Reconstituted Tobacco Composition

Abstract

A reconstituted tobacco sheet is disclosed in which finally divided tobacco is combined with an adhesive consisting essentially of ethyl cellulose with an ethoxyl content of 45.5 percent to 46.8 percent and a viscosity at a 5 percent concentration of at least 5,000 cps at 25.degree. C. The product produced is characterized by a substantial amount of wet strength and can be plasticized with conventional glycol humectants.

Parent Case Text

This is a Divisional Application of Ser. No. 688,663, filed Dec. 7, 1967, now U.S. Pat. No. 3,500,833.

Description

This invention relates to the preparation of reconstituted tobacco products characterized by resistance to degradation by moisture. More particularly, it relates to tobacco products containing a particular grade of water-insoluble adhesive material.

In recent years, tobacco manufacture from finely divided tobacco and adhesives has assumed substantial commercial importance. Products have been made which include sheets, shreds and other shaped articles. In general, these products have either had a very substantial resistance to disintegration in the presence of moisture or else have had hardly any such resistance. Effectively, the water-soluble tobacco products have suffered when exposed to the action of saliva and various treatment solutions used in the application of flavors and the like.

Two basic types of water-insoluble tobacco products are possible. Most water-insoluble products used commercially today are made from combinations of tobacco, water-soluble adhesives and insolubilizing or crosslinking agents which react with or crosslink the hydrophilic hydroxyl groups on the water-soluble adhesives to render the products water insoluble. Some of these water-insoluble products, while generally satisfactory, particularly when first manufactured, have tended under some storage conditions to lose much of their water insolubility. This loss of water insolubility is related to hydrolysis of insolubilizing crosslinks caused in some cases by instability of these linkages to high moisture conditions, at which such products are frequently stored, or to ammoniacal vapors created by continuing fermentation of the filler tobacco in smoking articles such as cigars. Virtually all of such wet-strength tobacco products will lose at least a portion of their wet strength at some combination of conditions involving moisture content, temperature, pH and time.

A second basic class of water-insoluble tobacco products achieves its insolubility through the use of water-insoluble, organic-solvent-soluble adhesives. Such products may be made from nonaqueous suspensions of tobacco particles in a viscous dispersion of the adhesive in a suitable organic solvent. In principle, one would expect that such tobacco products would enjoy a dominant position commercially, since they avoid the problems of stability of wet strength associated with crosslinked aqueous adhesive systems. However, such is not the case.

It has been found that water-insoluble adhesives which are sufficiently hydrophobic to produce tobacco products with the requisite water resistance result in distinctive, nontobacco, objectionable aromas on combustion, which render the resultant products unacceptable commercially. Water-insoluble, organic-solvent soluble adhesives in this category include cellulosic derivatives with hydrophobic substituents such as ethyl or benzyl groups. The problem is increased by the fact that the hydrophobic adhesives generally require unusual plasticizers in order to give the resultant tobacco sheet the elongation and pliability required for satisfactory performance on automatic machinery. These plasticizers, such as the polyester types used to plasticize tobacco sheets with hydrophobic adhesives described by Hotelling et al. in U.S. Pats. Nos. 2,984,244, 2,976,873 and 2,957,478, contribute nontobacco objectionable aromas on combustion. The combination of such plasticizers with hydrophobic adhesives in tobacco products results in products whose combustion aroma is unacceptable commercially. Accordingly, the only tobacco products including water-insoluble adhesives which are in commercial use are cellulosic types with a substantial degree of methyl substitution. Since the methyl group is decidely less hydrophobic than the ethyl group, highly substituted methylcellulose is compatible with conventional glycol humectants. However, the drawback of such adhesives is that, although soluble, they are extremely water sensitive, and they invariably result in products with only minimal wet strength.

It is an object of this invention to provide tobacco products characterized by a substantial amount of wet strength.

It is a further objective of this invention to provide a wet-strength tobacco product utilizing a particular grade of a hydrophobic adhesive.

It is another objective of this invention to provide tobacco products with substantial amounts of wet strength made with a hydrophobic adhesive that can be plasticized with conventional glycol humectants normally employed in tobacco manufacture.

It is also an objective of this invention to provide wet-strength tobacco products with commercially-acceptable taste and aroma properties including a particular grade of a hydrophobic adhesive.

Additional objectives will become apparent from the description of the invention which follows.

While the invention will be described in connection with tobacco sheet, the adhesive of the present invention may likewise be advantageously used with tobacco in other shapes such as rods, cylinders, plugs shreds, and the like. Accordingly, it will be understood that the invention contemplates also tobacco manufacture of this kind.

Ethylcellulose, a water-insoluble hydrophobic adhesive, has been considered as a potentially useful adhesive for reconstituted tobacco products for many years. It is mentioned in this regard in several patents, including U.S. Pats. Nos. 2,957,478, 3,062,688 and 2,797,689. Frankenburg, in U.S. Pat. 2,797,689, recognized that the combustion aroma of ethylcellulose and other hydrophobic adhesives was unacceptable in tobacco products, and attempted to overcome this problem through the use of siliceous catalysts. Detert et al. in U.S. Pat. No. 3,062,688, discloses a tobacco product employing highly methylated methylcellulose as the adhesive, to which he adds sufficient ethylcellulose or acetylcellulose to provide some degree of water resistance. This is a "compromise"-type product, since products containing highly methylated methylcellulose as adhesive are stated by Detert to be capable of taking up a very high content of pulverized tobacco which has a desirable effect with respect to taste and burn, and also has desirable mechanical properties which allow it to be worked by machine or hand, but suffer because of a lack of wet strength. On the other hand, tobacco sheets made with hydrophobic adhesives such as acetylcellulose or ethylcellulose had good wet strength, but would not take high tobacco loadings and would not handle satisfactorily on machines or by hand. It is obvious that by blending ethylcellulose with highly methylated methylcellulose that the resultant wet strength is less than would be obtained with ethylcellulose alone, and the tobacco loading, taste and burn and machine workability properties are poorer than would be obtained with highly methylated methylcellulose alone.

Hotelling et al. in U.S. Pats. Nos. 2,984,244, 2,976,873 and 2,957,478 obtains good wet strength in his tobacco products by using medium ethoxy 100 cps ethylcellulose as the sole adhesive, and also obtains good machine workability by his discovery that certain polyester types will plasticize tobacco sheets with ethylcellulose adhesives. However, it is stated in U.S. Pats. Nos. 2,957,478 and 2,984,244 that such products can only be made at tobacco contents up to 85 percent, at which point the decrease in tensile strength and elongation makes the product marginal. The ethylcellulose content, even in the product with 85 percent tobacco content, is still about 12 percent, and is even higher in the lower tobacco content products. This combination of high ethylcellulose content and the presence of polyester plasticizers, both materials having unusual, nontobaccolike burn aromas, results in products which we have found to be unacceptable in commercial smoking articles.

In the present invention, the disadvantages associated with the use of ethylcellulose as a tobacco adhesive in the prior art have been overcome through the use of a particular grade of ethylcellulose having an ethoxyl content of 45.5--46.8 percent (degree of substitution of 2.28 to 2.38 ethoxyl groups per anhydroglucose unit) and a viscosity of at least 5,000 cps. The viscosity is for a 5 percent concentration of ethylcellulose by weight in 80.20 toluene: ethanol by weight at 25.degree. C., as measured with a Brookfield viscometer.

Use of this particular grade of ethylcellulose has several unusual and as yet unexplainable results. First, the tobacco loading which the ethylcellulose can bind to produce tobacco products which still exhibit the type of properties required for good machine workability is increased two to six fold with this grade of ethylcellulose, allowing preparation of tobacco products containing 2--7 percent ethylcellulose in place of the 12--20 percent levels required previously. Second, use of this particular grade of ethylcellulose in tobacco formulations at the 2--7 percent level unpredictably allows plasticization with standard glycol-type humectants to produce tobacco sheet products with 15--35 percent wet elongation and with the requisite strength and pliability for satisfactory workability on tobacco machinery. Accordingly, the need for the polyester plasticizers described by Hotelling et al. is eliminated. Overall, the combination of low ethylcellulose content, high tobacco content, and the use of conventional glycol humectants, all made possible by the use of this particular grade of ethylcellulose, results in wet-strength tobacco products which closely resemble natural tobacco in taste and aroma and are accordingly of significant commercial value.

The properties of ethylcellulose are known to be dependent on the degree of substitution (ethoxyl content) and on the molecular weight, which in most cases can be measured by viscosity. The degree of substitution of ethylcellulose affects the softening point, hardness, water absorption, solubility in ethanol and solubility in 80.20 toluene: ethanol. On the other hand, there are certain other properties such as tensile strength, elongation and flexibility which are not greatly affected by the degree of substitution, but which depend largely upon the degree of polymerization or molecular weight. For pure (unloaded) ethylcellulose films, the tensile strength and elongation increase as the molecular weight or viscosity increases. However, there is a marked leveling off of the curves for tensile strength and elongation versus viscosity grade between the 50 and 100 cps types. This means that very little additional tensile strength or elongation can be gained by using higher viscosity types than about 100 cps ethylcellulose. Such higher viscosity grades are used for applications where increased viscosity is desirable, since improvements in film properties do not result.

With a knowledge of the factors and relationships involved in the properties of pure ethylcellulose films as background, it was unexpected to find that one particular grade of ethylcellulose, that with 45.5 to 46.8 percent ethoxyl and at a 5 percent concentration a viscosity of at least 5000 cps, results in a completely different effect when highly loaded with ground tobacco. This grade of ethylcellulose, when loaded with tobacco, results in films which have substantially greater tensile strength than comparable formulations made with all other grades of ethylcellulose. Equally unexpected is the finding that tobacco-loaded films of this grade of ethylcellulose are readily plasticized with conventional glycol humectants for tobacco, such as triethylene glycol, propylene glycol or glycerine, to produce products with 15--35 percent wet elongation. When other grades of ethylcellulose are plasticized with such humectants in tobacco formulations, wet elongations of 10 percent or less invariably result.

Any of the solvents which dissolve ethylcellulose with a degree of substitution of 45.5--46.8 percent ethoxyl may be employed in the manufacture of tobacco products according to this invention. Such solvents include methanol, ethanol, methylene chloride, toluene-ethanol mixtures and isopropanol-water mixtures containing from 88 percent to 97 percent isopropanol. The best solvents for this grade of ethylcellulose are 80:20 toluene: methanol or 80:20 toluene: ethanol (weight/weight), and use of either of these solvent mixtures results in tobacco products with maximum tensile strength and elongation properties.

The procedure involved in the manufacture of tobacco products involves dispersion of the ethylcellulose adhesive in the solvent for ethylcellulose, followed by the addition of tobacco dust. The viscosity of the resultant dispersion should be at least sufficient to prevent separation or settling of the tobacco dust. Generally, a minimum of 3,000 cps viscosity for the resultant dispersion, as measured by a Brookfield viscometer, is required to prevent separation. Other additives such as humectants or plasticizers, fibers, fungicides, ash additives such as silicious earth or color additives may be incorporated into the tobacco suspension prior to shaping. If tobacco sheet is to be prepared, the resultant tobacco slurry may be cast or otherwise applied to a moving belt at a thickness which, on drying, will result in the desired tobacco film thickness. Depending on the solvent employed and its volatility, the shaped tobacco slurry may be air dried or dried at elevated temperatures, such as by steam-air mixtures or warm or hot air impinging on the underside of the belt. The drying temperature should be kept below the boiling point of the solvent employed, or bubbling of the solvent and disruption of the resultant film occur. For toluene: methanol 80/20, weight/weight) solvent systems, drying at temperatures of about 50.degree. C. results in both good film properties and sufficiently rapid drying rates. The organic solvents evaporated from the tobacco products are recoverable by conventional processes and can be reused. The shaping of the resultant slurry may be made by any one of the well known methods now in use in the art. A suitable method and apparatus for the casting of the slurry into a sheet may, for example, be found in the following U.S. Pats. Nos. to R. C. Osborne et al. 3,250,315 and 3,294,554 and in the U.S. Pat. No. 3,145,716 issued to R. C. Gertz et al.

The following examples are provided as further illustrations of the inventive concept, and should not be construed as limitations on the invention.

Example 1

A sample of ethylcellulose with an ethoxyl content of 46.8 percent and at a 5 percent concentration a viscosity in 80/20 toluene/ethanol of 5,400 cps at 25.degree. C. was used in this example. The Brookfield viscometer is used to measure viscosity. The first step in the preparation of a tobacco slurry is the preparation of a 2 percent solids dispersion of one part of this ethylcellulose in 80/20 toluene/ethanol (weight/weight), with agitation being continued until dispersion is complete. To the resulting dispersion is added, with agitation, 0.2 parts triethylene glycol, 30 parts of tobacco ground to minus 80 mesh U.S. Standard sieve size, and sufficient additional 80/20 toluene/ethanol solvent to produce a final total solids of 25 percent in the tobacco slurry. The resultant uniform tobacco dispersion is cast on a moving stainless steel belt at a thickness such that the final dried film will weigh approximately 9 grams per square foot. The cast tobacco slurry film is dried with warm (45.degree. C.) water impinging on the underside of the belt. The dried tobacco film is remoistened to 20 percent moisture to facilitate doctoring from the belt. The resulting product is particularly suitable for use as a cigarette or cigar filler, depending on the particular type of tobacco employed. The product handles well on machinery required for such applications, and, due to the low ethylcellulose content, has taste and aroma qualities comparable to natural tobacco.

Example 2

A sample of ethylcellulose with an ethoxyl content of 45.5 percent and at a 2 percent concentration a viscosity in 80/20 toluene/ethanol of 10,000 cps at 25.degree. C. was employed in this example. A 1.2 percent solids dispersion of one part of this ethylcellulose in 80/20 toluene/methanol (weight/weight) was prepared, using agitation sufficient to insure complete dispersion. To the resulting dispersion was added 0.5 parts glycerine, 0.2 parts diatomaceous earth and 14 parts of Wisconsin tobacco ground to minus 120 mesh U.S. Standard sieve size. Agitation is continued until a uniform dispersion is obtained. The resulting tobacco slurry is cast on an endless moving stainless steel belt at a thickness such that, after drying, a tobacco sheet weighing 3.0--3.5 grams/ft.sup.2 will be obtained. The cast tobacco-slurry film is dried at 50.degree. C. with a suitable steam-air mixture impinging on the underside of the belt. The dried tobacco composition is remoistened to 30 percent moisture content to facilitate doctoring from the belt. The product was found to be particularly suitable for use as a cigar wrapper, by virtue of its tensile strength, elongation and pliability. The average properties, as measured on a Scott Tester after equilibration at 80 percent Relative Humidity and 72.degree. F. for 24 hours, were as follows: L-6* a 2 percent concentration was taken since it was found that the material was too viscous at a 5 percent concentration for accurate measurement in the Brookfield viscometer.

Sheet Weight: 3.24 grams/ft.sup.2

Percent Moisture: 18.7 percent

Tensile Strength, Equilibrated: 280 grams/inch

Tensile Strength, Wet: 200 grams/inch

Elongation, Equilibrated: 17 percent

Elongation, Wet: 32 percent

The tobacco composition of this invention has many useful applications and smoking articles such as cigars, cigarettes, pipe tobacco as well as chewing tobacco made in whole or in part from this material, are within the contemplation of the invention. As sheet material it may be fed from rolls to automatic machines, for example, cigar machines, for use as a binder or wrapper. It may also be shredded for filler in pipes, cigarettes, and cigars. It may be mixed with shredded whole tobacco or used alone. It may serve as an outside wrapper for cigars or cigarettes and has the advantage of uniformity in appearance and in physical properties as well as uniformly blended flavor.

While the invention has been described in its preferred embodiment, it will be understood that the invention is not limited to the specific details set out for purposes of illustration and that those skilled in the art may make various changes in these details within the scope of the claims without departing from the spirit of the invention.

Claims

What we claim is:

1. A smoking composition comprising finely divided tobacco and adhesive therefor consisting essentially of ethyl cellulose with an ethoxyl content of 45.5 percent to 46.8 percent and a viscosity at a 5 percent concentration of at least 5,000 cps at 25.degree. C.

2. The composition of claim 1 in which said ethyl-cellulose adhesive has a viscosity at a 2 percent concentration of not more than about 10,000 cps at 25.degree. C.

3. The composition of claim 1 in which said ethyl-cellulose adhesive comprises 2--7 percent of the final smoking composition.

4. The composition of claim 1 comprising additionally a glycol humpectant.