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INDUSTRIAL AND ENGINEERING CHEMISTRY
German hydrogen peroxide plant utilizing thir equipment. Reichert and Pete (19) describe the uses of various materials of sonstruction with hydrogen peroxide. The manufacture of 2hlorine and hydrogen peroxide are electrochemical industi ies. and an article on the use of chemical stoneware in the electro-hemica1 industries in general is reported by Kingsbury (13) Chemical stoneware, besides its use as a material of construction, is utilized in the manufacture and handling of acetic acid (6), in metal plating (8), in the rayon industry ( f O ) , and in .he manufacture of foodstuffs such as vinegar ( 2 7 ) ; it has also wen utilized, although generally only for very large pieces, for +lectrical insulators (24). CompanieG of the pharmaceutical industry, where the slightest contamination is not permissible, are also large wers, as are, l o a limited eutent, the food indiistries The utmost advantage car1 be obtained from chemical stoneware when it is installed and maintained in a manner such ab to minimize its fragility and susceptibility to thermal ihock. Methods of installation for ceramic equipment are rlPsrribPd h> Kingsbury (9, 11) and Pryce (18).
Vol. 39, No. 10
General Ceramics Bulletin, “Properties of Ceramic Bodies for Chemical Stoneware Equipment,” 1946. Herstein, F. E., Chem. Eng., 53,No.12, 214-16 (1946). Ibid., 54,No. 3, 216-20 (1947). Hodson, G. N., PotteTy Gaz., 59,No.679, 65-70 (Jan. 1934,. Hogsboom, G . B., Jr., and Hall, N., ,Metal Finishing, 44,KO.2, 63-6 (Feb. 1946). Kingsbury, P. C., Chem. Inds., 45,564-6 (1939). Kingsburs, P. C.. IND. EPG.CHEM.,22, 130-2 (1930). . . Ibid;, 29,402-5 (1937). Kingsbury. P. C., Trans. Am. Inst. Chem. Enyrs.. 36, No. 3. 433-42 (1940). Kingsbur)., P. C., Trans. Electrochem. Soc., 75,131-9 (1939).
Kingsbury, P. C., and Rlehrof, F. E., Am. Inst. Chern Eners., Mtg., Berlin, N. H., June 21-23, 1926. Knisek, J. O., Ceram~icInd.,37, X o . 6, 74-6 (Dec. 1941). Olive. T. R.. Chem. & Met.. 40.369-71 11933).
Ihid.. 46, 512-16 (1939). Pryce, -%. C. H., I n d . Chemist, 244-0 (Oct. 1941). Reichert, J. S.. and Pete, R. H., Chsm. Eng., 54,X o . 1.L13-Lb (194ij. Robitschek, J. H., Ceramic A g e , 40,S o . 5, 134-6 [Nov. 1942j. Robitachek, J. H., Ceramic Ind., 41,No. 1, 48-51 (July 1943); 41,So. 3, 64--6 (Sept. 1943). Singer, F., Address before Assoc. of Czechslovak Scientists & Technicians, Communication 119 (Feb. 23, 1944). Singer, F., Ceramic Age, 17, No. 6, 300-5 (June 1931j. Singer, F., Helios Elec. Ezport Trade J., 38,355 (1929). Velisek, J., and Vasicek, A., Kolloid-Z., 1, No.1, 36-48 (19353. Wuldenburg, M., and White, L. M.,C . S. Dept. of Commerce. Office of Pub. Board, R e p t . 197 (June 1945). Wustenfeld, H., Deut. Easigind., 30, No. 17-18, 137, 138. 145 (1926).
LITERlTCRE CITED lr Anonymous, Chimle & industrie, 28, No. 3, 507-23 (1932). !2) Anonymous, Ullman Encyclopedla, 10, 420-34 (1932). 13) Chamberlain, J. hl. W., Machane Derign, 6, S o . 6, 23-5, 80-2 (1934).
WOOD ALFRED J. STARIM, U . S . Forest Products Laboratory, Madison, Wis.
F
RON the beginning of Vorld War I1 UJI to the present time
the supply and demand for wood as a structural material have undergone drastic changes. During the early stages of the war when practically all metals were in short supply, wood was called upon to fill a large part of the gap. I n some cases wood served as an excellent substitute, whereas in others it could be considered only an emergency substitute. This burden on wood as a substitute for so many items, added to the normal evtensive uses where it naturally excels, finally resulted in the demand greatly exceeding the supply. Fortunately, M hen this occurred, the supply of metals was materially improving. The drain on wood has not abated since the end of the war, because military demands have been replaced by domestic housing and industrial structural demands. This cycle of events has been a healthy situation from the standpoint of wood research. The need for modifying wood for special uses was for the first time fully appreciated and resulted in research that has, in a number of instances, already paid dividends. Kood is, in many respects, an ideal structural material. ETcept for the last two years of the Tar and the first postwar year, it has been readily available. It has eytremely high strength per unit weight. It is noncorrosive and has the highest thermal insulating value of the structural materials, and above all it is extremely easy to fabrlcate. Its chief drawbacks are that it is susceptible to decay, it isill burn, and it will shrink and swell. These shortcominA5 can be overcome to an appreciable extent by
PRESERVATIVE TRE4TBIENT
The preservstivc treatment of wood is an old, well developed industry in d u c h there have been no revolutionary advances since the beginning of the Tar. Creosote is still considered the
most effective preservative against decay, termites, arid niariiir borers (40). Preservatives of the so-called clean types, comprising both the inorganic salts, such as chromated zinc chloride (36, 40), and toxic organic compounds dissolved in a clear organic solvent, such as pentachlorophenol (24, 34), have nevertheles~ gained in uqe because they do not discolor or impart an odor t c wood and can be painted over. Background on all phases of the wood preservation indu3try can be obtained from the most up-to-date book on the subject (40). The important features of toxicity and permanence of the preservative, together with the adequacy of the treatment, from the standpoint of amount of preservative taken up, its distribution, and the depth of treatment, should all be considered. Inforniation on specifications is given in two recent publications ( 2 , 96). The special problems of protection against termites (43, 7 1 ) and marine borers (8, 66) are covered in special reports on the subjects. Methods of treating by pressure impregnation and bj steeping are covered in several Forest Products Laboratory reports and Cnited States Department of Agriculture bulletins (14, 38, 39, 4 6 ) . (The former are available from the Forest I’roducts Laboratory on request without cost. The bulletins are available from the Superintendent of Documents, Kashington, D. C., a t slight costs.) An up-to-date general discussion of factors influencing decay and the natural decay resistance of various species has been compiled (36, 40). General reports on available preservatives and testing of preservatlves have been issued (27, 29, 40). T o obtain optimum service life of timbers used outdoors as equipment supports, permanent scaffolding, etc., the material should be creosoted. Slmilar wood structures under roof cover but still subject to decay may be treated with accepted toxicsalts inqtead of creosotes. The service life of wooden pipes, sluices
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INDUSTRIAL AND ENGINEERING CHEMISTRY
and water-storage tanks is sufficiently increased by a creosote treatment to much more than repay the cost. Creosoting is also well worth while in the case of timber and lumber used in watercooling towers. FIRE-RETARDANT TREATMENTS
The amount of wood impregnated with fire retardants is a very small fraction of that treated with preservatives. In 1944, for example, 3330 million board feet of wood were treated with preservatives in contrast to 8,500,000 board feet treated with fire retardants (35). Fire retardants find most of their normal use in various industrial buildings and in structures erected in localities where the use of materials having a low degree of flammability is prescribed. During the recent war the chief use was for large dirigible hangars. Military use, chiefly for this purpose, reached an all-time high of 65,000,000 board feet in 1943 (35). Wood beams and other heavy structural members are not so hazardous from a fire standpoint as the general public has been led to believe. Because of the low heat conductivity of wood, char tends to progress inward very slowlv in large timbers. When subjected to the intense heat of a fire, wood structural members have been known to continue to support their load when unprotected steel members have softened sufficiently to fail (40). To reduce the fire hazard further in industrial buildings and structures that support or are part of processing equipment, it may frequently be desirable to use wood treated with fire-retirdant chemicals. A number of chemicals have been found to possess fire-retardant properties (3, 40, 94). Ammonium salts, including the ammonium phosphates and ammonium sulfate, borax, boric acid, phosphoric acid, zinc chloride, and chromated zinc chloride are the most commonly used fire retardants, the ammonium phosphates being the most effective (40). Some of the laboratory methods used for evaluating fire-retardant treatments are described in government publications (51,56,5?) Tests have been made to show that fire-retardant treatments have a considerable effect in reducing the spread of fire caused by incendiary bombs in simulated attic and roof structures (48). Tests on doors (50) have been described for evaluating the effectiveness of fire retardants. Information on ignition and charring temperatures has been summarized (49). Data on the corrosive action of fire-retardant salts upon metal fastenings have been obtained, together with data on the inhibiting action by sodium dichromate (98). The most up-to-date thought and practices on fire-retardant treatments are covered in a recent American Wood Preservers' Association committee report (3). Valuable work has been done on developing fire-retardant surface coatings for wood (9, 15, 92, 96, 97). The effectiveness of coatings in retarding the spread of fire depends upon the amount of coating applied and the character of the igniting fire, as well as the fire-retarding properties of a specific formulation. The numerous preparations that have been proposed fall into three general classes: water solutions of fire-retarding chemicals with or without a suitable thickening agent or pigment (15,96);water-soluble fire-retarding chemicals in a vehicle such as linseed oil or a synthetic resin (9, 92, 96, 97); and mater-insoluble chemicals in an organic solvent or vehicle (96). The coatings of the first two classes are, unfortunately, subject to leaching and therefore should always be used under cover. To date no proposed water-insoluble fire retardant has been found to be so effective as ammonium phosphate, borax, or sodium silicate. Coatings of the third class proposed to date, although possessing greater water resistance, are inherently l e v effective against fire than those of the othrr two classrs. TANKS FOR WATER AND ACIDS
Wood has established itself through the years as an excellent tank material, both because of its noncorrosive properties and its
1257
ease of fabrication (16,33). Experience has shown the heartwood of cypress, southern yellow pine, Douglas fir, and redwood to be the most suitable (33). This appears to be due to a combination of difficulty of water penetration and natura1 resistance to decay and hydrolysis. The strength properties of water-swollen wood are, in general, considerably less than those of wood a t 12% moisture content, in some cases even less than half (53, 101). This must be taken into account in designing tanks for water or aqueous solutions. Sonswelling petroleum oils, on the other hand, have no effect upon the strength. Acids have a hydrolytic effect upon the cellulose of wood and thus cause some permanent loss in strength. A series of test on the modulus of rupture of three different coniferous species and three broadleaf species, in which the specimens were soaked for 4 weeks in various acids and alkalies and compared with controls soaked in water to eliminate the effect of normal swelling, showed negligible weakening due to acetic, lactic, and nitric acids in concentrations up to 10% and only slight weakening in hydrochloric and sulfuric acid of this concentration (44). Ammonium hydroxide in concentrations of more than 5 percent caused considerable loss in strength (up to one half), especially in the case of broadleaf species. Sodium hydroxide had an even greater weakening effect (44). In the case of alkalies the weakening appears to be due to excessive swelling and softening of the lignin. Other testa in which pitch pine was soaked in 20% sulfuric acid, 15% hydrochloric acid, and SO% acetic acid for 135 days gave only a 16% loss in strength after drying for the specimens soaked in sulfuric acid, but a 46% loss for specimens soaked in the hydrochloric acid, while the acetic acid caused no loss in strength (1). The effect of acids, alkalies, and salts in several different concentrations upon several species of mood has been visually observed (4,5, 33). I t appears that acids with pH values above 2 or bases with pH values below 10 n*ill have little weakening effect upon wood (44). Acid-resistant coatings of the bitumen type are claimed to improve the acid resistance, in cases where they can be used, as a result of cutting down the liquid absorption by the wood. Sufficient moisture and solute will pass through these coatings, however, to swell the wood in time (4). Improving the acid resistance of wood by resin treatments will be considered in a later section. GLUED LAMINATED STRUCTURES
The properties of plynrood and various other laminated structures and the conditions under which they can be used depend largely upon the nature of the bonding glue. One of the most important advances in wood utilization as a structural material during the last decade can be credited to a large degree to the improvement in glues and gluing techniques. I t is important that, the glue bond of both structural plywood and laminated structures be as strong as the wood in shear parallel to the grain and in tension across the grain throughout the service life of the material. This condition is readiiv met by most good woodworking glues under dry condit'ions (I.?, 38, 31, 99). Casein glue, although not water resistant in the modern sense, is much more so than the ordinary starch and gelatin glues (28). Caseinbonded plywood maintains its dry strength well at relative humidities of about 90% but loses half or more of its strength on water immersion (68). The relatively recent :Lddition of toxic chemicals to casein glue has greatly retarded the development of molds and other microorganisms and, as a result, has considerably increased its durability a t high relative humidit,ies (28). Casein glues have a good resistance to dry heat. Prolonged exposures to t,cmperatures as high as 158" F. sliuiv but a slight, weakening effect (28). They can be applied t o mood over the broad moisture content range of 2 to lS%, although G to 12% moisture content is preferable. They will set up a t room temperature in about 4 to 6 hours to the extent that glue clamps can be removed. Glue pressures of 100 to 200 pounds per square inch are adequate
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INDUSTRIAL AND ENGINEERING CHEMISTRY
for gluing the coniferous species which are normally used for this purpose. Casein glues were extensively used during Korld War I for such severe exposure uses as aircraft plywood and propellers. Considering the adverse use conditions, the service records are reasonably good. Heavy laminated construction using casein glue was first introduced into this country from Europe only a little over a decade ago. Laminated arches glued nith casein glue were used in the interior construction of a service building a t the Forest Products Laboratory in 1934. Since then, hundreds of structures employing glued laminated arches and other interior supporting members have been erected in the United States (7, 22,63,45,106). These structures have stood up well under all conditions of reasonable exposure. It has been demonstrated that such laminated structures have a number of advantages over solid wood: (a) the greater availability of the small size stock from which the structures are laminated; ( b ) the fact that the stock can be preseasoned before assembly, to simplify drying and eliminate the severe seasoning checks that often occur in large timbers; (c) the fact that the laminations can be prebent and laminated into shapes unobtainable in solid wood; and ( d ) the possibility of selecting the superior laminates for use in the part of the structure where the stresses are to be greatest (106). Synthetic resin glues of urea-formaldehyde and phenol-formaldehyde resin types came into prominent use for the bonding of plywood more than a decade ago. The urea resins are somewhat cheaper than the phenolic resins and have the advantage of setting a t lower temperatures. They are, however, not so durable, especially a t elevated temperatures (13, 31, 99). Urea rebins are available that set at temperatures ranging from room temperature to 200-300" F. All of them are acid-catalyzed, the lower temperature resins being the most acid. The room temperaturesetting urea resins were tried during the war in making special laminates requiring high water resistance, such as laminated oak keels for various vood boats, but these attempts proved unsuccessful ( 2 3 ) . Although the room temperature-setting urea glues have been successfully used in bonding birch veneer that does not delaminate on prolonged water soaking (S1,99), both oak and Douglas fir laminated timbers bonded with this type of resin showed considerable delamination on mathering and on salt-water soaking after less than a year's exposure ( 7 , 23). Hot-setting phenol-formaldehyde resins are alkaline in reaction and highly durable (99). They are, however, suitable for gluing up thick structural laminates only with high frequency dielectric heating (24) because of the difficulty of conducting heat to the inner glue line. Setting the glue by dielectric heating methods is not only expensive but technically involved, because of the difficulty of obtaining uniform and controlled heat generation (94). Intermediate temperature-setting phenolic resin glue., 1%-hich set a t temperatures slightly above room temperature, are generally acid-catalyzed. Excessive acid in such glues is liable to damage the wood adjacent to the glue line and thus cause reduced durability in spite of the durability of the resin itself. Approximately neutral and alkaline phenolic glues that sct a t temperatures of about 120' to 200" F. do not have this shortcoming (99). They, however, have to be cured in a kiln or heating chamber, which materially adds to the cost ( 7 , 23)). Intermediate temperature-setting melamine-formaldehyde resin glues have been recently developed (19, 0'8, 99). When these are cured a t about 120' to 190" F., they appear to have durabilities similar to hot-press phenolic resin glues. When excessive acid is added to lower the temperature of cure, inferior joints are obtained. Resorcinol-formaldehyde resin glues have recently been developed that combine the desirable low temperature-setting properties of urea resin glucs and the resistance to weathering and durability of phenolic resin glues ( I S , 19, 68, 63, 99). These
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glues, although rapid setting, are practically neutral and hence should have no hydrolytic effect upon the wood. They are catalyzed by the addition of paraformaldehyde or formalin, which is added just prior to use. They will cure a t temperatures of 70" to 80" F. when used on soft-textured woods that are held under pressure for several hours (63). On harder species, such as oak, it is preferable to glue a t somewhat higher temperatures. To assure complete cure, the glued-up laminates should be conditioned for about a week a t room temperature before being loaded or exposed to the weather. Although resorcinol glues have been so recently developed that service records of only about 3 year's duration are available, they appear to be as durable as hotpress phenolic resin glues. A large number of laboratory tests have been made on the various room temperature- and intermediate temperature-setting urea, phenolic, melamine, and resorcinol-formaldehyde resin glues to determine the effect of the moisture content of the wood (58) on the pot life of the glue (61); open and closed assembly periods (60, 61) ; variations in glue-line thicliness (61); temperature and time of cure and time of conditioning (19, 62, 63, 99) on the shear strength and percentage glue-line failure before and after various cyclic exposures (13, Si, 99); and the effect of several variables on the fatigue strength (65, 59). Types of glue and their manufacturers have been compiled (SO). It has been shown that wood treated with oil solutions of chlorophenol preservafives can be glued (42). Treatments with fire-retardant salts in effective concentrations have a detrimental effect upon subsequent gluing with some adhesives ( 1 2 ) . Laboratory durability tests have, in general, been substantiated by service tests to date. Over 1,000,000 board feet of laminated oak timbers have been fabricated with intermediate temperature-setting phenol, resorcinol, and melamine-formaldehydr resin glues and put into service, some as boat keels that are intermittently exposed to salt-water immersion and drying with little or no delamination (23). Douglas fir and shortleaf pine laminates have been succesqfully made for such uses as railroad bridge stringers (7, 23). It is felt that similar laminates can be used to advantage in various forms of chemical engineering structures and equipment, both for indoor and outdoor use. WOOD CONhECTORS AND BOLTED COh STRUCTION
Yo structure is stronger than its joints Nailed and ordinary bolted joints are usually less strong than the structural members themselves. To overcome this difficulty to a large extent, various types of connectors were developed in Europe and introduced into this country several decades ago (64, 93). Connectors are various types of metal inserts that are used in conjunction with bolted joints to help distribute the stresses and thus avoid the necrssity for the bolt to take the full load. They have proved effective in accomplishing their purpose (64,66, 67, 93). Both wood and modified-vood connector plates or bearing plates have proved of value in obtaining improved bolt-bearing properties (32, 41, 47, 93'). Recent data have been collected relative to the effect of size and shape of the bearing members, and size, number, and position of bolt holes on the bearing strength (36,41, 47). These data are of considerable importance in the design of the most efficient wood structures and equipment. General information on wood as an engineering material is given in a recent publication (52). Average strength data for the various species suitable for use in design have been collected and compiled (53) MODIFIED WOODS
Modified wood is a recently coined term used to designate wood that has been either chemically treated, mechanically compressed, or both so as to improve its water resistance and thus minimize swelling and shrinking, warping and checking, or to improve certain mechanical properties. Several materials of this class were developed just before and during the war. The earlier developed
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INDUSTRIAL AND ENGINEERING CHEMISTRY
materials found quite prominent war use. All of them, it is felt, will find specific postwar uses in places where the improvement in properties warrants the increased cost. h t least for t,he present., none of these materials can be considered to be substitutes for general utility lumber. COATIXGS. Earlier attempts to stabilize the dimensions of wood were all focused on supplying wat'er-resistant coatings to the surface or impregnating wood with water-resistant materials. Such treatments have proved effective in retarding the rate of moisture absorption and swelling, but they have not been effective in reducing the final amount of swelling under prolonged exposure to high relative huniidity ( 1 7 , 37). This is due to the facts that all coatings that ahdere readily to wood allow the passage of some moisture and that internal coatings cannot be made perfectly continuous ( 7 4 ) . Fairly good moisture-excluding efficiencies can be obtained, however, with surface coatings of pigmented paints, especially aluminum paint and synthetic resin varnishes (17, 37) and somewhat lesser effects with wax treatmenh (31')or dipping in water-repellent chemicals iu petroleum solvents (18). Coatings significantly retard the absorption of liquid water on intermittent exposures and the rate of adsorption of water vapor under rapidly oscillating relative humidity conditions. Consequently, they reduce the steepness of moisture gradients and subsequent grain raising, checking, and warping, but they do not prevent the aggravating swelling of drawers and doors that occurs during prolonged seasons of high relative humidity. BULKIXG THE FIBERS.Fundamental studies have shown that t,he swelling of wood can be reduced by depositing a water-soluble salt ( 7 3 ) or sugar ( ? 2 ) within the cell-wallstructure. Such materials can, however, be readily leached from the wood, and they tend to keep the wood in a moist condition. Treatments of this type, therefore, have never found much commercial use. They do, hoivever, show that shrinkage can be reduced by bulking the fiber. Bulking the fibers with a water-insoluble material, such as a wax, has been accomplished by a replacement method (75, 7.9). R a t e r is replaced by a liquid, such as ethylene glycol monoethyl ether, which is also a solvent for waxes. This liquid, in turn, is replaced by a was; thus it is possible for wax to be deposited witliin the cell walls. Although effective, this method is too involved for most practical uses. IMPREG.In seeking a one-treatment means of bulking the fiber Tyith a water-insoluble material, it was found that this can be accomplished with a water-soluble, low-molecular-weight, polar resin-forming system, which penetrates the cell-wall structure and, subsequent to removal of the water, is polymerized in place (83). Wood treated in this way with a water-soluble phenol-formaldehyde resinoid is called impreg (81). Phenolic resins have proven to be most suitable for this purpose (20, 56, 81, 83, 84). Urea resin-forming systems have been extensively tried for the purpose ( I O ) , but they have been shown to be inferior to the phenol-formaldehyde resin-forming systems both in stabilizing the dimensions of wood and improving other properties (55). When about 307, of phenolic resin (on the basis of the weight of the dry untreated wood) is formed within the structure, the equilibrium swelling is reduced to about 30% of normal (81,84). The specific gravity of the wood is increased by about 18% rather than 30%, because the wood is increased in bulk to the extent of about 12%. This treatment, when applied to veneer, practically eliminates the face checking, even in the case of such woods as Douglas fir (84). It greatly reduces moisture transfusion through the wood (84), imparts good decay, termite, and acid resistance to wood (81, 84), and increases the electrical resistance to a high degree, especially under high relative humidity conditions (100). Resin treatment has a negligible effect on reducing flammability. Some resistance to the spread of flame can be imparted to the wood, however, by incorporating fire-resistant salts in the treating resin (81). Resin treatment increases only a few of the strength properties more than it increases the specific gravity-namely,
1259
compressive strength and hardness both parallel and perpendicular to the grain and other across-the-grain properties (81, 83, 84). The toughness, however, is decreased significantly by resin treatment (64). The more intimate treatments, which result in the greatest dimensional stabilization, embrittle the wood to the greatest extent. Four methods for treating wood with resins have been developed, all of which are suitable for veneer (74, 77, 81). Only the sapwood of readily treated species can be treated with any degrce of uniformity in solid wood form even in lengths of only 6 feet. Impreg found its only war use in housings for electrical control equipment in which its improved electrical resistance mas utilized to advantage. I t might be used for lining of acid tanks and in chemical engineering equipment where normal wood is suitable in all respects except dimensional stability. COMPREG.Compreg is resin-treated wood that has been compressed prior to setting of the resin (88,86). I t may have a specific gravity anywhere between that of impreg and 1.4. The term is usually used to designate material in the specific gravity rltnge of 1.25 to 1.35. Lighter material is usually referred to as semicompreg. Compreg is similar to impreg in dimensional stability, resistance to checking, decay, and termites, and electrical resistance (88,85, 100). It is superior to impreg in its resistance to moisture transfusion (@). I t has a natural lustrous finish that, when scratched, can be restored by sanding with fine sandpaper followed by buffing (82, 85). Xost of its strength properties are increased over those of the normal mood about in proportion to the increase in specific gravity (6, 26, 60, 82,85); the face conipression and hardness are increased considerably more, the hardness increase frequently being fifteen to twenty-five fold. Compreg is significantly tougher than impreg but imt so tough as the original wood (54). Semicompreg with specific gravities in the range of 0.6 to 0.9 can be made under pressures as low as 250 pounds per square inch, which is insufficient to compress most species of dry, untreated xood. For this reason, semicompreg faces can be compressed and assembled with an untreated core in one operation without compressing the core (82, 86, 87). Compreg can be cut and machined with saws and tools used for fabricating the softer metals. Two methods for molding it have been developed (82, 90), the first being used during the war for molding of compreg motor test propellers and airplane antenna masts. The second method, known as expansion molding, was developed too late to find mi1itar.y use. I t shows great possibilities not only for molding compreg, but for molding fabric and paper-base laminates and for making moldings with metal inserts or face parts. The pressure is exerted irom within the material, which expands on molding. Compreg was used chiefly during the war for airplane propellers, motor-test propellers, antenna masts, metal drawing dies, tooling jigs, and connector plates. It shows promise for uses in pulleys, gears, and bearings where more expensive fabric laminates with less stiff ness have previously been used. Compreg also shows promise for use in shuttles, bobbins, and picker sticks for looms and other moving parts of machines and equipment that are subject to wear and for which metals are not entirely suitable. Compreg is also suitable for handles of various sorts and high strength electrical insulators. An English product, Permali, which is similar to compreg except that the veneer is treated with an alcohol-soluble rather than water-soluble phenol-formaldehyde resinoid, is used chiefly for its combined mechanical and electrical properties. STAYPAK.Resin-treated wood in both the uncompressed and compressed forms is, unfortunately, more brittlc than the original wood. To meet the demand for a tougher compressed product than compreg, a special compressed wood containing no resin was developed (68). I t will not lose its compression under swelling conditions as will ordinary compressed untreated wood (11, 44). This material, named staypak, is made by modifying the compressing conditions so as to cause the lignin-cementing material be-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
tween tlic cellulose fibers to flow sufficiently to eliminate the internal stresses (68, 70). Staypak is not so water resistant as compreg, but it is twice as tough and has higher tensile and flesural properties (68). The natural finish of staypak is almost as good as that of compreg. Under weathering conditions, however, it is definitely inferior to compreg. For outdoor use staypak should have a good synthetic resin varnish or paint finish. The lieat treatment used in making staypak is not sufficiently severe to give the wood a significant reduction in hygroscopicity. Staypak, consequently, is only slightly more resistant to decay, termites, or marine borers than normal untreated wood of the same species. Staypak can be used in the same way as compreg where extremely high water resistance is not needed. It shows promise for use in propellers, tool handles, forming dies, and connector plates where high impact strength is needed. It is not being manufactured commercially as yet. Less dimensionally stable compressed wood in which the lignin has not been made to flow has been in production in England and Germany for several years (CQ)-English Jicwood and Jablo, and German Lignostone and Lignofol. The strength properties of these materials are about the same as those of staypak. STAYBWOOD. The cheapest and simplest method of imparting dimensional stability to wood thus far developed is to heat the wood under conditions that just avoid charring (76, 78, 80). This can be done with a minimum loss in strength properties by passing wood beneath the surface of a molten metal or fused salt and thus subjecting it to controlled high temperatures in the range of 500” to 600” F. for a few minutes under nonoxidizing conditions (76, 78). The wood becomes tan to dark brown in color. Reductions in hygroscopicity and in equilibrium swelling and shrinking to half of normal are readily attained without too serious a loss in strength for some uses. Toughness is the strength property most seriously affected. I n one series of tests it was reduced to about half of normal when the hygroscopicity was reduced by 40% (78). Under these conditions a high degree of decay resistance results (78). ACETYLATED WOOD. The most recently developed method for stabilizing the dimensions of wood is by acetylation with acetic anhydride and pyridine as the catalyst (88, 89, 91). It can be done by either a liquid-phase or vapor-phase treatment. Vaporphase treatment requires the use of less chemicals and avoids the removal of a large excess of chemical from the wood. I n its present form the treatment is suitable only for lignocellulose and not isolated cellulose, and for wood in veneer thicknesses. The highest degree of dimensional stabilization of wood thus far obtained results from this treatment when the weight increase from acetyl groups is 20% for broadleaf wood species and 25% for conifers (88, 91). The specific gravity is increased by 6 to 12% for the different species. The treatment imparts a high degree of decay and termite resistance to the wood, and what so far a p pears to be an excellent resistance to marine borers. The wood is not darkened in color or embrittled as it is with resip and heat treatments; in fact, an increase in toughness of about 20% has been obtained in some cases (91). The compressive strength is increased somewhat. Other strength properties are inappreciably affected by the treatment (91). Acetylated wood is not being manufactured as yet. The treatment, it is felt, may be somewhat cheaper than resin treatment. It should find use wherever dimensional stability, together with lightness in weight and toughness, are sought. It can be compressed t o give a product similar to compreg, except that it is tougher than compreg. Of the various forms of modified wood, compreg, staypak, and acetylated wood show the greatest promise for use in chemical engineering structures and equipment. Prior to the war the Germans showed METALTREATMENT. that short pieces of solid wood can be impregnated with molten metal of the lead, tin, and low melting alloy types (44). It is
Vol. 39, No. 10
claimed that this material makes excellent bearings for certain t,ypes of use. There are no records of such treatments being used in the United States. LlTERATURE CITED
Alliott, E. A., J . SOC.Chem. Znd. (London), 45, 463T (1926). Am. Wood-Preservers’ Assoc., “Manual of Recommended Practice,” revised (June 1944). ,4m. Wood-Preservers’ Assoc., Committee Rept., Proc. Am. Wood-Preservers’ Assoe., 40, 261 (1944).
Anonymous, Chem. & Met. Eng., 36, 567 (1929). Ibid., 49 (9), 104 (1942).
Army-Navy-Civil Committee on Aircraft Design Criteria. “Wood Aircraft Fabrication Manual,” War Dept. Army Air Forces, Navy Dept. Bur. Aeronautics, Dept. of Commerce Civil Aeronautics Administration. U. S. Govt. Ptg. Office (July 1942). Arneson, G. N., Cosgrove’s Mag., 18 ( l ) , 80, 82, 86, 88, 90, 92 (May-June 1946). Atwood, W. G., and Johnson, -4. A., “Marine Structures: Their Deterioration and Preservation,” Rept. of Committee on Marine Piling Investigations of Div. of Eng. and Ind. Research, Natl. Research Council (1924). Barsky, G., and Wohnsiedler, H. P., U. S. Patent 1,896,276 (1933).
Berliner, J. F. T., Chem. Znd., 54 (5), 680 (1944). Bernhard, R. K., Perry, T. D., and Stern, E. G., Mech. Eng., 62, 189 (1940).
Black, J. M., Forest Products Lab., Mimeograph R1427 (1943). Black, J. M., and Bruce, H. D., Ibid., 1537 (1945). Blew, J. O., Ibid., R1445, revised (1945). Brit. Standards, Air Raid Precaution Series 39 (Feb. 1940). Brophy, M. J., Dept. of Mines and Resources, Canada Dominion Forest Service, Circ. 55 (1939). Browne, F. L., IND.ENQ.CHEM.,25, 835 (1933). Browne, F. L., and Downs, L. E., Forest Products Lab., Mimeograph R1495 (1945).
Bruce, H. D., Olson, W. Z., Black, J. M., and Rauch, A. H., Zbid., 1531 (1946).
Burr, H. K., and Stamm, A. J., Zba‘d., 1384 (1943). Cockrell, R. A., and Bruce, H. D., Ibid., R1616 (1946). Dosker, C. D., Proc. Am. Wood-Preservers’ Assoc., 40, 212 (1945).
Dosker, C. D., and Knauss, A. C., Mech. Eng., 66 (12), 763 (1944).
Dunlap, M. E., and Bell, E. R., Forest Products Lab., Mimeograph R1638 (1947).
Eickner, H. W., Mraz, E. A,, and Bruce, H. D., Iba‘d., 1545 (1946).
Findley, W. N., Worley, W. J., and Kacalieff, C. D., Modern Plastics, 22 (12), 143 (1946).
Forest Products Lab., Mimeograph R1190 (1938). Ibid., R280, revised (1939). Zbid., R149, revised (1944). Zbid., 1336-A (1947).
Gabriel, A. E., Forest Products Lab., iMimeograph 1355 (1946). Goodell, H. R., and Phillips, R. S., Zbid., 1523 (1944). Harte, C. R., IND. ENO.CHEY.,28, 176 (1936). Hatfield, I., Proc. Am. Wood-Preservers’ Assoc., 40, 47 (1944). Helphenstine, R. K., Zbid., 41, 236 (1945). Hunt, G. M., Forest Products Lab., Mimeograph R68 (1941). Hunt, G. M., U. S.Dept. Agr., Circ. 128 (1930). Hunt, G. M., Forest Products Lab., Mimeograph R919, revised (1945). rbid., R154, revised (1944). Hunt, G. M., and Garratt, G. A., “Wood Preservation,” New York, McGraw-Hill Book Co., Inc., 1938. Hunt, P. J., Goodell, H. R., and Phillips, R. S., Forest Products Lab., Mimeograph 1523-A and B (1945, 1946). Kaufert, F. H., and Hutchins, W. F., Zbid., R1484 (1945). Kofoid, C. A., ”Termites and Termite Control,” Univ. of Calif. Press, Berkeley, Calif., 1934. Kollmann. F.. “Technologie des Holies,” Julius Springer, __ . Berlin (1936). Luxford, R. F., and Krone, R. H., Forest Products Lab., ~
Mimeograph R1625 (1946).
MacLean, J. D., U. S. Dept. Agr., Mwc. Pub. 224 (1935). McLeod, A. M., Forest Products Lab., Mimeograph 1523-C (1946).
McNaughton, G. C., Natl. Fire Protection Assoc. Quurt., 36, 211-18 (Jan. 1943). McNaughton, G. C., Forest Products Lab., Mimeograph R1464 (1944).
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1947
McNaughton. G. C., and Martin, T. J., Am. Buildw and Buildi n g Age (dealers’ ed.), 62 (31,145-7 (Mar. 1940). McNaughton, G. C., and VanKleeck, A., Forest Products Lab., Mimeograph R1443 (1944). Markwardt, L. J., Am. SOC.Testing Materials, Proc., 43,43592 (1943). Markmardt, L. J., and Wilson, T. It. C., U. S. Dept. Agr., Bull. 479 (1935). Millett, M. A., Seborg, R. M., and Stamm, -1.J., Forest Products Lab.. Mimeoarash 1386 (1943). Millett, M. A., and Stamm,‘A. J., hiodern Plastics, 24 (2),150 (1946); 24 (B), 159 (1947). Navy Dept. (U.S.) Specification 51-C-38. Ibid., 51-C40. Olson, R. Z., Forest Products Lab., Mimeograph 1534 (1945). Olson, W. Z.,Bensend, D. W., and Bruce, 11. D., Forest Products Lab., Mimeograph 1539 (1946). Olson. W. Z., and Bruce, H. D., Ibid., 1542 (1946). Ibid., 1546 (1946). Olson, W. Z.,Bruce, H. D.. and Souer, V. R.. Forest Products Lab., Mimeograph 1547 (1946). I h i d . , R1629 (1946). Porkins, N. S.,Landson, P., and Trayer, G. W., “Modern Connectors for Timber Construction,” Joint Pub., Natl. Com. on Wood Utilization & Forest Products Lab. (1933). San Francisco Bay Marine Piling Com., “Marine Borers and Their Relation to Marine Construction on the Pacific Coast,” Univ. of Calif. Press, Berkeley, Calif. (1927); Proc. Am. Wood-Preservers’ Assoc., 24,253 (1928). Scholten, J. A., Forest Products Lab., Mimeograph R1202, revised (1946). Scholten, J. A.,Agr. Eng., 19,201 (1938). Seborg, R. M., Millett, M. A,, and Stamm, A. J., Ibid., 67,25 (1945). Seborg, R. M., and Stamm, A. J., Forest Products Lab., Mimeograph 1383,revised (1945). Seborg, R. M., and Stamm, A. J., Mech. Eng., 63,211 (1941). Snyder, T. E.,“Our Enemy the Termites,” Comstock Pub. Co., Ithaca, N. Y. (1935). Stamm, A. J., IND. ESG. CHEM.,29, 833 (1937). Stamm, A. J., J. Am. Chem. Soc., 56, 1195 (1934). Stamm. A. J., Proc. Wood-Preservers’ Assoc., 42,150-67 (1946).
12 61
1751 Stamm. A. J.. U. S. Patent 2.060.902(199ti). (76j Ibid., i,296,3i6 (1942). (77) Ibid., 2,350,135(1944). (78) . . Stamm, A.J.. Burr, H. K., and Kline, A. A., IND.ENG.CHEM., 38, 630-4 (1946). (79) Stamm, A. J., and Hansen, L. A,, Ibid., 27, 1480 (1935). (80) Ibid., 29, 831 (1937). (81) Stamm, A. J., and Seborg, R. M., Forest Products Lab., Mimeograph 1380,revised (1943). (82) Ibid., 1381,revised (1944). ENG.CHEM.,28, 1164 (83) Stamm, A. J., and Seborg, R. M., IND. (1936). - (84) Ibid., 31,897 (1939). (85) Stamm, A. J., and Seborg, R. M., Trans. Am. Inst. Chem. Engrs., 37, 385 (1941). (86) Stamm, A. J., and Seborg, R. M., U. 8. Patent 2,321,558 (1943). (87) Ibid., 2,354,090(1944). (88) Stamm, A. J., and Tarkow, H., J. Phys. Colloid Chem., 31, 493 (1947). (89) Stamm, A. J., and Tarkow, I?., U. S. Patent 2,417,995(1947). (90) Stamm, A. J., and Turner, H. D., Ibid., 2,391,489(1945). (91) Tarkow, H.,and Stamm, A. J., Forest Products Lab., Mimeograph 1593 (1946). (92) Tramm, H., Cler, C., Kuhnel, P., and Schoff, R., U. S. Patent 2,106,938(1938). (93) Trayer, G. W.,U. S. Dept. Agr., Bull. 332 (1932). (94) Truax, T. R.,Harrison, C. A,, and Baechler, R. H., Proc. Am. Wood-Pmservers’Assoc., 31,231 (1935). (95) U. S. Treasury Dept., Procurement Div., Federal Specifications, Federal Standard Stock Catalog, Sect. 4,Pt. 1 (1945). (96) Van Kleeck, A., Forest Products Lab., Mimeograph R1280, revised (1946). (97) Van Kleeck, A.,News Ed. (Am. Chem. Soc.), 19, 626 (1941). (98) . . Van Kleeck, A., Proc. Am. Wood-Preservers’ Assoc., 38, 160 (1942). (99) Wangaard, F. T., Forest Product Lab., Mimeograph 1530, revised (1946). (100) Weatherwax, R. C.,and Stamm, A. J., Elec. Eng., 64, 833 (1945). (101) Wilson, T. R. C., U. S. Dept. Agr., Tech. Bull. 282 (1932). (102) Wilson, T.R. C., Ibid., 691 (1939).
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.~~I
Codification of Materials BS
C. S. GROVE, J R . ~ ,State University of Zowa, Zowa City, Zowa
J. W. PERRY, Massachusetts Institute of Technology, Cambridge, Mass.
ROBERT S. CASEY,
w.A .
Sheafler Pen Co., Ft. Madison, Iowa
T
HE complexity of published scientific knowledge has been
greatly increased by the multiplicity of wartime developments. This has resulted in increasing difficulty in locating desired information from the mass of such data. This is particularly true of information about the properties of chemical engineering materials of construction. The changing emphasis and broadening field of chemical engineering materials of construction may be obvious, especially to those who worked on design and construction during World War 11. Previous to World War I, chemical equipment was largely made of cast iron, wood, stoneware, or lead. The group of chromenickel alloys, including the stainless steels, became available shortly after the beginning of the 1920’s. Their use became more prominent through the late 1920’s and early 1930’s. In the late 1930’s and early 1940’s a multitude of new materials, chiefly nonmetallic-plastics, synthetic rubber, carbon and graphite, glass and glass-lined, porcelain, and modified natural product~ of rubber and wood-came into being and greatly increased ‘Present address, Syracuse University, Syracuse, N. Y.
the number of materials which were used for chemical construction. With this added impetus given t o development of new materials, tailor-made for special uses, the necessity for codification becomes more evident. The problem of choosing materials for chemical equipment and plants, as well as for a wide variety of uses in many different manufacturing industries, is rapidly becoming more complicated. At the same time the difficulties in finding the proper material have been greatly increased, I n searching for information about materials of construction, one usually seeks, not single facts, but areas of information definable in terms of combinations of attributes. For example, an application may require a material in the form of pipe and fittings, t o resist 10% hydrochloric acid. Also, there may be needed equipment such as pumps and stills. Perhaps, in addition, there is to be fabricated a gadget from the same material which must be machined to close tolerance. Certain words in the preceding example-material, form, resist, some of the variables which, equipment, fabricated-suggest
