Courtesy, E . I . d u Pont d e Nemours & Company, Inc.
EFFECTOF MILDEWREPELLENT The untreated fabria a t the left was inoculated with mildew: the dark spots show the extent of the mildew ravage. The same fabric (right) waa proteoted by a mildew repellent a n d inoculated in the same manner: there was no mildew attack.
CHEMICAL REPELLENTS F. J. VAN ANTWERPEN 60 East 42nd Street, Xew York, N. Y.
RESERVATION of utility in many materials by repelling harmful agents through the medium of chemicals has become a commonplace procedure in our industrial and everyday life. Damage to clothing, houses, furniture, and other familiar objects by fire, moths, water, and stains has been part of man’s travail since he acquired possessions. What Sir Walter Raleigh would have given for a waterproof, stainproof jacket is a matter of speculation, for aside from the chivalrous niceness of his gesture to the Queen, he did have a mess after she was safely over the mud puddle. I n fact, most of mankind, coming from more practical environments, looks askance a t Sir Walter’s impetuosity; it appears not so much as a gentleman’s courtliness, but as a peculiar way of getting a lady over muddy spots and as an unnecessary waste of whole cloth. The oddness of the incident helped to make it history, for we are unusually circumspect in the presence of mud because of its power to soil our garments. If by some magic our clothes became immune to destructive forces, not many generations would pass before our progeny would be quite a t home sitting in dirt, be unconcerned in the rain, check lighted cigarets in pockets, and never clean or press clothing. All this not because of some lowering of standards, but because there would be no reason to do otherwise. What civilization would be like if this became possible should cause some concern to the small army of chemists who are doing their best to bring this state nearer reality. The properties of all materials are continually under study and countless remedies are
advanced to circumvent shortcomings. The purpose of this article is to review what has been done in this respect and to present, where possible, the methods now in vogue for making any substances repellent to moisture, moths, fire, mildew, termites, and insects.
Fire Retardants Impregnation of wood, stage settings and drapes, clothing, and organic house insulation as a means of preventing loss by combustion is an old art. There are imposing lists of compounds which may be used alone and in combination for impregnation. Another familiar method of conferring fire repellency is to paint or cover the substance with a protective film such as that obtained with a dope of cellulose acetate or a combination of asbestos and sodium silicate. The theory behind the use of impregnation chemicals and dopes is rather vague. Selections and recommendations are predicated on experience rather than theory. Suitable tests for evaluating the efficiency of fireproofing materials have been slow in developing, and indications are lacking as t o the best materials and techniques to use. One of the most commonly recommended ways to render a substance fire retardant is by coating or soaking with a solution of borax and other salts which are usually ammoniacal. Borax, under heat, fuses and seals off the material from the air. Recently (1I) the London County Council recommended the use of a borax and boric acid solution for fireproofing textiles, 1514
INDUSTRIAL AND ENGINEERING CHEMISTRY
on the subject, but because of its importance it is reviewed a practical necessity because of the hazard from incendiary here. bombs. Another substance which acts in the same manner is The three most commonly accepted explanations of the sodium tungstate. To utilize this salt, fabrics are usually mechanism of fire retardation, are: ( a ) Some compounds processed in a bath containing acetic acid, which effectively fuse and seal off the fiber; (b) other compounds decompose prevents crystallization of the tungstate salt. Aluminum into nonflammable gases which dilute the oxygen of the air tungstate may be used instead of the sodium compound. and prevent combustion; and (c) the decomposition gases Most of the effective chemical salts are water soluble. Alblanket the material and prevent oxygen from seeping in, though this aids processing materials, it is a drawback because This first theory may be correct but the other explanations laundering or wetting will leach out the compounds. EXare due for a rather vigorous investigation, as it seems unamples of those substances which are water soluble and which likely that enough gas could be given off by the small amounts have fire repellent properties are ammonium sulfate, ammoof chemicals used to blanket effectively or to dilute the oxygen nium chloride, sodium tungstate, magnesium chloride, and to a point where combustion would not be supported. The various tin salts. Sodium carbonate, lead acetate, sodium new theory advanced is that the action is due mostly to the sulfate, zinc sulfate, and ferric sulfate are of little or no value, catalytic repression of combustion and the corresponding and other chemicals, such as the alkaline sulfites, are thought formation of greater amounts of charcoal. to increase combustibility. Tyner (12)recently published an Wood may be protected either by impregnating or by coatextensive study on the effectiveness of fire extinguishing ing its surface. The class of materials here used is similar to chemicals in water. Though his findings were limited to those applied to fabrics. For coating, sodium silicate plus wood and application of the chemical was made after the other fireproofing agents-alumina, alum, and calcium chloblaze had started, the general principles are akin and his conride and carbonate-have been used. When wood is treated, clusions are thought to be applicable t o the impregnation attention must be given to possible harmful effects, not only technique. Potassium carbonate, potassium acetate, potasto the wood itself but to the other construction materials, such sium bicarbonate, sodium acetate, and zinc and lithium chloas iron and plastics, used with it. Also, if a gas is given off rides possess some flame retardant properties. Phosphoric from the fireproofing compound when the wood burns, toxic acid, mono- and diammonium phosphate, and boric acids are effects must be considered. outstanding. Insoluble fireproofing compounds that will not leach from Mildew Repellents processed material may be obtained by using a two-bath procChaetomium globosum is the proper name for the species of ess in which soluble salts are made to react in such a way as mildew which is credited with causing most damage to textile to form insoluble substances in the interstices and pores of materials. Other tvDes of the treated object. There are fungi are unsightly b,; aside many ways of doing this-for from discoloration of t h e example, a pass through a bath fabrics, cause no great damage. of aluminum sulfate followed Chaetomium globosum attacks by a dip into sodium silicate the fiber directly and causes solution. This will form an loss of tensile strength. Cominsoluble aluminum silicate monly attacked are rugs, sails, combination which has fire refish nets, fire hose, and, of tardant properties. Another current interest, barricade recommended procedure resandbags. quires a preliminary padding Fungus growth on paint with sodium stannate and a films is well known, especially final treatment in a complex on those low in pigment and bath containing soluble zinc exposed to a warm, humid atsalts; this treatment results in the deposition of an insolumosphere. Though not parble zinc complex. The adticularly destructive to paint, this condition is unsightly. In vantage of insoluble retardants is obvious, and the permutafood and pharmaceutical plants where infection of product may tions and combinations possibe serious, elimination and preble with the many soluble and vention become important. insoluble substances possessing Rotting of wood is the result desirable noncombustive propof another type of well known erties are enormous. Each fungus attack. processing mill has its own pet A g r e a t m a n y chemical methods. New compounds are agents provide necessary probeing discovered every day. tection. For fabrics a recent Thus, it is impossible to cover this field completely. Ammostudy (1) with tests and results nium sulfamate is a recent adlists more than eighteen difdition to the list and sodium ferent compounds and treatborophosphate has been used ment for protection of cotton for a number of years as a against loss of strength due t o flame retardant. mildew. Some of the satisfacAn important advance in tory treatments and materials the art is the development of a described are: an alkylated Courtcay, E. I. du Pant de Nemours & Company, Inc. theory of the action of the fire dimethyl benzyl ammonium retardant compounds. Tyner phosphate alone and with an SPRAYTESTBR FOR DETERMINING WATEIR RE(12) summarized the thought acrylic resin, salicylanilide, PELLENCY OF TREATED FABRICS
INDUSTRIAL AND ENGINEERING CHEMISTRY
o-phenylphenol, 2-chloro-o-phenylphenol,pentachlorophenol, sodium pentachlorophenolate, thymol with phenyl salicylate, chlorothymol, the dye catechu, many organometallic compounds such as copper propionyl acetonate, p-tolyl mercury salicylate, cadmium and copper soaps, and inorganic salts. Many of these substances, in fact most of them, are commercial developments and are available for general use. Some, such as the two-bath process in which the cloth is dipped for 10 minutes in a soap bath of 0.5 per cent strength and then into a 1 per cent cadmium chloride or copper sulfate solution for 30 minutes, are reasonably good mildew preventives requiring only the use of easily available chemicals. For sails, nets, and washables, water-soluble preservatives are not suitable for obvious reasons. For such cases a method of placing an insoluble deposit on the fabric is necessary, and this is sometimes done by forming insoluble soaps, mordants, and resins by two or three bath methods. Another way to protect materials which will come in contact with water is to use water-insoluble compounds dissolved in a solvent and impregnate the fabric with the solution. Copper propionyl acetonate, dihydroxy hexachlorodiphenyl methane, and p-chloro-m-xylenol are examples of the water-insoluble compounds which are applied in this manner. The last named is used in paints and baths of wax finishes also. One recently proposed method (10) calls for a preliminary impregnation of fabric with 3 per cent of sodium pentachlorophenate t o be followed immediately by a squeezing operation and another impregnation in an alkaline bath of lead acetate. This forms an insoluble lead pentachlorophenate which is not washed out by water. @-Naphtholhas been used for many years as a mold preventive in sizing baths for textiles. Silk throwsters have used cresylic acid t o prevent fungus attack on processed silk, and zinc sulfate was utilized years ago in cotton mills as an antimildewing agent. For use in manufacturing processes odor is of no consideration-witness the extensive use of cresylic acid by silk throwsters. For consumers, however, care must be exercised not only to have a pleasant smelling material, but one which will not cause eruptions when in contact with the skin. Preservation of wood is a matter of some economic importance for, aside from fungus attacks, the wood must withstand termite, rodent, borer, and insect ravages. Hubert (9) conducted tests on twenty-five chemicals and eighteen proprietary wood preservatives with the object of finding the most effective and most economical substances for preserving wood by a nonpressure method. Of the many tested, four were found most promising-pentachlorophenol, o-phenylphenol, 2-chloro-o-phenylphenol, and tetrachlorophenol. Also recommended (7) have been dips in solutions of ethyl mercuric chloride and also a mixture of sodium tetrachlorophenoxide and sodium-2-chloro-o-phenyl phenoxide. Organic mercurials have been used to protect freshly cut lumber against superficial molds, stain, and decay fungi. S o t all wood is necessarily subject to such destructive forces. Cypress and cedar have natural oils which apparently protect them. Although fungi can live in wood containing less than 20 per cent moisture or in wood which is so deep in soil or water that oxygen is excluded, they cannot reproduce. For protecting wood against termite and fungus attack, impregnation with creosote has been practiced for many years; zinc chloride is also a known specific against termites and decay. Both are highly successful; the creosote is used where color and odor are not important, such as in railroad ties and telephone poles, and zinc chloride and more recently chromated zinc chloride are utilized where clean odorless surfaces are needed. The United States Department of Agriculture (13) sponsored crude liquid o-dichlorobenzene as a soil poison for termite protection.
Vol. 33, No. 12
Mothproofing Three kinds of moths and four kinds of carpet beetles are principally responsible for damage t o stored clothing, rugs, blankets, and other textiles. Though these insects usually attack proteinaceous fibers-wool, fur, and leather-occasionally fabrics which are not protein are ravaged. There are two reasons: The size or finish used on the cloth contains protein matter, or the larvae which attack cloth must supplement its supply of silk with extraneous matter for the completion of its cocoon. It is immaterial whether the fiber is proteinaceous or not because the larvae do not utilize it as food. The adult carpet beetle, unlike the mature cloth moth which has imperfect mouth parts and starves shortly after mating, is able to eat after reaching the mature state but it evinces no interest in fibers, confining itself to other foods. Like the clothes moth larvae, the growing worm or grub of the carpet beetle causes the damage. Chemical protection may take severalforms. The breeding ground may be freed of the attacking insects by a fumigant, the intended food is impregnated with a quick-acting poison which stops the damage by killing the larvae, or a repellent chemical is used to make the fabric unpalatable to the larvae which either starves or moves t o other feeding grounds. Repellents are usually a metal combination (such as aluminum, magnesium, or ammonium) of sodium silicofluoride or sodium silicofluoride itself (6). About 90 per cent of the commercial products sold are of this type. They are not removed by dry cleaning but can be leached out by washing in water and, though not permanent, retain their potency for a long time. Another repellent is dixylylguanidine which, dissolved in naphtha, is applied by a pressure spray t o fabrics and upholstery. The dixylylguanidine, left behind in amorphous form when the naphtha evaporates, renders the feeding ground unpalatable to the larvae. Of the toxic compounds only a few are successful. One of the main difficulties is that of a skin dermatitis produced by the action of the toxic compounds. Antimony and arsenious fluorides are used for this type of protection. A colorless organic dye is also commercially available which may be added to the goods along with the conventional dyes in an acid bath. Immersion in baths containing as little as 2 per cent of the textile weight of this compound, pentachlorodioxy triphenyl methane sulfonic acid, is said to confer an immunity against carpet beetles and moths which resists washing, dry cleaning, perspiration, and sun exposure. It is not toxic to human beings. A chlorinated phenyl benzyl phosphonium compound which is toxic to the feeding larvae is another commercially available preparation. Fumigation chemicals such as sulfur dioxide, hydrocyanic acid gas, methyl bromide, ethylene oxide, a mixture of three parts of ethylene dichloride and one of carbon tetrachloride, many familiar household treatments with naphthalene, pdichlorobenzene, camphor, and cedar chips, have all been tried and found workable if properly used as regards concentration and time of exposure. Martius Yellow (2,4-dinitro-or-naphthol) has often been mentioned as having protective properties. Pyrethrum and rotenone (5) deposited on fabric from a petroleum solution have been investigated, as have the rare earth soaps ( 4 ) . Aliphatic thiocyanates, which have replaced much of the rotenone and pyrethrum used in fly sprays, dissolved in refined kerosene along with a little perfume is being introduced to the home as a mothproofing spray. The thiocyanate is a contact poison and must hit the larvae in order t o be effective. Quinidine and various other cinchona derivatives ( 3 ) have been used with success. An index of patented mothproofing material is available (8) which is an excellent resume of the work done on this subject.
I N D U S T R I A L A N D EN G I N E E R I N
Courtesy, E . I . du Pont de Nemoure & Company, Inc. STANDARD CHART FOR RATINQ
FOR WATER REPELLENCY 70. Partial wetting of whole of upper surface. SO. Complete wetting of whole of upper surface.
100. No stioking or wetting of upper surfaoe. 90. Slight random sticking or wetting of upper surface. 0. Complete wetting of whole of upper and lower surfaoes. 80. Wetting of upper surface at spray points. (Colored water was used for photograpic effect.)
Water Repellents The methods and chemicals that have been advanced as a means of conferring water repellency to porous absorbent substances are so numerous that only those used most in present-day practice can be mentioned here. The greatest commercial outlet for water repellents is in the textile field, although some market has been developed for building cements, wood, and materials closely allied to textiles such as cellophane and wrapping paper. I n the textile industry two types of treatments are employed-those which produce waterproofness and those which produce water repellency. The waterproofing treatment is essentially a coating operation which produces a fabric having closed pores. Examples are tarpulins, ducks, rubberized textiles, and awning materials. Water repellent characteristics are obtained essentially by impregnation operations in which the fibers are rendered water resistant without closing the pores of the fabric. Examples may be seen in many of the cloth raincoats now on the market and in other articles of clothing such as golf and hunting jackets, children’s play suits, and cotton work clothing, all of which possess water repellent
characteristics and yet allow proper ventilation or breathing of the body pores. A typical impregnation treatment would consist in passing the fabric through a bath containing 1 or 2 per cent of an aluminum acetate wax and/or soap emulsion in which the pH is controlled between 4 and 6 per cent by means of an organic acid, after which the fabric is hydroextracted and is dried in the usual manner. One of the earliest techniques of waterproofing made use of two baths. Here an impregnation in a soap bath, which left some soap and oil on the fabric, was followed by a dip in a metallic salt solution. An insoluble metallic soap with water repellent characteristics was thus formed on the fiber. Variations of this method are both numerous and ingenious. The processing may be done in an organic solvent or in water, but in general they follow closely the example given above. However this practice has been practically outmoded in favor of the wax-soapaluminum acetate emulsion used in one bath. Waterproof effects may be obtained by coating with rubber, viscose, cellulose acetate resins, and varnishes. Waxes and derivatives of waxes are used in waterproofing paper and fabrics, and are applied either in solvent or emulsion form.
INDUSTRIAL AND ENGINEERING CHEMISTRY
An important recent advance which has already received much attention in the literature is the use of a chemical which reacts with the textile fiber in such a manner as to form a water-insoluble complex. The material is a long-chain quaternary ammonium compound (9). I n textile applications the fabric is immersed in water solution of the chemical so that about 6 per cent of the substance is deposited. The fabric is then dried quickly in a low-temperature air blast of 200" E'. The fabric, however, does not become warmer than 100' F. A heating or curing operation is next in which the now dry cloth is subjected to a 3-minute heat treatment a t 300" F. It is during this period that the compound breaks down and forms the water-insoluble complex which confers the water repellent effect upon the goods. The final step is a washing operation which neutralizes the slight residual acidity on the fabric and removes unreacted and by-product compounds.
Vol. 33, No. 12
Literature Cited (1) Furry, M. S., Robinson, H. M., and Humfeld, H., IND.ENQ.
CHEM.,33, 538 (1941). ( 2 ) Hubert, E. E., Ibid., 30, 1241 (1938).
(3) (4) (5) (6)
Jackson, L. E., and Wassel, H. E., Ibid.. 19, 1175 (1927). Jones, H. I., U.S. Patent 1,921,926 (Aug. 8, 1933). McGill, W. J., Ibid., 1,854,948 (April 19, 1932). Minaeff, M. G., and Wright, J. H., IND. ENG.CHEM.,21, 1187 (1929).
(7) Prescott, S. C., and Dunn, C. G., "Industrial Microbiology", 1st ed., New York, McGraw-Hill Book Co., 1940. (8) Roark, R. C., and Busby, R. L., U. S. Dept. Agr., Bur. Entomology and Plant Quarantine, 1st. 2nd, 3rd Indices of Patented Mothproofing Materials, 1931, 1933, 1936. (9) Slowinske, G . A., Am. Dyestuff Reptr., 28,647-50 (1939). (10) Stringfellow, W . A., Ibid., 29, 266 (1940). (11) TeztiZe Colorist, 63, No. 747, 164 (1941). (12) Tyner, H. D., IND. ENO.CHEM.,33, 60 (1941). (13) U. S. Dept. Agr., Leaflet 101 (revised June, 1936).
Cellulose from Hardwoods Wood Pulp Purification GEORGE A. RICHTER' Brown Company, Berlin, N. H.
REVIOUS papers in this series dealt with the chemical and physical properties of New England hardwoods (2) and described their behavior when pulped with acid sulfite liquors (3). This paper describes the processing of such unbleached pulps to yield substantially white fibers with a variety of property combinations that have value in the paper industry and for esterification. So that their behavior may be compared with more widely known wood pulps, comparison treatments and tests for corresponding softwood pulps are frequently cited. Most of the discussion has to do with pulps produced when the respective woods are digested with sodium bisulfite cook liquors; it has been found impractical to use the all-calcium base liquors satisfactorily with some of the hardwood species. Table I gives typical values of unbleached wood pulps obtained when the several unseasoned wood species were chipped and digested in acid liquors that contained 5 per cent free and 1 per cent combined sulfur dioxide (defined in the previous article, 3), where the liquor volume was such that 6 per cent combined sulfur dioxide was present, based on wood. I n each case the cook schedule prescribed an increase in temperature from 25' to 140' C. in 4 hours and a maintenance a t that level for 4 hours. Maximum gage pressure was held a t 85 pounds by causing some gas escape from the digester. Tests given are representative of pulps prepared from wood chips produced with a large rotary knife chipper (3). When the raw stocks of Table I were bleached by a sequence that comprised chlorination followed by oxidation with hypochlorite, the bleached pulps took on the characteristics listed in Table 11. Results in Tables I and I1 may be summarized as follows: 1
Present address. Eaatman Hodak Company, Rochester, N. Y.
Unbleached hardwood pulps can be processed to yield substantially white products that possess properties and chemical composition suitable for esterification and for conversion into stable papers. Means are given for the elimination of resinous bodies and for the extraction of pentosans and nonalpha-cellulose constituents. All procedures cited are accompanied by parallel treatments made with the better known softwood pulps. Occasional reference is made to the purification of the kraft pulps although the discussion is confined for the most part to treatments of stocks prepared by the acid sulfite cooking process. No attempt is made to indicate preferred commercial procedures inasmuch as a chosen purification sequence depends largely upon local conditions and the outlets for which the end product is intended.
1. As shown in a previous article the unbleached hardwood pulps are richer in pentosans and lower in papermaking strength than the softwood ulps. This difference carries through to the bleached pulps ma$ by the sequence iven. 2. There is a distinct tendency for the hardwood pulps to have lower solution viscosities when dissolved in cuprammonium reagent than is found with the softwood products. This same relation holds in the case of the bleached pulps. 3. Although the maple and the beech pulps have low percentages of extractables, the birches (particularly the white birch pulps) are characterized by high ether-soluble content. In all