The present invention relates to a method for producing a plant-based sheet. The present invention further relates to an apparatus configured for producing a plant-based sheet.

Plant-based materials such as tobacco are natural products and often show great differences in their properties between different batches. Mixing these plant-based materials with sheet-forming agents, such as cellulose and water is used in order to produce a slurry for producing sheets of the plant-based materials. This mixing process is often very difficult and time-consuming due to the changing nature between different batches of the plant-based materials. Drying the slurry is often very energy consuming and time-consuming. Furthermore, prolonged handling of the plant-based materials in powder form may generate a great wear of the machinery due to the abrasive nature of the powder particles.

It would be desirable to provide a method for producing a plant-based sheet, which provides easy-to-handle solutions. Furthermore, it would be desirable to provide a method for producing a plant-based sheet, which allows an easy and quick drying of the slurry in order to produce the plant-based sheet. Furthermore, it would be desirable to provide a method for producing a plant-based sheet, which is less energy consuming.

According to an embodiment of the present invention a method for producing a plantbased material sheet is provided. The method may comprise providing a plant-based powder material and a cellulose-based sheet-forming agent. The method may furthermore comprise determining a moisture content of the plant-based material. The method may comprise mixing the plant-based powder material, the cellulose-based sheet-forming agent and an amount of water to form a slurry. The method may furthermore comprise drying the slurry to form the plant-based sheet. The amount of water added for slurry formation may be calculated based on the determined moisture content of the plant-based powder material.

Another embodiment of the present invention provides a method for producing a plantbased material sheet. The method comprises providing a plant-based powder material and a cellulose-based sheet-forming agent. The method also comprises determining a moisture content of the plant-based material. The method includes mixing the plant-based powder material, the cellulose-based sheet-forming agent and an amount of water to form a slurry. The method furthermore comprises drying the slurry to form the plant-based sheet. The amount of water added for slurry formation is calculated based on the determined moisture content of the plant-based powder material.

Such a method may provide are more easy way to dry the slurry for forming the plantbased sheet. This may be due to the more uniform water content of the slurry taking the moisture content of the plant-based powder material into consideration. This method may produce a slurry with more uniform water content among different batches of plant-based powder material with different moisture contents. This may ease the handling of the slurry during production of the plant-based material sheet. This may reduce the handling time in the machinery during drying the slurry. This may reduce the wear of the machinery.

The moisture content of the plant-based powder material may in particular be a water content of the plant-based powder material. This moisture content may vary between different batches of the plant-based powder material. This different water content may impede a more uniform handling of the plant-based powder material during the manufacturing of the plantbased material sheet. The method of the present invention may allow to take these different water contents of different batches into consideration when producing a slurry with a more uniform water content.

The slurry may have a predestined target water content range. The amount of water added for slurry formation maybe calculated so that the slurry reaches a water content within the predestined target water content range.

This may allow different batches of the slurry to be within the same predestined target water content range despite having different moisture contents of the plant-based material. This may facilitate a more uniform handling and drying of the slurry to form the plant-based sheet.

The predestined target water content range of the slurry may be between 55 weight percent to 85 weight percent of water based on the total weight of the slurry. Preferably, the target water content range of the slurry may be between 60 weight percent to 80 weight percent water based on the total weight of the slurry.

Such a predestined target water content range may be easy to achieve taking the moisture content of the plant-based powder material into consideration. Such a predestined target water content range of the slurry may allow for a more uniform and easy drying of the slurry to form the plant-based sheet.

A predestined target water content between 55 weight percent to 85 weight percent may reduce the appearance of defects in the plant-based sheet which may occur if the water content is below the lower limit of 55 weight percent. Similarly, a water content outside of this predestined target water content may result in a reduced tensile strength of the plant-based sheet and may complicate handling of the plant-based sheet.

A plant material moisture detector may be employed for determining the moisture content of the plant-based material.

The plant-based powder material may be dispersed on a conveyor belt. The radiation emitted from the plant material moisture detector may be positioned on one side of the conveyor belt and a radiation receiver of the plant material moisture detector may be positioned on an opposing side of the conveyor belt. This may allow radiation of the plant material moisture detector to pass through the plant-based powder material.

This may allow a transport of the plant-based powder material on a conveyor belt while simultaneously determining the moisture content of the plant-based material.

The plant material moisture detector may be one of a microwave detector or an infrared detector. Preferably the plant material moisture detector may be a microwave detector.

The microwave detector may comprise an emitting antenna and a receiving antenna. The emitting antenna may emit microwave radiation and the receiving antenna may receive microwave radiation which was sent from the emitting antenna through the plant-based powder. The plant-based powder material may be arranged between the emitting antenna and the receiving antenna of the microwave detector and may be transported on a conveyor belt.

This may allow the transportation of the plant-based powder material for slurry formation. This may allow an easy determination of the moisture content of the plant-based powder material while the plant-based powder material is transported on the conveyor belt.

The microwave detector may be the microwave detector MicroPolar LB 567/LB 568 Microwave Moisture Analyser marketed by Berthold Technologies GmbH & Co. KG.

The plant-based powder material may comprise one or both of tobacco powder or hemp powder. Preferably, the plant-based powder material may comprise tobacco powder. The plant-based powder material may be tobacco powder and the material sheet may be a sheet of an aerosol-forming substrate.

As used herein, the term ‘aerosol-forming substrate’ relates to a substrate capable of releasing one or more volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. An aerosol-forming substrate may conveniently be part of an aerosol-generating article or smoking article.

The aerosol-forming substrate may comprise a solid aerosol-forming substrate. The aerosol-forming substrate may comprise both solid and liquid components. The aerosolforming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds which are released from the substrate upon heating. The aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may comprise an aerosol former that facilitates the formation of a dense and stable aerosol. Examples of suitable aerosol formers are glycerine and propylene glycol.

The aerosol-forming substrate may be a solid aerosol-forming substrate, the solid aerosol-forming substrate may comprise, in some embodiments, one or more of: powder, granules, pellets, shreds, spaghettis, strips or sheets containing one or more of: herb leaf, tobacco leaf, fragments of tobacco ribs, reconstituted tobacco, homogenised tobacco, extruded tobacco, cast leaf tobacco and expanded tobacco. The solid aerosol-forming substrate may be in loose form, or may be provided in a suitable container or cartridge. Optionally, the solid aerosol-forming substrate may contain additional tobacco or non-tobacco volatile flavour compounds, to be released upon heating of the substrate. The solid aerosolforming substrate may also contain capsules that, for example, include the additional tobacco or non-tobacco volatile flavour compounds and such capsules may melt during heating of the solid aerosol-forming substrate.

As used herein, homogenised tobacco refers to material formed by agglomerating particulate tobacco. Homogenised tobacco may be in the form of a sheet. Homogenised tobacco material may have an aerosol-former content of greater than 5% on a dry weight basis. Homogenised tobacco material may alternatively have an aerosol former content of between 5% and 30% by weight on a dry weight basis. Sheets of homogenised tobacco material may be formed by agglomerating particulate tobacco obtained by grinding or otherwise combining one or both of tobacco leaf lamina and tobacco leaf stems. Alternatively, or in addition, sheets of homogenised tobacco material may comprise one or more of tobacco dust, tobacco fines and other particulate tobacco by-products formed during, for example, the treating, handling and shipping of tobacco. Sheets of homogenised tobacco material may comprise one or more intrinsic binders, that is tobacco endogenous binders, one or more extrinsic binders, that is tobacco exogenous binders, or a combination thereof to help agglomerate the particulate tobacco; alternatively, or in addition, sheets of homogenised tobacco material may comprise other additives including, but not limited to, tobacco and non-tobacco fibres, aerosol-formers, humectants, plasticisers, flavourants, fillers, aqueous and non-aqueous solvents and combinations thereof.

In a particularly preferred embodiment, the aerosol-forming substrate comprises a gathered crimped sheet of homogenised tobacco material. As used herein, the term ‘crimped sheet’ denotes a sheet having a plurality of substantially parallel ridges or corrugations. Preferably, when the aerosol-generating article has been assembled, the substantially parallel ridges or corrugations extend along or parallel to the longitudinal axis of the aerosol-generating article. This advantageously facilitates gathering of the crimped sheet of homogenised tobacco material to form the aerosol-forming substrate. However, it will be appreciated that crimped sheets of homogenised tobacco material for inclusion in the aerosol-generating article may alternatively or in addition have a plurality of substantially parallel ridges or corrugations that are disposed at an acute or obtuse angle to the longitudinal axis of the aerosol-generating article when the aerosol-generating article has been assembled. In certain embodiments, the aerosol-forming substrate may comprise a gathered sheet of homogenised tobacco material that is substantially evenly textured over substantially its entire surface. For example, the aerosol-forming substrate may comprise a gathered crimped sheet of homogenised tobacco material comprising a plurality of substantially parallel ridges or corrugations that are substantially evenly spaced-apart across the width of the sheet.

The aerosol-forming substrate may be used in an aerosol-generating article. The aerosol-generating article may be used together with an aerosol-generating device. The aerosol-generating device may comprise a cavity configured for receiving the aerosolgenerating article. The aerosol-generating device may comprise a heating element configured for heating the aerosol-generating article received in the cavity. The aerosol-generating device of the present invention may be configured to heat the aerosol-forming substrate to a temperature below a combustion temperature of the aerosol-forming substrate, but at or above a temperature at which one or more volatile compounds of the aerosol-forming substrate are released to form an inhalable aerosol.

The plant-based powder material, preferably the tobacco powder may have an average particle size of between 20 micrometres to 200 micrometres, preferably an average particle size of between 50 micrometres to 100 micrometres. The average particle size may be determined by laser scattering. The average particle size of the plant-based powder material may be adjusted to a predestined average particle size range by grinding in a mill. The average particle size of the plant-based powder material may be adjusted before forming the slurry.

This may ease the formation of the slurry. This may provide a more homogeneous slurry.

The average particle size of the plant-based powder material may be determined before determining the moisture content of the plant-based material. The average particle size of the plant-based powder material may affect the moisture content of the plant-based powder material. Therefore, the average particle size of the plant-based powder material may be adjusted to a predestined average particle size range of between 20 micrometres to 200 micrometres before determining the moisture content.

A particle size sensor may be employed when determining the average particle size of the plant-based powder material. The particle size sensor may be a laser scattering particle size distribution analyzer, such as Horiba LA-950.

A water flow rate controller may be employed. The flow rate controller may control the amount of water added for slurry formation based on the determined moisture content of the plant-based powder material.

This may provide an easy way of controlling the amount of water added for slurry formation.

An open control loop system may be employed. The open control loop system may adjust a pump speed of the flow rate controller based on the determined moisture content of the plant-based powder material. This may allow the flow rate controller to control the amount of water added to form the slurry.

The cellulose-based sheet-forming agent may comprise cellulose fibers. Preferably a water/cellulose fiber pulp is prepared and the pulp is subsequently mixed with the plant-based powder material. The water/cellulose pulp may comprise cellulose fibers having a mean length of between 0.2 millimeters and 4 millimeters. Preferably the mean length of the cellulose fibers may be between 1 millimeter and about 3 millimeters. Preferably, the cellulose fibers are soft wood fibers.

The water-cellulose fiber pulp may have a concentration of between 3 weight percent to 5 weight percent of cellulose fibers of the total weight of the pulp before being added to the slurry. The total amount of cellulose fibers in the slurry after mixing of the pulp with the water and the plant-based powder material is between 1 weight percent to 3 weight percent, preferably between 1 .2 weight percent to 2.4 weight percent of dry weight of the slurry.

The slurry may be dried to form the plant-based sheet, wherein the plant-based sheet has a moisture content of between 7 percent to 15 percent of dry weight of the sheet. Preferably, the plant-based sheet may be dried to have a moisture content of between 8 percent to 12 percent of the dry weight of sheet.

The slurry may be prepared in a slurry tank. Subsequently, the slurry may be transferred to a casting box. This may allow the slurry to be casted by a casting knife on the movable conveyor belt. The conveyor belt may be made of a thermally conductive material, in particular steel. After drying a continuous plant-based material sheet of a thickness of between 500 micrometers to 700 micrometers may have been formed. If the plant-based powder material comprises tobacco powder, then the plant-based material sheet can be a continuous sheet of tobacco cast leaf. These tobacco cast leaf sheets can be wound up into bobbins and can be further processed in order to produce aerosol-generating articles including the tobacco cast leaf sheets as part of the aerosol-forming substrate.

Instead of forming tobacco cast leaf sheets, a sheet of gel-like material including tobacco may be formed as well.

Drying may be done by subjecting the slurry arranged on the conveyor belt to drying air in a drying device. Additionally, steam may be provided from below the conveyor belt for drying the plant-based material sheet in a more uniform way. The slurry may be transported on the conveyor belt through the drying device. The temperature of the drying air may be between 90 degrees Celsius and 140 degrees Celsius. In an embodiment, the drying device may comprise different drying segments. The temperature of the drying air, the flow rate of the drying air and the flow rate distribution of the drying air may be independently controlled in the different drying segments of the drying device. The flow rate of the drying air in the drying device may be between 80 kilogram/hour and 300 kilogram/hour. The length of the drying device may be a few hundred meters.

This may allow for a prolonged drying process of the slurry while passing on the conveyor belt through the drying device. This may allow a slow and controlled decrease of the moisture resulting in the plant-based sheet.

This may allow to reduce the moisture of the slurry in a controlled way without subjecting the plant-based material sheet forming from the slurry to excessive temperatures or moisture differences.

One or both of a thickening agent and an aerosol-former may be added to form the slurry. The thickening agent may comprise guar. An aerosol-former is any suitable known compound or mixture of compounds that, in use, facilitates formation of a dense and stable aerosol and that is substantially resistant to thermal degradation at the temperature of operation of the system. Suitable aerosol-formers are well known in the art and include, but are not limited to: polyhydric alcohols, such as triethylene glycol, 1 ,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Aerosol formers may be polyhydric alcohols or mixtures thereof, such as triethylene glycol, 1 ,3-butanediol and glycerine. The aerosol-former may be propylene glycol. The aerosol former may comprise both glycerine and propylene glycol. Preferably, the aerosolformer may comprise one or more of triethylene glycol, 1 , 3-butandiol and glycerin.

An exemplary slurry composition may include between 70 weight percent to 78 weight percent of water, between 17 weight percent to 22 weight percent of plant-based powder, in particular tobacco powder. This exemplary slurry composition may furthermore comprise between 3 weight percent to 6 weight percent of glycerin as an aerosol-former. Cellulose fibers may be added in an amount of 0.5 weight percent to 4 weight percent. The optional thickening agent may be present in an amount of 0 weight percent to 1 weight percent. All the weight percent ranges indicated are based on the total weight of the exemplary slurry composition.

The slurry may have a predestined target water content range. A sum of the determined moisture content of the plant-based powder material and the amount of water added for slurry formation may result in a water content of the slurry being within the target water content range.

Another embodiment of the method of the invention may also include a method step of determining a moisture content of the cellulose-based sheet-forming agent. In this case, a sum of the determined moisture content of the plant-based powder material, the amount of water added for slurry formation and the moisture content of the cellulose-based sheet-forming agents may result in a water content of the slurry being within the target water content range. This embodiment of the method of the invention may take the moisture content not just of the plant-based powder material but also the moisture content of the cellulose-based sheetforming agents into consideration when determining the overall amount of water to be added for slurry formation. This may provide a method which is able to more accurately adjust the water to be added to be within the predestined target water content range.

In another embodiment of the method of the invention a moisture content of one or both of the thickening agent and the aerosol-former may be determined. In this case a sum of the determined moisture content of the plant-based powder material, the amount of water added for slurry formation, the moisture content of the cellulose-based sheet-forming agent and one or both of the moisture content of the thickening agent and the aerosol-former may result in a water content of the final slurry being within the target water content range.

In this embodiment of the method of the invention the moisture content of the aerosolformer, the thickening agent and the cellulose-based sheet-forming agent also may be determined and may be taken into consideration together with the moisture content of the plant-based powder material when calculating the amount of water to be added for slurry formation.

This may provide a method to more accurately adjust the final water content of the slurry to be formed.

The moisture content of the cellulose-based sheet-forming agent, of the aerosol-former end of the thickening agent may be determined in the same way as the moisture content of the plant-based powder material. In particular, a cellulose moisture detector, such as a microwave detector or an infrared detector may be employed for determining a moisture content of the cellulose-based sheet-forming agent.

In particular, a cellulose fiber feeding and preparation line may be employed for preparing the above-mentioned water/cellulose pulp. The cellulose fiber feeding and preparation line may comprise a cellulose conveyor belt for transporting raw cellulose fiber material, such as boards, sheets or fluffed fibers to a pulper for preparing the water/cellulose pulp. A cellulose moisture detector may be present at the cellulose conveyor belt. The cellulose moisture detector may be configured to determine a moisture content of the raw cellulose fiber material. The cellulose fiber feeding and preparation line may furthermore comprise a water line configured for introducing water into the pulper. The flow rate of water through the water line may be controlled by a cellulose flow rate controller. The cellulose flow rate controller may be configured to receive data about the moisture content of the raw cellulose fiber material from the cellulose moisture detector. The cellulose flow rate controller may adjust the speed of a pump taking the moisture content of the raw cellulose fiber material and the moisture content of the plant-based powder material into consideration in order to prepare the water/cellulose pulp. This water/cellulose pulp may then be mixed with the plant-based powder material to prepare the final slurry. Therefore, the water content of the water/cellulose pulp will also affect the final water content of the slurry to be prepared.

The step of mixing of water and cellulose fibers may last between 20 minutes and 60 minutes. The temperature in the pulper may be between 15 degrees Celsius and 40 degrees C Celsius. A storage time for the water/cellulose pulp before being mixed with the plant-based powder material may be between 0.1 days to 7 days.

Preferably, the water/cellulose pulp may be mixed with additional water before being mixed with the plant-based powder material. This mixing step of the water/cellulose pulp with additional water may last between about 120 minutes and 180 minutes. The temperature during the mixing may be between 15 degrees Celsius and 40 degrees Celsius, more preferably 18 degrees Celsius and 25 degrees Celsius.

The weight percent of water, in particular the final water content range of a slurry comprising the plant-based powder material, the cellulose-based sheet-forming agent, the thickening agent and the aerosol-former may be calculated as follows:

Weight percent of water in slurry = [water quantity added to slurry + water content of cellulose + water content of the aerosol-former + water content of thickening agent + water content of plant-based powder material]/[(thickening agent quantity + water content of thickening agent) + (aerosol-former quantity + water content of the aerosol-former) + (quantity of the plant-based material + water content of plant-based material) + water quantity added to slurry].

Another embodiment of the invention provides an apparatus configured for producing a plant-based material sheet. The apparatus may comprise a mixing tank including a stirrer. The mixing tank may be configured for mixing a plant-based powder material and a cellulose- based sheet-forming agent for forming a slurry. The apparatus may comprise a plant material moisture detector configured for determining a moisture content of the plant-based powder material. The apparatus also may comprise a water flow rate controller. The water flow rate controller may be configured for controlling the flow rate of water to the mixing tank, the water flow rate controller may be connected to a water pipe. The water pipe may be configured to transport water to the slurry container for forming the slurry. The water flow rate controller may be further configured for providing an amount of water to the mixing tank for slurry formation. The amount of water may be calculated based on the determined moisture content of the plantbased powder material. The apparatus may comprise a drying device for drying the slurry performed plant-based sheet.

A further embodiment of the invention provides an apparatus configured for producing a plant-based material sheet. The apparatus comprises a mixing tank including a stirrer. The mixing tank is configured for mixing a plant-based powder material and the cellulose-based sheet-forming agents for forming a slurry. The apparatus furthermore comprises a plant material moisture detector. The plant material moisture detector is configured for determining a moisture content of the plant-based powder material. The apparatus also comprises a water flow rate controller. The water flow rate controller is configured for providing water to the mixing tank. The water flow rate controller is further configured for providing an amount of water to the mixing tank for slurry formation, wherein the amount of water is calculated based on the determined moisture content of the plant-based powder material. The apparatus also comprises a drying device for drying the slurry to form the plant-based sheet.

Such an apparatus may be configured to carry out the method for forming the plantbased material sheet as discussed herein. This apparatus may be easily able to control the amount of water added for slurry formation via the water flow rate controller.

The apparatus may furthermore comprise an open loop control system. The open loop control system may be configured for adjusting a pump speed of the flow rate controller based on the determined moisture content of the plant-based powder material.

The apparatus may comprise a data processing unit. The data processing unit may comprise a module for communicating with the plant material moisture detector. The data processing unit may comprise a module for a calculating the amount of water to be added for slurry formation based on the determined moisture content of the plant-based material. The data processing unit may comprise at least parts of the control system.

This may ease the addition of the suitable amount of the water for slurry formation based on the determined moisture content of the plant-based powder material.

The slurry may have a predestined target water content range. The open loop control system may be configured for providing such an amount of water to the mixing tank, so that a sum of the determined moisture content of the plant-based powder material and the amount of water added for slurry formation results in a water content of the slurry being within the target water range.

Such an apparatus may easily be able to take the determined moisture content of the plant-based powder material into consideration when calculating the amount of water to be added for slurry formation, so that the water content of the slurry is within the target water content range.

The apparatus also may comprise a cellulose moisture detector configured for determining a moisture content of the cellulose-based sheet-forming agent. The open loop control system of the apparatus may then be configured for providing such an amount of water to the mixing tank, so that a sum of the determined moisture content of the plant-based powder material, the determined moisture content of the cellulose-based sheet-forming agent and the amount of water added for slurry formation results in a water content of the slurry being within the target water content range.

This apparatus may additionally also take the moisture content of the cellulose-based sheet-forming agent into consideration when calculating the amount of water to be added for slurry formation.

The apparatus also may comprise one or both of a thickening agent moisture detector and aerosol-former moisture detector configured for determining a moisture content of one or both of a thickening agent and an aerosol-former.

The open loop control system of the apparatus may then be configured for providing such an amount of water to the mixing tank so that a sum of the determined moisture content of the plant-based powder material, the determined moisture content of the cellulose-based sheet-forming agent, one or both of the moisture content of the thickening agent and the aerosol-former, and the amount of water added for slurry formation results in a water content of the slurry being within the target water content range.

Such an apparatus may be configured to take into consideration the moisture content of all major components of the slurry when calculating the amount of water to be added for slurry formation.

Below, there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

Example E1 : Method for producing a plant-based material sheet comprising:

- providing a plant-based powder material and a cellulose-based sheet-forming agent,

- determining a moisture content of the plant-based material,

- mixing the plant-based powder material, the cellulose-based sheet-forming agent and an amount of water to form a slurry,

- drying the slurry to form the plant-based sheet,

- wherein the amount of water added for slurry formation is calculated based on the determined moisture content of the plant-based powder material.

Example E2: Method according to example E1 , wherein the slurry has a predestined target water content range and wherein the amount of water added for slurry formation is calculated so that the slurry reaches a water content within the predestined target water content range.

Example E3: Method according to any of the preceding examples, wherein a plant material moisture detector is employed for determining the moisture content of the plant-based material, preferably wherein the plant material moisture detector in one of a microwave detector or an infrared detector. Example E4: Method according to the preceding example, wherein the plant-based powder material is dispersed on a conveyor belt and wherein a radiation emitter of the plant material moisture detector is positioned on one side of the conveyor belt and a radiation receiver of the plant material moisture detector is positioned on an opposing side of the conveyor belt for radiation of the plant material moisture detector to pass through the plantbased powder material.

Example E5: Method according to any of the preceding examples, wherein the plantbased powder material comprises tobacco powder, preferably wherein the plant-based powder material is tobacco powder and wherein the material sheet is a sheet of an aerosol-forming substrate.

Example E6: Method according to any of the preceding examples, wherein the plantbased powder material is adjusted to a particle size of between 20 pm to 200 pm, preferably to a particle size of 50 pm to 100 pm before forming the slurry.

Example E7: Method according to any of the preceding examples, wherein a particle size of the plant-based powder material is determined, preferably wherein the particle size of the plant-based material is determined before determining the moisture content of the plantbased material.

Example E8: Method according to any of the preceding examples, wherein a water flow rate controller is employed, wherein the flow rate controller controls the amount of the water added for slurry formation based on the determined moisture content of the plant-based powder material.

Example E9: Method according to the preceding example, wherein an open loop control system is employed, the open loop control system adjusting a pump speed of the flow rate controller based on the determined moisture content of the plant-based powder material.

Example E10: Method according to any of the preceding examples, wherein the cellulose-based sheet-forming agent comprises cellulose fibers, preferably wherein a water/cellulose fibres pulp is prepared and mixed with the plant-based powder material, more preferably wherein the water/cellulose fibres pulp comprises cellulose fibres having a mean length of between 0.2 millimetres and 4 millimetres, more preferably between 1 millimetre and about 3 millimetres.

Example E11 : Method according to any of the preceding claims, wherein the predestined target water content range of the slurry is between 55 weight percent to 85 weight percent water, preferably wherein the target water content range of the slurry is between 60 weight percent to 80 weight percent water based on the total weight of the slurry.

Example E12: Method according to any of the preceding examples, wherein the slurry is dried to form the plant-based sheet, wherein the plant-based sheet has a moisture content of between 7 percent and 15 percent of dry weight of the sheet, preferably wherein the plantbased sheet has a moisture content of between 8 percent and 12 percent of dry weight of the sheet.

Example E13: Method according to any of the preceding examples, wherein one or both of a thickening agent and an aerosol-former are added to form the slurry, preferably wherein the thickening agent comprises guar and wherein the aerosol-former comprises one or more of triethylene glycol, 1 ,3-butanediol and glycerine.

Example E14: Method according to any of the preceding examples, wherein the slurry has a predestined target water content range and wherein a sum of the determined moisture content of the plant-based powder material and the amount of water added for slurry formation results in a water content of the slurry being within the target water content range.

Example E15: Method according to the preceding example, wherein a moisture content of the cellulose-based sheet-forming agent is determined and wherein a sum of the determined moisture content of the plant-based powder material, the amount of water added for slurry formation and the moisture content of the cellulose-based sheet-forming agent results in a water content of the slurry being within the target water content range.

Example E16: Method according to the preceding example, further being dependent on Example E13, wherein a moisture content of one or both of the thickening agent and the aerosol-former is determined and wherein a sum of the determined moisture content of the plant-based powder material, the amount of water added for slurry formation, the moisture content of the cellulose-based sheet-forming agent and one or both of the thickening agent and the aerosol-former results in a water content of the slurry being within the target water content range.

Example E17: Apparatus configured for producing a plant-based material sheet, the apparatus comprising

- a mixing tank including a stirrer, the mixing tank configured for mixing a plant-based powder material and a cellulose-based sheet-forming agent for forming a slurry,

- a plant material moisture detector configured for determining a moisture content of the plant-based powder material,

- a water flow rate controller configured for providing water to the mixing tank, wherein the water flow rate controller is further configured for providing an amount of water to the mixing tank for slurry formation, wherein the amount of water is calculated based on the determined moisture content of the plant-based powder material, and

- a drying device for drying the slurry to form the plant-based sheet. Example E18: Apparatus according to the preceding example, comprising a open loop control system, the open loop control system configured for adjusting a pump speed of the flow rate controller based on the determined moisture content of the plant-based powder material.

Example E19: Apparatus according to the preceding example, wherein the slurry has a predestined target water content range and wherein the open loop control system is configured for providing such an amount of water to the mixing tank, so that a sum of the determined moisture content of the plant-based powder material and the amount of water added for slurry formation results in a water content of the slurry being within the target water content range.

Features described in relation to one embodiment may equally be applied to other embodiments of the invention.

The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 shows a schematic drawing of an embodiment of an apparatus for producing a plant-based material sheet comprising a plant material moisture detector; and

Fig. 2 depicts a more detailed schematic drawing of a radiation emitter and a radiation receiver of the plant material moisture detector in relation to the plant-based powder material whose moisture content is to be determined.

In the following elements with the same functionality are marked with the same reference numerals throughout all the figures.

Fig. 1 shows a schematic drawing of one embodiment of an apparatus 30 for producing a plant-based material sheet. Preferably, this apparatus 30 is configured for producing a tobacco-based material sheet for forming an aerosol-forming substrate.

The apparatus 30 includes a conveyor belt 14 for transporting plant-based powder material 10 to plant-based powder material hopper 15. A plant material moisture detector 12 is present. This plant material moisture detector 12 is configured for determining a moisture content of the plant-based powder material. The plant material moisture detector 12 is connected to a flow rate controller 26. This flow rate controller 26 is able to determine the amount of water to be added for slurry formation based on the determined moisture content of the plant-based powder material. The flow rate controller 26 can control the water inlet 20 in order to control the overall quantity of water added for slurry formation. This water inlet 20 is part of the first delivery line 20A for the water to be added for slurry formation and for delivery of the cellulose-based sheet-forming agent. A second delivery line 22A is present which is controlled by a separate water inlet 22. This second delivery line 22A delivers the thickening agent, for example guar and an aerosol-former to the mixer 18 for slurry formation. The plantbased powder material hopper 15 transports the plant-based powder material to a silo 16A for storage via a first conveyor belt 17A. The plant-based powder material is then further transported by a second conveyor belt 17B to a mixer 16B which finally transports the plantbased powder material to the slurry mixer 18. The mixer 16B may receive the plant-based powder material and a quantity of water in order to produce a mixture of the plant-based powder material and water. This mixture can then be added to the slurry mixer 18. In the slurry mixer 18 the plant-based powder material is mixed with the water quantity determined by the flow rate controller, the cellulose-based sheet-forming agent and with the thickening agent and the aerosol-former for slurry formation. Such an apparatus allows the water flow rate of the water to be added for slurry formation to be adapted based on the calculated moisture content of the plant-based material which was determined via the plant material moisture detector 12.

Fig. 2 depicts a schematic drawing of a plant material moisture detector 12 with a radiation emitter 12A and a radiation receiver 12B. Microwave radiation indicated by the dashed lines is emitted by the radiation emitter 12A of the plant material moisture detector 12. This emitted microwave radiation passes through plant-based powder material 10 located on the conveyor belt 14 and is received by the radiation receiver 12B. This microwave radiation which passed through the plant-based powder material can be employed in order to calculate the moisture content of the plant-based powder material. The moisture in the plant-based powder material will cause an attenuation and a phase shift of the microwave radiation passing through the material. A comparison of the microwave radiation received by the radiation receiver and of the microwave radiation emitted by the radiation emitter allows a determination of the overall attenuation and phase shift of the microwave radiation owing to the interaction of the microwave radiation with both the plant-based powder material and the moisture content of the material. The flow rate controller 26 includes a module 26A for the calculation of the moisture content and a module 26B for communication between the data processing unit and the plant material moisture detector 12. The communication module 26B can communicate with a modem 32 for communication. This modem 32 can further communicate with the data processing unit 34. This data processing unit is also configured for controlling the apparatus configured for producing the plant-based material sheet. A conveyor belt compensating device 36 can be present which is able to generate a compensating signal due to any incidental absorption of the microwaves by the material of the conveyor belt. The compensating device may provide a compensating signal in the range of 4 milliampere to 20 milliampere. The arrow denoted with “1” shows a communication line for the amplitude attenuation. The arrow denoted with “2” shows a communication line for phase shift. These two communication lines provide further information about the amplitude attenuation and the phase shift which is only caused by the plant-based powder material, but not by the moisture content of the material. This allows the module 26A for the calculation of the moisture content to correctly determine the amplitude attenuation and the phase shift of the microwave radiation which is only caused by the moisture, not by the plant-based material itself. This allows an accurate determination of the moisture content of the plant-based powder material.