Trends Biomater. Artif. Organs. Vol. 16 (1) pp 46-51 (2002) http://www.sbaoi.org ADSORPTION OF IODINE ON NYLON-6 Jai Paul Singhal and Alok R. Ray Centre for Biomedical Engineering Indian Institute of Technology New Delhi - 110 016 All India Institute of Medical Sciences New Delhi - 110 029 Antibacterial activity has been imparted to nylon-6 by adsorption of iodine. Iodine adsorption has been carried out by two ways: a) dipping nylon-6 fibers into solution of iodine in acetone and b) exposing nylon-6 fibers to iodine vapours. The amount of iodine adsorbed has been found to be very high as compared to theoretical amount of iodine required to form single layer on the surface of fibers. Iodine adsorption from solution in acetone does not follow Langmuir adsorption, but adsorption in vapour phase appears to follow pseudo-Langmuir adsorption isotherm. In case of adsorption of iodine from vapour phase, equilibrium is established between nylon-iodine complex and iodine vapours. However, in case of adsorption from solution, no such equilibrium appears to be established. This may be due to change in nature and ratio of different iodine species in the nylon-iodine complex. Possible mechanism of iodine adsorption has been discussed. INTRODUCTION additional iodine to give triiodide or pentaiodide ions. Iodine is well known for its antibacterial properties  and is used to impart The present study addresses the antibacterial activity to polymers [2-4]. adsorption of iodine on nylon both from solution Polymer-iodine complexes (i.e. iodophors) are and vapour phase and role of solvent on the widely used as antiseptic products during adsorption behaviour of iodine. surgical interventions [5-7]. The deficiency of EXPERIMENTAL iodine in human beings causes goiter, a Materials disease prevalent in hills of India. A controlled Un-pigmented multifilament braided release formulation of iodine can be used for nylon-6 (nylon-6) fibers (denier 44) were eradication of the iodine deficiency [8,9]. Iodine obtained from Modipon Limited, India. has also been used to remove biological Analytical grade acetone (BDH, India) and contaminations from water . Further, Iodine (E. Merck, India) were used without controlled release of iodine in water is likely to purification. improve its effectiveness as water disinfectant. The antibacterial activity of iodophors is exerted Methods by free iodine released from the complex that Iodine doping using solution subsequently binds to bacteria. So the Nylon fibers were doped with iodine by effectiveness of iodophor depends upon the immersing in acetone solution of iodine for 48 availability of free iodine that is directly related hours at room temperature. Iodine to the nature of iodine interaction with the concentration in the solution was varied from polymer. In iodophors, iodine may exist in 0.6 to 3.7 g/dl in the present study. The fibers various forms like 2, I-, I3-, I5-[11-13]. Nylon-6 I were removed from iodine solution, washed also forms iodophor by adsorbing iodine either twice with pure acetone, dried and weighed. from its solution or vapours phase. Nylon-6 can Iodine content of the fibers was estimated from adsorb Iodine either in molecular form or ionic the resulting weight increase of the fibers as form. The iodide ions can form complex with shown below. Increase in weight of Nylon fibers Percent iodine uptake = X 100 - (1) Original weight of Nylon fibers Iodine doping from vapours adsorption of Iodine from the aqueous solution in KI . Nylon-6 fibers were iodized by All the repeat units of nylon can form exposure to iodine vapours for period of eight adduct with iodine. However, adduct formation hours. The experiment was carried out in a is restricted by geometry of nylon material. It tube with constriction towards lower side. had been observed that iodine moles adsorbed Iodine was taken in the lower portion and nylon per mole of repeat units remains for less than fibers in the upper portion. Iodine was unity (fig. 3). Although adsorption does not vapourized by heating in water bath. System follow Langmuir equation, but iodine may be was cooled to room temperature and fibers adsorbed as molecular I or other forms such 2 were washed with acetone to remove the - as I, I3- etc. If iodine has been adsorbed as loosely held iodine from the surface of fibers. molecular iodine, following equilibrium will be Fibers were dried and weighed. Iodine uptake established was calculated from the increase in the weight of fibers using equation (1). Nylon-6 + I2 Nylon – RESULTS AND DISCUSSION Iodine adduct Adsorption of Iodine from solution (N6) (NI) It was observed from fig. 1 that nylon-6 [NI] adsorbs iodine from its solution and the amount KNI = - (3) [N6] [I2] of iodine adsorbed increased with the increase in concentration of iodine in the solution. Where KNI is the equilibrium constant, [N6] and However, increase in iodine adsorbed was not [NI] are the absorption sites and complex linear initially. Sukawa et al  have reported formed per mole of nylon repeat unit at linear increase in adsorption of iodine on nylon- equilibrium, and [I2] is the concentration of 6 from aqueous solution of iodine containing iodine in the solution. If ‘a’ and ‘r’ are the initial potassium iodide. This difference of adsorption number of adsorption sites and complex formed may be due to different solvent. The adsorption per mole of nylon repeat unit, after substitution behaviour of solute is generally explained by equation (3) can be rewritten as the empirical Freundlich adsorption isotherm, r KNI = - (4) x / m = k . cn - (2) (a-r) [I2] where x/m is the amount of solute adsorbed by 1 1 1 1 a given weight of adsorbent (micromoles/gm), c = x + - (5) r KNI . a [I2] a is the molar concentration of solution, and k and n are the constants for the given adsorbent Since KNI and a are constant for a given and solute. The values of k and n are system, so plot of 1/r vs 1/[I2] should be linear. determined by plotting log (x/m) vs log c. From It was found that in the present system of fig. 2 values of k and n are found to be 60400 iodine adsorption on nylon from iodine solution and 1.5625 respectively. According to Langmuir in acetone, plot of 1/r against 1/[I2] is not linear theory of unimolecular adsorption, value of n initially (fig. 4). Similar observation has also should be between zero and one. Since the been made for adsorption of iodine from value of n is found to be more than one, it aqueous solution . This deviation has been seems that iodine adsorption on nylons does attributed to either a large value of `a' with small not follow unimolecular adsorption. This value of KNI. This deviation may be due to observation is similar to that made for change in value of 'a' and 'K NI'. The change in number of adsorptions sites, 'a' and 'K NI' may be caused by change in structure of the iodine nylon adduct. Iodine is known to form complex with various polymers through lone Adsorption of Iodine from vapours pair of electrons . It appears that iodine Fig. 6 shows that nylon also adsorbs adsorption on nylon is not a simple physical iodine in vapour phase. It has been observed adsorption but a chemisorption. Several steps that the weight of iodine adsorbed on nylon might be involved in the iodine adsorption on fibers from vapour phase also does not nylons (fig. 5). In the first step iodine might increase linearly (fig. 6). Freundlich empirical interact with lone pair of electron on oxygen of equation for adsorption of gases on a solid amide group. Yamamoto et al. [16,17] has surface is given as reported that nylon-iodine adduct may undergo a transition to form iodide ion. Subsequently, x/m = k pn - (6) iodide ion may take up more iodine molecules to form polyiodide (I3-, I5-) ions [11-13]. This will where p is the pressure of gas adsorbed. increase the number of adsorptions sites and Pressure of iodine vapours is directly shift the equilibrium. Hence, both 'a' and 'K NI' proportional to the amount of iodine vapourized. will be affected. So, the equation may be written as x/m = k' Mn - (7) where M is the number of iodine moles vaporized and k' is the new constant. The values of k' and n for iodine adsorption from vapour phase has been found to be 40000 and 0.59 respectively using plot of log (x/m) vs log M (fig. 7). Unlike adsorption from solution, the value of n has been found to be less than unity. It appears that iodine adsorption follows Langmuir unimolecular adsorption theory. However, theoretical calculations shows that Adsorption of lodine on Nylon-6 49 the quantity of iodine required to form a single c oncluded that iodine absorption follows pseudo- Langmuir adsorption isotherm. It has also been observed that the number of iodine moles per mole of repeat unit remains for less than unity (fig. 8). Attempt has been to find equilibrium layer on the surface of nylon fibers is much constant ‘KNI‘ from equation (5) by taking less than that actually adsorbed. So it may be number of moles of iodine [M] vaporized in place of iodine concentration [I2]. 50 Jai Paul Singhal et. al. CONCLUSION From fig. 9, the value for equilibrium constant, Solvent plays an important role not KNI has been found to be 9.69 mol-1. only in determining the extent of iodine adsorption on nylon, but also on adsorption These observations indicate that the behaviour and iodine-nylon interactions. Solvent iodine adsorption from vapours is different from facilitates the change in nature of iodine that observed in case of adsorption from species adsorbed on nylon. solution. Solvent appears to play an important role by facilitating change in nature of iodine Acknowledgments adsorbed and affecting iodine-nylon interactions. In vapour phase, Iodine is This work has been supported by adsorbed on nylon mainly in molecular form. In Board of Research in Nuclear Sciences, the presence of solvent, iodine changes to ionic Department of Atomic Energy, Government of form, I-, that may form complex with more India. iodine molecules to form polyiodide ions like I3-, I5- etc. REFERENCES 1. Messager S., Goddard P. A., Dettmar P. W. and Maillard J. Y. : Determination of the antibacterial efficacy of several antiseptics tested on skin by an 'ex-vivo' test. J. Medical Microbiology 50(3) : 284-292 (2001). 2. Tyagi M., Singh S. and Singh H. : Iodinated natural rubber latex: preparation, characterisation & antibacterial activity assessment. Art. Cells, Blood Substitutes and Immobilization Biotechnology 28(6) : 521-533 (2000). 3. Lin K. J., Tani T., Endo Y., Kodama M. and Teramoto K.: Antimicrobial activities of iodinated polystyrene derivatives. Artificial Organs 20(11) : 1191-1195 (1996). 4. Singhal J. P., Singh J., Ray A. R., Singh H. and Rattan A. : Antibacterial multifilament nylon sutures. Biomater. Art. Cells Immob. Biotech. 19(3) : 631-648 (1991). 5. David A. T., Kurien S., Udupa N. and Verma B. R. : Formulation and evaluation of controlled release dental implants of povidone iodine for periodontitis. Ind. J. Dental Res. 5(3) : 101-104 (1994). 6. Lawrence J. C. : A povidone-iodine medicated dressing,. J. Wound Care 7(7): 332-336 (1998). 7. IsenbergL S. J. and Wood A. : A controlled trial of povidone-iodine as prophylaxis against ophthalmia neonatorum, Int. J. Gyne. Obst. 51(2) : 191-192 (1995). 8. Foo L. C., Zainab T., Goh S. Y., Letchuman G. R., Nafikudin M., Doraisingam P. and Khalid B. : Iodization of village water supply in the control of endemic iodine deficiency in rural Sarawak, Malaysia. Biomedical Environ. Sci. 9(2- 3) : 236-241 (1996). 9. Fisch A., Pichard E., Prazuck T., Sebbag R., Torres G., Gernez G.and Gentilini M. : A new approach to combating iodine deficiency in developing countries: the controlled release of iodine in water by a silicone elastomer. Am. J. Public Health 83(4) : 540-545 (1993). 10. Mazumdar N.A. and Singh H.: Inactivation of Escherichia coli in waterby iodine containing polymer. Water supply Res. Tech.-Aqua 42(3): 351-356 (1993). 11. Faria D. L. A. de, Gil H. A. C. and de Queiróz A. A. A. : The interaction between polyvinylpyrrolidone and I2 as probed by Raman spectroscopy. J. Molecular Struc. 478(1-3): 93-98 (1999). 12. Brown I. M. and Wilbur J. M. : Charge transfer complexes of a conjugated oligomers with iodine evidence for polaron, bipolaron and ionized bipolaron formation. Macromolecules, 21(6): 1859-1863 (1988). 13. Murthy N. S. : Structure of iodide ions in iodinated nylon-6 and the evolution of hydrogen bonds between parallel chains in nylon-6. Macromolecules, 20(2) : 309-316 (1987). 14. Sukawa H., Yoda Y., Sugimoto H., Yoshida S., Yamamoto T., Kuroda S., Sanechika K. and Hishinuma M. : Absorption of iodine by polymers and electrochemical response of polymer film in aqueous solution of iodine. Polym. J., 21(5) : 403-408 (1989). 15. Yamamoto T. and Kuroda S. : Iodine-polymer adducts as active materials for positive electrodes of galvanic cells. J. Electroanal. Chem., 158 : 1-11 (1983). 16. Yamamoto T., Sugimoto H. and Hishinuma M. : Electrical conductivity of iodine adducts of nylon 6 and other non- conjugated polymers. J. Mater. Sci., 21(2) : 604-610 (1986). 17. Yamamoto T., Hishinuma M. and Yamamoto A.: Lithium-iodine solid electrolyte galvanic cells using iodine adducts of nylon-6 as active material for positive electrodes. J. Electroanal. Chem., Interfacial Electrochem. 185(2) : 273- 284 (1985).
Pages to are hidden for
"ADSORPTION OF IODINE ON NYLON-6"Please download to view full document