive in the additive coating is less than or equal to 80:20. More preferably, a ratio between the content of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol and the content of the further additive in the additive coating is less than or equal to 75:25. A ratio between the content of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol and the content of the further additive in the additive coating may at least 50:50. Preferably, a ratio between the content of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol and the content of the further additive in the additive coating is at least 60:40. More preferably, a ratio between the content of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol and the content of the further additive in the additive coating is at least 65:35.

[0090] For example, a ratio between the content of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol and the content of the further additive in the additive coating may be from 50:50 to 90:10, preferably from 60:40 to 90:20.

[0091] As described briefly above, the downstream element comprises a plug element comprising a cellulosic filtration material. The cellulosic filtration material comprises a fibrous material. The fibrous material thus acts as a carrier material which forms the downstream element and retains the additive coating.

[0092] In some embodiments, the fibrous material comprises a plurality of fibres and the additive coating is applied to the plurality of fibres.

[0093] Suitable fibrous materials for forming a filtration material would be known to the skilled person.

[0094] In a first preferred embodiment, the fibrous material comprises a plurality of regenerated cellulose fibres. Suitable regenerated cellulose fibres include but are not limited to viscose fibres, modal fibres, Lyocell fibres, viscose rayon fibres and combinations thereof.

[0095] The term “regenerated cellulose fibres” is used herein to mean cellulose fibres which have been formed by processing a naturally occurring cellulose material to provide cellulose fibres having a desired physical property. A typical process for forming regenerated cellulose fibres includes the steps of: pulping a naturally occurring cellulose material, such as wood chips, to form a pulp; subjecting the pulp to one or more treatment steps to alter the physical properties of the cellulose; and forming fibres of regenerated cellulose from the treated pulp.

[0096] For example, the one or more treatment steps to alter the physical properties of the cellulose may involve reacting the cellulose with carbon disulfide and sodium hydroxide to form a so called cellulose xanthate, and subsequently spinning the solution of cellulose xanthate in a bath containing sulphuric acid.

[0097] In another example, the one or more treatment steps to alter the physical properties of the cellulose may involve dissolving the pulp in a suitable solvent and then precipitating the cellulose so that it can be separated from the solvent.

[0098] Preferably, the regenerated cellulose fibres are crimped staple fibres. This helps to reduce mechanical degradation of the fibres during processing of the filtration material to form the downstream element, and during subsequent assembly of the aerosol-generating article. The fibres can be crimped using a known method for crimping textile fibres.

[0099] The regenerated cellulose fibres may have a substantially round cross-section, a flattened round shape, or a multilobate shape such as a so called “Y” or “X” shape.

[0100] Preferably, the regenerated cellulose fibres have a denier per filament (dpf) of at least about 2.0, more preferably at least 2.5, more preferably at least 3.0, more preferably at least 3.2, more preferably at least 3.5, more preferably at least about 4.0, more preferably at least 4.5, more preferably at least 5.0.

[0101] Preferably, the regenerated cellulose fibres have a denier per filament of no more than 10.0, more preferably no more than 9.0, more preferably no more than 8.0, more preferably no more than 7.0.

[0102] The denier per filament, corresponding to the average denier of an individual regenerated cellulose fibre within the filter, is the weight in grams of a single fibre or filament having a length of 9000 metres. In the present invention, the value of dpf therefore gives an indication of the thickness of each of the individual regenerated cellulose fibres within the filtration material. The denier per filament is expressed in units of denier, where 1 denier corresponds to 1 gram per 9000 metres. The dpf of a filter or filter segment can be readily determined based on the measurement of weight and length of a sample of representative fibres from the filtration material.

[0103] Preferably, the total denier of the cellulosic filtration material comprising the regenerated cellulose fibres is between about 20,000 and about 50,000, more preferably between about 25,000 and about 40,000, more preferably between about 30,000 and about 40,000. The “total denier” of the filtration material defines the total weight in grams of 9000 metres of the combined fibres forming the filtration material. The total denier for the filtration material therefore corresponds to the denier per filament multiplied by the total number of fibres in the filtration material.

[0104] Preferably, the fibrous material comprises at least 50 percent of regenerated cellulose fibres, more preferably at least 60 percent of regenerated cellulose fibres, more preferably at least 70 percent of regenerated cellulose fibres, more preferably at least 80 percent of regenerated cellulose fibres, more preferably at least 90 percent of regenerated cellulose fibres.

[0105] Preferably, the fibrous material comprises at least 50 percent of viscose fibres, more preferably at least 60 percent of viscose fibres, more preferably at least 70 percent of viscose fibres, more preferably at least 80 percent of viscose fibres, more preferably at least 90 percent of viscose fibres.

[0106] The fibrous material preferably consists of the regenerated cellulose fibres, so that the regenerated cellulose fibres account for 100 percent of the fibrous material and the regenerated cellulose fibres are not combined with any other type of fibre. In a second preferred embodiment, the fibrous material comprises a plurality of natural cellulosic fibres. Suitable natural cellulosic fibres include but are not limited to: flax fibres, hemp fibres, jute fibres, kenaf fibres, ramie fibres, abaca fibres, phormium fibres, sisal fibres, coir fibres, cotton fibres, kapok fibres, or combinations thereof. Particularly preferably, the fibrous material comprises cotton fibres or a combination or cotton fibres and kapok fibres. In certain embodiments of the invention, the natural fibres comprise mercerised fibres.

[0107] Preferably, the natural fibres are crimped continuous or staple fibres, which helps to reduce mechanical degradation of the fibres during processing of the filtration material to form the downstream element, and during subsequent assembly of the aerosol-generating article. The fibres can be crimped using a known method for crimping textile fibres.

[0108] The natural fibres may have a substantially round cross-section.

[0109] Preferably, the natural fibres have a denier per filament (dpf) of at least about 2.0, more preferably at least 2.5, more preferably at least 3.0, more preferably at least 3.2, more preferably at least 3.5, more preferably at least about 4.0, more preferably at least 4.5, more preferably at least 5.0.

[0110] Preferably, the natural fibres have a denier per filament of no more than 10.0, more preferably no more than 9.0, more preferably no more than 8.0, more preferably no more than 7.0.

[0111] The denier per filament, corresponding to the average denier of an individual natural fibre within the filter, is the weight in grams of a single fibre or filament having a length of 9000 metres. In the present invention, the value of dpf therefore gives an indication of the thickness of each of the individual natural fibres within the filtration material. The denier per filament is expressed in units of denier, where 1 denier corresponds to 1 gram per 9000 metres. The dpf of a filter or filter segment can be readily determined based on the measurement of weight and length of a sample of representative fibres from the filtration material.

[0112] Preferably, the total denier of the filtration material comprising the natural fibres is between about 20,000 and about 50,000, more preferably between about 25,000 and about 40,000, more preferably between about 30,000 and about 40,000. The “total denier” of the filtration material defines the total weight in grams of 9000 metres of the combined fibres forming the filtration material. The total denier for the filtration material therefore corresponds to the denier per filament multiplied by the total number of fibres in the filtration material.

[0113] Preferably, the fibrous material comprises at least 50 percent of natural fibres, more preferably at least 60 percent of natural fibres, more preferably at least 70 percent of natural fibres, more preferably at least 80 percent of natural fibres, more preferably at least 90 percent of natural fibres.

[0114] Preferably, the fibrous material comprises at least 50 percent of cotton fibres, more preferably at least 60 percent of cotton fibres, more preferably at least 70 percent of cotton fibres, more preferably at least 80 percent of cotton fibres, more preferably at least 90 percent of cotton fibres.

[0115] The fibrous material preferably consists of the natural fibres, so that the natural fibres account for 100 percent of the fibrous material and the natural fibres are not combined with any other type of fibre.

[0116] Preferably, the fibrous material does not include cellulose acetate fibres or any other fibres formed of non-biodegradable polymers.

[0117] In alternative preferred embodiments, the filtration material comprises a non-woven sheet material to which the additive coating is applied. Preferably, the additive coating is applied to at least one surface of the non-woven sheet material. Preferably, the non-woven sheet material is a sheet of paper material. As observed above, the additive coating may be provided over an outer surface of the non-woven sheet material, such as to form a layer containing the additive over at least a portion of the outer surface of the non-woven sheet material. Alternatively, or in addition, the additive coating may impregnate or be absorbed into the non-woven sheet material, such that at least some of the additive is present within the fibres contained within the non-woven sheet material. Thus, when describing downstream elements for use in aerosol-generating articles in accordance with the present disclosure, the term “applied to the non-woven sheet material” means that additive is present on, within, or both on and within the fibres contained within the non-woven sheet material.

[0118] For the purposes of the invention, the term "paper material" generally denotes a web of cellulosic fibres in sheet form. As used herein with reference to the invention, the term “sheet” is used to describe a laminar element having a width and a length substantially greater than a thickness thereof. The sheet may have a thickness ranging from 0.03 to 2 millimetres and a basis weight of from 10 grams per square metre to 200 grams per square metre.

[0119] The downstream element may comprise a single sheet of paper material that is gathered or otherwise processed to be formed into a rod shape. Alternatively, the downstream element may comprise two or more sheets that are gathered or otherwise processed together to be formed into a rod shape. For example, two or more sheets of paper material may be laid on top of each other and gathered or otherwise processed at once to form the downstream element. Two or more sheets of paper material may also be gathered or otherwise processed independently, in parallel to each other, and then combined to form the downstream element.

[0120] The downstream element may, as an alternative, comprise a plurality of sheets of paper material stacked on top of each other. The resulting stack may have a thickness of up to 10 millimetres. The stack may be slitted into rod-shaped elements to form downstream elements for use in an aerosol-generating article according to the present invention. Prior to being formed into a downstream element, the web or sheet of paper material may be textured. Texturing of the web or sheet of paper material may advantageously facilitate gathering of the sheet into a rod.

[0121] As used herein, the term “textured sheet” denotes a sheet that has been crimped, embossed, debossed, perforated or otherwise deformed. Textured sheets of paper material may therefore comprise a plurality of spaced-apart indentations, protrusions, perforations or a combination thereof.

[0122] Also, a suitable paper may be produced by a wet-laid process or by an air-laid process and may include a variety of additives.

[0123] Gathering or winding the sheet of paper material to form the plug element has the benefit that by adjusting the number of convolutions or how tight the sheet is gathered it is possible to ensure that the plug element displays the required resistance to mechanical deformation, such that in the aerosol-generating article the plug element can withstand being grasped by the consumer during smoking.

[0124] A sheet of paper material used for forming the plug element of the downstream element in aerosol-generating articles in accordance with the present disclosure may have a basis weight of at least 10 grams per square metre. Preferably, the sheet of paper material may have a basis weight of at least 15 grams per square metre. More preferably, the sheet of paper material may have a basis weight of at least 20 grams per square metre. Even more preferably, the sheet of paper material may have a basis weight of at least 30 grams per square metre.

[0125] The sheet of paper material may have a basis weight of less than or equal to 200 grams per square metre. Preferably, the sheet of paper material may have a basis weight of less than or equal to 180 grams per square metre. More preferably, the sheet of paper material may have a basis weight of less than or equal to 160 grams per square metre. Even more preferably, the sheet of paper material may have a basis weight of less than or equal to 120 grams per square metre. In particularly preferred embodiments, the sheet of paper material may have a basis weight of less than or equal to 100 grams per square metre.

[0126] The basis weight of the sheet of paper material may be selected based on a balance between the ability of the plug element to withstand a compressive load during use, and the need to preserve a certain pliability of the sheet of paper material to be able to form it into a desired shape. Further, the basis weight of the sheet of paper material may be selected such that the plug element is able to resist deformation during storage, transportation and use of the aerosolgenerating article.

[0127] The sheet of paper material may have a thickness of up to 800 micrometres. Preferably, the sheet of paper material has a thickness of less than or equal to 600 micrometres. More preferably, the sheet of paper material has a thickness of less than or equal to 600 micrometres. Even more preferably, the sheet of paper material has a thickness of less than or equal to 500 micrometres.

[0128] In preferred embodiments, the sheet of paper material has a thickness of less than or equal to 300 micrometres, preferably less than or equal to 200 micrometres, more preferably less than or equal to 100 micrometres.

[0129] The sheet of paper material may have a thickness of at least 10 micrometres. Preferably, the sheet of paper material has a thickness of at least 15 micrometres. More preferably, the sheet of paper material has a thickness of at least 20 micrometres. Even more preferably, the sheet of paper material has a thickness of at least 30 micrometres.

[0130] In preferred embodiments, the sheet of paper material has a thickness of at least 40 micrometres, preferably at least 50 micrometres, more preferably at least 60 micrometres.

[0131] The thickness of the sheet may be selected to ensure a certain pliability of the sheet, so as to enable one or more of crimping, gathering, pleating, and folding of the sheet.

[0132] The plug element may have a weight of less than or equal to about 100 milligrams, less than or equal to about 75 milligrams, or less than or equal to about 50 milligrams.

[0133] The plug element may have a weight of at least about 10 milligrams, at least about 15 milligrams, or at least about 20 milligrams.

[0134] The plug element may have a weight of between about 10 milligrams and about 100 milligrams, between about 10 milligrams and about 75 milligrams, or between about 10 milligrams and about 50 milligrams.

[0135] The plug element may have a weight of between about 15 milligrams and about 100 milligrams, between about 15 milligrams and about 75 milligrams, or between about 15 milligrams and about 50 milligrams.

[0136] The plug element may have a weight of between about 20 milligrams and about 100 milligrams, between about 20 milligrams and about 75 milligrams, or between about 20 milligrams and about 50 milligrams.

[0137] The plug element may have an average weight per unit length of less than or equal to about 20 milligrams per millimetre, less than or equal to about 15 milligrams per millimetre, or less than or equal to about 10 milligrams per millimetre.

[0138] As used herein with reference to the invention, the average weight per unit length of the plug element is equal to the weight of the plug element divided by the length of the plug element. For example, where the plug element has a weight of 25 milligrams and a length of 5 millimetres, the average weight per unit length of the plug element is 5 milligrams per millimetre.

[0139] The plug element may have an average weight per unit length of at least about 2 milligrams per millimetre, at least about 3 milligrams per millimetre, or at least about 4 milligrams per millimetre. The plug element may have an average weight per unit length of between about

[0140] 2 milligrams per millimetre and about 20 milligrams per millimetre, between about 2 milligrams per millimetre and about 15 milligrams per millimetre, or between about2 milligrams per millimetre and about 10 milligrams per millimetre.

[0141] The plug element may have an average weight per unit length of between about

[0142] 3 milligrams per millimetre and about 20 milligrams per millimetre, between about 3 milligrams per millimetre and about 15 milligrams per millimetre, or between about 3 milligrams per millimetre and about 10 milligrams per millimetre.

[0143] The plug element may have an average weight per unit length of between about

[0144] 4 milligrams per millimetre and about 20 milligrams per millimetre, between about 4 milligrams per millimetre and about 15 milligrams per millimetre, or between about 4 milligrams per millimetre and about 10 milligrams per millimetre.

[0145] As described above, the downstream element comprising the cellulosic filtration material advantageously provides improved biodegradability compared to conventional cellulose acetate segments.

[0146] Preferably, the plug element is substantially free from cellulose acetate.

[0147] The coating additive may be applied to the fibrous material or non-woven sheet material in any suitable manner. Preferably, the coating additive is applied to the fibrous material or nonwoven sheet material by spraying. More preferably, a solution of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol is applied to the fibrous material, such as for example by spraying. A content of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol in the plug element is preferably at least 5 percent by weight of the plug element, on a dry weight basis.

[0148] When the fibrous material is a non-woven such a wet-laid paper or air-laid paper the additive may be included during their manufacturing process. In particular, in the case of a wet- laid paper, dipropylene glycol or trypropylene glycol or tetrapropylene glycol may be included in the wet end together with other typical wet-end additives (such as starches or wet strength additives), or in the size press section. Similarly, in the case of an air-laid paper or air-laid nonwoven material, one or more additives may be included in the binder formulation.

[0149] After the solution has been applied to the fibrous material or non-woven sheet material, the coated material can be dried by any suitable means, such as conventional heating or microwave heating.

[0150] The aerosol-generating articles according to the present invention comprise a downstream element formed of the filtration material described above. Preferably, the downstream element comprises a segment of the filtration material circumscribed by a wrapper, such as a paper wrapper. The segment of the filtration material is preferably in the form of a solid plug. Alternatively, as described in more detail below, the segment of the filtration material may be in the form of a hollow tubular segment.

[0151] The wrapper circumscribing the filtration material may have a basis weight of at least 50 grams per square metre (gsm). Where the downstream element is positioned at the downstream end of the aerosol-generating article, this may help to provide a desired firmness for the aerosolgenerating article. In certain embodiments, it may be desirable to use a stiff wrapper, for example, a wrapper having a basis weight of at least about 80 grams per square metre (gsm), or at least about 100 gsm, or at least about 110 gsm.

[0152] Preferably, the downstream element comprising the filtration material has an average radial hardness of at least 75 percent, more preferably at least 80 percent, more preferably at least 85 percent. Preferably, the downstream element has a radial hardness of less than 100 percent, more preferably less than 95 percent. This can provide an aerosol-generating article having a downstream end with a satisfactory hardness for the consumer.

[0153] As used herein, the term “radial hardness” refers to resistance to compression is a direction transverse to a longitudinal axis. Radial hardness of an aerosol-generating article around a filter may be determined by applying a load across the article at the location of the filter, transverse to the longitudinal axis of the article, and measuring the average (mean) depressed diameters of the articles. Radial hardness is given by:

[0154] Radial hardness (%) 100 % where Ds is the original (undepressed) diameter, and Dd is the depressed diameter after applying a set load for a set duration. The harder the material, the closer the hardness is to 100%.

[0155] To determine the hardness of a portion (such as a filter) of an aerosol-generating article, 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. This test is performed using a known DD60A Densimeter device (manufactured and made commercially available by Heinr. Borgwaldt GmbH, Germany), which is fitted with a measuring head for aerosol-generating articles, such as cigarettes, and with an aerosol-generating article receptacle.

[0156] For the standard operating procedure for such an apparatus, an overall load of 2 kg is applied for a duration of 20 seconds. After 20 seconds have elapsed (and with the load still being applied to the smoking articles), the depression in the load applying cylindrical rods is determined, and then used to calculate the hardness from the above equation. The temperature is kept in the region of 22 degrees Centigrade ± 2 degrees. The test described above is referred to as the DD60A Test. The standard way to measure the filter hardness is when the aerosol-generating articles have not been consumed. Additional information regarding measurement of average radial hardness can be found in, for example, U.S. Published Patent Application Publication Number 2016 / 0128378.

[0157] As described above, the downstream element comprising the filtration material can advantageously provide improved biodegradability compared to conventional cellulose acetate segments.

[0158] Preferably, the downstream element is substantially free from cellulose acetate.

[0159] As described briefly above, the downstream element is provided downstream of the aerosol-generating substrate and in axial alignment with the aerosol-generating substrate.

[0160] In some embodiments, the aerosol-generating article is formed essentially of an aerosolgenerating substrate and of a downstream element as described above provided in abutting arrangement with the rod of aerosol-generating substrate. For example, the aerosol-generating substrate may be in the form of a cylindrical rod of shredded tobacco material circumscribed by a wrapper, and the downstream element may be attached to the wrapped rod by a band of tipping paper so as to form a mouthpiece of the aerosol-generating article.

[0161] In other embodiments, the aerosol-generating article comprises one or more additional elements also provided downstream of the aerosol-generating substrate and in axial alignment with the aerosol-generating substrate. The downstream element and any further element provided downstream of the aerosol-generating substrate and in axial alignment with the aerosolgenerating substrate form a downstream section of the aerosol-generating article.

[0162] In some preferred embodiments, the downstream element is a mouthpiece element.

[0163] The aerosol-generating article may comprise a mouthpiece at the downstream end or mouth end or proximal end of the aerosol-generating article, the mouthpiece consisting of the downstream element alone.

[0164] Alternatively, the aerosol-generating article may comprise a mouthpiece at the downstream end or mouth end or proximal end of the aerosol-generating article, the mouthpiece including the downstream element and one or more further elements axially aligned in an abutting end to end relationship with each other. The downstream element and the one or more further elements may be formed of the same material. Alternatively, the one or more further elements may be formed of a material other than the material of the downstream element.

[0165] Parameters or characteristics described herein in relation to the downstream element used as the sole component of the mouthpiece may equally be applied to a downstream element used as one of multiple components of the mouthpiece.

[0166] Advantageously, aerosol-generating articles according to the present invention wherein the downstream element is a mouthpiece element provide an acceptable visual impact and tactile experience for the consumer, thanks to the density and firmness of the downstream element. Additionally, in aerosol-generating articles according to the present invention wherein the downstream element is a mouthpiece element, the filtration material is capable of efficiently reducing undesirable compounds (for example, phenols) from the aerosol generated from the substrate, with little to no impact on the taste perceived by the consumer during use of the aerosolgenerating article. As such, aerosol-generating articles according to the present invention wherein the downstream element is a mouthpiece element provide a much more sustainable alternative to aerosol-generating articles comprising a cellulose acetate filter segment as a mouthpiece filter segment.

[0167] The mouthpiece element may have a low particulate phase filtration efficiency or even substantially no particulate phase filtration efficiency. Whilst capable of preventing substrate material from the aerosol-generating substrate potentially reaching the mouth of the consumer during use, a mouthpiece element having low particulate phase filtration efficiency has a reduced impact on delivery of aerosol species to the consumer. This is especially advantageous in aerosol-generating article wherein the aerosol-generating substrate is heated as opposed to being combusted.

[0168] In preferred embodiments, the particulate phase filtration efficiency of the downstream element is less than about 30 percent, more preferably less than about 20 percent.

[0169] In some embodiments, the mouthpiece element may have an RTD of less than or equal to about 25 millimetres H2O, less than or equal to about 20 millimetres H2O, or less than or equal to about 15 millimetres H2O. In such embodiments, the mouthpiece element may have an RTD of at least about 10 millimetres H2O.

[0170] The mouthpiece element may have an RTD of between about 10 millimetres H2O and to about 25 millimetres H2O, between about 10 millimetres H2O and to about 20 millimetres H2O, or of between about 10 millimetres H2O and to about 15 millimetres H2O.

[0171] Preferably, the mouthpiece element has a substantially circular cross-section.

[0172] Preferably, the mouthpiece element has an external diameter that is substantially the same as the external diameter of the aerosol-generating article.

[0173] A length of the mouthpiece may be at least about 3 millimetres, or at least about 5 millimetres.

[0174] The length of the mouthpiece element may be less than or equal to about 11 millimetres, or less than or equal to about 9 millimetres.

[0175] The length of the mouthpiece element may be between about 3 millimetres and about 11 millimetres, or between about 3 millimetres and about 9 millimetres. The length of the mouthpiece element may be between about 5 millimetres and about 11 millimetres, or between about 5 millimetres and about 9 millimetres. For example, the length of the mouthpiece element may be about 7 millimetres.

[0176] The length of the mouthpiece element may be selected based on a desired total length of the aerosol-generating article. The mouthpiece element may be circumscribed by a plug wrap.

[0177] The mouthpiece element may be unventilated such that air does not enter the aerosolgenerating article along the mouthpiece element.

[0178] The mouthpiece element may be connected to one or more adjacent components of the aerosol-generating article by means of a tipping wrapper.

[0179] The aerosol-generating article may define a mouth end cavity at the downstream end of the aerosol-generating article. For example, the mouthpiece element may itself be in the form of a hollow tubular element. As an alternative, the mouthpiece may include a non-hollow downstream element as described above immediately upstream of a hollow tubular segment provided at the downstream end of the mouthpiece. As a further alternative, the mouth end cavity may be defined by an outer wrapper of the mouthpiece extending beyond a downstream end of a downstream element as described above.

[0180] In some embodiments, the downstream element may be an additional element provided downstream of the aerosol-generating substrate other than a mouthpiece element. That is, the aerosol-generating article comprises a mouthpiece and the downstream element is provided between the aerosol-generating substrate and a mouthpiece of the aerosol-generating article.

[0181] For example, the downstream element may be a support element provided immediately downstream of the aerosol-generating substrate, preferably adjacent to the aerosol-generating substrate. One such support element is adapted to impart structural strength to the aerosolgenerating article. The support element is advantageously configured to resist downstream movement of the aerosol-generating substrate during insertion of the heating element of the aerosol-generating device into the aerosol-generating.

[0182] In some embodiments, the downstream element may form part of an aerosol-cooling element provided downstream of the aerosol-generating substrate, the aerosol-cooling element being adapted to facilitate cooling of the aerosol generated during use of the aerosol-generating article prior to reaching the downstream end of the aerosol-generating article.

[0183] The aerosol-cooling element preferably has a low resistance to draw. That is, the aerosolcooling element preferably offers a low resistance to the passage of air through the aerosolgenerating article. Preferably, the aerosol-cooling element does not substantially affect the resistance to draw of the aerosol-generating article.

[0184] At least one of the support element and the aerosol-cooling element may be in the form of a hollow tubular element formed of the cellulosic filtration material described above. In some embodiments, both the support element and the aerosol-cooling element are in the form of hollow tubular elements, which may differ in length, internal diameter or both.

[0185] In an aerosol-generating article in accordance with the present invention, such a hollow tubular element provides an unrestricted flow channel. This means that the hollow tubular element provides a negligible level of RTD. As used herein with reference to the invention, the term “negligible level of RTD” is used to describe an RTD of less than 1 mm H2O per 10 millimetres of length of the hollow tubular substrate element, less than 0.4 mm H2O per 10 millimetres of length of the hollow tubular substrate element, or less than 0.1 mm H2O per 10 millimetres of length of the hollow tubular substrate element. The flow channel should therefore be free from any components that would obstruct the flow of air in a longitudinal direction. Preferably, the flow channel is substantially empty.

[0186] The hollow tubular element may have a total length of at least about 10 millimetres, at least about 12 millimetres, or at least about 15 millimetres.

[0187] The hollow tubular element may have a total length of less than or equal to about 30 millimetres, less than or equal to about 25 millimetres, or less than or equal to about 23 millimetres.

[0188] The hollow tubular element may have a total length of between about 10 millimetres and about 30 millimetres, between about 10 millimetres and about 25 millimetres, or between about 10 millimetres and about 23 millimetres. The hollow tubular element may have a total length of between about 12 millimetres and about 30 millimetres, between about 12 millimetres and about 25 millimetres, or between about 12 millimetres and about 23 millimetres. The hollow tubular element may have a total length of between about 12 millimetres and about 30 millimetres, between about 12 millimetres and about 25 millimetres, or between about 12 millimetres and about 23 millimetres.

[0189] The total length of the hollow tubular element or elements may be selected based on a desired total length of the aerosol-generating article.

[0190] In some embodiments, a ventilation zone may be provided at a location downstream of the aerosol-generating substrate.

[0191] By way of example, cooling of a stream of smoke generated upon combusting the aerosolgenerating substrate may be achieved by providing a ventilation zone at a location along a mouthpiece of the aerosol-generating article.

[0192] As another example, a ventilation zone may be provided at a location along the hollow tubular element forming the cooling element. Without wishing to be bound by theory, the temperature drop caused by the admission of cooler, external air into the aerosol-generating article downstream of the aerosol-generating element via the ventilation zone may have an advantageous effect on the nucleation and growth of aerosol particles.

[0193] The ventilation zone may comprise a plurality of perforations, for example provided through a tubular wall of the hollow tubular element. The ventilation zone may comprise at least one circumferential row of perforations. The ventilation zone may comprise two circumferential rows of perforations. Each circumferential row of perforations may comprise from 8 to 30 perforations. In some embodiments, the downstream section of the aerosol-generating article may comprise, in sequential order, a support element, an aerosol-cooling element, and a mouthpiece. Preferably, one or more of the support element, aerosol-cooling element, and mouthpiece are in the form of a downstream element as described above.

[0194] In some embodiments, the aerosol-generating article comprises an upstream section located upstream of the aerosol-generating substrate. The upstream section is preferably located immediately upstream of the aerosol-generating substrate. The upstream section preferably extends from an upstream end of the aerosol-generating article to an upstream end of the aerosolgenerating substrate. The upstream section preferably comprises an upstream element located immediately upstream of the rod of aerosol-generating substrate.

[0195] Where the aerosol-generating substrate comprises shredded tobacco, such as tobacco cut filler, the upstream section or element thereof may additionally help to prevent the loss of loose particles of tobacco from the upstream end of the article.

[0196] The upstream section, or upstream element thereof, may also additionally provide a degree of protection to the aerosol-generating substrate during storage, as it covers at least to some extent the upstream end of the aerosol-generating substrate, which may otherwise be exposed. For aerosol-generating articles that are intended to be inserted into a cavity in an aerosol-generating device such that the aerosol-generating substrate can be externally heated within the cavity, the upstream section, or upstream element thereof, may advantageously facilitate the insertion of the upstream end of the article into the cavity.

[0197] An upstream element of the upstream section may be made of any material suitable for use in an aerosol-generating article. Suitable materials for forming the upstream element include filter materials, ceramic, polymer material, cellulose acetate, cardboard, zeolite or aerosolgenerating substrate.

[0198] In preferred embodiments, the upstream element may comprise the same filtration material as the downstream element described above.

[0199] From an environmental perspective, this is advantageous in that a greater portion of the aerosol-generating article as a whole is more readily degradable. Additionally, from a manufacturing viewpoint, it is advantageous to form different components of a same aerosolgenerating article of the same material, as it will generally require less adjustments to the settings of existing apparatus.

[0200] Preferably, the upstream section, or an upstream element thereof, has an external diameter that is approximately equal to the external diameter of the aerosol-generating article. Preferably, the external diameter of the upstream section, or an upstream element thereof, is between about 6 millimetres and about 8 millimetres, more preferably between about 7 millimetres and about 7.5 millimetres. Preferably, the upstream section or an upstream element has an external diameter that is about 7.1 millimetres. Preferably, the upstream section or an upstream element has a length of between about 2 millimetres and about 8 millimetres, more preferably between about 3 millimetres and about 7 millimetres, more preferably between about 4 millimetres and about 6 millimetres. In a particularly preferred embodiment, the upstream section or an upstream element has a length of about 5 millimetres. The length of the upstream section or an upstream element can advantageously be varied in order to provide the desired total length of the aerosol-generating article.

[0201] The upstream section is preferably circumscribed by a wrapper, such as a plug wrap. The wrapper circumscribing the upstream section may be a stiff plug wrap, for example, a plug wrap having a basis weight of at least about 80 grams per square metre (gsm), or at least about 100 gsm, or at least about 110 gsm. This provides increased structural rigidity to the upstream section.

[0202] The upstream section is preferably connected to the rod of aerosol-generating substrate and optionally at least a part of the downstream section by means of an outer wrapper.

[0203] The aerosol-generating article may be a combustible smoking article. A combustible smoking article typically comprises a cylindrical rod of tobacco cut filler surrounded by a paper wrapper and a cylindrical filter axially aligned, most often in an abutting end-to-end relationship, with the wrapped tobacco rod. The cylindrical filter typically comprises one or more plug elements of a fibrous filtration material circumscribed by a paper plug wrap. The wrapped tobacco rod and the filter are typically joined by a band of tipping wrapper, that circumscribes the entire length of the filter and an adjacent portion of the wrapped tobacco rod. In combustible smoking articles according to the present invention, the cylindrical filter comprises a downstream element having the characteristics described above.

[0204] The aerosol-generating article may be an aerosol-generating article for generating an aerosol upon heating (a heated aerosol-generating article). A heated aerosol-generating article typically comprises a cylindrical rod of aerosol-generating substrate surrounded by a paper wrapper and a downstream section downstream of the rod of aerosol-generating substrate. The downstream section typically comprises at least one hollow tubular element immediately downstream of the rod of aerosol-generating substrate and a mouthpiece.

[0205] The aerosol-generating article preferably has an overall length of from 40 millimetres to 80 millimetres, or from 40 millimetres to about 70 millimetres, or from 40 millimetres to about 60 millimetres, or from 45 millimetres to about 80 millimetres, or from about 45 millimetres to about 70 millimetres, or from 45 millimetres to 60 millimetres, or from 50 millimetres to 80 millimetres, or from 50 millimetres to about 70 millimetres or from about 50 millimetres to about 60 millimetres. In an exemplary embodiment, an overall length of the aerosol-generating article is about 45 millimetres.

[0206] Preferably, the aerosol-generating article has a substantially circular cross-section. The aerosol-generating article preferably has an external diameter of from about 5 millimetres to about 12 millimetres, or from about 6 millimetres to about 12 millimetres, or from about 7 millimetres to about 12 millimetres, or from about 5 millimetres to about 10 millimetres, or from about 6 millimetres to about 10 millimetres, or from about 7 millimetres to about 10 millimetres, or from about 5 millimetres to about 8 millimetres, or from about 6 millimetres to about 8 millimetres, or from about 7 millimetres to about 8 millimetres. In other embodiments, the aerosol-generating article has an external diameter of less than 7 millimetres.

[0207] The overall RTD of the aerosol-generating article is preferably at least 10 millimetres H2O, more preferably at least 15 millimetres H2O, more preferably at least 20 millimetres H2O, more preferably at least 25 millimetres H2O, more preferably at least 30 millimetres H2O.

[0208] The overall RTD of the aerosol-generating article is preferably no more than 70 millimetres H2O, more preferably no more than 60 millimetres H2O, more preferably no more than 55 millimetres H2O, more preferably no more than 50 millimetres H2O, more preferably no more than 45 millimetres H2O.

[0209] For example, the overall RTD of the aerosol-generating article may be between 10 millimetres H2O and 70 millimetres H2O, or between 15 millimetres H2O and 60 millimetres H2O, or between 20 millimetres H2O and 55 millimetres H2O, or between 25 millimetres H2O and 45 millimetres H2O, or between 30 millimetres H2O and 45 millimetres H2O.

[0210] As described above, an aerosol-generating article in accordance with the present invention comprises an aerosol-generating substrate. In several embodiments, the aerosolgenerating article comprises a rod of aerosol-generating substrate circumscribed by a rod plug wrap.

[0211] Preferably, the rod of aerosol-generating substrate has a length of at least 8 millimetres, more preferably a length of at least 9 millimetres, more preferably a length of at least 10 millimetres. Preferably, the length of the rod of aerosol-generating substrate is less than 16 millimetres, more preferably less than 15 millimetres, more preferably less than 14 millimetres. For example, the rod of aerosol-generating substrate may have a length of between 8 millimetres and 16 millimetres, or between 9 millimetres and 15 millimetres, or between 10 millimetres and 14 millimetres. In a particularly preferred embodiment, the rod of aerosol-generating substrate has a length of about 12 millimetres.

[0212] Preferably, the ratio between the length of the rod of aerosol-generating substrate and the overall length of the aerosol-generating article is at least 0.10, more preferably at least 0.15, more preferably at least 0.20, more preferably at least 0.25. Preferably, the ratio between the length of the rod of aerosol-generating substrate and the overall length of the aerosol-generating article is less than 0.50, more preferably less than 0.45, more preferably less than 0.40, more preferably less than 0.35. For example, the ratio between the length of the rod of aerosol-generating substrate and the overall length of the aerosol-generating article may be between 0.1 and 0.5, or between 0.15 and 0.45, or between 0.2 and 0.4, or between 0.25 and 0.35.

[0213] Preferably, the rod of aerosol-generating substrate has an external diameter that is approximately equal to the external diameter of the aerosol-generating article.

[0214] Preferably, the rod of aerosol-generating substrate has an external diameter of at least 5 millimetres, more preferably at least 6 millimetres, more preferably at least 7 millimetres. Preferably, the rod of aerosol-generating substrate has an external diameter of less than 12 millimetres, more preferably less than 10 millimetres, more preferably less than 8 millimetres. For example, the external diameter may be between 5 millimetres and 12 millimetres, or between 6 millimetres and 10 millimetres, or between 7 millimetres and 8 millimetres. In a particularly preferred embodiment, the rod of aerosol-generating substrate has an external diameter of about 7.1 millimetres.

[0215] Preferably, the rod of aerosol-generating substrate has a substantially uniform crosssection along the length of the rod. Particularly preferably, the rod of aerosol-generating substrate has a substantially circular cross-section.

[0216] The aerosol-generating substrate may have a density of at least about 150 milligrams per cubic centimetre, at least about 175 milligrams per cubic centimetre, at least about 200 milligrams per cubic centimetre, or at least about 250 milligrams per cubic centimetre.

[0217] The aerosol-generating substrate may have a density of less than or equal to about 500 milligrams per cubic centimetre, less than or equal to about 450 milligrams per cubic centimetre, less than or equal to about 400 milligrams per cubic centimetre, or less than or equal to about 350 milligrams per cubic centimetre.

[0218] The RTD of the rod of aerosol-generating substrate may be at least about 4 millimetres H2O, at least about 5 millimetres H2O, or at least about 6 millimetres H2O.

[0219] The RTD of the rod of aerosol-generating substrate may be less than or equal to about 10 millimetres H2O, less than or equal to about 9 millimetres H2O, or less than or equal to about 8 millimetres H2O.

[0220] The aerosol-generating substrate may be a solid aerosol-generating substrate. Suitable types of materials for use in the aerosol-generating substrate are described below and include, for example, tobacco cut filler, homogenised tobacco material such as cast leaf, aerosolgenerating films and gel compositions.

[0221] The aerosol-generating substrate preferably comprises an aerosol former. Suitable aerosol formers are for example: polyhydric alcohols such as, for example, triethylene glycol, 1 ,3- butanediol, propylene glycol and glycerine; esters of polyhydric alcohols such as, for example, glycerol mono-, di- or triacetate; aliphatic esters of mono-, di- or polycarboxylic acids such as, for example, dimethyl dodecanedioate and dimethyl tetradecanedioate; and combinations thereof. Preferably, the aerosol former comprises one or more of glycerine and propylene glycol. The aerosol former may consist of glycerine or propylene glycol or of a combination of glycerine and propylene glycol.

[0222] In certain embodiments, the aerosol-generating substrate preferably comprises at least 5 percent by weight of aerosol former on a dry weight basis of the aerosol-generating substrate, more preferably at least 10 percent by weight on a dry weight basis, more preferably at least 15 percent by weight on a dry weight basis. In such embodiments, the aerosol-generating substrate preferably comprises no more than 30 percent by weight of aerosol former on a dry weight basis of the aerosol-generating substrate, more preferably no more than 25 percent by weight on a dry weight basis, more preferably no more than 20 percent by weight on a dry weight basis. For example, the aerosol former content of the aerosol-generating substrate may be between 5 percent and 30 percent by weight, or between 10 percent and 25 percent by weight, or between about 15 percent and about 20 percent by weight, on a dry weight basis. In such embodiments, the aerosol former content is therefore relatively low.

[0223] In other embodiments, the aerosol-generating substrate preferably comprises at least 40 percent by weight of aerosol former on a dry weight basis of the aerosol-generating substrate, more preferably at least 45 percent by weight on a dry weight basis, more preferably at least 50 percent by weight on a dry weight basis. In such embodiments, the aerosol-generating substrate preferably comprises no more than 80 percent by weight of aerosol former on a dry weight basis of the aerosol-generating substrate, more preferably no more than 75 percent by weight on a dry weight basis, more preferably no more than 70 percent by weight on a dry weight basis. For example, the aerosol former content of the aerosol-generating substrate may be between 40 percent and 80 percent by weight, or between 45 percent and 75 percent by weight, or between about 50 percent and about 70 percent by weight, on a dry weight basis. In such embodiments, the aerosol former content is therefore relatively high.

[0224] In some preferred embodiments, the aerosol-generating substrate comprises tobacco material. For example, the aerosol-generating substrate may comprise shredded tobacco material. For example, the shredded tobacco material may be in the form of cut filler, as described in more detail below. Alternatively, the shredded tobacco material may be in the form of a shredded sheet of homogenised tobacco material. Suitable homogenised tobacco materials for use in the present invention are described below.

[0225] Within the context of the present specification, the term “cut filler” is used to describe to a blend of shredded plant material, such as tobacco plant material, including, in particular, one or more of leaf lamina, processed stems and ribs, homogenised plant material.

[0226] The cut filler suitable to be used with the present invention generally may resemble cut filler used for conventional smoking articles. The cut width of the cut filler preferably may be between 0.3 millimetres and 2.0 millimetres, or between 0.5 millimetres and 1.2 millimetres, or between 0.6 millimetres and 0.9 millimetres.

[0227] Preferably, the strands have a length of between about 10 millimetres and about 40 millimetres before the strands are collated to form the rod of aerosol-generating substrate.

[0228] Preferably, the cut filler is soaked with the aerosol former. Soaking the cut filler can be done by spraying or by other suitable application methods. Preferably, the aerosol former in the cut filler comprises one or more of glycerol and propylene glycol. The aerosol former may consist of glycerol or propylene glycol or of a combination of glycerol and propylene glycol.

[0229] In other preferred embodiments, the aerosol-generating substrate comprises homogenised plant material, preferably a homogenised tobacco material.

[0230] As used herein, the term “homogenised plant material” encompasses any plant material formed by the agglomeration of particles of plant. For example, sheets or webs of homogenised tobacco material for the aerosol-generating substrates of the present invention may be formed by agglomerating particles of tobacco material obtained by pulverising, grinding or comminuting plant material and optionally one or more of tobacco leaf lamina and tobacco leaf stems. The homogenised plant material may be produced by casting, extrusion, paper making processes or other any other suitable processes known in the art.

[0231] The homogenised plant material can be provided in any suitable form.

[0232] In some embodiments, the homogenised plant material may be in the form of one or more sheets. As used herein with reference to the invention, the term “sheet” describes a laminar element having a width and length substantially greater than the thickness thereof.

[0233] The homogenised plant material may be in the form of a plurality of pellets or granules.

[0234] The homogenised plant material may be in the form of a plurality of strands, strips or shreds. As used herein, the term “strand” describes an elongate element of material having a length that is substantially greater than the width and thickness thereof.

[0235] The aerosol former content of the homogenised tobacco material is preferably within the ranges defined above for aerosol-generating substrate having a relatively low aerosol former content.

[0236] In other preferred embodiments, the aerosol-generating substrate is in the form of an aerosol-generating film comprising a cellulosic based film-forming agent, nicotine and the aerosol former. The aerosol-generating film may further comprise a cellulose based strengthening agent. The aerosol-generating film may further comprise water, preferably 30 percent by weight of less of water.

[0237] As used herein, the term “film” is used to describe a solid laminar element having a thickness that is less than the width or length thereof. The film may be self-supporting.

[0238] In the context of the present invention the term “cellulose based film-forming agent” is used to describe a cellulosic polymer capable, by itself or in the presence of an auxiliary thickening agent, of forming a continuous film. Preferably, the cellulose based film-forming agent is selected from the group consisting of hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), ethylcellulose (EC), hydroxyethyl methyl cellulose (HEMC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), and combinations thereof. In particularly preferred embodiments, the cellulose based film-forming agent is HPMC.

[0239] The aerosol former content of the aerosol-generating film is within the ranges defined above for aerosol-generating substrates having a relatively high aerosol former content.

[0240] Suitable aerosol-generating films for use as the aerosol-generating substrate of aerosolgenerating articles according to the invention are described in WO-A-2020 / 207733 and WO-A- 2022 / 074157.

[0241] Preferably, the aerosol-generating film comprises between 0.5 percent and 10 percent by weight of nicotine, or between 1 percent and 8 percent by weight of nicotine, or between 2 percent and 6 percent by weight of nicotine, on a dry weight basis.

[0242] The aerosol-generating film may be a substantially tobacco-free aerosol-generating film.

[0243] In alternative embodiments of the invention, the aerosol-generating substrate may comprise a gel composition that includes nicotine, at least one gelling agent and the aerosol former. The gel composition is preferably substantially tobacco free.

[0244] The preferred weight ranges for nicotine in the gel composition are the same as those defined above in relation to aerosol-generating films.

[0245] Suitable gel compositions for use as the aerosol-generating substrate of aerosol-generating articles according to the invention are described in WO-A-2021 / 170642.

[0246] The gel composition preferably comprises at least 50 percent by weight of aerosol former, more preferably at least 60 percent by weight, more preferably at least 70 percent by weight of aerosol former, on a dry weight basis. The gel composition may comprise up to 80 percent by weight of aerosol former. The aerosol former in the gel composition is preferably glycerol.

[0247] In certain embodiments of the invention, the aerosol-generating article further comprises one or more elongate susceptor elements within the rod of aerosol-generating substrate. For example, one or more elongate susceptor elements may be arranged substantially longitudinally within the rod of aerosol-generating substrate and in thermal contact with the aerosol-generating substrate.

[0248] As used herein with reference to the present invention, the term “susceptor element” refers to a material that can convert electromagnetic energy into heat.

[0249] Suitable susceptor elements for use in the aerosol-generating substrate of aerosolgenerating articles according to the present invention are described in WO-A-2021 / 170673.

[0250] Preferably, the rod of aerosol-generating substrate is circumscribed by a wrapper. The wrapper may be a paper wrapper or a non-paper wrapper. Suitable paper wrappers for use in specific embodiments of the invention are known in the art and include, but are not limited to: cigarette papers; and filter plug wraps. Suitable non-paper wrappers for use in specific embodiments of the invention are known in the art and include, but are not limited to sheets of homogenised tobacco materials.

[0251] According to a second aspect of the present invention, there is provided an aerosolgenerating system comprising: an aerosol-generating article according to the first aspect of the invention; and an aerosol-generating device configured to heat the aerosol-generating substrate of the aerosol-generating article.

[0252] The aerosol-generating device comprises means for heating the aerosol-generating substrate to a temperature sufficient to generate an aerosol from the aerosol-generating substrate. Preferably, the aerosol-generating device comprises a housing defining a cavity configured to receive the aerosol-generating article, and means for heating the aerosolgenerating substrate to a temperature sufficient to generate an aerosol from the aerosolgenerating substrate when the aerosol-generating article is received within the cavity.

[0253] The aerosol-generating device may be a handheld aerosol-generating device.

[0254] The aerosol-generating device may be an electrically-operated aerosol-generating device.

[0255] The aerosol-generating device may comprise a power supply and control electronics.

[0256] The aerosol-generating device may comprise a battery and control electronics.

[0257] The aerosol-generating device may be configured to heat the aerosol-generating substrate internally. That is, the aerosol-generating device may be configured to supply heat to the aerosol-generating substrate from a location internal to the aerosol-generating article.

[0258] For example, in some embodiments the aerosol-generating device comprises a heater element configured to be inserted into the aerosol-generating element when the aerosolgenerating article is received within the cavity of the aerosol-generating device.

[0259] In other embodiments, the aerosol-generating article comprises a susceptor element provided at a location within the aerosol-generating element, and the aerosol-generating device comprises an inductor coil positioned on or within the housing, a power supply of the aerosolgenerating device being connected to the inductor coil and configured to provide a high frequency oscillating current to the inductor coil.

[0260] The aerosol-generating device may be configured to heat the aerosol-generating substrate externally. That is, the aerosol-generating device may be configured to supply heat to the aerosol-generating substrate from a location external to the aerosol-generating article. For example, in some embodiments the aerosol-generating device comprises a heater element located about a perimeter of the cavity and configured to heat the aerosol-generating substrate of the aerosol-generating article from an exterior of the aerosol-generating element of the aerosolgenerating article. Examples will now be further described with reference to the drawings of the accompanying Figures in which:

[0261] Figure 1 shows a schematic side sectional view of an aerosol-generating article in accordance with an embodiment of the invention;

[0262] Figure 2 shows a schematic side sectional view of another aerosol-generating article in accordance with another embodiment of the invention; and

[0263] Figure 3 shows a schematic side sectional view of another aerosol-generating article in accordance with a further embodiment of the invention.

[0264] The aerosol-generating article 1000 shown in Figure 1 comprises an aerosol-generating element 1002 in the form of a substantially cylindrical rod 1004 of shredded tobacco circumscribed by a wrapper 1006. Further, the aerosol-generating article 1000 comprises a substantially cylindrical mouthpiece 1008 comprising a segment 1010 of a cellulosic filtration material circumscribed by a plug wrap 1012.

[0265] The mouthpiece 1008 is attached to the aerosol-generating element 1002 by a band 1014 of tipping paper. Perforations 1016 formed through the tipping paper and the plug wrap are provided to enable admission of ventilation air into the segment 1010 when the consumer draws upon the mouthpiece 1008 during use. The aerosol-generating article 1000 has a length of 70 millimetres and an external diameter of 7.6 millimetres.

[0266] The segment 1010 is in the form of a plug element comprising a cellulosic filtration material comprising viscose fibres and a coating additive applied to the viscose fibres, the coating additive comprising one of dipropylene glycol, tripropylene glycol and tetrapropyleneglycol.

[0267] The aerosol-generating article 10 shown in Figure 2 comprises a rod 12 of aerosolgenerating substrate 12 and a downstream section 14 at a location downstream of the rod 12 of aerosol-generating substrate. Further, the aerosol-generating article 10 comprises an upstream section 16 at a location upstream of the rod 12 of aerosol-generating substrate. Thus, the aerosolgenerating article 10 extends from an upstream or distal end 18 to a downstream or mouth end 20, and has an overall length of about 45 millimetres.

[0268] The downstream section 14 comprises a support element 22 located immediately downstream of the rod 12 of aerosol-generating substrate, the support element 22 being in longitudinal alignment with the rod 12. In the embodiment of Figure 2, the upstream end of the support element 18 abuts the downstream end of the rod 12 of aerosol-generating substrate. In addition, the downstream section 14 comprises an aerosol-cooling element 24 located immediately downstream of the support element 22, the aerosol-cooling element 24 being in longitudinal alignment with the rod 12 and the support element 22. In the embodiment of Figure 1 , the upstream end of the aerosol-cooling element 24 abuts the downstream end of the support element 22. In the embodiment of Figure 2, the support element 22 and the aerosol-cooling element 24 together define an intermediate hollow section 50 of the aerosol-generating article 10. The support element 22 comprises a first hollow tubular segment 26. The first hollow tubular segment 26 is provided in the form of a hollow cylindrical tube made of filtration material. The first hollow tubular segment 26 defines an internal cavity 28 that extends all the way from an upstream end 30 of the first hollow tubular segment to an downstream end 32 of the first hollow tubular segment 20. The internal cavity 28 is substantially empty, and so substantially unrestricted airflow is enabled along the internal cavity 28.

[0269] The first hollow tubular segment 26 has a length of about 8 millimetres, an external diameter of about 7.25 millimetres, and an internal diameter of about 1.9 millimetres. Thus, a thickness of a peripheral wall of the first hollow tubular segment 26 is about 2.67 millimetres.

[0270] The aerosol-cooling element 24 comprises a second hollow tubular segment 34. The second hollow tubular segment 34 is provided in the form of a hollow cylindrical tube made of filtration material. The second hollow tubular segment 34 defines an internal cavity 36 that extends all the way from an upstream end 38 of the second hollow tubular segment to a downstream end 40 of the second hollow tubular segment 34. The internal cavity 36 is substantially empty, and so substantially unrestricted airflow is enabled along the internal cavity 36.

[0271] The second hollow tubular segment 34 has a length of about 8 millimetres, an external diameter of about 7.25 millimetres, and an internal diameter of about 3.25 millimetres. Thus, a thickness of a peripheral wall of the second hollow tubular segment 34 is about 2 millimetres. Thus, a ratio between the internal diameter of the first hollow tubular segment 26 and the internal diameter of the second hollow tubular segment 34 is about 0.75.

[0272] The aerosol-generating article 10 comprises a ventilation zone 60 provided at a location along the second hollow tubular segment 34. In more detail, the ventilation zone is provided at about 2 millimetres from the upstream end of the second hollow tubular segment 34. A ventilation level of the aerosol-generating article 10 is about 25 percent.

[0273] In the embodiment of Figure 2, the downstream section 14 further comprises a mouthpiece element 42 at a location downstream of the intermediate hollow section 50. In more detail, the mouthpiece element 42 is positioned immediately downstream of the aerosol-cooling element 24. As shown in the drawing of Figure 2, an upstream end of the mouthpiece element 42 abuts the downstream end 40 of the aerosol-cooling element 18.

[0274] The mouthpiece element 42 is provided in the form of a cylindrical plug element 44 comprising paper material and a coating additive applied to the paper material, the coating additive comprising one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol.

[0275] The mouthpiece element 42 has a length of about 12 millimetres and an external diameter of about 7.25 millimetres.

[0276] The rod 12 comprises an aerosol-generating substrate of one of the types described above. The rod 12 of aerosol-generating substrate has an external diameter of about 7.25 millimetres and a length of about 12 millimetres.

[0277] The aerosol-generating article 10 further comprises an elongate susceptor 46 within the rod 12 of aerosol-generating substrate. In more detail, the susceptor 46 is arranged substantially longitudinally within the aerosol-generating substrate, such as to be approximately parallel to the longitudinal direction of the rod 12. As shown in the drawing of Figure 2, the susceptor 46 is positioned in a radially central position within the rod and extends effectively along the longitudinal axis of the rod 12. In more detail, the susceptor 46 is in thermal contact with the aerosolgenerating substrate. The susceptor 46 extends all the way from an upstream end to a downstream end of the rod 12. In effect, the susceptor 46 has substantially the same length as the rod 12 of aerosol-generating substrate.

[0278] In more detail, in the embodiment of Figure 2, the susceptor 46 is provided in the form of a strip and has a length of about 12 millimetres, a thickness of about 60 micrometres, and a width of about 4 millimetres.

[0279] The upstream section 16 comprises an upstream element 48 located immediately upstream of the rod 12 of aerosol-generating substrate, the upstream element 48 being in longitudinal alignment with the rod 12. In the embodiment of Figure 2, the downstream end of the upstream element 48 abuts the upstream end of the rod 12 of aerosol-generating substrate. This advantageously prevents the susceptor 46 from being dislodged. Further, this ensures that the consumer cannot accidentally contact the heated susceptor 46 after use.

[0280] The upstream element 48 comprises a segment of material 50 in the form of a cylindrical plug of filtration material and a first wrapper 52 circumscribing the segment of material 50. The segment of material 50 has a length of about 5 millimetres. The RTD of the segment of material 50 is about 30 millimetres H2O.

[0281] The aerosol-generating article 10 further comprises a combining wrapper 54 which attaches the upstream element 48 to the remaining components of the aerosol-generating article. In the embodiment of Figure 2 a single combining wrapper 54 is depicted, which circumscribes and holds together the upstream element 48, the rod 12, and the downstream section 14 to form the aerosol-generating article.

[0282] However, it will be clear that alternative configurations are possible, wherein two or more combining wrappers are employed to assemble the different components of the aerosolgenerating article. For example, a first combining wrapper could be used to attach the support element 22 to the aerosol-cooling element 24, and the resulting assembly could then be attached by means of a second combining wrapper to the upstream section 16 and the rod 12. The resulting combination of components could then be attached to the mouthpiece element 42 by means of a tipping wrapper. As shown in the drawing of Figure 1 , the aerosol-generating article 10 further comprises a wrapper 70 circumscribing the rod 12 of aerosol-generating substrate. The wrapper 70 is separate and distinct from the first wrapper 52 circumscribing the segment of material 50. Neither one of the first wrapper 52 and the wrapper 70 comprises a metallic foil.

[0283] In the aerosol-generating article 10 of Figure 2, one or more of the first hollow tubular segment 26 of the support element 22, the second hollow tubular segment 34 of the aerosolcooling element 24, and the segment of material 50 of the upstream element 48 may be made of the same material according to the present invention used in the mouthpiece element 42.

[0284] The aerosol-generating article 100 shown in Figure 3 comprises a rod of aerosol-generating substrate 112 and a downstream section 114 at a location downstream of the rod 112 of aerosolgenerating substrate. Additionally, the aerosol-generating article 100 comprises an upstream section 116. Thus, the aerosol-generating article 100 extends from an upstream or distal end 118 - which substantially coincides with an upstream end of the upstream section 116 - to a downstream or mouth end 120, which coincides with a downstream end of the downstream section 114. The downstream section 114 comprises a hollow tubular element 122 and a mouthpiece element 150. The upstream section 116 comprises an upstream plug element 124.

[0285] The aerosol-generating article 1 has an overall length of about 45 millimetres and an outer diameter of about 7.2 mm.

[0286] The rod of aerosol-generating substrate 112 comprises a shredded tobacco material. The rod of aerosol-generating substrate 112 comprises 150 milligrams of a shredded tobacco material comprising from 13 percent by weight to 16 percent by weight of glycerine. The density of the aerosol-generating substrate is about 300 mg per cubic centimetre. The RTD of the rod of aerosol-generating substrate 112 is between about 6 to 8 mm H2O. The rod of aerosol-generating substrate 112 is individually wrapped by a plug wrap (not shown).

[0287] The hollow tubular element 122 is located immediately downstream of the rod 112 of aerosol-generating substrate, the hollow tubular element 122 being in longitudinal alignment with the rod 112. The upstream end of the hollow tubular element 122 abuts the downstream end of the rod 112 of aerosol-generating substrate.

[0288] The hollow tubular element 122 defines a hollow section of the aerosol-generating article 110. The hollow tubular element 122 does not substantially contribute to the overall RTD of the aerosol-generating article. In more detail, an RTD of the hollow tubular element 122 is about 0 mm H2O.

[0289] As shown in Figure 3, the hollow tubular element 122 is provided in the form of a hollow cylindrical tube made of cardboard. The hollow tubular element 122 defines an internal cavity that extends all the way from an upstream end of the hollow tubular element 122 to a downstream end of the hollow tubular element 122. The internal cavity is substantially empty, and so substantially unrestricted airflow is enabled along the internal cavity. The hollow tubular element 122 has a length of about 21 millimetres, an external diameter of about 7.2 millimetres, and an internal diameter of about 6.7 millimetres. Thus, a thickness of a peripheral wall of the hollow tubular element 122 is about 0.25 millimetres.

[0290] The aerosol-generating article 100 comprises a ventilation zone 160 provided at a location along the hollow tubular element 122. The ventilation zone 160 comprises a circumferential row of openings or perforations circumscribing the hollow tubular element 122. The perforations of the ventilation zone 160 extend through the wall of the hollow tubular element 122, in order to allow fluid ingress into the internal cavity from the exterior of the article 100. A ventilation level of the aerosol-generating article 10 is about 16 percent.

[0291] On top of a rod 112 of aerosol-generating substrate and a downstream section 14 at a location downstream of the rod 12, the aerosol-generating article 100 comprises an upstream section 140 at a location upstream of the rod 112. As such, the aerosol-generating article 10 extends from a distal end 116 substantially coinciding with an upstream end of the upstream section 140 to a mouth end or downstream end 118 substantially coinciding with a downstream end of the downstream section 114.

[0292] As described briefly above, the upstream section 116 comprises an upstream plug element 124 located immediately upstream of the rod 112 of aerosol-generating substrate, the upstream plug element 124 being in longitudinal alignment with the rod 112. The downstream end of the upstream plug element 124 abuts the upstream end of the rod 112 of aerosol-generating substrate. The upstream plug element 124 is provided in the form of a hollow cylindrical plug of filtration material having a wall thickness of about 1 mm and defining an upstream internal cavity. The upstream element 124 has a length of about 5 millimetres. An external diameter of the upstream plug element 124 is about 7.1 mm. An internal diameter of the upstream plug element 42 is about 5.1 mm.

[0293] The mouthpiece element 150 extends from the downstream end of the hollow tubular element 122 to the downstream or mouth end of the aerosol-generating article 100. The mouthpiece element 150 has a length of about 7 mm. An external diameter of the mouthpiece element 150 is about 7.2 mm.

[0294] The mouthpiece element 150 is provided in the form of a cylindrical plug element comprising a fibrous material comprising cotton fibres and a gel additive applied to the cotton fibres, the gel additive comprising one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol.

[0295] In the aerosol-generating article 100 of Figure 3, the plug element 124 of the upstream section 116 may be made of the same material according to the present invention used in the mouthpiece element 150.

[0296] Phenol-scavenging performance

[0297] Tests were conducted with a view to assessing the capability of plug elements for use in downstream elements of aerosol-generating articles in accordance with the foregoing description. A plug element comprising paper as the cellulosic filtration material and no additive coating was provided and tested as a Comparative Plug.

[0298] Sample Plugs A, B, C, D, were prepared by applying respective additive coatings on plug elements comprising paper as the cellulosic filtration material identical to the Comparative Plug. Details about the additive coating compositions are provided in Table 1 below.

[0299] The phenol-scavenging performance of the Sample Plugs and the Comparative Plug was assessed by measuring their o-cresol retention. To this purpose, a gaseous flow with a known concentration (KC) of o-cresol was supplied to flow through each individual plug, and the residual concentration (RC) of o-cresol in the gaseous flow downstream of the plug was determined by gas chromatography-mass spectrometry (GC-MS). The [(KC - RC) I KC] ratio was taken as the o-cresol retention for the plug.

[0300] The o-cresol retention determined for each one of the Sample Plugs was compared with the o-cresol retention determined for the Comparative Plug. Data relating to the variation in o- cresol retention determined for the Sample Plugs with respect to the o-cresol retention of the Comparative Plug provided in Table 1 below.

[0301] Table 1

[0302] Sample Plugs B and D in accordance with the present invention clearly displayed phenol- scavenging properties compared with equivalent plugs free of coating additives. Furthermore, while the application of smaller amounts of DPG or TPG on the paper plugs appeared to actually be detrimental, use of an additive coating containing DPG or TPG in the amounts set out in the accompanying claims appears to provide an effective, more sustainable alternative to conventional cellulose acetate filter plugs for use in aerosol-generating articles.

[0303] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± 5% of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

Claims

CLAIMS1. An aerosol-generating article comprising: an aerosol-generating substrate; a downstream element provided downstream of the aerosol-generating substrate and in axial alignment with the aerosol-generating substrate, the downstream element comprising a plug element comprising: a cellulosic filtration material comprising a fibrous material; and an additive coating applied to the fibrous material, the additive coating comprising at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol; wherein the plug element comprises at least 5 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol based on the dry weight of the cellulosic filtration material on a dry weight basis.

2. An aerosol-generating article according to claim 1 , wherein the additive coating further comprises starch, modified starch, alkenyl succinate starches, pullulan, alginate, and combinations thereof.

3. An aerosol-generating article according to claim 1 , wherein the additive coating further comprises hydrogenated ethoxylated castor oil.

4. An aerosol-generating article according to claim 1 , wherein the additive coating further comprises a liquid polyester oligomer.

5. An aerosol-generating article according to claim 1 , wherein the additive coating further comprises a polyadipate plasticiser or a polylactate plasticiser.

6. An aerosol-generating article according to claim 1 , wherein the additive coating further comprises a lactate-based surfactant.

7. An aerosol-generating article according to claim 1 , wherein the additive coating further comprises triacetin, triethyl citrate, triethylene glycol-diacetate, sucrose acetate isobutyrate and polyethylene glycol.

8. An aerosol-generating article according to any one of the preceding claims, wherein the plug element comprises less than or equal to 10 percent by weight of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol on a dry weight basis.

9. An aerosol-generating article according to any one of the preceding claims, wherein the cellulosic filtration material comprises at least 1 percent by weight of the additive coating.

10. An aerosol-generating article according to any one of claims 1 to 9, wherein the fibrous material comprises a plurality of regenerated cellulose fibres, wherein the regenerated cellulose fibres are one or more of viscose fibres, modal fibres, Lyocell fibres and viscose rayon fibres, and wherein the additive coating is applied to the plurality of regenerated cellulose fibres.

11. An aerosol-generating article according to any one of claims 1 to 9, wherein the fibrous material comprises a plurality of natural fibres, wherein the natural fibres are one or more of are one or more of flax fibres, hemp fibres, jute fibres, kenaf fibres, ramie fibres, abaca fibres, phormium fibres, sisal fibres, coir fibres, cotton fibres, and kapok fibres, and wherein the additive coating is applied to the plurality of natural fibres.

12. An aerosol-generating article according to any one of claims 1 to 9, wherein the fibrous material comprises paper material, and wherein the additive coating is applied to the paper material.

13. An aerosol-generating article according to any one of the preceding claims, wherein the plug element is substantially free from cellulose acetate.

14. An aerosol-generating article according to any preceding claim, wherein the downstream element is a mouthpiece filter segment comprising the plug element and a filter wrapper circumscribing the plug element.

15. A method of producing a cellulosic filtration material for forming a plug element of an aerosol-generating article according to claim 1 , the method comprising the steps of: providing a cellulosic fibrous material; forming an additive coating solution comprising at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol; applying the additive coating solution to the cellulosic fibrous material; drying and optionally curing the coated cellulosic fibrous material; and forming a plug element comprising the coated cellulosic fibrous material;wherein a content of the at least one of dipropylene glycol, tripropylene glycol and tetrapropylene glycol in the plug element is at least 5 percent by weight of the plug element, on a dry weight basis.

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