Ind. Eng. Chem. Res. 2010, 49, 12513–12520
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Thickeners in Vat Dye Textile Printing: Rheology and Morphology Ziad Saffour,† Chuang C. Wang,‡,§ Pierre Viallier,† and Dominique Dupuis*,† Laboratoire de Physique et Me´canique Textiles, EAC 7189 CNRS-UHA, 11 rue A. Werner, F-68093 Mulhouse cedex, France, and Laboratoire de Chimie Physique, UHA, Mulhouse, France
This paper is a study of the thickeners used in two-phase vat dye textile printing. Throughout this complex process, the thickener dispersion undergoes several transformations, especially spreading on the textile material, drying, and coagulation. Empirical knowledge prescribes several requirements in terms of viscosity but also concerning the dried thickener. But, a better understanding of the phenomena is necessary to determine the origin of possible failure if the basic recipe is modified. Three different thickeners are considered: guaranate, alginate, and modified starch, as well as a combination of these three polymers. Their rheological properties are characterized in both permanent and oscillatory shear flow. Use of a mixture of polymers instead of a simple one avoids undesirable effects of thixotropy, yield stress, and elasticity, for a given value of the viscosity. The process involves the gelation of the thickener by cross-linking of guaranate chains with borate ions. The mechanical properties of such gels strongly depend on the pH, and their stability is affected by the presence of salt. Additionally, thickener films are dried under different conditions, and the morphology of the film is observed at different scales. It is shown that rapid drying at high temperature prevents crystalline structures obtained in the case of slow drying under ambient conditions. This is propitious to a good flexibility of the polymer film, suitable for fabric handling, good swelling in the steamer, and easy washing off. Introduction Among the different techniques of textile printing, the twophase vat dye process, used for cellulosic fibers, is known to give excellent results, well-defined patterns, and a good washing fastness. It consists of a sequence of various operations in order to get the penetration and the fixation of the dye molecule within the fiber. The printing paste mainly contains thickeners and the dye. During the process, it is submitted to different transformations. The printing paste is deposited on the fabric through a flat or a rotary screen and is then dried. The fabric is subsequently padded (dipped and squeezed) in an alkaline solution of a reducing agent which converts the dye to a watersoluble alkaline leuco form. The solution also includes borate which coagulates the thickener, reduces dye migration, and thus maintains a sharp edge to the printed image. The fabric is immediately steamed to allow the alkaline leuco form of the dye to diffuse from the thickener into the fibers. Finally, the fabric is passed through a succession of baths in which the alkali and thickener are removed, the dye is reoxidized to its insoluble form, and any unfixed surface dye is removed.1 To summarize, the first phase of the two-phase printing process consists of printing and drying. The second phase consists of padding, steaming, and finishing, which is washing, oxidation, and soaping (Figure 1). The aim of this paper is to contribute to a better understanding of this complex process. Indeed, it appears that several features of both the rheology of the thickeners and the drying conditions of the fabrics are very important especially to control the spreading of the paste and to prevent dye migration.2 Generally, the thickener is prepared by dissolving polymers at a concentration in a range recommended by the supplier. A “stock-paste” is obtained, which is used to prepare the printing * To whom correspondence should be addressed. E-mail: d.dupuis@ uha.fr. † Laboratoire de Physique et Me´canique Textiles, EAC 7189 CNRSUHA. ‡ Laboratoire de Chimie Physique, UHA. § Current address: University of Yantai, 264005, Yantai, P. R. China.
paste by addition of aqueous dye dispersion. The polymers are combinations of several polysaccharides. Especially, guar gum3,4 and modified starch are widely used. Several requirements have to be fulfilled in terms of viscosity but also concerning the dried thickener. The latter has to be flexible; it has also to provide a good swelling during steaming and to be easily eliminated by washing off.5 In this paper, a study of the rheological properties of several thickeners and of the gels formed by complexation of polymer chains is presented. These two points are related to printing, padding, and steaming (Figure 1). The viscosity of the samples is measured in simple shear flow. The oscillatory shear flow is more convenient to get the viscoelastic properties of the materials. In oscillatory shear flow, a sinusoidal stress is applied to the fluid. The shear strain is measured. It is sinusoidal too in the so-called linear domain, i.e., for “small” stress and/or strain. The ratio stain/stress defines the complex modulus G*. The results are generally expressed in terms of storage and loss moduli G′ and G′′. G′ and G′′ are, respectively, the real and imaginary part of G*. They are respectively related to the elastic and viscous character of the sample. Stress sweeps are done to determine the onset of the nonlinear regime: G′ and G′′ are
Figure 1. Two-phase textile printing process. (a) The fabric is printed through flat or rotary screens and dried. (b) The dye is fixed within the fibers by padding of the dried printed fabric, steaming, and finishing.
10.1021/ie100416m 2010 American Chemical Society Published on Web 11/11/2010
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Table 1. Concentration Range of the Different Thickeners guaranate
alginate
etherified starch
ternary system
1%-6%
1%-5%
2%-10%
5% 1.25% E1, 1.25% alginate, and 2.5% starch
measured as a function of the shear stress at a given frequency. This characterization gives information on the stress the sample may undergo without significant change of its microstructure. The viscoelastic properties of the fluids are obtained from the measurement of G′ and G′′ as a function of the frequency in the linear domain.6 The effect of the conditions of drying of the polymer dispersions on the quality of the polymer film is analyzed through microscopic observations. Experimental Section Three thickeners of industrial grade from CHT-France are investigated: E1, which is mainly guaranate, alginate, and etherified corn starch. In the following, they will be respectively named guaranate, alginate, and etherified starch. A mixture of these three polymers, the so-called ternary system, is also considered; the amounts of the different constituents are in agreement with an industrial recipe. The dispersions are carefully prepared to obtain a good dispersion and swelling of the polymers. The concentrations (% w/w) are chosen in the range corresponding to the recommendations of the suppliers for printing (Table 1). The suitable amount of thickener is dispersed in distilled water at 40 °C. The guaranate powder is always dispersed in a small quantity of ethanol (1 mL of ethanol for 1 g of powder) to avoid formation of lumps. The aqueous dispersions are stirred for 20 min to obtain homogeneous fluids. The preparation of the samples generally requires the elimination of air bubbles under vacuum after dissolution. Then, the real concentration is obtained by weighing after this treatment. The samples are kept at rest in the refrigerator for 24 h to get complete swelling. The reducing agent is the sodium dithionite (concentration up to 1%), and the cross-linking agent is the boric acid (concentration 0.57%). The adjustment of the pH is obtained by adding small amounts of acetic acid or of 5N NaOH solution. The rheological characterizations, in permanent and oscillatory shear flow, have been performed with two constant stress rheometers: the Bohlin CS10 (cone and plate geometry; diameter 40 mm; angle 4°) and the Rheoscope 1 from Thermo Electron (cone and plate geometry; diameter 35 mm; angle 2°). The measurements have been done at room temperature (24 °C). In permanent shear, the sample is submitted to increasing followed by decreasing shear stresses. The viscosity is plotted vs the shear stress. The up- and down-flow curves allow the observation of thixotropy, which is related to microstructural changes of the sample due to the mechanical stress. For the study of the morphology of the films of thickeners, the polymer dispersions are spread on silicium wafers (from Siltronix). These solid substrates are previously cleaned with an organic solvent (toluene). Then, they are immersed for 30 s in a “piranha” solution (mixture of 30% v/v % H2O2 and 70% v/v % H2SO4) and rinsed with distilled water. This treatment gives a highly hydrophilic surface. The films are dried in ambient conditions or in an oven at 110 °C for 10 min. Rheological Properties of the Thickeners. As shown in Figure 2, the guaranate and alginate dispersions are shearthinning and thixotropic especially for the higher concentration values. The zero shear viscosity increases with concentration. The specific viscosity at zero shear rate ηsp0 is defined by ηsp0 ) (η0 - ηs)/cηs, η0 being the viscosity of the solution at zero
Figure 2. Shear viscosity of alginate and guaranate dispersions. Guaranate, [ 2.1%, 9 4.4%; alginate, ]2.1%, 0 4.3%.
Figure 3. Specific viscosity at zero shear rate vs the concentration for guaranate and alginate dispersions.
shear rate, ηs the viscosity of the solvent, and c the concentration. When it is plotted vs the concentration, three domains may usually be observed and two critical concentrations are defined: c* is the upper limit of the dilute regime and c** is the limit between the semidilute and the concentrated regimes. When c > c*, interpenetration of the macromolecular chains appears and when c > c**, the coil dimensions become independent from the concentration. Here (Figure 3), for concentrations c larger than 2%, ηsp0 increases approximately like c5.3, meaning that c > c**. This condition is necessary to get a good efficiency of the thickener.7 The behavior of the etherified starch dispersions is more complicated. These fluids are shear-thinning and highly thixotropic, but the shape of the viscosity curves indicates a probable yield stress for concentrations larger than 3%. The down-flow curves show that the yield stress tends to disappear or to be reduced after shearing the dispersion at high shear stresses (Figure 4). This effect is due to the breakdown, under stress, of a macromolecular network formed at rest. It is empirically known that using mixtures of several thickeners gives more reproducible printed patterns. So, it is interesting to compare the ternary system to the individual polymer dispersions in terms of viscosity. The measurements are performed with the same procedures. The ternary system is shear-thinning with a Newtonian plateau at low shear stress and
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Figure 4. Shear viscosity of etherified starch dispersions for different concentrations: [ 3.2%, 2 4.5%, b 5.7%, * 8%.
Figure 5. Comparison of the shear viscosity of four different thickeners: 0 guaranate 5.6%, ] alginate 4.3%, ∆ etherified starch 8%, and s ternary system 5%. The inset is a comparison between these dispersions at the same 5% concentration.
very low thixotropy, i.e., a small sensitivity to the mechanical history (Figure 5). The comparison can be done with the same polymer concentration (5%) for all the dispersions (inset of Figure 5; the curves related to the individual polymers are obtained by nonlinear interpolation of the experimental data). But it is also useful to consider concentrations giving the same order of magnitude of the viscosity in the shear-thinning domain (Figure 5), i.e., for stresses corresponding to those undergone by the fluids during the process. At a given concentration, the ternary system combines a sufficient viscosity at high shear stress and the elimination of both yield stress and thixotropy. Figure 5 especially displays the specificity of etherified starch. This element is necessary because it has some advantage for the color yield,1 but it cannot be used alone. Indeed, at 5% concentration and high shear stress, the viscosity is 1 order of magnitude lower than the ternary system one. Then, undesirable smudges are highly probable. If its concentration is increased
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Figure 6. Storage and loss moduli G′ and G′′ vs the angular frequency in the linear domain for 8% etherified starch dispersion (G′ 2, G′′ 4); ternary system (G′ *, G′′ ×) Inset: storage and loss moduli G′ and G′′ vs the shear stress at 10 Hz for the same fluids.
to get a suitable viscosity value at high stresses, the yield stress becomes more important. The result is an increase of difficulty for the paste to flow through the orifices of the screen. Additionally, the advantage of a low thixotropy is a better control of the paste viscosity along a dynamic process. A uniform shade, despite some small variations of pressure or of speed of the fabric or of the geometry of this fabric, can therefore been obtained. The oscillatory study confirms the specificity of the etherified starch dispersions (Figure 6). In the linear domain, the 8% etherified starch dispersion behaves like a weak gel in the range of frequency which is explored. The G′ and G′′ curves are roughly parallel with G′ ≈ 5G′′. The ternary system displays a typical viscoelastic polymer solution behavior: at low frequency, the loss modulus is larger than the storage one and the viscous character of the fluid is predominant. At high frequency, it is the contrary and the elasticity prevails. The crossover frequency (corresponding to G′ ) G′′) gives an evaluation of the longest relaxation time of the systems (≈0.1 s). The inset of Figure 6 shows the result of a stress sweep at a given frequency (10 Hz) for etherified starch dispersions and for the ternary system. Hereto the case of starch is different: one observes a progressive decrease of G′ while G′′ increases, presents a maximum, and becomes larger than G′, indicating that the viscous character of the dispersion prevails over the elastic one at high shear stress. It could be related to a progressive rupture of macromolecular chains associations and, therefore, to the breakdown of an elastic network as the shear stress increases leading to a viscouslike behavior. These results confirm the existence, for the etherified starch, of an elastic network at rest, which could be induced from the viscosity measurements (yield stress) and from the frequency sweep. On the other hand, the ternary system appears to be very stable and to be able to undergo larger stress with no change of its microstructure. Rheological Properties of the Gels. During the second step of the process, there is gelation of the thickener: the guaranate chains are cross-linked by the borate ions from boric acid contained in the padding fluid. The gelation of polysaccharides is generally the result of physical cross-linking through polymer-polymer interactions.7 Different mechanisms of interchain associations may be at the origin of gelation, such as double helix formation or helix-helix associations.8 But, gels can also be formed by complexation reactions.9 It is the case of guaranate with borate ions. Indeed, by adding a small amount
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Figure 8. Time-pH superposition for the storage and loss moduli of the guaranate-borate systems. Inset: horizontal (a) and vertical (b) shift factors vs the pH. Figure 7. Storage and loss moduli G′ (black symbols) and G′′ (open symbols) at 6.28 rad/s vs shear stress for guaranate/borate (9 0 pH 5.5; [ ] pH 9.3) and guaranate/borate/sodium dithionite (2 ∆ pH 9.4).
of boric acid in a solution of guaranate and vigorously stirring, there is formation of a gel. This kind of gel is characterized by several specific properties: it is quasi-instantaneously formed; its mechanical properties depend on the pH value; it is not a true gel since it flows at sufficiently long times because of the very labile nature of the junctions.10-12 But, the padding fluid also contains sodium dithionite, and the strength and stability of the gel are widely influenced by the presence of salt. The rheological properties of the gels formed with a 2% guaranate solution and 0.57% boric acid are studied in oscillatory shear flow. The influence of sodium dithionite is discussed. The results of stress sweeps are given in Figure 7. At low pH, G′′ > G′ and the two moduli decrease as the shear stress exceeds some critical value characterizing the onset of the nonlinear regime. The shape of the curves is typical of a viscoelastic polymer solution. For pH > 8, there is a jump of the G′ plateau value, which is approximately multiplied by 100, with G′ ≈ 10G′′. As the shear stress increases, G′′ increases, presents a maximum, and becomes larger than G′ which sharply decreases. The viscous behavior is prevalent on the elastic one, meaning the rupturesdue to mechanical stresssof the junctions between the guaranate chains. The results obtained from frequency sweeps in the linear domain, at different pH values, can be superimposed by a time-pH superposition analogous to the time-temperature superposition, according to the procedure proposed by Kesavan and Prud’homme13,14 (Figure 8). The reference curve corresponds to pH 9.3. The horizontal and vertical shift factors a and b are plotted vs the pH (inset of Figure 8). At low pH, the system behaves like a viscoelastic polymer solution. G′′ is larger than G′ and G′′ ∝ ω, while G′ ∝ ω2. For pH larger than 8, the behavior of the fluids is totally different and characterizes a gel-like behavior. The shape of the master curve indicates that we have a highly elastic system contrary to that observed at low pH. The elastic modulus displays a plateau value related to the density of interchain associations. The loss modulus presents a minimum. The extent of the plateau of G′ is limited when the frequency decreases, indicating that the system is not a true gel, in good agreement with the results of the literature. In other words, there is a flow region at very low frequencies since the interchains junctions are not permanent. The crossover
Figure 9. Phase diagram for the guaranate-borate-sodium dithionite systems. The dotted lines are only for eye guidance.
frequency corresponding to G′ ) G′′ allows an evaluation of the longest relaxation time τC of the material. At pH ) 9.3, one obtains τC ≈ 25 s. The horizontal shift factor a being proportional to τC, it appears that, when the pH varies from 8.8 to 12, the relaxation time varies over three decades. The material does not flowswhat is desiredsif the characteristic time of the process is lower than τC. It is the case since the residence time of the printed fabric in the steamer is less than 10 s. In the industrial process, the presence of sodium dithionite in the padding fluid can greatly modify the mechanical properties of the guaranate/borate gels. Indeed, a phase separation occurs quite rapidly for amounts of sodium dithionite larger than 0.5%. A phase diagram has been obtained (Figure 9) indicating the sol, gel, and phase separation states vs the pH and the sodium dithionite concentration cs. The rheological measurements have been performed for cs ) 0.5% which is currently used in industry. The results of the stress sweep (Figure 7) show that the presence of sodium dithionite produces a decrease of the elastic modulus and a rupture of the gel at lower shear stress. This effect has been already observed for guar galactomannan/ borax gels with NaCl.15 When the 2% guaranate dispersion is replaced by an 1% guaranate-1% alginate dispersion, the number of junction sites decreases, the strength of the gel is reduced,14 and the phase separation occurs at lower sodium dithionite concentrations. For instance, for cs ) 0.1%, the phase separation is observed after 20 min. The presence of salt in the padding fluid and the use of mixtures of polymers such as guaranate and alginate lead to a decrease of the lifetime of the guaranate/borate gels and of their strength. But, the padding and steaming steps of the process are only a few seconds or 10 s long. So, the presence of salt should not have any
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Figure 11. Films dried in oven at 110 °C for 10 min: (a) guaranate, (b) alginate, and (c) etherified starch.
Figure 10. Films dried under ambient conditions: (a) guaranate, (b) alginate, and (c) etherified starch.
consequence on the efficiency of the gelation because of the rapidity of the process. Then, in practice, the use of a flash steamer is particularly convenient to avoid problems resulting from the effect of salt especially as the salt concentration is generally larger than 0.1%. Nevertheless, these results explain why the printer empirically adjusts these two parameters (amount of salt and mixture of polymers) to get an optimal process answer in terms of sharpness and penetration, for good coloration yield and wet rubbing fastness. Morphology of the Polymer Films. After printing, the printed fabric is dried and then folded for transport and, sometimes, kept in stock before the second step of the process. The dried polymer film has to be flexible especially to avoid brittle fracture during mechanical handling.1 It also has to swell easily during steaming and to be easily removed at the end of
the process. It has been already shown that the conditions of drying have a great influence on the morphology of the polymer.16 Since it is not possible to observe the microscopic structure of the polymer films on a fibrous material, drops of the different thickener solutions (concentration: 2%) are deposited on highly hydrophilic silicium wafers. The drops spontaneously spread and are dried by two different methods: slow drying under ambient conditions and rapid drying in an oven at 110 °C for 10 min, close to industrial conditions. Macroscopically, in the first case, a rich polymer region appears in the central part of the spot and a quasi-transparent poor one at the periphery. It means that, during the evaporation of the solvent, there is a transport of the polymer toward the central part of the drop. At a microscopic scale, for the three polymers, “crystalline” treelike structures are observed (Figure 10). These photographs have been done after 75 min. Such kind of morphology has been already described, for instance, in the case of long chain alkanes.17 It results from the solvent evaporation which induces the transport of the polymeric chains and their aggregation according to a diffusion-limited-aggregation process. The shape of the structures depends on the polymer concentration and may be characterized by a fractal dimension.18
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Figure 12. Films dried in oven at 110 °C for 10 min: (a) guaranate (center of the drop), (b) guaranate (intermediate zone), (c) alginate, and (d) etherified starch.
Figure 11 shows that, for a rapid drying, the films of polymers are homogeneous, especially for guaranate and alginate. The film of etherified starch displays a globular structure, characteristic of starch properties. At another scale, the AFM photographs exhibit the specific morphology of each polymer: smooth large grains for alginate (Figure 12c), fine granulous structure for guaranate in the central part of the drop (Figure 12a), and rough globular grains for starch (Figure 12d). For guaranate, one obtains larger structures in an intermediate region of the spot, between the central zone and the periphery (Figure 12b). It is perhaps an effect of the kinetics of the spreading of the drop and of the transport of the polymer during this phase of spreading. After that, a rapid evaporation of the solvent does not allow further polymer transport. It can also been noticed that a film which has been dried in the oven and after that which is stored in ambient conditions for a sufficiently long time may recrystallize. For instance, Figure 13 is obtained from a film of alginate in the center region of the spot and at the periphery. The crystalline structure appears more clearly with lower polymer concentrations as it is shown in the figure for 0.2%. This can explain problems induced by
storage of the dried fabric for some days before padding: the polymer film has lost its quality, and the coloration yield is smaller. Conclusion This paper first examines how a well-formulated printing paste is able to fulfill a number of requirements for good results in the two-phase printing process and, especially, why a mixture of thickeners (guaranate, alginate, starch) is used instead of only one. To be transferred on the textile material, the paste has to flow through the orifices of the screen. Additionally, enough time for this flow is necessary since the fabric is moving during the process at about some 30-40 m/min velocity. This flow is easier if the viscosity of the fluid is not too large and its elasticity is weak. Indeed, it has been already shown that the flow of elastic fluids through orifices may be difficult because of the development of normal stresses.19 But, the viscosity has also to not be too low to avoid the streading on the fabric and the capillary drawing by the fibers and the yarns.1 It is shown that the ternary
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Figure 13. Alginate film dried in oven and stocked under ambient conditions for four weeks: (a) in the central region of the drop; (b) in the periphery; (c) 0.2% concentration.
system provides a sufficiently high viscosity at high shear stresses, while avoiding yield stress and elasticity due to the presence of etherified starch which has some advantage for the color yield.1 Additionally, for the ternary system, the thixotropy is drastically decreased compared to the individual polymer one. This effect warrants a uniform shade, despite some small variations of pressure or of speed of the fabric or of its geometry. The presence of guaranate is necessary to get intermolecular associations induced by borate ions, leading to the coagulation of the thickener during the second step of the process. The gelation of the dispersions is quasi-instantaneous under vigorous stirring. This property is of great interest since, during the padding, the fluid undergoes a strong mechanical action for a matter of seconds, which have to be sufficient for the coagulation of the paste. The strength of the gel can be adjusted by varying the pH or the amount of salt or by using a mixture of polymers. More, it is shown that, in the presence of sodium dithionite, a phase separation occurs within several minutes. Nevertheless, that has no consequence since a flash steamer is used where the steaming duration is less than 10 s. Second, the effect of drying conditions on the polymer dispersion is considered. Indeed, the dried thickener has to be flexible especially to avoid brittle fracture The microscopic study of the dried films structure shows that rapid drying at high temperature is better than slow drying in ambient conditions. Indeed, it leads to a homogeneous, noncrystalline film. Such a film should easily swell during steaming and should be easily removed at the end of the process. A similar result was obtained in a study of inkjet printing thickeners.16 On the other hand, keeping a stock of the dried fabrics before the second strep of the process may be a problem since recrystallization of the polymer films has been observed.
Although the recipe of a two phase vat dye process is the result of a long and totally empirical research, this recipe is probably the best one. Especially, the rheological and coagulation properties of the printing paste exactly correspond to the optimal process control. The results explain the reasons for empirical adjustments of some parameters. For instance, when a dark nuance is desired, the printer uses a more concentrated thickener in order to get a weaker penetration of the paste. On another hand, the compounds of thickeners provided by the supplier do not always contain exactly the same amount of guar. Indeed, the composition is adjusted so as to obtain a nominal value of the viscosity for a fixed mass of thickener. So, for a given quantity of borax, the efficiency of the gelation is not still the same, and the printer knows that, when the color smudges, it is necessary to increase the amount of borax. Despite the complexity of this process, this study allows a better understanding of the conditions which promote its efficiency. It should be an aid to determine the origin of possible failure occurring when modifications of the recipe are introduced. Literature Cited (1) Gutjahr, H.; Koch, R. R. Direct Print Coloration. In Textile Printing; Miles, L. W. C., Ed.; Society of Dyers and Colourists: West Yorkshire. U.K., 1994; pp 139-195. (2) Lapasin, R.; Pricl, S. Rheology of Industrial Polysaccharides: Theory and Applications, Blackie Academic and Professional: Glasgow, U.K., 1995. (3) Whitcomb, P. J.; Gutowski, J.; Howland, W. W. Rheology of Guar Solutions. J. Appl. Polym. Sci. 1980, 25, 2815. (4) Oblonsek, M.; Sostar-Turk, S.; Lapasin, R. Rheological Studies of Concentrated Guar Gum. Rheol. Acta 2003, 42, 491. (5) Miles, L. W. C. The Production and Properties of Printing Pastes. In Textile Printing; Miles, L. W. C., Ed.; Society of Dyers and Colourists: West Yorkshire. U.K., 1994; pp 240-274.
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(6) Barnes, H. A. A Handbook of Elementary Rheology; Institute of NonNewtonian Fluid Mechanics: University of Wales, 2000. (7) Doublier, J. L.; Cuvelier, G. Gums and Hydrocolloids: Functional Aspects. In Carbohydrates in Food; Eliasson, A. C., Ed.; Marcel Dekker Inc.: New York, 1996; pp 283-318. (8) Clark, A. H.; Ross-Murphy, S. B. Structural and Mechanical Properties of Biopolymer Gels. AdV. Polym. Sci. 1987, 83, 55. (9) Te Nijenhuis, K. Thermoreversible Networks. AdV. Polym. Sci. 1997, 130, 1. (10) Carnali, J. O. Gelation in Physically Associating Biopolymer Systems. Rheol. Acta 1992, 31, 399. (11) Pezron, E.; Ricard, A.; Lafuma, F.; Audebert, R. Reversible Gel Formation Induced by Ion Complexation. 1. Borax-Galactomannan Interactions. Macromolecules 1988, 21, 1121. (12) Pezron, E.; Leibler, L.; Ricard, A.; Audebert, R. Reversible Gel Formation Induced by Ion Complexation. 2. Phase Diagrams. Macromolecules 1988, 21, 1126. Tayal, A.; Pai, V. B.; Khan, S. A. Rheology and Microstructural Changes during Enzymatic Degradation of a Guar-Borax Hydrogel. Macromolecules 1999, 32, 5567. (13) Kesavan, S.; Prud’homme, R. K. Rheology of Guar and HPG Crosslinked by Borate. Macromolecules 1992, 25, 2026.
(14) Saffour, Z.; Viallier, P.; Dupuis, D. Rheology of Gel-like Materials in Textile Printing. Rheol. Acta 2006, 45, 479. (15) Pezron, E.; Ricard, A.; Leibler, L. Rheology of GalactomannanBorax Gels. J. Polym. Sci., Part B: Polym. Phys. 1990, 28, 2445. (16) Haidara, H.; Baffoun, A.; Viallier, P. Morphology-Dependent Properties and Swelling-Induced Transition in “Sodium-Alginate/Urea” Thin Films. Polymer 2004, 45, 8333. (17) Knu¨fing, L.; Schollmeyer, H.; Riegler, H.; Mecke, K. Fractal Analysis Methods for Solid Alkane Monolayer Domains at SiO2/Air Interfaces. Langmuir 2005, 21, 992. (18) Witten, T. A.; Sander, L. M. Diffusion-Limited Aggregation. Phys. ReV. B: Condens. Matter Mater. Phys. 1983, 27, 5686. (19) Davard, F.; Dupuis, D. Blade Coating of Fabrics: Rheology and Fluid Penetration. Coloration Technol. 2002, 118, 1.
ReceiVed for reView February 25, 2010 ReVised manuscript receiVed September 29, 2010 Accepted October 11, 2010 IE100416M
