EP4734779A1

EP4734779A1 - Smoking or aerosol generating product

Info

Publication number: EP4734779A1
Application number: EP24745803.7A
Authority: EP
Inventors: Ivan Eusepi; Valentina DI LALLO; Federico QUARELLI DI LESEGNO; Carlo Punta; Martina LIPPI; Alessandro Sacchetti
Original assignee: GD SpA
Current assignee: GD SpA
Priority date: 2023-06-27
Filing date: 2024-06-26
Publication date: 2026-05-06
Also published as: WO2025003909A1; IT202300013224A1

Abstract

The present invention regards a product which generates aerosols or smoke, in particular a product of the tobacco industry and/or intended for smokers, which contains or does not contain tobacco. Preferably, the product which generates smoke is a cigarette, a cigar or a cigarillo. The product which generates aerosols is preferably an electronic cigarette or a HNB cigarette (heat-not-burn), comprising a filter, wherein the filter consists of nanocellulose, obtained from cellulose subjected to oxidation with an opportune oxidising agent and in the presence of a nitroxide radical catalyst preferably 2,2,6,6-tetramethylpiperidine 1-oxyl, 2,2,6,6-tetramethyl-1- piperidinyloxy (TEMPO), and then subjected to cross-linking with at least one cross-linking agent selected between a polyamine and a linear or branched polyimine. The material obtained by oxidation and cross-linking is then subjected to freezing, lyophilization and baking to obtain a porous aerogel to be used for filtering the harmful substances present in the smoke generated by the combustion of the tobacco.

Description

SMOKING OR AEROSOL GENERATING PRODUCT

Technical field

The invention relates to a product which generates aerosols or smoke preferably belonging to the tobacco industry and/or intended for smokers. In particular, the product which generates smoke is a cigarette comprising an oxidised cellulose cross-linked filter in the form of aerogel characterised by an appropriate porosity.

Background art

The cigarette filter, normally cylindrical in shape, is located at one end of the cigarette in order both to mechanically stop the inhalation of tobacco and the inhalation of the harmful agents produced by the combustion of the paper and the tobacco itself.

An important secondary effect resulting from the use of cigarette filters is due to the disposal of these filters which are normally made of cellulose acetate, a compound characterised by a slow biodegradability.

There is a strong need in the sector for filters made of material characterised by a better biodegradability compared with cellulose acetate and which at the same time have performance levels of filtration of the harmful components of smoke which are comparable or better than the prior art filters. Moreover, from a circular economic point of view, the filter should be made from waste materials.

Aim of the invention

The present invention relates to a product which generates aerosols or smoke provided with a filter at one end. The product which generates aerosols is preferably an electronic cigarette or a HNB cigarette (heat-not- burn). The product which generates smoke is preferably a cigarette with tobacco. Both the products comprise a filter. The filter comprises or is made of a composite material based on oxidised and cross-linked nanocellulose. According to an embodiment, the filter is in the form of aerogel obtained by oxidation and subsequent cross-linking of the nanocellulose.

The filter is provided with micro and nano-porosity which allows an effective filtration of the harmful components of the smoke generated by the combustion of the tobacco and paper, or of the harmful components contained in the aerosol.

The invention also relates to the use of a composite material based on oxidised and cross-linked nanocellulose to prepare a filter for a smoking product or aerosol, preferably a filter for a tobacco cigarette or an electronic cigarette or HNB cigarette, as well as the filter for a smoking product or aerosol which can be obtained by the oxidation and cross-linking reaction of the cellulose.

The oxidised and cross-linked nanocellulose-based filter is used to filter and retain the harmful substances contained in the smoke generated by the combustion of the tobacco or to retain the harmful substances contained in the aerosol.

According to an embodiment the invention also relates to a method for filtering the smoke generated by the combustion of the tobacco or by the generation of an aerosol which comprises: a) providing a smoking product or a product which generates aerosol comprising an oxidised and crosslinked nanocellulose-based filter and a tobacco-based mixture or an aerosol mixture; b) generating the smoke by burning the tobacco or generating an aerosol by heating a mixture suitable for generating an aerosol when heated; c) inhaling the smoke or the aerosol through the filter.

Brief description of the drawings

Figure 1 shows SEM photos which show the microporous morphology of the material resulting from Example 1 . Figure 2 shows SEM photos which show the microporous morphology of the material resulting from Example 5.

Figure 3 shows SEM photos which show the microporous morphology of the material resulting from Example 6.

Figure 4 shows SEM photos which show the microporous morphology of the material resulting from Example 7.

Figure 5 shows SEM photos which show the microporous morphology of the material resulting from Example 8.

Figure 6 shows SEM photos which show the microporous morphology of the material resulting from example 1 1 .

Figure 7 shows SEM photos which show the microporous morphology of the material resulting from example 12.

Detailed description of preferred embodiments of the invention

The term “smokers’ product provided with a filter” or “smokers’ product” is used to mean a product which comprises a filter at one end, in particular a cigarette, a cigar, a cigarillo or the like.

The term “aerosol product” or “product which generates aerosol” is used to mean a product which comprises a mixture, for example an aromatic mixture or a pharmaceutical mixture, which if heated generates an aerosol. According to the invention, the smoking product or aerosol comprises an oxidised and cross-linked nanocellulose-based filter.

In particular, the filter is obtained by subjecting the cellulose to an oxidation reaction which transforms the hydroxyl groups (-OH) in position C6 of the glucopyranose core into carboxyl groups (-COOH), available to a crosslinking reaction.

The oxidation of hydroxyl groups to carboxyl groups promotes the nanodefibrillation of the cellulose in a basic aqueous solution (pH-8-10). Indeed, under basic conditions the carboxyl groups deprotonate, facilitating the introduction of negative charges on the skeleton of the nanofibers, which tend to separate and disperse in solution by electrostatic repulsion, favoured by mechanical action such as ultrasonication or homogenisation. Moreover, the introduction of carboxyl groups on the nanofibers facilitates the subsequent cross-linking with an appropriate agent chosen from at least one polyamine and at least a linear or branched polyimine, resulting in the formation of amidic bonds between the carboxyl groups of the oxidised nanocellulose and the amino groups of the cross-linking agent.

With the cross-linking promoted by thermal treatments an aerogel is formed provided with micro and nano-pores having a size suitable for retaining the harmful substances present in the smoke deriving from the combustion of the tobacco. The aerogel is provided with mechanical properties which make it suitable for use in a smoking product for filtering harmful substances.

According to an embodiment, during the cross-linking step, a co-cross- linking agent is used, for example a polycarboxylic acid, which helps to increase the degree of cross-linking, therefore allowing the improvement of the mechanical and structural properties of the aerogel systems obtained. The filter for a smoking product or aerosol, preferably a cigarette with tobacco or an electronic cigarette or HNB, is obtained/obtainable from a process comprising the following steps: a) oxidising cellulose by treating with an oxidising agent selected between HCIO, HCIO2 and salts thereof, in the presence of a nitroxide radical catalyst, and one or more alkaline or alkaline earth salts of HBr. b) dispersing the oxidized cellulose in a basic solution and subjecting it to mechanical action, for example by sonication, or homogenization until obtaining a homogeneous dispersion of cellulose nanofibers (nanocellulose); c) adding at least one cross-linking agent selected between a polyamine and a linear or branched polyimine to obtain a hydrogel; d) freezing the hydrogel at a temperature of between -20 °C and -210 °C followed by lyophilization to obtain a porous aerogel; e) heating the porous aerogel to a temperature of between 50°C and 1 10°C so as to cause cross-linking of the oxidized cellulose.

The starting cellulose used in step a) of the process for producing the filter comes from various sources, such as, for example: hydrophilic cotton, linters, wood or directly from a tree such as fir-tree. Alternatively, the cellulose is recycled cellulose, for example from the recycling of paper or cardboard, from agricultural waste products and from food waste products. In step a), the oxidation occurs in water in the presence of one or more of the HCIO, HCIO2 derivatives and their salts, one or more alkaline or alkaline earth salts of HBr, and a nitroxide radical as catalyst, preferably 2, 2,6,6- tetramethylpiperidine 1 -oxyl (TEMPO), at a basic pH, preferably between 8 and 12.

The reaction is performed for a time of between 2 and 16 hours at a temperature preferably between 10°C and 60°C.

At the end of the reaction, the oxidized cellulose has a degree of oxidation of between 0.8 mmol/g and 2 mmol/g, understood as millimoles of carboxyl groups per gram of nanocellulose, preferably between 1 mmol/g and 1 .7 mmol/g. The degree of oxidation can be controlled. Indeed, it has been observed that it is advantageous to modify the degree of oxidation, and therefore the number of carboxyl groups present on the nanofiber, as a function of the cross-linking agent used, in order to obtain an ideal crosslinking to guarantee optimum performance both in terms of mechanical strength and filtration, properly modulating the porosity of the filter. At the end of the oxidation, the oxidised cellulose nanofibers are preferably filtered and washed and then re-dispersed in a basic aqueous solution.

In step b), the basic solution preferably has a pH of between 9 and 12, more preferably between 10 and 1 1 . The basic pH promotes the deprotonation of the carboxylic groups and promotes the electrostatic repulsion of the individual negatively charged fibres. In this way, a better dispersion of oxidised cellulose nanofibers is obtained.

The dispersion of oxidised cellulose nanofibers is subjected to mechanical action, for example sonication for a time of between 5 and 30 minutes, preferably between 10 and 20 minutes, or homogenisation, until a homogeneous dispersion is obtained.

According to an embodiment, after step b), the dispersion of cellulose nanofibers is acidified and then subjected to filtration to remove the excess water (step b1 )). The suspension is acidified in order to re-compact the oxidised cellulose nanofibers and allow an easy filtration, preferably followed by a washing with deionised water until the pH is completely neutralised.

In step c), the cellulose nanofibers, preferably previously acidified and filtered according to step b1 , are again dispersed in water, preferably in a ratio of between 0.2% and 5% w/w, more preferably between 1 % and 3% w/w, and at least a cross-linking agent selected between a polyamine and a linear or branched, aliphatic or aromatic, polyimine, is added to the dispersion, obtaining a hydrogel. Mixing is preferably performed at room temperature, for a duration between 5 and 30 minutes, preferably between 5 and 10 minutes. According to an embodiment, the dispersion is subjected to sonication or homogenisation to help the formation of the hydrogel.

The at least a cross-linking agent is preferably chosen from among: linear and branched polyalkylenimine chitosan, an amino derivative of polyalkylene glycols, preferably polyethylene glycol (PEG), such as, for example, 4-arm PEG-Amine and 8-arm PEG-Amine, and a Jeffamine, such as Jeffamine EG-2003 and combinations thereof.

The chemical formulations of some preferred cross-linking agents are as follows:

Preferably, the at least one cross-linking agent is branched polyethylenimine.

Preferably, the at least one cross-linking agent is chitosan. Preferably, the at least one cross-linking agent is selected from among: chitosan, an amino derivative of polyethylene glycol (PEG), such as 4-arm PEG-Amine and 8-arm PEG-Amine, and a Jeffamine, such as Jeffamine EG-2003 and combinations thereof.

According to an embodiment, in addition to the at least a cross-linking agent, a polycarboxylic acid is added, for example citric acid, succinic acid and/or adipic acid, which acts as a co-cross-linking agent. The use of a co-cross- linking agent, such as citric acid, is useful in some cases for the better fixing of polyamine cross-linking agents, thereby improving mechanical strength to the material and modifying its morphology. Preferably, the polycarboxylic acid is used in a quantity between 10% and 30% in millimoles with respect to the primary amino groups of the crosslinking agent, more preferably between 15% and 20%.

According to an embodiment, in step c) the branched polyethylenimine together with a carboxylic acid is used; preferably the carboxylic acid is citric acid.

According to an embodiment, in step c) chitosan together with a carboxylic acid is used; preferably the carboxylic acid is citric acid.

According to an embodiment, in step c) it is used at least a cross-linking agent selected among: chitosan, an amino derivative of polyethylene glycol (PEG), such as 4-arm PEG-Amine and 8-arm PEG-Amine, and a Jeffamine, such as Jeffamine EG-2003 and combinations thereof, together with a carboxylic acid, preferably citric acid.

Once the hydrogel is formed, the freezing is performed at a temperature between -20°C and -210°C (step d)). The morphology of the aerogel obtained at the end of the process is dictated by an internal micro and nanoporosity. The micro-porosity may be varied by properly modifying the freezing temperature within the intervals described. Therefore, varying the freezing temperature results in a different sizing of the ice crystals and therefore a different size of the pores resulting after the subsequent lyophilization treatment.

The lyophilization is preferably performed at a temperature of between -40°C and -70°C and at a pressure of between 40 and 80 pPa. After the lyophilization an aerogel is formed, characterised by micro and nanoporosity which is particularly suitable for retaining the harmful substances present in the smoke generated by the combustion of the tobacco.

According to an embodiment, the hydrogel is inserted in a suitable mould before the freezing and the lyophilization to impart a shape suitable for use as a filter for tobacco products, for example a cylindrical shape.

Lastly, in step e), the aerogel is subjected to heating at a temperature between 50°C and 1 10°C determining the cross-linking of oxidised cellulose by the formation of amidic bonds. The heating is preferably performed with a thermal ramp which determines a gradual increase in the temperature for a period of time of between 1 and 5 hours, preferably for 2-4 hours, followed by the maintaining of the temperature reached for a time between 10 and 30 hours, preferably between 15 and 20 hours.

For example, the thermal ramp starts from 55°C until reaching 95°C in a time of 1 to 5 hours, preferably 2 to 4 hours.

According to an embodiment, the aerogel is obtained in the form of a powder with a particle size preferably between 100 microns and 2 mm. In order to obtain the aerogel in the form of a powder, the aerogel is, for example, mechanically milled followed by a passage through sieves for selecting the desired particle size.

According to the embodiment wherein the aerogel is obtained in the form of a powder, the powder is then agglomerated in a suitable mould to obtain a filter of the desired shape, for example with a cylindrical shape.

The filter obtained/obtainable from the process of oxidation and crosslinking of the cellulose described here is characterised by a micro and nanoporosity suitable for retaining the harmful components of the smoke generated by the combustion of the tobacco. The smoke generated by the combustion of the tobacco includes partially unburnt particulate matter and different types of substances, including harmful substances that have been classified as carcinogenic, e.g. acetaldehyde, acetamide, formaldehyde, benzene, arsenic, metals (e.g. cadmium, chromium, mercury, lead, etc.), nitrobenzene, vinyl chloride, etc.; addictive substances, such as, for example, nicotine and acetaldehyde; toxic substances for the cardiovascular system, such as acrolein, benzene, butyraldehyde, phenol, propionaldehyde, etc.; toxic substances for the respiratory system, such as cresols, ethylene oxide, resorcinol, selenium etc.

The filter obtainable with the process of the invention has proved to be capable of retaining both an amount of particulate and toxic substances comparable with or greater than commercial cellulose acetate-based filters, lowering their concentration and therefore helping to protect the smoker’s health as far as possible.

The filter obtained/obtainable from the process of oxidation and crosslinking of cellulose described here is characterised by a micro- and nanoporosity suitable for retaining the harmful components present in the aerosol generated by the heating of an aromatic or pharmaceutical mixture. According to an embodiment, the filter is obtained with the process described, wherein the at least one cross-linking agent is selected between: branched polyethylenimine, chitosan, an amino derivative of polyethylene glycol (PEG), such as 4-arm PEG-Amine and 8-arm PEG-Amine, and a Jeffamine, such as Jeffamine EG-2003 and combinations thereof. Preferably, the at least one cross-linking agent is used together with a carboxylic acid, preferably citric acid.

According to an embodiment, the filter is obtained with a process of oxidation and cross-linking of the cellulose wherein the at least one crosslinking agent is branched polyethylenimine, preferably used together with a polycarboxylic acid, preferably citric acid.

According to an embodiment, the filter is obtained with a process of oxidation and cross-linking of the cellulose wherein the at least one crosslinking agent is chitosan, preferably used together with a carboxylic acid, preferably citric acid.

According to an embodiment, the filter is obtained with a process of oxidation and cross-linking of the cellulose wherein the at least one crosslinking agent is selected among: chitosan, an amino derivative of polyethylene glycol (PEG), such as 4-arm PEG-Amine and 8-arm PEG- Amine, and a Jeffamine, such as Jeffamine EG-2003 and combinations thereof, preferably used together with a carboxylic acid, preferably citric acid.

The filter obtained according to the various embodiments is used to filter and retain, reducing the concentration, the harmful substances present in the smoke generated by the combustion of the tobacco. In other words, the filter is used to filter the smoke produced by the combustion of the tobacco and is therefore advantageously used as a filter element of a tobacco product selected from among: a cigarette, a cigar or a cigarillo.

According to an embodiment, the filter obtained according to the various embodiments is used for filtering and retaining, reducing the concentration, the harmful substances present in the aerosol generated by the heating of an aromatic or pharmaceutical mixture. According to this embodiment, the filter is applied in a product for generating aerosols selected from: an electronic cigarette or an HNB cigarette.

The invention relates to a smoking product which comprises, at one end, a filter or an oxidised and cross-linked nanocellulose-based filter element obtained with the process described here in its various embodiments, and a mixture of tobacco. Preferably, the smoking product is a cigarette comprising a filter according to the invention at one end, a cigar comprising a filter according to the invention at one end, a cigarillo comprising a filter according to the invention at one end.

The invention relates to a product for generating aerosols which comprises, at one end, a filter or an oxidised and cross-linked nanocellulose-based filter element obtained with the process described here in its various embodiments, and an aromatic or pharmaceutical mixture.

The filter may have any shape designed to be incorporated in a smoking or aerosol generating product. Preferably, the shape of the filter is an elongate cylindrical shape. According to the embodiment in which the filter is obtained in the form of powder, the desired shape is obtained by agglomeration of the powder in a suitable mould having the desired shape, for example cylindrical.

The oxidised and cross-linked cellulose-based filter is in the form of porous aerogel.

According to an embodiment, the invention relates to the use a composite material based on oxidised and cross-linked cellulose obtained/obtainable with the process according to the steps a) to e) described above, according to the various embodiments, for preparing a filter for a smoking or aerosol product. In this case, the composite material based on oxidised and crosslinked cellulose obtained/obtainable with the process according to the steps a) to e) , as described above in the various embodiments, is shaped in an appropriate shape, for example cylindrical, to provide a filter which can be used inside a smoking or aerosol product.

The filter according to the invention has a high degree of oxidation of the starting nanocellulose of between 0.8 mmol/g and 2 mmol/g, understood as millimoles of carboxyl groups per gram of nanocellulose, preferably between 1 mmol/g and 1.7 mmol/g, from which the degree of cross-linking derives. In effect, the greater the quantity of -OH cellulose groups which are oxidised to -COOH groups, the greater the degree of cross-linking (and vice versa) since there is a greater number of carboxyl groups available for the subsequent reaction with the cross-linking agent. The possibility of varying the degree of oxidation, and, consequently, the degree of cross-linking, allows to obtain filters with various filtering characteristics and adaptable to the various filtering requirements. Another feature of the filter according to the invention is the micro and nano-porosity. The first is determined by the freezing temperature of the hydrogel, between -20°C and -210°C. Varying the freezing temperature varies the dimensions of the ice crystals which are formed and consequently of the pores which are created in the final aerogel following the lyophilization. It has been determined that by operating in the indicated freezing temperature intervals, it is possible to obtain an aerogel with a microporosity structure which is particularly suitable for retaining the harmful substances present in the smoke generated by the combustion of the tobacco. The nano-porosity is determined by the degree of cross-linking of the filtering system.

The filter according to the invention has a good level of biodegradability, due to the use of substances of natural origin such as cellulose and organic cross-linking agents such as polyimines and polyamines, preferably selected from among the biodegradable ones which contribute to imparting biodegradability to the filter. This feature makes it possible to overcome the problem of disposal of the so-called “cigarette butts” which are often thrown into the environment and at present require long times for their degradation. According to an embodiment, the invention also relates to a method for filtering the smoke generated by the combustion of the tobacco or for filtering an aerosol which comprises: a) providing a smoking product or a product which generates aerosol comprising a filter based on oxidised and cross-linked nanocellulose and a tobacco-based mixture or an aromatic or pharmaceutical mixture; b) generating the smoke by burning the tobacco or generating an aerosol by heating an aromatic or pharmaceutical mixture; c) inhaling the smoke or the aerosol through the filter.

The smokers’ product is chosen from among: a cigarette, a cigar or a cigarillo. The aerosol product is chosen from between an electronic cigarette and an HNB cigarette.

The oxidised and cross-linked cellulose-based filter is obtained with the process described above according to steps a) to e) and all the embodiments described. In particular, the filter is obtained according to steps a) to e) using at least one cross-linking agent selected from among: branched polyethylenimine, chitosan, an amino derivative of polyethylene glycol (PEG), such as 4-arm PEG-Amine and 8-arm PEG-Amine, and a Jeffamine, such as Jeffamine EG-2003 and combinations thereof, preferably together with a carboxylic acid, preferably citric acid.

According to an embodiment, the filter is obtained with the process according to invention wherein at least one cross-linking agent is branched polyethylenimine, preferably used with a polycarboxylic acid, preferably citric acid.

According to an embodiment, the filter is obtained with the process according to the invention wherein at least one cross-linking agent is chitosan, preferably used with a carboxylic acid, preferably citric acid. According to an embodiment, the filter is obtained with the process according to the invention wherein the at least a cross-linking agent is selected between: chitosan, an amino derivative of polyethylene glycol (PEG), such as 4-arm PEG-Amine and 8-arm PEG-Amine, and a Jeffamine, such as Jeffamine EG-2003 and combinations thereof, preferably used together with a carboxylic acid, preferably citric acid.

The method reduces the concentration of the harmful substances contained in the smoke after passage of the smoke through the filter, since the substances are at least partially retained inside the pores of the filter.

EXAMPLES

Example 1

The cellulose obtained from sources of hydrophilic cotton was TEMPO- oxidised reaching a degree of oxidation of 1 .5 mmol of COOH per gram of fibers. 1 g of these fibers were dispersed uniformly in 34 mL of deionised water thus obtaining a dispersion of 3% w/w. To this dispersion, 2 equivalents of branched polyethylenimine and 18% of citric acid with respect to the mmol of amino groups present per gram of polyamine are added. There is the formation of a hydrogel which is left in agitation for about 5 minutes keeping the dispersion completely homogeneous. The hydrogel is placed in steel moulds containing cylindrical holes with diameters variable from 7.8, 8.0, 8.2 to 8.4 mm and height of 10 mm. The hydrogel contained in the mould is then frozen at -20°C for 18 hours and then lyophilized to allow the sublimation of the ice and the formation of the aerogel. The final step is represented by a baking, inserting the mould in a stove, and carrying out a thermal ramp from 60°C to 100°C for 2 hours until maintaining the maximum temperature for 18 hours. This thermal reaction is important for the formation of the amide bond between the nanocellulose fibers and the cross-linking agent. The SEM analysis reported in Figure 1 shows the nanoporous morphology of the resulting material.

Example 2 The procedure is performed as in example 1 , varying the freezing temperature of the hydrogel from -20°C to -70°C. This reduces the freezing kinetics, thus reducing the size of the ice crystals formed and, therefore, the size of the pores resulting from the sublimation.

Example 3

The procedure is performed as in example 1 , using TEMPO-Oxidised Nanocellulose fibres (TOCNFs) with a degree of oxidation of 1.19 and deriving from sources of linters.

Example 4

This was carried out as in example 3 but by freezing the hydrogel at -70°C instead of -20°C.

Example 5

1 g of chitosan (with low molecular weight and with a degree of deacetylation > 85%) was dissolved in 40 mL of a 1 % v/v acetic acid solution in water. To this solution, TEMPO-Oxidised Nanocellulose deriving from spruce has been added, with a degree of oxidation of 1 .5 mmol of COOH per gram of fibres. The mixture was left at 40°C under agitation for 20 hours. At this point, the mixture was distributed inside the mould and was then frozen at - 20°C; this was followed by lyophilization for 24 hours and by baking in a stove as shown in example 1 . The SEM images shown in Figure 2 show the nanoporous morphology of the resulting material.

Example 6

The procedure was performed as in example 3, in this case varying the nature of the cross-linking agent.

TOCNFs derived from sources of linters and with a 1.19 oxidation degree were used as matrix, and an amino derivative of polyethylene glycol (PEG), in particular 4-arm PEG-Amine, was used as cross-linking agent. The stoichiometric ratio TOCNFs : 4-arm PEG-Amine was 1 :2. The addition of citric acid does not occur in this case. Figure 3 shows the nanoporous morphology of the resulting material.

Example 7

This was carried out as in Example 6 but using a stoichiometric ratio TOCNFs : 4-arm PEG-Amine of 1 :1. Also in this case, citric acid was not added to the formulation.

Figure 4 shows the nanoporous morphology of the resulting material.

Example 8

This was carried out as in example 7 but with the addition of citric acid at 18% with respect to the mmol of amino groups present for each gram of cross-linking agent (4-arm PEG-Amine) during the formation of the hydrogel. Figure 5 shows the nanoporous morphology of the resulting material.

Example 9

This was carried out as in example 5 using the 4-arm PEG-Amine crosslinking agent in a 2:1 stoichiometric ratio with respect to the TEMPO- oxidised nanocellulose fibers.

Example 10

This was carried out as in example 9 but adding citric acid at 18% with respect to the mmol of amino groups present for each gram of 4-arm PEG- Amine.

Example 11

This was carried out as in example 3, again varying the nature of the crosslinking agent; in this case another amino derivative of the polyethylene glycol, (8-arm PEG-Amine) has been added maintaining a stoichiometric ratio of 0.25 equivalent with respect to the TOCNFs. Figure 6 shows the nanoporous morphology of the resulting material. Example 12

This was carried out as in example 1 1 , using an 8-arm PEG-Amine : TOCNFs stoichiometric ratio of 0.5 : 1. Also in this case, there was no addition of citric acid. Figure 7 shows the nanoporous morphology of the resulting material.

Example 13

This was carried out as in example 1 1 but adding 18% of citric acid to the formulation with respect to the mmol amino groups present for each gram of 8-arm PEG-Amine.

Example 14

This was carried out as in example 1 but using as a cross-linking agent a polyetheramine (Jeffamine 2003) with a stoichiometric ratio of 0.5 equivalent to the TEMPO-oxidised nanocellulose. The citric acid was not used for this formulation. Figure 7 shows the nanoporous morphology of the resulting material.

Table 1 summarises the examples described.

eq* = compared to the quantity of TOCNFs

Notes:

TOCNFs = “TEMPO-Oxidized Cellulose Nanofibers”.

In all the examples, the initial dispersion of TOCNFs in water is 3% w/w (1 gram of TOCNFs in 34 mL of water), except for example 3. In example 3, the % w/w of TOCNFs is determined on the basis of the amount of acid solution (1% v/v acetic acid) in which the chitosan is dissolved. Therefore, if 1 gram of chitosan is dissolved in 40 mL of acid solution, using a mass:mass ratio of 1 :1 chitosamTOCNFs, we would have 1 gram of TOCNFs in 40 mL of solution, so a concentration of 2.5% w/w.

Example 15 - Filtration Test

A filtration test was performed by comparing a cigarette provided with commercial cellulose acetate filter with dimensions of 7 to 31 mm in length and 4.5 to 9 mm in diameter with the closed aeration holes and a cigarette provided with a filter according to the invention. In particular 7 filters were tested, made from branched polyethylenimine, with 8-arm PEG-Amine and 4-arm PEG-Amine.

The filtration test was performed as follows:

A smoking machine of the brand Cerulean was used, it was provided with channels, holders to house the cigarette and 44 mm diameter filter pads on which the particulate is collected. The pad is weighed before the filtration test, 5 samples for each type of filter are then smoked and subsequently, the pad is weighed. This evaluates the weight of the particulate deposited on the pad. The parameters selected for the filtration test are as follows: Number of puffs: 8

Duration of puff: 2 seconds

Puff Volume: 35 ml

Time between puffs: 30 seconds.

The results obtained refer to 7 examples reported according to the invention and show a better particulate filtration capacity compared with the commercial cellulose acetate filter. In particular, from the test performed on the filter described in example 3 with lengths of 10 and 20 mm, the weight of the particulate deposited on the pad is of 28.6 and 22.2 mg respectively. The filters with a length of 10 mm were made up of the materials described in examples 9 and 10, and they provided particulate values of 23.2 mg and 26.8 mg, respectively. The filters with lengths of 10 and 20 mm made up of the material described in example 12, revealed quantities of particulate equal to 23 and 1 1.6 mg, respectively. The filters with lengths of 10 mm made from the materials described in examples 6, 7, and 1 1 revealed particulate quantities of 36.2, 30.6 and 39.8 mg, respectively. The results were compared to the particulate quantity values obtained from tests performed on the commercial cellulose acetate filter with lengths of 10 and 27 mm, equal to 41 .8 and 22.4 mg respectively.

Claims

1. A smoking or aerosol generating product comprising a filter, characterized in that the filter comprises or is constituted by oxidized nanocellulose cross-linked using at least one of the following cross-linking agents: a linear or branched polyamine or polyimine.

2. The smoking or aerosol generating product according to claim 1 , wherein the at least one cross-linking agent is one of the following: branched polyethylenimine, chitosan, an amine derivative of polyethylene glycol (PEG), preferably chosen from one of the following: 4-arm amine PEG and 8-arm amine PEG, and a jeffamine, preferably Jeffamine EG-2003 and combinations thereof.

3. The smoking or aerosol generating product according to claim 1 or

2, wherein a polycarboxylic acid, preferably citric acid, is used as an additional cross-linking agent, preferably in a quantity of between 10% and 30% in mmol compared to the primary amine groups of the cross-linking agent, more preferably between 15% and 20%.

4. The smoking product according to any one of claims 1 to 3, wherein the product is one of the following: a cigarette, a cigar or a cigarillo.

5. The aerosol generating product according to any one of claims 1 to

3, wherein the product is one of the following: an electronic cigarette or an HNB cigarette.

6. The smoking or aerosol generating product according to any one of claims 1 to 5, wherein the oxidized nanocellulose is obtained by treating the cellulose with one of the following oxidizing agents: HCIO, HCIO2 and salts thereof in the presence of a nitroxy radical catalyst, and one or more alkaline or earth-alkaline salts of HBr.

7. The smoking or aerosol generating product according to any one of claims 1 to 6, wherein the filter is in the form of a porous aerogel.

8. The smoking or aerosol generating product according to any one of claims 1 to 7, wherein the filter is obtained through a process comprising the following steps: a) oxidizing cellulose by treating it with one of the following oxidizing agents: HCIO, HCIO2 and salts thereof in the presence of a nitroxyl radical catalyst, and one or more alkaline or earth-alkaline salts of HBr; b) dispersing the oxidized cellulose in a basic solution and subjecting it to mechanical action, preferably by sonication, or homogenization until obtaining a homogeneous dispersion of cellulose nanofibres; c) adding at least one cross-linking agent selected from a linear or branched polyamine or polyimine to obtain a hydrogel; d) freezing the hydrogel at a temperature of between -20 °C and -210 °C followed by lyophilization to obtain a porous aerogel; e) heating the porous aerogel to a temperature of between 50°C and 1 10°C so as to cause cross-linking of the oxidized cellulose.

9. The smoking or aerosol generating product according to claim 8, wherein at the end of step a), the oxidized cellulose has a degree of oxidation of between 0.8 mmol/g and 2 mmol/g, understood as millimoles of carboxyl groups per gramme of nanocellulose, preferably between 1 mmol/g and 1 .7 mmol/g.

10. The smoking or aerosol generating product according to claim 8 or 9, wherein after step b), the dispersion of cellulose nanofibres is acidified and then subjected to filtration to remove the excess water (step b1)).

1 1 . The smoking or aerosol generating product according to any one of claims 8 to 10, wherein before freezing and lyophilization, the hydrogel is placed in a mould to give it a shape suitable for use as a filter for a smoking product, preferably a cylindrical shape.

12. A filter for a smoking or aerosol generating product, preferably for a cigarette, a cigar, a cigarillo, an electronic cigarette or an HNB cigarette, characterized in that it comprises or is constituted by oxidized cellulose cross-linked using at least one of the following cross-linking agents: a linear or branched polyamine or polyimine.

13. A use of oxidized nanocellulose cross-linked using at least one of the following cross-linking agents: a linear polyamine or polyimine to prepare a filter for a smoking or aerosol generating product.

14. The use of the filter according to claim 13 to filter and retain a plurality of harmful substances contained in the smoke generated by burning tobacco or contained in an aerosol generated by an aromatic or pharmaceutical mixture.

15. A method for filtering the smoke generated by burning tobacco or to filter an aerosol generated by an aromatic or pharmaceutical mixture, comprising the following steps: a) providing a smoking or aerosol generating product comprising a filter according to any one of claims 1 to 12; b) generating the smoke by burning the tobacco or generating an aerosol by heating an aromatic or pharmaceutical mixture; c) inhaling the smoke or the aerosol through the filter.