Document 1g50MGYaBYwDZXpbGJK3pnqxo

FILE NAME: National Lead (NATL) DATE: 1975 Dec 23 DOC#: NATL101 DOCUMENT DESCRIPTION: US Patent - Composition and Method for Inhibiting Asbestos Fiber Dust United States Patent [19] Smith et al. [in 3,928,060 [45] Dec. 23, 1975 [54] COMPOSITION AND METHOD FOR INHIBITING ASBESTOS FIBER DOST [75] Inventors: Malcolm Kent Smith, Mountainside; Robert Winslow White, Califon, both of N.J. [73] Assignee: N L Industries, Inc., Hightstown, N.J. [22] Filed: Aug. 13,1973 [21] Appl. No.: 387,919 [52] U.S. Cl....... 106/308 Q; 117/126 AQ; 106/309 [51] In tC l.2...............................................C 08J7/04 [58] Field of Search................ 106/308 Q, 309, 306; 117/126 AQ; 65/3 [56] 2,626,213 References Cited UNITED STATES PATENTS 1/1953 Novak.............................. 106/308 Q 2,668,785 2,882,177 2/1954 Jefferson...................... 117/126 AQ 4/1959 Newton............................ 106/308 Q Primary Examiner--Winston A. Douglas Assistant Examiner--J. V. Howard Attorney, Agent, or Firm--Darby & Darby [57] ABSTRACT The tendency of asbestos fibers to become airborne as particles under dusting conditions is inhibited by treat ing them with the ester of a polyhydroxy compound and a C, through C6 carboxylic acid or a derivative thereof. 18 Claims, No Drawings J,^*U ,V VU 1 performance criteria (e.g., thixotropic, thickening, COMPOSITION AND METHOD FOR INHIBITING coflocculating, softening, bulking, and viscosity con ASBESTOS FIBER DUST trol) which an asbestos ingredient is normally expected to provide in a given formulation. For example, one This invention relates to a method for inhibiting the 5 procedure which has been proposed for reducing the release of asbestos fibers into the atmosphere in the dusting level of chrysotile asbestos fibers involves treat form of dust. More specifically, the invention relates to ing the raw fibers with methyl acetyl ricinoleate or a method of treating asbestos fibers to control the dis ricinoleic acid. However, treatment of chrysotile asbes persion of released fibers into the atmosphere as dust tos fibers with either of these materials results in severe particles. Also, the invention relates to a coated asbes 10 lumping o f the product and virtually eliminates its utili- tos product. ity as a thixotropic agent or rheological additive in It has long been recognized that exposure to asbestos organic resins. fibers of sufficient intensity and long enough duration is It has now been unexpectedly discovered that the causally related to asbestosis, lung cancers, and meso ability of asbestos fibers to become airborne is greatly thelioma. 15 reduced by treating them with an anti-dusting agent Asbestos is a native magnesium calcium silicate and which is die ester of a polyhydroxy derivative of a is generally found in two different forms, chrysotile, or branched or straight chain C2through C6alkyne and a white asbestos and amphiboles (crocidolite), or blue Q through C6carboxylic acid or anhydride. The reac asbestos. Both varieties appear in compact form or in tion product may be generally described as a polyhy- silky fibers which are acid and heat resisting and may 20 droxy compound which has been partially esterified, be spun or woven. The term "asbestos" as used herein from approximately about 0 to about 80% with lower includes not only the preceding varieties, but also those aliphatic acids. Treatment of chrysotile, amosite, cro known as amosite, termolite, anthophyllite and actino- cidolite, tremolite, anthophyllite and actinolite asbes lite. tos fibers or particles with the ester reaction product of The fibrous or colloidal forms of asbestos especially 25 this invention provides a marked reduction in the abil chrysotile asbestos, are useful as viscosity control addi ity of the fibers to become airborne as dust particles tives, thixotropes, extenders and reinforcing agents in a which may be inhaled by humans. When compared broad range of plastisols and organosols which are in with untreated asbestos fibers, the asbestos fibers turn employed in adhesives, coatings, paints, and mas treated in accordance with this invention generally tics. Because of their geometry, chrysotile asbestos 30 show about a three to four-fold decrease in the number fibers are used to provide whisker reinforcement in of airborne particles released under dusting conditions. rigid and plasticized PVC, nylon molding materials and Furthermore, the special properties (i.e., viscosity con various other resin systems. Asbestos fibers are also trol, thixotropic, rheological, etc.) of the asbestos fi used in the manufacture of vinyl asbestos floor tile to bers of this invention are unaffected, hence, their utility provide dimensional stability and high brightness. 35 in those specialized applications for which asbestos In view of the undisputed grave consequences to fibers are usually employed is not diminished. humans from continued exposure to asbestos fibers, it It is therefore an object of this invention to provide a is essential that the exposure of individuals who must method for treating asbestos fibers to reduce or limit work with such materials be minimized to the greatest their ability to become airborne. extent possible. To this end, the Federal Occupational 40 Another aspect of this invention is to provide a Safety and Health Act of 1970 has been amended to method for reducing the dusting level of asbestos parti provide maximum permissible concentrations of asbes cles to comply with the Federal Occupational Safety tos fibers. The revision limits the occupational expo Hazard Act requirements. sure of an individual worker to an 8-hour time- Another aspect of the invention is the provision of weighted average (TWA) airborne concentration of 43 treated asbestos particles, including fibers, tendrils, asbestos dust not exceeding five fibers longer than fiver pellets and granules having reduced dusting levels as micrometers, per cubic centimeter of air. Commencing compared to their untreated counterparts. in 1974, the standard will become more stringent and the eight hour TWA co n cen tratio n of asbestos fibers Other objects and advantages of the present inven tion will become apparent from a consideration of the longer than five micrometers will not be allowed to 50 ensuing description. exceed two fibers per cubic centimeter of air. In view of Briefly stated, this invention involves treating asbes the critical importance of asbestos as a constituent in tos fibers on the order of about 1 to about 25 microme many different products, and the lack of inexpensive ters in length with an anti-dusting agent which is the substitutes, the art has been actively seeking a method ester of a polyhydroxy derivative of a branched or of inhibiting the release of asbestos particles and fibers 55 straight chain C2- C6alkyne and a Q through C6car into the air as dust. Typically, this release occurs during boxylic acid or anhydride. Generally, the polyhydroxy the handling or pouring of asbestos fibers incident to and acidic components are reacted in equimolar pro their incorporation in a finished chemical product, e.g., portions, however the proportion of reactants is not paint, resin, etc. critical and may be adjusted to provide minimum dust- Although several different procedures have been 60 ing levels for different varieties of asbestos ores and used to treat asbestos fibers and particles in order to fibers. reduce or limit their ability to become airborne, these Especially useful as anti-dusting agents are those treatments have concomitantly diminished or elimi polyhydroxy compounds which have been partially nated altogether those specific properties which an esterified (from about 0 to about 80%, preferably be- asbestos additive was expected to provide to a given 65 tween about 10% and 30%) with lower (Ci - C6) ali chemical product. Accordingly, these procedures for phatic carboxylic acids or their anhydrides. Suitable limiting the dusting tendency of asbestos fibers are of little or no practical value since they eliminate the polyhydroxy alkyne derivatives include ethylene, prop ylene, and butylene glycols, glycerine, pentaerythritol, 3,928,060 3 di- and tri-pentaerythritol, sorbitol and hexoses, such as 4 between 5 minutes and several hours, generally about dextrose, trimethylolethane, and trimethylol propane. 30 minutes. The exact treatment time is not critical and Preferably trimethylol propane is employed as the poly will vary depending upon the reaction product being hydroxy reactant in preparing the anti-dusting agents of used, the amount of asbestos being treated and rate of the invention. Esterification of the foregoing polyhy 5 treatment. During the spray treatment the asbestos droxy compounds is carried out with aliphatic C, - CG material is agitated, preferably by stirring or tumbling carboxylic acids such as formic, acetic, propionic, bu tyric, isobutyric, valeric, trimethylacetic or caproic within the mixing device or container in which it is held. Preferably, between 5 and 10 parts by weight of acids; or their anhydride analogs or unsaturated ana asbestos of the anti-dusting reaction product is em logs. Preferably the anhydrides of the foregoing acids, 10 ployed. Especially good inhibition of chrysotile asbes especially acetic and butyric acid anhydride, are em tos fiber dusting levels have been obtained when about ployed in carrying out the esterification reaction. When the esterification is carried out using one of the 7 to 8 parts by weight of asbestos fibers of the anti-dust ing agent is sprayed over a thirty minute period onto foregoing acids, the reaction is preferably conducted in the tumbling asbestos fibers. the presence of a suitable catalyst such as stannous 15 The anti-dusting agents of this invention are prefera chloride, P-toluene sulfonic acid or sulfuric acid. The bly prepared by reacting approximately equimolar pro catalyst is not required when the anhydride of the se portions of the polyhydroxy alkyne derivative com lected acid (e.g., acetic anhydride or butyric anhy pound and the C2 - C6 carboxylic acid or anhydride. dride) is employed in esterifying the polyhydroxy com However, the precise amount of either constituent is pound. The preferred anti-dusting ester of this inven 20 not critical and may be varied depending upon the tion is prepared by reacting trimethylol propane and type, size, and dusting tendency of the asbestos fiber to acetic anhydride in approximately equimolar amounts be treated. The esterification reaction is carried out to provide an antidusting agent having the approximate using conventional esterification techniques (and cata structure depicted in FIG. I. lysts in the case of the carboxylic acids) which are well 25 known to those skilled in the art. Generally speaking, CHjOH the anti-dusting reaction products are viscous liquids which may be used to treat the dry asbestos fibers by CHaCHiCCH2OCOCH3 FIG. 1 spraying, mixing or any other suitable technique which h,oh ensures that a large portion of the surface area of the 30 asbestos fibers to be treated are likely to be exposed to the esterified anti-dusting agent. The anti-dusting agents of this invention are espe The following examples illustrate the manner of pre cially useful in inhibiting the dusting levels of short paring asbestos fibers having reduced dusting proper purified chrysotile asbestos fibers of the type available ties in accordance with this invention. from Union Carbide Corporation, Bound Brook, N.J., 35 under the trademark CALIDRIA asbestos. Typical EXAMPLE I physical characteristics of one form of these short puri Five hundred grams of Union Carbide "RG-144 Ca fied chrysotile asbestos fibers are set forth in Table I lidria", purified chrysotile asbestos containing about below. 1.0 X 1014 colloidal fibers per gram of material and Table I 40 exhibiting the approximate physical characteristics set Typical Physical Specific Gravity Moisture Content. % by Wt. Surface Area. Sq. meters per gram Reflectance, G.E. Brightness Nature of Surface Charge pH in Water (2% slurry) Bulking Value, gal. /100 lb. Oil Absorption (OOP) lb./lOO lb. Refractive Index, n,, 25"C Aspect Ratio (Average L/D) Tensile Strength, psi Tensile Modulus, psi Dry Bulk Density, Ib./cu. ft. (fully aerated) Shipping Density, Ib./cu. ft. Characteristics 2.45 2.0 max. 60 approx. 72-76 Electropositive (Cationic) 9.0 4.8 120 1.54-1.56 200:1 824,000 max. 23.2 X 10 4 12-14 forth in Table I was charged into a large mechanical mixer. An anti-dusting agent for treating the fibers was pre pared by reacting one mole of trimethylol propane and 45 one mole of acetic anhydride for about 60 minutes. After the esterification reaction had been terminated, a partially esterified (about 15%) reaction product hav ing the structure shown in FIG. 1 herein was isolated. Thirty-seven and one half grams of the isolated reac 50 tion product was loaded into an, industrial sprayer whose nozzles were positioned within the mixing device containing the dry asbestos fibers. The mixing device motor was then started and the esterified reaction product sprayed in mist fashion, at a uniform rate 55 through the nozzles onto the dry asbestos fibers which The Union Carbide "Calidria" asbestos fibrils differ were being agitated in the mixing device. The spraying from conventional chrysotile asbestos because of the operation was carried out at a uniform rate for about unusual mineralogy of the California deposit from 30 minutes at which time the liquid anti-dusting agent which they are mined. Also, they contain a higher con had been completely sprayed onto the asbestos fibers in centration o f fiilly liberated asbestos fibrils (whiskers) 60 the mixing device. The fibers were then allowed to dry than other chrysotile products. at room temperature. Asbestos fibers which are to be treated according to The tendency o f the fibers treated in accordance with the invention are charged into a large tumbler or mix this example to become airborne particles was com ing device. After the dry asbestos fibers have been pared to untreated fibers using the following proce loaded, they are treated, e.g., by spraying with from 65 dure: a two pound sample of asbestos fibers treated in about 2 to about 25 parts by weight of the esterified accordance with Example I was rapidly poured be anti-dusting agent of this invention. The spraying oper tween two open mouthed containers. Samples of the ation is generally carried out over a period of time particulate matter in the air immediately adjacent to / A f U jV W the pouring area were collected on membrane filters of 3. The method according to claim 2 wherein said 0. 8 micrometer porosity mounted in open face filter polyhydroxy compound is partially esterified up to holders. The same procedure was followed for the un treated asbestos fibers. In each case, the membrane filter was exposed to the atmosphere adjacent the pour ing site for a period of fifteen minutes from the time that the asbestos pouring operation was commenced. After the sampling period had been terminated, each filter was microscopically examined at 400-450X (magnification) with a four millimeter objective using phase contrast illumination. The membrane filter which was exposed to the untreated asbestos fibers entrapped approximately four times as many asbestos about 80% with lower aliphatic acids. 4. The method according to claim 3 wherein said 5 polyhydroxy compound is selected from the group consisting of ethylene, propylene and butylene glycol, glycerine, pentaerythritol, di and tri-pentaerythritol, sorbitol, dextrose, trimethylolethane, and trimethylol propane. 10 5. The method according to claim 3 wherein said polyhydroxy compound is trimethylol propane. 6. A method according to claim 2 wherein said acid is selected from the group consisting of formic, acetic, propionic, butyric, isobutyric, valeric, trimethylacetic fibers having a length of about five micrometers or 15 and caproic acids. longer on its surface than the identical filter exposed to 7. A method according to claim 3 wherein said poly the asbestos fibers treated in accordance with Example hydroxy compound is trimethylolethane. 1. 8. A method according to claim 7 wherein said car EXAMPLE II boxylic acid is acetic acid. 20 9. An anti-dusting asbestos particle which comprises The same operation was carried out as in Example I, except that the esterification reaction was allowed to continue until the reaction product (anti-dusting agent) was approximately 30% esterified and fifteen parts by weight (75 grams) of the esterified anti-dusting agent was applied to 500 grams of the asbestos fibers. The particulate assay of the dusting level of the as bestos fibers treated in accordance with this example was carried out according to the sampling procedure outlined in Example I. The membrane filter exposed to a chrysotile asbestos fiber coated with a composition consisting essentially of the partially esterified reaction product o f an ester of a polyhydroxy derivative of a C2 - C6 alkyne and a compound selected from the group consisting of saturated and unsaturated C, - C6carbox25 ylic acids and their anhydrides said fiber being from about 1 to about 25 micrometers in length and said coated particle being dry. 10. An anti-dusting asbestos particle as recited in claim 9 wherein said polyhydroxy compound is se30 lected from the group consisting of ethylene, propylene the treated asbestos fibers contained approximately and butylene glycol, glycerine, pentaerythritol, di- and one-fourth the number of asbestos fibers having a tri-pentaerythritol, sorbitol, dextrose, trimethyloleth length of about 5 micrometers or longer as compared ane, and trimethylol propane. with the membrane filter exposed to the untreated 11. An anti-dusting asbestos particle as recited in asbestos sample. 35 claim 9 wherein said acid is selected from the group The treated asbestos fibers of Examples I and II were consisting of formic, acetic, propionic, butyric, isobu successfully used as rheological additives in several tyric, valeric, trimethylacetic and caproic acids. different plastisols and organosols designed for end use 12. An anti-dusting asbestos particle as recited in applications as modifiers in adhesives, coatings and claim 9 wherein said acid anhydride is selected from mastics. Use of the treated asbestos fibers of this inven 40 the group consisting of formic anhydride, acetic anhy tion as additives conferred substantially identical rheo dride, propionic anhydride, butyric anhydride, isobu tyric anhydride, valeric anhydride, trimethylacetic an logical properties to all the organosols and plastisols as hydride and caproic anhydride. addition of untreated asbestos fibers. 13. An anti-dusting asbestos particle as recited in While not wishing to be bound by any particular 45 claim 12 wherein said polyhydroxy compound is tri theory of operation for the invention, it is believed that methylol propane and said anhydride is acetic anhy the partially esterified reaction product (anti-dusting dride. agent) forms a thin coating on each asbestos fiber 14. An anti-dusting asbestos particle as recited in thereby inhibiting its ability to become airborne with claim 11 wherein said polyhydroxy compound is tri- out affecting its specialized rheological properties. 50 methylol propane and said acid is acetic acid. What is claimed is: 15. An anti-dusting asbestos composition comprising 1. A method of processing asbestos fibers to inhibit a plurality of finely divided asbestos fibers from about dusting of said fibers which comprises charging asbes one to about 25 micrometers in length coated with an tos fibers of from about 1 to about 25 micrometers in effective amount for inhibiting asbestos fiber dusting of length into a treatment zone, coating said asbestos 55 an anti-dusting agent consisting essentially of the reac fibers with an effective amount to inhibit fiber dusting tion product of a polyhydroxy compound which has of an anti-dusting agent consisting essentially of the been partially esterified from about 0 to about 80% partially esterified reaction product of a polyhydroxy with a lower aliphatic acid anhydride said coated parti compound derived from a C2to C6alkyne and a com cles being dry. pound selected from the group consisting of saturated 60 in 1c6l.aiAmn 1a5ntiw-dhuesrteining asasbidesptooslychoymdrpooxsyiticoonmapsoruencditeids and unsaturated Q through C6 carboxylic acids and trimethylol propane. their anhydrides for a predetermined time period, agi 17. An anti-dusting asbestos composition as recited tating said fibers during said coating step and drying in claim 16 wherein said lower aliphatic acid anhydride said fibers at room temperature after agitation. is acetic anhydride. 2. The method according to claim 1 wherein said 65 18. An anti-dusting asbestos composition as recited effective amount for inhibiting dusting comprises from in claim 15 wherein said asbestos fibers are formed about 2 to about 25 parts by weight of said asbestos from chrysotile asbestos. fibers of said anti-dusting agent.