Swollen, Impregnated, and Compressed Wood Samples X-RAY DIFFRACTION STUDIES G. L. Clark and J . A . Howsmon UNIVERSITY OF ILLINOIS, URBANA, ILL.
values of the lattice dimensions of the untreated and swelled specimens indicated that no compound f o r m a t i o n between the cellulose and the molecules of the swelling agent had taken place. The swelling of wood b y both pyridine and morpholine was classified as intermicellar. The technique of microradiography w a s applied to the study of impregnated wood. A n improved procedure w a s developed for m a k i n g microradiographs of wood. The microradiographs were f o u n d to be characteristic of the wood and the distribution of the i m p r e g n a n t . A comparison of the relative effectiveness of alcohol-soluble and water-soluble resins as i m p r e g n a n t s w a s possible b y this technique. The alcohol-soluble resins were more evenly distributed on the cell walls of the wood a f t e r preliminary swelling w i t h morpholine than were water-soluble resins
and, therefore, were probably more efficient in decreasing dimensional c h a n g e s w i t h c h a n g e s in h u m i d i t y . O n the other h a n d , the water-soluble resins are more evenly distributed a f t e r vacuum treatment of the wood and impregnation under pressure. The orientation of cellulose crystallites in wood w h i c h had been subjected to heat and pressure were s t u d i e d and compared w i t h the orientation in untreated wood. For this purpose a microphotometer w i t h a n e w rotating stage w a s used for graphical evaluation of x-ray patterns. In general, compression of wood seems to decrease the preferred orientation of the cellulose crystallites, whereas the preferred o r i e n t a t i o n of heated wood increases as a result of heat treatment. Absolute correlation between c h a n g e s i n orientation and physical properties of wood are not complete, but heat treatment w i t h attendant increase in preferred orientation improves tensile s t r e n g t h b y 10% or more.
S H R I N K I N G , swelling, and the accompanying warping with changes i n moisture content are the most detrimental properties of wood from the standpoint of structural use. The artificial minimizing of these properties has been one of the greatest problems of the wood technologist, and, with the advent of molded products from wood, dimensional stability has become vitally important. I n recent years the use of a phenolformaldehyde resin as impregnant (.% 83, SI), I,heat (19), and pressure (8,62)or a combination of these have been predominant among the methods for improving wood. The studies of these methods have been very extensive and only a brief treatment can be given here. The process of impregnation by phenol-formaldehyde resins is carried out as follows: The wood is subjected t o high vacuum (the common industrial process) or is swelled by some suitable agent t o open up the c a p illary structure so t h a t the resin may be easily introduced, the wood is steeped i n a solution containing the resin-forming conqtituents, and the resin is polymerized in the pores of the wood. The finished product has a high degree of dimensional stability because of the impermeability of the resin t o moisture. Merritt and White (19) reported t h a t wood partially pyrolyzed at 210" C. under 1 atmosphere pressure has only 50% as much expansion when soaked i n water as wood dried a t 105" C. Bernhard, Perry, and Stern (a) showed t h a t the tensile strength of plywood compressed under pressures u p t o 1500 pounds per square inch seems t o increase i n direct proportion t o the density, and work at the Forest Products Laboratory (7) indicated t h a t the combination of high temperature and pressure gives a degree of dimensional stability with changes i n humidity. This research was undertaken i n conjunction with the Forest Products Laboratory a t Madison, Wis., in an effort t o gain academic knowledge of the various treatments of wood. The specific problems involved are the following: (a) the study of swelling of wood by morpholine and pyridine, which are of interest because of the high degree of swelling they produce when
compared with water, to determine whether any compound formation occurs between the swelling agent and the cellulose; (b) the study of distribution of the resin in the wood as a function of solvent used and resin concentration; and (c) the study of effects of heat and pressure on the orientation of the cellulose crystallites. The literature concerning x-ray studies of cellulose and its derivatives is extensive. Numerous investigations were made concerning the swelling of cellulose i n various solvents and the orientation of cellulose crystallites i n many natural and synthetic fibers. The studies of impregnation of cellulose by the xray method are, however, comparatively few. Sisson (U) summarized all these investigations and the results of the experimental observatiom. SWELLING OF CELLULOSE. Since cellulose contains both crystalline and amorphous areas, there are two types of swelling which may take place. When the swelling liquid penetrates only the intercrystalline areas, there is no change in the x-ray pattern crystal structure, and the swelling is known as intermicellar swelling. If, however, the liquid actually penetrates the crystal interior, there are definite changes in the pattern and hence the structure, and the resulting swelling is called intramicellar swelling. Both of these types of swelling have been observed when cellulose is swelled in organic liquids, and some attempts a t classification of the compounds causing each type have been made. Stamm (88)studied the swelling of wood 6 y normal alcohols, benzene, and various benzene derivatives, such as toluene, aniline, and benzaldehyde. The swelling in all these cases is intermicellar. Normal alcohols give decreased swelling a s molecular weight increases, whereas t h e swelling i n benzene and its derivatives increases with increasing dipole moment of the swelling liquid. Kate (14) showed t h a t many nondissociated organic substances, such as thiourea, resprcinol, and benzene sulfonates, as well as many compounds containing sulfur and halogen, cause
T h e swelling of wood and ramie fibers b y pyridine and m o r p h o l i n e w a s studied. The a g r e e m e n t of calculated
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I N D U S T R I A L AND. E N G I N E E R I N G C H E M I S T R Y
intermicellar swelling beyond the normal water-swollen dimensions. Katz also observed th:Lt the atomic groupings =X-N= and =S-R--N= have a strong affinity for cellulose and that, in general, compounds containing thr,se groups cause intermicellar swelling. Intramicellar swelling in most cases results in a definite relation between the glucose units and the molecules of the swelling agent. The products formed in this way are known as swelling compounds. These swelling compounds are not, necessarily the result of a chemical reaction between the cellulose and srr-elling agent, but' in any case the molecules are distributed throughout the expanded lattice of the cellulose in some definite geometric pattern. Probably the best known reaction of this t,ype is the mercerizing action of sodium hydroxide on cellulose (16, 28, 33). Sisson and Saner (d7) showed that alkali swelling agents, such as the quaternary ammonium hydroxides, produce both interand intramicellar swelling. The combination of the two swelling actions is shown by an increase in fiber diameter; this increase is too great t o be explained by the lattice expansion resulting from the formation of the swelling compound. Trogus and Hess (34) reported that certain diamines, such as hydrazine and ethylene diamine, produce swelling which is largely intramicellar, for the expansion of the lattice is of the same order as that of the fiber as a whole. The work of Barry, Peterson, and King ( 1 ) on nonaqueous alkyl amines, and of Clark and Parker (6) on liquid ammonia, showed that these compounds produce intramicellar swelling. The marked swelling of wood by such basic compounds as pyridine and morpholine has long been known, but no study of the action of these substances on cellulose has been made. However, pyridine was shown by Hess and Trogus (13) to produce a swelling compound with cellulose triacetate having a lattice expansion a t right angles to the fiber axis, but intramicellar swelling is more characteristic of cellulose esters than of cellulose itself. IYPREGXATION OF CELLULOSE.Early attempts a t studying deposits within cellulose fibers were carried out t o gain information concerning the fiber itself rather than the impregnant. Frey-Wyssling (9) and Kratky and Mark (17) investigated the x-ray intensity scattered by fibers containing metal deposits; by comparing that intensity scattered by fibers containing no metal deposits, they reached certain general conclusions concerning supermolecular structure of the fibers studied. Lokschin (18) used a similar method in th@st,udyof spruce wood impregnated with ammonium sulfate and was able t o determine quantitatively the amount of impregnant present. None of these studies, however, yielded any information concerning the distribution of impregnant within the fiber. The technique of microradiography which was suggested by Goby (10) in 1913 and extended for practical use in the study of metals and alloys by Clark and Shafer ( 7 ) seemed to offer great possibilities for this problem. By this method several microradiographs of wood sections were obtained and found t o be characteristic of the type of wood studied. For this purpose specimens a few hundredths of an inch thick are penetrated by an essentially monochromatic x-ray beam from a regular diffraction tube usually with copper target. Film with very fine-grained emulsion, such as Lippmann, is placed in close contact with the specimen. The radiographic image so produced is photographically enlarged up to 300 diameters wit,hout undue interference from graininess. Any variations in density or structure in the specimen are delineated in the microradiograph. Even though cellulose and plastics are similar in absorbing power, it should still be possible to discover the distribution in impregnated samples. ORIENTATIOK OF CELLULOSE CRYSTBLLITES. That the Orientation of the structural units of cellulose varies widely in different fibers or even in the same fiber is well known and has been discussed by many investigators (8, 20). The influence of this orientation in wood fibers upon the physical and chemical proper-
Vol. 38, No. 12
ties has been extensively studied, particularly with reiPrence to the density, tensile strength, and expansion of the Tvood (16, $ 2 ) . The use of x-rays in studying the orientation and diffeientiating between various fibers was discussed by Clark (4),Hcrmans ( 1 1 ) ,and many others. All the methods for comparisonof oricntation of fibers are based on the length of the arcs or the relative intensities along the circle on which the 002 interference maxima are located. Sisson and Clark (26) first described a quantitative x-ray method for the comparison of crystallite orientation in cellulose fibers. Intensity measurements were made a t 5" intervals around the 002 diffraction ring, and distribution curves were made by plotting the percentage of crystallites over these 5" angular ranges against the angle to the fiber axis. Comparison of these curves for diff'erent fibers gives an immediate evaluation of the orientation in these fibers. Berkley ( 3 ) developed a similar method using a photoelectric comparator which eliminatd the personal error. The present routine method of comparing orientation in cotton and rayon fibers is described by Rerkley (2) and by Sisson (25). An index of the orientation is obtained by measuring the angle on the x-rjy pattern a t which the density of the 002 diffraction arc is half the maximum density. Comparison of the angle values so obtained for different fibers gives an immediate evaluntion of the relative orientation in these fibers. Hermans and de Rooys (12) employed a method similar to this and reported that it failed in many cases vvhere the orientation is less perfect than that found in cotton and rayon fibers. It is probable, then, that complete distribution curves should be made for a fiber in which the orientation qualities are unknorvn. EXPERIMEKTAL PROCEDURE
SX'ELLISG O F \T-OOD BY PYRIDINE AND MORPHOLIXE. The samples studied were tangential sections of spruce sapn ood, one of which was swelled in pyridine, one in morpholine, and one untreated section for control. The specimens were mounted with the long axis of the wood perpendicular to a parallel beam of xrays, which was defined by 0.025-inch pinholes. The patterns were recorded on a flat film which was placed perpendicular t o the x-ray beam 5 cm. from the sample. All patterns were made with filtered copper radiation obtained from a Machlett diffraction tube operated a t 40 kilovolts and 15 milliamperes. An exposure time of 1 hour was found to be satisfactory. A series of exposures was taken on each sample. The first exposure was taken with the fibers saturated with solvent and kept a t a constant solvent concentration by placing one end of the wood specimen in the solvent during exposure. Then successive patterns were taken as the samples dried, so that, a pattern could be obtained relatively free of the diffuse halo of the solvent but with enough solvent present to keep the wood in the swollen condition. Samples of ramie fibers were swelled with pyridine and morpholine, and patterns were obtained under similar conditions t o determine whether the cellular structure of the wood caused any differences in the tendency of the cellulose t o form swelling compounds. The breadth of the interferences recorded on the film made accurate measurements of the corresponding spacings impossible by any method which depended on visual choice of the points of' maximum intensity. Therefore microphotometer tracings were made across the equator line of the pattern, and the distance between peaks was measured on this paper.
~IICRORADIOQRAPHIC STUDIESOF RESIN DISTPJB~~TION IN WOOD. The woods chosen for this investigation were spruce and yellow birch, For each species of wood, tangential and transverse sections with the following resin contents were prepared in the Forest Products Laboratory: (a) no resin, ( b ) 15 and 30% alcohol-soluble resin, and ( e ) 15 and 307' water-soluble resin.
December, 1S46
A.
C.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Spruce, untreated
Spruce, 30% water-soluble resin
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over wide ranges to determine the best conditions for wood examination. The tube voltage was found t o have little effect on the radiographs except a t exceedingly low voltages, when long exposure times were necessary. Either copper or cobalt characteristic radiation gave good radiographic d e t a i l . Longer wave lengths were avoided because of the accompanying increase in air scattering and subsequent long exposure times. As would B. Spruce, 15% alcohol-soluble resin be expected from the divergent natureof thex-ray beam, the best definition of the cell structure was obtained a t long focal spot-film distances, but the difference in detail obtained with the specimen 25 om. and 4 cm. from the tube were not great enough t o warrant the use of the longer distance because of the longer exposure time required a t this distance. Various sample thicknesses were studied, and the best detail was, observed using a thickness of 0.015 inch for tangential D. Birch, 15 % water-soluble redn sections and 0.04 inch for transverse sections. Sections of greater thickness Figure 1. Microradiographs of Tangential result in loss of detail; Sections of Impregnated Wood ( X W ) sections of lesser thickness are exceedingly hard t o prepare without splitting the wood. Thinner sections of the transverse sections would be desirable but would necessitate a tedious grinding process, whereas sections 0.04 inch thick can be prepared with a microtome.
As a result of the above trials the following technique was adopted and used for all specimens: (a) unfiltered cobalt-K a-radiation from a tube operating at 28 kilovolts and 10 milliamperes; (b) a focal spot film distance of 4 inches; (c) exposure time of 3 minutes for 0.01binch tangential sections; 5 minutes for 0.04-inch transverse sections; ((t) Lippmann film, emulsion 3741-A; (e) development time of 5 minutes in Eastman x-ray developer a t 20° C. The microradlographs were viewed under a microscope and enlargements made with a Zeiss Ultra Phot. E.
Spruce, 15% alcohol-soluble resin
The control of experimental conditions which would yield the best results was studied; particularly with respect to tube voltage, wave length of radiation used, focal spot-film distance, and sample thickness. In all trials the specimen and film were placed in contact perpendicular t o the x-ray beam, using a camera of the type described by Clark and Gross (6). Tbe variables listed were studied
ORIENTATION STUDIES. Clark (4)reported that the orientation of wood as observed on x-ray patterns was different for the tangential and. radial sections even though, in both cases, the x-ray beam was perpendicular t o the fiber axis. Therefore, to obtain comparable results for different samples, the tangential face was placed perpendicular to the beam for all patterns. Other experimental conditions were identical with those used for the studies of swelling. The density measurements around the 002 diffraction ring were made on a Leeds I% Northrup recording microphotometer
.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I. INTERPLANAR DISTAKCES IN ANGSTROM UNITS Plane 101, ioi 002 Untreated Pyridine-swollen &Iorpholine-swollen
3.97 8.97
5.71 5.62 5.54
3.99
TABLE11. RAMIEI N T E R P L A N A R DISTANCES IS UNITS Plane 101 1oi Untreated Pyridine-swollen Morpholine-swollen
6.09 6.07 6.03
ANGSTROM
002
5.38
3.98
5,43 5.39
3.95
3.95
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wmpresied under 2000-pound hydraulic pressure a t 212' F., and natural maple and maple heated at 430' F. for 4.5 hours. DISCUSSIOY OF RESULTS
S\T'EI,LING STUDIES.The x-ray diffraction patterns oi spruce saturated with morpholine and pyridine showed an intense halo of the solvent which partially obscured the interferences caused by the 101 and 101 planes. Therefore, the measurements of the lattice dimensions had to be made from patterns of partially dried specimens in which enough solvent remained to keep the wood in the swollen condition. Table I lists the observed interplanar distances for the swollen wood specimens as compared with those of untreated wood. The interferences of the 101 and 101 planes in patterns of wood are diffuse and tend to merge into one interference so that only one measurement could be obtained. The differences noted in the l O 1 - 1 O i spacing of the various samples seems to indicate a lattice contraction. However, the halo of the solvent appears on the x-ray pattern between the interference of these plancs and the interference of the 002 plane. The calculation of the values given in Table I was made by measuring the distances of intensity maxima from the center of the pattern. The presence of the solvent halo would tend to shift the intensity maxima of the 101 and l 0 i planes away from the center, and the observed interplanar distances would be smaller than the abtual distances. To determine whether this was actually the case, ramie fibers were used because the more perfect orientation of these fibers would make possible individual measurements of the 101 and 101 interplanar distances. The effect of the solvent halo would be minimized, for capillary imbibition is much less in ramie than in wood because of structural differences. The results of these measurements are given in Table 11. The values in this table are in fairly good agreement and seem to uphold the belief that the variations in the 101-lOi distances for the TTood samples resulted from the shift in intensity peaks caused by the halo of the solvent. If intramicellar swelling had taken place to any extent, an expansion of the lattice would have been noted. When the lattice dimensions of a swelling compound are compared with those of the original cellulose, a marked increase in the distance between the 101 planes is observed. From the values given in Tables I
equipped with a rotating stage instead of the visual microdensitometer used by Sisson ( 2 6 ) . The film is mounted for measurement between two glass plates. The plates and film are mounted on a threaded shaft and held perpendicular to this shaft by nuts and washers. The shaft is fitted in a tubular bearing which in turn is mounted perpendicular t o a brass rod. The brass rod is then attached t o a vertical stand. Vertical adjustment of the position of the plates was made by a rack and pinion gear mechanism on the stand. The stage of the microphotometer was moved for horizontal adjustment. The system n a s rotated by a pulley attached to the shaft holding the plates, The pulley system was constructed so that 0.5 em. on the recording paper was equivalent to 5' rotation of the film when the light system was focused on the 002 ring. The original plate adjustment was made by centering the light on the most dense portion of the 002 ring. From the microphotometer tracing density readings were made every 5" around the diffraction ring. A background correction is necessary for each reading. This was made by measuring the density of the lightest portion of the f ilm between the 002 ring and the next ring of larger diameter for each quadrant and taking the average as the correction factor for all readings. The corrected readings were then converted to a percentage basis by dividing each reading by the sum of all readings and multiplying by 100. Representing the data on this basis eliminates the necessity of carefully controlling such experimental variables as time of exposure, sample thickness, and the intensity of the x-ray beam. For best results, however, these factors should be kept as nearly alike as possible. The percentage data obtained were then plotted against the angle measured on the film between a line drawn perpendicular to the fiber axis and a line drawn through the point at which the reading mas taken. The values finally used in plotting the distribution curves are the average of a t least four independent trials for each sample. This was necessary because the accuracy of the method is approximately 5%. The samples studied by this method were natural poplar and poplar compressed by a pressure of 2000 pounds a t a temperaNormal Poplar Compressed Poplar ture less than 212" F., natuFigure 2. Fiber Diffraction Patterns Showing Change in Orientation on Compression ral chestnut and chestnut (X90)
December, 1946
.
INDUSTRIAL AND ENGINEERING CHEMISTRY 194a
192a
-
____
_ _ _ _ COMPRESSED
NORMAL POPLAR COMPRESSED POPLAR
- NORMAL
251
CHESTNUT
CHESTNUT
A v)
a w
0 > VI w c
-I -I
U
t t v)
a u
x (
I
8
6
I
I
60
80
I
N
I
ANGLE T O FIBER AXIS
I
,
8
1
1
40
80
60
ANGLE T O F I B E R A X I S
Figure 4. Distribution Curves for Chestnut
Figure 3. Distribution Curves for Patterns of Normal and Compressed Poplar of Figure 2
____ and I1 it is apparent that no compound formation has taken place. The swelling of cellulose by pyridine and morpholine can be classified as intermicellar. MICRORADIOGRAPHIC STU~IES OF IMPREGNATED WOOD. Typical microradiographs of radial, tangential, and transverse sections of untreated wood (with oak) have been published previously (6). The microradiographs of impregnated wood proved t o be characteristic of the wood and the impregnant. Figure 1 shows typical microradiographs illustrating various effects which were commonly noticed. The microradiographic technique employed is capable of giving good definition of wood structure. This is.shown in microradiograph A of Figure 1, in which the light portions are the walls of the longitudinal cells in the wood. Microradiograph B shows the effect of the impregnant on the observed image. No actual distinction can be made between the cellulose fibers and the phenol-formaldehyde resin, but the uniform increase in the thickness of the cell walls is striking. Microradiographs B , C, and D illustrate the relative effectiveness of alcohol-soluble and water-soluble resins as impregnants. I n B it can be seen that the alcohol-soluble resin is uniformly deposited on the surfaces of the wood cells. The nonuniform distribution of the water-soluble resin is shown in D by the random appearance of resin "bridges" between the cell walls, whereas other portions of the walls are relatively free of resin. I n C no resin "bridges" are apparent, but the resin is localized and little increase in cell wall thickness can be noted. Microradiograph E shows the effect of sample thickness on the resulting image. Several distinct patterns of cellular structure superimposed upon one another can be seen. The superposition of images results in a loss of definition and detail. This effect was generally noted in microradiographs of the transverse sections. The difficulties encountered in preparing transverse sections of such a thickness that these layers would not be observed makes the study of these sections impractical. However, the conclusions concerning the relative distribution of alcoholand water-soluble resins drawn from the study of tangential sections are in agreement with observations on transverse sections even though only a qualitative comparison can be made. . I n general, the best technique for studying wood by microradiography involves the use of tangential sections. I n these particular cases, in which wood was first swollen by morpholine, the alcohol-soluble resin was found to be more evenly distributed through the wood than the water-soluble resins and would, therefore, probably give a higher degree of dimensional stability with changes in humidity. The cell walls of wood containing 30% by weight of a n alcohol-soluble resin are shown to be completely coated with the resin. Wood of higher resin content would have the intercellular cavities more completely @led, but the dimensional stability would probably not be greatly affected.
'
20
0
20
40
NORMAL MAPLE
-
b
HEATED MAPLE
&
A
1
8 80
#
1
60
l
t
40
/
I
4
,
I
I
20 0 20 ANGLE'TO F I B E R A X I S
1
I
40
I
I
60
I
I
80
Figure 5. Distribution Curves for Maple That this is actually the case was shown by experiments carried out in the Forest Products Laboratory. For impregnation under pressure following subjection of the wood t o high vacua, there is evidence that the water-soluble resins are more evenly distributed. Obviously molecular weight and viscosity of the resin are important factors concerned in impregnation. The chief interest here is the demonstration of the value of microradiography in extended impregnation studies. ORIENTATION STUDIES OF TREATED WOOD. Readings were obtained which give distribution curves of the density around the 002 diffraction ring of x-ray patterns of wood. These readings were made comparable by converting observed density values to percentages. Each curve plotted from these values has a constant area, and the value a t any point represents the relative per cent of the total crystallites over a 5" angular range a t that, point. Figure 2 shows patterns of normal and compressed poplar which were used in the orientation study. Intensity distribution curves plotted in terms of crystallite orientation for these specimens are shown in Figure 3; Figure 4 shows the curves for normal and compressed chestnut. Inspection of the distribution curves for normal and compressed wood shows t h a t the orientation of cellulose crystallites is less perfect in the compressed than in the normal wood. This difference in orientation is also shown by the values of the angle a t which the density of the 002 ring is half the maximum density. The half maximum angles for normal and compressed poplar are 11.32' and 12.80°, respectively; for normal and compressed chestnut, 9.0" and 9.3', respectively. As the degree of preferred orientation of fibers in a specimen decreases, the tensile strength of the specimen perpendicular to the preferred fiber axis decreases. The increase in tensile strength of a compressed wood in this direction must, therefore,
INDUSTRIAL AND ENGINEERING CHEMISTRY
1262
be wholly attributed to the resulting close packing and cementing of the cellulose fibers, for the orientation effects alone would decrease the tensile strength. The observed decrease in relative orientation for wood which has been subjected t o high compression is in agreement with previous studies (4, 24). Compression wood growing on the leaning side of a tree was shown to have a less perfect preferred orientation than the normal wood, which grows in a portion of the tree relatively free from strain. Figure 5 presents distribution curves for normal maple and maple which has been heated at 400” F. for 4.5 hours. The half maximum anglesfor these specimen; are 10.65’ and 9.85’, respectively. The distribution curves and the smaller half maximum angle for the heated specimen indicate that the cellulose crystallites are more nearly parallel to the fiber axis in the heated wood than in the normal wood. .is a result of this more perfect preferred orientation, the tensile strength should increase; it does to the extent of a t least 10%. The changes in orientation do not explain the incre mensional stability of vood treated by either heat or pressure. 111 compressed wood the increase in stability is probably a result of the decrease in size of the capillary channels anti the subsequent small moisture absorption. The dimensional stability induced by heating may be the result of chrmicnl chanffesbrought about by the partial pyrolysis of the lignin in the wood or of the cellulose itself. It was observed ( 5 ) that increase in preferrrd orientation results in reduced shrinknpe of wood but sufficient data arc not yet available for quantitative evaluation of this effect. It is doubtful that the small increase in orientation observed for the heated wood would greatly affect the dimensional s tabilit 57.. LITERATURE CITED
(1) Barry, A. J., Peterson, F. C., and King, A. J., paper presented before Division of Cellulose Chemistry of A.C.S. a t Pitts-
Vol. 38, No. 12
(3) Beinhard, R . K., Perry, T. D., and Stern, E. G., M e c h . Eng., 62, 189 (1940). (4) Clark, G . L., IKD.E X G .CHEIM., 22, 474 (1930). (5) Clark, G . L., and Gross, S.T., ISD. E X G .CHEM..ANAL.ED.. 14, 676 (1942). (6) Clark, G . L., and Parker, E. *L,J . Phys. Chem., 41, 777 (1937). (7) Clark, G . L., and Shafer, TI’. M.,Trans. Am SOC.Metals, 13, 732 11941). (8) Farr, %’. K.’, and Clark, G. L., C‘ontTib. Boyce Thompson Inst., 4, 273 (1932). (9) Frey-Wyssling, A, Kolloid-Z., 85, 148 (1938). (10) Goby, P., Compt.rend., 156, 686 (1918). (11) Hermans, P. H., Kolloid-Z., 97, 223 (1941). (12) Hermans, P. H., and Booys, J. de, Ibid., 97, 229 (1941). (13) Hess, K . , and Trogus, C., 2.physik. Chem., B5, 161 (1929). (14) Katz, J. R., Trans. Faraday Soc., 29, 279 (1933). (15) Katz, J. R., and Hess, K., 2.physik Chem., 122, 126 (1926). (16) Koehler, A., Trans. Am. SOC.X e c h . Engrs., 53, 17 (1931). (17) Kratky, O., and Mark, H . , Z. physik. Chem., B36,129 (1937). (18) Lokschin, F. L., Holzchem. I n d . . 2, 45 (1939). (19) llerritt,, K. TI’., and White, 4 A., ISD.ENG.CHEX., 35, 297 (1943). (20) illeyer, K., and Mark, H., Der dufbau der hochpolymeren organischen Naturstoffe, Leipzig, Akad. Verlagsges., 1930. (21) O t t , E., ”Cellulose and I t s Derivatives”, chapter by W. A. Sisson, pp. 203-85, Kew York, Interscience Publishers, 1943. (22) Schmidt, B., Z. Physik., 71, 696 (1931). (23) Schramek, W., and Gorp. H., Kolloid Beihefte, 42, 302 (1935). (24) Sisson, W. A , , IND.E X G .CHEY.,27, 51 (1935). (25) Sisson, R. A , , Textile Research, 7, 425 (1937). . (26) Sisson, W.A., and Clark, G. L., IND.Esc. CHEM.,X x . 4 ~ ED., 5, 296 (1933). (27) Sisson, u’.A , , andSaner, W. K., J . Phys. Chem., 43, 687 (1939). (28) Stamm, A. J., IND. ENG.CHEM.,27, 401 (1935). (29) Stainm, A. J., Trans. Am. Inst. C h t m . Engis., 37, 385 (1941). (30) Stamm, .A. J., and Sehorg, l i . >I., IND.EXG.CHEM.,28, 1184 (1936). (31) Ihid., 31, 897 (1939). (32) Stanim, A . J.. and Seborg, 11. A I . , “Resin-Treated, Laminated, Compressed Wood”, mimeograph, Forest Products Lab., 1941. (33) Trogus, C . , and Hem, K., 2 . pbysik (’hem., B11,387 (1931). (34) Ibid., B14, 387 (1931).
burgh, Pa., 1936. (2) Berkley, E. E., arid T o o d y a r d , 0. D., IND.>:NO. CHEM.,.IN.~I..PRESSTED on the program of the Division of Cellulose Chemisthy of the 1945 Meeting-in-Print, AMERICAS CHEUICAL SOCIETY. ED., 10, 451 (1938).
Control of pH of Neoprene Latex H. IC. LIVINGSTON k N D R . H. WALSH E. Z. du Pont de h’emours & Compcrny, Znc., Wilmington, Del.
0
i\;E of the major contributions to the development of the use
of rubber latex in manufacturing processes has been the introduction of methods for regulating the pH of the latex compounds ( 5 ) . On the basis of this knowledge the coagulating dip process, the use of heat-sensitive latex mixes, and the use of gelling agents have become standardized and accepted methods of manufacturing rubber goods. Most of the techniques used in rubber latex manufacturing processes have been applied to the alkaline neoprene latices such NS Types 571 and 60. However, in the case of the gelling agents the methods normally used to control coagulation of natural rubber latex do not always apply to neoprene latex. An investigation was made of the effect of pH reduction on the reaction between neoprene latex and gelling agents, and also of methods for the control of this reaction. The effectiveness of the gelling agents as coagulants arises from the delayed formation of hydrogen ions or multivalent metallic ions in the latex which these agents produce under certain specified conditions. h good example of this phenomenon is thr reaction that takes place when sodium fluosilicate is added t o either natural rubber or neoprene latex. The sodium fluosilicate liydro-
lyzes in the latex forming sodium fluoride, hydrofluoric acid, and silic
