polyester nonwoven fabric functionalization for metal ion adsorbent synthesis via electron beam-induced emulsion grafting

Radiation Physics and Chemistry 90 (2013) 104–110

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Abaca/polyester nonwoven fabric functionalization for metal ion adsorbent synthesis via electron beam-induced emulsion grafting Jordan F. Madrid a,n, Yuji Ueki b, Noriaki Seko b a b

Chemistry Research Section, Philippine Nuclear Research Institute, Diliman, Quezon City, Philippines Environmental Polymer Group, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Watanuki, Takasaki City, Gunma, Japan

H I G H L I G H T S








An amine type adsorbent from abaca/polyester nonwoven fabric was synthesized. Pre-irradiation method was used in grafting glycidyl methacrylate on nonwoven fabric. Radiation-induced grafting was performed with monomer in emulsion state. The calculated adsorption capacity for Cu2+ is four times higher than Ni2+ ions. Grafted adsorbent can remove Cu2+ faster than a chemically similar commercial resin.

art ic l e i nf o

a b s t r a c t

Article history: Received 26 February 2013 Accepted 4 May 2013 Available online 14 May 2013

A metal ion adsorbent was developed from a nonwoven fabric trunk material composed of both natural and synthetic polymers. A pre-irradiation technique was used for emulsion grafting of glycidyl methacrylate (GMA) onto an electron beam irradiated abaca/polyester nonwoven fabric (APNWF). The dependence of degree of grafting (Dg), calculated from the weight of APNWF before and after grafting, on absorbed dose, reaction time and monomer concentration were evaluated. After 50 kGy irradiation with 2 MeV electron beam and subsequent 3 h reaction with an emulsion consisting of 5% GMA and 0.5% polyoxyethylene sorbitan monolaurate (Tween 20) surfactant in deionized water at 40 1C, a grafted APNWF with a Dg greater than 150% was obtained. The GMA-grafted APNWF was further modified by reaction with ethylenediamine (EDA) in isopropyl alcohol at 60 1C to introduce amine functional groups. After a 3 h reaction with 50% EDA, an amine group density of 2.7 mmole/gram adsorbent was achieved based from elemental analysis. Batch adsorption experiments were performed using Cu2+ and Ni2+ ions in aqueous solutions with initial pH of 5 at 30 1C. Results show that the adsorption capacity of the grafted adsorbent for Cu2+ is four times higher than Ni2+ ions. & 2013 Elsevier Ltd. All rights reserved.

Keywords: Abaca/polyester nonwoven fabric Emulsion graft polymerization Glycidyl methacrylate Electron beam Adsorption

1. Introduction Radiation-induced grafting is widely used for expanding the utilization of synthetic and natural polymeric materials. This was achieved by modifying the original polymers through introduction of graft chains from different types of monomers. Vinylic monomers were successfully grafted onto synthetic materials like polyethylene (PE) fibers (Seko et al., 2007), PE nonwoven fabric (Ueki et al., 2011) and PE/polypropylene (PP) nonwoven fabric (Ma et al., 2011; Kavakli et al., 2007), and materials composed of natural polymers such as nonwoven cotton fabric (Sekine et al.,

n

Corresponding author. Tel.: +63 2 9296011; fax: +63 2 9201655. E-mail addresses: [email protected], [email protected] (J.F. Madrid). 0969-806X/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radphyschem.2013.05.004

2010), cotton–cellulose (Takacs et al., 2005) and water hyacinth fibers (Madrid et al., 2013). Some of these grafted polymer chains contain functional groups which are responsible for the new properties of the polymer material while other grafted polymers serve as precursors for introduction of other functional groups after post-grafting reactions. Properties that can be imparted to both synthetic and natural polymers using this method include improved hydrophilicity/hydrophobicity, sorption activity, permselectivity, flame retardancy and improved electrochemical properties to mention a few. Among these, improving the sorption activity, particularly for metal ions, has been an active field of research over the past years. The attention given by the world on environmental problems due to input of heavy metal ions to different bodies of water has been increasing. This heightened awareness is driven by the different diseases caused by these metal pollutants. High level of

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exposure to copper may lead to weakness, anorexia, and damage to gastrointestinal tract (Theophanides and Anastassopoulou, 2002). At high concentrations, nickel is known to be toxic to plants and animals and at very high levels of exposure, nickel salts are known to be carcinogenic (Smith-Sivertsen et al., 1997). Hence, water treatment is necessary for water systems containing high amounts of these metals. Although there are several methods for heavy metal removal from polluted or waste waters, adsorption is considered as one of the most effective and popular process. Adsorbents synthesized from natural polymers have several advantages over their synthetic counterparts. Natural polymers are renewable and abundant in nature, unlike synthetic polymers which are mostly petroleum based. Furthermore, it has been found that cellulosic polymers can be grafted with high efficiency using the method of emulsion polymerization (Ueki et al., 2011; Sekine et al., 2010). This method uses water instead of organic solvents as primary component of the monomer mixture which contributes to the green chemistry of the process (Seko et al., 2007). Also, high degree of grafting can be achieved even at low dose, making it an economical alternative over the traditional grafting techniques. This work aims at the synthesis of an amine type adsorbent from an abaca/polyester nonwoven fabric. Abaca (Musa textilis), more popularly known as Manila hemp, is a primary product of some farming regions in the Philippines. The adsorbent is developed by using pre-irradiation technique followed by emulsion grafting of GMA with subsequent ring opening reaction of the epoxy groups with ethylenediamine. The effects of pH, initial concentration and time of contact on the adsorption of Cu2+ and Ni2+ from prepared aqueous solutions by the amine type adsorbent were studied. The performance of the synthesized adsorbent was compared with a commercial resin.

2. Experimental 2.1. Materials and reagents Abaca-polyester nonwoven fabric (APNWF) was supplied by Philippine Textile Research Institute. The glycidyl methacrylate (GMA, 495.0%) monomer was obtained from Tokyo Chemical Industry Co., while ethylenediamine (EDA, 499.0%), polyoxyethylene sorbitan monolaurate (Tween 20), Ni(CH3COO)2  4H2O (4 98.0%), CuSO4  5H2O (499.5%), ultrapure nitric acid, and the copper and nickel standard solutions (1000 ppm) for quantitative tests were purchased from Kanto Chemical Co., Inc. The isopropanol (IPA, 499.7%) used in functionalization was acquired from Chameleon Reagent. Reagent grade methanol was used in all washing steps. 2.2. Irradiation of nonwoven fabrics The APNWF was cut into 3 cm  3 cm square pieces which were placed in polyethylene bags. The air inside the polyethylene bags was displaced with nitrogen gas. The samples were then irradiated at dry ice temperature with electron beam of 2 MeV energy and 3 mA current up to doses of 50, 100 and 200 kGy. The dose of electron beam was evaluated from the response of cellulose triacetate dosimeter (CTA). 2.3. Grafting of GMA onto APNWF and amination process The irradiated APNWF samples were placed in a glass ampoule which is immediately evacuated of air using a vacuum line. Afterwards, a previously deaerated emulsion composed of GMA and Tween 20 in deionized water was drawn into the glass ampoule. The emulsion grafting was carried out by keeping the

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glass ampoule in a thermostated water bath at 40 1C for 1–4 h. After grafting, the grafted APNWF pieces were washed repeatedly with methanol, to remove the remaining non-reacted GMA, and dried in vacuo. The amount of GMA grafted onto APNWF was expressed in terms of degree of grafting (Dg) and was calculated using the equation: Dg (%) ¼(Wg−Wo)/Wo  100, where Wg corresponds to the weight of APNWF after grafting and Wo is the initial weight of APNWF. Five parallel samples were grafted and Dg value was reported as an average. GMA-grafted APNWF was reacted with EDA to introduce amine functional groups. A solution of EDA in IPA was added to a glass ampoule containing the sample. The reaction was performed for 15–180 min in a thermostated water bath at 60 1C. After the reaction time, the aminated APNWF was removed from the solution and washed thoroughly with methanol. After drying in vacuo, the amine group density was determined using two methods. One is gravimetrically, using the equation: amine group density (mmole/gram-adsorbent) ¼ [(Wf−Wg)/Wf]  (1000/MW), where Wg and Wf are the weights of GMA-grafted APNWF before and after amination and MW is the molecular weight of EDA. The other method is based on the nitrogen content of aminated APNWF which was determined using an elemental analyzer. 2.4. Batch adsorption The Cu2+ and Ni2+ ion solutions were prepared by dissolving cupric sulfate pentahydrate (CuSO4  5H2O) and nickel acetate tetrahydrate (Ni(CH3COO)2  4H2O) in deionized water. The initial concentration ranged from 10 to 1000 ppm. A weighed amount of the aminated GMA grafted APNWF was added to a 50 mL solution of the metal ion. The batch adsorption studies were conducted in a continuously stirring batch process for 20 h at room temperature with the stirring rate kept at 300 rpm. The metal ion concentrations were measured before and after adsorption. The metal ion uptake by the synthesized adsorbent was calculated by the equation: amount adsorbed (mg metal ion/gram-adsorbent) ¼ (Co−Cf)  V/W, where Co and Cf are the initial and final concentration (ppm) of the metal ion in the aqueous phase, V is the volume of the solution (mL) and W the mass of the aminated GMA-grafted APNWF. 2.5. Effect of contact time on Cu2+ and Ni2+ ion uptake Approximately 0.2 g of aminated GMA-grafted APNWF was mixed with 100 mL of 7 ppm solution of the metal ion with initial pH of 5. The solution was stirred in a 30 1C thermostated water bath. At appropriate time intervals, the stirring is stopped and 0.2 mL supernatant solution was obtained. The supernatant solutions were filtered with 0.2 mm filter disk and analyzed for residual ion concentration. The amount of adsorbed Cu2+ and Ni2+ was expressed in terms of percentage removal which was calculated by the equation: percentage removal ¼(Co−Ct)/Co  100, where Co is the initial ion concentration and Ct is the ion concentration of the solution at time t. 2.6. Analysis The infrared spectra of APNWF, grafted samples and aminated APNWF were examined by a Perkin Elmer Spectrum One FTIR spectrophotometer in attenuated total reflectance (ATR) mode. The samples were scanned in the range 600–4000 cm−1 with a resolution of 4 cm−1. Metal ion concentrations before and after adsorption were determined using a Perkin Elmer Inductively Coupled PlasmaOptical Emission Spectrometer (ICP-OES) Optima 4300 DV. Samples were made 0.1 M in HNO3 prior to analysis. The wavelengths

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used for analysis were 324.75 and 341.48 nm for Cu2+ and Ni2+ ions, respectively. The nitrogen content of APNWF and aminated APNWF was analyzed with a Perkin Elmer Series II CHNS/O Analyzer 2400. Samples weighing 2.5–3 mg were sealed in tin caps for analysis. Acetanilide (Perkin Elmer, C ¼71.09%, H¼6.71%, N ¼10.36%) was used as standard.

3. Results and discussion 3.1. Emulsion grafting of GMA The process of radiation-induced grafting of polymeric matrices using aqueous emulsions was found as a more efficient process compared to the use of organic solvents for introducing graft chains on the surface of various materials (Wada et al., 2008). Previous studies showed that absorbed dose, monomer concentration and reaction time affect the Dg of the grafted material, hence the variation of Dg as a function of these variables was studied. 3.1.1. Effect of absorbed dose The interaction of electron beam with APNWF results in the production of radicals. Higher absorbed dose results in higher concentration of radicals which translates to more initiation sites for graft polymerization. Fig. 1 shows the relationship between Dg and grafting time at different absorbed doses. It can be observed that at a fixed reaction time, higher absorbed dose gives grafted APNWF with higher Dg and this corroborates with the previous statement. APNWF exposed to a dose of 200 kGy gave 303% Dg after an hour of reaction with 5% GMA emulsion and this increased to 550% after 4 h of reaction time. However, at these conditions, the grafted APNWF is brittle due to the very high Dg. This brittleness makes handling of the grafted APNWF difficult for the next processes. With an absorbed dose of 100 kGy, the Dg increased from 207% to 252% when the reaction time was increased from 1 to 4 h. At both absorbed doses, prolonged contact of the irradiated APNWF with the GMA emulsion resulted to increase in Dg. This can be attributed to the fact that an increase in reaction time allows more GMA molecules to react with the active sites (i.e. radicals) on the surface of irradiated APNWF. Prolonged contact with the GMA emulsion also increases the propagation of the poly(glycidyl methacrylate) chains, resulting to higher Dg. According to Sekine et al., (2010), a Dg greater than 100% is required for synthesis of a metal ion adsorbent via chemical

modification. APNWF exposed to 50 kGy absorbed dose gave a Dg of 93% after 1 h contact with the GMA emulsion. Similar to grafting at higher doses, the Dg increase with time. An almost constant value of 180% was achieved after 3 h of reaction time and this is sufficient for preparation of metal ion adsorbent. A 180% Dg corresponds to an epoxy group density of 4.5 mmole/gram-adsorbent. The grafted APNWF obtained at these conditions was more flexible compared to those exposed at higher absorbed dose. Attaining a sufficient Dg after irradiation at a low dose of 50 kGy is valuable for development of a metal ion adsorbent. It was found that irradiation at higher doses results in degradation of the molecular chain of the polymeric material which leads to reduction of tensile strength (Takacs et al., 2005). Lower absorbed dose also gives economic advantage for the process.

3.1.2. Effect of monomer concentration The effect of GMA concentration on Dg was investigated. It can be observed from Fig. 2 that an increase in GMA concentration from 3% to 5% resulted to a significant increase in Dg after 3 h of reaction time. Higher Dg was expected with increase in GMA concentration because more monomers were able to interact with the radicals and propagating polymer chains on the APNWF. Further increase in GMA concentration from 5% to 7% GMA did not result in any significant increase in Dg. The Dg of the grafted material reached 120% after 2 hours of reaction with 3% GMA. At 5% GMA, a higher Dg of 180% was attained after 3 hours. Increasing the reaction times beyond this numbers did not result to increase in Dg. The retardation in Dg increase after 1 and 3 h of reaction time for 3% and 5% GMA, respectively, might be due to the depletion of monomer available for reaction on available grafting sites and growing grafted polymer chains. However, the plateau in the Dg curve for 7% GMA almost coincided with that of 5% GMA, even though the former mixture contains higher amount of monomer. This is possibly due to the fact that at certain Dg, the reaction became a diffusion controlled process (Hebeish et al., 1973). The grafted GMA polymer chains on the surface might slowed down or prevented further diffusion of more monomers to the available active sites which resulted to an almost constant Dg despite the increase in reaction time. The study also showed that the prepared GMA emulsions with 10:1 monomer/surfactant ratio were stable while being deaerated using nitrogen gas and during grafting at 40 1C. The emulsions were in a milky state and no phase separation was observed throughout the experiments. This is in concurrence with a previous research which showed that an aqueous emulsion with 5% GMA and 0.5% Tween 20 are stable up to 48 h (Seko et al., 2007).

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Fig. 3. Variation of amine group density with reaction time at (a) 15%, (b) 30%, (c) 50% and (d) 70% EDA concentration. Amine group density was determined gravimetrically (♦) and by an elemental analyzer (■).

3.2. Amination of GMA-grafted APNWF The GMA-grafted APNWF with approximately 160–180% Dg were functionalized by reacting with EDA. This process resulted to the introduction of amine groups by ring opening reaction of the epoxy group in GMA. The effects of reaction time and EDA concentration on the amine group density were studied. Fig. 3 shows the amine group density of the aminated APNWF as a function of reaction time at different EDA concentrations. It can be observed from Fig. 3 that the values obtained gravimetrically and using an elemental analyzer are almost the same for GMA-grafted APNWF reacted with 15% and 30% EDA. However, evident differences between the values obtained from the two methods were observed starting at 120 and 60 min reaction times with 50% and 70% EDA, respectively. The amine group density derived from the elemental analyzer reached an almost constant value with increasing reaction time while the values determined using gravimetric method decrease. This indicates that the final weight of the grafted nonwoven fabric after amination decrease with prolonged reaction with 50% and 70% EDA. This decrease in weight is attributed to the degradation of GMA-grafted APNWF at long reaction times with solutions of high EDA concentrations. Therefore, for consistency, the results derived from the elemental analyzer will be used for succeeding discussions. The data shown on Fig. 3 indicate that the amount of incorporated amine groups increases with reaction time. The amine group density reached almost constant values of 1.50, 2.10 and 2.70 mmole/gram-adsorbent after 120, 45 and 30 min of reaction with 15%, 30% and 50% EDA, respectively. This signified that increasing the concentration of EDA allows the amination process to reach an equilibrium state faster. It can also be noted from Fig. 3 that at a given reaction time, the amine group density increases with EDA concentration. At fixed reaction time, higher EDA concentration means more EDA molecules can react with the

epoxy groups on the GMA-grafted APNWF which results in more conversion and higher amine group density. The results of all the preceding experiments show that the optimum conditions for the preparation of an amine type adsorbent from APNWF were as follows: irradiation of APNWF up to 50 kGy dose, reaction with aqueous emulsion consisted of 5% GMA and 0.5% Tween 20 at 40 1C for 3 h, and amination with 50% EDA at 60 1C for 30 min. These conditions afforded us to have a GMAgrafted APNWF with a Dg more than 150% which after amination gave 2.70 mmole amine groups for every gram of adsorbent. Also, based from our literature search, this is the first attempt on grafting a nonwoven fabric made of natural and synthetic polymer components.

3.3. FTIR-ATR analysis The grafting of GMA onto APNWF and the incorporation of amine groups by reaction of EDA with the epoxy groups on GMAgrafted APNWF can be verified using FTIR analysis. Fig. 4 shows the results of the FTIR analysis. The FTIR spectrum of APNWF, Fig. 4a, exhibited absorptions corresponding to the abaca cellulose portion: O-H stretch at 3334.01 cm−1, C-H stretch at 2886.55 cm−1, glycosidic C–O–C stretch at 1100.02 cm−1, C–OH stretch at 1017.07 cm−1; and absorptions due to the polyester region: C ¼ O stretch at 1712.09 cm−1, C–O stretch at 1241.20 cm−1. After grafting to a Dg of 150%, the FTIR spectrum of grafted APNWF, Fig. 4b, shows characteristic peaks at 1254.73, 903.79, 843.03 cm−1 corresponding to the IR absorption of the epoxy group of GMA. Similar characteristic peaks were observed by other researchers (Sokker et al., 2009; Wojnarovits et al., 2010). Besides the epoxy group absorption frequencies, peaks from APNWF were observed on the FTIR spectrum of GMA-grafted APNWF which indicates successful grafting.

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Fig. 4. FTIR-ATR spectra of (a) abaca-polyester nonwoven fabric, (b) GMA-grafted APNWF (Dg ¼ 150%) and (c) aminated GMA-grafted APNWF.

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Fig. 4c shows the FTIR spectrum of the aminated APNWF. Some of the peaks observed from Fig. 4b were retained after the reaction of GMA-grafted APNWF with EDA. The peak at 3341.84 cm−1, due to the O–H stretch peak from abaca has a small shoulder overlapping at around 3420.60 cm−1, and this corresponds to the –NH2, –NH stretches from the reacted EDA. The peak at 1595.01 cm−1 is attributed to the N–H bend while the C–N absorption gave a peak at around 1155.90 cm−1. The peaks which corresponds to the epoxy group from GMA from Fig. 4b were almost absent at Fig. 4c. This was expected as the epoxy group opens up on reaction with EDA. The absence of the characteristic peaks for the epoxy group and the presence of new peaks corresponding to N–H and C–N stretches confirmed the successful amination of the GMA-grafted APNWF.

The batch adsorption tests showed poor affinity of the aminated APNWF for both Cu2+ and Ni2+ at very low pH values. Similar trend was observed with EDA functionalized cotton (Ghali et al., 2011). The low adsorption can be attributed to either competition of H+ for the adsorption sites or electrostatic repulsion between the protonated EDA and the metal ions. The high H+ concentration of low pH solutions causes most of the EDA to be protonated and this result to electrostatic repulsion between the positively charged metal ions and the adsorbent. The amount of adsorbed metal ions increased with pH of the solution. The maximum adsorption of the metals by the aminated APNWF was found to occur at pH 5 for Ni2+ and between pH 4–5 for Cu2+. At pH higher than these optimum values, the amount of adsorbed metal ion decreased and the metal ions started to precipitate out of the solution.

3.4. Cu2+ and Ni2+ adsorption studies 3.4.1. Effect of pH on metal ion uptake The adsorptive property of modified adsorbents towards metal ions was found to be related to the pH value of the original solution (Ma et al., 2011; Sekine et al., 2010; Lee et al., 2001). In order to evaluate the effect of pH on Cu2+ and Ni2+ uptake by the aminated GMA-grafted APNWF, batch adsorption run was performed using 50 ppm of each metal. Fig. 5 illustrates the relationship between the amount of metal adsorbed and the initial pH of the solution.

3.4.2. Effect of initial concentration on metal ion uptake Fig. 6 shows the dependence of the amount of adsorbed metal on the initial concentration of the metal in the solution. The quantity of adsorbate on the solid phase increases with the initial amount of the metal ion in the original solution. However, the amount of removed metal expressed in terms of percentage removal, decreased with increasing initial concentration. When the amount of Cu2+ was raised from 10 to 1000 ppm, the adsorption capacity increased from 2.3 to 141.9 mg/gram-adsorbent but

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141.9 and 49.4 mg/gram-adsorbent for GMA-grafted APNWF and DIAION WA20, respectively. The results show that both adsorbents have higher Cu2+ than Ni2+ adsorption capacity. Specifically, the adsorption capacity of the synthesized aminated APNWF is four times greater for Cu2+ ions compared to Ni2+ ions. The data also shows that at the specified conditions, the adsorption capacity of the synthesized adsorbent for both Cu2+ and Ni2+ is greater than that of DIAION WA20 commercial resin.

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the percentage removal decreased from 99.4 to 52.0%. The same trend was observed for Ni2+. A similar increase in initial Ni2+ concentration resulted to an increase in adsorption capacity from 2.7 to 31.5 mg/gram-adsorbent but a decrease in percentage removal from 96.2 to 16.0%. The data shows that the Ni2+ and Cu2+ uptake is concentration dependent. The available metal ion adsorption sites of aminated APNWF became fewer at higher initial concentrations. The total available adsorption sites are limited so increasing the amount of metal ion in the solution will not result to complete removal of the added metal ions. This caused a decrease in percentage removal when the initial sorbate concentration was increased. The performance of the aminated GMA-grafted APNWF towards adsorption of Ni2+ and Cu2+ is compared to a commercial resin, DIAION WA20. This commercial resin has amine functional groups almost similar to EDA. From elemental analysis, it has 3.66 mmole amine groups for every gram of resin when calculated in moisture-free basis. This number is larger than the 2.70 mmole/ gram amine group density of aminated GMA-g-APNWF. Weighed amounts of the commercial adsorbent, with similar functional group content as the aminated APNWF used in the initial concentration test, were added to solutions containing different concentrations of Cu2+ and Ni2+. The batch adsorption tests were conducted at conditions similar to the tests using aminated APNWF. Result of the experiment is also shown on Fig. 6. It is seen from Fig. 6 that DIAION WA20 follows the same trend for the adsorption of metal ions as that of aminated APNWF. The Ni2+ adsorption capacity was calculated to be 31.5 and 21.7 mg/ gram-adsorbent for GMA-grafted APNWF and DIAION WA20, respectively. These values are lower compared to the Cu2+ adsorption capacity of both adsorbents which were determined to be

3.4.3. Kinetics of metal ion uptake Adsorption kinetics is important in determining the efficiency of new adsorbents. Kinetics studies are significant in evaluating the adsorption efficiency. It also helps to determine the effluent flow rate to achieve maximum removal of target metal ions or organic compounds from solutions. The effect of contact time on the adsorption of Cu2+ and Ni2+ ions by aminated APNWF and DIAION WA20 were investigated and the results are shown in Fig. 7. Fig. 7a shows that the aminated APNWF removed almost 90% of the Cu2+ ions after 5 minutes of contact with the solution. This is significantly higher compared to 3.3% removed by the commercial resin DIAION WA20 at the same period of time. Complete uptake of Cu2+ ions in the solution by the aminated APNWF was achieved after stirring for 30 min. The amount of Cu2+ removed from the solution by DIAION WA20 increased fast, reaching 60.2% after 40 min, followed by a slow steady increase until it reached an almost constant value of 77.2% after 130 min of stirring. A trend similar to that of Cu2+ adsorption was observed for Ni2+ ion removal by both the synthesized adsorbent and the commercial resin. It can be seen from Fig. 7b that the amount of Ni2+ ions removed by aminated APNWF increased up to 33.4% after 60 min

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of stirring. Afterwards, gradual increments in Ni2+ removal were observed until the percentage removal levelled at approximately 62.1% after 450 min. DIAION WA20 showed even lower adsorption of Ni2+ ions. It adsorbed negligible amounts of Ni2+ for the first 20 min and reached only 13.8% removal after 60 min of adsorption. The kinetics experiments revealed important things about the synthesized adsorbent. The aminated GMA-grafted APNWF removes Cu2+ faster than Ni2+ ions from the solution. After 30 min of contact time, the aminated APNWF had removed almost 100% of the Cu2+ ions from the solution while the amount of Ni2+ ions was reduced by only 26.3%. Also, the results of the kinetics experiment indicated that the ion sorption ability of the aminated GMAgrafted APNWF is greater than the commercial resin DIAION WA20, corroborating the results obtained from the previous section. The swiftness of Cu2+ adsorption by the aminated APNWF is significantly greater than that of DIAION WA20. The aminated APNWF required 30 min to completely remove the Cu2+ ions from a 100 mL of 7 ppm solution while at the same amount of contact time and solution, the percentage removal attained by DIAION WA20 was 48.5%, less than half the amount removed by the aminated APNWF. It was shown that the rate limiting step in ion sorption by spherical resins in a well-stirred system is either intraparticular diffusion (i.e. the transfer from the surface to the intraparticular active sites) or chemical reaction (i.e. uptake of ions by the adsorption sites) (Lee et al., 2001). Both the synthesized adsorbent, aminated GMA-grafted APNWF, and commercial resin, DIAION WA20, have almost similar amine groups on the surface; hence chemical reactivity can be assumed to be similar for both cases. Indeed, this was seen from the results as both adsorbents show higher adsorption capacity for Cu2+ than Ni2+. Fibrous adsorbents have small fiber diameter size which is typically ten times smaller than the size of spherical resin adsorbents (Sekine et al., 2010), making the diffusion rate of metals into fibrous adsorbents higher compared to its spherical resin counterpart. This resulted to the observed faster ion uptake by the aminated GMA-grafted APNWF than the commercial resin, DIAION WA20. 4. Summary Synthesis of GMA-grafted abaca/polyester nonwoven fabric was achieved by electron beam induced graft polymerization. A degree of grafting sufficient for an adsorbent was achieved by using the following conditions: irradiation with 50 kGy dose of 2 MeV electron beam at dry-ice temperature and nitrogen atmosphere and emulsion grafting for 3 h at 40 1C in 5% GMA stabilized with 0.5% Tween 20. Chemical modification of the grafted APNWF with EDA gave an aminated adsorbent with 2.7 mmole amine groups for each gram of adsorbent, based from elemental analysis. The introduction of GMA and subsequent reaction with EDA were verified by FTIR in ATR mode. The synthesized adsorbent showed higher adsorption capacity for Cu2+ than Ni2+. The amount of metal ion removed was found to

be dependent on pH of the solution, initial metal ion concentration and contact time with the adsorbent. A comparison with a commercial resin was done. Results indicate that the synthesized adsorbent has greater Ni2+ and Cu2+ adsorption capacity and higher rate of adsorption than the commercial resin.

Acknowledgments The researchers acknowledge Philippine Textile Research Institute, Department of Science and Technology, Philippines for providing the nonwoven fabric used in this research. This study was supported by MEXT Nuclear Researchers Exchange Program 2012 from the Ministry of Education, Culture, Sports, Science and Technology Japan.

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