MAY, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
agglutination of the more bulky powder by means of tabletmaking machines into preformed disks, tablets, or slabs of automatically determined shape and weight, which afherwards were loaded into the mold before the latter was closed in the hot hydraulic press. This improvement made possible the u v of shallon-er and less expensive molds and quicker operation. Early molding outfits, as well as preforming machines (similar to the tablet-making machines used by druggists), were all of the hand type. Then came the automatic preforming machine and the semi-automatic press with a fixed multicavity mold arranged for automatic discharge. Then followed the “tilting-head” press which permitted a better view of the interior of the mold between molding cycles. A still more recent development in the molding of heathardening plastics is injection or transfer molding, which was first employed with cold-setting thermoplastic materials. In this adaptation of the process, the plastic phenolic material undergoes a preliminary softening in a separate container or pot and, while moderately hot and still plastic, is injected directly through one or more small ducts into a heated mold whence it is ejected hot after hardening. The advantages of this type of molding are that it allows the manufacture of deep, thin-walled objects. It also avoids the fin or flash owing to exress material which oozes or spurts out of the open sides of the mold.
Acid-Resisting Equipment Since the very earliest years of the manufacture of phenol resinoids, applications have been found for their corrosionresisting properties by using them for containers or as linings for equipment or machinery which has to withstand chemical action. However, relatively little headway was rnade in
this special field. Lately, an American firm has been introducing the successful methods gradually developed in Germany, under the name of “Haveg.”
Prospects and Retrospects The relatively new industry of synthetic plastics seems to follow the history of the much earlier discovery of the synthetic dyes. After Sir William Perkin in 1856 opened in England a new field by the introduction of the first practical synthetic dye, then called “Anilin Purple” or “hiIauve,” chemists of various other countries were spurred to similar efforts. This rapidly brought forth an endless variety of new synthetic dyes. Some of them mere merely of theoretical interest. Others proved suitable for special purposes or indicated the Ray for the synthetic creation of other important substances, now used in medicine, sanitation, and the various arts, and reaching far beyond the field of dyestuffs. Thus when chemical research is stimulated, i t advances our knowledge in many fields far beyond the original aims. I n terminating this short sketch of the history of one of the younger branches of chemical industry, I desire to mention the valuable work of that excellent group of men it has been my good fortune to gather about me as collaborators in the corporation over which I have presided for about a quarter of a century, and also those who have contributed to the progress of the a r t in our affiliated foreign companies. Nor do I overlook the merits of the many distinguished chemists and engineers all over the world who, by their independent work, have enlarged the synthetic plastics industry in several new and important directions. RECEIVED March 18,1935.
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543
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Paraffin-Impregnated Wood Resistance to Water and Sulfuric Acid Solutions J. WIERTELAK AND J. CZARNECKI University of Poznah, Poland
H
YGROSCOPICITY iz one of the chief disadvantages in the use of wood. Shrinking and swelling caused by moisture changes and accompanied by undersirable secondary plienomena, such as increased conductivity of heat and electrical current, have caused wood to be considered a low-grade raw material. Because of its remarkable strength, lightness, and working properties, it should easily rank as the best material for building and other purposes. Even in chemical industry, wood is a first rate material for the construction of containers and apparatus, since it absorbs shocks and impact b1cwr.s. Its only disadvantage is its ability to absorb liquids, followed, eventually, by chemical disintegration. I n order to protect wood from immediate contact with liquids, it is usually impregnated with some oil, or coated with paints, lacquers, tar products, asphalts, etc. I n addition to these products, paraffin wax is often used, if protection from water or water solutions is desired. The literature on the impregnation of wood with paraffin
wax consists almost entirely of patents, which give neither the detailed procedure nor the exact conditions of the process. Some information is given by Eberlin and Burgess (W), a n d one of their formulas could have been used in the present work. However, the data of Eberlin and Burgess are incomplete and sometimes indefinite, and it seemed desirable, therefore, to repeat and extend their investigations, with the special object of obtaining maximum impregnation under comparatively mild conditions. Special attention was given to alder, since this wood is naturally quite water-resistant. The main purpose of the investigation was to find a use for thio species of wood, which is abundant, especially in East Poland, but is of no value a t present except for fuel. Furthermore, since the purpose of impregnating with paraffin Fax is to render wood impenetrable to liquids, it was important to test the impregnated boards for penetrability. Therefore, its resistance to the action of sulfuric acid solutions and of water was studied. In addition, some experiments were performed to ascertain changes in the surface hardness
545
INDUSTRIAL AND ENGINEERING CHEMISTRY
MAY, 1935
I n the foregoing experiments, the startling observation was made that paraffin-impregnated wood still contained some moisture. Thus, in the immersing process, n hen the temperature was high and the impregnation lasted a long time, the moisture content of the impregnated wood was still about 2.00 t o 7.50 per cent. It is interesting to note that even wood of 163 per cent moisture content lost its moisture to about the same extent. Wood impregnated in an autoclave with the application of pressure alone contained 9 to 10.5 per cent moisture; that impregnated with the aid of vacuum and pressure contained 12 to 13 per cent moisture. Since the impregnated samples were not in equilibrium as to moisture content with the surrounding air, they absorbed moisture, although very slowly. This problem is connected with the mechanism of the impregnation of wood with paraffin wax. First it was proved experimentally that the absorption of oil proceeded more easily along than across the grain, either in the tangential or radial direction. The ends of a board were covered with a layer of collodion, and lead and iron plates were screwed tightly over these ends; when impregnated with paraffin wax, the board absorbed 45.86 per cent. A similarly treated board, without the plates, absorbed 90.89 per cent paraffin wax. The impregnation of the wood mith paraffin wax was accompanied by a slight shrinkage of the wood, as shown by fifteen measurements of the dimensions of air-dry and impregnaied boards. This shrinkage, varying from 1.13to 4.17 per cent by volume, may be a simple phenomenon caused by loss of moisture; or it may be a combined result of loss of moisture and a very slight swelling due to absorption of paraffin wax. I t is probable that shrinking alone took place,
TABLE I. ParaffinImpregnated
and that paraffin wax did not cause any swelling.‘ It would follow, therefore, that paraffin wax neither enters the cell walls nor is it absorbed by the hydrophyllic fibers, but fills only the cell cavities and empty spaces between the cells. Thus, absorption of water by paraffin-impregnated wood is readily explained. The water enters wood only by way of the cell walls which are free of paraffin wax, dry, and therefore very hygroscopic.
Effect of Water on Paraffin-Impregnated Wood From the above experiments it was evident that paraffinimpregnated wood absorbed moisture from the air. It would be expected that this phenomenon would take place to a greater degree if the wood were placed in water. Impregnated boards, when immersed in distilled water a t 25” C. for 24 hours, absorbed, on the average, 4.35 per cent water (based on the oven-dry weight of the wood) and swelled, on the average, 3.05 per cent (based on the volume of paraffinimpregnated wood) ; unimpregnated air-dried boards absorbed, under the same conditions, 35.5 per cent water and swelled about 9 per cent. In another experiment, untreated boards, kept in distilled water for 67 days a t room temperature, absorbed from 66.3 to 87 per cent water, and swelled from 8.5 to 10 per cent; impregnated boards, treated identically, absorbed from 18.0 to 21.6 per cent of water and swelled 9.3 to 11.6 per cent. It is striking that the swelling in both impregnated and untreated boards was about the same, although the paraffin-impregnated boards absorbed three or four times less water. This permits the assumption that in both cases swelling was caused only by water held in the cell walls. This question was dealt with in t h e second paper of this series (6).
It
v a s proved that sorption of paraffin wax b y wood does not cause swelling.
EFFECT O F S E L F r R I C ACID SOLETIONS O S VTSTREATED AXD PARAFFIN-IMPREGNATED W O O D Contact with
HBOI
Absorption of HnSOc
Swelling Due to Absorption
24 hr. 24 hr. 67 days
48.6 3.8 22.5
No Yes Yes
24 hr. 24 hr. 67 days
41.4 4.0 21.1
NO
Yes Yes
24 hr. 24 hr. 67 d a y s
44.2 3.1 21.7
Yes Yea
24 hr. 67 d a y s
Yes
24 hr.
One Per Cent Sulfuric Acid 7.6 1.19 2 2 1.19 9.1 1.1s Two Per Cent Sulfuric Acid 2.12 2.3 2.12 9.2 2.12
..
i:1 i:23 1
Boards unchanged; soln. greenish Boards were pale on surface
2.14 2.14 2.21
Boards unchanged; s o h greenish Boards and soln. unchanged Boards were darker throughout; soln. wan yellowish
Five P e r Cent Sulfuric Acid 5.6 4.58 4.70 2.4 4.58 4.71 10.1 4.58 5.08 Ten P e r Cent Sulfuric Acid 1.9 1.1 10.15 10.39 19.5 10.0 10.15 10.62 Twenty-Five Per Cent Sulfuric Acid 1.3 0.3 25.04 25.42 Storage Battery Acid (28.58 Per Cent Sulfuric) 48.4
..
...
...
1.5
1.4
28.55
28.88
24 hr. 24 hr. 14 days
1.0 1.4 11.9
4:0 .92
28.5: 98.93 28.91
28.95 29.40 29.42
67 days 67 days
115.6 26.5
NO
24 hr.
Yea
24 hr.
Yes, / n autoclave (run XV) Yes, in autoclave (run XVI) Yes
No Y PO
Color Changes
Per cent
r
NO Y esn Yes
Concn. of HISOA Before After immersion immersion
6.6 28.Q1 7.i 28,Ql F i f t y Per Cent Sulfuric Acid 13.1 53.31
E:E 1
No
24 hr.
45.3
Yea
24 hr.
8.1
3.0
53.31
52.83
52.41
Yen, in autoclave NO Yes
24 hr. 67 d a y s 67 days
7.1 155 37.1
2.6 7.8 14.2
53.31 51.02 51.02
2::; 1
52.84
Boards unchanged. soln. yellowish Boards and soln. inchanged Boards darkened throuahout Boards unchanged Boards darkened throughout Boards and s o h . unchanged Boards, !ight brown throughout, acid n o t colored. distinct odor of acetic acid Boards dkrkened to 1.5-mm. deoth: soln. not colored
............. .............
Boards turned brown t o 2-mm. d e p t h . 2 mm. further they appeared brighter. inher a r t unchanged; s o h bright brbwn. Fronounced odor of acetic acid Boards brown throughout. s o h 3 . brow-n. Pronounced odor of a c e d acid Soln. reddish; boards red t h r o u g h o u t . Pronounced acetic acid odor S o h . brighter t h a n preceding; boards paler towards inner part. Acetic acid odor
.............
Boards black throughout: acid also black, containing a suspension. Pronounced acetic acid odor T h e boards designated “yes” were impregnated b y immersion according t o Eberlin and Burgess ( a ) ,unless otherwise stated.
546
INDUSTRIAL AND ENGINEERING CHEMISTRY
Effect of Sulfuric Acid Solutions
VOL. 27, NO. 5
however, are naturally resistant to the action of chemicals (3). I t may well be that paraffin impregnation increases only slightly the resistance of wood to sulfuric acid. In the present experiments, paraffin-impregnated alder, immersed for 24 hours in a 5 per cent sulfuric acid solution, gained 3.14 per cent in weight and swelled 2.4 per cent. Sulfuric acid of other concentrations also attacked paraffin-impregnated alder; the attack was more noticeable, the longer the boards were in contact with the solution (Table I). I n cases where the contact of the impregnated boards with the acid lasted 24 hours, the absorption of sulfuric acid decreased a i t h increasing concentration of the acid, attaining a minimum in 25 per cent sulfuric acid solution. Similarly, swelling Tyas least a t this concentration. Probably the increasing viscosity of the solutions prevented a quick penetration of the liquid through the cell walls into the boards, as is seen by the fact that water, being the least viscous medium, TABLE 11. ACETICACIDCOXTENT OF SULFURIC ACIDSOLUTIONS was absorbed readily (the increase in weight was 4.32 per cent) and caused a swelling of 3.2 per cent. The effect of 28.6 per AFTER IMMERSION OF UNTREATED .4ND PARAFFIS-IMPREGNATED cent sulfuric acid (storage battery acid) was similar to that of WOOD 25 per cent acid. Acetic Acid Concn. of Content Per The effect of sulfuric acid of lower concentrations cannot Time of HtSOd, Cent oi ' D T ~ Para5n Contact with Weight Weight of be compared with that of a higher concentration (50 per cent). Impregnation HzSOk Per Cent Wood This 50 per cent solution, even after only 24 hours, became 24 hr. 5 No 0.10 reddish brown and turned black on heating, when dark par28.6 0.61 50 0.87 ticles were flocculated. I t is evident that a t higher concentra24 hr. 10 Yes 0.08 tions sulfuric acid reacts partially with the wood substance, 28.6 0.13 forming decomposition products and separating lignin. 50 0.67 (Sulfuric acid is usually used in the quantitative determinaYea 14 dsya 28.6 1.97 No 67 days 28.6 4.15 tion of lignin according to Ost and Wilkening, 6). 50 4.96 I n 24 hours untreated boards absorbed much larger amounts (ten to twenty-five times more) of sulfuric acid of various concentrations, and exhibited greater swelling than the impregnated specimens. The action of sulfuric acid of different concentrations was enhanced with increasing time of contact of acid with wood In 67 days the increase in weight of the impregnated boards The percentage increase in weight due to the sorption of was about 20 per cent in 1, 2, 5, and 10 per cent solutions, sulfuric acid was calculated on the basis of the weight of the and attained 26.50 per cent in the storage battery acid. The boards before immersion. Similarly the swelling, as deterswelling a t lower acid concentrations was about the same mined by displacement of water in a modified xylometer, was (9 to 10 per cent of the original volume) but was distinctly calculated on the basis of the volume of the sample before smaller (7.7 per cent) in the storage battery acid, in spite of immersion. The changes in the concentration of the acid were a higher weight per cent absorption of the acid. The 50 per determined by titration. cent sulfuric acid caused profound disintegration in 67 days The action of the acid solutions on wood was studied as of both untreated and impregnated boards, resulting in the follows: (1) by immersing untreated and paraffin-impregformation of black suspensions. nated boards for 24 hours in the acid solution a t constant The absorption of sulfuric acid by wood caused the formatemperature (25' C.) and stirring both the bath and the acid tion of acetic acid, This reaction is known and is applied in solution; (2) by immersing the boards in the solutions a t the determination of acetyl groups in wood according to room temperature (about 20' C.) for 67 days without stirring; Schorger (7). An increase of the reaction period or an increase and (3) by keeping the boards immersed in storage battery of the sulfuric acid concentration caused an increase in the acid for 14 days a t constant temperature (25" C.) without yield of acetic acid (Table 11). Since the impregnation of stirring. The results of the determinations with 11-mm. wood with paraffin wax did not check the formation of acetic boards are given in Table I. acid, the use of paraffin-impregnated wood for storage battery Table I showed that the sulfuric acid solutions, as well as containers instead of glass or the like is not advkable the boards tested, exhibited a strong acidic odor. I n several instances, therefore, the organic acid content of the solutions Surface Hardness of Untreated and Impregnated was determined quantitatively by steam distillation accordWood ing to Schorger ( 7 ) . The acidic distillate, which was free from The impregnation of wood with paraffin wax and its treatsulfur dioxide, was titrated with standard alkali and phenolment with sulfuric acid would be expected to have some phthalein as an indicator, and the acid was calculated as effect on the mechanical properties of wood, in addition to acetic in per cent of the oven-dry weight of the boards. The physical and chemical changes. Some information as to the results of these determinations are given in Table 11. effect of impregnation on the mechanical properties of wood Eberlin and Burgess (2) claim that paraffin-impregnated was obtained by measuring its surface hardness. The tests wood resists comparatively well the action of sulfuric acid were performed with the aid of Amsler's universal testing solutions. Spruce and cypress boards impregnated by immachine on air-dried, oven-dried, paraffin-impregnated, mersing in paraffin wax, gained only 2.8 per cent in weight, paraffin-impregnated and subsequently acid-treated, and and swelled 1per cent when immersed in a 5 per cent solution finally on acid-treated unimpregnated samples. The general of sulfuric acid for 48 hours. Spruce and especially cypress, I t has been claimed ( 2 ) that paraffin-impregnated wood resists the action of dilute acids. If this were true, paraffin impregnated wood could be used in chemical industry, especially for storage battery containers in place of glass which is breakable and comparatively heavy. Therefore, an extensive study was made to determine the effect of various concentrations of sulfuric acid on wood. This effect was tested on the basis of (1) the increase in weight of the immersed samples, (2) their change in volume, and (3) the production of acetic acid, as measured by its presence in the sulfuric acid solution. I n addition, the surface hardness of the boards was determined before and after immersion, as described later. In all cases, similar tests were made on unimpregnated airdried boards.
M A k , 1935
INDIIS~'HIALAYI) ENGINEERING CIIEMISTKY
conclusions drawn iruin these t are as follows: Ovendried samples always showed a liigl around ti2 per cent) lateral (tangential and radial) surface hardness than air-dry samples. The paraffiti-itnpreRnaM samples exhibited a still liiglrcr lateral sorfar:e Irarrlneas-viz., up to 178 per cent. This surface Iianiness of the impregnated boards was prachcally the same if only tiiilf of tlie amount of paraffin wax was absorbed by the \ w d Ol,vii,udy, if a board is iinpregnat.cd with parafKrr wax t,o a lesser degree, only the iruser part contaiiis le96 larraflin wax, while a t the surface, where tlie hardness test is perforrrieil, the same conditions prevail, \
