ac

zilg

alays

uce granin inmerizeerizationrm

Aziz et al., 2005; Clemons and Sanadi, 2007). With such

mer for graftingsurface can giveon capacity, acidah et al., 2012;

btained by twoation and pre-backbone poly-er solution. In

monomer under controlled condition. The degree of grafting

Contents lists available at SciVerse ScienceDirect

evi

Radiation Physics

Radiation Physics and Chemistry 91 (2013) 125131polymer substrates is advantageous because the epoxy group offath_aries@yahoo.com (J. Sharif).may be adjusted by selection of absorbed dose and reactionparameters to develop specially designed selective copolymersfor specic uses (Nasef and Guven, 2012)

Graft copolymerization of glycidyl methacrylate (GMA) onto

0969-806X/$ - see front matter & 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.radphyschem.2013.05.035

n Corresponding author. Tel.: +63-89112000; fax.: +6389202968.E-mail addresses: jamaliah@nuclearmalaysia.gov.my,paper, textiles industries as well as reinforcement ller for poly-mer composites (Kaldor et al., 1990; Song and Obendorf, 2006;

preirradiation method, the backbone polymer is irradiated in inertcondition to generate radicals and subsequently react with a1. Introduction

Kenaf (Hibiscus Cannabinus L) is a herbaceous annual plant inthe Malvaceae family belonging to the division of Magnoliophyta(Kaldor et al., 1990). Kenaf grows very quickly and can reach aheight of 4 to 5 m in 4 to 5 months therefore suitable as agrobersresources. Kenaf bers are a lignocellulosic bers mainly consist-ing of cellulose, hemicelluloses and lignin. Noncellulosic com-pounds such as lignin, hemicelluloses and pectins hold thecellulose brils together. Kenaf bers have been used in pulp,

abundance and renewable resources, it is an advanew application for kenaf bers as trunk polycopolymerization. Grafting polymer onto kenafmany new specic properties including adsorptiresistance and wetting capability (Nor HashimEromosele and Bayero, 1999).

Radiation induced graft copolymer can be omain methods that are simultaneous irradiirradiation method. In simultaneous method, themer is irradiated while immersed in monomshowed that degree of crystallinity of graft copolymers decreased with the increase in degree of grafting.& 2013 Elsevier Ltd. All rights reserved.

ntage to explorePre-irradiationFormation of graft copolymer was conrmed with SEM, FTIR analysis. The structural investigation by XRDAvailable online 6 June 2013

Keywords:Radiation induced graft polymerizationKenaf bersDelignicationGlycidyl methacrylate

emulsion system. The degree of grafting was determined as a function of absorbed dose, reaction time,reaction temperature and concentration of monomer. The results showed that the lignin content wasdecreased from 14.3% to as low as 3.3% with the increased of sodium chlorite concentration. This wasevidenced by SEM pictures which show the surface of treated kenaf bers was cleaner and smoothercompared to that of untreated one. The degree of grafting increased with the increase of absorbed dose,reaction temperature, reaction time and monomer concentration as well as with decreasing lignin content. We used kenaf bers for radiation ind Kenaf bers was treated to remove lig Treated kenaf bers were graft copoly Optimum conditions for graft copolym Formation of graft copolymer is also c

a r t i c l e i n f o

Article history:Received 26 April 2013Accepted 28 May 2013ft copolymerization with GMA.order to increase grafting yield.through preirradiation technique.on of kenaf bers were established.ed with SEM, FTIR and XRD.

a b s t r a c t

Glycidyl methacrylate grafted kenaf (GMA-g-Kenaf) was prepared by pre-irradiation grafting technique.Kenaf bers were treated with different concentration of sodium chlorite solution before used as trunkpolymer. Treated kenaf bers were irradiated by electron beam followed by grafting reaction in GMA/waterH I G H L I G H T SGraft copolymerization of glycidyl methbers through pre-irradiation technique

Jamaliah Sharif a,n, Siti Fatahiyah Mohamad a, Nor ANurul Azra Bakaruddin a, Hasnul Nizam Osman a, Oa Radiation Processing Division, Malaysian Nuclear Agency, Kajang, Selangor 43000, Mb Hacettepe University, Department of Chemistry, Beytepe, 06800 Ankara, Turkey

journal homepage: www.elsrylate onto delignied kenaf

lah Fatimah Othman a,un Gven b

ia

er.com/locate/radphyschem

and Chemistry

Sodium chlorite (NaClO ) solution was prepared by dissolving

2.4. Sample characterization

Morphology of the sample was studied using a ScanningElectron Microscopy (SEM) using FEI Quanta 400. Samples weresputter coated with gold using Bio Rad coating system.

Fourier transform infrared spectroscopy (FTIR) spectra weretaken by using Nicolet IS10 FTIR spectrometer (Thermo Scientic)at a resolution of 4 cm1 with single reection diamond universalattenuated total reection (ATR) accessory.

X-ray diffraction (XRD) analysis was performed at room tem-perature by using a Shimadzu XRD 600 X-ray diffractometer. The

content. Therefore combination of low concentration of NaClO2with long reaction time can improve delignication as shown by

J. Sharif et al. / Radiation Physics and Chemistry 91 (2013) 1251311262

sodium chlorite in distilled water. The pH of the solution wasadjusted to 4 by adding diluted nitric acid (1 M). 1 l sodiumchlorite solution was poured to a conical ask containing 5 g ofkenaf bers and heated at 70 1C for 6 h with continuous stirring.After that, the kenaf bers was drained and washed repeatedlywith distilled water and dried in an oven at 60 1C for 12 h.

2.3. Radiation graft copolymerization

About 0.2 g of the treated kenaf bers was placed in a poly-ethylene zipper bag, purged with nitrogen and sealed. The samplewas placed on dry ice box and irradiated with electron beam. Theenergy of electrons was 2 MeV and the current 10 mA at dosesranging from 10 to 200 kGy. The irradiated bers were immedi-ately transferred to an ampoule and 100 ml GMAwater emulsionwas added to the ampoule. (Note that the 3% GMAwater emulsionwas purged with nitrogen before use). The ampoule was placed ina water bath at selected temperature. After predetermined periodof time, the grafted kenaf was removed from the ampoule andwashed repeatedly with methanol to remove excess monomer.The weight of GMA grafted kenaf was measured after dryingovernight in an oven at 40 1C.

Degree of grafting (Dg) was determined gravimetrically andcalculated according to the following formula:

Dg (%)((W1W0)/W0)100where, W0 is initial weight ofGMA can be easily modied to provide functions such as ionexchange, adsorption of toxic gases while the original propertiesremain intact (Hwang et al., 2004). Radiation induced grafting ofnatural bers have been studied by several researchers. Jordan et al.(2013) has grafted GMA onto water hyacinth bers (Eichhorniacrassipes) through simultaneous grafting technique using -rays.They found optimum grafting conditions such as absorbed dose,dose rate and monomer concentration as 10 kGy, 8 kGy/h1 and 5%,respectively. At the optimum conditions, degree of grafting of GMAonto water hyacinth was found to be 58%. Other researchers hadgrafted GMA onto kapok bers through pre-irradiation techniqueusing gamma rays. The kapok was treated with sodium chlorite toremove phenolic compounds before used as backbone polymer. Theauthors found that grafting yield increased with increasing tempera-ture from 30 1C to 60 1C, and absorbed dose from 40 to 100 kGy(Kang et al., 2007). Recent work on kenaf bers was done by NorHashimah et al. (2012), who investigated the effect of partialdelignication of kenaf bers for radiation graft copolymerizationof chloro methyl styrene (CMS). Lignin plays important role inradiation grafting of kenaf bers. Removal of lignin is crucial forenhancement of grafting yield (Nor Hashimah et al., 2012). In thepresent study we report on the effect of absorbed dose, reactiontemperature, reaction time and monomer concentration on pre-irradiation grafting of glycidyl methacrylate onto kenaf bers treatedwith low concentration of sodium chlorite solution.

2. Experimental

2.1. Materials

Kenaf bast bers were bought from Lembaga Kenaf danTembakau Negara (LKTN) Pasir Putih Kelantan Malaysia. Sodiumchlorite (Sigma), Glycidyl Methacrylate (Sigma Aldrich) and Tween20 (Sigma Aldrich), Isopropanol and methanol were purchasedfrom Sigma Malaysia and used without purication.

2.2. Treatment of kenaf bast berskenaf and W1 is weight of kenaf after grafting.our results shown in Table 1.Removal of lignin by sodium chlorite treatment was also

supported by SEM pictures shown in Fig. 1. The pictures clearly

Table 1Effect of sodium chlorite (NaClO2) concentration on lignin content and degree ofgrafting of kenaf ber (Grafting condition: Dose100 kGy, time24 h,temperature25 1C and GMA concentration 3%).

Concentration of NaClO2 (%) Lignin content (%) Degree of grafting (%)

0.0 14.3 290.1 9.1 460.3 6.6 1040.5 4.0 1690.7 3.4 1851.0 3.3 172X-ray beam was nickel ltered CuK (1.542 A) radiation oper-ated at 30 kV and 30 mA. Data were obtained from 2 of 21 to 301at a rate of 1 1/min.

3. Results and discussion

3.1. Treatment of kenaf bers

Kenaf bers were treated with different concentrations ofNaClO2 at 70 1C for 6 h. Lignin content of treated and untreatedkenaf was determined according to TAPPI T222 om-02 standardmethod. The results are presented in Table 1. It can be seen fromthe table that lignin content of untreated kenaf bers is 14.3%. Thelignin content was decreased to 9.1, 6.6, 4.0, 3.4 and 3.3% aftertreated with 0.1, 0.3, 0.5, 0.7 and 1.0% NaClO2, respectively. Theresults indicate that low concentration of NaClO2 is able to reducelignin content from 14.3% to 3.3% at long reaction time that is 6 hand at temperature 70 1C. This result is in good agreement withthat of (Nor Hashimah et al., 2012), who studied the effect oftemperature and time for delignication of kenaf bers usingsodium chlorite. During heating NaClO2 produced chlorine dioxidewhich reacted with lignin that binds the lignocellulosic bers. Thisprocess resulted to a change in properties of the kenaf bers fromhydrophobic to hydrophilic owing to the cleavage and removal ofthe phenolic compounds (Nor Hashimah et al., 2012). Removal oflignin is important in radiation grafting of kenaf bers becauseradiation can change phenolic compound into quinone structuresconsequently enhance formation of homopolymer instead of graftpolymerization of cellulosic bers (Ghost et al., 1994; Wojnarovitset al., 2010). It was reported that the removal of lignin content inlignocellulosic bers can be enhanced by the increase of NaClO2concentration (Hubbell and Ragauskas, 2010; Yu et al., 2011).However, Gupta et al. (2010) reported that NaClO2 at concentra-tion range 1 to 5% did not cause any signicant improvement ondelignication. According to Archibald et al. (1997) extendeddelignication time can led to a massive reduction in lignin

J. Sharif et al. / Radiation Physics and Chemistry 91 (2013) 125131 127show that surface of untreated kenaf bers were coated and wereglued together with compounds that is noncellulose. On the otherhand the surface of sodium chlorite treated kenaf bers lookscleaner, smoother due to the removal of the noncellulose com-pound by the NaClO2 treatment.

Table 1 also shows the degree of grafting of kenaf bers atdifferent lignin content. It can be seen from the table that degreeof grafting of untreated kenaf bers with lignin content 14.3% is29%. The degree of grafting increases to 46, 104, 169, 185 and 172%with the decrease of lignin content to 9.1, 6.6, 4.0, 3.4, and 3.3%,respectively. These results indicate that removal of lignin isnecessary in order to enhance the formation of grafting of GMAonto kenaf bers. Delignication process also changes the proper-ties of kenaf bers from hydrophobic to hydrophilic due to thecleavage and removal of the phenolic compounds therefore easierfor the monomer to penetrate the kenaf bers for graftingreaction. Lignin is a branched, three dimensional, complex poly-mer with both aliphatic and aromatic constituents built mainlywith p-hydroxycinnamyl alcohol with different degree of

Fig. 1. SEM pictures of kenaf bers before amethoxylation (Wojnarovits et al., 2010). Upon irradiation withelectron beam, the phenolic compounds change into quininestructures consequently enhances the formation of homopolymerinstead of graft polymerization. Therefore removal of ligninsignicantly improves grafting of kenaf bers.

3.2. Effect of absorbed dose

Effect of absorbed dose on grafting yield was studied usingkenaf bers treated with 0.7% sodium chlorite. Kenaf bers wasirradiated at different doses and then reacted with 3% GMAwateremulsion at room temperature for 24 h. Degree of grafting wascalculated and the result is presented in Fig. 2. It can be seen fromthe gure that the degree of grafting increased rapidly to 154% at50 kGy and further increase in absorbed dose increased the degreeof grafting continuously. This result indicates that higher absorbeddoses lead to formation of more free radicals in the kenaf bers.Consequently more free radicals are available for grafting reactionof GMA onto kenaf bers. These results are in good agreement

nd after treated with sodium chlorite.

with the results obtained by Sekine et al. (2009), who observedthat the degree of grafting of GMA onto nonwoven cellulose bersincreased with the increase in absorbed dose. Jordan et al. (2013)also showed that the degree of grafting of GMA onto waterhyacinth increase with the increase of absorbed dose. Theincreased formation of graft co-polymerization of GMA onto kenafbers was evidenced by SEM pictures shown in Fig. 3. It is clearlyseen from the gure that kenaf bers irradiated at 10 and 20 kGywere grafted with thin layer GMA copolymer. However, when theabsorbed doses were increased to 50, 100, 150 and 200 kGy thekenaf bers were coated with thick layer of GMA copolymer.

3.3. Effect of reaction temperature and time

Kenaf bers treated with 0.7% sodium chlorite solution wereirradiated with electron beam at a dose of 50 kGy in nitrogenatmosphere at dry ice temperature (20 1C). Graft copolymeriza-tion of GMA onto the preirradiated kenaf bers was carried out atdifferent temperatures and times. Fig. 4 shows the relationshipbetween degree of grafting (Dg) and reaction temperature. Asshown in the gure the degree of grafting was increased with the

0

50

100

150

200

250

300

0 50 100 150 200

Deg

ree

of g

rafti

ng (%

)

Irradiation dose (kGy)

Fig. 2. Effect of absorbed dose on degree of grafting of GMA onto kenaf berstreated with 0.7% NaClO2, grafted at 25 1C for 24 h.

10 kGy 20 kGy

50 kGy 1

150 kGy 2

Fig. 3. SEM pictures of kenaf bers grafted

J. Sharif et al. / Radiation Physics and Chemistry 91 (2013) 12513112800 kGy00 kGy

with GMA at different absorbed doses.

J. Sharif et al. / Radiation Physics and Chemistry 91 (2013) 125131 129100

150

200

250re

e of

gra

fting

(%)increase of reaction temperature. The degree of grafting wasincreased from 105% to 110%, 140% and 180% as the temperatureincreases from 25 1C to 30, 40 and 60 1C, respectively. However, at60 1C there was a lot of homopolymer and it was difcult to washthe kenaf bers. Therefore, for reaction time effect on degree ofgrafting study, the reaction temperature is limited to 40 1C only.Fig. 5 shows the relationship between degree of grafting andreaction time. The gure shows that the degree of grafting wasincreased to 154% with the increase of reaction time up to 3 h and

0

50

20 25 30 35 40 45 50 55 60

Deg

Reaction Temperature (C)

Fig. 4. Effect of temperature on the degree of grafting of GMA onto kenaf bertreated with 0.7% NaClO2 and irradiated at 50 kGy and reaction time 3 h.

020406080

100120140160180

0 1 2 3 4 5

Deg

ree

of g

rafti

ng (%

)

Reaction time (hours)

Fig. 5. Effect of time on degree of grafting of GMA onto kenaf ber treated with0.7% NaClO2, irradiated at 50 kGy and reaction temperature 30 1C.

0

50

100

150

200

250

300

0 0.5 1 1.5 2 2.5 3

Deg

ree

of g

rafti

ng (%

)

rection time (hrs)2% 3% 5%

Fig. 6. Effect of monomer concentration on degree of grafting of kenaf berstreated with 0.7% NaClO2, irradiated at 50 kGy at grafting temperature 40 1C for 3 h.further increased in reaction time increased the degree of graftingmarginally. The increase in degree of grafting at high temperatureand long reaction time could be due to the increase of interactionbetween free radicals and GMA monomer due to the increasedmobility of monomer molecules and their collision with backbonepolymer (Najjar et al., 2000).

3.4. Effect of monomer concentration

In this work the GMA concentration was varied in the range2 to 5% while the Tween 20 concentration was xed at 1% forpreparation of emulsion which was stable for the whole period ofgrafting process. Effect of GMA concentration on degree of graftingof kenaf bers was studied at xed absorbed dose of 50 kGy. Thegrafting reaction was carried out at 40 1C up to 3 h. The relationshipbetween degrees of grafting with grafting time at various GMAconcentrations is presented in Fig. 6. It can be seen from the gurethat the degree of grafting was increased with the increase ofmonomer concentration from 2% to 5%. Higher degree of graftingat high GMA concentration is expected since radicals generated atkenaf bers after preirradiation able to interact with more monomermolecules at higher monomer concentration. Overall the degree ofgrafting increase with time, with rapid increase at 1 h and reachingplateau after that. The increase of Dg with time due to propagation ofgrafting chains takes place due to availability of more active species(Tripathy et al., 2009). It is also observed that the degree of graftingincrease abruptly after 3% GMA due to the availability of more GMAmolecules to interact with radicals on kenaf bers.

3.5. FTIR analysis

FTIR analysis was conducted on raw kenaf bers, bleachedkenaf bers and grafted kenaf bers with degree of grafting of 76%and 157%. Fig. 7 shows the FTIR spectra for the samples. It can beseen from the gure that there is not much difference in thespectra of kenaf bers and bleached kenaf bers. In the spectrumof grafted kenaf bers however, due to high graft ratio, thespectrum of poly(GMA) dominates, the underlying kenaf berspeaks are seen as weak absorbances. Some peaks due to substratecan be seen for spectrum of the sample grafted to 76% (of1623 cm1 and 1016 cm1). They are however fully covered withthe peaks due to poly(GMA) for 157% grafted sample. Both rawkenaf bers and bleached kenaf bers show O-H stretchingabsorption at 3340 cm1, CH stretching at 2904 cm1, CCstretching for lignin at 1623 cm1 and CO stretching fromcellulose unit at 1016 cm1. However, for GMA grafted kenaf bersthere are a peaks at 1730 cm1 assigned to CO streching vibra-tion and 1140 cm1 to CO stretching vibration indicating thepresence of ester group COO. The characteristic peak for epoxyat 1233, 905 and 842 cm1 are present in GMA grafted kenafspectrum which indicates successful grafting of GMA onto kenafbers. The presences of these three peaks are also reported byother researchers (Jordan et al., 2013; Wojnarovits et al., 2010).

3.6. X-ray diffraction measurement

X-ray diffraction (XRD) measurement was carried out on kenafbers before and after grafting in order to study the crystallinestructural changes owing to the introduction of GMA onto kenafber. XRD patterns of ungrafted kenaf ber and kenaf ber withdifferent degree of grafting are shown in Fig. 8. It can be seen fromthe gure that the crystallinity peak for the ungrafted and graftedkenaf bers occurs at the same 2 angle which means no changesin crystalline structure. However, the reection peak intensity ofall grafted kenaf ber are lower and decrease with the increase in

degree of grafting. This result indicates that crystallinity content

-0.16

500enu

d (c

J. Sharif et al. / Radiation Physics and Chemistry 91 (2013) 125131130-0.24-0.22-0.20-0.18

230003500Wav

Fig. 7. FTIR spectra for (a) raw kenaf ber (b) bleached kenaf ber an-0.14-0.12-0.10-0.08-0.06-0.04-0.02-0.000.020.040.06

Abs

orba

nce

(a) raw kenaf fiber (b) bleach kenaf fiber and (c) grafted kenaf fibers at Dg=76% (d) grafted kenaf fiber Dg=157% decreases with the increase in the degree of grafting. The decreasein crystallinity is due to the dilution of the inherent crystallinity byincorporation of amorphous poly GMA graft. This result is inagreement with Takacs et al. (2005), who reported crystallinityof grafted cellulose decrease with the increase of grafting yield.Nasef et al. (1999) also found that grafting of styrene onto poly(tetrauoroethylene-co-peruorovinyl ether) semicrystalline poly-mer reduces its crystallinity.

4. Conclusion

This study shows that raw kenaf bers contain about 14.3%lignin. The lignin was removed by treatment with sodium chloritesolution. The lignin content was decreased to as low as 3.3% withthe increased of sodium chlorite concentration from 0.1 to 1 wt%.Radiation induced grafting of GMA onto treated kenaf bersproduces higher degree of grafting compared to untreated kenafbers. The effects of grafting parameters such as absorbed dose,reaction temperature and time and monomer concentration wereinvestigated using kenaf bers treated with 0.7% sodium chlorite.At absorbed dose of 50 kGy, reaction time 3 h, reaction tempera-ture 40 1C and monomer concentration 3%, we manage to producedegree of grafting about 150%. The formation of radiation induced

graft copolymerization was conrmed by SEM pictures which

Fig 8. XRD patterns for kenaf grafted with GMA at different degrees of grafting(a) ungrafted kenaf, (b) 65%, (c) 146% and (d) 196%.The authors are very grateful to Mr. Wilfred Sylvester Paula andMrs. Zaiton Selamat for their help in getting the XRD results andSEM pictures. We also thank the Ministry of Science, Technologyand Innovation Malaysia for funding the project under ScienceFund grant 03-03-01-SF0171.show thick formation of poly GMA at high absorbed dose. FTIRspectrum of GMA grafted kenaf bers also show clearly thepresence of characteristic peaks due to GMA. While XRD resultsshow the degree of crystallinity was decreased with the increaseof degree of grafting.

Acknowledgements(a)

(b)

(c)

(d)

100015002000mbers (cm-1)

) grafted kenaf bers at Dg76% (d) grafted kenaf ber at Dg157%.References

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J. Sharif et al. / Radiation Physics and Chemistry 91 (2013) 125131 131

Graft copolymerization of glycidyl methacrylate onto delignified kenaf fibers through pre-irradiation techniqueIntroductionExperimentalMaterialsTreatment of kenaf bast fibersRadiation graft copolymerizationSample characterization

Results and discussionTreatment of kenaf fibersEffect of absorbed doseEffect of reaction temperature and timeEffect of monomer concentrationFTIR analysisX-ray diffraction measurement

ConclusionAcknowledgementsReferences