JULY, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
the speed of agitation in some phases of the reaction (14). The addition of certain types of inert solids and liquids (la) may also help in some cases. I n this connection, the fact may be mentioned that there is a divergence of opinion as to the usefulness of inert solvents as reaction media or diluents for the etherifying agent (IS, 20). In general, both etherification and hydrolysis are retarded; the important question is, which is retarded the more? Uniformity of the reaction is increased if the diluent is a good solvent for the cellulose ether formed. This effect (e. g., in ethylation) may counterbalance the disadvantage of longer treatment. The writer has had no favorable experience with diluents in benzylation.
Acknowledgment The author is indebted to W. H. Fravel for carrying out the hydrolytic experiments, and to W. A. Kirklin for helpful suggestions on the anaIytic procedure.
Literature Cited (1) Bock, L.H., IND.ENO.CHEM.,29, 985-7 (1937). (2) Brandt, K.,“Benzylcellulose”, dissertation, Univ. of Berlin, 1933. (3) Frank, G., and Mienes, K., German Patent 555,930 (Aug. 1, 1932). (4) Ibid., 575,349 (April 27, 1933). (5) Frey-Wissling, A., Protoplasma, 25, 261-300 (1936).
897
(6) Helferich, B., and Koester, H., Be?., 57, 587-91 (1924). (7) Hess, K.,Ann., 506, 295-8 (1933). (8) Heas, K., Trogus, C., Eveking, W., and Garthe, E., Ibid., 506, 260-95 (1933). (9) Lautenberg, A. (to “Chatillon”), U. S. Patent 1,920,702 (Aug. 1, 1933). (IO) Leuchs, O., and Doerr, E. (to I. G. Farbenindustrie), U. 8. Patent 1,694,127(Dec. 4, 1928). (11) Lorand, E . J., IND. ENG.CREM.,30,527-30 (1938). (12) Lorand, E.J. (to Hercules Powder Co.), U. S.Patent 2,001,102 (May 14, 1935). (13) Ibid., 2,051,492(Aug. 18, 1936). (14)Ibid., 2,056,324(Oct. 6,1936). (15) Lorand, E. J., and Georgi, E . A., J . Am. Chem. SOC.,59, 1166 (1937). (16) Mienes, K., “Celluloseester und Celluloseaether”, BerlinSteditz. Chem.-tech. Verlae: Dr. Bodenbacher. 1934 (17) NikitL, N. I., and Avidon, M.A., Izvest. Lesotbkh. Akad., 39, 26-7 (1932). (18) Nikitin, N. I., and Avidon, M. A., J . Applied Chem. (U.S. S . R.), 6, 60-74 (1933). (19) Ibid., 6, 710-15 (1933). (20) Okada, H.,Cellulosechem., 12, 11-17 (1931). (21) Reid, E. E. (to du Pont Co.), U. S.Patent 1,864,554(June 28, 1932). (22) Sakurada, I., and Kitabatake, T.,J . Soo. Chem. I n d . Japan, 37, Suppl. binding 604-5B (1934). (23) Seel, P. C. (to Eastman Kodak Co.), U. S. Patent 1,635,013 (July 5, 1927). P R E S E N Tbefore ~ D the Division of Cellulose Chemistry a t the 96th Meeting of the American Chemical Sooiety, Milwaukee, Wis.
Resin-Treated Plywood ALFRED J. STAMM AND R. M. SEBORG Forest Products Laboratory, Madison, Wis.
The previously developed method for treating wood with synthetic resin-forming materials to minimize shrinking and swelling (4) has been applied to the treatment of veneer for making plywood. Treated plies have been successfully assembled with the different types of commercial glue. Unfinished resin-bonded plywood with treated face plies shows a marked decrease in face checking under exterior weathering conditions as compared with the standard resin-bonded plywood. Treated fancy
P
LYWOOD is so constructed, with its alternate odd number of plies a t right angles to one another, that it mechanically minimizes external dimension changes under varying moisture-content conditions. The change in width of a piece of plywood on swelling or shrinking is only about one tenth of the change of the separate plies in the across-the-fiber direction. This does not mean that swelling a n d shrinking have been mechanically prevented, but that the direction in which swelling and shrinking take place has been changed. A piece of plywood takes up the same percentage of moisture under a definite relative humidity as the plies from which it is made. This moisture, except for a slight adsorption-compression correction (S), adds its volume
crotch veneer also shows less tendency to crack and check. The resin treatment greatly reduces moisture transfusion through the plywood under a relative humidity gradient. Water-soluble dyes can be dissolved in the treating solution and fixed by the polymerization of the resin to resemble permanently dyed plywood. The treated wood shows only a slight increase in heat conductivity, and what seems to be a relatively large increase in acid resistance and decay resistance.
to the volume of the cell walls. The fibers must thus swell the normal amount, irrespective of the restraining force within the force range involved. Since the dimension changes in the plane of the plywood are restrained, the changes must occur either in the thickness direction of the plywood or into the fiber cavities. For the latter to occur, the fibers must be distorted or even ruptured. Within the last few years synthetic-resin glues have been developed (2) that produce joints equal to or greater in strength than the wood even under high moisture-content conditions. The glue line of plywood assembled with these hot-press phenol-formaldehyde or urea-formaldehyde glues will withstand rather severe weathering conditions. In spite
898
INDUSTRIAL AND ENGINEERING CHEMISTRY
of this, the plywood is subject to pronounced deterioration due to failure of part of the structure under the severe stresses caused by alternate swelling and shrinking of the fibers. Since the outer surface of the outer plies (unless protected) is not restrained as are the inner surfaces, differential stresses will be set up across the face plies. These stresses, which will continually vary with changing moisture-content conditions, will eventually cause face checking. Because of these stresses, plywood is much more subject to surface checking than is a solid board of the same size when neither is mounted on a restraining support. It seemed highly probable that the application of the recently developed means of minimizing the swelling and shrinking of wood by forming synthetic resins within the cell walls of the wood (4)would materially reduce the stresses set up in plywood by reducing the swelling and shrinking under weathering conditions and hence materially reduce the degrade. It also appeared that this treatment would add other beneficial properties to plywood. Plywood further appeared to be the most promising form of wood on which to apply this treatment; the difficulties of treating massive material are eliminated and the high cost of the treatment is effectively minimized because of the relatively large surface that can be covered by plywood for its bulk.
Synthetic-Resin Formation within the Wood Structure I n order to minimize effectively the swelling and shrinking of wood with a synthetic-resin treatment, three essential requirements were found (4): (a) The resin-forming materials must be unpolymerized or only slightly polymerized so that their molecules are sufficiently small to penetrate the cell walls of the wood completely; (6) the resin-forming constituents must be soluble in polar solvents that swell the wood appreciably and thus open up the cell-wall structure and make diffusion of the resin-forming constituents into the cell wall possible; (c) the resin-forming constituents must themselves be sufficiently polar t o be strongly bonded to the wood. A good index of this affinity is the extent to which the solution of the resin-forming intermediate swells the wood beyond the swelling that is caused by the solvent alone. A large number of different resin-forming materials have been tried. Phenol-formaldehyde-catalyst intermediates that are but slightly polymerized and are soluble in water have been found to meet the requirements best and to give the greatest and most permanent reduction in swelling and shrinking. Urea-resin intermediates are slightly effective, whereas vinyl, styrene, Glyptal, and methyl methacrylate resin-forming materials give but little reduction in the swelling and shrinking of wood. The average swelling of four different species of wood in a 40 per cent by volume aqueous solution of a phenol-formaldehyde-resin intermediate was 33 per cent greater than the swelling of matched pieces in water. The swelling in a 50 per cent solution of a urea-formaldehydecatalyst intermediate was only 10 per cent greater than in water. I n the case of the other resins tested there was practically no additional swelling in the solutions over the swelling in the solvents alone. The following treatments were made with Bakelite liquid resin XR5995 (amber color) and XV9030 (colorless), both of which contain about 85 per cent solids and have a specific gravity of about 1.15. The results obtained with these materials were practically identical except that the clear liquid caused less discoloration of the wood. Phenol-formaldehyde intermediates of other manufacturers, that were practically unpolymerized and water soluble, gave results comparable to the foregoing. I n the previous research on this subject (4) both water and alcohol solutions of the resin-forming intermediates were
VOL. 31, NO. 7
used. It has since been found that there is no real advantage in using alcohol as the solvent when proper precautions are taken in drying the veneer after treatment. The following treatments were made entirely with aqueous solutions of the resin-forming intermediates, The veneer can be treated by either the cylinder treating method in which the solution flows into the coarse capillary structure of the wood under pressure, or by the diffusion method in which green wood is merely soaked in the solution and the solute diffuses into the water within the wood structure. It is of importance to compare these two methods in order to determine which would be the preferable method to use in the treatment of plywood. A series of tests was made on air-dry l/l8-inch Douglas fir veneer sheets, 14 inches s uare. The sheets were placed on edge in a galvanized iron tan% inside the treating cylinder. A vacuum of 27 inches of mercury was pulled, and then a solution of the resin-forming intermediate in water was run into the tank until it completely covered the veneer. The vacuum was held for 15 minutes. In some cases this was followed by an applied pressure to increase the penetration. The amount of solution taken up and the final amount of resin formed in the veneer are given in Table I for several different concentrations of the resin-forming intermediate. This treatment carries the solution only into the coarse capillary structure of the wood. In order for the treating solution to distribute itself throughout the structure, the veneer must be stacked in a high-humidity unheated cabinet or room for several days. The high humidity prevents drying and the absence of heat prevents premature polymerization of the resin. In these tests the veneer was stacked for 3 days. I t was TABLEI. TREATMENT OF AIR-DRY l / l e - I DOUGLAS ~~~ FIR VENEERWITH RESIN-FORMING SOLUTION, AND CHECKING OF PLYWOOD PANELS FACED WITH THISVENEER" Conon. of Treating Soln. % by vol.
60
Treatment
Total No. Resin Content of Checks S o h Taken of Wood, after in Exposed U by Wood Polymerisstion Faces of (8ry-Weight (Dry-Weight Five 14 X 14 Basis) b Basis)b In. Panels
%
%
Vacuum and pressureo Vacuumd Vacuumd
162 61.8 3 60 4 92 33.9 29.2 50 9 87 11 40 Vacuum d 24.5 87 19.1 30 Vacuumd 38 83 20 86 Vaouumd 82 14.8 20 Soaked6 127 12.3 67 0.0 0 0 1385 None After 3 months of southern exposure to sun and weather. b Average value for five-face plies. 0 27-inch He vacuum for 15 minutes. followed bv - air -measure of 60 uounds per square in& for 15 minutes. d 27-inch Hg vacuum for 15 minutes, followed by soaking for I6 minutes. e In solution for 30 minutes.
then slowly dried at 50" C. and about 75 per cent relative humidity so that the resin-forming intermediate in the coarse capillary structure could diffuse into the cell walls as drying progressed. When the free water was removed (2 to 3 days) the temperature was raised to 75 C. for a day, after which the material ap eared quite dry. The temperature was then raised to 95-100" for a day to polymerize the resin completely. An appreciable amount of resin intermediate is lost during the slow evaporation process in the case of the higher concentrations. This in some cases has exceeded a third of the resin. In commercial practice it might thus pay to condense the vapor being lost from the drying chamber. Veneer was also treated by the simple soaking method. Sheets of veneer with moisture contents of 100 and 6 per cent on the basis of the dry weight of the wood were used in order t o compare green and seasoned wood. Both were placed in a 50 per cent by volume solution of the resin-forming intermediate which was continuously stirred. Veneer specimens were removed after different intervals of time, and stacked, dried, and cured under the same conditions as was the cylinder-treated material. The amount of synthetic resin remaining in the veneer after curing is plotted against the time in solution (Figure 1). The amount of resin taken up by the dry wood during the first hour, which is largely by capillarity, is practically the same as the amount taken up by the green wood by diffusion. The green wood, however, attains a higher resin content much more rapidly. It will be shown later that the resin content of the wood on the basis of the dry weight of the untreated wood (the basis on which all the resin contents will O
8.
JULY, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
899
be expressed) should be between 25 and 30 per cent to gain the most efficient improvement in properties. This would require 8 to 15 hours of soaking for the green wood and 40 to 80 hours for the dry wood. It is thus obvious that if the simple diffusiontreating method is to be used, it should be applied to the green veneer just after it comes from the rutter knives. When thicker veneer is treated, the time for the cylinder treatment will not be materially increased when easily treated species are used whereas the diffusion time will be increased as the square of the thickness. In the case of the treatment of '/*-inch veneer, the cylinder method might be the most economical; but for veneer thinner than inch and for thicker veneer of the more difficultly treated species the diffusion method would undoubtedly be preferable.
The following tests were made on treated veneer assembled with a pheno~-forma~dehyde resin glue. When the veneer was dried to a moisture content of 10 to 15 per cent, and the assembly into plywood and the polymerizationof the resin both took place simu~taneous~y in the hot pressures (O' pounds per 'quare press at inch), a product with a gloSsY surface Was obtained that aPpeared as if it had been varnished. Unfortunately this procedure resulted in a product with a raised grain. The presence of the uncured resin made the wood more compressible, Compressing the less compressible summerwood to the same extent as the more compressible springwood set up differential stresses that were relieved upon subq 50 sequent swelling by differential dimension changes. 8 L Face checking was also more serious when the 40 assembly was made this way, presumably because Q of these stresses, so that the procedure was finally 3 hs abandoned. Attempts were also made to assemble k $ 30 t.0 the veneer containing the unpolymerized synthetic$2 resin intermediate without the use of glue-that EO is, to let the treating solution serve both as the * A antishrink agent and the bond for the plies. In SQ order to obtain a good contact and bond, the as2: ," l o 5 sembly pressures had to be doubled. The resultP ing product was considerably compressed. This is & O 0 lo zo 30 40 50 60 70 60 90 ibo not desirable fornormalplywood usebutmaybeexTIME Of JV.4UlNG I N REJIN-FORMING JOLUnON (HOURS) tremely so for special uses. Tests were made in assembling fifteen sheets of treated l/ls-inch Douglas fir OF SYNTHETIC-RESIN-FORMING CONFIGURE1. RATEOF ABSORPTION STITUENTS FROM SOLUTION BY GREENAND DRYl / l a - IDOUGLAS ~ ~ ~ FIR veneer, containing approximately 40 per cent of unVENEER polymerized resin, into plywood without the use of glue under a pressure of 500 pounds per square inch. The final product had a thickness which was half that of the The antishrink efficiency (the reduction in the shrinkage combinedthickness of the plies. The density of the final prodcaused by the treatment divided by the shrinkage of the conuct was about 1.3. The bond was very good and the water trol) of Douglas fir veneer containing different amounts of synthetic resin (Figure 1) is plotted in Figure 2 against the resin content. It increases with increasing resin content of the wood up to a resin content of 30 to 40 per cent, above which additional resin has but little effect. I n the lower concentration range the synthetic resin is undoubtedly formed almost entirely within the cell walls. At concentrations above 30 to 40 per cent the cell walls are saturated with synthetic resin and the excess resin is formed in the coarse capillary structure where it, can show very little antishrink effect. There is thus no object in forming more than 30 to 40 per cent of synthetic resin within the wood.
s$
Assembly of Treated Veneer The treated and cured veneer has been successfully assembled with the following glues: animal, vegetable (starch), soybean, casein, and phenol-formaldehyde and urea-formaldehyde hot-press resin glues. For the longer assembly periods (15 minutes) all of these glues gave joints of practically equal strength to those obtained with untreated veneer. When the assembly period was only a few minutes, the joints were definitely inferior to those obtained with untreated wood. This appears to be due to the fact that the treatment has reduced the tendency for the wood to absorb the glue solvent, so that the longer assembly periods are necessary to obtain the desired increase in glue consistency by evaporation or absorption. Wet-strength tests gave results comparable to those for untreated veneer (1, 2 ) ; the animal and starch glues lost practically all of their bonding power, the soybean and casein glued joints retained one third to one half of their original strength, and the hot-press glues gave joints that retained a high percentage of their original strength. As the chief object of the treatment described in this paper is to obtain a more weather-resistant plywood, the treatment should in most cases be followed by a synthetic resin-glue assembly.
REJiN CONTENT O f WOOD (PERCENT O f DRY WEIGHT O f UNTREATED WOOD)
FIGURE2. ANTISHRINK EFFICIENCYOF l / ~ a - DOUGLAS I ~ ~ ~ FIR VENEER CONTAINING DIFFERENTAMOUNTS OF SYNTHETIC RESINOBTAINED BY TREATING BOTHGREEN AND DRYWOOD
resistance very high, no raising of the grain resulted, and the hardness was a t least four times that of the untreated, unpressed wood. The absence of raised grain in this case is probably due to the fact that the pressure was sufficient to crush the structure and thus relieve differential stresses which would otherwise have been set up.
Weathering of Treated Plywood The deterioration of the normal treated plywood without any protective surface coating under a southern exposure of
,
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VOL. 31, NO. 7
FIGnaE 3. FACECHECKING OF RESIN-BONDED l/CINCn DonGLAs F I R PLYWOOD AFTER &MONTHExposnm Left, untreated; right, surface plies treated with 30 per cent by weight of synthetic resin on the basis of the dry weight of the untreated wood.
trabea Upper, untreated; lower, treated with 30 per cent of synthetic resin on the basis of the dry wcight of the untreated wood.
month exposure of '/rinch plywood panels with treated '/SF inch surface plies on an untreated "&ch three-ply core for different resin contents of the treated plies. The weathering is expressed in terms of the number of checks visible to the naked eye on five panels. The veneer used on the exposed and unexposed faces of each of the eight panels was cut from a single piece to give the best possible matching. Table I indicates that satisfactory protection, as far as the tests go, is obtained when the treated plies contain 25 to 30 per cent resin, even when the surface plies constitute only one fourth of the thickness of the Dlvwood. Examination of the edees showed a slight checkingo? the end-grain ends of the untrGted cores, but this was not sufficiently extensive to be serious. Further, in normal use these edges would be better protected. Resides the difference in checking there is also a large increase in the smoothness of the specimens caused by the resin trratrnent. Preliminary tests on panels faaed with treated fancy crotcli veneer indicate that the treatment greatly reduces face checking of this check-susceptible material. If the treatment is made on the green veneer just after cutting, the large losses in stock veneer due to checking and splitting prior to use should also be appreciably minimized. The treatment should thus he of considerable value to furniture manufacturers.
6 months to weathering conditions was compared with that of matched untreated panels. Figure 3 shows two pieces of I/,inch plywood with '/*inch cores, and '/&nch faces. Left is the untreated control and right is the treated specimen with approximately 30 per cent of resin in the two surface plies, the core being untreated. The treated specimen is practically free from checks, whereas the control is badly checked. Table I gives the comparative weathering resistance after 3-
Wood siding on houses is painted for two reasons-namely, to reduce the weathering degrade of the wood and to give pleasing esthetic effects. Since the weathering degrade is reduced to a minimum by the synthetic-resin treatment, it seemed highly possible that pleasing effectscould he obtained by dyeing, which would not involve the high cost of paint upkeep.
OF SUGAR PINE SPECIMENS U T E R 3-MONTH 4. DECAY IXCWATIONwiTn TEE WOOD-DESTROYING FUNGUS,Lenzites FIGURE
Dyeing the Veneer
JULY, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
Tests were made on incorporating inexpensive watersoluble dyes with the resin-forming intermediate and fixing them with the resin. Black, red, orange, and yellow Calco condensation dyes were used. The last two dyes dyed the wood much more uniformly than did the first two. The dyeing of 1/16-inch veneers of tupelo, black gum, yellow poplar, sugar maple, aspen, Douglas fir, and yellow birch decreased in uniformity in the order given. The birch showed a definite tendency t o filter out the dye on treatment, whereas the gum and poplar veneer dyed completely throughout the thickness of the plies. The dyes are like stains, in that the grain of the wood is visible. The contrast between the light and dark portions is, however, considerably less pronounced than is obtained with ordinary stains. Tests on the leaching out of the dyes after polymerization of the resin indicated that a n insignificant amount of dye WE/S removed after continuous soaking in water for over a month. Weathering tests indicate that there is some fading of the dyes, most of which takes place in the first few weeks. Dyes more permanent to light exposure might be found than those tested. Sufficient evidence has been obtained, however, to indicate the possibilities of making a permanently dyed plywood.
901
transfusion through both treated and untreated yellow birch plywood was about double the corresponding values given for Douglas fir in Table 11. The large reduction in the passage of moisture through the treated plywood suggested that the treated plywood could be used to good advantage for interior paneling of houses because of its tendency t o reduce the passage of moisture through the walls during the winter and thus decrease condensation within inner and outer walls (6). The treated Douglas fir plywood was found to form a moisture barrier as good as the best asphalt- or tar-impregnated and -coated building papers and almost as good as metal foil.
Decay Resistance of Treated Wood
Decay-resistance tests were made on small specimens of Douglas fir heartwood containing 32 and 49 per cent of synthetic resin. These specimens, together with matched controls, were incubated in contact with cultures of the wooddestroying fungus, Trametes serialis, for 8 months. The controls lost, on the average, 40 per cent of their dry weight and the treated specimens lost between 3 and 5 per cent. The former could easily be crumbled with the fingers, whereas the Moisture Transfusion through Treated Plywood latter were mechanically sound. The large reduction in the decay is apparently due to the fact that the treated wood Measurements were made to compare the rate a t which could not take up enough water to support decay rather than water vapor passed through the treated plywood in contrast to any inherent toxic effect on the part of residual phenol or to similar untreated plywood under a relative-humidity graformaldehyde. This conclusion is based on the fact that dient. Pieces of plywood 1-foot square were sealed on top fungus grew on the surface of the treated blocks, whereas it of metal trays containing water so that 100 square inches of would have shunned the blocks had they been toxic. surface were exposed. These were placed in a 30 per cent Further tests were made with a more decay-susceptible relative humidity room. Moisture passed through the plywood, sugar pine, and another decay fungus, Lenzites trabea. wood under a relative-humidity gradient of 100 to 30 per cent. T o ensure further a favorable moisture content for developAfter a steady-state moisture gradient was set u p through the ment of the fungus in the wood, the specimens were imspecimen, loss of moisture occurred a t a uniform rate. The mersed in water, and the air was removed by alternate appliloss in weight of the tray and plywood after this condition cation of vacuum and pressure. I n this way the moisture had been reached in 15 days is given in Table I1 for untreated content of the treated specimens was made to exceed 100 per plywood and plywood with different proportions of the total cent. The specimens were incubated for 3 months. The thickness treated. Treatment of all the plies with 20 per average loss in weight of three controls was 42 per cent of cent of resin reduces the moisture transfusion to about one their dry weight. The average loss of weight of four specitenth of normal. Treating only the outer plies is almost as mens containing 15 per cent resin was 5.3 per cent, and of effective as treating all the plies. seven specimens containing 30 per cent resin was 1.2 per cent (Figure 4). Again the controls could be crumbled with the fingers and the treated specimens were mechanically sound. TABLE 11. MOISTURE TRANSFUSION THROUGH RESIN-BONDED Even with a supply of free water throughout the coarse capilFIR PLYWOOD UNDER A STEADY-STATE RELATIVE- lary structure of the treated specimens, a n insufficient amount DOUGLAS HUMIDITY GRADIENT OF 100 TO 30 PERCENT of water entered the cell walls to support normal decay.
No. of Plies
Ply Thickness Inch
Plies Treated
3 3 3
1/16 1/12 1/8
None
3
1/18 l/8 I/$
All
3
3
2
Moisture Lost through 100 Sq. In. of Surface in 15 Davsa
%
Grams
0 0 0
51
20 20
5
40
43
35 3 1
Outer 1/16 in. 20 6 Outer l/g in. 20 4 These values are averages of the results for two t o four specimens.
1 3 a
Approx. Synthetic Resin Content of Treated Plies (Dry-Weight Basis)
'/le] 1/8
1/8
The synthetic-resin glue line adds somewhat to the resistance to moisture passage. If the untreated controls given in Table I1 were assembled with casein or soybean glue, about twice as much moisture would have passed through the plywood in 15 days. The synthetic-resin glue, though effective in reducing moisture transfusion, is not nearly so effective as the forming of the resin within the cell walls. The moisture
Acid Resistance of Treated Wood Tests were made of the acid resistance imparted to wood by the synthetic-resin treatment. Small specimens of southern yellow pine containing 35 per cent of synthetic resin were compared with the controls. Since the action of cold acid on the untreated wood is quite slow, the acids were boiled to accelerate the tests. Sixteen hours of boiling in 10 per cent hydrochloric acid gave a weight loss of the treated wood of 5 per cent and of the untreated wood of 48 per cent. The controls could be readily crumbled with the fingers after drying, whereas the treated pieces were perfectly sound. Sulfuric acid did not show so large a difference between the treated and untreated specimens. Sixteen hours of boiling in 25 per cent sulfuric acid gave a weight loss of the treated wood of 22 per cent, and of the untreated wood of 39 per cent. These data indicate the possibility of using treated veneer as a liner for acid tanks. Although the acid resistance of the treated wood is good, the alkali resistance is very poor and the action on the treated pieces is much greater than on the controls.
I
%,'\
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902
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 31, NO.7
Fire Resistance of Conclusions and Treated Wood Costs The fire resistance M a k i n g plywood tests were made with from veneer treated the Forest P r o d u c t s with a phenolformalLaboratory firedehyde resin-forming t u b e a p p a r a t u s (6). intermediate improves T r e a t e d s t i c k s of many of the properties: southern yellow pine reduces swelling and containing 15, 28, and s h r i n k i n g and, con47 per cent resin were sequently, face checkcompared with an uning under weathering treated control. The conditions; makes possible the fixing of inexpercentage loss i n weight when burning pensive water-soluble ceased, relative to the dyes in the structure; loss in weight of the reduces moisture transcontrols, was practifusion through the plycally equal to the perwood; increases decay centage by weight of resistance; increases the wood in the treated acid rcsistanoe; inwood. creases hardness and In other words, the compressive strength; same proportion of the possibly improves fire wood burned in each resistance when incorcase. Evidently the porated with phosphate wood is sufficiently salts; and loses only more combustible than slightly in thermal inthe resin under the sulating properties. test conditions so that This array of improved it alone was burned. properties can be obEven though the resin tained a t only a did not prevent the nominal increase in wood from burning, cost. On the basis of the fact that t,he resin the undiluted resinitself did not burn forming intermediate shows that it could aid costing 25 cents per in holding the burning pound, the chemicals Treated, Untreated, Untreated, wood intact and thus required per square water-swollen water-swollen oven-dried possibly minimize fire foot of '/,&ch veneer Evmm 01 ANTISHRINKTREATMENT ON TEE SWELLING ox' Woon spread. A few preof average specific Shrinking and swelling of the treated block have been greatly reliminary q u a l i t a t i v e gravity, in order to give duced by the antishrink treatment. The blocks are of equal tests indicate t h a t an adequate improvelengths when dried. ammonium phosment in properties, n h a t e s c a n h e incost. wo,,ld ~.~~~~ .... 1 cent,. If corporated with the resin and appreciably increase the fire the treatment were to cost '/*cent per square foot additional, resistance. the total increased manufacturing cost of three-ply plywood with two '/,ginch treatedfaces and an untreated core would be Thermal Conductivity and Other Properties about 3 cents per square foot. This would be an increase of about 50 to 75 per cent over present wholesale cost of *j4-inch Tests were made to determine the thermal conductivity of Douglas fir resin-bonded plywood (three '/&nch plies). the treated plywood. Specimens of Z/s-inch Douglas fir plywood with all of the plies treated with approximately 60 per Acknowledgment cent of resin gave a thermal conductivity of 1.00 X. t. u. per Thanks are due the following members of the Forest Prodhour per square foot per inch of thickness, whereas the control ucts Laboratory staff for aid in determining the properties of gave 0.87. The increase in thermal conductivity is thus the treated wood: Don Xronse, gluing; C. A. Harrison, fire much less than the increase in weight and is no higher than resistance; T. C. Scheffer, toxicity; and J. D. MacLean, that of many woods. These specimens, too, contain more thermal conductivity. resin than would normally be used. The data thus indicate that the treatment does not materially reduce the insulating Literature Cited value of the plywood. (I) Iliouse, Don. Mech. Ew., 60,3 0 6 8 (1938). Tests have been started on the paint-holding power of the (2) Sontsp,L.A.,8ndNorton,A. J..IND.ENR.CHE~.. 27.1114 (1935). treated plywood. These will have to be reported later be(3) Stamm, A. 3.. and Hamen. L A . . J.Phys. Chom.. 41,1007(1937). (4) Stamm,A. J.,bndSeborg, R _ M . , I N D . E I ~ . C B E _28. M .l,lt?4(1936). cause insufficient time has elapsed for noticeable deterioration ( 5 ) Teesdde, L. V., Am. Builder and Bsiiding A m dealers' ed., p i . of the paint films. 132-S. Dec.. 1937. ~ . ~ ~ ~ ~ The improvement of mechanical properties was reported in !Gj Truax, T. R.,and Harrison, C.A,, Pmc. Am. SOC.T e a t i , Mate~ a previous paper (4). Hardness and compressive strength rid*, 29.975-88 (1Y)29j. properties were appreciably improved, but other strength PREBEWT~D beiors the Division of Colloid Chemistry at the 96th Meeting of properties were practically unaffected. the American Chemical Society, Milwsukes, Wis. ~~
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