Patent Publication Number: US-7910054-B1

Title: Decontamination and/or cleaning of fragile materials

Description:
RELATED CASES 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 11/451,294 now U.S. Pat. No. 7,494,629 entitled “Decontamination System and Method of Decontamination,” filed on Jun. 12, 2006, which itself is a continuation-in-part of U.S. patent application Ser. No. 10/154,428, now abandoned entitled “Decontamination System and Method of Decontamination,” filed on May 23, 2002, and which claims priority from U.S. Provisional Patent Application No. 60/293,016, which was filed on May 23, 2001 for a “Decontamination System and Methods of Decontamination.” 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates generally to decontamination and/or cleaning, and more specifically to decontamination and/or cleaning of fragile materials, for example certain historic artifacts. 
     2. Background Information 
     Decontamination and/or cleaning of materials typically involves the application of a solvent along with substantial mechanical energy, for example, mechanical energy in the form of shear caused by a high pressure spray, a stirred or ultrasonic bath, mechanical scrubbing, or other techniques. The application of mechanical energy generally causes the removal of contaminates by convective mass transfer. 
     However, many conventional decontamination and/or cleaning techniques are unsuited for cleaning fragile materials, for example, delicate historic artifacts such as textiles, skins, papers, and other frail items. These types of historic artifacts are often mechanically fragile, and thus respond adversely to high pressure spraying, stirred or ultrasonic baths, mechanical scrubbing and other aggressive techniques. Similarly, such historic artifacts are often incompatible with many solvents, as the solvents may remove, in addition to the undesired contaminates, desired pigments, dyes, inks, paints, stains, and/or other types of substances present on the artifact. Due to the typically high monetary and cultural value of historic artifacts, even very minor damage due to decontamination and/or cleaning is generally deemed unacceptable. 
     Yet the need to decontaminate and/or clean fragile materials, such as delicate historic artifacts, still exists despite the challenges the process presents. In addition to cleaning rather innocuous contaminates from artifacts for largely aesthetic reasons, decontamination and/or cleaning may be needed to remove toxic contaminates that are potentially harmful to people handling the artifacts. Some historic artifacts are contaminated from the environment in which they were discovered or historically maintained. More often, historic artifacts have been unintentionally contaminated by museum personnel or others, who applied toxic chemicals to the artifacts in preservation efforts. 
     In the nineteenth and early twentieth century many historic artifacts in museum collections were treated with a variety of pesticide, fungicides, and other preservative agents. For example, during the ninetieth and early twentieth centuries tobacco, camphor, strychnine, carbolic acid, sulfur, mercuric chloride, thymol, naphthalene, and several forms of arsenic were often used for preservation. In the later half of the twentieth century other types of chemicals were often used, including various organochlorides (such as DDT and lindane), organophosphates (such as malathion), and organometallic compounds (such as methyl mercury acetate and or triethyl arsine). These chemicals were often liberally brushed, sprayed, and/or sprinkled onto the surfaces of the historic artifacts. Despite the passage of time, many historic artifacts in museum collections are still highly contaminated with toxic residues from these chemicals. Prolonged exposure to the artifacts may cause any of a variety of maladies to exposed persons. This hazard hinders the work of museum personnel and researchers, who need to handle the artifacts to create exhibits or to study the artifacts. Similarly, this hazard inhibits the return of some historic artifacts to native peoples who may have legal rights to the artifacts. 
     Accordingly, there is a need for techniques to decontaminate and/or clean fragile materials, such as delicate historic artifacts, that address their special needs, while effectively decontaminating and/or cleaning the materials. 
     SUMMARY 
     A fragile material, such as a delicate historic artifact, may be decontaminated and/or cleaned by novel diffusion cleaning and/or evaporative cleaning techniques. 
     In one embodiment, diffusion cleaning is conducted by first wetting a piece of activated carbon fabric with a solvent for the contaminates. The solvent used to wet the activated carbon fabric is preferably chosen to be compatible with the fragile material, such that contaminates to be removed are soluble in the solvent, yet pigments, dyes, inks, paints, stains, and/or other types of substances desirably present on the fragile material are not soluble in the solvent, and thus not removed. Depending on the particular application, the contaminates may be rather innocuous substances whose removal is desired for largely aesthetic reasons and/or more toxic substances, for example pesticides, fungicides, and other preservative agents, that that are potentially harmful to people handling the artifacts. 
     The wetted activated carbon fabric is brought into contact with the surface of the fragile material in a substantially vapor-tight environment. In some configurations, a weight is applied to the upper face (i.e., the face not contacting the fragile material) of the activated carbon fabric, to promote full contact between the fabric and the fragile material. The solvent dissolves the contaminates present on the surface of the fragile material. Thereafter, the contaminates molecularly diffuse in the solvent and are thereafter adsorbed by the activated carbon fabric, with operates as an adsorptive blotter. The process of molecular diffusion and adsorption typically requires extended periods of time, in some cases on the order of 24 hours to 120 hours. Adsorption into the activated carbon fabric substantially depletes the contaminates (or at least a portion of the contaminates to be removed in a current round of diffusion cleaning) from the surface of the fragile material. The now contaminated activated carbon fabric is removed and any remaining solvent present on the surface of, or adsorbed into, the material is allowed to evaporate. 
     Further, in some embodiments, evaporative cleaning may be employed in addition to, or rather than, diffusion cleaning. Evaporative cleaning may be conducted by maintaining solvent-wetted activated carbon fabric (or other type of fabric) in contact with the fragile material while evaporation takes place. At least the upper face of the activated carbon fabric (or other type of fabric) is exposed to the surrounding environment. As the solvent evaporates from the upper face of the activated carbon fabric (or other type of fabric), a substantial portion of the contaminates migrate from the surface of the fragile material into the activated carbon fabric (or other type of fabric), where they become captured and contained. After the solvent has substantially fully evaporated, the now contaminated activated carbon fabric (or other type of fabric) is removed. In some embodiments, a weight is applied to some portion of the upper face of the activated carbon fabric (or other type of fabric), to promote contact with the material. 
     As discussed below a variety of modifications and additions may be made to these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description below refers to the accompanying drawings, of which: 
         FIG. 1  is a flow diagram showing an example sequence of steps for decontaminating and/or cleaning the surface of a fragile material, such as a delicate historic artifact, utilizing diffusion cleaning; 
         FIG. 2  is a schematic diagram of an example arrangement for diffusion cleaning of the surface of a fragile material; 
         FIGS. 3   a - 3   h  are schematic diagrams of an example progression of diffusion cleaning of a porous surface of a fragile material; 
         FIG. 4  is a flow diagram showing an example sequence of steps for decontaminating and/or cleaning the surface of a fragile material, such as a delicate historic artifact, utilizing evaporative cleaning; and 
         FIG. 5  is a schematic diagram of an example arrangement for evaporative cleaning of the surface of a fragile material. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
       FIG. 1  is a flow diagram  100  showing an example sequence of steps for decontaminating and/or cleaning the surface of a fragile material, such as a delicate historic artifact, utilizing diffusion cleaning.  FIG. 2  depicts an example arrangement  200  for diffusion cleaning of the surface of a fragile material  220  that may be used in performing the steps shown in  FIG. 1 . 
     At step  110 , a piece of activated carbon fabric  210  sufficiently sized to cover a piece of fragile material  220  is wetted with a solvent. Activated carbon fabric  210  (i.e., activated carbon woven, bonded or otherwise integrated into a textile form) is commercially available from a number of vendors, for example Charcoal Cloth International Ltd., which markets different such fabrics under the trade name Zorflex®. The designations and properties of several representative Zorflex® activated carbon fabrics are given in the following table: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Properties of Zorflex ® Activated Carbon Fabrics 
               
            
           
           
               
               
               
               
               
            
               
                 Fabric Designation 
                 FM 10 
                 FM 70 
                 FM 100 
                 FM 50K 
               
               
                   
               
               
                 Construction 
                 1/1 plain 
                 Compound 
                 1/1 double 
                 Double jersey 
               
               
                   
                 weave 
                 Weave 
                 weave 
                 (knit) 
               
               
                 Surface Density, g/m 2   
                 120 
                 190 
                 240 
                 130 
               
               
                 Tensile Strength,, kg/cm 
                   
                   
                   
                   
               
               
                 Warp 
                 1.0 
                 2.5 
                 2.0 
                 0.7 
               
               
                 Waft 
                 1.5 
                 2.0 
                 2.0 
                 0.8 
               
               
                 Ethyl Acetate Uptake,  
                   
                   
                   
                   
               
               
                 wt-% 
                   
                   
                   
                   
               
               
                 min 
                 30 
                 30 
                 30 
                 30 
               
               
                 max 
                 40 
                 40 
                 40 
                 40 
               
               
                 Air Permeability (*) 
                 130 
                 75 
                 75 
                 75 
               
               
                 Thickness, mm 
                 0.5 
                 0.8 
                 1.0 
                 0.4 
               
               
                   
               
               
                 (*) cm 3 /cm 2 /sec at 10 mm water gauge 
               
            
           
         
       
     
     It is expressly contemplated that any of a wide variety of activated carbon fabrics may be employed, and, as such, the techniques described herein are in no way limited to this the specific activated carbon fabrics enumerated in Table 1. 
     Further, in some embodiments a combination of two or more fabrics may be employed, with such fabrics laminated, bonded or otherwise integrated together. For example, in one embodiment, a laminate of Zorflex® FM 50K activated carbon fabric and Zorflex® FM 100 activated carbon fabric may be employed. Similarly, in another embodiment, a laminate of a Zorflex® activate carbon fabric and a non-adsorptive facing fabric may be employed. Accordingly, when the term “activated carbon fabric” is used herein the term should be interpreted broadly to encompass many different fabrics and/or combinations of fabrics. 
     The solvent used to wet the activated carbon fabric  210  is preferably chosen to be compatible with the fragile material, such that contaminates  230  to be removed are soluble in the solvent, yet desired pigments, dyes, inks, paints, stains, and/or other types of substances present on the material are not soluble in the solvent. Similarly, the solvent is preferably chosen as one that does not cause physical damage to the structure of the material, for example, does not cause the material to become brittle, wrinkled, or otherwise adversely affected. In one embodiment, the solvent may be 3M™ Novec™ Engineered Fluid HFE-7200 otherwise known as ethoxy-nonafluorobutane (C 4 F 9 OC 2 H 5 ) (hereinafter referred to as “HFE-7200”), commercially available from 3M Corp. HFE-7200 is typically compatible with a wide variety of substances that may be found in historic artifacts, yet easily dissolves many toxic contaminates, such as malathion and other organophosphate pesticides, as well as methyl mercury acetate, triethyl arsine, and other organometallic compounds. In alternate embodiments, a variety of other solvents may be employed, for example Novec™ 3M™ Engineered Fluid HFE-7100 otherwise known as methoxy-nonafluorobutane (C 4 F 9 OCH 3 ) (hereinafter referred to as “HFE-7100”), commercially available from 3M Corp., or any of a variety of other solvents appropriate for the application. 
     At step  120 , the now wetted activated carbon fabric  210  is brought into contact with the surface of the fragile material  220  in a substantially vapor-tight environment  240 . In some cases, additional solvent may applied directly to the fragile material  220 . 
     The vapor-tight environment  240  may be achieved in a number of ways. For example, the vapor-tight environment  240  may be a sealed plastic bag or other container that is substantially air-tight. Alternately, the activated carbon fabric  210  may be covered with a vapor barrier (or the activated carbon fabric  210  may have an integrated vapor barrier) to create a substantially vapor-tight environment  240  between a solid surface on which the fragile material is resting, such as a table top, and the vapor barrier. 
     In some embodiments, a weight  250 , for example, a metal plate or other object, is applied to the upper face (i.e., the face not contacting the fragile material) of the activated carbon fabric  210 , to promote full contact of the fabric with the fragile material  220 , thereby minimizing air gaps between the two. Alternately, contact may be promoted by pressure applied by a device, for example, a clip or arm (not shown), that holds the activated carbon fabric  210  in contact with the surface of the fragile material  220 . 
     At step  130 , the solvent dissolves the contaminates  230  present on the surface of the fragile material  220 . As discussed above, depending on the particular application, the contaminates  230  may be rather innocuous substances whose removal is desired for largely aesthetic reasons and/or more toxic substances, for example pesticides, fungicides, and other preservative agents, that are potentially harmful to people handling the artifacts. At step  140 , the contaminates  230  molecularly diffuse in the solvent. At step  150 , the contaminates  230  are adsorbed, by the activated carbon fabric  210 , with operates as an adsorptive blotter. The process of molecular diffusion and adsorption in steps  140  and  150  typically requires extended periods of time, during which the molecules of the contaminates  230  slowly make their way through the solvent. The exact period of time required depends on the nature of the fragile material  220 , the particular contaminates  230  present, the solvent, the environment, and a variety of other factors. Accordingly, while in some embodiments the time period may be on the order of 24 hours to 120 hour, a variety of other time periods are expressly contemplated. 
     Further, in some cases during the extended period of time the activated carbon fabric  210  and/or the surface of the fragile material  220  may be re-wetted with solvent. Re-wetting is desirable should the solvent appear to evaporate significantly despite the substantially vapor-tight environment  240 , leaving the activated carbon fabric  210  and/or the surface of the fragile material  220  dry. 
     At step  160 , adsorption into the activated carbon fabric  210  substantially depletes the contaminates (or at least a portion of the contaminates to be removed in a current round of diffusion cleaning) from the surface of the fragile material  220 . Through adsorption the activated carbon fabric  210  captures and contains the contaminates  230  as well as at least a portion of the solvent used in the decontamination and/or cleaning process. At step  170 , the now contaminated activated carbon fabric  210  is removed and disposed of, for example, by sending the contaminated fabric to an appropriate waste disposal facility. Any remaining solvent present on the surface of, or adsorbed into, the fragile material  220  is allowed to evaporate. The material  220  may be removed from the vapor-tight environment  240  and exposed to the surrounding environment, for example exposed to the free-moving air of a room, placed under a fume hood, or placed in some other space to promote evaporation. If additional decontamination and/or cleaning is desire, the above described sequence of steps  110 - 180  may be repeated. 
       FIGS. 3   a - 3   h  are schematic diagrams of an example progression of diffusion cleaning of a porous surface  310  of a fragile material. The progression provides a more specific example of an application of the techniques described above in reference to  FIG. 1 . In  FIG. 3   a , a porous surface  310  includes a plurality of pores  320 . Various contaminates  230 , such as organophosphates, may be disposed in the pores  320 . As shown in  FIG. 3   b , an activated carbon fabric  210  may be wetted with a solvent, for example HFE-7200. In some configurations, a vapor barrier  330  may be affixed or integrated into the activated carbon fabric, to substantially prevent evaporation of the solvent. As shown in  FIG. 3   c , the activated carbon fabric  210  is contacted with the porous surface  310 . In  FIG. 3   d , the solvent displaces air in the pores of the porous surface  310 , and dissolves the contaminates  230 . As shown in  FIG. 3   e , the contaminates diffuse over time in the solvent, contaminating the solvent while spreading through the porous surface  310 . The contaminates in the solvent are adsorbed over time into the activated carbon fabric  210 , as depicted in  FIG. 3   f .  FIG. 3   g  shows that the concentration of contaminates in the pores of the porous surface  310  is reduced as contaminates are adsorbed into the activated carbon fabric  210 . In  FIG. 3   h , after the adsorption of the contaminates has substantially depleted the contaminates from the pores, the activated carbon fabric  210  may be removed and disposed of in an appropriate manner. Any solvent still present in the now substantially clean pores  320  may be allowed to evaporate, thus completing the progression. 
     While the above described diffusion cleaning techniques may be advantageously employed to decontaminate and/or clean the surface of a fragile material, in certain instances evaporative cleaning may be employed in addition to, or rather than, diffusion cleaning. For example, a preferred solvent that is highly compatible with a certain fragile material may contain components that interfere with the adsorption of some contaminates into activated carbon fabric, and thus may hinder the removal of some contaminates by diffusion cleaning. Accordingly, it may be desirable to first conduct a diffusion cleaning session and subsequently perform an evaporative cleaning session. For example, after step  160  of  FIG. 1 , where adsorption has depleted at least some of the contaminates  230  from the surface of the fragile material  220 , evaporative cleaning may be performed. Alternately, it may be desirable to only conduct an evaporative cleaning session in certain cases. 
       FIG. 4  is a flow diagram  400  showing an example sequence of steps for decontaminating and/or cleaning the surface of a fragile material, such as a delicate historic artifact, utilizing evaporative cleaning.  FIG. 5  is an example arrangement  500  for evaporative cleaning of the surface of a fragile material  220  that may be used in performing the steps shown in  FIG. 4 . 
     At step  410 , a solvent-wetted activated carbon fabric (or other type of fabric, for example a gauze sponge)  510  is maintained in contact with the fragile material  220 . In some cases, additional solvent may applied directly to the fragile material  220 . The activated carbon fabric (or other type of fabric)  510  is wetted with a solvent in which the contaminates are soluble, yet which is compatible with the material to be decontaminated and/or cleaned. For example, the solvent may be HFE-7200, HFE-7100, or another suitable solvent. In some embodiments, a weight (not shown) is applied to some portion of the upper face of the activated carbon fabric (or other type of fabric)  510 , to promote full contact with the fragile material  220 . Alternately, contact may be promoted by pressure applied by a device, for example a clip or arm. Care should be taken, however, to ensure that any weight or device does not impede evaporation where decontamination and/or cleaning is desired. 
     At step  420 , the solvent dissolves contaminates  230  present on the surface of the fragile material  220 . At step  430 , at least the upper face (i.e., the face not contacting the fragile material) of the activated carbon fabric (or other type of fabric)  510  is exposed to the surrounding environment, for example, exposed to the free-moving air of a room, placed under a fume hood, or placed in some other space to promote evaporation. At step  440 , the solvent evaporates from the upper face of the activated carbon fabric (or other type of fabric)  510 . At step  550 , as the solvent evaporates, a substantial portion of the contaminates  230  migrate from the surface of the material  220  into the activated carbon fabric (or other type of fabric)  510 , where they become captured and contained. At step  560 , after the solvent has substantially fully evaporated, the now contaminated activated carbon fabric (or other type of fabric)  510  is removed and disposed of, for example, sent to an appropriate waste disposal facility. If additional decontamination and/or cleaning is desired, the sequence of steps  510 - 560  may be repeated. 
     The foregoing has been a detailed description of several embodiments. Further modifications and additions may be made without departing from the disclosure&#39;s intended spirit and scope. For example, while the above descriptions discuss fragile materials, for example delicate historic artifacts, the techniques disclosed herein are in no way limited to use only with fragile materials. They alternately may be applied to a variety of robust, sturdy, or otherwise non-fragile materials. Further, the techniques described above need not be applied in isolation, and it is expressly contemplated that they may be used in conjunction with other decontamination and/or cleaning techniques, as part of a multi-stage decontamination and/or cleaning process. Accordingly, it should be remembered that the above descriptions are meant to be taken only by way of example, and the invention is not restricted to any one particular embodiment, configuration or implementation discussed above. Rather, the invention is defined by the following claims.