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Ind. Eng. Chem. Res. 2005, 44, 852-856
Durable and Regenerable Antimicrobial Textiles: Chlorine Transfer among Halamine Structures Lei Qian† and Gang Sun*,‡ Institute of Textile Technology, College of Textiles, North Carolina State University, Raleigh, North Carolina 27695, and Division of Textiles and Clothing, University of California, Davis, Davis, California 95616
An intermolecular chlorine transfer reaction has been considered as a possible cause for improved durability and power of biocidal functions on cotton fabrics containing a mixture of amine, amide, and imide halamine structures. To prove the chlorine transfer reaction, model compounds of amine halamine and imide were employed. The results indicated that the chlorine transfer reaction from stable amine halamine to imide and the formation of an active imide halamine occurred in both water and chloroform solutions. The transfer is a second-order reaction related to the concentrations of both amine halamine and imide bonds but is more significantly affected by the concentration of amine bonds. The reaction is endothermic, and the rate is very slow, on the order of 10-4-10-5 mmol/min in both water and chloroform. Introduction N-halamine structures are effective biocides and have been successfully incorporated into cellulose and other textile materials to produce durable and regenerable biocidal functions.1,2 The biocidal functions of the treated fabric are rendered by the chloramine bonds (N-Cl) in three different forms, i.e., imide, amide, and amine. These N-chloramines can kill microorganisms by directly transferring positive chlorine atoms from the N-chloramine bonds to appropriate receptors and/or initiating oxidative reactions in the microorganism cells. These reactions could effectively destroy or inhibit enzymatic or metabolic cell processes, consequently resulting in the inactivation of the organisms.3,4 After the interaction with microorganisms, the halamine structures on fabric are reduced to their precursor imide, amide, and amine N-H bonds, which can then be refreshed to corresponding halamines by chlorine bleaching to renew their biocidal functions. The antimicrobial power of chloramine structures is dependent on the activities of the halamine bonds and is in the order opposite to the bond strength of the halamines, i.e., imide halamine > amide halamine > amine halamine.5 Cotton fabrics treated by 1,3-dimethylol-5,5-dimethylhydantoin (DMDMH) possess predominantly imide halamine bonds after chlorine bleaching, which can kill bacteria more rapidly than the same cotton fabrics containing only amine halamine structures. These fabrics were prepared by using a similar finishing process with 3-methylol-2,2,5,5-tetramethylimidazolidin-4-one (MTMIO).6 However, the imide halamines on the fabrics are less durable in maintaining biocidal function than the amine ones, particularly against repeated laundering. The amine halamines could survive more than 50 repeated washes on the fabrics, while the imide halamine would lose all active chlorine after a few washings. The easy loss of imide * To whom correspondence should be addressed. Tel.: (530) 752-0840. Fax: (530) 752-7584. E-mail:
[email protected]. † North Carolina State University. ‡ University of California, Davis.
halamine structures and the powerful biocidal effect could be explained by the labile imide halamine bonds. More interestingly, a study on fabrics treated with mixtures of both DMDMH and MTMIO compounds demonstrated that the coexistence of imide and amine halamine structures could provide both rapid killing power and improved durability of the biocidal functions.6 Such an interesting result indicates that the easily lost imide halamine bonds could be recharged in the fabrics, possibly by the stable amine halamines. Otherwise, the rapid biocidal functions would not be possible after the labile imide halamines are consumed. An intermolecular chlorine transfer from imide halamine (N-Cl) to amide N-H is a rapid reaction, which should be a major reason for the inactivation of microorganisms.7 The intermolecular chlorine transfer from an imide halamine (N-Cl) bond to an amine N-H bond was validated in a study by mixing N-chlorosuccinimide (NCS) with 2,2,5,5-tetramethylimidazolidin4-one (TMIO) in a CHCl3 solvent at room temperature. The chlorine intermolecular transfer from the imide halamine bond on NCS to the amine bond took place through a two-step mechanism, i.e., chlorine on imide N-Cl first shifting from the nitrogen to an amide nitrogen in TMIO and then moving from the amide nitrogen to an amine nitrogen on another TMIO molecule.8,9 These transfers are a thermodynamically spontaneous process because the amine halamine bond as a resultant is more stable than both the amide and imide halamine bonds. The study also concluded that the transfer rate fits both first- and second-order reaction patterns but lean toward the second-order pattern, and the transfer rate is affected by the reaction medium and temperature. To investigate the special effect between imide N-H and amine halamine (N-Cl) bonds on fabric, compounds containing different imide, amide, and amine halamine structures as well as their unhalogenated precursors were selected in this study. Two model compounds, 1-chloro-2,2,5,5- tetramethylimidazolidin-4-one (MC) and succinimide, shown in Scheme 1, were employed in the chlorine transfer reactions. An UV-vis spectrophotometer was used to monitor concentration changes
10.1021/ie049493x CCC: $30.25 © 2005 American Chemical Society Published on Web 01/13/2005
Ind. Eng. Chem. Res., Vol. 44, No. 4, 2005 853 Scheme 1. Chlorine Transfer from MC to Succinimide
of the halamine compound and their precursor structures in both H2O and CHCl3 media at the maximum absorption wavelengths of MC (270 nm) and succinimide (250 nm), respectively. The rate constants, activation energies, and possible mechanisms of the chlorine transfer reactions under different media were also explored. Experimental Section Chemicals and UV Absorbance. TMIO and MC were supplied by Vanson-HaloSource Inc. (Redmond, WA) and recrystallized with isopropyl alcohol and toluene, respectively. Succinimide and NCS were purchased from Acros Organics (Pittsburgh, PA) and used without further purification. UV-vis absorbance spectroscopy was conducted on a Hitachi UV-2000 spectrophotometer with two 1-cm quartz cells. UV absorbance values of MC and succinimide were obtained at selected maximum wavelengths of 270 and 250 nm, respectively. H2O as a Reaction Medium. The reaction temperature was selected at either 30 or 60 °C, respectively. The reaction mixtures with the initial molar ratios of succinimide/MC at 1:1, 2:1, 4:1, and 6:1 were monitored by using the UV spectrophotometer for a reaction duration of up to 10 h. The initial concentration of MC in each solution was 0.004 M, and the initial concentration of succinimide was adjusted following the succinimide/MC ratios. Calibration curves for different molar ratios of the mixture were prepared by using a series of solutions with MC concentrations at 0.002, 0.003, 0.004, and 0.005 M and succinimide concentrations determined by the ratio of succinimide/MC. CHCl3 as a Reaction Medium. The chlorine transfer reactions in CHCl3 were conducted at 30 °C. A molar ratio of the succinimide/MC mixture was selected at 1:1 only. The initial concentration of MC was 0.004 M, and the initial concentration of succinimide was based on the ratio of 1:1, also 0.004 M. The calibration curves of succinimide and MC in a CHCl3 solution were prepared using the same method as that in a H2O solution. In both deionized water and chloroform, MC showed a maximum UV absorbance at a wavelength of 270 nm, while succinimide revealed a major UV absorbance at 250 nm. Changes of concentrations within the experimental range did not vary the maximum UV absorption wavelengths for both MC and succinimide. Meanwhile, the resultants of the reaction, TMIO and NCS, showed no major absorption at these two UV wavelengths. Therefore, the absorbance values at 270 and 250 nm were employed in the monitoring of the concentration changes of MC and succinimide in solutions. Results and Discussion MC contains only one amine chloramine. This amine halamine was proven to be the most stable and least
Figure 1. UV absorbance of succinimide and MC in an aqueous solution versus mixing time (temperature ) 30 °C, initial [MC] ) 0.004 mol/L).
powerful halamine in providing biocidal functions compared with all other halamine structures.10-14 To study the possible chlorine transfer reaction between the amine halamine and imide N-H, the changes of the UV absorbance of MC and succinimide at wavelengths of 270 and 250 nm were monitored to reflect their concentration changes. Two aqueous solutions with molar ratios of succinimide/MC at 1:1 and 2:1 were prepared, and the UV absorbance values at these two specific wavelengths were measured at room temperature. Figure 1 shows the results of the absorbance at both 270 and 250 nm wavelengths after the two chemicals were mixed for up to 6 days at room temperature. The absorbance of MC and succinimide showed a steady drop during the reaction, indicating that the concentration decreases of both MC and succinimide in the mixtures occurred simultaneously. The rates of both concentration decreases were very consistent, showing that both chemicals were consumed at the same reaction rate in the system. The reaction was very slow, which is also consistent with the feature of stable amine halamine.8-10 In a separate test, both MC and succinimide aqueous solutions were found to be stable for more than 6 days, without showing any reduction at the characteristic UV absorbance wavelengths. Thus, the decrease of the UV absorbance at these wavelengths must be a result of a chlorine transfer reaction between these two compounds. Because the resultants of the transfer reaction (NCS and TMIO) have no visible characteristic absorption in the UV region, the concentration decreases of MC and succinimide in the mixture could be used as evidence of the formation of both NCS and TMIO according to Scheme 1. Chlorine Transfer in a H2O Medium. After demonstration of the chlorine transfer from amine halamine to imide N-H, a kinetic study on the transfer reaction in a deionized water solution was conducted under both 30 and 60 °C with four selected molar ratios of succinimide/MC. Upon mixing of two compounds at a specific ratio, collection of the UV absorbance of MC (270 nm) was begun and continued for a period of 600 min, and the values of the absorbance were changed into concentrations of MC according to a calibration curve. The concentrations of MC decreased steadily during the course of the reaction, revealing that the chlorine transfer reaction occurred in all four succinimide/MC molar ratios (Figure 2). The reduction of the MC concentration under 60 °C was faster than that under 30 °C, meaning that the chlorine transfer reaction was accelerated at the elevated temperature.
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Figure 4. Plot of 1/[MC] versus reaction time (initial [MC] ) 0.004 M).
Figure 2. MC concentration versus mixing time in aqueous solutions (initial [MC] ) 0.004 M, and S stands for succinimide in the figure).
Figure 5. Plot of ln[MC] versus reaction time (initial [MC] ) 0.004 M).
Then Figure 3. MC concentration changes versus succinimide/MC ratios (initial [MC] ) 0.004 M).
On the basis of the reaction scheme (Scheme 1), the reaction rate can be written in eq 1.15 We selected reaction times at 120 and 240 min and plotted the MC concentration changes (∆[MC]) versus the concentration increase of succinimide or the increase of succinimide/ MC initial concentration ratios in the system (Figure 3). As the succinimide/MC concentration ratio was raised, the ∆[MC] concentrations in the system increased smoothly in almost linear relationships under both reaction temperatures of 30 and 60 °C. At a higher temperature, the reaction proceeded more rapidly, showing a higher slope in the plot. The slopes of the lines at reaction times of 120 and 240 min are basically the same based on the plots, with a higher slope at 60 °C than at 30 °C. The linear relationship between the ∆[MC] concentration and the increase of the succinimide concentration suggests that the reaction rate is in a first-order relationship with the concentration of succinimide according to eq 1, where R is the reaction rate,
R ) -d[MC]/dt ) k[MC][succinimide]
(1)
k is the rate constant, [MC] is the concentration of MC, [succinimide] is the concentration of succinimide, and t is the reaction time. According to eq 1, if the succinimide/MC molar concentration ratio is 1:1, [MC] equals [succinimide], eq 1 can be rewritten into the following equation assuming that the chlorine exchange reaction is an overall secondorder reaction:
R ) -d[MC]/dt ) k[MC]2
(2)
1/[MC]0 - 1/[MC] ) kt
(3)
Plotting the reciprocal MC concentration 1/[MC] versus reaction time should result in a straight line if the reaction is a second-order reaction. Thus, values of 1/[MC] in reactions of an equal succinimide/MC molar ratio (1:1) versus reaction time at both 30 and 60 °C are plotted in Figure 4. Interestingly, the plots showed a good linear relationship between 1/[MC] and time, suggesting an overall second-order reaction for the chlorine transfer between MC and succinimide. Because the reaction rate is a first-order reaction to the concentration of succinimide and a second-order reaction in the overall reaction, the reaction rate to [MC] must be a first-order reaction. Thus, eq 1 is a correct description of the chlorine transfer reaction in an aqueous solution. However, when the results are carefully examined in Figure 3, it was found that the ∆[MC] changes were fairly small when the concentration of succinimide was increased from equal to 6 times more than the MC concentration. In fact, if these plots were horizontal lines, the reaction would be zero order to succinimide. Because these lines are so close to horizontal, it means that the succinimide concentration was not important in affecting the reaction rate. To confirm such an assumption, we also plotted ln [MC] versus reaction time using the MC concentration decreases at succinimide/MC concentration ratio 1:1 at both 30 and 60 °C, shown in Figure 5. As expected, the plots again show a linear relationship between ln [MC] and the reaction time. Thus, the chlorine transfer reaction could be approximately considered as a first-order reaction to the concentration of the amine halamine [MC]. In other words, the reaction rate is mostly determined by the concentration of the amine halamine compound in the system.
Ind. Eng. Chem. Res., Vol. 44, No. 4, 2005 855 Scheme 2. Chlorine Transfer Mechanism
Figure 6. Plot of 1/[MC] versus reaction time (chloroform; initial [MC] ) 0.004 M).
The rate constants of the chlorine transfers could be calculated using the slopes of the linear equations,15 with results of 0.000 08 and 0.0002 mmol/min at 30 and 60 °C, respectively. Evidently, the speed of the chlorine transfer is faster at a raised temperature. On the basis of the Arrhenius equation (eq 4), the activation energy Ea of the chlorine transfer in an aqueous solution was derived as Ea ) 25.6 kJ/mol by using rate constants at 30 and 60 °C, where Ea is the activation energy, A is an
k ) A exp(-Ea/RT)
(4)
Arrhenius constant, k1 and k2 are rate constants under 30 °C (303 K) and 60 °C (333 K), respectively, and T1 and T2 are temperatures of 30 °C (303 K) and 60 °C (333 K), respectively. Chlorine Transfer in CHCl3. In chloroform, the maximum UV absorbance wavelengths of MC and succinimide are the same as those in deionized water. The chlorine transfer between MC and succinimide was conducted in CHCl3 at 30 °C only, and the concentration of MC (UV adsorption at 270 nm) was monitored during the reaction. Because the overall reaction rate is a second-order reaction in water, we assumed the reaction mechanism in chloroform to be the same as that in water and then plotted the reciprocal concentration of MC versus reaction time (Figure 6). The figure shows that the plot of succinimide/MC molar ratios at 1:1 is basically linear during a reaction time of 90 min, proving that the overall reaction is still a second-order reaction in chloroform. However, the reaction constant in chloroform (k ) 0.0004 mmol/min) is much higher than that in water at the same reaction temperature (30 °C), almost close to the reaction constant at 60 °C in water. Possible Mechanisms of Chlorine Transfer. Kinetic studies of the chlorine transfer between amine halamine (MC) and imide N-H (succinimide) showed that the reaction follows both second- and first-order reactions but is mostly determined by the concentration of amine halamine. In other words, the reaction could be a pseudo-first-order reaction. The rate constants of the reaction at both 30 and 60 °C were quite small, in the range of 10-4-10-5 mmol/min, which are several magnitudes smaller than that of a chlorine transfer from imide halamine to amine.8,9 The chlorine transfer from the amine nitrogen in MC to the imide nitrogen in the succinimide structure could proceed through two different paths. One path is through dissociation of chlorine from an amine halamine bond (Scheme 2) and then formation of a free chlorine as a migrating species. In a deionized solution, the chlorine cations (Cl+) should
be the migrating species because the high polarity of H2O could facilitate the cleavage of the N-Cl bond into N- and Cl+ and stabilize Cl+. The free chlorine will react with succinimide to form an imide halamine bond. However, the dissociation of amine halamine has a very low equilibrium constant (Ka) at 10-12,10 which means the production of free chlorine is not favored thermodynamically. The following interaction between the free chlorine and the imide bond N-H could be relatively rapid. This reaction path may explain why the reaction rate is mostly determined by [MC]. Therefore, the entire chlorine transfer in the deionized water involves cleavage of the chlorine cation from the MC structure and replacement of H+ on the imide nitrogen in the succinimide structure with Cl+ (Scheme 2). The second hypothesized path could be a colloidal interaction between MC and succinimide in the system, and a chlorine transfer reaction directly occurred between the two reagents. This mechanism might be the reaction pathway in chloroform because the formation of the chlorine cation from MC is not favored because of the low polarity of chloroform. Conclusions The chlorine transfer from a stable amine halamine bond to an imide bond to form the most active imide halamine was proved and should be the cause of improved durability and killing power of biocidal functions on DMDMH/MTMIO-treated fabrics. The chlorine transfer reaction follows a second-order reaction mechanism but is predominantly controlled by the concentration of MC. The rate constants of the chlorine transfer in the deionized water medium were in the range of 10-4-10-5 mmol/min at temperatures of 30-60 °C, and the activation energy was 25.6 kJ/mol. The chlorine transfer reaction from amine halamine to imide bond is a slow reaction. The reaction rate in the CHCl3 medium was higher than that in water. Acknowledgment This research was supported by an NSF CAREER award (Grant DMI 9733981) and financially sponsored by Vanson-HaloSource Inc. (Redmond, WA). Literature Cited (1) Sun, G.; Xu, X. Durable and Regenerable Antibacterial Finishing of Fabrics. Biocidal Properties. Text. Chem. Color. 1998, 30, 26-30. (2) Sun, G.; Xu, X.; Bickett, J. R.; Williams, J. F. Durable and Regenerable Antimicrobial Finishing of Fabrics with a New Hydantoin Derivative. Ind. Eng. Chem. Res. 2001, 41, 1016-1021. (3) Kaminski, J. J.; Bodor, N.; Higuchi, T. N-Halo Derivatives III: Stabilization of Nitrogen-Chlorine Bond in N-Chloroamino Acid Derivatives. J. Pharm. Sci. 1976, 65, 553-557.
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(4) Wayman, M.; Salamat, H.; Dewar, E. J. Chlorine Exchange Resins. Can. J. Chem. Eng. 1968, 46, 282-287. (5) Qian, L.; Sun, G. Durable and Regenerable Antimicrobial Textiles: Synthesis and Applications of 3-Methylol-2,2,5,5-tetramethyl-imidazolidin-4-one (MTMIO). J. Appl. Polym. Sci. 2003, 89, 2418-2425. (6) Qian, L.; Sun, G. Durable and Regenerable Antimicrobial Textiles: Improving Efficacy and Durability of Biocidal Functions. J. Appl. Polym. Sci. 2004, 91, 2588-2593. (7) William, D. E.; Elder, E. D.; Worley, S. D. Is Free Halogen Necessary for Disinfection? Appl. Environ. Microbiol. 1988, 54, 2583. (8) Naquib, I.; Tsao, T. C.; Sarathy, P. K.; Worley, S. D. Kinetic Versus Thermodynamic Control in Chlorination of Imidazolidin4-one Derivatives. Ind. Eng. Chem. Res. 1991, 30, 1669. (9) Naquib, I.; Tsao, T. C.; Sarathy, P. K.; Worley, S. D. Kinetic Study of the Halogenation of Imidazolidin-4-one Derivatives. Ind. Eng. Chem. Res. 1992, 31, 2046-2050. (10) Nelson, G. D. Chloramines and Bromamines. Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Wiley-Interscience: New York, 1979; p 565.
(11) Tsao, T. C.; Williams, D. E.; Worley, S. D. A New Disinfectant Compound. Ind. Eng. Chem. Res. 1990, 29, 21612163. (12) Tsao, T. C.; Williams, D. E.; Worley, C. G.; Worley, S. D. Novel N-Halamine Disinfectant Compounds. Biotechnol. Prog. 1991, 7, 60-66. (13) Worley, S. D.; Williams, D. E.; Barnela, S. B. The Stabilities of New N-Halamine Water Disinfectants. Water Res. 1987, 983. (14) Worley, S. D.; Williams, D. E. CRC Crit. Rev. Environ. Control 1988, 18, 133. (15) Espenson, J. H. Reactions with a Simple Kinetic Form. Chemical Kinetics and Reaction Mechanisms; McGraw-Hill: New York, 1981.
Received for review June 10, 2004 Revised manuscript received October 31, 2004 Accepted November 17, 2004 IE049493X
