Reconstituted tobacco sheets and related methods

Abstract

The invention relates to a reconstituted tobacco sheet having a basis weight of less than about about 230 grams per square metre and comprising tobacco stem or tobacco stalk refined fibres having an average length of at least about 200 micrometres and tobacco cast leaf material. There is further provided a method of making a reconstituted tobacco sheet, the method comprising providing tobacco stems and conditioning the tobacco stems such that their moisture content is increased to at least about 40% Oven Volatiles (OV). The tobacco stems are processed in a twin screw extruder to so as to obtain a pulp suspension having a Schop-per-Riegler index of at least about 30 degrees and comprising tobacco stem or tobacco stalk refined fibres having an average length of at least about 200 micrometres. This pulp suspension is combined with tobacco cast leaf material to obtain a slurry and a sheet is formed from this slurry.

Claims

1. A method of making a reconstituted tobacco sheet, comprising: providing tobacco stems or tobacco stalks or a mixture thereof; conditioning the tobacco stems or tobacco stalks such that their moisture content is increased to from about 40% Oven Volatiles (OV) to about 60% Oven Volatiles (OV); processing the conditioned tobacco stems or tobacco stalks in a twin screw extruder to so as to obtain a pulp suspension having a Schopper-Riegler index of at least about 30 degrees and comprising tobacco stem or tobacco stalk refined fibres having an average length of at least about 200 micrometres; combining the pulp suspension with tobacco cast leaf material to obtain a slurry; and forming a sheet from the slurry.

2. A method according to claim 1, wherein the conditioned tobacco stems or tobacco stalks are extruded to obtain a pulp suspension containing tobacco stem or tobacco stalk refined fibres having an average length of less than about 1200 micrometres.

3. A method according to claim 2, wherein the step of processing the conditioned stems or stalks is carried out at a temperature of at least about 50 degrees C.

4. A method according to claim 1, wherein the step of processing the conditioned stems or stalks is carried out at a temperature of at least about 50 degrees C.

5. A method according to claim 4, wherein the step of processing the conditioned stems or stalks is carried out in a twin screw extruder comprising at least a first and a second conveying sections adapted to advance the material being processed along an axial direction of the extruder and at least a kneading section adapted to restrict the flow of the material being processed along the axial direction and to exert a kneading and shearing action on the stems, wherein the at least one kneading section is located between the first and the second conveying sections.

6. A method according to claim 1, wherein the step of processing the conditioned tobacco stems or tobacco stalks comprises one or more passes of the conditioned tobacco stems or tobacco stalks through the twin screw extruder.

7. A method according to claim 1, wherein the step of processing the conditioned stems or stalks is carried out in a twin screw extruder comprising at least a first and a second conveying sections adapted to advance the material being processed along an axial direction of the extruder and at least a kneading section adapted to restrict the flow of the material being processed along the axial direction and to exert a kneading and shearing action on the stems, wherein the at least one kneading section is located between the first and the second conveying sections.

8. A method according to claim 7, wherein the twin screw extruder has a Length/Diameter ratio of from 25 to 70.

9. A method according to claim 8, wherein the at least one kneading section extends over a length of at least 10 times the screw diameter.

10. A method according to claim 7, wherein the at least one kneading section extends over a length of at least 10 times the screw diameter.

11. A reconstituted tobacco sheet obtainable by a method according to claim 1.

Description

COMPARATIVE EXAMPLE

(1) A reconstituted tobacco sheet was prepared according to a conventional cast leaf process with the following composition:

(2) Tobacco Material:

(3) Lamina dust: 66 percent by dry weight

(4) Ground stem: 34 percent by dry weight

(5) Binder:

(6) Guar: 8 parts by dry weight per 100 parts of dry tobacco material

(7) The dry tobacco material was fed to a grinder where it was dry ground and screened and subsequently contacted with an aqueous medium including guar as the binder in a high-shear mixer to form a tobacco slurry. The tobacco slurry was then cast onto a moving endless belt. The cast slurry was subsequently passed through a drying assembly to remove moisture so as to form a reconstituted tobacco sheet. Finally, the sheet was removed from the belt with a doctor blade.

(8) A reconstituted tobacco sheet was obtained with a basis weight of 12.50.5 grams per square foot (about 135 grams per square metre) and a tensile strength of about 25 kgf/m (about 245 N/m).

Example 1

(9) Tobacco stem refined fibres were prepared by an embodiment of a method in accordance with the present invention. In more detail, tobacco stems were conditioned to moisture content of about 50 percent OV. Subsequently, the conditioned tobacco were processed with two subsequent passes in a twin-screw extruder with an L/D ratio of 48 and a screw diameter of 53 mm. The screw profile was composed of a sequence of conveying sections and kneading (restrictive) sections. In more detail, the screw profile included 6 kneading sections, for an overall length of kneading section of about 20 D. Consecutive kneading sections were separated by conveying zones. The first two kneading sections were provided as reverse screw elements with large grooves. The following kneading sections were provided as kneading elements with positive, neutral or negative pitches, as well as reverse screw elements. The kneading elements were bilobal, but monolobal or trilobal could also have been used.

(10) First Pass

(11) The conditioned tobacco stems were fed to the extruder at a feed rate of 25 kg/hour. The extruder screw speed was set at 250 rpm. The temperature along the screw extruder was regulated in order to prevent the stems to reach a temperature above 100 degrees C. In more detail, in a first section of the extruder, the temperature was set at about 90 degrees C. In a second section of the extruder downstream of the first section, the temperature was set at about 100 degrees C. The moisture of the stems at the exit of the extruder after the first pass was about 45 percent OV. The freeness (drainability) measured on the stems at the exit of the extruder after the first pass was about 62 degrees Schopper-Riegler.

(12) Second Pass

(13) The conditioned tobacco stems were fed to the extruder at a feed rate of 25 kg/hour. The extruder screw speed was set at 250 rpm. The temperature along the screw extruder was regulated in order to prevent the stems to reach a temperature above 100 degrees C. In more detail, in a first section of the extruder, the temperature was set at about 90 degrees C. In a second section of the extruder downstream of the first section, the temperature was set at about 100 degrees C. The moisture of the stems at the exit of the extruder after the first pass was about 37 percent OV. The freeness (drainability) measured on the stems at the exit of the extruder after the first pass was about 75 degrees Schopper-Riegler.

(14) Tobacco stem refined fibres having a average length of about 350 micrometres were obtained. The tobacco stem refined fibres thus obtained were mixed with humectants and tobacco dust and binder to form a slurry, which was then cast to form a sheet and let dry.

Example 2

(15) Tobacco stem refined fibres were prepared by an alternative embodiment of a method in accordance with the present invention. In more detail, tobacco stems were conditioned to moisture content of about 50 percent OV. Subsequently, the conditioned tobacco were processed with two subsequent passes in a twin-screw extruder with an L/D (length to diameter) ratio of 28 and a screw diameter of 42 mm. The screw profile was composed of a sequence of conveying sections and kneading (restrictive) sections. In more detail, the screw profile included 6 kneading sections, for an overall length of kneading section of about 19 times the screw diameter D. Consecutive kneading sections were separated by conveying zones. The kneading sections were provided as kneading elements of different sizes with positive or negative pitches, as well as reverse screw elements. The kneading elements were bilobal, but monolobal or trilobal could also have been used. The reverse screw elements were without grooves.

(16) First Pass

(17) The conditioned tobacco stems were fed to the extruder at a feed rate of 25 kg/hour. The extruder screw speed was set at 250 rpm. In the downstream section of the screw extruder the temperature was regulated in order to prevent the stems to reach a temperature above 100 degrees C. The moisture of the stems at the exit of the extruder after the first pass was about 44 percent OV. The freeness (drainability) measured on the stems at the exit of the extruder after the first pass was about 33 degrees Schopper-Riegler.

(18) Second Pass

(19) The conditioned tobacco stems were fed to the extruder at a feed rate of 25 kg/hour. The extruder screw speed was set at 250 rpm. In the downstream section of the screw extruder the temperature was regulated in order to prevent the stems to reach a temperature above 100 degrees C. The moisture of the stems at the exit of the extruder after the first pass was about 40 percent OV. The freeness (drainability) measured on the stems at the exit of the extruder after the first pass was about 52 degrees Schopper-Riegler.

(20) Tobacco stem refined fibres having an average length of about 400 micrometres were obtained. The tobacco stem refined fibres thus obtained were mixed with humectants and tobacco dust and binder to form a slurry, which was then cast to form a sheet and let dry.

Example 3

(21) A reconstituted tobacco sheet was prepared by a method according to the present invention as described above with reference to Example 2 with the following composition:

(22) Tobacco Material:

(23) Lamina dust: 62 percent by dry weight

(24) Refined stem fibres: 30 percent by dry weight

(25) Binder:

(26) Guar: 8 parts by dry weight per 100 parts of dry tobacco material

(27) A reconstituted tobacco sheet was obtained with a basis weight of about 160 grams per square metre) and a tensile strength (about 300 N/m).

Example 2

(28) A reconstituted tobacco sheet has been prepared by a method according to the present invention with the following composition:

(29) Tobacco Material:

(30) Lamina dust: 57 percent by dry weight

(31) Refined stem fibres: 43 percent by dry weight.

(32) Binder:

(33) Guar: 8 parts by dry weight per 100 parts of dry tobacco material.

(34) A reconstituted tobacco sheet was obtained with a basis weight of about 150 grams per square metre and a tensile strength of about 340 N/m.