Abstract:
A smoking article filter having a porous resin with a high surface area to mass ratio comprised of a chitosan derivative. Preferred embodiments include chitosan cross-linked with glutaraldehyde and chitosan cross-linked with glyoxal. The chitosan derivative provides for the selective filtration of cigarette smoke, particularly for the removal of aldehydes, hydrogen cyanide, heavy metals and carbonyls.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This patent application is a divisional patent application of and claims priority to and benefit from, currently pending, U.S. patent application Ser. No. 10/842,165, filed on May 10, 2004. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not applicable.  
     FIELD OF INVENTION  
       [0002]     This invention concerns improvements relating to tobacco smoke filters. More particularly, the invention relates to a cigarette filter that can selectively remove undesirable constituents from tobacco smoke.  
       BACKGROUND OF THE INVENTION  
       [0003]     A wide variety of materials have been suggested in the prior art as filters for tobacco smoke. Examples of such filter materials include cotton, paper, cellulose acetate, and certain synthetics. Many of these filter materials, however, are only effective in the removal of particulates, tars and condensable components from tobacco smoke. The art is replete with a myriad of filtration techniques and materials for removing undesirable components in smoke and for causing other reactions as the smoke passes through filtration beds or other reactive media. Among the problems encountered with prior filters has been the plugging or clogging with use and the consumption or rendering ineffective of reactive filtering surfaces and materials.  
         [0004]     Filters made from filamentary or fibrous material such as cellulose acetate tow or paper are somewhat effective in the removal of particulate phase constituents of tobacco smoke. However, they have little or no effect in removing certain gaseous components in the vapor phase of the tobacco smoke such as hydrogen cyanide, aldehydes, carbonyls, metals and sulphides. These volatile constituents can be removed by adsorption and absorption on a suitable surface or by chemical reaction.  
         [0005]     Some known substances which act as absorbents and adsorbents include activated carbon, porous minerals, and ion exchange resins. Ion-exchange resins of porous structure have been found to be somewhat effective, but their efficiency diminishes during smoking, as does that of carbon and porous minerals. This may be due to the material becoming saturated and, therefore, increasingly inactive or it may be due to the release of adsorbed material by thermal desorption of retained substances.  
         [0006]     Resins which contain major proportions of tertiary amino or quaternary ammonium groups have been found not to be suitable for removing aldehydes from tobacco smoke. Chitosan and chitosan with a maximum number of amino groups have been found not to be effective. Among the problems encountered with these materials is that they do not provide a filtration media allowing for the continuous flow of smoke at a low pressure differential or gradient. Other problems with selective filtration medias have been found. For example, the use of certain amino acids, such as glycine, have been found effective in removing aldehydes in tobacco smoke. However, it has been discovered that while glycine can reduce the level of formaldehyde in tobacco smoke, it is not stable in the cigarette filter manufacturing process. Moreover, the use of amino acids causes the release of ammonia odor during storage.  
       SUMMARY OF THE INVENTION  
       [0007]     It has been discovered that chitosan can be chemically modified to have the physical attributes of a filter medium and have a chemical composition capable of effectively adsorbing and absorbing undesirable smoke ingredients, yielding superior performance as a cigarette filter.  
         [0008]     Thus, it is an object of the present invention to provide cigarette filter arrangements and, more particularly, cigarette filters that can selectively remove undesirable constituents in the vapor phase of tobacco smoke such as hydrogen cyanide, aldehydes, metals and sulphides without the drawbacks or disadvantages associated with the prior art as previously described.  
         [0009]     A further object is to provide a novel cigarette and smoke filter embodying a porous resin of cross-linked chitosan.  
         [0010]     An additional object is to provide cross-linked chitosan reactive materials having a high ratio of surface-to-volume and having a reduced number of reactive amino groups for selective smoke filtration in a smoking article.  
         [0011]     According to the present invention, a tobacco-smoke filter includes an adsorbent/absorbent for removal of undesirable volatile tobacco-smoke constituents such as hydrogen cyanide, aldehydes, carbonyls, metals and sulphides. Specifically, the instant invention is directed to particularly efficient tobacco smoke filtration compounds of chitosan cross-linked with glutaraldehyde and chitosan cross-linked with glyoxal.  
         [0012]     Chitosan is cross-linked with glutaraldehyde and glyoxal to form porous resins having a high surface area to mass ratio for the selective filtration of cigarette smoke, particularly for the removal of undesirable smoke constituents such as aldehydes, hydrogen cyanide, carbonyls, sulphides and metals.  
         [0013]     Chitosan is a linear polyglucosamine polymer obtained from the deacetylation of chitin, a polysaccharide found in the exoskeleton of crustaceans. Chitin also occurs in insects and in lesser quantities in many other animal and vegetable organisms. Chitin is a linear polymer of 2-deoxy, 2-acetyl-amino glucose analogous to cellulose in chemical structure. It is insoluble in almost all media except strong mineral acids and due to the acetylated amino group is relatively unreactive.  
         [0014]     When chitin is deacetylated by treatment with strong alkalis, the product is chitosan which contains one free amino group for each glucose building unit in the polymer. It is still a long chain linear polymer but is now a highly reactive cationic poly-electrolyte material. It will form salts with simple organic acids, such as formic, acetic, tartaric, citric, etc. and is soluble in dilute aqueous solutions of such substances. Chitosan is nontoxic and biodegradable, and it has found utility in numerous applications, including chromatography, drug delivery, and cosmetics.  
         [0015]     A porous chitosan resin may be formed by a phase inversion technique. This is accomplished by dissolving flaked or powdered chitosan in a suitable solvent, such as aqueous acid, and then coacervating in a solution of aqueous base to form water swollen chitosan gel beads. The beads may be cross-linked using glutaraldehyde, and separately with glyoxal, to improve the mechanical strength and reduce the solubility of the beads. The wet beads are then freeze dried to yield a porous cross-linked resin. Drying may also be accomplished by vacuum or air drying.  
         [0016]     A porous resin may also be prepared using a thermally induced phase separation technique. This is accomplished by dissolving flaked or powdered chitosan in a suitable solvent, such as aqueous acetic acid, and then adding the solution to a non-solvent, such as methanol, and cooling the resulting solution below the freezing point of the chitosan solution which yields frozen beads. These beads may then be neutralized with a base and cross-linked with glutaraldehyde and separately with glyoxal to modify the final properties of the chitosan resin. The resulting beads may then be freeze dried to yield a porous cross-linked chitosan resin. Drying may also be accomplished by vacuum and by air drying.  
         [0017]     The cross-linked resins produced by both methods have a reduced number of reactive amino groups. The reduced number of reactive amino groups is a result of the cross-linking reaction with glutaraldehyde or glyoxal. It has been surprisingly discovered that the described invention, having a reduced number of reactive amino groups, is selective in removing hydrogen cyanide and formaldehyde from tobacco smoke. It has also been surprisingly found that the cross-linked chitosan resin having a reduced number of reactive amino groups exhibits greater selective removal activity than that associated with the prior art where a maximum number of reactive amino groups have been employed.  
         [0018]     The porous resin of the present invention may be incorporated into a cigarette in a variety of ways. The resin may be disposed between filter sections wherein these sections may be comprised of fibrous, filamentary and paper materials. The resin may also be dispersed throughout a filter tow. Alternatively, the resin may be placed within a filter bed in a filter section and the resin may be packed along the filter bed. The resin may also be incorporated into a part of the cigarette filter such as the tipping paper, a shaped paper insert, a plug, a space, or even a free-flow sleeve. Additionally, the resin may be incorporated into cigarette filter paper, attached to the tobacco rod with tipping paper or even incorporated within a cavity in the filter. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     Examples of the present invention are given below by way of illustration and not by way of limitation. These examples include two distinct methods of preparing chitosan beads as well as several distinct methods of cross-linking the chitosan beads. All of the following examples yield porous cross-linked chitosan resin beads having a reduced number of reactive amino groups.  
       EXAMPLES  
     Example I  
       [0020]     Porous chitosan resin was synthesized according to a phase inversion technique. This was accomplished by preparing a 7% chitosan solution by dissolving approximately 20 grams of chitosan flakes (practical grade) in 3.5% acetic acid. The mixture increased in viscosity and gelled upon the completion of the chitosan addition. Further dilution with acetic acid resulted in a solution having approximately 3% chitosan flake. This provided for a chitosan solution having a more manageable viscosity. The total amount of acetic acid used to dissolve the chitosan flake was approximately 665 milliliters. The solution was then filtered to separate any undissolved materials. This chitosan solution was then added dropwise to a precipitation bath of 2 molar sodium hydroxide to yield water swollen gel beads. The gel beads were then filtered and washed with deionized water until neutral, pH of the wash water being approximately 7.  
         [0021]     Heterogeneous cross-linking of the chitosan beads was then accomplished by suspending the beads for several hours in approximately 1 liter of 2.5% aqueous solution of glutaraldehyde. After cross-linking, the beads were then filtered and washed with warm deionized water to remove any excess glutaraldehyde. Subsequently, the beads were freeze dried which resulted in porous glutaraldehyde cross-linked chitosan resin beads. The BET surface area of the resin was measured to be approximately 120 m 2 /g. The beads were then milled and sieved to retain particles having approximately 16 to 70 mesh. A surface area analysis of the milled resin showed no appreciable change in surface area. The BET surface area of the sieved sample was measured to be approximately 117 m 2 /g.  
       Example II  
       [0022]     Porous chitosan resin was synthesized according to the phase inversion technique in Example 1. In this example the heterogeneous cross-linking of the chitosan beads was accomplished by suspending the beads for several hours in a 2.5% aqueous solution of glyoxal. After cross-linking, the beads were filtered and washed with warm deionized water to remove any excess glyoxal. The beads were then freeze dried which resulted in porous glyoxal cross-linked chitosan resin beads.  
       Example III  
       [0023]     Porous chitosan resin was prepared according to a thermally induced phase separation procedure. A 4% chitosan solution was prepared by dissolution of chitosan powder (Vansen Chemical; 92% deacetylation) in 3.5% acetic acid. A precipitation bath of sodium hydroxide (2 molar) in 20:80 methanol/water solution was prepared and cooled to 0° C. The chitosan solution was then added dropwise to the precipitation bath with moderate stirring. Precipitation of chitosan occurred shortly after addition of the solution to the precipitation bath. The precipitation bath having the chitosan precipitate was then allowed to return to room temperature. The resulting beads were filtered and washed with deionized water until the wash water became neutral, having a pH of approximately 7.  
         [0024]     Heterogeneous cross-linking of the chitosan beads was then accomplished by suspending approximately 396 grams of wet beads in approximately 1980 milliliters of 2.5% aqueous glutaraldehyde solution for several hours. After cross-linking, the beads were filtered and washed with both warm and cold deionized water to remove any excess glutaraldehyde. Subsequent freeze drying of the beads resulted in porous glutaraldehyde cross-linked chitosan resin beads. The beads were then milled and sieved to approximately 16 to 70 mesh. The BET surface area of the resin was measured to be approximately 210 m 2 /g.  
       Example IV  
       [0025]     Porous chitosan resin was prepared according to the thermally induced phase separation procedure in Example III. In this example, the heterogeneous cross-linking of the chitosan beads was accomplished by suspending approximately 261 grams of wet beads in approximately 1300 milliliters of 2.5% aqueous glyoxal solution for several hours. After cross-linking, the beads were filtered and washed with both warm and cold deionized water to remove any excess glyoxal. Subsequent freeze drying resulted in porous glyoxal cross-linked chitosan resin beads. The beads were then milled and sieved to approximately 16 to 70 mesh. The BET surface area of the cross-linked resin was measured to be approximately 145 m  2 /g.  
       Example V  
       [0026]     Porous chitosan resin was prepared according to the thermally induced phase separation procedure in Example III. In this example, the heterogeneous cross-linking of the chitosan beads was accomplished by suspending the beads in a solution of glutaraldehyde and ethanol for several hours. After cross-linking, the beads were filtered and washed with ethanol to remove any excess glutaraldehyde. Subsequent vacuum drying resulted in porous glutaraldehyde cross-linked chitosan resin beads.  
       Example VI  
       [0027]     Porous chitosan resin was prepared according to the thermally induced phase separation procedure in Example III. In this example, the heterogeneous cross-linking of the chitosan beads was accomplished by suspending the beads in a solution of glutaraldehyde and water for several hours. After cross-linking, the beads were filtered and washed with ethanol to remove any excess glutaraldehyde. Subsequent vacuum drying resulted in porous glutaraldehyde cross-linked chitosan resin beads.  
         [0028]     Even though these examples specify amounts or concentrations of materials used in making several embodiments of the present invention, a wide range of concentrations and amounts of materials may be used to practice the present invention. For example, the crosslinker solution may be in a range of concentration of about 0.1% to about 50%, the chitosan solution may be in a range of concentration of about 0.1% to about 20%, the acetic acid solution may be in a range of about 0.1% to about 10%, and the base solution may be in a range of about 1 to about 5 molar sodium hydroxide. Additionally, the range of hours for cross-linking reaction may be from about 1 hour to up to about 24 hours.  
       Examples of Use  
       [0029]     A cigarette typically contains two sections, a tobacco-containing portion sometimes referred to as the tobacco or cigarette rod, and a filter portion which may be referred to as the filter tipping. A cigarette sample with a cavity filter was prepared by removing the existing filter on a cigarette made by standard production techniques, and replacing with a filter tipping having a cellulose acetate section at the tobacco end of the filter and a cellulose acetate section at the mouth end of the filter leaving a middle cavity. Sample sets of semolina (an inert filler material), chitosan resin synthesized by phase inversion technique and cross-linked with glutaraldehyde (Ex. I), chitosan resin synthesized by the thermally induced phase separation procedure and cross-linked with glutaraldehyde (Ex. III), chitosan resin synthesized by the thermally induced phase separation procedure and cross-linked with glyoxal (Ex. IV), chitosan resin synthesized by the thermally induced phase separation procedure and cross-linked with glutaraldehyde in ethanol, washed with ethanol, and vacuum dried (Ex. V), and chitosan resin synthesized by the thermally induced phase separation procedure and cross-linked with glutaraldehyde in water, washed with ethanol, and vacuum dried (Ex. VI), were prepared using a 50 mg sample load in the middle cavity of the filter tipping. This loading was consistent for each sample to provide comparable results. Resin loading in a filter of the present invention may be in a range of about 10 mg to about 200 mg. Each sample was pressure drop selected to minimize smoke delivery variances.  
         [0030]     Several tests were conducted to determine the ability of the cigarette filter of the present invention to remove undesirable constituents from tobacco smoke as compared to conventional devices. The tests measured the amount of undesirable constituents removed from the mainstream smoke after the cigarette was fully smoked. The following data sets illustrate the performance achieved in the filtration of volatile constituents of tobacco smoke for each of the preferred embodiments as compared to the control material, semolina. Analytical results are reported on the vapor phase and whole smoke analyses as indicated in the following tables. Percent reduction refers to the difference, in %, between the amount of the analyte measured in the vapor phase or whole mainstream smoke of cigarettes having filter tipping containing semolina and chitosan resin.  
         [0031]     Vapor Phase Smoke Analysis for Chitosan Resin Prepared by Phase Inversion Technique [Ex. I] 
                                                 Percent Reduction (%)           Chitosan cross-linked with glutaraldehyde       Analyte   Ex. I                                Hydrogen Cyanide   49       Acetaldehyde   10       Acetonitrile   11       Acrolein   15       Propionaldehyde   11       Acetone   7       Methyl Ethyl Ketone +   16       Butyraldehyde       Crotonaldehyde   13                  
 
         [0032]     Whole Smoke Hydrogen Cyanide Analysis for Chitosan Resin Prepared by Phase Inversion Technique [Ex. I] 
                                                       Percent Reduction (%)               Chitosan cross-linked with glutaraldehyde           Analyte   Ex. I                           Hydrogen Cyanide   41                      
 
         [0033]     Whole Smoke Carbonyl Analysis for Chitosan Resin Prepared by Phase Inversion Technique [Ex. I] 
                                                             Percent Reduction (%)           Chitosan cross-linked with glutaraldehyde           Ex. I                                        Formaldehyde   36           Acetaldehyde   13           Acetone   5           Acrolein   11           Propionaldehyde   16           Crotonaldehyde   9           Butyraldehyde   17                      
 
         [0034]     Vapor Phase Smoke Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Exs. III-IV] 
                                                                           Percent Reduction (%)                Chitosan cross-linked   Chitosan cross-linked           with glutaraldehyde   with glyoxal           Ex. III   Ex IV                        Acetaldehyde   13   31       Acetone   21   30       Acetonitrile   18   26       Acrolein   29   36       Acrylonitrile   21   29       Crotonaldehyde   7   42       Hydrogen cyanide   60   45       Methyl ethyl   21   29       ketone       Propionaldehyde   23   36       i-Butyraldehyde   27   35       n-Butyraldehyde   27   40                  
 
         [0035]     Whole Smoke Hydrogen Cyanide Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Exs. III-IV] 
                                                                           Percent Reduction (%)                Chitosan cross-linked   Chitosan cross-linked           with glutaraldehyde   with glyoxal           Ex. III   Ex IV                        Hydrogen cyanide   54   29                  
 
         [0036]     Whole Smoke Carbonyl Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Exs. III-IV] 
                                                                           Percent Reduction (%)                Chitosan cross-linked   Chitosan cross-linked           with glutaraldehyde   with glyoxal           Ex. III   Ex IV                        Acetaldehyde   1   2       Acetone   5   0       Acrolein   10   3       Butyraldehyde   14   8       Crotonaldehyde   20   9       Formaldehyde   50   46       Propionaldehyde   17   19                  
 
         [0037]     Whole Smoke Trace Metals Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Exs. III-IV] 
                                                                                   Percent Reduction (%)                    Chitosan cross-linked   Chitosan cross-linked           with glutaraldehyde   with glyoxal           Ex. III   Ex IV                            Cadmium   32   38                      
 
         [0038]     Vapor Phase Smoke Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Ex. V] 
                                                         Percent Reduction (%)           Chitosan cross-linked with glutaraldehyde           Ex. V                                    Acetaldehyde   9       Acetone   6       Acetonitrile   3       Acrolein   13       Crotonaldehyde   7       Hydrogen Cyanide   36       Methyl Ethyl Ketone   6       Propionaldehyde   11       i-Butyraldehyde   9       n-Butyraldehyde   10                  
 
         [0039]     Whole Smoke Hydrogen Cyanide Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Ex. V] 
                                                             Percent Reduction (%)           Chitosan cross-linked with glutaraldehyde           Ex. V                                        Hydrogen Cyanide   27                      
 
         [0040]     Whole Smoke Carbonyl Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Ex. V] 
                                                             Percent Reduction (%)           Chitosan cross-linked with glutaraldehyde           Ex. V                                        Acetonitrile   3           Acetaldehyde   27           Acetone   24           Acrolein   32           Butyraldehyde   41           Crotonaldehyde   30           Formaldehyde   58           Propionaldehyde   33                      
 
         [0041]     Whole Smoke Trace Metals Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Ex. V] 
                                                             Percent Reduction (%)           Chitosan cross-linked with glutaraldehyde           Ex. V                                        Cadmium   38                      
 
         [0042]     Vapor Phase Smoke Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Ex. VI] 
                                                         Percent Reduction (%)           Chitosan cross-linked with glutaraldehyde           Ex. VI                                    Acetaldehyde   3       Acetone   4       Acrolein   9       Crotonaldehyde   11       Hydrogen Cyanide   30       Methyl Ethyl Ketone   11       Propionaldehyde   6       i-Butyraldehyde   7       n-Butyraldehyde   11                  
 
         [0043]     Whole Smoke Hydrogen Cyanide Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Ex. VI] 
                                                             Percent Reduction (%)           Chitosan cross-linked with glutaraldehyde           Ex. VI                                        Hydrogen Cyanide   30                      
 
         [0044]     Whole Smoke Carbonyl Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Ex. VI] 
                                                             Percent Reduction (%)           Chitosan cross-linked with glutaraldehyde           Ex. VI                                        Acetaldehyde   0           Acetone   0           Acrolein   0           Butanone   1           Butyraldehyde   14           Crotonaldehyde   36           Formaldehyde   37           Propionaldehyde   0                      
 
         [0045]     Whole Smoke Trace Metals Analysis for Chitosan Resin Prepared by Thermally Induced Phase Separation [Ex. VI] 
                                                             Percent Reduction (%)           Chitosan cross-linked with glutaraldehyde           Ex. VI                                        Cadmium   26                      
 
         [0046]     The data surprisingly showed the cross-linked chitosan resin described in this invention is selective in removing aldehydes and hydrogen cyanide in cigarette smoke compared to the inert semolina control. The glutaraldehyde cross-linked chitosan resin reduced the vapor phase delivery of hydrogen cyanide by 60% versus a control sample (Ex. III). In a separate test, non-crosslinked ground chitosan particles showed no effect on the vapor phase hydrogen cyanide delivery. The glutaraldehyde cross-linked chitosan resin also decreased whole smoke hydrogen cyanide delivery by 54%, and mainstream whole smoke formaldehyde delivery was decreased by 50% compared to the control sample (Ex. III).  
         [0047]     While the invention has been described with reference to preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the invention as defined by the claims appended hereto.