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432 Table I.
Market for Fire-Retardant Fabrics
6,000,000 Brushed napped and pile fabric Lace curtains 12,000,000 Other curtains 30,000,000 Sheer goods 36,000,000 Cotton 9,000,000 Rayon 270,000,000 T o r k clothinn Chenille bedspreads 7,700,000 Chenille robes 160,000,000 Bed linens Upholstery 84,000,000 10,000,000 Seat cover cloths 625,600, 00 Total
50 75 50
3,450,000 9,000,000 15,000,000
75 75 5 0 75 2 25 25
27,000,000 6,750,000 13,500,000 5,000,000 3,200,000 21,000, 00 2,500,000 106,4 0,000
and the man in each mill who is responsible for this particular department is asked what proportion of his market iyould be interested in a fire-retardant finish, other things being equal, a pretty accurate guess as to the total market should be obtained. These estimates of the proportion of thc present market that might desire a fire-retardant finish were found to vary from zero for chenille bedspreads t o 7594 of the total market on lace curtains, for example. To show how these figures run, Table I is presented. COSTS
The possible market of 100,000,000 pounds of fire-retardant fabrics, mostly cotton and rayon, is of course a huge one, and the interest in such a finish covers so many classifications that it also is very broad. In making this survey, SO% of the men asked for their opinion replied, which is a very satisfactory percentage,
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as most market surveys get a response of only 20%. The price or cost of the treatment was not mentioned, but most mills based their estimates on a very low cost or one no greater than that of their regular finishes. Naturally, if costs were higher, and they are bound to be with any chemical finish, the market would be much smaller. I t is probable that a cost of 10 cents per pound of cotton treated would reduce the above estimate to one tenth of the figures given. However, even with this drastic reduction, there is a huge demand for fire-retardant cottons and rayons. Cost figures can be viewed from two different angles. To a fire chief or anyone responsible for keeping fire losses down, the cost of making the textile nonflammable would be of little concern, but to a retail merchant selling aprons, for instance, it is very important, for even a slight change in the price tag might turn a customer away to the next counter, or worse still, to the next store. It is said that a burnt child dreads the fire, and certainly the mother of such a child would be vitally interested in fire-retardant clothing a t any reasonable price; but, fortunately for children, perhaps only one in a thousand really gets burned in this way. CONCLUSIONS
The net result of all of this is merely that the average consumer is interested in just what interests you and me. We want to eliminate as many of the hazards of daily life as possible, but in this busy world we often do not rcalize such hazards exist, unless they are pointed out and properly impressed upon us. Furthermore, to be of any real buying interest, the cloth or clothing so treated must maintain most of its other useful characteristics and, finally, it must not cost too much. RECEIVED September 26, 1949.
COMMERCIAL APPLICATION OF F L A M E - R E S I S T A N T FINISHES ROBERT W. LITTLE' WITH JALVMESM. CHURCH AKU SYDNET COPPICIP Colunibia University, New York, N. Y.
T
HE finishes commonly applied t o textile fabrics have for their purpose the improvement of the appearance or per-
formance of the final product. The qualities generally imparted are greater body or structural strength, resistance to soiling, and added stiffness, softness, luster, or drape. The latter are of prime importance, constituting a general enhancement of those characteristics which appeal to the eye and hand of the potential customer. The development of greatly diversified specialty finishes has addcd such properties a3 dimensional stability, crease resistance, waterproofness and water repellency, and resistance to moth damage and microbial attack. Flameresistant or flameproof finishes are unique in the field of tevtile processing in that their primary purpose is improvement of the personal safety of the consumer and that their use is required by law for certain fabric applications. Other papers of this symposium deal with mechanisms of flameproofing, the testing procedures employed in evaluating the flammability of fabrics, the value of flame-retardant fabrics t o the consumer, and legislative activity pertaining to fabric flammability. The following discussion reviews the nature of flame-retardant compositions and the methods by which they are applied commercially. 1 Present address, Experiment Station, Hercules Powder Company, Wilmington, Del. a P r w e n t address, Research Department, American Viscose Corporation, Marcus Hook, Pa.
NATURE OF RETARDANTS
A definition of the types of chemical compounds having flameretarding properties cannot be simply stated. In the final analysis, any noncornbustiblc material added to a flammable substance such as cellulose will serve as a fuel-diluent and hence reduce the flammability of the cellulose. This dilution effect often requires the presence of nearly IOO7, add-on of the additive, honever, before nonflammability is achieved and should not hc confused with the performance of true flame retardants which are effective at add-ons of 10 to 3OyO. The definition of retardants is further complicated by variations in the degree of combustibility of the substance to which they are applied. A compound which is effective in retarding the burning of wood may be relatively ineffective when applied t o a light-weight cotton fabric n-hich is both more easily ignited and more highly combustible because of its greater degree of subdivision. Although perhaps applicable to many other forms of cellulose, and to other substrata as well, the following discussion of retardants is based upon their effectiveness when applied to cellulosic teutilr fabrics. The many flameproofing compounds and treatments availalile couId be classified on the basis of the chemical nature of the active ingredients, the mechanisms by which they are thought to function, the permanence of the flameproof characteristics in terms of resistance to wet- and dry-cleaning operations, or the method of
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433
Flame retardants for application to textile fabrics may be subdivided into water-soluble salts and durable finishes, capable of resisting wet- and dry-cleaning operations. The two principal groups of water-soluble salts and mixtures are: those capable of forming thermostable foams at flame temperatures, and the thermolabile inorganic and organic salts of the mineral acids. Durable flameresistant finishes may be classified as double-bath treatments, dispersions of the emulsion or solvent-suspension type, and modified cellulose processes wherein reaction with the cellulose molecule is obtained. Because the protection afforded by soluble salts is of a transient nature, they are generally applied to fabricated textile items by dipping, spraying, and brushing or by commercial
laundry impregnations. Durable or semipermanent finishes are applied in the finishing mill, for the most part on routine padding and drying equipment. Two-bath processes appear to be of increasing interest, despite the careful controls required in plant processing. Although restricted in application because of solvent removal and recovery problems, soTvent suspension processes are regularly applied to heavy-weight fabrics. Emulsion formulations lend themselves readily to plant processing on available mill equipment. The modified cellulose finishes have been successfully adapted to mill operations. Continued improvement of flame-resistant finishes may be expected as a result of current research and development programs.
attachment to the fiber. I n the following discussion of the types of retardants employed to date, grouping has been based on all these criteria in varying degree. Because the water-soluble salts have played such a predominant part in the development of flameproofing, it is fitting that they be considered first. Water-Soluble Salts. Since the studies of water-soluble flame retardants carried out by Gay-Lussac in 1821 (11), practically all the common soluble inorganic salts have been proposed as flame retardants for wood, paper, and textile fabrics. No attempt is made in this discussion to cover the many compounds and mixtures that have been reported to date. Bibliographies on the subject contain references to many hundreds of formulations (1, $3) and contemporary transient compounds have recently been compared and reported (32). Most effective in the prevention of afterflaming are those inorganic salts which arc thought to function by the formation of a solid foam which serves as a barrier between fabric and flame. The retardants in this group consist of salts or mixtures which, when heated, melt at relatively low temperatures and subsequently resolidify in the form of a stable foam produced by the evolution of decomposition products. They are generally either highly hydrated salts possessing low melting points or mixtures of a lowmelting compound with a highly hydrated salt. Representative of this group are borax, aluminum sulfate, mixtures of borax and boric acid with and without added ammonium phosphates, borax and diammonium phosphate, and sodium phosphate-boric acid mixtures. In recent years highly effective flame-resistant coatings have been developed which function by this same foaming phenomenon. I n these instances the thermostable foam is produced by the carbonization of organic compounds of low thermoplasticity when pyrolyzed in the presence of large quantities of a thermally unstable phosphate or borate. Starch and methylolurea (14) have been employed as the organic constituents of these mixtures. A second group of water-soluble retardants consists of inorganic acids, their acid salts, or salts capable of liberating acids on heating. These are generally less effective than the preceding group in preventing afterflaming but more effective in the retardation of afterglow. Typical examples are sulfuric, sulfamic, boric, phosphoric, hydrochloric, hydrobromic, molybdic, and tungstic acids, their ammonium salts, and salts of organic bases such as urea, ethylenediamine, and the alkyl and alkylol amines. In addition, many of the salts of zinc, tin, chromium, aluminum, magnesium, and antimony may be cited, with particular reference to the chlorides and bromides. In the case of the metallic salts, flameproofing efficiency :is somewhat proportional to water solubility. The efficiency of these compounds and their mixtures in the prevention of afterflaming appears to be dependent upon their ability to furnish an acid or acid anhydride a t the time of incipient flaming. Using the potassium and sodium salts as examples, when the acid anhydride is balanced by an equivalent
amount of alkali oxide in the combustion residue, the salt does not possess flame-retardant properties. Borax is one of few exceptions and, as indicated above, is believed to owe its effectiveness to B different mechanism. The durable flameproofing treatments may be divided into two general classifications: those in which the active retardant is added to the unmodified fiber and those which depend for. flameproofness and durability on a chemical modification of the fiber itself. Double-Bath Processes. Early attempts at permanent flameproofing of fabric were directed a t deposition of an insoluble retardant in and on the fibers by means of two-bath techniques. The treatment consists essentially of saturating the fabric with a soluble salt, then immersing in a second solution, the contents of which react with the impregnated salt to render it insoluble. In the simplest case, double decomposition is produced with two aqueous solutions. Many variations are possible, using an organic solvent in one bath or even producing the desired reaction by subsequent treatment in a gaseous medium. A typical example is the Perkin (19) process where hydrated stannic oxide is precipitated by immersion in a solution of sodium stannate followed by an ammonium sulfate bath. This process has seen many modifications of the precipitating bath using sulfuric acid or the sulfates of copper, chromium, manganese, or iron. A similar process recently developed consists of treating the fabric with an aqueous solution of sodium tungstate followed by an impregnation in an acidic aqueous solution of an acid-soluble cyanamide-formaldehyde resin (31). A variation of this general technique, which has shown promise, is the dissolution of the two reactants in an organic solvent of suitable dielectric constant, employing water or an aqueous fixative solution as the second bath. As an example, fabric may be immersed in a solution of zinc chloride and borax in a glycol-type solvent followed by immersion in water or exposure to steam or air of high humidity (19). Still another modification of the double-bath process which has been investigated more widely of late is the use of aqueous solutions of inorganic salts, wherein the solubility of the salt is maintained by the presence of volatile acids such as hydrochloric or acetic, or a volatile base such as ammonia. In the course of the drying operation, the volatile acid or base is driven off, hydrolysis occurs, and an insoluble oxide or basic salt is deposited on the fabric. The second bath in this case is intended to further the hydrolysis reaction and remove excess soluble products and surface deposit of the insoluble retardant. Interest in doublebath processes has been revived recently by reinvestigation of the hydrolysis of antimony chlorides. One process (29), employing three separate impregnations, consists of padding the fabric with hot, aqueous sodium carbonate, and impregnating with antimony trichloride from organic solvent, followed by a second application of aqueous sodium carbonate. The cloth i s dried after each
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INDUSTRIAL AND ENGINEERING CHEMISTRY
impregnation. A later method ( $ 7 ) applies antimony trichloride or antimony pentachloride from organic solvent, hydrolysis being achieved by steaming, washing in water, aqueous ammonia, or a mater solution of a xeak base, or exposing the fabric to ammonia vapors or steam containing a volatile base. The latest development of this t,ype, and the one showing the most promisc of successful industrial application, is described by Gulledge and Seidel(12). The process consists of impregnating the cloth in an aqueous solution of titanjrl chloride (TiOC1,) and ant,imony trichloride (SbCla) in the presence of excess hydrochloric acid, aging for a short time (1 to 15 minutes), and neutralizing in 1,5yosoda ash solution followed by a water rinse. The fabric is suhscquently scoured thoroughly, preferably by means of a rope wash. Suspensions and Emulsions. Although, as indicakd above, present developments indicate a renewed int,erest in multibath impregnations, the majority of commercial processing today is done with compositions \Therein the insoluble f-lameproofirig agent is suspended or emulsified in a suitable solvent system. Such treatments have been applied partially dissolved and partially suspended in organic solvents, as water-in-oil emulsions and as emulsions having water as the external phase. ils a result, of this type of application, the active flameproohg ingredients are generally less effective than when applied from solvcnt media, and require correspondingly higher add-ons to achieve a given degree of flame resistance. In their favor, however, is an improvement in permanence with respect to resistance to laundering, by virtue of resinous binders which may t)e included in the suspension or emulsion vehicle. Also, the resistance of thc fabric to afterglow and to mildew, etc., may be greatly improved by the addition of other components to the formulat,ion. Theoretically, any of the irisoluble inorganic or organic compounds which possess flame-resistant, properties could be applied to the fabric in the form of a suspension, emulsion, or solution in organic solvents. The composition which has attracted the most attention in the past has been the combination of a metallic oxide and a chlorinated vax or resin applied in solvent' suspension or emulsion form. These metallic oxide-chlorinated compound systems employ t x o insoluble components, neither of which is effective as a flame retardant' by itself, but which interact when the fabric approaches flaming temperatures, forming an active flameproofing compound. The chlorides and oxychlorides of zinc, antimony, and similar metals are effective flame retardants for cellulosic materials. \Then the insoluble oxychlorides are applied to the fabric as such, however, or by partial hydrolysis of the chloride, they tend to be unstable through susceptibility to progressive hydrolysis with the accompanying evolution of hydrochloric acid. By impregnating the fabric with a mixture of a metallic oxide and a relatively stable chlorinated material which is capable of releasing hydrochloric acid a t the time of incipient flaming, essentially the same flameproofing agent is employed without t.he disadvantage of fabric degradation resulting from acidic hydrolysis products. The comparative availability of hydrochloric acid from the several possible chlorinated compounds, the ratio of metallic oxide to chlorinated component, the method of application, and many similar factors all contribute to the effectiveness of the composition. The several variables existent in this flameproofing system have been discussed in some detail (17) and will not be considered further a t this time. Millions of yards of service tentage fabrics were proccssed with this type of formulation during the war and there has been considerable adaptation to civilian fabrics as well. The majority of n-artime finishing was carried out with a suspension of antimony oxide and chorinated paraffin or vinyl resin, with or without added zinc borate, suspended and dissolved in an organic solvent, supplemented by plasticizers, coloring pigments, fillers, stabilizers, and fungicides. A simple example would be a suspension of 20% antimony oxide and solution of 10% vinyl acetate-chloride copolymer (Vinylite VYHH) in methyl ethyl ketone (28).
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A great deal of development work has been done in improving the performance of the solvent-suspension systems and designing comparable emulsion compositions (17). The modifications made were aimed a t plasticizing and stabilizing the chlorinated resin or wax components, improving afterglow resistance by the addition of compounds such as zinc borate, incorporating the desired coloring and fungicidal constituents, and, in general, improving the applicability to commercial finishing processes. Nore recent developments have included the addition of a watcrsoluble urea-formaldehyde condensation product ( 8 )or suspension of a prepolymerized urea-formaldehyde resin in powdered form (9) in the aqueous emulsion, to improve glow resistance and permanence. h similar composition has been reported employing the oxide or hydroxide of zinc ( 1 5 ) in conjunction with a chloi inatcd resin, dehydrohalogenation catalyst, and low-temperature decomposition inhibitor. In addition to the compositions described above, recent research in the field of insoluble flame-retardant compounds has been extended greatly in the direction of organic compounds of sulfur, phosphorus, boron, and the halogens. Organic compounds were not considered to any great extent in early studies of flameproofing, possibly because of their association with the characteristic of flammability. Some attention was given to bromine derivatives such as tribromophenol ( 4 ) , diacetyl-2,4,6-tribromoanilide ( 6 ) , and the bromine substitution products of toluene, xylene, etc. ( 7 ) ,and to phosphate compounds such as tricresyl phosphate, triphenyl phosphate (16),the diphenyl or diethyl esters of phenyl phosphoric arid (33), and tribromo- and trichloromethyl phosphate (8). In recent years there has been considerable activity in the field of alkyl and aryl phosphates and borates as evidenced by the development of the borophosphate resins, allyl phosphates and phosphonates, and many others. A two-bath process indicative of the trend in the use of organic phosphates impregnates the fabiic with a polyethyleneimine, following ryith an aqueous solution of dipentaerythritol hexaorthophosphate (18). I t is to be expected that continued research in the field of organic derivatives of phosphorus, boron, and sulfur will result in many new compounds effective in the retardation of flaming combustion. Modified-Cellulose Processes. In tempo n ith the investigation of organic retardants, there has been considerable interest in the addition of organic compounds of sulfur and phosphorus to cellulosic fabrics by in-place polymerization of resinous products or actual esterification of the cellulose molecule. Which of the two mechanisms predominates is dependent upon the particular composition applied and the severity of drying or curing conditions. From purely fundamental considerations, the mineral acids are known to be particularly effective in reducing the flammability of cellulosic materials. Simple application from aqueous solution at normal temperatures results in a high degiee of flame resistance, the flameproof properties, however, being completely removed by immersion in water. The heating of cellulose in the presence of an acid favors the formation of a cellulose ester, and the resulting ester displays a certain degree 01resistance to leaching. Practical considerations make the majority of the esterification reactions unsuited to commercial flameproohg practices because of difficulty in adapting the processes t o eommeicial equipment and the degradation of the fabric which accompanies the esterification reaction. Transient flameproofing systems have been ieported which are based on the phosphate salts of urea (8, 5), alkylolamines (SO), guanidine (24), and dicyandiamide (26, 26). The compositions of Pollak result in insoluble retardants of the same general type: by immersion in an aqueous solution of urea or melamine, phosphoric acid, and formaldehyde (20); by a two-bath process, dipping first in pyrophosphoric acid solution followed by drying and impregnation with aqueous methylolmelamine (21); and by impregnation in a mixed solution of ammonium pyrophosphate and a melamine-formaldehyde condensation product ( 2 2 ) .
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At drying temperatures below 130' to 140" C. it is likely that little reaction with cellulose occurs and insolubilization is primarily due to the in situ formation of an insoluble melamineformaldehyde-pyrophosphate polymer. I n recent years, processes have been developed in which formation of the cellulose ester or nitrogenous salt may be accomplished under conditions which are commercially practical and which do not excessively impair the fibrous properties of the cellulose (IO). The process is accomplished in three steps: impregnation of the fabric from an aqueous solution of the retardant components, curing of the treated fabric to bring about the desired esterification reaction, and washing to remove unreacted solids. The simplest composition of this type may be represented by a 46% aqueous solution of urea and diammonium phosphat,e in the ratio of 2 to 1 by weight. A typical cure might be stated as 13 minutes a t 160' C. In commercial practice, the compositions and procedures are modified to obtain an effective flame resistance combined with maximum permanence and minimum loss of fabric strength. Urea has been partially or completely replaced with related compounds such as dihydroxyguanidine, guanylurea, aminoguanidine, biguanine, melamine, dicyanoguanidine, and dicyandiamide. Similarly, many of the acids of phosphorus and their salts may be used. The cellulose ester flameproofing processes are among the best of those currently available commercially, and continued research into the reactions of organic derivatives of sulfur and phosphorus with cellulose may be expected to result in improved processes of this type. PROCESSING APPARATUS AND PROCEDURES
The procedures employed in the application of flame-resistant finishes to textiles may be divided into two distinct categories: one as practiced with water-soluble salts and the second relating to the plant processes and apparatus made use of in applying more or less permanent treatments. The ease with which efficient and uniform impregnation can be accomplished with the water-soluble compounds lends itself to the treatment of articles of clothing, curtains, draperies, and other items after fabrication. Certainly the temporary nature of the protection afforded does not generally justify an initial treatment in yard goods form. The permanent finishes, on the other hand, are not adaptable to processing fabricated items and the permanence of the properties obtained justifies carrying out the treatment of piece goods in the finishing plant. Temporary Treatments. Because water-soluble flameproofing agents can be applied to fabrics in the form of a true solution, effective and uniform distribution is relatively easy to accomplish and several different application techniques may be employed. With any of the methods used, the instability of the majority of the soluble salts requires care in the drying of the treated cloth. Many of the more common retardant mixtures will hydrolyze or decompose a t temperatures below or near the standard ironing temperatures of 135' to 149" C. Mixtures of borax and boric acid lose hydrated water a t 127"to 134"C. and hence prolonged exposure to ironing temperatures will impair the effectiveness of the resultant treatment. Ammonium sulfamate and its mixtures with other compounds decompose in the neighborhood of 134' to 147' C., depending upon the mixture, and release inorganic acid residues which will reduce the strength of the treated fabric. The ammonium phosphates are not as serious offenders with respect to tendering but will lose ammonia, particularly in the presence of large amounts of water, with the resulting formation of acidic residues and tendering of the fabric. In order to avoid undue loss of either flameproofness or fabric strength, the mildest of drying and ironing conditions must be employed. IMMERSION. The dipping of fabrics or garments into a volume of retardant solution followed by hand or roll wringing is the simplest method of application and is adaptable for treating
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small batches of material in the home. It has one advantage in that it tends to produce a more uniform distribution than can readily be accomplished by means of apraying or brushing. A convenient method of home impregnation is to incorporate the proper amount of flameproofing agent into the final rinse of the laundering procedure. In the case of many of the common commercial preparations this would be approximately one pound of retardant per gallon of water. The final dry add-on required in most cases ranges from 10 to 15%. If the fabrics dipped into the retardant rinse are very wet, the concentration of the solution will have to be somewhat greater. SPRAYING.In many instances it is advantageous to apply the flameproofing agent to a textile article without removing the article from service. This is particularly true in the case of interior decoration textiles such as drapes, curtains, and buntings. The same method is applicable for rugs and slip covers and could be employed for any textile product. The fabric is hung up and thoroughly and evenly sprayed with a highly concentrated retardant solution until i t appears definitely moist. Any suitable spraying equipment may be employed; however, in order to avoid streaking of the fabric on drying, the spray should be as fine as possible. With heavier fabrics it is often necessary to apply the spray to both sides of the cloth. The method in general suffers from a tendency to produce an uneven distribution and requires some experience to achieve a satisfactory treatment. I n treating curtains and garments in the home, a modification of this technique can be used by applying the retardant when sprinkling the fabrics just prior to ironing. The cloth must be thoroughly moistened, however, and the fabric should be allowed to become nearly dry before ironing in order to avoid undue decomposition of the flameproofing agent. BRUSHING. If a suitable spray gun is not avaikble, a concentrated solution of retardant may be brushed onto the fabric. Again, care must be taken to moisten the fabric sufficiently and yet achieve a uniform application in order that the treated material will not have a streaked or spotty appearance. COMMERCIAL LAUNDRY TREATMENT. Where large quantities of clothing or other finished items are concerned, the only effective and, a t the same time, economical method of applying flameretardant treatments is by a mechanical means. The plant best equipped to carry out the impregnation is the commercial laundry, and because the fabrics are generally laundered prior to treatment, a saving in both time and expense is accomplished by impregnating at the time the fabrics are washed. This type of treatment has been carried out commercially and shown to be practical. There are many variations in the details of washing techniques employed in commercial laundries, but the apparatus and general procedures used are more or less universal. The items are washed in large cylindrical, reversing wash wheels, being subjected to two or more soapings and three or more rinses. Approximately 70% of the water is then removed by spinning in centrifugal extractors and the load is dried by tumbling for 15 to 20 minutes in rotating dry tumblers. The a plication of soluble flameproofing agents can be achieved with t&s standard equipment, adding only a reservoir for the storage of solution, and pump and piping for reclaiming the unused liquor from washer and extractor. A suggested procedure is shown diagrammatically in Figure 1. Experience has shown that considerable variation in the addon obtained is likely to occur if the flame-retarding salts are added to the final rinse of the regular washing procedure. Extraction of the load prior to immersion in the retardant solution produces very consistent add-ons, however, and no appreciable saving of compound is achieved by drying prior to the flameproofing treatment. Obviously, omitting the extra drying operation constitutes a great saving, for the drying process is generally the bottleneck in laundry operations. In order to achieve uniform saturation, the level of solution in the washer should be above a certain minimum. As an example,
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less than 4 inches of solution in a 30 X 30 inch washer / may give incomplete penetration e v e n w i t h 15 minutes' rotation. I I The critical stage in the process is the extraction of excess retardant solution. The usual practice is to employ a 10 to 12% s o l u t i o n and spin down to a 100% wet pickupi.e., 100% increase in wet weight over the initial dry weight. The proper impregnating conditions can be determined by maintaining a constant solution conI Our centration and Figure 1. Application of Watervarying the extracSoluble Flameproofing Treatments t i o n t i m e , or by in the Commercial Laundry holding the time of E. Extractor extraction constant P. P u m p R. Solution reservoir and varying the T. Tumbler W. Washer c o n c e n t r a t i o n of 1. Washing of fabric the solution. The Heavy extraction of rinse water 2. 3. Impregnation with tlameproofing latter procedure is agent 4. Light extraction of retardant solution preferable, because T u m b l i n g t o dryness 5. the time of extraction is of the order of 10 seconds and minor variations will greatly affect the add-on obtained, For reasons of economy it is desirable to reclaim the solution and extracted liquor for subsequent use. The introduction of moist fabric into the bath tends to dilute the retardant solution by virtue of water remaining in the extiacted load. This clilution will reach an equilibrium, however, after several runs, because the bath is restored to its initial level after each use by the addition of fresh solution. The simplest procedure is to adjust the initial concentration in such a way that the dilution which occurs does not reduce the percentage of salts present below the effective level. If desired, the bath may be reinforced by a booster of the flameproofing compound. In either case, effective concentration can readily be checked by means of a hydrometer reading. Many of the soluble flameproofing agents are acidic in nature and tend to form hydrolysis products n-hich attack copper, brass,
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bronze, or galvanized iron. Equipment constructed of these materials can be employed, provided it is washed out irnmedintely after .each use. Wherever possible, containers and piping of lead, stainless steel, black iron, ceramic ware, or wood can be employed advantageously. It is apparent that the above is a very contracted presentation of the procedures for the applicution of water-soluble flameproofing compounds. Many variat'ions in the apparatus and procedure will readily occur to the experienced finisher or laundryman. Permanent Treatments. In order to obtain uniform impregnation with the permanent types of flameproofing treatments it is necessary to process the fabric in the form of yard goods. Application at this stage in the life of the fabric is much simpler, cheaper, and more easily controlled and is justified when the finish applied is intended to remain effective throughout the life of t,hc fabric. The equipment and procedures employed are generally common to the dye house or finishing plant, though there may be considerable variation in the coinbinations used with t,lie different types of permanent treat,nients. TWO-BATHTECHXIQUES. The double-bath flameproofing processes have not found v-ide commercial usage in this country, partly because of the superiority of available dispersion-type formulations and partly because of lack of demand for thc particular qualities they impart to a fabric. In England these methods have found much wider application. The basic techniques involved in the application of ilamcresistant finishes are essentially the same as those employed in routine commercial padding operations. The fabric is immersed in the retardant solution, excess solution is removed by passage through squeeze rollers, and the fabric is dried. Impregnation can he carried out in a dye padder or quetch and the squeeze obtained with 2- or 3-roll mangles. The rsolution box may be adapted for any number of immersions of the fabric before passing to the nip. In some cases, several dips or a prolonged immersion are desirable in order to achieve complete penetration or allow sufficient time for a reaction to take place in the second bath. St,ainless steel boxes are preferable, though any construction material which is not affected by the retardant solution will serve. When a 3-roll mangle is used, the fabyic may be dipped in t,he bath t\Tice, squeezing after each immersion. Mangle rolls are commonly of steel and rubber, although brass, husk, and wood are also satisfactory. Drying can be carried out on heated cans or in flue, loop, or frame dryers. The tenter frame is to be preferred, particularly where water is the solvent, because shrinkage is prevented by holding the fabric under width tension n-hile passing through the drying chamber. The manner in which t'he various pieces of equipment are combined can be varied greatly. The fabric may be immersed, squeezed, and then batched or rolled for subsequent drying. After running through the dryer it is again batched and returned for a repetition of the same process in the second solution. Because the dryer is generally the bottleneck, one fast-running padder may feed two dryers. The most economical setup would be as shown in Figure 2, where the fabric is padded, squeezed, dried, padded again, squeezed, and dried in one continuous operation. Flameproofing solutions, suspensions, or emulsions arc essentially nonsubstantive in nature, in that they are picked up by absorption only and do not have any specific affinity for the
/ff
Figure 2.
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Continuous Range for Double-Bath Processes
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INDUSTRIAL AND ENGINEERING CHEMISTRY
I
Figure 3.
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Commercial Installation for Treatment of Fabrics by Modified Cellulose Process
fabric. With some of the two-bath processes, however, the second bath may be more or less substantive, in that its components are exhausted by rapid reaction with the salts already present on the fabric. In such cases, i t is necessary to replenish the second bath continually. In other instances, the desired interaction occurs prior to or during the h a 1 drying operation. In either case, the squeeze rolls must be carefully controlled to leave a minimum of unreacted salts on the fabric. The presence of a large excess of soluble salts will require an additional washing and drying operafion, which should be avoided in so far as possible. There are several variations of the double-bath process, depending on the nature of the salts deposited and whether the reaction occurs upon contact with the second solution or during the final drying operation. The fabric may be dried completely before entering the second solution, i t may be partially dried, or it may enter the second bath wet. The most reliable procedure is to dry the fabric completely after immersion in the first solution. In this case, add-ons can be carefully controlled because the material enters both baths in the dry state. The cloth should be cooled as it leaves the first dryer to assure uniformity and to avoid overheating the second bath. The method cannot be used if the salt deposited from the first bath has a degrading effect when dried upon the fabric. I n such cases, the cloth may be only partially dried before entering the second bath. Although this procedure avoids the degrading action of the first salt deposited and provides easier control of add-on than having wet fabric enter the second bath, it is probably the least desirable of the three. It is difficult to control accurately the moisture content of the cloth and, in addition, any stoppages result in damage to the material in the dryer. Partial drying is best suited to those processes wherein the ingredients of the second solution react rapidly and completely with the salts already present on the fabric. In such cases, the moisture content of the fabric becomes of much less importance.
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When the wet fabric enters the second bath directly, the relative pressures of the two mangles must be carefully controlled in order to obtain the desired wet pickup without leaving a high concentration of unreacted salts. The first rollers must be under high pressure to leave approximately 50% wet pickup. The second squeeze should be so regulated that an additional 50% is picked up by the fabric, for a total wet-weight increase of 100% over the initial dry weight. Where complete reaction occurs while the fabric is in contact with the second solution, the cloth may be deeply immersed or may be subjected to several dips before the squeeze. The finished fabric, in this case, will contain excess salt from the second solution. If the reaction occurs during the drying process, the fabric may pass just under the surface of the second bath. When the salts deposited from Solution 1 are extremely soluble in Solution 2, the fabric may pass directly into the second mangle, the lower roll of which is partially immersed in the solution. The amount of soluble salts remaining on the fabric can be reduced to a minimum by this procedure, inasmuch asaregulation of running speed and squeeze pressure can cause just the required amount of Solution 2 to be brought up to the fabric by the lower roll of the mangle. Mention was made previously of special variations of the twobath processes in which both reactants were dissolved in a suitable organic solvent. The desired reaction in such instances might occur on drying or on exposure to water or humid sir. I n the latter case, the second bath is a water rinse, which completes the interaction between the two salts and, a t the same time, removes any excess of soluble salts. The same general considerations hold for those aqueous solutions in which a salt is held in solution by the presence of a volatile acid or base. In these cases it is essential that the fabric be thoroughly dried before entering the second bath. MODIFIEDCELLULOSE PROCESS. The flameproofing bath in this case is a water solution and, therefore, like the majority of the double-bath treatments, the process is adaptable to the bleachery or finishing plant. The process produces almost no surface coating on the fabric and depends for its efficiency and permanence on obtaining thorough penetration of the fibers. For this reason, it is necessary to remove as much as possible of the sizing or natural waxes present on the fabric prior to treatment. This can be done by chemical or enzymatic desizing operations or, even better, by mercerizing prior to flameproofing. The application procedures and equipment are very similar to those just discussed for two-bath processes with a few important exceptions. There are a great many possible variations in the commercial process, and the following discussion attempts to present only the general method and the equipment felt to be most desirable. The cellulose ester process, as indicated in Figure 3, consists of three separate operations: padding the flame-retarding salts on the fabric, curing to effect the desired chemical reaction with cellulose, and washing to remove excess water-soluble salts. Each of these stages is considered separately.
PADDINQ. Impregnation of the fabric is best accomplished with a two- or three-roll mangle. Because thorough penetration and uniform distribution are particularly im ortant with this process, the double-dip three-roll mangle is pregrable. The box should be jacketed and steam- or hot-water-heated, because the concentrated salt solution is often applied warm in order to avoid crystallization in the bath. All stainless steel e uipment is preferred, for the acid salts present are corrosive wit% iron or steel. The presence of ammonia prevents the use of copper or brass materials. After padding, the fabric may be batched or rolled for a short time before drying, although from the standpoints of speed and economy i t is better to have the padding and drying take place in one continuous operation. Any of the common commercial drying equipment, as discussed for double-bath processes, can be used in this case, although again tenter frames are much preferred in order to prevent the shrinka e that would normally result from padding in an aqueous soyution Loop and air-lay dryers are not d e sirable with heavy goods, because the fabric is stiffened a p p r e ciabiy by the deposited solids and may be injured by creasing or
438
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 42, No. 3
-i.e., tlie flammability of the solvent vapors evolved on drying. This limits the applicability of t, h os e p r o c esses , b e c a u s e m o s t blenchcries and fini&ing plants arc) not equipped to handle combustiblo vapors. In spite of this, the principal application of permanent flamcproof finishes to date has been on heavy-weight fabrics using solventsuspension formulations. Thc tremendous t,entage program during the rccent war produced millions of yard.: by such processes. The compound in this case conqists essentially of a suspension of mtimony oxide, color pigments, arid certain inhibitors in a solvent, solu/mpregnat/nq tion of chlorinated p a r a h and ii Dry Cans Tank rosin, such as a rosin-modificd phenol-formaldehyde resin. T h e Loop D r i e r solvent is generally a mixture of aromatic and petroleum solvents. Figure 4. Commercial Installation for Application of Solvent-Suspension The actual composition and solids Formulations by Immersion content of the mixture may vary appreciably, being partially depeiidfolding a t this stage. The dried fabric may be somewhat acid ent upin the nature of the fabric, the impregnating procedure and should therefore be cooled before rolling. Heavy goods employed, and the type of drying equipment. The solids content should not be batched because of the danger of injuring the stiff may range from 45 to 80%, although 60 to 70% probably repfabric as pointed out above. resents the average operating range. Solvent suspensions are applied by immersing the fabric, rcCURING. The curing operation is the most critical stage of moving excess compound by squeezing and scraping, or by knifethe flameproofing process, because it is at this time that the recoating procedures similar to t,he techniques employed in appllraction between the fibers and the flameproofing salts is obtained. ing plastic coatings. In tlie hitter instance the compound can The properties of the finished fabric are greatly dependent upon be poured onto the fabric ahead of the knife or picked up by coil.. the curing temperature and the length of the curing period. In tact with feed rollers. Each of 1,hese possibilities is descaribed general, high temperatures or longer cure times result in greater briefly. permanence of the flameproof properties in terms of resistance to laundering and ion exchange reactions. The same conditions, IMMERSIOX. In order to increase its absorbency, the cloth is however, produce correspondingly greater losses of fabric strength. predried, generally on hot cans, and then passes through a tension Because the severity of the curing conditions is directly proporbar into the impregnating bath. The fabric is deeply immersed in the bath, passed through squeeze rollers, reimmersed, scraped tional to the permanence of the finish and inversely proportiond with a set of knives or "doctor blades," and proceeds to the to the strength of the treated fabric, it is necessary to select those dryers. The tank is steam-heated to keep the compound at conditions M hich compromise the permanence desired with 3 approximately 110" F. and is continually agitated to maintain minimum loss in tensile strength. uniform composition. The bars in the tank do not rotate, the rubbing action enhancing the penetration produced by the s ueeze rollers. A diagram of a typical commercial installation ?or a11 Curing temperatures of 300 ' to 350" F. can be employed with immersion process is shown in Figure 4. corresponding cure times of 15 to 3 minutes, respectively. With The drying may be carried out on hot cans, in a loop dryer, in most commercial drying equipment, these conditions result in a vertical drying tower, or in various types of ventilated hot-air either excessively high temperatures or exceedingly slow running dryers. As illustrated in Figure 4, it is often advantageous to speeds a t the lower temperatures. The best apparatus consists make use of more than one type of equipment in the drying procof an oversize curing oven of sufficient capacity to cure the fabric ess. The temperatures employed may vary from 175" to 250' at approxim&ely 335' F. for about 7 minutes and still maintain a F. depending upon the design, size, and efficiency of the equipfairly fast running speed. ment. Certain precautions must be taken to avoid marking the The fabric is still stiff, because of the high add-on of salts presfinish on the sticks in a loop dryer, baking the finish on hot cans ent, and therefore should not be cured in l o o p or air-lay-type or printing on the interior rollers of a drying tower. Predrying dryers or batched following the curing operation. In order to on a set of cans will generally prevent marking in a loop dryer minimize damage to the fabric by the acid salts present, the maand the finish can be prevented from printing on rollers with terial should a ain pass over a cold can before rolling. which it comes in contact by maintaining a differential in speed WASHING.%he final operation is a hot wash to remove the between the rollers and the fabric. large excess of soluble salts remaining in the fabric. Any comKNIFECOATING. There are two principal variations of this mercial washing equipment which processes the fabric in open procedure, differing with respect to the method of applying the width can be employed, such as jigs, open soapers, or vertical or suspension to the cloth. In the first case the compound is horizontal multiroll washers. The excess salts are readily soluble poured onto the upper surface of the fabric just ahead of the and can be removed with hot viater (180" to 190' F.) without knife. The second variation consists of passing the fabric over the use of detergents. a set of feed rollers, which are immersed in the bath and bring After squeezing, the washed fabric can be dried with any type of the compound up onto the bottom surface of the cloth, again drying equipment, although frame drying is again preferable in using a knife or doctor blade to secure penetration and remove order to maintain the fabric a t the desired width. excess material. In either case, the fabric may be coated on one side, dried, and then similarly processed on the other side, or, as is generally preferable, the fabric may be processed on one side, Solvent Suspensions. The formulations in which the flameturned around a roller system, and similarly treated on the other proofing ingredients me partially dissolved and partially susside in one continuous operation. A commercial installation for pended in an organic solvent present an additional problem continuous processing by knifc coating is shown diagrammatiwhich is not encountered with the processes thus far considered cally in Figure 5.
Pi
March 1950
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
When applied by knife-coating procedures, penetration of the fabric is accomplished by the pressure between the knife and the cloth, influenced somewhat by the temperature employed in drying. The higher the drying temperature, the better the penetration. In the case of the roller and knife technique, penetration is achieved not only by the pressure of the fabric against the knife, but also by the pressure of the cloth against the feed rollers, caused by the weight of the idler rollers resting on the upper surface. There are many variables in knife-coating techniques which must be controlled in order to obtain uniform results. The more important of these are the nature of the weave, moisture content, and tightness of the fabric; the composition, temperature, viscosity, and other physical properties of the suspension itself; and the pressure exerted by the knife or roller against the fabric. The use of inflammable organic solvents requires the adoption of many safety precautions, such as explosionproof electrical fixtures, motors and lights, efficient plant ventilation, automatic extinguisher systems, and highly effective exhaust system in the dryers. The air in the dryers should be checked continually as to the concentration of organic vapors present. The lack of safety equipment of this type in the majority of plants limits the use of such solvent formulations for general purposes. Furthermore, in spite of the fact that solvent suspensions are widely and successfully employed on tentage ducks and fabrics of similar weight, the nature of the h i s h is not conducive to use on lighter weight materials for clothing or decorative purposes. These limitations have led to the development of emulsion formulations. Emulsions. The active flameproofing ingredients in many emulsion formulations are essentially the same as those employed in the solvent suspensions-Le. , a mixture of metallic oxide and a chlorinated wax or resin. The incorporation of the retarding mixture in an emulsion vehicle, however, permits compounds of good stability with lower solids content, of the order of 40 to 55%. The nature of the emulsion and the apparatus with which i t can be applied greatly simplifies the problem of obtaining accurate and reproducible add-ons. In addition, better and more uniform penetration results in equal flameresistance with lower amounts of added flameproohg solids. Flameproofmg emulsions may be applied by the techniques described for the solvent suspension formulations, but, in addition, can readily be run on regular textile fmishing equipment as described for the application of the double-bath and cellulose ester processes. In the simplest case, a typical commercial installation would be as represented in Figure 2, omitting the first
439
mangle, dryer, and cooling can. The amount of flameproofing solids added to the fabric can be controlled by the speed of running and the pressure exerted by the squeeze rollers or, alternatively] by variations in the effective concentration or viscosity of the emulsion. The retention of good stability over a wide range of concentrations or viscosities renders the emulsions applicable to a much greater variety of fabrics than is possible with the wlvent suspension compounds. With water-in-oil emulsions, the presence of the water raises the flash point appreciably and makes the procms a much safer plant operation. One advantage of these formulations, in which an organic solvent is the external phase, is the ability to incorporate relatively large amounts of glow-reducing materials such as zinc borate or melamine pyrophosphate, without upsetting emulsion stability. The use of oil-in-water emulsions, wherein water is the external phase, completely removes the hazard of combustible vapors. The water emulsions can be run in any bleachery or finishing plant on existing equipment. Any textile padder or mangle can be employed and the fabric procemed a t exceedingly high running speeds. The drying equipment can be of any of the types thus far discussed, although, because the dispersion medium is water, tenter frames are generally preferred in order to prevent shrinkage. From the finishers’ viewpoint] each of the various types of flame-resistant finishes has its particular advantages and drawbacks. The water-soluble retardants are particularly suited for application to fabricated items by virtue of the ease of obtaining uniform distribution and their eflectiveness a t relatively low addons. The double-bath system which have been available commercially to date require careful control of a rather complex finishing procedure and have been generally inadequate from the standpoints of flame-resistance and durability. The cellulose ester processes can be readily applied to a variety of fabrics on available mill equipment with the possible requirement of a special curing cabinet. The tendency toward limited permanence and loss in fabric strength poses a problem to the finisher in adapting the finish to particular end uses. Solvent-suspension formulations are particularly suited to heavy fabrics of the tentage and awning class, although their general use is restricted to mills capable of handling organic solvents. The use of emulsions reduces or eliminates the solvent hazard, and these vehicles are probably most easily adapted to existing mill equipment. As is probably apparent from the preceding discussion, there is still much room for improvement in the field of flame-resistant finishes, and we may expect that present research in this field will result in compounds and processes of greater efficiency and permanence to meet the requirements of the textile industry and the consumer. ACKNOWLEDGMENT
Much of the information contained herein was accumulated in the course of N.R.C. Project Q.M.C. 27. The authors wish to acknowledge the contributions of the many persons engaged in that project work as well as representatives of industry and the armed forces who contributed greatly to its progress. LITERATURE CITED (1)
Figure 5.
Commercial Installation for Knife Coating of Fabrics
Akin, E. W., Spencer, L. H., and Macormac, A. R., Am. Dyestuf Reptr.! 29, 418-45 (1940).
Vol. 42, No. 3
INDUSTRIAL AND ENGINEERING CHEMISTRY Boller, E. R., U. 9. Patent 2,097,509 (Nov. 2, 1937). Campbell, K. S., and Sands, J. E., Ibid., 2,462,803 (Feb. 22, 1949). Carroll, S. J., Ibid., 1,631,468(June 7, 1927). Cuppery, M . E., I b i d . , 2,212,152 (Aug. 20, 1940). Daly, A. J., Ibid., 1,941,664 (Jan. 2, 1934). Dreyfnss, C., Ibid., 1,907,521(May 9, 1933). Eichengrun, A., I b i d . , 1,985,771 (Dec. 25, 1934). Fischer, E. K., Ibid., 2,461,538 (Feb. 15, 1949). Ford, F. M., and Hall, W.P., Ibid., 2,482,755, 2,482,756 (Scpt. 27, 1949). Gay-Lussac, J. L., Ann. (,him. phys., 18, 211 (1821). Gulledge, H. C., and Seidel, G . R . , Isn. ESG. C m k f . , 42, 440 (1950). Hopkinson, H., U. S.Patent 2,250,483 (July 29, 1941); 2,343,186 (Feb. 29,1944). Jones, G., Juda, W., and 6011, S., Ibid., 2,452,054, 2,452,055 (Oct. 26,1948). Leatherman, E. W., I b i d . , 2,463,983 (March 8,1949). Lindsav. W. G., Ibid., 1,133,385 (March 30, 1915). Little, k. W., “Flameproofing Textile Fabrics,” A.C.S. Monograph 104, New York, Reinhold Publishing Corp., 1947. McLean, A., and Marrian. S.F., U. S. Patent 2,470,042 (May 10,1949).
(19) Perkin, W. H., Ibid., 844,042 (Feb. 12, 1907). (20) Pollak, F. F., Ibid., 2,418,525 (April 8 , 1947). (21) I b i d . , 2,421,218 (May 27,1947). (22) Pollnk, F. F., and Fassel, J., Ibid., 2,464,342 (March 15, 1940). (23) Ramsbottom, J. E., and Snoad, A. W., “Fireproofing of Fabrics,” Fabrics Co-ordinating Research Comni., Dept. Sci. and Ind. Research (Gr. Brit.), First Report, 1925; Second Report, 1930; Third Report, 1947. (24) Rosser, C. -M., U. S.Patent 2,305,035 (Der. 15, 1942). (25) Ruhrchemie A,-G., Brit. Patent 486,766 (June 7, 1938). (26) Triggs, W., I b i d . , 476,043 (Oct. 31, 1936). (27) Truhlar, J., and Pantsios, A., U. S.Patent 2,461,302 (Feb. 8, 1949). (28) Van Tuyle, R., Am. Dl/estu$Reptr., 32,297 (July 5, 1943), (29) White, C. B., U. S. Patent 2,427,997 (Sept. 23, 1947). (30) Whitehead, W., I b i d . , 2,032,605 (March 3, 1936). (31) Woodruff, J. A , , Ibid., 2,454,245 (Nov. 16, 1948). (32) York Research Corp. of Conn., Stamford, Conn., Reports I and 11, “Textile Flameproofing Compounds,” distrihuted by Am. Hotel hssoc., 221 West 57th St., New York, X . Y. (33) Zelger, G. E., U. S. Patent 1,586,775(Nov. 8, 1932). RECEIVED September 26, 1949. N.R.C. Project Q.M.C. 28, Dermrtment of Chemical
Engineering,Columbia University, Kew York, N. Y.
DURABLY FLAME-RETARDING CELLULOSIC M A T E R I A L S HUGH C. GULLEDGE AND GEORGE R. SEIDEL Pigments Department, E. I. du Pont de Nemours & Company, Inc., Wilmington, Del. This paper describes a new method for durably flameretarding cellulosic materials such as cotton and viscose. The chemical employed is based on an aqueous titaniumantimony complex known as Erifon flame retardant which, after a two-step process, appears to combine chemically with the cellulose molecule. Methods and problems of
application and propertirs of a variety of treated fabrics are discussed, and limitations as to durability, dyeing, and fields of application are pointed out. Technical aid is necessary before an individual mill can satisfactorily apply this process; several mills are now equipped to operate on a commercial scale.
OST papers dealing with the chemistry of titanium begin by pointing out that this element is the ninth most abundant in the earth’s crust, exceeded by oxygen, silicon, iron, calcium, sodium, potassium, and magnesium and trailed by such familiar elements as sulfur, phosphorus, copper, zinc, and lead. In spite of its abundance, most of the world’s industrial processing of titanium compounds is carried out in the United States and in 1946 amounted to only 125,000 tons per year in terms of titanium content. Table I compares the abundance and consumption of titanium xith more common though less abundant elements. Practically all the titanium has been produced in the form of pigment titanium dioxide, although recently the production of metallic titanium has been started on a limited commercial scale. Although titanium is abundant and relatively cheap and certain fundamentals of titanium chemistry have been known for years, this branch of chemistry is unfamiliar to the average chemist and relatively unexplored by the fen- chemists specializing in this field. It has been recognized for many years that organic compounds containing hydroxyl groups !\-ill react with titanium compounds. Thornton states ( 4 ) :
be, is closely connected with the hydroxyl group, since it is exhibited by glycolic and not by aretic acid.
It has long been known that certain metallic elements, which normally form insoluble hydroxides, carbonates, phosphates, etc., with appropriate reagents, fail to do so when certain organic substances-e.g., citric acid, tartaric acid, dextrin, sucrose, glucose, lactose, etc.-are present in sufficient quantity.. , . Confining our attention then to the organic acids, we may generalize by saying that this property, whatever its mechanism may
It has now been firmly established that titanium forms stable and definite compounds with many organic molecules containing hydroxyl groups. But most titanium compounds readily hydrolyze and form a precipitate of titanium hydroxide according t o the reaction: Ti(0R)I
+ 41120 +Ti(OH), + 4ROH STRUCTURE
Besides its four primary valences, titanium also has two sccondary valences, which add up to a coordination number of six This permits ring formation 01’ a chelated structure. Whero chelates can be formed with titanium, the resulting conipounds
Abundance and Consumption of Common Elements Abundance in Tons Consumed Element Earth’s Crust, ( 1 ) in 1946 (6) Ti 0 63 125,000
Table I.
P
0.13
Mn
0.10
S
CI CU
Zn Ph
0.052 0.048 0.010 O.OO{ 0.002
1,130,000 829,000 4,094,000 1,166,000 1,135,000 988,000 950,000
