DISPERSE DYEING SYSTEMS FOR p-ARAMID FIBERS

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37 International Symposium on novelties in Textiles, 15 – 17 June 2006, Ljubljana, Slovenia

DISPERSE DYEING SYSTEMS FOR p-ARAMID FIBERS 1

Alexandros A. VASSILIADIS1, Maria ROULIA2 and Charalambos M. BOUSSIAS1

Dyeing and Finishing Laboratory, Department of Textiles, Technological Education Institute of Piraeus, 250 Thivon st., 122 41 Athens, Greece 2 Inorganic Chemistry Laboratory, Department of Chemistry, University of Athens, Panepistimiopolis, 157 71 Athens, Greece

Abstract o The aqueous dyeing of p-aramid fibers with C.I. Disperse Red 60 dye at temperatures below 140 C was investigated. Dyeability of poly(p-phenyleneterephthalamide) fibers under several treatment conditions was examined by spectrophotometrical determination of dyebath exhaustions. The p-aramid fibers proved to be dyeable but, in all cases, the exhaustion of the dye-liquor was lower than 79%. The greatest value was o obtained by dyeing at 135 C for 180 min with 7% dye. Exhaustion was found to be dependent on the fiber pretreatment, the liquor ratio, the concentration of dye and the presence of wetting agent. The texture of the dyed p-aramid fibers was studied by scanning electron microscopy. Keywords p-Aramids; Kevlar; Dyes; C.I. Disperse Red 60 INTRODUCTION Only a few methods of dyeing aromatic polyamide fibers have been reported in the literature. The m-aramid fibers are printed [1], dyed by cationic dyes [2] or in the presence of dye assistant compounds (such as swelling agents) [3] and flame retardants [4] at elevated temperatures under pressure by anionic or disperse dyes [5]. However, to dye p-aramid fibers by conventional techniques [6] is exceedingly difficult because of their very high glass transition temperature (Tg). Since these fibers are not all amorphous polymer and contain a substantial proportion of crystalline fraction, the Tg of the fiber is influenced by its crystallinity, crystal size and orientation. The paracrystalline structure of p-aramid fiber, changes in microparacrystal size [7] and paracrystalline disorder [8] may also be important. On the other hand, colored p-aramid fibers have been prepared [9] by including an organic pigment dye in a spinning dope wherein the solvent is concentrated sulfuric acid. The development of high-tenacity and highmodulus p-aramid fibers is based on the unique ability of selected aromatic backbone polymers to form molecularly ordered assemblies directly processed into strong fibers [10]. The relationship between the morphology and the macroscopic accessibility of poly(p-phenyleneterephthalamide) to water has been of particular interest [11]. Most synthetic hydrophobic macromolecules adsorb insignificant amount of water; thus, they are dyed with non-ionic dyes from aqueous suspensions [12]. Consequently, trials have been commenced to dye these fibers, consisting of polymers containing p-phenyleneterephthalamide units (Kevlar, DuPont) and 3,4-oxydiphenylterephthalamide units (Technora, Teijin), in an aqueous bath of a -1 -1 disperse dye with molecular weight ranging from 330 g·mol to 400 g·mol at a dyeing temperature of at o least 150 C [13–15]. However, no attempt has been made to investigate the dyeing of p-aramid fibers at relatively low temperatures. Obviously, the size of the dye molecule affects the dyeing behavior of a given fiber. Therefore, as the molecular size of the dye increases, the structure of the fiber [16] plays a more and more decisive role, as in the case of Kevlar, the long molecular chains of which are highly oriented with strong interchain bonding. Besides, the crystal structure of p-aramid fiber is not stable and changes with temperature [17]. This study is concerned with the aqueous dyeing of Kevlar fibers by using C.I. Disperse Red 60 (Serilene o Red 2BL 200), an anthraquinone dye, at temperatures below 140 C. The dyeability of the fibers under various dyeing conditions was examined by determining the exhaustion of the dye-liquors. EXPERIMENTAL The structural formula of C.I. Disperse Red 60 (1-amino-4-hydroxy-2-phenoxy-9,10-anthracenedione) is presented in Figure 1. The visible spectrum of Serilene Red 2BL 200 (Yorkshire) was acquired from aqueous

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dispersion diluted 1:1 with acetone (Lab-Scan, 99.5%). The dye absorbs light in the visible range with wavelength of maximum absorbance (λmax) at 514 nm. Figure 2 shows a typical spectrum of the dyestuff, recorded on a Varian Cary 300 3E UV–vis spectrophotometer. O

NH2 O

O

OH

Figure 1: Structural formula of C.I. Disperse Red 60 A linear calibration curve that related absorbance to concentration was constructed at λmax. The dye obeyed -1 the Beer–Lambert law up to a concentration of 0.06 g·L .

0.8

A 0.6

0.4

0.2

0.0 400

500

600

700

800

λ, nm Figure 2: Plot of absorbance against wavelength for C.I. Disperse Red 60 The percentage of dyebath exhaustion (E) is given by Eq. (1):

E(%) = 100 "

Co ! Ct Co

(1)

where Co and Ct are the initial concentration of the dye and the residual dye concentration after dyeing, respectively. Suspensions of C.I. Disperse Red 60 in distilled water were employed in the dyeing experiments. Disperol PE (Unichem) was used to aid dispersion. Carrier Optinol B (Yorkshire) or wetting agent Dyamul SN-MP (Yorkshire) was added and then the Kevlar fibers. The dyebath was placed in an Ahiba Texomat dyeing o o -1 o o -1 o machine and heated to 135 C at heating rates of 3 C·min up to 100 C and 2 C·min up to 135 C. The dyeing continued for preselected periods. After completion of the dyeing the fibers were removed, washed and dried. The liquid residue was diluted with acetone and the dye content was determined spectrophotometrically. Scanning electron microscopy (SEM) was applied by use of a JSM-5600 Jeol microscope. Prior to examination a thin layer of gold was sputtered on to the fiber surface to achieve sufficient electrical conductivity.

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RESULTS AND DISCUSSION In the following, all dyeing recipes refer to a liquor ratio of 150:1. All experiments with 1% and 2% dye were carried out in the absence of wetting agent. Dyed and untreated p-aramid fibers are shown in Figure 3.

a

b

Figure 3: Scanning electron micrographs of (a) undyed and (b) dyed with C.I. Disperse Red 60 Kevlar fibers The dyeing conditions and the exhaustions obtained from Eq. (1) for fibers dyed with 1% dyestuff are listed in Table 1. o

Table 1: Dyeing of Kevlar with 1% C.I. Disperse Red 60 at 135 C Sample a

DR1 b DR1-r a DR1-c c DR1-cr DR1120

Time, min

Carrier, %

Dispersing agent, g·L

90 90 90 90 120

– – 18 18 –

0.5 0.5 0.5 0.5 0.5

-1

-1

Wetting agent, g·L – – – – –

Exhaustion, % 67.00 27.76 66.55 24.48 56.12

a

Liquor ratio 50:1 Redyed sample DR1 c Redyed sample DR1-c b

Table 1 points out that fibers treated for 90 min gave values of exhaustion up to 67%. Particularly for sample DR1120, dyed for 120 min without adding carrier, less than 56% exhaustion was determined. The redyed samples, DR1-r and DR1-cr, showed much lower dye adsorption. This presumably is due to the fact that the thermal treatment during the initial dyeing process affects the fine structure of the fiber and reduces the diffusion of dye, decreasing the dyeability of the samples. Dyeing performed for 90 min using Optinol B as the carrier in the dye-liquor (sample DR1-c) led to a slightly lower exhaustion of the dye-liquor compared with sample DR1. The results show that treatment for 120 min in the absence of carrier (sample DR1120) decreased the dyeability more than dyeing for 90 min with 18% Optinol B (sample DR1-c). An explanation could be that longer treatment times at the temperature of dyeing induce destabilization of the crystal structure of the fiber. In general, dyeing experiments with 1% dye produced very pale shades due to the low accessibility of the fiber to the dye. The yellow color of the fiber affected the shade obtained. Additionally, in these experiments, C.I. Disperse Red 60 showed poor levelling properties on the p-aramid fibers. The laboratory dyeing conditions and the exhaustion results for dyeings with the use of 2% dye are summarized in Table 2.

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37 International Symposium on novelties in Textiles, 15 – 17 June 2006, Ljubljana, Slovenia o

Table 2: Dyeing of Kevlar with 2% C.I. Disperse Red 60 at 135 C

a

Sample

Time, min

Carrier, %


DR2 DR2-c a DR2180

120 120 180

– 18 –

0.5 0.5 0.5

-1

-1

Wetting agent, g·L – – –

Exhaustion, % 64.66 69.10 48.35

o

Thermosetting pretreatment (1 h, 200 C)

It can be seen that the presence of the carrier increases the exhaustion of dyebath. On the contrary, the o thermosetting pretreatment at 200 C for 1 h leads to a decreased diffusion of dye, as explained in the text above and, therefore, it is not unexpected that sample DR2180 exhibited a value of exhaustion about 48%. Typical results obtained by dyeing the poly(p-phenyleneterephthalamide) fibers with 5% dyestuff are shown in Table 3. o

Table 3: Dyeing of Kevlar with 5% C.I. Disperse Red 60 at 135 C for 180 min a

Sample DR5-sr DR5 DR5-w a b

b

Scouring o min ( C) 60 (80) – (–) – (–)

Carrier, %


– – –

0.5 0.5 0.5

-1

-1

Wetting agent, g·L – – 1

Exhaustion, % 78.53 73.78 69.04

. -1

Wetting agent 2 g L , liquor ratio 50:1 and then at ambient temperature for 24 h Redyed sample DR2180

Dyeings in Table 3 were carried out by using wetting agent instead of carrier in the dye-liquor. In the case of o -1 sample DR5-w the exhaustion is nearly 70%. This dyeing, performed at 135 C with an addition of 1 g·L Dyamul SN-MP, gave the lowest exhaustion amongst the samples dyed with 5% dye. The exhaustion is o higher at 135 C in the absence of wetting agent (sample DR5). In contrast to sample DR5, sample DR5-sr o was prescoured at 80 C for 60 min and stayed for 24 h at ambient temperature. Then it was dyed in the same manner as sample DR5. This dyeing gave 78.5% exhaustion. It may be concluded that the addition of the wetting agent to the scouring bath before dyeing facilitates the diffusion of the dye and increases the amount of dye present in the fiber when dyeing is complete. The experimental conditions and the exhaustion of dyebath for dyeings performed with 7% dye are recorded in Table 4. o

Table 4: Dyeing of Kevlar with 7% C.I. Disperse Red 60 at 135 C for 180 min Sample DR7-IU DR7-U DR7-dw DR7-ddw DR7-dww DR7 DR7-c a b

a

Invalon HTC , g·L 1 – – – – – –

-1

Carrier, % Dispersing agent, g·L b

– – – – – – 10

2 b 2 2 4 2 2 2

-1

-1

Wetting agent, g·L

Exhaustion, %

2 2 2 2 4 – –

74.43 73.47 66.68 66.19 68.53 50.21 48.52

Levelling agent from Ciba–Geigy Univadine DIF (Ciba–Geigy)

Table 4 indicates that the addition of Univadine DIF (sample DR7-U) in place of Disperol PE resulted in a -1 higher exhaustion (sample DR7-dw). Treatment with 2 g·L Dyamul SN-MP (sample DR7-dw) gives a better yield than when dyeing is carried out in the absence of wetting agent (sample DR7). Further increase in wetting agent being added (sample DR7-dww) leads to an increased exhaustion of the dyebath. In sample DR7, the absence of the carrier proved to be beneficial compared with sample DR7-c, because the levelling of the dye was improved and the exhaustion was increased. More effective results (sample DR7-IU) were obtained by adding Invalon HTC, a product specially suitable for levelling up unlevel dyeings, with the value of exhaustion being greater than 74% as shown in Table 4.

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All dyeings carried out in this study showed sufficient fastness to washing but, in general, they proved slightly unlevel. However, when dyeing with 7% dye (Table 4) better levelling properties were obtained. Apparently the dye penetration is adversely impacted by both the paracrystalline structure and the hydrophobic behavior of p-aramid polymer. The p-aramid fibers are highly fibrillar in nature [16] and comprise fibrils of 0.05 to 5.0 µm approximate diameters, resulting in a fiber diameter of about 12 µm. Fibrils buckle under small compressive loads, creating kinks and kink bands along the fiber. When the kinked fibers are strained, they fail at the kinks at much lower stress level than normal. SEM was employed to explore the texture of the dyed p-aramid fibers as shown in Figure 3b. Before dyeing the Kevlar fibers appear uniformly cylindrical and smooth (Figure 3a). Strains and discontinuities at the surface of the fibers induced by the dyeing process are observed in Figure 4a, exhibiting a fiber with a torn skin and fibrils scraped from fiber surface. The electron micrograph in Figure 4b reveals that dye particles of approximately 2 µm in diameter are present on the fiber.

a

b

Figure 4: Scanning electron micrographs of dyed Kevlar fibers The absence of chemically reactive groups in the p-aramid polymer of Kevlar [18] is responsible for making the p-aramid fibers difficult to dye. However, these fibers [19] adsorb much more water than the polyamide o fibers, attaining moisture regains between 4 and 7% at 30 C. This moisture sorption behavior is consistent with the fact that the p-aramid fibers have almost the same molar concentration of peptide linkages (which must act as moisture adsorption sites) as polyamide fibers, but is inconsistent with the other fact that paramids have a very much higher degree of crystallinity than polyamides. Actually, the water accessibility of the peptide group in p-aramid fibers is about 2.2 times greater than that of the polyamide fibers. Assuming that the bulky and rigid phenyl-ring in the aromatic polyamide chain opens the space for each peptide group to adsorb moisture more efficiently than the aliphatic polyamide chain, may be explained the difference in moisture adsorptivity between the two polyamides. Steric effects, with particular emphasis on π electron conjugation influence the water accessibility of the peptide group in the aromatic polyamide. It has been found that, upon heating, the bound water is removed [17] and, therefore, the higher the temperature the less moisture uptake. The observed insufficient exhaustion of the disperse dye on the p-aramid fiber is in accord with this conclusion. The adsorption of the dye onto poly(p-phenyleneterephthalamide) fibers may involve the formation of dye aggregates, the tilting of the dye molecules and the insertion of dye layers. Analogous behavior has been observed [20] in the case of dye-treated aluminosilicate sorbents. CONCLUSIONS The p-aramid fibers were found to be dyeable with C.I. Disperse Red 60. In all experiments the exhaustion of o dyebath was greater than 48%. Dyeing with 7% dye at 135 C for 180 min gave the highest degree of exhaustion. Samples dyed with at least 5% dye showed increased depth of shade and improved levelling properties. The presence of carrier in the bath had little influence on the penetration of fibers by the disperse -1 dye. With the addition of 1 g·L wetting agent a drop in dye adsorption was observed, but when further

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quantities of wetting agent were added the exhaustion of the dye-liquor was increased. Scouring with wetting agent before dyeing increases the dyeability of p-aramid fibers. Acknowledgements Thanks are due to DuPont Agro Hellas S.A. for providing the p-aramid fibers and to Chromatourgia Tripoleos S.A., Greece for samples of chemicals. REFERENCES [1] Cates, B.J., Riggins, P.H. and Kelly, D.R.: Nomex printing, U. S. Patent 4 981 488 (1991) ® [2] Moore, R.A.F. and Weigmann, H.-D.: Dyeability of Nomex Aramid Yarn, Text. Res. J., 56 (1986) 254– 260 [3] Cates, B.J., Davis, J.K., FitzGerald, T.E. and Russell, E.J.: Process for simultaneously dyeing and improving the flame-resistant properties of aramid fibers, U. S. Patent 4 759 770 (1988) [4] Riggins, P.Η. and Hauser, P.J.: Exhaust process for simultaneously dyeing and improving the flame resistance of aramid fibers, U. S. Patent 4 898 596 (1990) [5] Johnson, J.R.: Dyeing and fire retardant treatment for nomex, U. S. Patent 4 752 300 (1988) [6] Vassiliadis, A.A. and Roulia, M.: Application of C.I. Disperse Blue 56 to Poly(pphenyleneterephthalamide) Fibers, Appl. Res. Rev., 8 (2003) 131–137 [7] Hindeleh, A.M., Hosemann, R., Hinrichsen, G. and Springer, H.: Lateral Growth of Microparacrystals in 60 Kevlar 49 Fibers Irradiated by Co , J. Polym. Sci., Polym. Phys. Ed., 28 (1990) 267–279 [8] Hosemann, R.: Microparacrystals in PPTA fibers in thermodynamic equilibrium state, Colloid Polym. Sci., 264 (1986) 332–334 [9] Lee, K.-S.: Process for making colored aramid fibers, U. S. Patent 5 114 652 (1992) [10] O’Brien, J.P. and Aneja, A.P.: Fibres for the next millennium, Rev. Prog. Color., 29 (1999) 1–7 [11] Jackson, C.L., Schadt, R.J., Gardner, K.H., Chase, D.B., Allen, S.R., Gabara, V. and English, A.D.: Dynamic structure and aqueous accessibility of poly(p-phenylene terephthalamide) crystallites, Polymer, 35 (1994) 1123–1131 [12] Vassiliadis, A.A.: Aqueous Bath Dyeing of Vinylferrocene Copolymers with C.I. Disperse Blue 165, Chimika Chronika, New Series, 26 (1997) 429–440 [13] Kobayashi, S. and Okamoto, T.: Method of dyeing a high heat-resistant synthetic fiber material, U. S. Patent 5 447 540 (1995) [14] Kobayashi, S., Wakida, T., Niu, S., Hazama, S., Ito, T. and Sasaki, Y.: The effect of sputter etching on the surface characteristics of dyed aramid fabrics, J. Soc. Dyers Col., 111 (1995) 72–76 [15] Kobayashi, S., Wakida, T., Niu, S., Hazama, S., Doi, C. and Sasaki, Y.: Change in colour of dyed aramid fabrics by sputter etching, J. Soc. Dyers Col., 111 (1995) 111–114 [16] Mathur, A. and Netravali, A.N.: Mechanical Property Modification of Aramid Fibers by Polymer Infiltration, Text. Res. J., 66 (1996) 201–208 [17] Rao, Y., Waddon, A.J. and Farris, R.J.: The evolution of structure and properties in poly(p-phenylene terephthalamide) fibers, Polymer, 42 (2001) 5925–5935 ® [18] Benrashid, R. and Tesoro, G.C.: Effect of Surface-Limited Reactions on the Properties of Kevlar Fibers, Text. Res. J., 60 (1990) 334–344 [19] Fukuda, M., Ochi, M., Miyagawa, M. and Kawai, H.: Moisture Sorption Mechanism of Aromatic Polyamide Fibers: Stoichiometry of the Water Sorbed in Poly(para-phenylene Terephthalamide) Fibers, Text. Res. J., 61 (1991) 668–680 [20] Roulia, M. and Vassiliadis, A.A.: Interactions between C.I. Basic Blue 41 and aluminosilicate sorbents, J. Colloid Interf. Sci., 291 (2005) 37–44

Corresponding Author Alexandros A. Vassiliadis, Associate Professor Dyeing and Finishing Laboratory, Department of Textiles, Technological Education Institute of Piraeus, 250 Thivon st., 122 41 Athens, Greece E-mail: aavassiliadis@netscape.net; Tel: +30 210 5381171; Fax: +30 210 5381255 Co-author 1 Maria Roulia, Dr Inorganic Chemistry Laboratory, Department of Chemistry, University of Athens, Panepistimiopolis, 157 71 Athens, Greece E-mail: roulia@chem.uoa.gr; Tel: +30 210 7274780; Fax: +30 210 7274435

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Co-author 2 Charalambos M. Boussias, Professor Dyeing and Finishing Laboratory, Department of Textiles, Technological Education Institute of Piraeus, 250 Thivon st., 122 41 Athens, Greece E-mail: boussias@in.teipir.gr; Tel: +30 210 5381171; Fax: +30 210 5381255 Presenting Author Alexandros A. Vassiliadis

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