Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 , 140-144
140
The prepared GSE samples show an increase with time, both in the mean bubble size and in the mean interbubble distance. The commercial samples exhibit considerable variations in internal structure from point to point and in bubble distribution trends. Acknowledgment The authors wish to express their gratitude to Dr. Bauer and Mr. Heater at Queen's University, Kingston for their contribution with respect to the firing of the commercial samples. They also acknowledge the help of (i) J. O'Dette of the Aluminum Co. of Canada, for the examination of the aluminum content of the samples, (ii) S. De Kee, for help provided with the statistical analysis, and (iii) Reed Ltd., Quebec, for the calcium determinations. Finally, the authors wish to acknowledge financial support through Contract DREV 14/2: Defence Research Establishment, Valcartier, Quebec. Registry No. Powermex 300, 94294-02-7; Powermex 500, 94294-03-8; Iremite H, 94293-95-5. Literature Cited
Ahad, E. J. Appl. Potym. Sci. 1974, 78. 1587. American Society of Testing Materials, ASTM 1979, C457-71. Brockbank, S. M.; Clay, R. 6. US. Patent 3582411, 1971. Burgess, J. A.; Hwper, G. Phys. Techno/. 1977, 8(6), 257. Chaudry, M. M.; Field, J. E.; Heavens, S. N.; Coley, M. 10th International Congress on High-speed Photography, Nice, 1972. Chick. Fourth Symposium on Detonation, 1965, p 349. Clay, R. 6. US. Patent 3453 158, 1969. Clay, R. 6.; Cook, M. A,; M y , L. L. U S . Patent 3660181, 1972. Coley. G. D.; Field, J. E. Proc. R . SOC. London, Ser. A 1973, 335, 67. Cook, M. A. Ind. Eng. Chem. 1988, 60(7), 44. Dick, R. A. Information Circular 8560, U S . Department of the Interior, Bureau of Mines, 1972. Goring, D. A. 1.; Young, E. G. Can. J . Chem. 1855, 3 , 480. Hay, J. E.; Watson, R. W. Ann. N.Y. Acad. Sci. 1988, 752,621. Keirstead. K. F.: De Kee, D. Ind. Eng. Chem. Prod. Res. Dev. 1980, 79, 91. Keirstead, K. F.; De Kee, D.; Carreau, P. Can. J. Chem. Eng. 1980, 58, 549. Koldunov; Shevdov; Dremin. Combust. Explos. Shock Waves (USSR)1973, 9 , 255. O'Dette, J. Personal communication, Aluminum Co. of Canada, Kingston, 1979. Powers, T. C. Proc. Highway Res. Board 1949, 29, 184. Shaefer. A. Microskopion 1870, 7, 18. Taylor, J. "Detonation in Condensed Explosives"; Oxford Press, 1952. Underwood, E. E. J. Microsc. 1980, 89(2), 161.
Received for review January 17, 1984 Revised manuscript received October 10, 1984 Accepted October 20, 1984
Afifi, A. A,; Azen, S. P. "Statistical Analysis"; Academic Press: New York, 1979.
Absorption and Desorption of Water by Some Common Fibers John F. Fuzek Research Laboratories, Eastman Chemicals Division, Eastman Kodak Company, Kingsport, Tennessee 37662
All fibers, whether hydrophilic or hydrophobic, absorb some water from an atmosphere having a relative humidity above 0%. The equilibrium amounts of water absorbed at different relative and absolute humidiiies and at different temperatures are presented for some commonly used fibers. The amounts of water remaining in the fibers after equilibrium desorption are also shown. Consideration is given to the kinetics of absorption and desorption. The effect of water on some physical properties of the fibers as well as on subjective properties, such as comfort, is presented. Fibers that are considered include polyesters, nylons, acrylics, modacrylics, cellulosics, and polyolefins as well as natural fibers.
Introduction The interactions of moisture and fibers result in many technical and commercial consequences. The resulting weight changes can affect the blend level in fiber blends as well as the commercial weight of the fibers. Changes in mechanical properties as a result of moisture can influence the behavior of textile products under different atmospheric conditions. Fiber swelling caused by moisture can influence the rate of heat transfer and moisture-vapor transfer through a textile fabric. Consequently, changes will occur in the comfort perception as well as in the dimensional stability of the fabric. Moisture in a fiber reduces the fiber's glass-transition temperature; this reduction results in impaired wash-wear behavior and in changes in the aesthetics of the fabric. Furthermore, high levels of moisture in a fiber usually result in low static propensity. Because of these effects of moisture on fibers, the amount of water held a t equilibrium, the rate a t which water is absorbed and desorbed, and the effect that the amount of water has on fiber properties are of technical and commercial importance. These factors have been well established for the natural fibers cotton and wool (Speakman, 1936; Urquhart, 1924). Since the amount of moisture taken up by most synthetic fibers is substantially less than that taken up by cellulosic fibers and by wool, studies involving the effect of moisture on synthetic fibers have been generally less thorough. The objective of this 0196-4321/85/1224-0140$01.50/0
Table I % R.H.
10 20 30 40 50 60 70 80 90 95
salt system H3POJ/ZH20 CH3COOK CaCl2-6H20 Zn(N03)2.6H20 NaHS04.H20
NH4N03 NH4Cl+ KNO, (equimolar amounts) (NH4M04 ZnSO4-7HZO Na2SO3.7H20
paper is to present data showing the amount of water absorbed and desorbed in a few synthetic fibers and the rates at which these sorptions occur; the effect of water on some of the physical properties of these fibers will also be discussed. Experimental Section Fiber samples were scoured with a 1% neutral soap solution a t 40 "C for 30 min. The samples were then washed with water until they were free of soap. They were then allowed to air-dry for 24 h. For the absorption studies, 1-g samples of scoured fibers were placed in weighing bottles in a desiccator with P205 and dried under a vacuum for 2-3 days to obtain the dry weight of each sample. The samples were then placed in desiccators containing a salt-water system to maintain 1985 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 1, 1985 141 MOISTURE REGAIN 90
MOISTURE REGAIN, 56
0.6
,-
0.4
0.2
0
Figure 1. Moisture regain relative humidity curve for absorption and desorption on Verel modacrylic fiber.
relative humidities of 10, 20, 30,40, 50,60,70, 80,90, and 95% at 70 O F . The salt-water systems maintained the relative humidities (R.H.) within a range of less than 1% of the specified levels shown in Table I. In every case a substantial amount of the solid phase of the salt indicated was present along with some of the saturated solution. The actual relative humidity in each desiccator was monitored with a calibrated precision hygrometer. Weighings of the fiber samples were made at regular time intervals until no further weight change was detected. For the desorption studies, similar scoured samples were wet out with water, blotted dry,and weighed. The samples were then placed in desiccators at the same relative humidities used in testing absorption and weighed at regular time intervals until constant weight was reached. Studies that involved relative humidity of 65% and absolute humidity of 12.9 g/m3 at temperatures from 60 to 90 OF were conducted in a controlled environmental chamber. Physical properties were also determined in such a controlled environment. The determinations of moisture regain were simple determinations in most cases; hence no true standard deviation can be given. In the few cases where multiple replications were made, the coefficient of variation (CV)for these determinations was less than 4%. For determinations of tensile properties of filament yarns (nylon 6, nylon 66, viscose rayon, vinal, and acetate), 10 breaks were made on each sample at each condition. These results generally have coefficients of variation of about 3% for tenacity, 4.5% for elongation, and 25% for elastic modulus. For determinations of tensile properties of staple fibers (polyester, acrylic, and modacrylic), 25 breaks were made on each sample at each condition. Under these conditions, the tenacity CV was about lo%, the elongation CV was about 20%, and the elastic modulus CV was about 25%. Results and Discussion Equilibrium Moisture. The water absorbed by a dry fiber at equilibrium is given for some commercial fibers in Table 11. The residual water after desorption from a wet fiber at equilibrium is given for these fibers in Table 11. Typical sorption isotherms are shown in Figures 1and 2. These are typical type I1 isotherms in which the initial water absorption at low relative humidities is related to direct hydrogen bonding of the water to the fiber molecule, whereas the increased water level at higher relative humidities results from weaker van der Waals forces between the water molecule and the fiber. For fibers with no hydrogen bonding sites, such as polyproplylene, the low water level region of the isotherm is flatter because of weak van der Waals forces between the water and fiber molecules. All the fibers show a hysteresis between absorption and
Figure 2. Moisture regain-relative humidity curve for absorption and desorption on PET polyester fiber. MOISTURE REGAIN ?4
MOISTURE REGAIN %
FROM WET
FROM D R Y
50
O4 O5
0.2
t
P
I/
\
Figure 3. Rate of moisture regain for polyester (T2) to 65% R.H. and 70 O F . MOISTURE REGAIN, % 30 C
34HR -- ----. _. __---1bO
l$O
200 TIME, M I N
250
3d0
'3;O EQUIL
Figure 4. Rate of moisture regain for cellulose acetate fiber to 65% R.H. and 70 O C .
desorption of water. The hydrophobic polyesters and polyamides show a lower degree of hysteresis than do the cellulosics or wool. This difference probably results from a lower level of moisture regain and the lower affinity of these fibers for water. Generally, hydrophilic fibers show a large hysteresis, whereas hydrophobic fibers show little. Rate of Moisture Absorption and Desorption. Water pickup by fibers occurs with two simultaneous processes: diffusion and absorption. Of these processes, absorption takes place at the slower rate (Figure 3 and 4). For desorption from a wet fiber, three distinct processes occur: surface evaporation of water, diffusion of water to the surface, and finally desorption of the water. Absorption and desorption processes follow first-order kinetics
In M R = Izt where M R is moisture content at time t, and k is the
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 1, 1985
142
Table 11. Equilibrium Moisture Regain of Fibers at 70 OF from Dry Side 10 1.40 2.14 1.14 0.02 0.004 0.00 0.00 0.44 0.42 2.38 0.52 0.00 0.00 0.00 0.12 0.13 0.04 0.88 1.15 1.41
cotton wool silk polyester [poly(ethylene terephthalate)] polyester (T16) (Kodel 241) polyester (T4) polypivalolactone nylon 66 nylon 6 viscose rayon cellulose acetate Orlon acrylic Verel modacrylic Rhovyl poly(viny1 chloride) Vinal poly(viny1 alcohol) Qiana nylon" polypropylene Kevlar aramid Nomex aramid Kynol novolid
20 2.08 3.58 3.25 0.07 0.04 0.03 0.20 0.78 0.85 4.87 0.87 0.19 0.23 0.00 0.82 0.40 0.40 1.73 2.34 2.58
30 3.72 6.67 5.20 0.12 0.10 0.11 0.57 1.49 1.78 7.03 1.67 1.31 0.59 0.05 1.30 0.75 0.81 1.98 2.66
40 4.86 8.28 6.76 0.28 0.16 0.18 0.77 2.17 2.38 8.76 2.73 1.53 1.04 0.09 1.62 1.52 0.85 2.58 3.27 3.57
relative humidity, % 50 60 70 5.86 6.95 7.90 10.02 12.39 13.62 10.67 7.91 8.11 0.43 0.34 0.39 0.21 0.20 0.21 0.35 0.25 0.29 1.14 0.97 1.04 3.77 2.70 2.70 4.00 2.91 3.22 10.45 12.20 14.39 5.71 3.53 4.27 1.95 1.67 1.68 2.13 1.41 1.73 0.26 0.12 0.17 2.09 2.52 3.39 3.25 2.47 2.98 0.95 0.88 0.89 4.12 3.58 3.82 5.00 4.38 4.70 5.12 4.46 4.82
80 9.45 15.33 11.96 0.50 0.24 0.39 1.26 4.45 4.69 16.22 6.67 2.13 2.57 0.33 4.29 3.43 1.04 4.68 5.48 5.53
90 11.04 17.26 13.54 0.53 0.34 0.42 1.36 5.01 5.21 18.36 7.96 2.29 3.02 0.37 5.39 3.61 1.16 5.51 6.15 6.62
95 12.74 19.34 15.74 0.53 0.37 0.45 1.54 5.47 5.86 20.65 9.12 2.45 4.10 0.41 6.31 3.70 1.28 5.49 6.45 6.99
Dodecanedioic acid-p-diaminocyclohexylmethane polyamide
Table 111. Eauilibrium Moisture Regain of Fibers at 70 10 2.28 3.68 3.45 0.04 0.04 0.09 0.10 0.70 0.79 3.96 0.80 0.35 0.83 0.04 2.01 0.59 0.06 1.45 2.66 1.91
cotton wool silk polyester (T2) polyester (T16) polyester (T4) polypivalolactone nylon 66 nylon 6 viscose rayon cellulose acetate Orlon acrylic Verel modacrylic Rhovyl poly(viny1 chloride) Vinal poly(viny1 alcohol) Qiana nylon polypropylene Kevlar aramid Nomex aramid Kynol novolid
20 4.38 8.13 6.20 0.14 0.09 0.11 0.30 1.77 1.72 8.28 2.70 0.68 1.44 0.04 2.26 0.86 0.60 2.69 3.88 3.69
O F
from Wet Side
30 5.67 10.80 7.70 0.20 0.13 0.18 0.64 2.36 2.24 10.62 4.47 2.00 1.88 0.08 2.45 1.23 0.98 3.01 4.48 4.27
40 6.06 12.60 9.72 0.29 0.21 0.26 0.84 2.69 3.18 12.42 5.40 2.90 2.50 0.13 3.04 2.33 1.05 3.96 5.01 5.04
relative humidity, % 50 60 70 7.61 8.36 9.71 14.78 16.08 17.71 11.71 11.51 12.26 0.43 0.47 0.36 0.24 0.29 0.29 0.36 0.43 0.48 1.11 1.21 1.04 3.87 4.40 3.33 3.60 4.00 4.62 13.65 14.67 16.13 6.50 7.81 8.83 3.18 3.83 4.20 2.98 3.91 3.27 0.18 0.23 0.29 4.52 5.23 3.45 2.82 3.16 3.36 1.41 1.51 1.20 5.38 5.55 6.15 5.76 6.03 5.68 5.99 6.06 6.71
80 11.72 19.33 14.85 0.55 0.40 0.58 1.34 5.30 5.89 18.32 10.59 4.48 4.21 0.39 6.47 3.54 1.71 6.73 6.27 6.97
90 13.90 20.20 17.36 0.55 0.48 0.62 1.51 5.53 6.99 20.57 13.54 5.37 4.82 0.51 7.96 3.75 1.74 6.97 6.75 7.15
95 14.12 21.09 20.97 0.55 0.60 0.65 1.62 6.02 7.59 25.00 14.01 5.80 5.01 0.53 8.77 3.84 1.81 7.14 6.80
In M R
Table IV. First-Order Rate Constants for Moisture Absorption and Desorption
3
cotton wool silk polyester (T2) polyester (T16) polyester (T4) polypivalolactone nylon 66 nylon 6 viscose rayon cellulose acetate Orlon acrylic Verel modacrylic Rhovyl poly(iiny1 chloride) Vinal poly(viny1 alcohol) Qiana nylon polypropylene
4ck i I 20
I
I 40
I
I 60
I
I
80
I
i 100
TIME, MIN
Figure 5. Typical first-order kinetics for water absorption and desorption on cellulose acetate fibers.
first-order rate constant. For these processes, k , = diffusion rate constant for dry fibers, k 2 = absorption rate constant for dry fibers, 12, = evaporation rate constant for wet fibers, k , = diffusion rate constant for wet fibers, and
3000 2900 3900 6000 5000 2800 1250 4700 3800 2500 3000 2200 350 290 2900 5700 2800
2.5 -33.0 -48 -10.0 -27.7 -129 -1.7 6.5 14.0 -47.3 -60 -6.2 -12.0 8.9 -118 -220 -29 15.8 -1070 -60 -1025 -12.0 50.0 -461 -11.0 -2090 11.5 -475 -13.0 -790 6.1 -460 -260 -6.5 19.5 -192 -84 -1.1 5.3 -84 -6.0 -210 2.6 -720 -4.0 27 -605 -366 -250 -7.4 3.3 -250 4.0 -2200 -12400 -210 -67.5 -84 -6.8 32.8 -432 -6.0 23.3 -458 23.5 -121 -254 -400
k5 = desorption rate constant for wet fibers. Figure 5 shows the applicability of these kinetics to the
absorption and desorption of water by cellulose acetate
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 1, 1985
L
MOISTURE REGAIN 4,
Table V. Moisture-Related Properties of Some Fibers equilib moisture regain a t 70 O F and 65% R.H.,
65% R H
CONSTANT ABSOLUTE HUMIDITY
time to equilib from from from wet dry. h wet. daw 9.05 1.5 99 16.90 2.5 103 11.89 5.0 39 0.45 0.1 24 0.29 0.1 26 0.46 0.5 14 1.16 2.5 12 4.14 3.0 69 4.31 0.8 46 15.40 2.0 71 8.32 3.4 88 4.02 1.5 36 3.59 30.0 43 0.26 0.1 36
%
fiber cotton wool silk polyester (T2) polyester (T16) polyester (T4) polypivalactone nylon 66 nylon 6 viscose rayon cellulose acetate Orlon acrylic Verel modacrylic Rhovyl poly(viny1 chloride) Vinal poly(viny1 alcohol) Qiana nylon polypropylene Kevlar aramid Nomex aramid Kynol novolid
from den./fil dry 1.5 7.43 3.5 13.01 1.0 9.39 3.0 0.41 3.5 0.21 12.3 0.32 0.8 1.09 2.1 3.24 2.2 3.24 1.7 13.30 4.0 4.99 2.5 1.82 16 1.93 3.2 0.22
143
6.0
2.96
4.88
24.0
42
1.9 4.5 1.4 2.3 2.4
3.12 0.92 3.97 4.85 4.75
3.26 1.46 5.85 5.90 6.40
0.3 2.0 5.0 6.0 40.0
17 51 0.7 0.03 1.7
0
70 TEMPERATURE 80
100 0
90
F
Figure 6. Effect of temperature and humidity on the moisture regain of polyester T2 fiber. MOISTURE REGAIN, Yo
16
r
12
-
8 -
4 -
01
1 60
I 1 70 80 TEMPERATURE, "F
1
I
90
1w
Figure 7. Effect of temperature and humidity on the moisture regain of cellulose acetate fiber.
fibers. Similar plots were obtained for all the fibers considered in this investigation. Table IV lists the rate constants calculated for some of the fibers. The diffusion rates, It,, were generally very high for almost all the fibers. The absorption rates, k2,and desorption rates, k,, were very low. The evaporation rates, It,, varied considerably, probably because of different fiber deniers, cross sections, surfaces, and gross physical configurations. The time required to reach equilibrium for absorption or desorption of water by fibers is an important characteristic. ASTM has long recognized the importance of preconditioning a fiber to a lower moisture level prior to conditioning in a standard atmosphere (ASTM D1776-79, 1983). The rate at which equilibrium is reached from the dry side is always substantially faster than from the wet side (Table V). Effect of Temperature and Humidity on Equilibrium Moisture Regain. When fibers are conditioned in an atmosphere of constant temperature and relative humidity, an equilibrium moisture regain develops. Usually this conditioning takes place at 70 O F and 65% R.H.; however, the equilibrium moisture regain of fabrics under atmospheric conditions is frequently needed. The effect of relative humidity on the equilibrium moisture regain at 70 O F has already been shown. The effect of other temperatures will now be considered. Generally, temperature does not affect the equilibrium regain for a constant relative humidity over the temperature range of 60
TENACITY, GiDEN
I
POLYESTER IT21
NYLON 6 NYLON 66
ACRYLIC
VISCOSE RAYON
VEREL@ MODACRYLIC
o o l ' 1 ' 1 '
6
I
10 '
WATER I N FIBER. %
Figure 8. Effect of water in fiber on tenacity.
to 90 OF (Table VI). At constant absolute humidity, however, increasing the temperature results in a substantial decrease in equilibrium moisture regain over this tem-
Table VI. Effect of Atmospheric Humidity and Temperature on Equilibrium Moisture Regain of Some Fibers
cotton wool polyester (T2) nylon 66 cellulose acetate Verel modacrylic
60 O F 7.50 13.84 0.33 3.82 5.93 2.05
equilibrium moisture reaain, % 65% relative humidity absolute humidity = 12.9 g/m3 70 O F 80 O F 90 O F 60 O F 70 O F 80 O F 7.48 7.48 7.35 15.58 7.48 6.01 13.31 13.24 13.15 24.61 13.31 10.92 0.41 0.40 0.40 0.60 0.41 0.39 3.85 3.86 3.89 6.62 3.85 3.03 6.00 6.00 4.17 6.01 5.75 12.77 2.58 2.57 2.57 5.21 2.58 2.05
90 O F 5.04 8.86 0.35 2.49 3.14 1.70
144
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 1, 1985 ELASTIC UODULUS G DEN
ELONGATION A T BREAK. %
50
T2 POLYESTER 40
80
30
20
E N Y L O N 66
10
-
-I-w-z-,~
0
1
0
a
’
* NYLON 6
-
1
1
i
4 6 WATER I N FIBER,?/,
’
’
1
8
l
I
10
0
VINAL
WATER I N FIBER.$
10
Figure 9. Effect of water in fiber on elastic modulus.
Figure 10. Effect of water in fiber on elongation.
perature range (Figures 6 and 7). Effect of Moisture Content on the Properties of Fibers. It has long been recognized that fibers with high moisture regains have different mechanical properties when tested conditioned, dry, or wet. For most fibers, the tenacity decreases with increasing moisture in the fiber (Figure 8). Of all the fibers considered in this investigation, only the polyesters show an increase in tenacity with increased water content. It has been well established that cotton and flax yarns show increased tenacity with increasing water content, but this is not true for cotton or flax single fibers (Meredith, 1960). It is postulated that the small amount of water taken up by the polyester fibers acts as a hydrogen-bonding agent, which causes the tenacities of the fibers to increase slightly as the water content increases. For most other fibers (those showing equilibrium moisture regains much higher than those of the polyesters), the amount of water present may actually be sufficient to cause enough swelling to result in a molecular, fibrillar, or crystalline separation, which in turn would result in lower tenacity. The effect of water in the fiber on the elastic modulus is similar to the effect on tenacity; polyester fibers show an increase in modulus with increasing water content, and all the other fibers except the acrylics show a decrease. The postulated effect of the presence of water in the fiber on the tenacity applies equally well when considering the effect of water in the fiber on the elastic modulus (Figure 9). The acrylic fibers show a minimum effect on the modulus with a water content of about 1%. More water or less water in the acrylic fiber results in a higher elastic modulus. No ready explanation for this phenomenon is available.
The break elongation of most fibers is only slightly affected by water content at levels normally encountered from atmospheric regain. It is well known that rayons, as well as other fibers, exhibit increased elongations when totally wet; however, the increase in elongation with increasing water content (even for these fibers at moisture levels at the normal regain levels) is small (Figure 10). The effect of moisture content on subjectively assessed properties such as fabric hand, garment comfort, and drape has been the subject of much discussion. Increasing the amount of water in a fiber can result in decreased stiffness; hence fabrics made with a fiber having a larger amount of water would have a corresponding decrease in drape and an increase in softness in hand. The effect on comfort is still controversial. Earlier wear tests to determine the effect of moisture on the comfort of T-shirts show that moisture at the levels involved in normal regain does not correlate with subjectively assessed comfort under warm, humid environmental conditions (Fuzek, 1981). Registry No. Polypivalolactone (homopolymer), 24969-13-9; polypivalolactone (SRU), 24937-51-7; kevlar (homopolymer), 25035-37-4; kevlar (SRU), 24938-64-5; nomex (homopolymer), 25035-33-0; nomex (SRU), 24938-60-1; qiana (homopolymer), 25038-97-5; qiana (SRU), 25035-12-5; water, 7732-18-5.
Literature Cited ASTM D 1776-79, Annual Book of ASTM Standards, Part 07.02. 1983; p 408. Fuzek, J. F. Ind. Eng. Chem. Prod. Res. Dev. 1961, 2 0 , 254-59. Meredith, R. I n “Moisture in Textiles”; Hearle, J. W. L.; Peters, R. H., Ed.; Textile Book Publications, Inc.: New York, 1960; Chapter 12. Speakman, T. B.; Cooper, C. A. J. Text. Inst. 1936, 2 7 , T191. Urquhart, A. R.; Williams, A. M. J. Text. Inst. 1924, 75, T433, T559.
Received for review December 1, 1983 Accepted October 22, 1984
