Ind. Eng. Chem. Res. 1990,29, 1640-1646
1640
in the Temperature Range 19.5OC-25.5OC. f h y s . A 1988, 151, 246-280. Brockner, W.; Tarklep, K.; Oye, H. A. Viscosity of Sodium Fluoride-Aluminium Fluoride Melt Mixtures. Ber. Bunsenges f h y s . Chem. 1979,83, 1-11. Doolittle, A. K. Studies in Newtonian Flow, I, the Dependence of the Viscosity of Liquids on Temperature. J . Appl. Phys. 1951, 22, 1031-1035. Doolittle, A. K. Studies in Newtonian Flow, IV, Viscosity vs Molecular Weight in Liquids; Viscosity vs Concentration in Polymer Solutions. J . Appl. Phys. 1952, 23, 418-426. Doolittle, A. K.; Peterson, R.H. Preparation and Physical Properties of a Series of n-Alkanes. J. Am. Chem. SOC. 1951, 73,2145-2151. Ely, J. F.; Hanley, J. M. Prediction of Transport Properties, I. Viscosity of Fluids and Mixtures. Ind. Eng. Chem. Fundam. 1981. 20, 323-332. Flory, P. J.; Orwoll, R. A.; Vrij, A. Statistical Thermodynamics of Chain Molecule Liquids. I. An Equation of State for Normal Paraffin Hydrocarbons. J.Am. Chem. SOC.1964,86,3507-3514. Grunberg, L.; Nissan, A. H. Mixture Law for Viscosity. Nature 1949, 164, 799. Hertzberg, T. MODFIT-A General Multi-response Nonlinear Model Fitting Program. Internal Report; Department of Chemical Engineering, The Norwegian Institute of Technology: Trondheim, 1983.
Isdale, J. G.; Mac Gillivray, J., C.; Cartwright, G. Prediction of Viscosity of organic liquid mixtures by a group contribution method. National Engineering Laboratory Report; East Kilbride: Glasgow, Scotland, 1985. Kartsev, V. N.; Zabelin, V. A.; Andryuschenko, N. A. Temperature dependence of the Density of Liquid n-Alkanes. KLLSS.J . P h w . Chem. 1977,51, 1563-1564. Knapstad, B.; Skjdsvik, P. A.; 0ye, H. A. To be published, 1991. Knapstad, B.; Skjdsvik, P. A.; Oye, H. A. Viscosity of Pure Hydrocarbons. J . Chem. Eng. Data 1989,34, 37-43. Li, K.; Arnett, R. L.; Epstein, M. B.; Ries, R. B.; Bitler, L. P.; Lynch, J. M.; Rossini, F. D. Correlation of Physical Properties of Normal Alkyl Series of Compounds. J. fhys. Chem. 1956,60,1400-1406. Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids; McGraw-Hill: New York, 1987. Tmklep, K.; Qye, H. A. An Absolute Oscillating Cylinder (or Cup) Viscometer. J . Phys. E J . Sci. Instrum. 1979, 12, 875-885. van Velzen, D.; Cardozo, R. L.; Langenkamp, H. A Liquid Viscosity-temperaturechemical Constitution Relation for Organic Compounds. Ind. Eng. Chem. Fundam. 1972, 20-25.
Received for review October 24, 1989 Accepted March 27. 1990
Effects of Heat Treatment on Dyeability, Glass Transition Temperature, and Tensile Properties of Poly(acrylonitri1e) Fibers A. Majid Sarmadi* Department of Environment, Textiles and Design, IJniversity of Wisconsin-Madison, 1300 Linden Drive, Madison, Wisconsin 53706
Charles J. Noel Department of Textiles and Clothing, The Ohio State University, Columbus, Ohio 43210-1295
Jeffrey B. Birch Department of Statistics, Virginia Tech, Blacksburg, Virginia 24060
Acrylic filament fibers (Orlon 42 tow) were subjected to a series of heat treatments consisting of dry heat at 110 and 150 "C and saturated steam at 110 "C for a period of 5 min; samples were exposed N/tex (0.025 g/denier) and slack (no tension). Following the heat both under tension of 2.2 X treatments, denier, tenacity, elongation, initial modulus, glass transition temperatures (T 1, the ratio of the intensities of the CN/CH stretching bands, and dye uptake were measured. Physicd properties were found to be affected primarily by the presence or absence of tension during heat treatment. That is, the temperature of dry heat and the presence or absence of moisture a t 110 " C had less of an effect than tension. Heat treatment with moisture a t 110 "C, both slack and under tension, produced the highest values of Tg. Moist heat a t 110 "C, with slack, gave the highest dye uptake, while treatment a t 150 "C, dry under tension, produced the lowest dye uptake. Association of poly(acrylonitri1e) nitrile groups and thus polymer chain interactions were found to be correlated with T and dye uptake results. These results were interpreted as supporting the theory that both free volume and pore mechanisms are operative in the dyeing of acrylic fibers. Introduction The dimensional stability of thermoplastic fibers and their resistance to permanent deformation can be improved by heat setting under certain conditions. It is believed that heat setting causes structural changes which might affect the physical and dyeing properties of treated fibers (Dawson, 1975; Dumbleton, 1969; Gupta and Maiti, 1982; Rohner and Zollinger, 1986). Various researchers have investigated the relationship of the glass transition temperature (T,) and dielectric relation of poly(acrylonitri1e
* Author to whom correspondence should be addressed. 0888-5885/90/2629-1640$02.50/0
fibers) (Gupta and Chand, 1980; Gupta and Singhal, 1981; Gupta et al., 1981; and Gupta and Singhal, 1983a,b). Gupta and Singhal (1981) heat treated acrylic fibers for 24 h at two temperatures, one (120 "C) slightly above the Tgand the other (160 "C) much above the Tg;then the dielectric relaxation of heat-treated and untreated fibers was measured and compared, Their study showed that the heat treatment at 120 "C generated a greater change in the dielectric relaxation than that at 160 "C. They also used infrared spectroscopy to study the change in the intensity of the CN stretching band measured at 2240 cm-', relative to the CH stretching band at 2990 cm-'. Their comparison of untreated and heat-treated samples showed 0 1990 American Chemical Society
Ind. Eng. Chem. Res., Vol. 29, No. 8, 1990 1641 the relative intensity of CN stretching bands for samples heat treated at 120 "C was lower than that for samples heat treated at 160 "C. There are also other studies (Dawson, 1975; Gupta and Chand, 1980; Gupta et al, 1981; Gupta and Singhal, 1983a; Gupta and Singhal, 1983b) which indicate no change or little change on some selected properties of acrylic fibers treated at temperatures higher than 125 "C. Since a lower intensity of the CN band means a smaller number of unassociated nitrile groups, Gupta et al. (1981) concluded that heat treatment at 120 "C produced a higher degree of bound nitrile groups in the structure. The increase in the number of bound nitrile groups would limit the polymer's segmental mobility, which might affect dyeing and other properties of this fiber. Dynamic diffraction of heat-treated poly(acrylonitri1e) (PAN) fibers was also studied by Gupta and Maita (1982). This study showed that heat treatment at 110 and 150 "C resulted in some changes in bound nitrile groups. Although this study did not show a significant difference between the two temperatures, the magnitude of the changes was higher for samples treated at 110 "C. Layden (1971) studied the dimensional changes and tension generated by PAN filaments under load as a function of time. His study revealed that the significant change would occur within the first 10 min at temperatures up to 150 "C. Then the changes started to reverse when both time and temperature were increased. Stoyanov (1979) has investigated the influence of thermosetting in the presence of steam at 100 "C and drying on shrinkage, tenacity, and elongation of acrylic fibers. He measured the shrinkage of the fibers after each heat treatment and the residual shrinkage after boiling the fibers in water for 15 min. He found that thermosetting in steam produced greater shrinkage than drying at 125 "C. He attributed this to increased segmental mobility in the presence of water molecules, which also results in a tension-free fiber. A t a high temperature and in the presence of steam, the supermolecular structure becomes more mobile, resulting in significant axial shrinkage. He also found that elimination of tension in heat treatment increases the elongation and compactness of the fibers after drying. Materials and Methods Heat Treatment Methods. Samples for heat treatments were prepared in the following manner: Acrylic fibers (Orlon 42) in the form of tow were placed flat on a large piece of brown paper. Then the tow was pulled carefully by hand to remove as much crimp as possible without elongating the fibers. A sample consisting of 1m-long parallel fibers and weighing 6 g was knotted on a wooden rod in a way that the two ends of the sample hung freely; the nominal total denier of the sample was 54000 (6000 tex). To generate a tension of 2.2 X N/tex, a 1350-g weight was attached to one of the ends. This tension was low enough to not have a significant effect on the stress-train curve of untreated fibersand was high enough to remove the crimp introduced in the manufacturing processes. Then the wooden rod carrying the fibers, both hanging free and hanging under 2.2 X N/tex tension, was placed on a wooden stand designed for this study. A laboratory oven was modified by insertion of an inner door so that the oven temperature did not drop appreciably when the door was opened to insert the frame. The oven was preheated to the desired temperature. When the oven temperature was stable, the wooden stand was placed in the oven for the designated time. Samples were heat treated at two temperatures, 110 and 150 "C for 5 min, a
time period found to accomplish property changes in a preliminary study. Each treatment was replicated 3 times. An Amsco autoclave was used to heat treat samples in the presence of saturated steam, using the same frame and tension arrangement as for the dry heat treatment. A temperature of 110 "C was used for this treatment; the equipment was not capable of attaining 150 "C. Physical Testing. Specimens for all physical tests were conditioned for at least 24 h at 21 f 1"C and 65% f 2% relative humidity. Breaking load, elongation at break, and initial modulus were calculated by using the ASTM (1985) Standard Test Method D 3822. Denier of untreated and treated fibers was measured by the ASTM (1985) Standard Test Method D 1577. Fiber Shrinkage. A uniform parallel bundle of fibers was selected. Then the upper and the lower parts of the bundle were each marked by a knot. The distance between these two knots was carefully measured in standard atmosphere, and the bundle was loosely run through a galvanized screen with 1.3-cm openings. The ends of the bundle were secured to the screen in a way that the distance between the two knots would be long enough to allow at least 20% shrinkage. Then the screen was placed in a boiling water bath and was boiled for 15 min. The bundle then was removed, cooled, and reconditioned in standard atmosphere, and the distance between the knots was measured. Shrinkage was calculated from the two distance measurements. The use of the screen prevented entanglement of fibers. Scouring. A bundle of fibers weighing 0.150 g was scoured with 350 mL of a solution containing 1.00 g/L nonionic surfactant (Triton X-100) and 3.00 g/L tetrasodium pyrophosphate (TSPP) for 20 min at 150 O F (65 "C). Then the scoured goods were rinsed thoroughly with distilled water. Dyeing. C.I. Basic Red 18 was used in this study. This dye was selected because a preliminary study showed it is completely soluble in water and dimethylformamide (DMF); it is widely used, and its chemical structure is known. Other dyes tested, such as C.I. Basic Yellow 11, C.I. Basic Orange 21, C.I. Basic Blue 3, and C.I. Basic Violet 16, left some crystal residue at the bottom of the flask when 0.10 g of dye was dissolved in 100 mL of DMF. A dye solution containing 0.60 g/L dye, 0.50 mL/L acetic acid (56%),and 0.10 g/L Triton X-100 was made. A bundle of scoured fibers weighing 0.150 g was dyed in 350 mL of a solution containing 0.10 g/L Triton X-100 and 20 mL of the prepared dye solution. The temperature of the Ahiba dye bath was raised to the boil, and then the scoured fibers were entered into the dye bath. Dyeing at the boil proceeded for 15 min. The dyed samples then were removed and rinsed thoroughly with distilled water and scoured with 350 mL of a solution containing 2.00 g/L acetic acid (56%) and 1.00 g/L Triton X-100 at 55 "C. The scouring was performed to remove unbound dyes from the surface of the dyed fibers. Finally, the dyed and scoured fibers were rinsed thoroughly with distilled water and air-dried. Dye Uptake Measurement. A DMF mixture solution was prepared according to the method of Kissa (1975): 54.50 g (0.4 M) of dry granular zinc chloride (ACS reagent grade), 8 mL of concentrated hydrochloric acid, and 20.00 g of 2,6-di-tert-butyl-4-methylphenol (DBMP) (CP grade) were dissolved in DMF and placed in a volumetric flask. The volume was raised to 1000 mL with DMF. Then a weighed bundle (0.15 g) of dyed fiber was dissolved in 25 mL of the DMF mixture. The dissolved fibers were filtered by using a fine sintered-glass filter and suction to remove
1642 Ind. Eng. Chem. Res., Vol. 29, No. 8, 1990 Table I. Physical Promrties of Heat-Treated Fibers fiber properties" treatment conditions temp, OC moisture 150 dry 150 dry 110 dry 110 dry 110 moist 110 moist
tension slack tension slack tension slack tension
treatment no. 1 2 3 4 5 6
Cb
denier 10.35 9.25 10.32 9.21 10.22 9.22 10.24
tenacity, N/tex (lo-*) 25.6 28.4 25.0 27.9 25.3 28.7 25.3
initial modulus, N/tex 4.022 5.754 3.871 4.876 4.003 5.485 3.672
elongation, % 41.9 30.6 45.7 40.6 43.1 31.2 45.6
shrinkage, ?& 0.03 3.83 0.09 3.61 0.22 3.54 0.33
aNumber of specimens: 6 for denier; 36 for tenacity, elongation, and initial modulus; and 9 for shrinkage. *Control: as received, no treatment
Table 11.
LSD Pairwise Comoarisons between Means on Physical ProDerties treatment" tenacity, N/tex (lo-*)
3 25.0
5 25.3
C
1
25.5
25.6
4 27.9
2 28.4
6 28.7
B
treatmenta elongation, '70
2 30.56
6 31.17
4 40.62
1 41.88
5 43.11
C 45.59
3 45.67
C
treatmenta modulus, N/tex
C 3.672
3 3.871
5 4.003
1 4.022
4 4.876
6 5.485
2 5.574
D
treatment' shrinkage
2 3.830
4 3.606
6 3.538
C 0.329
5 0.223
3 0.086
1 0.033
A
a (1) 150 OC, dry, slack; (2) 150 "C, dry, tension; (3) 110 "C, dry, slack; (4) 110 sC, dry, tension; (5) 110 OC, moist, slack; (6) 110 OC, moist, tension; (C) control, no treatment.
TiOz. Then the volume of the solution was raised to 50 mL by adding DMF mix. Thereafter, the absorbance of the filtered solution was measured with a Bausch and Lomb Spectronic 2000 double-beam spectrophotometer, with a filtered solution of undyed fibers in the same solvent as the reference. The wavelength corresponding to maximum absorption was found (495 f 1 nm), and all absorbances were read at this wavelength. The standard curve (Figure 1)for dyed fibers was made by dissolving 0.10 g of dye in 100 mL of the above DMF mixture containing 3.00 g/L untreated fibers. Seven different dilutions from each one of the above solutions were made in order to obtain enough data to construct Beer's law plots. Glass Transition Temperature Measurement. The Perkin Elmer DSC-4 was used for all Tg measurements. Test fibers were cut very fine by using a razor blade. This helped to obtain a close packing and maximum contact surface between the DSC pan and sample. In this study, 4-6 mg of the finely cut fibers was placed in an aluminum pan. In order to keep the fibers inside the pan, the lid of the pan was crimped with a special lid-crimping device. A heating rate of 10 "C/min was used to heat the pan to 155 "C. Acrylic fibers decompose before true melting; therefore; most studies have reported Tgand not T,. The T, of acrylic fibers is different from type to type. However, most studies show a range of temperatures between 80 and 95 "C. Infrared Measurement of CN and CH Bands. The absorbance of the CN stretching band (at 2240 cm-') and of the CH stretching band (at 2900 cm-') was measured by using the KBr IR technique. An IBM Model 32 Fourier transform infrared spectrophotometer equipped with a MCT detector was used to obtain the spectra. Then the ratio of the absorbance of the CN stretching band to the absorbance of the CH stretching band was calculated.
Results and Discussion Effect of Heat Treatment on Physical Properties. The results of heat treatment on physical properties are
1.4
-
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-
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Concentration gfL
Figure 1. Concentration vs absorbance curve of C.I. Basic Red 18 in DMF mix with polymer: Y = -0.03 + 49.51C; R2 = 0.999.
presented in Table I. Separate one-way analyses of variance (ANOVA)were run to test for differences in tenacity, elongation, initial modulus, and shrinkage with treatments. In each case, the ANOVAs indicated the existence of a highly significantdifference between means associated with treatments. Therefore, Fisher's least significant difference (LSD) analysis was used for making pairwise comparisons between the means (Table 11). Fibers heat treated under tension had significantly higher tenacities, shrinkages,and initial modulus compared to those heat treated with slack and to the untreated control. Increases in tenacity were accompanied by decreases in elongation. The presence of applied tension during heat treatment appears to be of greater importance than either the temperature of the heat treatment or the presence of moisture during heat treatment, although smaller effects of these two variables can be noted. In summary, the tenacity, elongation, initial modulus, and shrinkage of heat-treated acrylic filament fibers (Du Pont Orlon 42 tow) were primarily affected by the presence of applied tension during heat treatment. Fibers heat
Ind. Eng. Chem. Res., Vol. 29, No. 8, 1990 1643 Table 111. Length Equivalents and Shrinkages for Heat-Treated and Boiled-Off Samples treatedo boiledb eauivalent eauivalent length % shrinkage" length conditions denier treatment 8904 1.07 8902 150 "C, dry, slack 10.35 9963 9.25 -10.70 9581 150 "C, dry, tension 8930 0.78 8922 10.32 110 "C, dry, slack 10007 9.21 -11.20 9646 110 "C, dry, tension 9018 10.22 -0.20 8998 110 "C, moist, slack 9996 9.22 -11.10 9642 110 "C, moist, tension 9000 8970 10.24 untreated
% shrinkage"
% shrinkaged
1.09 -6.46 0.87 -7.18 0.02 -7.13
0.03 3.83 0.09 3.61 0.22 3.54 0.33
In meters, calculated from denier. In meters, calculated from denier and measured shrinkage. Based on original length of 90oO m; negative values indicate length increase. Measured, based on boiled-off length relative to treated length.
Table IV. Chemical Properties of Heat-Treated Fibers treatment conditions temp, "C moisture tension 150 dry slack 150 . dry tension 110 dry slack 110 dry. tension 110 moist slack 110 moist tension
treatment no.
Tg,"C
1 2 3 4
106.1 103.5 102.2 106.1 108.6 109.2 98.9
5 6
Cb
fiber propertieso CN/CH dye uptake, % 1.807 1.808 1.833 1.803 1.781 1.794 1.828
0.397 0.373 0.406 0.406 0.449 0.393 0.415
Number of specimens: nine for Tgand CN/CH and three for dye uptake, except for control, where seven determinations of dye uptake were made. bControl: as received, no treatment.
treated under a tension of 2.2 X N/tex had higher tenacities, lower elongations, higher initial modulus, and higher shrinkages than fibers heat treated slack or not heat treated at all. The presence or absence of moisture during heat treatment at 110 "C and the use of 100 or 150 "C dry heat treatment had no appreciable effect on either tenacity or shrinkage but had a moderate effect on initial modulus and a somewhat greater effect on elongation. For both initial modulus and elongation, the response to applied tension was greater with both moist heat a t 110 " C and dry heat at 150 "C, compared to dry heat a t 110 "C. The increase in the tenacity and the initial modulus and the decrease in the elongation of the treated fibers are due to tension. Tension, in the presence of heat, increases the alignment of polymer molecules in the fiber direction. Higher molecular alignment means more intermolecular forces. As the result of higher molecular alignment and intermolecular forces, the amount of ordered areas (pseudocrystalline regions), which influences the physical properties of fibers, is increased. To check the change in the orientation of pseudocrystalline regions, fibers were examined by wide-angle X-ray scattering. As Figure 2 shows, the arcs in the picture (d) are smaller than the arcs in other pictures, especially the untreated fibers, indicating a higher degree of orientation for fibers that were heat treated under tension. Table I also contains denier values for each heat treatment and the untreated control. The denier values can be used to calculate equivalent length changes associated with the heat treatments. The shrinkage values given in Table I can be used to calculate a final equivalent length after heat treatment and boiling for 15 min. The results of these calculations are given in Table 111. It can readily be seen that heat treatments under tension produced an increase in fiber length, but this increase was not fully stable to boiling; only about 60-6570 of the length increase was retained when the fibers were boiled. Fibers heat treated slack contracted slightly during heat treatment; this contraction was completely stable to boiling. These results suggest that heat setting of fabrics made of acrylic fiber should be done with as little tension as possible.
a
b
C
d
Figure 2. Wide-angle X-ray diffraction patterns of Orlon 42: (a) untreated; (b) heat treated dry a t 110 "C with slack; (c) heat treated moist a t 110 "C with slack; (d) heat treated moist a t 110 "C under tension.
Effect of Heat Treatment on Glass Transition Temperature. The values of T obtained by DSC measurements are given in Table I$ a typical DSC thermogram is shown in Figure 3. The value of Tgobtained for the untreated control was 98.9 "C; this was significantly lower than the Tgvalues measured for all six heat-treated fibers. The highest Tgvalues were obtained by heat
1644 Ind. Eng. Chem. Res., Vol. 29, No. 8, 1990 Table
V. LSD Pairwise Comparisons between Means of Chemical Properties A
treatmenta Tg,"C
98.86
C
3 102.2
2 103.5
1 106.1
4 106.1
5 108.6
6 109.2
B
treatment"
5 1.781
6 1.794
4 1.803
1 1.807
2 1.808
C
CN/CH
1.828
3 1.833
treatmento 90 dye uptake
2 0.3732
6 0.3930
1 0.3969
4 0.4060
3 0.4661
C 0.4154
0.487
C
6
"(1) 150 O C , dry, slack; (2) 150 "C, dry, tension; (3) 110 O C , dry, slack; (4) 110 O C , dry, tension; (5) 110 "C, moist, slack; (6) 110 O C , moist, tension; (C) control, no treatment.
..
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i
om
wm
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0.3
i
I
110
m
ILO m
TEMPERATURE
110
(C)
m
0.01 80.0
I40 m
CSC
Figure 3. DSC thermogram of Orlon 42 heat treated moist at 110 OC.
treatment at 110 "C with saturated s t e m with or without applied tension. In a separate experiment, the dyeing transition temperature, Td,was measured for untreated Orlon 42 by measuring the uptake of Basic Red 18 at different temperatures using a dyeing time of 15 min at each temperature. Figure 4 shows that the Td for this fiber is approximately 92 "C, about 7 "C lower than its T . In general, the value of Tdis close to the value of Tg,and one can be used to estimate the other. Since Td IS usually measured in aqueous dyeing, and water acts as a plasticizer, Td is always lower than Tg. Effect of Heat Treatment on Nitrile Group Association. The results obtained for the measurement of nitrile group association as indicated by the CN/CH intensity ratio are also given in Table IV. A typical infrared spectrum for untreated Orlon 42 is shown in Figure 5. LSD analysis of the mean values of these measurements showed that all values fell into a single group; there was no statistically significant difference between any pair of CN/CH values. Even though the pairwise differences were not s t a t i s t i d y Significant, the values were associated with treatments in a manner which is entirely consistent with the way that the Tgvalues were associated with treatments. A low value of the CN/CH ratio means that the relative number of CN groups engaged in dipole-dipole interactions is greater; hence, there is a greater degree of intermolecular interaction, suggesting a higher value of TB' Conversely, a high value of this ratio implies less nitrile group association, with a lower T Effect of Heat Treatment on b y e Uptake. The results obtained in the measurement of dye uptake are also given in Table IV. LSD analysis of the mean values of dye uptake associated with the six heat treatments and the untreated control shows that these values fell into four groups with considerable overlap (Table V, C). Most of the heat treatments reduced the dye uptake of the fiber compared to the control, but treatment at 110 "C (moist,
1
.
.
. , .
. . , .
,
85.0
! .
90.0
. , . . . . , 100.0
95.0
Temperature OC Figure 4. Dye uptake of Orlon 42 dyed with C.I. Basic Red 18 vs dyeing transition temperature obtained by using a dyeing time of 15 min. Rbsorbance
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zeee.a
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-1
Figure 5 . Sample of infrared spectrum for untreated Orlon 42.
slack) produced a fiber with enhanced dye uptake. The lowest value for dye uptake (0.373%) was obtained for the sample heat treated at 150 "C (dry, under tension); the sample treated at 110 "C (moist, slack) took up about 20% more dye (0.449%). In summary, the results show that the glass transition temperature, nitrile group association, and dye uptake of heat-treated acrylic filament fibers (Du Pont Orlon 42 tow) were not affected by the presence or absence of applied tension during heat treatment as were the physical properties discussed earlier. Glass transition temperature was increased relative to the untreated control by all heat treatments; moist heat at 110 "C had the largest effect, and this was independent of applied tension during heat treatment. Nitrile group association as measured by the ratio of absorbances of the CN and CH stretching bands was statistically unaffected by heat treatment. Since this property can be interpreted as a measure of interchain
Ind. Eng. Chem. Res., Vol. 29, No. 8, 1990 1645
0.44
0.42
loo
\
1
\
0
981 1.78
,
8
1.79
.
I
1.80
-
I
,
1.81
1
1.82
.
,
I
1.83
I
1.84
Figure 6. Tgvs CN/CH ratio for all treatments and control.
0
0.461
-
0.42
-
0.38
4 I
98
8
100
104
1M
4
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0 . 3 6 4 . 1.78
8
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I
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CNKH Ratio
Figure 8. Dye uptake vs CN/CH ratio.
CNICH Ratio
0.44
j
106
108
110
Tg ("C) Figure 7. Dye uptake vs TB'
interaction, it would be expected to vary inversely with T ; a plot showing the variation in CN/CH ratio with ?$, (Figure 6) demonstrates this is observed. The correlation coefficient (-0.8906) indicates a strong relationship between the two measurements, in the expected direction. Dye uptake was highest for the fiber heat treated in the slack condition with moist heat at 110 "C and lowest for the fiber heat treated under tension with dry heat at 150 "C. For fibers in which dyeing proceeds by a free-volume mechanism, the dye uptake in a given time would be expected to decline as Tdincreases and, therefore, as T increases. Since Tgis inversely related to the CN/CI-! ratio, dye uptake would be expected to increase as this ratio increases. Plots of dye uptake vs TBand CN/CH ratio are given in Figures 7 and 8, respectively. In both of these plots, five of the points including the untreated control and four of the heat treatments can be fitted to a straight line in the postulated direction. For dye uptake
vs Tg,a strong inverse relationship is observed ( r = -0.9138); for dye uptake vs CN/CH, a fairly strong direct relationship can be inferred ( r = +0.7750). Only the two points corresponding to the extremes in both the experimental design and the measured dye uptake do not fit the relationship. Rohner and Zollinger (1986) suggest that the dyeing of acrylic fibers proceeds by both a free volume and a pore mechanism, operating simultaneously. The treatment providing the point lying well above the straight line is the treatment which would be expected to enhance any pore structure present in the fiber; the treatment providing the point lying well below the straight line is the treatment which would be expected to collapse any pore structure present in the fiber. Therefore, these results are interpreted as supporting the concept that both pore and free volume mechanisms are operative in the dyeing of acrylic fibers.
Summary and Conclusions The physical properties of heat-treated fibers were found to be affected primarily by the presence or absence of applied tension during heat treatment; the temperature of dry heat and the presence or absence of moisture at 110 "C had less effect. Chemical properties (Tgand dye uptake) responded to treatment variables in a less clear-cut fashion; applied tension in the presence of moisture at 110 O C produced the highest values of Tg, while treatment at 110 "C (moist, slack) gave the highest dye uptake. Nitrile group association was found to be unaffected by treatment, statistically, but the values correlated well with values of Tg.Dye uptake was related to both T and nitrile group association; the results were interpreted as supporting the theory that both free volume and pore mechanism are operative in the dyeing of this fiber. Fibers heat treated under tension had higher tenacity and initial modulus and lower elongation than fibers heat treated without applied tension. The denier of fibers heat treated under tension was also lower than the denier of fibers heat treated without applied tension. The lower denier indicates that the fibers were elongated during heating under the applied tension; the higher tenacity and initial modulus and lower elongation of these fibers suggests a greater degree of molecular orientation for the tension-treated fibers. This was confirmed by wide-angle X-ray scattering (WAXS). Shrinkage measurements on
1646 Ind. Eng. Chem. Res., Vol. 29, No. 8, 1990
the fibers treated with and without applied tension showed that the length increase induced by heating under tension was not completely stable; only about 63% of the length increase was retained after 15 min in boiling water. Dye uptake was found to increase linearly with nitrile group association over four of the heat treatments and the untreated control and to decrease linearly with glass transition temperature for the same conditions; regressions showed strong relationships in both cases. Two heat treatments did not fit the linear relationships treatment at 110 "C slack with saturated steam gave much higher dye uptake than the linear relationships would predict, and treatment with dry heat at 150 O C under tension gave a much lower dye uptake than predicted by the linear relationships. The treatment giving the higher dye uptake would be expected to enhance any pore structure present in the fiber; saturated steam would allow greater chain mobility and permit more nitrile-nitrile association (lower CN/CH ratio), and the increased nitrilenitrile association would result in greater interchain interaction (higher T ). The absence of tension prevents length extension, so t i e more compact chain structure in the same fiber length results in enhancement of porosity, leading to higher dye uptake than the T or CN/CH would predict. The treatment giving thetower dye uptake would be expected to minimize any pore structure present in the fiber. The high temperature would permit chain mobility, but the applied tension causes the fibers to elongate during heat treatment. The elongated fiber has enhanced molecular orientation as shown by WAXS, but the nitrile group association is very close to that of the untreated control and to the slack treated fiber. The Tgis increased only slightly compared to control and not as much as the slack treated fiber. Since the Tgand CN/CH indicated little increase in interchain interaction while the length increases and denier decreases, a similar polymer structure is present in a smaller volume, suggesting a reduction of porosity and a lower than expected dye uptake.
Acknowledgment This study was made possible by research funds from Virginia Polytechnic Institute and State University. Fibers were provided by E. I. du Pont de Nemours and Co., Inc. This contribution is indeed appreciated. We also wish to express our appreciation to the following for their stimu-
lating discussions and suggestions during this research: Marjorie Norton, Barbara Densmore, John Mason, Thomas Ward, Paul Harris, Garth Wilkes, Carolyn Harris, Carolyn Moore, and Dinesh Tyagi.
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Received for review October 10, 1989 Revised manuscript received March 21, 1990 Accepted April 5, 1990
