Safaa G. Abd Allaa, Murat. Senb , and Abdel Wahab M. El-Naggara

Radiation Synthesized Super Absorbent Hydrogels Based on Natural Polymer Tara Gum (TG) and Acrylic acid: Swelling and Mechanical Properties Safaa G. Abd Allaa, Murat. Senb , and Abdel Wahab M. El-Naggara

Radiation Chemistry Department, National Center for Radiation Research and Technology, Cairo, Egypt.a Department of Chemistry, Hacettepe University, Beytepe, Ankara, 06532, Turkey.b

Abstract In this study, radiation synthesis and characterization of swelling behavior and network structure of tara gum/acrylic acid (TG/AAc) super adsorbent hydrogels were investigated. Natural-synthetic hybrid TG/AAc hydrogels were prepared by irradiating the ternary mixtures of natural polymers tara gum and synthetic monomer acrylic acid in the presence of crosslinking agent, N,N`-methylene bisacrylamide (MBAAm) by gamma rays at ambient temperature in order to develop a new super adsorbent system especially for using in diaper applications. In order to develop materials for diaper application, we have prepared hydrogels based on Tara gum (TAG) / acrylic acid (AAc) by radiation-induced crosslinking in presence of N,N`-methylene bisacrylamide (MBAAm) as crosslinker. The polymeric networks formed were characterized by FTIR and evaluated by swelling studies as a function of crosslinking agent concentration, temperature and nature of the swelling medium. The swelling kinetics of the hydrogels were discussed in terms of the diffusion exponent "n" and the diffusion coefficient "D". The results showed that the water diffusion to hydrogels is a non-Fickian type diffusion and the diffusion coefficients varied from 4108 and 2.83108 m2min-1. Mechanical measurements (stress-strain) curves of hydrogels were evaluated to calculate the shear modulus values and the average molecular weight between cross-links (Mc). Moreover, the absorption under load at 37oC of saline water and urea aqueous solutions (as a major component of urine) by TG/AAc hydrogels was determined.

1. Introduction Super absorbent polymer (SAP) hydrogels are special polymeric material that can absorb large amounts of water, saline solutions or physiological fluids as high as 10- 1000 times their own weight due to a considerable hydrophilic groups in their structure. The super-swelling characteristics of SAPs make them ideal for use in water absorbing applications such as disposable diapers, feminine napkins, agriculture, cosmetic and absorbent pads and as an absorbent in environmental applications for the removal of some undesired agents such as heavy metal ions and dyes. [1- 8]. Because of their exceptional properties i.e. biocompatibility, biodegradability and non-toxicity, polysaccharides and proteins are the main part of the natural-based super absorbent hydrogels. Desired features of superabsorbents are swelling capacity, high swelling rate and strength of the swollen gel. The majority of reports on super absorbents cover the first and second features mentioned, i.e. high absorbency and high swelling rate. However, there are few studies on the swollen gel strength consideration [9,10]. When the super absorbents are under load, the swelling capacity is decreased. So, another parameter, i.e. absorbency under load (AUL) is defined and reported especially in technical data. Usually in the basic scientific literature the values of load-free absorbency (free swelling) are given, but AUL is the more real values. Since AUL are logically changed in proportion to mechanical strength of the swollen gel, AUL can be considered as a measure of the gel strength of SAPs. So, many efforts have been made to achieve super absorbents having higher AUL or higher strength of the swollen gel [11-13]. The properties of specific SAPs are extremely important for selecting a material for a given application. The properties are highly dependent on the environmental swelling conditions. It is imperative that SAPs properties are precisely determined under conditions as close to the real circumstances as possible. Tara gum is a low cost polysaccharide extracted from the Tara tree (Caesalpinia spinosa) by grinding the endosperm of the seeds. This polysaccharide is composed mainly of galactomannans [14]. The principal component consists of a linear chain of - (1-4) mannan (M) backbone with - D-galactose (G) branches attached by (1-6) linkages; the ratio of mannose to galactose in Tara gum is 3:1. Tara gum is listed as a food additive by the Codex Committee on Food Additives and Contaminants (CCFAC), with the INS (International Numbering System) as number 417 and with technical functions listed as thickener and stabilizer [15]. Tara gum also has a synergistic effect when used in combinations with other gums (such as guar and locust bean gums) to produce improved gel and colloid stabilities and properties.

2 Thus, the aim of this article is to prepare a new super absorbent Tara gum-based hydrogels by gamma radiation to be used in diaper applications.

2. Experimental 2.1. Materials and chemicals Tara gum (TG) was obtained by Sigma-Aldrich, whereas the monomer acrylic acid (AAc) was obtained from Merck Chemical Company, Germany. Methylene bisacrylamide (MBAAm) as a cross-linking agent was obtained from B.D.H (Poole, UK). Urea was provided from B.D.H (Poole, UK). All the chemicals were used as received without purification or further treatment. Distilled water was used for the hydrogel preparation.

2.2. Preparation of (TG) hydrogels The hydrogels were prepared by dissolving 2 wt % of TG gum and 0.4 ml of acrylic acid in water with 2 or 4 wt% of N,N`-methylene bisacrylamide (based on weight of acrylic acid). The homogenous viscous solutions were placed in PVC straw of 3 mm diameter and irradiated to 14.5 kGy in air at ambient temperature. Irradiation was carried out in the Gamma cell 220 type 60Co- gamma irradiator in Ankara, Hacettepe University. Hydrogels obtained in long cylindrical shapes were cut into pieces of 4-5 mm long and dried in air. The hydrogels were stirred for one day in distilled water to remove the soluble fractions and were then dried first in air and then in vacuum oven at 40oC.

2.3. FT-IR spectroscopy The infrared spectra of TG/AAc and pure AAc hydrogels were performed on a Mattson 5000 FT-IR spectrometer over the 500-4000 cm-1 range. Samples were ground to a very fine powder and mixed with a highly dried KBr powder, and then pressed to obtain transparent disks.

2.4. Swelling measurements Dry weight of hydrtogels (2-3 mm thickness, 3 mm diameter) was left to swell in different media [water, aqueous sodium chloride (0.5% w/v) and aqueous urea (2%w/v)] in room temperature and at 37oC. Swollen gels were removed from the swelling medium at regular time intervals and dried superficially with filter paper,

3 weighed and placed in the same medium. The measurements were continued until a constant weight was reached for each sample. The percentage swelling (S) was determined by using equation (1).

S ( % ) = [(mt – mo / mo)]  100 (1)

Where mo is the initial dry weight and mt is the weight of a swollen gel at time t.

2.5. Compression measurements Elastic properties and shear modulus of hydrogels were determined by using a Zwick Z010 model universal Testing Instrument and uniaxial compression module. The crosshead speed was 5 mm/min and 1kN load cell. After adjusting the experimental parameters, each measurement was performed at less than 1 minute to avoid the release of water from the hydrogel during the testing. The recorded results are the average of measurements (four times for each gel). However, before measuring, the gels were maintained in water until equilibrium at room temperature. The force necessary for compressing the hydrogels at 1 mm The magnitude of strain percentage at deformation was recorded and the stress values () were determined by using of the following equation [16]:  = F / A (2) Where, F is the force, and A is the cross-sectional area of the strained specimen.

2.6. Stress – strain measurements The parameters generated by the instrument are force and displacement. These information were then converted to elastic modulus (G), by the use of the following equation [17,18]:  = G (-2) (3) Where  is relative deformation of the specimen. The (-2) is the strain calculated from the following equation [18].

 = L/Lo (4)

Where L is the deformation of the sample and Lo is the initial sample length.

2.7. Absorbance under load (AUL) Measurement

4 A macro porous sintered glass filter plate (d=100 mm, h=7 mm) was placed in a Petri dish and the dry hydrogel sample was uniformly placed on the surface of a polyester gauze located on the sintered glass. A cylindrical solid weight (d=80 mm, variable height) which could slip freely in a glass cylinder was used to apply the desired load (applied pressure=0.6 psi) to the dry hydrogel particles as shown in scheme 1. The sample was then covered by 0.5% saline solution such that the liquid level was equal to the height of the sintered glass filter.

Scheme.1. Absorbency under load (AUL) tester.

The dish and its contents were covered to prevent surface evaporation and probable change in the saline concentration. The swollen particles were weighed at regular time intervals and AUL was calculated by using equation (5).

AUL (g/g) = W2 – W1 / W1 (5)

Where, W1 and W2 represent the weight of dry and swollen hydrogel, respectively.

3. Results and discussion 3.1. Composition of TG/AAc networks. When pure acrylic acid (AAc) monomer was irradiated with gamma rays, polymerization and cross-linking reactions took place simultaneously. The total dose required for gelation was determined to be 14.5 kGy. When an aqueous solution of Tara gum/acrylic acid monomer is exposed to gamma irradiation, free radicals are formed on the chains of both species. Also, the radiolysis products of water especially

5 hydroxyl free radicals, are very effective in generating free radicals on both AAc monomer and Tara gum polymer. Therefore, AAc is polymerized and crosslinking in the presence of TG gum chains and leads to the formation of semi-interpenetrating network structure.

OH HO

H H H OH

OH H H O

H O

HO OH HO O H OH H HO H OH O H H O HO O HO H H O H OH + CH2= CH-COOH H H H H HO H H

gamma radiation

Scheme.2. Representation of the chemical reaction between TG and AAc together with a photograph of the obtained hydrogel.

To decrease the gelation dose and increase the crosslinking density, N,N`- methylene bisacrylamide (MBAAm) as crosslinking agent was added to the mixture. The hydrogels obtained in the presence of 2 and 4 wt % (MBAAm) were very stable and showed uniform swelling properties in all solvents. Table.1. shows the effect of acrylic acid concentration on the gelation percent of TG/AAc and pure AAc hydrogels formed by gamma irradiation of aqueous solutions at a dose of 14.5 kGy. It can be seen that the increase of AAc weight fraction in the initial feeding mixture causes an increase in the gel percent.

3.2. FT-IR spectroscopy FTIR spectra of TG/AAc and pure AAc hydrogels with 2 and 4 wt% MBAAm are presented in Figs.1 and 2, respectively. The following points can be addressed: (1)

6 The broad absorption bands at 3412 cm-1 due to –OH stretching of the hydroxyl group in pure AAc hydrogels were shifted towards lower wavelength in the TG/AAc hydrogels. This shift is attributed to the formation of inter/intra molecular hydrogen bonding [19]. (2) The intensity of absorption band at 2925 cm-1 assigned to the C-H stretching of CH2 groups, is increased in the IR spectrum of TG/AAc hydrogels due to the occurance of crosslinking reaction. (3) The absorption bands at 1730 cm-1 due to the C=O groups present in pure AAc hydrogels has been observed with increased intensity in the spectrum of TG/AAc hydrogels. (4) The absorption bands at 1169, 1247 and 1449 cm-1 due to the stretching vibration of C-O in the rings, C-OH stretching, and stretching vibration of C-O-C in the repeating units of TG can be seen clearly in the spectrum of the hydrogel. This finding indicates the TG present in the hydrogel in a non-crosslinked form and that the formed networks is a mixture of interpenetrating and semi-interpenetrating structure.

3.3. Swelling characteristics of hydrogels A fundamental relationship exists between the swelling of a polymer in a solvent and the nature of the polymer and the solvent. Swelling kinetics of TG/AAc and pure AAc hydrogels prepared by radiation were studied as a function of crosslinking agent concentration and temperature in three media. To determine the mechanism of swelling, diffusion exponent "n" and diffusion coefficient "D" were evaluated in the case of swelling in water at room temperature.

3.3.1. Swelling in water Swelling kinetics of the hydrogels based on TG/AAc mixtures and pure AAc in water at different temperatures by using different concentrations of crosslinking agent are shown in Figs.3 and 4, respectively. The figures show that the swelling increases with time up to a certain value and then tend to level off especially at room temperature. The maximum swelling values reached with the TG/AAc hydrogels were relatively lower compared with pure AAc hydrogel prepared with the same crosslinking agent weight percent and temperature. The following equation was used to determine the nature of diffusion of water into hydrogels [20].

n F = Mt / M = kt (6)

7 Where Mt and M denote the amount of solvent diffused into the gel at time t and infinite time (at equilibrium), respectively, "k" is a constant related to the structure of the network, and the exponent "n" is a number determines the type of diffusion. Based on the relative rate of diffusion of water into polymer matrix and rate of polymer chain relaxation, swelling of polymers has been classified into three types of diffusion mechanisms [21,22]. These mechanisms are Case I simple Fickian diffusion, Case II diffusion, and Case III Non-Fickian or Anomalous diffusion. Simple Fickian diffusion is characterized by n=0.5, while case II diffusion is characterized by n=1 and Non-Fickian diffusion is characterized by n between 0.5-1. Equation 8 is applied to the initial stages of swelling for the hydrogels based on pure AAc and TG/AAc mixtures and plots of log Mt / M versus log t yield straight lines as shown in Fig.5. The exponent "n" and "k" were calculated from the slope and the intercept of the lines as shown in Table.2. The values in this table show that assumes values of "n" are between 0.56 and 0.65 and that the lower the crosslinking density the more non-Fickian swelling behavior of the hydrogels [23]. This can be explained as the dominance of solvent diffusion rate is over the relaxation rate of polymer chains in between crosslinking sites, i.e. the slow relaxation rate of the hydrogel. The study of water transport through hydrogels is important for better understanding of transport phenomena of aqueous solutes through these matrices. The diffusion coefficient of water can be calculated by various methods [24,25]. The short-time approximation method is used for the determination of diffusion coefficient of water and is valid for the initial 60% of swelling. The diffusion coefficient of water from the cylindrical hydrogels is calculated by the following relation [26 ]:

2 1/2 2 2 3/2 F = Mt / M = 4 (Dt /  r ) -  (Dt /  r ) – ( /3)(DT /  r ) + …. (7)

Where D is the diffusion coefficient, t is the time and r is the radius of cylindrical hydrogel sample. The diffusion coefficient of water in TG/AAc and pure AAc hydrogels can be calculated from the slope of the lines of the plots of Mt / M versus t1/2 as shown in Fig.6. The values of the diffusion coefficient varied from 2.83 10-8 to 5.07 10-8 m2min-1 as shown in Table 2. As expected, the diffusion coefficient increases with increasing the percentage swelling of the hydrogels in water.

8 3.3.2. Swelling in urea and saline solutions The swelling kinetics of the hydrogels based on TG/AAc and pure AAc in urea aqueous solution at different temperatures and by using different concentrations of crosslinking agent are shown in Figs.7 and 8. The figures show that the swelling increases with time continuously due to super absorbent character of these hydrogels, in which the samples almost reach do not reach to the equilibrium state after 9000 minutes. In this regard, the highest swelling (%) for TG/AAc-2wt%MBAAm at 37oC in urea solution is ~7500% while for pure AAc-2wt%MBAAm at 37oC is ~ 27000%. This big difference in the swelling (%) is due to the higher hydrophilicity and lower crosslink density of pure AAc hydrogels than that of TG/AAc hydrogels. It should be noted that pure AAc hydrogels after this time ruptured and can not controlled, which is most probably due to increase of the inhomogeneous distribution of crosslinks within the hydrogel. The internal pressure developed upon swelling of inhomogeneous network structure may be responsible for the poor mechanical properties of pure AAc hydrogels. On the other hand, the values of the swelling (%) of TG/AAc and pure AAc hydrogels in urea solution are higher than the swelling (%) of the hydrogels in water. The highest swelling (%) for TG/AAc-2wt%MBAAm at 37oC in water was ~ 4000%, while in urea solution reaches ~ 7500%. Also, the highest swelling (%) for pure AAc- 2wt%MBAAm at 37oC in water was 10000%, while in urea ~ 27000%. The reason for this difference is the hydrophilic character of urea molecules. Urea molecule has got more hydrophilic sites, as NH2 and C=O [27].

3.3.3. Swelling in NaCl To study the effect of salt concentration, the swelling of the hydrogels was carried out in 0.5% NaCl at room temperature and at 37oC. The swelling kinetices of the TG/AAc and pure AAc hydrogels in the NaCl solution are shown in Figs.9 and 10. The swelling (%) of all the hydrogels is lower than that in distilled water and urea aqueous solution.

3.4. Molecular weight between crosslinks For the characterization of the network structure and determination of molecular weight between crosslinks (Mc) of prepared hydrogels, the swelling in

9 water experiments were continued until a constant value of swelling was reached. The weight of the swollen hydrogels was used to calculate the polymer volume fraction in swollen gel (2m) by using Eq.8.

-1 1/ 2m = (1+ / w (W -1)) (8)

Where  and w are the densities of dry gel and water, whereas W is the weight of the hydrogel at equilibrium. The values of 2m for TG/AAc and pure AAc hydrogels are listed in Table3. At the end of the swelling experiments, uniaxial compression was applied on the swollen gel. Typical stress-strain curves of hydrogels are given in Fig.11. As can be seen from the figure, the magnitude of stress increases with increasing MBAAm ratio in the initial feeding solution of hydrogels at a given strain. Also, the magnitude of stress of TG/AAc hydrogels is much higher if compared with that of pure AAc hydrogels. Shear modulus values of hydrogels were calculated by using the elastic deformation theory and Eq.3. [28]. When equation 3 is applied to the initial stages of deformation, the plots of stress versus (--2) yield straight lines as shown in Fig.12. The G value was calculated from the slope of the lines as shown in Table 3. By using G values and other relevant experimental parameters, the average molecular weight values were calculated by using Eq.9. (Table.3).

2/3 1/3 G =  / (Mc) RT 2r 2m (9) Where  is the polymer density, R is the universal gas constant, T is the temperature and 2r is the polymer volume fraction in the relaxed state, i.e. after crosslinking but before swelling. As shown in Table 3. the average molecular weight between crosslink (Mc) of TG/AAc and pure AAc hydrogels decrease with increasing the ratio of MBAAm. The TG/AAc hydrogels have (Mc) lower than that of pure AAc hydrogels.

3.5. Absorbance under load (AUL) To determine the swollen gel strength, we used TG/AAc-2wt%MBAAm hydrogel to absorb saline and urea solution under 0.6 psi load and without load at temperature 37oC as shown in Fig.13. As can be seen from figure the % swelling of hydrogels in saline solution under 0.6 psi load is lower then swelling in zero pressure. On the other hand, the effect of pressure is relatively low in urea solution due to abruptly swelling of hydrogels in this solution. The results of AUL

10 showed that using 0.6 psi pressure during the swelling of the TG/AAc-2wt%MBAAm hydrogel did not highly change the swelling (%) up to 6 hours.

4. Conclusions A new super absorbent hydrogel based on Tara gum with acrylic acid has been synthesized by gamma irradiation. The swelling behaviors of the prepared hydrogels including sensitivity to the solvents were studied. So far in all relevant literature, the swelling capacity values of super absorbent polymers are reported as free-swelling data, i.e. load free swelling. It is obvious that the swelling conditions, and hence the data, are not real, because in all of the super absorbent polymers applications (agricultural, hygienic, etc.), the swelling particles must absorb aqueous solutions while they are under pressure, e.g. the weight of baby, soil, etc. In the present work, we experimentally evaluated the swollen gel strength using the absorbency under load (AUL) test and the compression mechanical test. Swelling capacity of the TG/AAc hydrogel (absorbed saline and aqueous urea solution under pressure of 0.6 psi) was measured at 37oC and show that: the presence of 0.6 psi pressure did not change the swelling capacity of hydrogels up to 6 hours in urea solution which is the major component of urine. Results of mechanical properties shows that: the presence of Tara gum with acrylic acid in the hydrogel was accompanied by an increase in the crosslink density. The increase in the crosslink density appear in the increase in the elastic modulus which is inherent to the more rigid structure. Consequently, due to high mechanical properties and anomalous swelling the natural/synthetic hybrid hydrogel systems prepared in this study can be considered as potential adsorbents for the body fluids such as urine and blood and may be used especially as diapers.

Acknowledgements Authors would like to thank Prof. Dr. Olgun Guven for the laboratory facilities he supplied and for his encouraging. The authors gratefully acknowledge the support provided by the International Atomic Energy Agency through the technical cooperation project EGY/8/020.

11 References [1] P.O. Riccardo, J.Macromol.Sci., Rev. Macromol. Chem. Phys. 34 (1994) 607. [2] V. Kudel, Encyclopedia of Polymer Science and Engineering, 2nd ed., Vol.7. New York: Wiley; 1985. 378. [3] A. Pourjavadi, M.Ayyari, M.S.Amini-Fazl, European polymer journal, 44 (2008) 1209. [4] A.S. Hoffman, Adv.Drug Deliv.Rev., 43 (2002) 3. [5] T. Kissel, Y. Li, U. Unger, Adv.Drug Deliv.Rev., 54 (2002) 99. [6] D. Saraydın, E. Karadağ , O. Güven, Sep. Sci. Technol., 31, (1996) 423. [7] D. Saraydın, E. Karadağ , O. Güven, Sep. Sci. Technol., 31 (1996) 2359. [8] D. Saraydın, E. Karadağ , O. Güven, Sep. Sci. Technol., 30 (1995) 329. [9] M. Sen and M. Sari, European polymer journal, 41 (2005) 1304. [10] N. Mahmudi, M. Sen, S. Rendevski, O. Guven, Nuclear Instruments and Methods in Physics Research B, 265 (2007) 375. [11] F.L. Buchholz, T. Graham, Modren Super ansorbent Polymer Technology, Wiley-VCH, New York, 1998, 1. [12] K. Kabiri, M.J. Zohuriaan-Mehr, Polym. Adv. Technol., 14 (2003) 438. [13] J.Qin, US Patent 5470964, 1995. [14] M.C.I. Dea and A. Morrison, Advances in Carbohydrate Chemistry, Biochemistry, 31 (1975) 29. [15] T.M. Kounga, A. Aotearoa, Food Standards Australlia New Zealand, Final assessment report, 2006. [16] R. de Paula, J.Rodrigues, Carbohydrate Polym., 26 (1995) 177. [17] E. Muniz, G. Geuskens, Macromolecules, 34 (2001), 4480. [18] G. Ferruzzi, N.Pan, W. Casey, Soil Sci., 165 (2000) 778. [19] S. Kumaresh , R. Anandrao, M. Tejraj, Journal of Controlled Release, 75 (2001) 331. [20] J. Crank, Mathematics of Diffusion, Oxford university press, Oxford, 1970. [21] P.L. Ritger and N.A. Peppas, Journal of Controlled Release, 5 (1987) 23. [22] P.L. Ritger and N.A. Peppas, Journal of Controlled Release, 5 (1987) 37. [23] M. Sen, N. Pekel, O. Guven, Die Angewandte Makromolekulare Chemie, 257 (1998) 1. [24] Y. Li, T. Tanka, J. Chem.Phys., 92 (1990) 1365.

12 [25] A.Y. Polishchuk, G.E. Zaikov, J.H. Petropoulos, Int.J. Polym.Mater., 19 (1993) 1. [26] N.A. Peppas, R. Gurny, E. Doelker, D. Buri, J.Membr.Sci., 7 (1980) 241. [27] E.Karadag, O.B. Uzum, D. Saraydin, O. Guven, Materials & Design, 27 (2006) 576. [28] J.E. Mark, Erman, (editors), Rubber like Elasticity a Molecular Primer, New York:Wiley; 1988.

13 Table 1: The effect of weight fractions of AAc monomer, and the weight % of the crosslinking agent in the feed solutions on the % gelation.

Gelation (%) TG/AAc Pure AAc Weight 0 wt% of 2 wt% of 4 wt% of 2 wt% of 4 wt% of fraction MBAAm MBAAm MBAAm MBAAm MBAAm of AAc 0.954 89 98.7 98.7 93.6 96.2 0.913 81 94 95 94 96 0.84 75 91 93.5 95 97

14 Table.2. Kinetic parameters of the swelling in water for pure AAc and TG/AAc hydrogels.

Hydroel n K 100 D 108 m2min-1 AAc-2wt%MBAAm 0.654 1.79 4.01 TG/AAc-2wt%MBAAm 0.635 2.46 5.07 AAc-4wt%MBAAm 0.625 2.15 4.3 TG/AAc-4wt%MBAAm 0.560 1.91 2.83

15 Table.3. The structural properties of TG/AAc and pure AAc hydrogels.

   G(kPa) Hydrogel 2m 2r M c Pure AAc-2wt 0.3062 0.0604 1.02 8.9 29600 %MBAAm Pure AAc-4wt 0.2207 0.0611 1.04 14.8 16400 %MBAAm TG/AAc-2wt 0.0996 0.0554 1.05 30.2 5800 %MBAAm TG/AAc-4wt 0.0551 0.0280 1.02 45.7 1950 %MBAAm %

e c n a t t i m s n a r T 8 0 6 7 . 7 3 6 9 1 ( 1 ) . 2 1 3 5 1 4 6 5 4 . . 4 9 3 9 7

6 0 7 3 1 1 . 1 (2 ) 5 6 9 2 . 0 9 9 . 2 4 7 4 0 1 4 3 9 2 2 5 . . 7 9 0 4 6 5 2 1

4 0 . 1 1 2 1 4 3 7 3 4 . 2 . 6 0 2 3 9 7 2 1

2 0

3 5 0 0 3 0 0 0 2 5 0 0 2 0 0 0 1 5 0 0 1 0 0 0 5 0 0

16 Fig. 1 Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

17 Safaa G. Abd Alla, G. Alla, Safaa Abd Fig. 2 Transmittance % 0 3 0 4 0 5 0 6 0 7 0 8 0 9 Murat. Sen, 0 0 5 3

3412.50 ) 3 ( ) 4 ( 3234.75 0 0 0 3 and Abdel Wahab M. Abdel Wahab El-Naggar and

2926.43 2926.88 18 0 0 5 2

2533.88

2378.68

2167.76 0 0 0 2

1730.27 1723.22 0 0 5 1

1531.93 1524.78

1449.61 1409.46

1247.29

1169.52 1163.56 0 0 0 1

799.46 0 0 5

492.44

4500 4000 2% MBAAm-room temp. 4% MBAAm-room temp. 3500 2% MBAAm -37oC 4% MBAAm -37oC 3000 ) % (

2500 g

n i l l 2000 e w

S 1500 1000 500 0 0 100 200 300 400 2000 4000 6000 8000 10000 Time (min.)

Fig. 3 Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

12000 2% MBAAm-room temp. 10000 4% MBAAm-room temp. 2% MBAAm-37oC 4% MBAAm-37oC 8000 ) % (

g 6000 n i l l e

w 4000 S

2000

0 0 100 200 300 400 2000 4000 6000 8000 10000 Time (min.)

Fig. 4 Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

20 0.0

-0.2 1-TAG/AAc-4wt%MBAAm 2-TAG/AAc-2wt%MBAAm 3-pure AAc-2wt%MBAAm -0.4 4-pure AAc-4wt%MBAAm ) -0.6 M / t M

( -0.8

g o l -1.0 1 2 3 -1.2 4

-1.4 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 log t

Fig. 5 Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

0.50 1-TAG/AAc-4wt%MBAAm 0.45 2-pure AAc-4wt%MBAAm 3-pure AAc-2wt%MBAAm 1 0.40 4-TAG/AAc-4wt%MBAAm 2 0.35

) 3

 0.30 M

0.25 4 M ( 0.20 0.15 0.10 0.05 3 4 5 6 7 8 9 10

(t1/2)

Fig. 6 Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

8000

7000 2wt% MBAAm-room temp. 4wt% MBAAm-room temp. o 6000 2wt% MBAAm-37 C 4wt% MBAAm-37oC 5000 ) % (

g 4000 n i l l e

w 3000 S 2000

1000

0 0 50 100 150 200 250 300 350 2000 4000 6000 8000 10000 Time (min.)

Fig. 7 Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

28000 2wt % MBAAm-room temp. 24000 4wt% MBAAm-room temp. 2wt% MBAAm-37oC 20000 4wt% MBAAm -37oC ) % (

g 16000 n i

l l

e 12000 w S 8000

4000

0 0 50 100 150 200 250 300 350 2000 4000 6000 8000 10000 Time (min.)

Fig. 8 Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

1400 1300 2wt% MBAAm-room temp. 1200 4wt% MBAAm-room temp. 1100 2wt% MBAAm -37oc 1000 4wt% MBAAm -37oC

) 900 % (

800 g

n 700 i l l 600 e

w 500 S 400 300 200 100 0 0 50 100 150 200 250 2000 4000 6000 8000 10000 Time (min.)

Fig. 9 Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

2500 2wt% MBAAm-room temp. 4wt% MBAAm-room temp. o 2000 2wt% MBAAm-37 C 4wt% MBAAm-37oC )

% 1500 (

n i l l e 1000 w S

500

0 0 100 200 300 400 2000 4000 6000 8000 Time (min.)

Fig. 10 Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

6000 TAG/AAc-2% MBAAM TAG/AAc-4% MBAAM 5000 AAc-2% MBAAM AAc-4% MBAAM 4000 ) a P k (

3000

s s e r t 2000 S

1000

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Strain (%)

Fig. 11 Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

27 250

4 1) AAc-2%MBAAm 2) AAc-4%MBAAm 200 3) TG/AAc-2%MBAAm 4) TG/AAc-4%MBAAm ) a

P 150 3 k (

s s e r t 100 S

50 1

0 0 1 2 3 4 5 6

(--2)

Fig. 12. Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

20 18 Saline-0.6 psi Urea-0.6 psi 16 Saline-0.0 psi Urea- 0.0 psi 14 ) ) 12 g / g (

10 L

U 8 A ( 6 4 2 0 0 50 100 150 200 250 300 350 400 Time (min.)

Fig. 13. Safaa G. Abd Alla, Murat. Sen , and Abdel Wahab M. El-Naggar

29 Captions for the figures

Fig.1. FTIR Spectra of (1) pure AAc- 2 wt % MBAAm and (2) TG/AAc-2 wt %MBAAm hydrogels.

Fig.2. FTIR Spectra of (3) pure AAc- 4 wt% MBAAm and (4) TG/AAc-4 wt %MBAAm hydrogels.

Fig.3. Swelling curves of TG/AAc hydrogels in water at room temperature and 37 ºC The amount of crosslinking agent, MBAAm, in initial mixture is indicated in the insert.

Fig.4. Swelling curves of pure AAc hydrogels in water at room temperature and 37 ºC The amount of crosslinking agent, MBAAm, in initial mixture is indicated in the insert.

Fig.5. Plots of log Mt / M∞ versus log t for TG/AAc and pure AAc hydrogels.

½ Fig.6. Plots of Mt / M∞ versus t for TG/AAc and pure AAc hydrogels.

Fig.7. Swelling curves of TG/AAc hydrogels in aqueous urea solution (2% w/v) at Room temperature and 37 ºC.

Fig.8. Swelling curves of pure AAc hydrogels in aqueous urea solution (2% w/v) at Room temperature and 37 ºC.

Fig.9. Swelling curves of TG/AAc hydrogels in NaCl aqueous solution (0.5% w/v) at room temperature and 37 ºC.

Fig.10.Swelling curves of pure AAc hydrogels in NaCl aqueous solution (0.5%) at room temperature and 37 ºC.

Fig.11. Strain versus stress curves of TG/AAc and pure AAc hydrogels.

Fig.12. (--2) versus stress curves of TG/AAc and pure AAc hydrogels.

Fig.13. Time dependence of the AUL values for TG/AAc-2wt% MBAAm hydrogel swollen in saline and urea solution at 37oC (under 0.6 psi) and free load.