Abstract:
Disclosed are filter materials which are effective for the selective removal of gaseous aldehydes from a cigarette smoke stream. The filter materials comprise a tobacco smoke filter comprising a filter support material and an alkyl acetoacetate that is capable of reacting with and removing aldehydes present in tobacco smoke. Also disclosed are a method of removing gaseous aldehydes from tobacco smoke by contacting tobacco smoke with a filter comprising a filter support material and an alkyl acetoacetate and a smoking article such as a cigarette comprising the tobacco smoke filter described herein.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to filter materials which are effective for the selective removal of gaseous aldehydes from a cigarette smoke stream. More specifically, this invention pertains to a tobacco smoke filter comprising a filter support material and an alkyl acetoacetate that is capable of reacting with and removing aldehydes present in tobacco smoke. Another embodiment of the present invention pertains to a method of removing gaseous aldehydes from tobacco smoke by contacting tobacco smoke with a filter comprising a filter support material and an alkyl acetoacetate. 
       BACKGROUND OF THE INVENTION 
       [0002]    Tobacco smoke resulting from tobacco combustion contains numerous gaseous molecules and particulates. These gaseous molecules are responsible for both the pleasure and the health risks experienced by users of tobacco products. Among the many molecules produced by tobacco combustion or vaporization are nicotine, carbon monoxide, ammonia, aldehydes such as formaldehyde, acetaldehyde, and acrolein, and compounds from any added flavoring materials. Tobacco smoke filters are utilized to remove undesirable gases and particulate materials from tobacco smoke while retaining the flavor and taste essential for the enjoyment of smoking. The selective removal of gaseous molecules from tobacco smoke stream therefore is required for an active filtration material to be acceptable. Active materials such as activated carbon, silica gel, alumina, and zeolites commonly used for the removal of gaseous contaminates are not particularly suitable for this purpose. Although such materials may remove undesirable gaseous molecules, they also adsorb molecules considered necessary for acceptable tobacco smoke flavor. Moreover, the adsorption by these porous materials is not considered effective since the molecules are only physically bound to the surface and not chemically reacted. In addition to selective adsorption and chemical adsorption, other desired properties for active materials to be used in a tobacco smoke filter are light weight, low cost, stable in air, low pressure drop, safe to handle, and ease of fabrication. 
         [0003]    U.S. Pat. No. 6,595,218 discloses a tobacco smoke filter comprising a reagent consisting essentially of aminoethylaminopropylsilyl silica gel or aminoethylamino-ethylamino-propylsilyl silica gel wherein the reagent chemically reacts with and removes gaseous components such as aldehydes of a tobacco smoke stream. U.S. Pat. No. 6,481,442 discloses a smoking article comprising a wrapper and a selective filter element having at least one carrier and a polyaniline having a plurality of moieties selected from the group consisting of an amino group, an imino group, a hydrazide group, a hydrazone group, a semicarbazide group and combinations thereof capable of a nucleophilic attack of carbonyl-containing combustion products of the smoking article. Optionally, a spacer having a composition of —CO—[CH 2 ] n —CO—, with n having a value from 1 to 4 or greater than 4, may be used to attach said active moieties containing amino groups to the carrier. The spacer is used for the purpose of extending out the chemically active amino moieties from the carrier. 
         [0004]    U.S. Pat. No. 4,182,743 discloses a gas-permeable substrate, particularly adapted for the selective removal of aldehydes from gases, comprising a granular containing concentrated hydrogen peroxide, water and a hydrophilic stabilizer for said hydrogen peroxide. U.S. Pat. No. 4,753,250 discloses a process for producing cigarette filters comprising a compound containing L-ascorbic acid to react with and remove aldehydes. U.S. Pat. Re. 28,858 discloses an improved tobacco smoke filter material comprising a porous particulate carrier impregnated with polyethylene-imine for the removal of volatile smoke acids and aldehydes. U.S. Pat. No. 5,009,239 also describes the removal of aldehydes using polyethyleneimine as the active component in a cigarette filter. For the same purpose, an aminobenzene acid salt is used in U.S. Pat. No. 5,603,927 and an organic salt of mercapto-alkane-sulphonate is used in U.S. Pat. No. 4,532,947. U.S. Pat. No. 5,206,204 discloses an adsorbent for lower aldehydes which comprises a saturated cyclic secondary amine and a halogenide of an alkali metal or alkaline earth metal supported on a porous carrier. 
         [0005]    Various technologies have been cited in the prior art for the purpose of removing airborne formaldehyde. U.S. Pat. No. 5,352,274 discloses air filtration utilizing a plurality of corrugated base sheets which are stacked or nestled and which have entrapped carbon dust for adsorption of impurities such as formaldehyde, acetaldehyde, and acrolein. The corrugated structure provides very little pressure drop as the air passes through available channels and large, powerful fans are not necessary to move air therethrough. This technology provides a method to adsorb formaldehyde molecules physically but not by chemically reaction. U.S. Pat. No. 5,830,414 discloses an air cleaning filter comprising activated carbon fibers in the form of a web supporting at least one kind of chemical reagent selected from the group consisting of (a) an alkali agent selected from a hydroxide or carbonate of an alkali metal, (b) an acidifying agent selected from acid aluminum phosphate or phosphoric acid, and (c) an oxidizing agent composed of active manganese dioxide resulting from an alkali permanganate and an alkali iodate. U.S. Pat. No. 5,830,414 discloses the treatment of carbon fibers with an active small molecule such as a strong acid, strong base, or strong oxidizing agent. These chemicals can only be used to treat fibers having high chemical resistances such as activated carbon fibers. Further, fibers thus treated are potentially hazardous to handle. 
         [0006]    U.S. Pat. No. 4,517,111 provides a composition comprising a permanganate salt adsorbed onto a solid alkaline support useful for irreversiblly removing formaldehyde from air. The composition can be employed in molded, pellet, particle, or powder form as, for example, in a respirator filter cartridge. The application of this technology is limited to the solid forms as stated. U.S. Pat. No. 4,892,719 discloses a method of reducing the indoor air concentration of aldehydes by coating a porous support filter with a water soluble polymeric amine such as polyethyleneimine, polyallylamine, or polyvinylamine. The coating is further plasticized with a low volatile liquid such as glycerol in order to extend the useful life of the coating. This technology has a deficiency in that the reactive component, i.e., an amine, may be consumed by carbon dioxide present in air. The description of the reaction of carbon dioxide with amine adsorbents may be found in  Int. J. Environmental Technology and Management , Vol. 4, Nos 1/2, 2004, p. 82. Furthermore, the reaction product of said polyamine and formaldehyde has the same end group as has urea-formaldehyde and, as a result, over time will undergo the same degradation to release formaldehyde. 
         [0007]    It is known that compounds having active methylene groups are capable of reacting with formaldehyde. JP 57,032,729 described a method for removal of residual formaldehyde in microcapsule dispersion by adding a compound having an active methylene group such as methyl acetoacetate, ethyl acetoacetate, or diethyl malonate. Active methylene compounds also have been used as formaldehyde scavengers in the textile industry to reduce the amount of formaldehyde released from durable press-treated fabrics as described in  Textile Chemist and Colorist , Vol. 16, No. 12, p. 33, December 1984 (published by the American Association of Textile Chemists and Colorists). Such a compound is added to finishing formulations of the fabrics to react with formaldehyde released from urea-formaldehyde resins used for cellulose crosslinking. Dimethyl 1,3-acetonedicarboxylate having two highly activated methylene groups was found to be most effective. 
         [0008]    U.S. Pat. No. 5,160,503 discloses a water-soluble blend composition for scavenging formaldehyde in textile fabrics. The composition consists of a substituted or unsubstituted polyhydric alcohol such as diethylene glycol and an active methylene compound selected from the group consisting of dialkyl malonates and alkyl acetoacetates. U.S. Pat. Nos. 5,194,674; 5,268,502; and 5,446,195 disclose water-soluble compositions prepared by reacting a glycol or polyether with an acetoacetate or malonate that may be used as formaldehyde scavengers in the fabric finishing formulations. Again, in these references, liquid reaction media are required for the effective removal of formaldehyde. Formaldehyde scavengers containing active methylene hydrogens also may be added to coating compositions containing urea/formaldehyde or melamine/formaldehyde resin to reduce formaldehyde concentration. U.S. Pat. No. 5,795,933 discloses a waterborne coating compositions comprising a formaldehyde-containing resin and a formaldehyde scavenger containing active methylene hydrogen with a pKa of about 5 to 13. 
         [0009]    The reaction of acetoacetate-functional polymers with formaldehyde also has been disclosed in the prior art. JP 58,059,263 describes a curable polymer composition consisting of a water soluble polymer, a water soluble polymer having an acetoacetate group such as acetoacetylated polyvinyl alcohol resin, and a crosslinking agent capable of reacting with the acetoacetate group such as formaldehyde or glyoxal. U.S. Pat. No. 5,767,199 discloses an air-curable composition containing an acetoacetate functional polymer and an end-blocked polyformaldehyde chain. According to the patent, the composition is stable to reaction until the formaldehyde is released from the polyformaldehyde chain. These references relate to either the utilization of active methylene compounds to remove formaldehyde in a liquid mixture or to suppress formaldehyde emission by mixing a formaldehyde scavenger with formaldehyde-containing resins. None of the references pertain to air filter applications. 
         [0010]    U.S. Pat. No. 3,227,164 describes a tobacco smoke filter comprising a plasticizer bonding agent selected from the group consisting of the alkylene glycol, polyalkylene glycol, and glycerol esters of acetoacetic acid. This reference discloses that such a tobacco smoke filter is effective in removing phenol and other undesirable toxic metal ions such as nickel, cobalt, etc.; however, it does not disclose aldehydes removal. 
         [0011]    The preparation of cellulose esters having acetoacetate functionality is known. U.S. Pat. No. 2,521,897 discloses the preparation of esters of acetoacetic acid by reacting a partially esterified cellulose with diketene in the presence of a tertiary organic base. U.S. Pat. No. 5,292,877 discloses water soluble cellulose acetoacetates prepared by contacting a cellulose material with diketene, an alkyl acetoacetate, 2,2,6-trimethyl-4H-1,3-dioxin-4-one or a mixture thereof in a solvent system comprising lithium chloride plus a carboxamide. U.S. Pat. No. 5,770,726 discloses a process for preparing a cellulose acetoacetate by contacting cellulose in a carboxylic acid diluent with an acetylating compound, an acetoacetylating compound selected from the group consisting of diketene, an alkyl acetoacetate, and 2,2,6-trimethyl-4H-1,3-dioxin-4-one, and a mineral acid catalyst. In these two references, the reactions are carried out in a homogeneous mixture by dissolving cellulose pulp in an organic solvent. GB Patent 940,954 discloses an improved dyeing process for cellulosic fibrous materials by pre-treating the fibers with diketene before dyeing. The patent, however, does not disclose or characterize the product composition after the treatment with diketene. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    We have found that gaseous aldehydes such as formaldehyde, acetaldehyde and acrolein may be removed selectively from tobacco smoke by contacting tobacco smoke containing one or more aldehydes with a filter element comprising a filter support material and an alkyl acetoacetate. The filter element permanently removes aldehydes from the tobacco smoke. Thus, one embodiment of the present invention is a filter element comprising a filter support material and an alkyl acetoacetate. A second embodiment is a method of removing a gaseous aldehyde from tobacco smoke by contacting tobacco smoke containing one or more aldehydes with a filter element comprising a filter support material and an alkyl acetoacetate. A third embodiment is the invention is a smoking article comprising a first section comprising burnable tobacco and a second filter plug section comprising a filter element comprising a filter support material and an alkyl acetoacetate. The smoking article typically is in the form of a generally cylindrical, paper-wrapped tube containing tobacco and the filter element. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Examples of gaseous aldehydes which may be removed in accordance with the present invention include formaldehyde, acetaldehyde, acrolein, propanal, butanal, crotonaldehyde and other gaseous aldehydes present in a tobacco smoke stream. Although the present invention pertains primarily to the removal of aldehydes from the tobacco smoke stream, the removal of other carbonyl compounds such as ketones capable of reacting with the acetoacetate residues is within the scope of the invention. 
         [0014]    The filter support material may be a fibrous or a porous substrate suitable for smoke filtration. Examples of such material include materials fabricated from cotton, cellulose esters, woven and non-woven fabrics, paper, glass, carbon, ceramics, metals and synthetic polymeric materials. Examples of porous substrates include sheets, pleated, fluted and corrugated sheets, tubes, membranes, sieves, and screens. The filter support material preferably is fibrous such as a bundle of fibers. Examples of fibrous materials include fibers of cellulose, cellulose esters, rayon, lyocell, cotton, wool, glass, carbon, polyesters, polyamides, acrylic, modacrylic, polypropylene, and polyethylene. Such fibrous materials may be produced by conventional techniques such as solution spinning, melt spinning and melt blowing. The fiber substrates may have various cross-section shapes and thicknesses, e.g., having a denier per filament of about 1 to 20, more typically about 2 to 8. A filter element in a tobacco smoke filter may be any component that is used to construct a tobacco smoke filter. The filter support material of tobacco smoke filter elements preferably is cellulose acetate fiber tow, a crimped bundle of fibers having a denier per filament of about 2 to 8 and a total denier of about 15,000 to 60,000. The cellulose acetate from which the cellulose acetate fibers and tow are prepared have an acetyl degree of substitution of about 2.3 to 2.5 per anhydroglucose unit and a viscosity of about 15 to 60 seconds, as measured according to ASTM D 1343-69. The cellulose acetate fibers typically are produced by a dry spinning process such as those disclosed in U.S. Pat. Nos. 2,829,027 and 2,838,364. The cellulose acetate fibers normally are dry spun from a cellulose acetate spinning solution comprising a solution of cellulose acetate in acetone. The cellulose acetate fibers may contain other optional components such as titanium dioxide. The dry spinning process of producing the cellulose acetate fibers normally produces fibers having an average denier per filament (dpf) of about 2 to 8, although fibers having an average denier per filament of 1 to 20 dpf may be made. The spinning process can produce various fiber cross sections, for example a triangular hole is used to form the Y cross section, which is the most common cross section. The cellulose acetate resins and processes for preparing fibers therefrom are described in U.S. Pat. Nos. 5,612,230 and 6,184,373 and the publications cited therein. 
         [0015]    Tobacco smoke filters may be prepared by collecting a large number of fibers or filaments into a bundle of fibers typically referred to as tow. The tow then is crimped to improve physical filtration properties. The crimped tow is bloomed according to known techniques to produce a voluminous bundle of fibers which are passed through a funnel-shaped device to reduce the diameter of the bloomed tow to the size of a tobacco smoke filter, e.g., to about 7.8 mm. The tobacco smoke filters typically include one or more of fiber-to-fiber bonding agents such as triacetin, cellulose based filter material such as paper, thermoplastic-based fibers, plugwrap, fiber-to-plugwrap adhesive, plugwrap hot-melt adhesive, and powder additives such as activated carbon, silica gel, alumina, and zeolite. 
         [0016]    The filter elements of the present invention include or contain an alkyl acetoacetate, i.e., an alkyl ester of acetoacetic acid wherein the alkyl group contains up to about 20 carbon atoms, preferably about 4 to 12 carbon atoms. Examples of such alkyl acetoacetate esters include ethyl acetoacetate, methyl acetoacetate, isobutyl acetoacetate, isopropyl acetoacetate, n-propyl acetoacetate, n-butyl acetoacetate, t-butyl acetoacetate, and other alkyl acetoacetates. A less volatile ester such as t-butyl acetoacetate is preferred. The alkyl acetoacetate may be coated or applied to the fibrous substrate using conventional techniques commonly used in the coating or textile industry. Examples of some common methods are spraying, brushing, spray drying, dip (immersion) coating, roll coating, curtain coating, rotary screen coating, air knife coating, and gap coating. The alkyl acetoacetate may be applied first to a substrate to form a coated substrate which can then be fabricated into a filter element. The coating also may be applied to the substrate component of a finished filter element. The alkyl acetoacetate may be dissolved or dispersed in an additive such as a plasticizer/bonding material typically used in the manufacture of tobacco smoke filters. The amount of alkyl acetoacetate present on the filter support material may range from about 1 to 30 weight percent, more typically from about 5 to 10 weight percent, based on the total weight of the filter element. 
         [0017]    The smoking article, e.g., a cigarette, of the present invention comprises a first section comprising burnable tobacco and a second filter plug section comprising the filter element described above. The smoking article typically is cylindrical in shape having a diameter of about 7.8 mm and a length of about 84 to 120 mm. The tobacco and filter section normally are affixed by means of a paper wrap. 
       EXAMPLES 
       [0018]    The preparation of the filter elements of the present invention and the use thereof to adsorb formaldehyde are further illustrated by the following examples wherein all percentages are by weight unless specified otherwise. 
       Example 1 
     Preparation of t-Butyl Acetoacetate Tobacco Smoke Filters 
       [0019]    To illustrate the invention in a cigarette smoking environment, t-butyl acetoacetate (tBAA) was sprayed onto cellulose acetate filter tow by means of a compressed air spray gun (Preval spray gun from Precision Valve Corporation) at an addition level of approximately 10%. The filter tow consisted of cellulose acetate fibers or filaments having a dpf of 2.7, a total denier of 35,000 and a “Y” cross section. The filter tow had an average 20 crimps per inch and was hand bloomed before being sprayed. The sprayed tow was pulled into a straw, and then into a paper tube, to produce hand-make filter rods. The rods were cut into 21-mm length filter tips and sorted to an average pressure drop of 60-mm of water per tip. These tips were taped onto commercial 63-mm full-flavor tobacco columns using masking tape with dextrin-based glue used to prevent air leaks. 
       Comparative Example 1 
     Preparation of Tobacco Smoke Filters with Triacetin 
       [0020]    As an experimental control, cigarette filters were prepared as described in Example 1 but with the conventional fiber bonding agent, triacetin, sprayed onto the filter tow. The cigarettes were constructed and tested in an equivalent process, thus allowing a direct comparison. 
         [0021]    The table below summarizes the results of the smoke testing comparison of cigarettes from Example 1 and Comparative Example 1. The cigarettes were tested using an industry&#39;s standard smoking procedure (CORESTA No. 23) using a Borgwalt rotary smoking machine. The tobacco smoke vapor phase from 5 cigarettes for each example was captured in 100 ml of derivatization solution by bubbling through an impinger. The vapor phase is defined as the vapors that pass through the Cambridge pad. A Cambridge pad is a glass-fiber-based high-efficiency filter that is commonly used in the industry to capture the smoke produced by cigarettes. The derivatization solution was made with 5 grams of dinitrophenyl hydrazine (DNPH), 250 ml of diglyme, 1.8 ml of concentrated hydrochloric acid, and filled to volume with high purity acetonitrile in a 1-L volumetric flask. Aldehydes in the vapor phase were determined by injecting the derivatized vapor phase solution into a liquid chromatograph. A reverse phase LC column (Agilent Zorbax SB-C18, 4.6×100 mm, 3.5 um) was used to separate the aldehyde-DNPH adducts. UV/Vis absorbance at 365 nm was used to detect the chromatographic peaks. The results reported in Table 1 show that the tobacco smoke filters (TSF) treated with tBAA (Example 1) were found to effectively remove a significant amount (23-45%) of various aldehydes from the tobacco smoke as compared to those treated with the conventional fiber bonding agent, triacetin (Comparative Example 1-Example C-1). Table 1 shows the results from smoke testing five cigarettes per example. The results are reported as the average amount (in micrograms per cigarette) of aldehydes acetaldehyde, propanal, acrolein and butanal present in the vapors produced from the combustion of the tobacco and the percent of the amount of each aldehyde removed by the filter of Example 1. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Aldehyde Component 
                 Filter of 
                 Filter of 
                 Aldehyde 
               
               
                 of Tobacco Smoke 
                 Example C-1 
                 Example 1 
                 Removal 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Acetaldehyde, ug/cig. 
                 1015 
                 780 
                 23 
               
               
                 Propanal, ug/cig. 
                 86 
                 49 
                 43 
               
               
                 Acrolein, ug/cig. 
                 58 
                 32 
                 45 
               
               
                 Butanal, ug/cig. 
                 32 
                 18 
                 44 
               
               
                   
               
             
          
         
       
     
         [0022]    The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.