Moisture Absorption of Jute Effect of Bituminous Treating Mixtures J. H. INGM.~.IVSOIV AND G. N. V ~ c c aBell , Telephone Laboratories, New York, X. Y. about 25' C. No effort was made Moisture absorption by textile fibers is generto control the temperature more waterproofing textiles, ally assumed to be prevented or at least greatly closely because, as shown by Wiltextile fibers, and son (6), the relative vapor pressure reduced by treating with bituminous materials. papers are recorded in the literaof most sulfuric acid solutions is Although bituminous treating materials absorb practically constant over 5" or IO' ture. The waterproofing procC. ranges, which is a wider range little moisture, they are permeable to moisture. esses which are usually conthan that involved over the period sidered most efficacious are those It might be expected fhat, when these materials of the test. involving treatment of the texThree samples of jute were seare coated on textile fibers, the rate at which lected for investigation as follows: tile or fiber with oil, wax, asphalmoisture is taken u p by the fiber would be greatly (1) commercial 48-pound (21.8tic material, coal-tar mixtures, kg.) jute roving, (2) commercial reduced but the total quantity taken u p would be vegetable pitch, rubber, or simi48-pound jute roving treated by Ihe same without regard to impregnation. The lar materials. It appears t o be the vacuum process with a molten asphalt-wax composition, and generally assumed that moisture theory has been tested by determining the water (3). commercial 12/3 ply jute yarn absorption by textile fibers is absorption of untreated and treated jute over a treated by the vacuum process prevented or a t least greatly rewith a molten mixture of 80 per wide range of humidity conditions. cent anthracene oil and 20 per cent duced by treating or "impregThe usual treatment of jute with a mixture of medium coal-tar pitch. nating," as the process is comEach sample was cut into small asphalt and wax or of anthracene oil and coal-far monly termed, with bituminous pieces about 3.0 mm. in length and materials which themselves abpitch has practically no effect o n equilibrium packed into a U-tube having a sorb little moisture. ground-glass stopper. The weight moisture content of the jute. Both treated jute of material in each case was about Although bituminous treating and untreated jute show the hysteresis effect 20 grams. Also, smaller samples materials absorb little moisture, of the treated jutes were dried in in other fibrous materials: commonly observed they are permeable to moisture a desiccator over P105, weighed, i. e., that after exposure to high humidity they extracted with benzene to remove (1). It might therefore be exthe saturant, dried, and again show higher equilibrium moisture content at repected that, when these mateweighed in order to indicate the duced humidities than they did previous to high rials are coated on textile fibers, quantity of jute present in the samples used for moisture dethe rate a t which moisture is humidity exposure. Cutting jute fibers into terminations. taken up by the fiber would be short lengths does not increase equilibrium moisIn order to determine whether greatly reduced but the total cutting the jute fibers and thus ture content. Treatment of jute with a n asphaltquantity taken u p would be the exposing a great many cross secwax compound decreases rate of approach to tions had any effect on equilibrium same without regard to treatmoisture content, one 27-foot (8.2equilibrium moisture content. ment, unless there was at least meter) length of jute yarn treated a pseudochemical union of the with the mixture of anthracene oil treating material with the fiber and coal-tar Ditch was Dacked into similarto that which takes place in dyeing. Such a union a U-tube intact for test. The U-tubes containing the jute specimens were each inseems improbable between a hydrocarbon and a cellulose fiber. serted in a drying train consisting of one tower half filled with I n order to test this theory, jute samples treated m~itha concentrated sulfuric acid, two towers three-quarters filled with mixture of asphalt and wax and with a mixture of coal-tar P205, and one tower tightly packed with glass wool. In addition, pitch and anthracene oil were selected for investigation of their another bottle containing a small electric heating element was in the train just ahead of the U-tube containing the jute. moisture absorption over a wide range of humidity conditions inserted Air was passed through the drying train at the rate of about 100 in comparison with untreated jute. ml. per minute until three weighings at 6-hour intervals were Humidity equilibria of various common substances have constant. This weight was taken as dry weight for specimens. After bringing the U-tubes containing jute specimens to conbeen investigated by Wilson and Fuwa (7). Their work indry weight, each one was inserted in a train consisting of volved determinations of equilibrium moisture content of stant three bubble towers containing sulfuric acid solutions of a convarious fibers, including jute, up to 90 per cent relative hu- centration corresponding to the vapor pressure desired and one midity at room temperature. Others have investigated the tower tightly packed with glass wool. Air was passed through moisture absorption of fibrous materials, particularly cotton, the train and U-tube containing the jute specimen again until three consecutive weighings at 6-hour intervals were practically wool, and silk, but not jute. No equilibrium moisture data identical. Those weighings were taken as equilibrium moisture have been found in the literature for jute treated with as- content of the specimens for the particular vapor pressure of the phalts or other saturating materials. sulfuric acid solution used. The specimens, after being dried, were brought t o equilibrium with sulfuric acid solutions of decreasing strength corresponding EXPERIMENTAL PROCEDURE to 10, 25, 50, 75, and 90 per cent relative humidity and then with For the purpose of this investigation a method described by sulfuric acid solutions of increasing strength corresponding to 75, 50, 25, and 10 per cent relative humidity. Wilson (6)was used for humidity control:
M
ANY p r o c e s s e s f o r
The method involves the passage of air through sulfuric acidwater solutions having concentrations corresponding to the relative humidity required and then through a tube containing the material under investigation. The determinations were made a t the room temperatures prevailing in the laboratory over a period of two summer months in 1932. The average was
With regard to saturant content of the samples, the specimen treated with the asphalt-wax compound contained 52.7 per cent saturant, and those treated with the mixture of anthracene oil and coal-tar pitch contained 40.8 per cent saturant as determined by extraction with benzene.
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INDUSTRIAL AND ENGINEERING
December, 1934
RESULTS OF JUTETREATMEKTS The moisture content of the specimens brought to equilibrium a t various percentages of relative humidity as calculated on the dry jute basis is given in Table I and plotted in Figure 1. TABLEI. MOISTURE CONTENT OF TREATED AND UNTREATED JUTEAT VARIOUSRELATIVE HUMIDITIES r
REILATIVE HUYIDITY AT
25’
c
10
Decreasing 75 vapor 50 pressure 25
i
10
Finely divided iute 2.80 4.68 8.01 12.43 18.03 14.28 9.21 5.36 3.14
MOISTURB CONTBNT Finely 27-ft. (8.2-m.) Finely divided jute jute yarn divided anthracene anthracene jute asphalt and oil and coal-tar oil and coal-tar pitch pitch wax
+
+
2.91 5.01 8.51 13.02 19.65 15.53 10.04 5.84 3.31
3.83 5.59 S.58 12.98 18.62 15.02
.....
+
..... ..... .....
13.54
..... .....
..... .....
.....
For the purpose of this discussion the equilibrium moisture content of these samples a t any given relative humidity may be considered as of the same order, since the method employed did not attempt to reproduce accurately the individual test conditions in each case. The equilibrium moisture contents for treated jute are consistently higher for increasing humidities than is the case with untreated jute, probably because the treating materials themselves absorb small quantities of moisture. These results, however, are sufficiently concordant to indicate that the amount of moisture taken up by jute is not influenced by treatment with mixtures of asphalt and wax or of anthracene oil and coal-tar pitch. However, treatment of jute with water-proofing materials does influence the rate of moisture absorption. Figure 2 shows the relative rates of approach to equilibrium a t 75 per cent relative humidity for specimens of untreated jute and jute treated with the asphalt-wax compound. After 1.5 hours the untreated jute had taken up 90 per cent of its equilibrium moisture content, while over 22 hours mere required for the treated sample to absorb a n equal quantity of moisture.
0 RELATIVE HUMIDITY N PER CENT
FIGURE 1. MOISTURECONTENTOF JUTE WITH VARIATION IN RELATIVE HUMIDITY AT ROOMTEMPERATURE
A . Untreated B . Treated with mixture of asphalt and wax C. Treated with mixture of anthracene oil and coal-tar pitch
As shown in Figure 1A and B , untreated jute and jute treated with asphalt-wax mixture showed, for each relative humidity, higher moisture contents with decreasing relative humidity than with increasing relative humidity after having once been exposed to 90 per cent relative humidity. Figure 1C also shows this to be true for jute treated with the mixture of anthracene oil and coal-tar pitch for higher humidities. It is believed that in this case also a similar hysteresis effect would be found a t lower humidities. It is suggested that the hysteresis effect noted for jute is due to the same phenomena which causes this effect in cotton since the two fibers resemble each other physically and chemically, jute being a lignocellulose. The hysteresis phenomenon has been explained by Urquhart
CHEMISTRY
1275
(4), Pierce (5)) and Walker ( 5 ) . Vrquhart and Walker suggest that moisture absorption is largely a function of free hydroxyl groups, I n the case of cotton, exposure to increasing humidities results in swelling of the fiber; and this involves a reorientation of hydroxyl groups from the interior of the micelles, where their hygroscopic properties have been, in effect, neutralized by attraction of associated molecules, to the surface where they can hold absorbed moisture. After coming to equilibrium a t high humidity, exposure to lower humidities or drying would not be accompanied by ready return of as large a portion of the hydroxyl groups to the interior of the micelles. Thus a greater number of water molecules are held a t any given humidity, accounting for the hysteresis effect observed in the relationship between moisture content and relative humidity. The alternative explanation of both Pierce and Walker accounts for the phenomenon on the basis that with decreasing relative humidity a few tightly held water molecules, strategically located within but near the entrance of pores, effectively block them, preventing water molecules within from escaping. UNTREATED JUTE
TREATED WITH
I-
20
TIME IN HOURS
FIGURE2. RATE OF MOISTUREABSORPTIONOF JUTE AT 25’ c. .4ND 7 5 PER CENT RELATIVE HUMIDITY
The 27-foot (8.2-meter) specimen of treated jute which was not cut was brought to equilibrium a t one humidity only-namely, 75 per cent. The quantity of moisture absorbed mas almost identical with that absorbed by the other three cut specimens, leading to the opinion that transverse cutting of the fibers, some of which are hollow ( 2 ) , has no effect on equilibrium moisture content. Under the microscope, treated jute fibers have the appearance of being superficially and nonuniformly coated with the saturant. After careful wiping, the fibers appear to be almost entirely freed from the saturant. The moisture equilibria data further indicate that ordinary treatment with bituminous materials does not involve penetration of the saturant into pores or between micelles of the fibers, The penetration of moisture through the coating of saturant on the fibers is to be expected since moisture diffuses a t a comparatively slow rate through all of the commonly used organic insulating materials (1). This accounts for the lower rate of approach to equilibrium moisture content for jute treated with asphalt-wax mixture than was found for untreated jute. ACKNOWLEDGMEST
The authors wish to acknowledge their indebtedness to A. R. Xemp for counsel and assistance during the prosecution of the work and the writing of this paper. LITERATURE CITED (1) Herrmann, D. B., Bell Lab. Record, 13, 45-8 (1934). (2) Matthews, J. M., “The Textile Fibres” 4th ed., p. 764, John Wiley & Sons, N e w York, 1924. (3) Pierce, F.T . , J. TeztileInst., 20, T 133-50 (1929). (4) Urquhart, A. R . , Ibid., 20, T 125-32 (1929). (5) Walker, A. C., Ibid., 24, T 145-60 (1933). (6) Wilson, R.E., J. IND. ENG. CHEM.,13,326-31 (1931). (7) Wilson, R. E., and Fuwa, T . , Ibid ,12,913-18 (1922). R ~ C D I VAugust ~ D 25, 1934.
