Tobacco Based Smoking Material

This invention relates to the production of an improved smoking material from tobacco.

In our U.S. Pat. No. 3,545,448, it is proposed to replace at least a portion of the tobacco in smoking mixtures by a modified carbohydrate material produced by subjecting carbohydrate to a catalysed degradation at 100.degree.-250.degree. C until the weight of the degraded material is less than 90% of the weight of the original carbohydrate.

It has now been found that catalysed thermal degradation of tobacco also produces beneficial results.

According to the invention a process for the manufacture of an improved material suitable for smoking mixtures comprises subjecting tobacco to a catalysed degradation process at a temperature of at least 100.degree. C, suitably 100.degree. to 300.degree. C and preferably 100.degree. to 250.degree. C, especially 160.degree. to 250.degree. C until the weight of degraded material is less than 90% of the weight of the original tobacco. Desirably the weight of the degraded material should not be less than 70% of the weight of the original tobacco.

All kinds of tobacco may be used in the process of the invention, including cigarette tobaccos such as flue-cured Virginia (FCV) tobacco, and stronger tobaccos such as Burley and Rustica tobaccos.

The catalyst used in the process may be any substance which accelerates the thermal degradation of tobacco or lowers its thermal degradation temperature. Acidic substances are especially effective, preferred catalysts being strong acids and salts of strong acids with weak bases. Mineral acids e.g. sulphuric, phosphoric and hydrochloric acids may be used, and weak base salts which are of value include ammonium sulphate, diammonium hydrogen phosphate, ferric chloride and especially ammonium sulphamate. Alkaline substances are also effective catalysts, for example alkali hydroxides e.g. sodium hydroxide, and alkali salts of weak acids e.g. sodium carbonate. When alkaline catalysts are used, however, the degraded material should preferably be washed substantially free of catalyst before it is used for smoking.

Preferably the catalyst is used in amounts ranging from 1 to 20%, preferably 3 to 8% by weight of the tobacco.

The process of the invention may be carried out with the tobacco in any convenient form for example as leaf, powder or sheet. The possible presence of other substances which are inert under the degradation conditions is not excluded. Thus neutral salts and inert binders may be present if desired.

In the process all volatile matter is permitted to escape from the zone in which thermal degradation takes place. The process appears to be degradative in its effect upon the cellulose and other carbohydrate constituents of the tobacco, evolving water and other volatile matter.

Duration of the process will depend upon the temperature, the catalyst, the physical state of the tobacco and the extent of the effect desired.

The process changes the colour of the tobacco to dark brown-black. Quite surprisingly, however, the thermally degraded material, when smoked, possesses enhanced tobacco flavour, indicating that the flavourants present have unexpected stability under the conditions used.

When heated in absence of any catalyst tobacco may lose weight and by continuing the heating a residue weighing less than 90% of the original tobacco may be produced. Such residues do not have improved smoke flavour compared with the original tobacco and they are definitely inferior in smoke flavour to the materials made by the present process. It is within the scope of the invention to heat tobacco in the absence of any catalyst and then to continue heating in the presence of a catalyst.

A further benefit from the process of the invention is that there is a reduction in formaldehyde delivery in the smoke from the products, compared with the untreated tobacco. Formaldehyde is known to be a severe ciliatoxic component in tobacco smoke.

When an acid catalyst, such as sulphuric acid, has been used in the process of the invention, it is advantageous to neutralise any residual acidity in the thermally degraded material by adding ammonia.

The thermally degraded material produced by the process of the invention may, if desired, be compounded with other materials which are normal constituents of smoking mixtures, for example, tobacco, carbohydrates, modified carbohydrates, especially thermally degraded carbohydrates (and in particular thermally degraded cellulose) made by the process of our U.S. Pat. No. 3,545,448, or other smoke-producing materials and as desired any of the modifying agents commonly used in smoking mixtures.

Thus for example smoking mixtures containing thermally degraded material made by the process of the present invention may also contain glow-promoting catalyst, materials to improve ash coherence or colour, nicotine, flavourants, humectants, medicaments or inorganic fillers.

As glow-promoting catalysts for ensuring "fire-holding capacity", alkali metal compounds are preferred.

As materials to improve the ash, salts of ammonia, alkali metals or alkaline earth metals can be used and of these, salts of magnesium, calcium or ammonium are preferred. Bentonite is an especially effective ash cohesion agent.

Numerous beneficial flavouring materials may be included in the mixture. These include tobacco extracts, organic esters, essential oils, menthol, tonka bean or vanillin.

Glycerol and glycols, such as, for example, ethylene glycol and di-, tri- and tetra-ethylene glycol are convenient humectants.

Desirably, inorganic fillers are incorporated in order to control the burning rate of the mixture. By balancing ions which accelerate combustion against ions which retard combustion, in the manner described in our U.K. Pat. No. 1,299,296 (Application No. 13860/70) acceptable combustion rates may be achieved even when large amounts (e.g. 40% or more by weight) of filler are incorporated. Carbonates, particularly calcium and magnesium carbonates are valuable fillers, especially when used in combination to produce an acceptable burning rate. Porous inert fillers may facilitate combustion, imparting a more open texture to the mixture and thereby facilitating access of oxygen.

It is convenient for smoking mixtures to simulate tobacco and the thermally degraded material is therefore preferably prepared in sheet form and, when required as a cigarette of pipe filling, shredded into strips. To prepare the sheeted smoking mixture, the thermally degraded material, if already in sheet form, may be merely treated with the desired additives and shredded. Thermally degraded material in other forms, or in a sheet form which is too weak to shred properly, may be comminuted to powder and made into a sheet by the methods used in making reconstituted tobacco. For example the material may be mixed with a solution of binding agent such as a water-soluble cellulose derivative, polyvinyl alcohol, starch, pectin, gum or mucilage, formed into a film and dried. Water-soluble methyl cellulose or sodium carboxymethyl cellulose, preferably in grades such that a 2% aqueous solution has a viscosity of at least 1500 centipoises at 25.degree. C, may advantageously be used as the binding agent. Other ingredients may be incorporated with the thermally degraded material into the binding agent. Soluble ingredients may, if desired, be sprayed on to the sheeted mixture.

For use in cigarettes or pipes the shred mixture is preferably conditioned in a humid atmosphere to a moisture content of 5 to 15% by weight.

The process of the invention may be an advantageous manner of improving the flavour of low-grade tobacco material (for example stalks and finely powdered material) of the kind used in reconstituted tobacco.

The invention is further illustrated by the following Examples in which all parts and percentages are by weight. Flavour assessments recorded in the Examples were carried out by a panel of smokers especially selected for their high consistent flavour sensitivity and long experience in testing the flavour of tobacco cigarettes.

Powdered flue-cured Virginia (FCV) tobacco was impregnated with an aqueous solution of ammonium sulphamate and dried to give a powder containing 5% of ammonium sulphamate. This was heated for 15 minutes at 225.degree. C in an oven, thereby losing 20% of its original weight.

The resultant thermally degraded product, a dark brown to black powder, was slurried with an aqueous solution of sodium carboxymethyl cellulose (SCMC) and the ingredients indicated below, and the slurry was spread into a film and dried to give a film of the following composition.

The film was shredded and made up into cigarettes. When smoked these had a tobacco flavour.

This exemplifies the superior tobacco flavour of the thermally degraded FCV tobacco compared to untreated FCV tobacco.

95 parts of flue-cured Virginia (FCV) tobacco were sprayed with 5 parts of ammonium sulphamate in 95 parts of water. The tobacco was then air dried, followed by heat treatment at 220.degree.-225.degree. C for 20-25 minutes giving 75 parts of a dark brown material which was ball milled and formulated into a sheet as follows.

4 parts of sodium carboxymethyl cellulose was dissolved in 160 parts of water with stirring and an aqueous solution of 5.6 parts of glycerol, 2.0 parts of potassium citrate and 1.6 parts of citric acid in 40 parts of water was added. A dry mixture consisting of 4.0 parts of calcium carbonate and 22.8 parts of the dark brown material was then added. The resultant slurry was stirred for at least 1 hour, then cast on a drier to give a film with a dry basis weight of 48-52 grams/square meter.

The film was shredded and made into cigarettes. These cigarettes were compared by a panel of smokers with equivalent cigarettes which contained untreated ball milled FCV tobacco. A unanimous preference was expressed for the cigarette containing the thermally degraded tobacco on account of its much stronger tobacco flavour.

This example illustrates the use of sulphuric acid as catalyst and again shows a better tobacco flavour resulting from thermally degraded FCV tobacco compared to untreated FCV tobacco.

95 parts of flue-cured Virginia tobacco was sprayed with 5 parts of concentrated sulphuric acid in 100 parts of water. The tobacco was then air dried followed by heat treatment at 220.degree.-225.degree. C for 20-25 minutes giving 80 parts of a drak brown material, which was ball milled and formulated into a sheet as follows:

4.0 parts of sodium carboxymethyl cellulose was dissolved in 160 parts of water with stirring and an aqueous solution of 5.6 parts of glycerol, 2.0 parts of potassium citrate and 1.6 parts of citric acid in 40 parts of water was added. A dry mixture consisting of 4.0 parts of calcium carbonate and 22.8 parts of the dark brown material was then added. The resultant slurry was stirred for at least 1 hour, then cast on a drier to give a film with a dry basis weight of 48-52 grams per sq. meter.

The film was shredded and made into cigarettes. Flavour assessment of these cigarettes by a panel of experts against equivalent cigarettes in which the thermally degraded tobacco was replaced by ball milled untreated tobacco showed that they had a superior tobacco flavour to those containing the untreated tobacco. This opinion was unanimous among the panellists.

This Example illustrates the superior flavour produced by the thermal degradation of Burley tobacco.

95 Parts of Burley tobacco was sprayed with 5 parts of ammonium sulphamate in 95 parts of water and heated at 220.degree.-225.degree. C for 20 minutes, to give 83.6 parts of a dark brown material which was ball milled and formulated into a film as follows:

4.0 parts of sodium carboxymethyl cellulose was dissolved in 160 parts of water with stirring and an aqueous solution of 5.6 parts of glycerol, 2.0 parts of potassium citrate and 1.6 parts of citric acid in 40 parts of water was added. A dry mixture consisting of 4.0 parts of calcium carbonate and 22.8 parts of the dark brown material was then added. The resultant slurry was stirred for at least 1 hour then cast on a drier to give a film with a dry basis weight of 48-52 grams per sq. meter.

The film was shredded and made into cigarettes. A panel of expert smokers was unanimously of the opinion that these cigarettes showed improved tobacco flavour compared with similar cigarettes which contained ball milled Burley tobacco which had not been thermally degraded. The ordinary Burley tobacco cigarette had only a slight tobacco/woody flavour compared to the distinct tobacco flavour of the cigarette containing thermally degraded Burley tobacco.

This example illustrates the superior tobacco flavour of the thermally degraded FCV tobacco compared to FCV tobacco which had been heated under similar conditions without a catalyst.

4.0 Parts of sodium carboxymethyl cellulose was dissolved in 160 parts of water with stirring and an aqueous solution of 5.6 parts of glycerol, 2.0 parts of potassium citrate and 1.6 parts of citric acid in 40 parts of water was added. A dry mixture consisting of 4.0 parts of calcium carbonate and 22.8 parts of a material (ground to pass a 120 B.S. Sieve) prepared by heat treating flue cured Virginian tobacco rag without a catalyst at a temperature of 220.degree.-225.degree. C for 20-25 minutes resulting in a 20% weight loss, was then added. The resultant slurry was stirred for at least 1 hour then cast on a drier to give a film with a dry basis weight of 48-52 grams per sq. meter.

The film was shredded and made into cigarettes. Flavour assessment of these cigarettes by a panel of experts compared with equivalent cigarettes containing the thermally degraded FCV tobacco (see Example 2) showed that the panellists unanimously preferred the cigarettes containing the catalysed heat treated tobacco because of its superior tobacco flavour.

This example illustrates the superior tobacco flavour of the thermally degraded Burley tobacco compared to Burley tobacco which has been similarly heated in the absence of a catalyst.

Burley tobacco was heated without a catalyst at a temperature of 220.degree.-225.degree. C for 20-25 minutes to give a material which had lost 13.4% of its weight. This material was ground into a powder and formulated as follows:

4.0 parts of sodium carboxymethyl cellulose were dissolved in 160 parts of water with stirring and an aqueous solution of 5.6 parts of glycerol, 2.0 parts of potassium citrate and 1.6 parts of citric acid in 40 parts of water added. A dry mixture consisting of 4.0 parts of calcium carbonate and 22.8 parts of the above heat treated Burley tobacco rag was then added. The resultant slurry was stirred for at least 1 hour then cast on a drier to give a film with a dry basis weight of 48-52 grams per sq. meter.

The film was shredded and made into cigarettes. Flavour assessment of these cigarettes by a panel of experts with equivalent cigarettes containing powdered thermally degraded Burley tobacco prepared as described in Example 4 showed a unanimous preference for the latter cigarettes on account of their superior tobacco flavour. The cigarettes containing the Burley tobacco heated without a catalyst had essentially the flavour of burning cellulose and very little tobacco flavour.

95 Parts of flue-cured Virginia tobacco were sprayed with 5 parts of ammonium sulphamate in 95 parts of water. The tobacco was then air dried and heated at 180.degree. C for 6 hours to give a weight loss of 20%. The product was ground to pass a 120 B.S. Sieve.

4.0 parts of sodium carboxymethyl cellulose was dissolved in 160 parts of water with stirring and an aqueous solution of 4.8 parts of glycerol, 2.0 parts of potassium citrate and 1.6 parts of citric acid in 40 parts of water was added. A dry mixture consisting of 4.0 parts of calcium carbonate and 22.8 parts of the heat-treated FCV tobacco prepared as described in the previous paragraph was then added. The resultant slurry was stirred for 1 hour, then cast on a drier to give a film with a dry basis weight of 48-52 gram per sq. meter. The film was then shredded and made into cigarettes.

Assessment of these cigarettes compared with similar cigarettes containing ball-milled FCV tobacco by a panel of experts showed that the tobacco character of the smoke was increased in the cigarettes containing the ammonium sulphamate catalysed heat-treated Virginian tobacco.