WOOD ALFRED J. STAMM, Forest Products Laboratory, U . S. Department of Agriculture, Madison, Wis. treated with chlorinated naphthalene were still intact at each of the four locations after 20 years, although all showed evidence of some attack. Salt preservatives produced quite variable results. Those which form relatively insoluble precipitates, such as zinc meta-arsenite and nickel arsenate, gave the best protection. Under the most severe exposure conditions (at the Canal Zone), moderate concentrations of some salts subject to leaching only doubled the service life of the stakes compared to that of the controls. Under less Eevere leaching conditions and in larger wood specimens, leaching and reduced service life should not be so serious. Reports including recent inspections were issued on post and stake ground service tests being conducted in Mississippi (14, 18). The tests include material treated mith Preservatives and modified Foods. Cooperative field and laboratory tests comparing the protective action of various creosote fractions have been started recently by the William F. Clapp Laboratories, the U. s. Forest Products Laboratory, Bell Laboratories, and Koppers Co. (5). I t ryill be some time before any conclusions can be drawn from this research. A report recently appeared on the effectiveness of various preservatives in protecting Food against marine borers (53). Hatfield (40)reviewed the history of pentachlorophenol as a wood preservative. Its use is recommended in industrial buildings, textile mills, and food-processing plants where “clean” treatments are especially desirable. The increased use of pentachlorophenol resulted in its inclusion in Federal Specifications (TT-W-570) in 1947. Blew (17) has revised the U. S. Forest Products Laboratory report on preservative treatment of m-ood with oil solut,ions of pentachlorophenol, copper naphthenate, and creomte by the cold soaking method. He also discussed recent developments in wood preservatives in other reports (16, 16). The nat,ure, composition, characteristics, and appropriate uses for waterrepellent preservatives of the dip type were described by Browne (28) and by Garlick (38). These materials, when applied by short-dip methods, are effective in preserving wood used only under mildly hazardous conditions, as in window sash and frames. An extensive report by Duncan and Richards (25) covered the effect of carriers on the toxicity of pentachlorophenol solut,ionP for different wood-destroying cultures. The effectiveness of mixtures of coal tar creasote with petroleum solutions of pentachlorophenol, creosote, and copper naphthenate, and varioue mixtures of the three agents, was also compared. Soil-block tests made both before and after aging of the wood showed that creosote plus pentachlorophenol dissolved in a catalytic gas-base oil was the most effective decay inhibitor. Baechler (9) showed that aeration of creosote greatly decreases its toxicity to wood-destroying agents, and washing it with a solution of sodium chloride has a less pronounced effect’. In t,esting new preservatives of the oil type by the simple agar test, it is recommended that the oil be aerated and leached prior to making the test; the fresh unleached oil is used as a control to obtain rough approximations of its permanence. Baechler (10) also studied the corrosion of metal fastenings in untreated and zinc chloride-treated wood that had been ex-
New developments that increase the service life of wood or produce wood products with improved properties have been reported in the literature since the last review on the subject in October 1949. Included are reviews on investigations of preservative and fire-retardant treatments for wood, strength properties of wood, wood structures, and production and properties of plywood, laminated wood, and modified woods. Structural fiberboards are included for the first time. These are gaining rapidly in importance and show promise of being suitable for various chemical engineering uses.
G
ENERAL information on the factors influencing the decay of untreated wood in service and the comparative decay resistance of various species of untreated wood mas revised (33). Dry wood or wood protected from contact with air by continued water immersion or burial deep in the ground is not subject to decay. Decay also will not occur in wood containing less than 20% of moisture. Decay of posts in arid and semiarid regions is concentrated near the ground line In damp climates it may occur over the entire post. Natural durability varies in different species of wood primarily because of differences in amount and nature of their extractives. The heartwood of commercial woods may be grouped roughly into three degrees of natural decay resistance, as follows (33): High Bald cypress Catalpas Cedars Chestnut Junipers Locust, black Mesquite Mulberry, red Osage-orange Redwood Walnut, black Yew. Pacific
Intermediate Douglas fir Honey locust Larch, western Oak, chestnut Oak, white Pine, eastern white Pine, southern yellcI W Sassafras
Low Ashes Aspen Basswood Beech Birch Cottonwood Firs (true) Hemlocks Maple, sugar Oak, northern red Spruces Willows
PRESERVATIVE TREATiMENTS
Bescher (13) reviewed the types of wood preservatives available and the relative importance of each for specific uses. Recommended practices for treating wood for different uses also have been summarized (4). A study of wood preservative statistics (73) shows the diversity of Food items treated and the amounts of each type of preservative used during the years 19471949. Information is continuing to accumulate on the benefits of using preservative-treated wood in contact with the ground or exposed to conditions of high relative humidity. Exposure records covering 20 years have been reported on treated, matched pine sapwood stakes (2 x4 X 18 inches) driven into the ground in such diverse locationd as Barro Colorado Island in the Panama Canal Zone; Canberra, Australia, Honolulu, Hawaii and Pienaar’s River Experiment Station, Transvaal, South Africa (44). The chief destruction of wood in these places is due to termites. Coal tar creosote had the best performance record of all the preservatives tested Only about one third of the epeoimens were destroyed a t Barro Colorado Island and Honolulu in the 20 years, whereas the average life of the controls varied from 0.7 year in the Canal Zone to 2.3 years in Australia. These stakes were small and had larger exposed surfaces per unit of weight than railroad ties, poles, piles, and timbers. The larger items, therefore, would be expected to have considerably longer life under the same exposure conditions. Some of the stakes
2276
October 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
posed for 20 years to weathering and different controlled relative humidities. Specimens exposed at 30% relative humidity showed no corrosion of wire nails, galvanized nails, brass screws, or aluminum taga. Specimens exposed at 65%relative humidity showed only a slight rusting of the heads of ordinary wire nails. In specimens exposed a t 90% relative humidity, considerable corrosion of the heads of wire nails occurred, even on the painted halves of the blocks. Nails in the treated blocks were somewhat more corroded than the untreated controls. Galvanized nails were dull but not corroded. Brass screws appeared to be unaffected but some were embrittled enough to break on removal. A11 the aluminum tags were corroded and some were destroyed. More corrosion of wire nails occurred in specimens weathered outdoors than at 65% relative humidity, especially in treated wood. Exposure outdoors had less effect on the aluminum tags and only mild corrosive action on galvanized nails and brass screws, similar to that which occurred at 65% relative humidity. Englerth (26) investigated the decay resistance of plywood bonded with various glues. Addition of toxic agents to casein glues is desirable when the plywood is to be used under conditions where decay may take place. Phenolic-resin glues added somewhat to the decay resistance of plywood in the soil-block tests. In stake tests, however, phenolic resin-bonded laminates had a shorter life than solid wood (18). The fabrication of laminated arches and other bridge members from salt preservative-treated lumber was described (3). Such material should be suitable for chemical plant structures. Cooling towers are made almost exclusively of redwood because of its natural decay resistance, small dimensional changes with changes in moisture content, and availability in large, clear specimens. Recent surveys showed that in some installations decay and chemical degradation have occurred, but in others the wood is perfectly sound after years of service. Limited tests indicate that in many cases the difficulty is due to the fact that the concentration of sodium carbonate in the water is too high. In a few instances, chlorine added as an algaecide may have been used in harmful concentrations. Leaching tests a t the U. S. Forest Products Laboratory have shown that addition of as little as 0.2% of sodium carbonate to the leach water will increase the removal of natural toxic extractives and make the wood more susceptible to decay (11). A concentration of 0.01% of chlorine has the same effect but to a smaller degree. Raising the pH of the water or adding chlorine to inhibit algae growth should therefore be practiced with caution. Verrall (79) discussed the hazards of faulty use of wood in exterior woodwork and how to overcome or minimize them by
2277
proper construction and treating practices. Verrall and Scheffer (80) summarized recommended practices for dipping or surface treating of green lumber prior to air-seasoning in order to prevent damage from mold, stain, and decay while the moisture content is still high FIRE-RETARDANT TREATMENTS
Methods for making mood fire retardant were reviewed by Truax (76). Various salt-impregnation treatments and surface coatings were discussed, and the limitations of each were indicated. Van Kleeck (77) revised his older U. s. Forest Products Laboratory report on fire-retardant coatings. Formulations are given for borax-linseed oil fire-retardant paints, sodium silicate applicants, fire-retardant salt combinations with alginate or methylcellulose gel, and whitewash containing casein, borax, and lime. These coatings are suitable only for interior use, where leaching is practically negligible. No very effective extrr nal coatings with a long service life have been developed. Some success has been attained, however, with zinc borate paints and with chlorinated rubber and paraffin (77) coatings. Van Kleeck and Martin (78)studied the flame-spread resistance of fiber insulation boards. Considerable variation in flamespread behavior was found for the boards of different manufacturers. The factory finish applied by some manufacturers had some flame-retarding properties. Coatinge of monoammonium phosphate were quite effective when applied to the extent of 5 grams per square foot or more. Borax-linseed oil paints and chlorinated hydrocarbon coatings were effective on some of the insulating boards. Fire-retardant impregnating solutions recommended for use by the American Wood-Preservers' Association were disclosed, together with analytical methods for determining their retention by the wood (2). The fire resistance of pier piles was materially increased by a pressure treatment with creosote (64). Fire-retardant treatments in which a t least 3 pounds of salts are impregnated into a cubic foot of wood raised the ignition temperature from around 400' to about 1200' F. (7). GLUlNG PLYWOOD AND LAMINATED WOOD
Several of the older U. S.Forest Products Laboratory report8 on gluing were revised, notably reports on vegetable (starch) casein glues ( S I ) , and control of conditions in gluing glues (L?$), (SO). A general report on the gluing of wood waa published by Brouse (21). A summary of the gluing of treated wood also was
Test Exposure Plot for Stakes to Determine Service Life of Wood Treated with Preservatives
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
issued (35). Selbo discussed the durability of woodworking glues for dwellings (71) and the durability of glue joints in laminated lumber (72). Blomquist (19) studied the effect of alkalinity of phenol and resorcinol-resin glues on the durability of plywood joints. High alkalinity reduced the strength of hotrpress phenolic-resin bonds for birch but not for Douglas fir. The effect of extending hotpress urea-resiu gluep \Fith various types of cereal flours was studied by Ropella (67).
Vol. 43, No. 10
MODIFIED WOODS
No new methods of modifying wood to improve its propcrtien were reported during the last few years. The strengths of resin-impregnated birch veneer laminates in both the uncompressed form (impreg) and compressed form (compreg) were compared hy Elrickson and Faulkes (27), using phenolic and urea resins. Tu general, the strength properties and the dimensional stabilitv are superior in the phenolic resinimpregnated material. The method of manufacture and
Laminated White Oak Ship Keel
STRENGTH PROPERTIES OF WOOD AND WOOD STRUCTURES
properties of commercial compreg were described by M c k n (51). Campreg has such diverse uses as for picker sticks in weaving looms, molding forms and jigs for aluminum forming in aircraft plants, knife handles, and clarinets. I t is undoubtedly suitable for a number of chemical equipment applications. Vogel (81) described the impregnation of small block8 of wood with metal alloys for use RS hearings.
Variations in the strength properties of wood used for structural purposes were considered by Wood (81). Johnson (46) described the development of methods for assigning working stresses to lumber and design stresses to built-up members. Dohr (24) showed that Virginia pine is equal in strength properties to previously reported values for southern pines (56). Wood (83)developed formulas for calculating the effects of side loads and eccentricity on the strength of wood columns. Norris (58) theoretically analyzed the effect of combined stresses on orthotropic materials. Liska (50) studied the effect of rapid loading on the compressive and flexural strength of wood. The modulus of rupture and maximum strength in compression parallel to the grain were increased or decreased about 8% for a tenfold decrease or increase in loading time. Considerable attention has been focused on the strength propertiesof plywood. Markaardt (55) and Liska (@)reported revised approximate methods for calculating the strength and modulus of elasticity of plywood in compression. Additional information on the buckling of plywood was obtained by Norris and Palma (59) and Ringelstetter (64). They also studied the use of stiffeners to increase edgewise compression (42, 65). Perkins (63) compared the performance of exterior plywood with the percentage of wood failure. A comprehensive report was issued on wood aircraft inspection and fabrication (1). This book explains in detail different methods for fabricating lumber and plywood into parts varying from flat spars to intricate curved parts. Some of this information may be of value in the fabrication of special chemical equipment, Miles (57)discussed the molding of plywood and the conditions under which it can be used to advantage. Die molding was found to be preferable to bag molding. Several reports also were published on the nailholding properties of wood and the strength of nailed joints (41, 68, 69). Freas (36, 3'7) studied the strength of glued laminated construction. Peck (61) prepared a detailed report on the bending of wood which may prove useful in construction of equipment parts.
Wet-Felted Boards. The production of both insulating and hard-board types of fiberboards increased markedly in recent years. There also is a growing trend to replace plywood by hard boards in some applications. Boehm and Harper (& discussed I) some of the advantages of hard boards over plywood and lumber and briefly described the Masonite process for making hard boards. Asplund (8)described the preparation and characteristics of pulps prepared for hard boards by the Defibratm method. The method of making wallboards from acid-hydrolyzed wood in Italy was outlined (60) Anderson (6) found that considerable bark can be left on the wood used to make hard boards without significant loss in properties. Schwarte and Baird (1'0) investigated the effect of molding temperature on the strength and dimensional stability of hard boards. Hohf, Turner, and Gabriel (43) and Farber (89) described simple methods of making structural fiberboards by combining highly beaten fibers with coarse fibers or sawdust. DePan (23) described the equipment needed for small scale wet-felted structural fiberboard plants. Thweatt (74) and Lingell (48) also gave information on equipment for making structural fiberboards. The U. S. Forest Products Laboratory publication on the methods of test for evaluating the properties of structural fiberboards was revised (34). Dry-Form and Semidry-Form Boards. The difficulties encountered in making structural fiberboards on a small scale by the wet-felted method, the need for large quantities of water for processing, and the fact that the raw material must be in a fibrous form have induced investigators to try to make boards from sawdust and shavings by a dry-forming process, using resin binders. Several such boards made with either phenolic or urea binders are now on the market. These boards are being used for door panels, kitchen cabinets, and interior paneling. Unfortunately, only limited data have been published on the properties of theee
Several reports on laminated structures appeared which cover design, construction, and performance (46,47', 62). Interest has increased in plastic-surfaced Douglas fir plyrood during the past few years. The applications of this material and its future possibilities were described by Ritchie (66).
STRUCTURAL FIBERBOARDS
October 1951
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
boards, and it ie uncertain what use they may have as chemical engineering materials of construction. Several dry-form hard boards now id commercial production and several under consideration for construction were described in a bulletin of the Northeastern Wood Utilization Council (60). Other boards made by dry and semidry forming processes were MacDonald (62),Gottstein (39),and described by Evans (a), Bender (18). Turner and Kern (76) found that varying the sawdust particle sizes from coarse (8 to 20 mesh) to fine (40 to 100 mesh) and the powdered phenolic resin content from 5 to 20% are of minor importance in determining the strength of the dry-form boards compared to variation in the specific gravity to which the boards are compressed. The flexural strength of dry-form boards increases approximately as the cube of the specific gravity, whereas that of wet-felted fiberboards increases approximately aa the square of the specific gravity, The flexural strerfgth of the two types of boards is about the same at the high specific gravities of 1.2 to 1.3, but at low specific gravities the wet-felted boards are much stronger. The oonsiderably greater strength of the wetfelted boards a t lower specific gravitieR is probably due to the more fibrous nature of the wet-felted material, which permit8 a lesser degree of packing for the same extent of bonding. Another factor is the drawing together of soft, flexible fibrillated fibers by surface tension forces w water is removed to form fiber-to-fiber bonds without collapsing the fiber cavities, aa is the case when compacting is accomplished entirely by externally applied forces. For these reasons, investigators have had little success in making good dry-form boards with specific gravities below 0.5, except from excelsior or similar long, s t 8 fibers. Hard boards with normal specific gravities of 0.9 to 1.0 usually have flexural strengths of 5,000 to 10,000 pounds per square inch when made by the wet-felted process. Those made by the dry-form process from sawdust have flexural values about 50% lower The production and interest in dry-form boards may be temporarily curtailed because of the present qhortage of the resins med as binders. LITERATURE CWED
Air Force-Navy-Civil Aircraft Design Committee, Munitions Board, National Military Establishment, A N C Bull. 19a (1951). Am. Wood-Preservers’ Assoc., Proc., 45, 46 (1949); 46, 50 (1950). Ibid., 45, 242 (1949). Ibid.. 45, 348-64 (1949): 46, 279-303 (1950). Ibid., 46, 68 (1950). Anderson, A. B.. Fmest Products Research Soc., Proc., 4, 301 (1950). Angell, H. W., Gotkrchalk, F. W., and McFarland, W. A., Ibid., 3, 250 (1949). Asplund, A.. Northeastern Wood Utilization Council, New Haven, Conn., Bull. 31 (1950). Baechler, R. H.. Am. Wood-Preservers’ Assoc., Proc.. 45, 90 (1949). Baechler, R. H., Ibid., 45,390 (1949). Baechler, R. H., and Richards, C. A . . Am. SOC.Mech. Engrs., Paper No. 51-511 (1951). Bender, F., Forest Products Research Soc., Proc. 3, 209 (1949). (13) Bescher, R. H., Ibid., 3,227 (1949). (14) Blew, J. O., Am. Wood-Preservers’ Assoc., Proc., 45, 255 (1949). (15) Blew. J. 0.. Chem. I d s . . 64. 218 (1949). (16j Blew; J. O.,‘Forest Products Lab. Rept. R149 revised (1949). (17) - . , -Ihid. . .. R1445. (18) Ibid.: Ri757 and R1761. (19) Blomquist, R. F., Fmesl Products Lab. Rept. R1748 (1949). (20) Boehm, R. M., and Harper, J. S., Forest Products Research SOC., Proc., 3, 216 (1949). (21) Brouse, Don, “U. S. Dept. Agr. Yearbook,” p. 636, Washington 25, D. C., Supt. Documents, 1949, (22) Browne, F. L., Arch. Record, 105, 131 (March 1949). (23) DePan, R. T., Forest Products Research Soc., Proc., 4, 279 (1950). (24) Dohr, A. W., Southern Lumberman, 181,225 (Dee. 15, 1950). ~
2279
(25) Duncan, C. G., and Richards, C. A., Am. Wood-Preseruers’ Assoc., Proc. 46, 131 (1950). (26) Englerth, G. H., Forest Products Research Soc., Proc., 4, 248 (1950). (27) Erickson, E. C. O., and Faulkes, W. F., Fmest Products Lab. Rept. R1741 (1949). (28) Evans, H. R., Forest Products Research Soc., Proc., 4, 268 (1950). (29) Farber, E., Ibid., 4, 271 (1950). (30) Forest Products Lab. Rept., 1340 revised (1950). (31) Ibid., D280 revised. (32) Ibid., R30 revised. (33) Ibid., R68, revised. (34) Ibid., R1712 revised (1949). (35) Ibid., R1789 (1950). (36) Freas, A. D., Am. SOC.Testing Materials, Bull. 170, 48 (1950). (37) Freas, A. D., Forest Products Lab. Rept. R1749 (1949). (38) Garlick, G. G., Forest Products Research Soc., Proc., 4, 241 (1950). (39) Gottstein, J. W., Ibid., 4, 310 (1950). (40) Hatfield, I., Am. Wood-Preserters’ Assoc., Proc., 45, 84 (1948) (41) Heck, G. E., Southern Lumberman, 180, 58 (June 1, 1950). (42) Heebink, T. B., and Norris, C. B., F w w t Products Lab. Rrpt 1812 (1950). (43) Hohf, J. P‘.,Turner, H. D., and Gabriel, A. E., Ibid., R1666-i (1947). (44) Hunt, G. M., and Snyder, T. E., Am. Wood-Preservers’ Assoc. Proc., 45, 383 (1949). (45) Johnson, R. P. A., and Hanrahan, F. J., Forest Products RPsearch SOC.,Proc., 3, 301 (1949). (46) Kennedy, D. E., Ibid., 3,307 (1949). (47) F t c h u m , V., Ibid., 3, 318 (1949). (48) Lingell, H. K., Northeastern Wood Utilization Council, h e w Haven, Conn., Bull. 31 (1950). (49) Liska, J. A., Forest Products Lab. Rept. 1315, revised (1950). (50) Liska, J. A,, Ibid., R1767 (1950). (51) MacDonald, M. D., Forest Products Rwearch SOC.,Proc., 4, 2 % ~ (1950). (52) MoLean, G. K., Ibid., 3,220 (1949). (53) MacLean, J. D., Fmest Products Lab. Rept. D1773 (1950). (54) Mann, R. H., Am. Wood-Preservers’ Assoc., Proc.. 46, 3% (1950). (55) Markwardt, L. J., Forest Products Lab. Rept. 1640, revised (1950). (56) Markwardt, L. J., and Wilson, T. R. C., U.S. Dept. Agr. Bull. 479 (1935). (57) Miles, T . R., Forest Products Research Soc., Proc., 3, 156 (1949). (58) Norris, C. B., Forest Products Lab. Rept. 1816 (1950). (59) Norris, C. B., and Palma, J., Ibid., 1316-H. (60) Northeastern Wood Utilization Council, New Haven, Conn., Bull. 31 (1950). (61) Peck, E. C., Forest Products Lab. Rept. R1764 (1950). (62) Pederson, A. V., Forest Products Research SOC.,Proc., 3, 32i (1949). (63) Perkins, N. S., Ibid., 4, 352 (1950). (64) Ringelstetter, L. A., Forest Products Lab. Rept. 1316-J (1949). (65) Ringelstetter, L. A., and Norris, C. B., Ibid., 1553-D (1949). (66) Ritchie, J. D., Forest Products Research Soc., P ~ o c . 347 , ~ ,(1950). (67) Ropella, L., Ibid., 3, 121 (1949). (68) Scholten, J. A,, Southern Lumberman, 181, 208 (Dec. 15, 1950). (69) Scholten, J. A., and Molander, E. G., Agr. Eng., 31, No. 11. 551 (1950). (io) Schwartz, S.L., and Baird, P. K., Forest Products Research Soc., Proc., 4, 322 (1950). (71) Selbo, M. L., Ibid., 3, 361 (1949). (72) Selbo, M. L., Southern Lumberman, 179, 60 (Oct. 1, 1949). (73) Steer, H. B., Am. Wood-Presercers’ Assoc., Proc., 45, 369 (1949); 46, 407 (1950). (74) Thweatt, H. D., Northeastern Wood Utilization Council, New Haven, Conn., Bull. 31 (1950). (75) Truax, T. R., Forest Products Lab. Rept. R1760 (1950). (76) Turner, H. D., and Kern, J. D., Forest Products Lab. Rept. R1786 (1950). (77) Van Kleeck, A., Forest Products Lab. Rept. R1280,revised (1948). (78) Van Kleeck, A,, and Martin, T. J., Forest Products Lab. Rept. D1756 (1950). (79) Verrall, A. F., Southern Lumberman, 178, 74 (June 15, 1949). (80) Verrall, A. F., and Scheffer, T. C., Forest Products Research Soc., Proc. 3, 480 (1949). (81) Vogel, F. H., Ibid., 4, 199 (1950). (82) Wood, L. W., Forest Products Lab. Rept. R1780 (1950). (83) Ibid., R1782. RECEIVED May 23, 1951. The Forests Products Laboratory of the U. 8. Department of Agriculture is maintained at Madison, Wis., in cooperation with the University of Wisconsin.
