Nuclear Instruments and Methods in Physics Research B 267 (2009) 2416–2422

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Nuclear Instruments and Methods in Physics Research B

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Functional polymers synthesized by grafting of glycidyl methacrylate ontoswift heavy ions irradiated BOPP films using chemical initiator

Shashi Chawla a, Anup K. Ghosh b, Devesh K. Avasthi c, Pawan K. Kulriya c, Sharif Ahmad d,*

a Amity School of Engineering and Technology, New Delhi, Indiab Centre for Polymer Science and Engineering, Indian Institute of Technology, New Delhi, Indiac Inter University Accelerator Center, Aruna Asaf Ali Marg, New Delhi, Indiad Materials Research Laboratory, Department of Chemistry, Jamia Millia Islamia, New Delhi 110 025, India

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a r t i c l e i n f o

Article history:Received 21 May 2008Received in revised form 4 March 2009Available online 8 May 2009

PACS:82.35.�x78.30.Jw61.05.Cp68.37.Hk82.80.Gk

Keywords:Poly(propylene)Tailored synthesisGraft copolymersFunctional polymers

0168-583X/$ - see front matter � 2009 Elsevier B.V.doi:10.1016/j.nimb.2009.04.012

* Corresponding author. Tel.: +91 26981717x3268;E-mail address: sharifahmad_jmi@yahoo.co.in (S. A

a b s t r a c t

Commercially available biaxially oriented polypropylene (BOPP) films were irradiated with 90 MeV Ni8+

ions and 120 MeV Ag11+ ions at different fluencies varying from 1010 to 3 � 1011 ions/cm2 and thengrafted with glycidyl methacrylate (GMA) using benzoyl peroxide (BPO) as chemical initiator. As the reac-tion temperature was below the melting point, PP was modified in the solid phase. A comparative studyfor the GMA grafting using BPO initiator in virgin as well as in the SHI irradiated BOPP indicates that theheterogeneity of the grafted GMA domains on the BOPP surface was higher in SHI irradiated system. Con-tact angle measurements showed an increasingly hydrophilic nature in the direction from pure PP tografted PP-g-GMA. These results are intended to benefit the synthesis and properties of a functional poly-mer, useful in developing a compatibilizer for PP/Cloisite 30B nanocomposites.

� 2009 Elsevier B.V. All rights reserved.CTE

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1. Introduction

A process by which chemical groups are attached by covalentbonds to a polymer backbone is known as grafting. When an activesite in a polymer (P) initiates the polymerization of a monomer(M), a graft copolymer (P-g-M) may be achieved. When the graftsare long, properties will be very different from those of the originalpolymer substrate. If the grafts are short with less than five moie-ties, most of the physical and/or mechanical properties will be re-tained. However, the chemical properties of the modified polymermay become quite different, this often being the ultimate objective[1].

Graft polymers can be made by radiation grafting, plasma in-duced grafting and chemical grafting. However, there are still somelimitations in the conventional grafting methods: radiations likegamma (c) rays can damage the polymer structures over long-timeexposures; plasma grafting is expensive, slow and has found onlylimited applications. The use of chemical initiators in chemicalgrafting has resulted in the production of homo-polymers which

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fax: +91 26980229.hmad).

not only waste expensive starting materials but also make process-ing more laborious [2].

Swift heavy ions possess kinetic energies of the order of 1 MeVper nucleon. They are used for the nanometer-scale tailoring ofsurfaces in materials research [3]. When a beam of swift heavy ions(SHI’s) penetrate in a polymer film, it induces a continuous trail ofionizations and excitations leading to bond cleavages and genera-tion of ‘‘free radicals”. Rearrangements and reactions of these pri-mary and secondary defects lead to the formation of thecylindrical region of latent tracks which are in general stable intime. The latent track consists of a relatively small region, with atypical diameter up to about 10 nm along ion path and is alsoknown as deactivated inner core region. Inside this core region,the irradiation dose is so high that no active site remains for thegrafting process [4,5]. The core region is surrounded by a largerouter region called penumbra, which is created by delta rays (cloudof electrons) with enough energy to leave the core [6]. In the caseof ion-beams, two different energy deposition mechanisms actsimultaneously. One is the electronic energy loss dominating atenergies >1 MeV per nucleon and the second is nuclear stoppingor elastic binary collision dominating mainly in the low energyregion. The presence of these different energy deposition

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mechanisms induces the creation of active sites (radicals) for graft-ing in the halo or chemical zone, which is a region between thecore and the penumbra. Therefore the grafting is heterogeneousand localized preferentially along the ion tracks [7].

In SHI grafting process, the polymer is first kept in air after SHIirradiation. Therefore excited chemical species and radicals are ableto react with oxygen leading to the formation of peroxides andhydroperoxides which can be decomposed at high temperaturesfor initiating the grafting process in the peroxide method [8]. SHIgrafting is unique from the point of view that it can generate surfaceswith micro domains of modified and unmodified polymer. Thus, it ispossible to reveal the latent tracks by grafting. The latent tracks canalso be revealed by etching process in which suitable chemical re-agents are used that dissolve the polymeric material in the irradi-ated zone faster than the bulk material. The etching procedure is awell-known technique to produce pores of different shape and sizein polymeric materials. The obtained nuclear track membranes(NTM’s) have been extensively used to separate biological cells, sta-bilizing beverages, filtering polluted air streams, etc. [9–11].

The modified NTM can also exhibit intelligence if it is providedwith the characteristic of changing pore size in response to achange in environmental conditions such as pH, temperature, elec-tric fields, etc. Experimentally such intelligent membranes aredeveloped through chemical bonding of the grafted domains ofsuitable polymers to the NTM [12–18]. Following this idea severalresearchers reported results using processes that produce graftedcopolymers in and outside the pore thus changing the surface ofthe substrate [19–23].

Polypropylene plays big roles in our daily life because of its all-round good performance, versatile properties and low cost.However, its poor surface properties, such as low wettability,print-ability and dyeability etc. limit its fields of application [24].One of the most common methods used for the improvement ofthese disadvantages is to graft polar monomers onto the surfaceof PP.

Glycidyl methacrylate (GMA) is a bifunctional monomer. It con-tains carbon–carbon double bond which makes it capable of free-radical grafting onto polyolefin’s. Moreover it also possesses highlyelectrophilic epoxide moiety which can react with different nucle-ophilic functional groups such as hydroxide and amine groups.Through such reactions, GMA-grafted polymer can be modified toalcohols [25], amines [26], and so on.

Our group has performed a study analyzing the GMA graftingcharacteristic of irradiated polypropylene film with 120 MeV Ag9+

ion-beams in the fluence range of 1010–3 � 1011 ions/cm2 withoutan additional initiator [27]. The purpose of the present work is tocontinue with this research program using 90 MeV Ni8+ ions,120 MeV Ag11+ ions with and without using benzoyl peroxide(BPO) as chemical initiator. The effects on the measured graftingyields of different swift heavy ions alone and in combination withBPO were studied. In this article, a comparative analysis was con-ducted to learn the grafting process. To our knowledge, a system-atic study which takes into account the use of BPO for graft co-polymerization on SHI irradiated PP is lacking. The purpose of thiswork is to study the grafting of GMA onto PP for its potential use asa compatibilizer in PP/Cloisite 30 B nanocomposites.

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Table 1Irradiation specifications.

SHI Energy Chargestate

Velocity(m/s)

Fluence(ions/cm2)

Electronicstoppingpower (keV/nm)

(MeV) (MeV/amu)

Ni 90 1.55 +8 1.73 � 107 1010–3 � 1011 4.92Ag 120 1.11 +11 1.46 � 107 1010–3 � 1011 7.34

2. Experimental

2.1. Materials

Commercially available biaxially oriented polypropylene(BOPP) films (15 lm in thickness) were supplied by Flex industries,Ltd. (Noida, India). GMA, xylene, benzoyl peroxide (BPO), and ace-

tone (analytical reagent grade) were purchased from Sigma Aldrich(Steinheim, Germany) and were used ‘‘as received”.

2.2. Irradiations

The experimental set-up consisted in target BOPP films of 1 cm2

arranged perpendicular to the SHI direction. Irradiations of BOPPfilm samples were performed in a vacuum of 10�6 torr at roomtemperature using a 15UD Pelletron accelerator at the Inter Uni-versity Accelerator Center (New Delhi, India). The 90 MeV Ni8+

ion and 120 MeV Ag11+ ion-beams in the fluence range of 1010–3 � 1011 ions/cm2 were used for irradiation. The ion-beam currentwas about 0.5–1 particle nA. The ion-beam was scanned in an areaof 10 mm � 10 mm with an electromagnetic scanner. The irradia-tion specifications are summarized in Table 1.

2.3. Grafting procedure

2.3.1. Grafting of GMA on swift heavy ions irradiated BOPP filmsThe BOPP grafted with GMA was prepared according to a previ-

ous work [27].

2.3.2. Grafting of GMA on either virgin BOPP film or swift heavy ionsirradiated BOPP film using benzoyl peroxide (BPO) as chemicalinitiator

The procedure of grafting polymerization was as follows: In thefirst step, an aqueous solution of 1 wt.% Mohr’s salt and 0.5 wt.%BPO was prepared. In the second step, BOPP film containing0.04 mL GMA was placed in the glass tube. An aqueous solutionof BPO and Mohr’s salt was added to it. The glass tube was subse-quently deoxygenated with bubbling nitrogen for 5 min andsealed. Afterwards, the glass tube was placed in an oven at 85 �Cso that grafting reaction could take place. After a given graftingperiod, the film was taken out from the glass tube, and the unre-acted GMA monomer was extracted by the soaking and washingof the film in acetone and the drying of the film at room tempera-ture in air to a constant mass. The GMA homo-polymer adsorbedonto the film was washed off with a larger amount of acetone at25 �C for 24 h. Finally, the samples were dried in an oven at 70 �Cin a vacuum upto a constant weight.

For the studies of the effects of the various parameters on thegrafting polymerization, the grafting percentage (Gp) was deter-mined according to the following equation:

Gp ¼ ½ðWg �WoÞ=Wo� � 100%: ð1Þ

In Eq. (1), Wo and Wg denote the weights of the BOPP film samplesbefore and after grafting, respectively.

2.4. Analysis

The following characterization techniques have been employedto study the SHI induced grafting of GMA onto BOPP:

2.4.1. Fourier transform infrared spectral analysisInfrared (IR) measurements were performed on a Perkin Elmer

Cetus Instruments (Norwalk, CT, USA) FTIR spectrophotometer

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Fig. 1. FTIR Spectra of (a) un-irradiated BOPP, (b) GMA, and (c) PP-g-GMA.

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model RX1 at a resolution of 4.0 cm�1. The scanned wave numbersranged from 4000 to 500 cm�1.

2.4.2. Scanning electron microscopy analysisThe surface morphologies of virgin BOPP and grafted BOPP (PP-

g-GMA) film samples were investigated using a JEOL- JSM-840model scanning electron microscope (Tokyo, Japan). For thesestudies the film samples were gold-coated by a sputtering tech-nique to a depth of about 150 Å. Gold-coating of the samples pre-vented charge build-up and provided better emissivity ofsecondary electrons.

2.4.3. Contact angle analysisThe contact angle measurements of water droplets on the BOPP

and the PP-g-GMA surfaces were done with a Rame-Hart model100-00-230 goniometer (Netcong, NJ, USA).

2.4.4. Wide-angle X-ray diffraction analysisWide-angle X-ray diffractograms of virgin BOPP and grafted

BOPP samples were obtained using a Philips analytical X-rayPW1710 diffractometer (Almelo, The Netherlands) with the CuKaradiation at room temperature. The operating condition of the X-ray source was set at a voltage of 40 kV and a current of 30 mA.The scanning was performed in a scattering angle (2h) range of5–35�. The scanning rate used for WAXD was 2.4� min�1. TheWAXD measurements were performed with a data acquisitiontime of 25 s per scan.

The crystallite size of PP was calculated according to the Scher-rer equation [28]:

L ¼ Kk=b cos h; ð2Þwhere L is the crystallite size (Å), b is the full width at half-maxi-mum (fwhm; rad) k is the wavelength of the X-ray beam(1.5425 Å), and K is a constant usually equal to 1.

The strain in PP was calculated by:

b ¼ 4e tan h; ð3Þwhere b is peak width (in radians), and e is strain.

The degree of crystallinity, Xc, is expressed in mass fraction ofthe crystalline phase, and can be determined from the WAXD pat-terns based on the ratio of the integrated intensities under thecrystalline peaks Ac to the integrated total intensities, A = Ac + Aa

in which Aa, is the integrated intensities under the amorphous halo[29]:

Xcð%Þ ¼ ½Ac=ðAc þ AaÞ� � 100 ð4ÞTR

3. Results and discussion

3.1. FTIR spectroscopic analysis

With the purpose of establishing the existence of GMA graftingon BOPP, the FTIR spectrum of BOPP, GMA and GMA-grafted-PPsamples were recorded and respectively shown in Fig. 1(a)–(c).The details of the FTIR Spectroscopic Analysis of the virgin BOPP,swift-silver-ions irradiated and GMA-grafted BOPP film is pub-lished elsewhere [27,30,31,33]. As discussed in these papers,Fig. 1(a) indicates that the industrial BOPP film was made from iso-tactic PP. We assume that the grafted systems are composed of twoindependent components, the substrate (BOPP) and the graftedpolymer (poly GMA) and that each component has a specificabsorption band [32]. A comparison of the FTIR spectra (Fig. 1(b)and (c)) shows clearly the absence of absorption at 1639 cm�1

(C@C of GMA) in the grafted polymer, together with a red-shift inthe ester carbonyl absorption (a shift from 1729 to 1733 cm�1),which is ascribed to the formation of a saturated ester. These results

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indicate that the grafting of GMA onto the BOPP film is clearlyachieved.

3.2. WAXD crystallographic studies

Figs. 2(a) and 3(a) present a typical WAXD pattern of the virginBOPP. The WAXD curves of modified PP are shown in Figs. 2(b) and(d) and 3(b) and (d). These WAXD patterns show that the virginBOPP film and the PP-g-GMA samples mainly consist of the a mod-ification. The details of the WAXD crystallographic studies of thevirgin BOPP, swift-silver-ions irradiated and GMA-grafted BOPPfilm is published elsewhere [27].

The full width at half-maximum (fwhm) values and crystallitesizes of the virgin and PP-g-GMA samples are shown in Tables 2and 3. The peaks for the PP-g-GMA samples were shifted to smallerangles than that of the original BOPP. This clearly indicated that theinterspacing of PP layers was swollen to larger distance by thegrafted GMA chains [34].

The average crystallite sizes of the virgin BOPP and GMA-grafted PP (PP-g-GMA) were calculated using the Scherrer equationand the results are shown in Table 4.

3.2.1. Influence of grafting percent (Gp) and length of grafted chains onthe size of PP crystals

The evolution of crystallite size as a function of the grafting per-cent for swift nickel (Ni) and swift silver (Ag) ions in peroxide-ini-tiated grafting system are comparatively shown in Fig. 4. Thesecurves in Fig. 4 shows that a general trend is followed for theexperimental points independently of swift heavy ion velocityand stopping power.

Fig. 5 compare the evolution of change in average crystallitesize (%) as a function of the fluency of swift Ni and Ag ions in per-oxide-initiated grafting system. Fig. 6 compare the evolution ofchange in crystallinity (%) as a function of the fluency of swift Niand Ag ions in peroxide-initiated grafting system.

Initially, in the low fluence range, with an increase in the flu-ence, the number of irradiated zones (and latent tracks and num-

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Fig. 2. WAXD Plots of (a) un-irradiated BOPP, (b) Ni8+ irradiated (U = 3 � 1010) andGMA-grafted BOPP using BPO initiator (Gp = 4.41%), and (c) Ni8+ irradiated(U = 1 � 1011) and GMA-grafted BOPP using BPO initiator (Gp = 4.17%). (d) Ni8+

irradiated (U = 3 � 1011) and GMA-grafted BOPP using BPO initiator (Gp = 3.92%).

Fig. 3. WAXD plots of (a) un-irradiated BOPP, (b) Ag11+ irradiated (U = 1 � 1010) andGMA-grafted BOPP using BPO initiator (Gp = 5.0%). (c) Ag11+ irradiated (U = 3 � 1010)and GMA-grafted BOPP using BPO initiator (Gp = 4.0%), (d) Ag11+ irradiated(U = 1 � 1011) and GMA-grafted BOPP using BPO initiator (Gp = 2.22%).

Table 2fwhm (b), and crystallite size (L) of virgin BOPP and PP-g-GMA samples obtained fromperoxide-initiated grafting system containing monomer (GMA) and polymer (swift-nickel-ions irradiated industrial polypropylene films).

2h� Full width of the WAXDpeak at half-maximum (b) (�)

Crystallitesize (L) (Å)

Virgin BOPP14.0 0.701 127.016.9 0.641 139.318.6 0.598 149.7

PP-g-GMA114.0 0.693 128.416.9 0.645 138.418.6 1.144 78.2

PP-g-GMA214.0 0.657 135.516.8 0.615 145.218.6 0.6 149.2

PP-g-GMA314.0 0.671 132.716.9 0.653 136.918.5 0.879 101.8

PP-g-GMA414.0 0.657 135.516.9 0.628 142.318.5 0.833 107.5

Table 3fwhm (b), and crystallite size (L) of virgin BOPP and PP-g-GMA Samples obtained fromperoxide-initiated grafting system containing monomer (GMA) and polymer (swift-silver-ions irradiated industrial polypropylene films.)

2h� Full width of the WAXD peakat half-maximum (b) (�)

Crystallitesize (L) (Å)

Virgin BOPP14.0 0.701 127.016.9 0.641 139.318.6 0.598 149.7

PP-g-GMA514 0.6381 139.516.9 0.6033 148.018.6 0.6033 148.4

PP-g-GMA614 0.6684 133.216.9 0.6233 143.318.6 0.6233 143.6

PP-g-GMA714 0.6741 132.116.9 0.606 147.418.6 0.8181 109.4

PP-g-GMA814 0.6609 134.716.9 0.6102 146.418.6 0.6102 146.7

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ber of macro-radical reactive sites) also increases. An increasingnumber of macro-radicals propagate simultaneously, and graftchains grow to shorter lengths. Large amounts of short graft chainsacting as the nucleus agent speed up the crystallization process,and therefore increase the percentage crystallinity and decreasethe size of the crystal. At higher fluencies, when the latent tracksintersect each other, the core or deactivated zone of one latenttrack can eliminate the activated zone of the other latent track,consequently less PP radicals are involved in propagation stepsas a consequence the graft chains grow to longer lengths [36–39]. The long graft chains hinder the crystallization, resulting in a

large crystal particle and less percentage crystallinity. Thus, we ob-serve the opposite trends when changes in average crystallite sizeas well as crystallinity are calculated w.r.t. the virgin BOPP. The ob-tained results are in agreement with the previously reported re-sults by Pan et al. [35].

3.3. Morphological studies

The surfaces of virgin and graft modified PP film samples wereexamined by SEM and the results are shown in Fig. 7. The virginBOPP film surface was plain and smooth (Fig. 7(a)). Initially, withan increase in the fluence, the number of irradiated zones (and la-tent tracks and number of reactive sites) also increases. An increas-

Table 4Grafting percent, fluence, change in average crystallite size, change in average strain, change in percentage crystallinity and contact angles of virgin BOPP and PP-g-GMA samples.

Sample Chemical initiator/swift heavy ion

Fluency ofswiftheavy ion(ions/cm2)

Grafting percentGp (Wt.%)

Wettingpropertycontactangle (o)

Crystallization behavior

Crystallineform

Change in averagecrystallite size (%)

Averagestrain

Change incrystallinity (%)

Un-irradiated BOPP – – 0.0 78 Monoclinic(a form)

0 0.019 0

PP-g-GMA1 90 MeV Ni8+

ion + BPO1 � 1010 4.4 70 Monoclinic

(a form)�23.4 0.025 105.3

PP-g-GMA2 90 MeV Ni8+

ion + BPO3 � 1010 4.4 69 Monoclinic

(a form)3.9 0.019 48.9

PP-g-GMA3 90 MeV Ni8+

ion + BPO1 � 1011 4.2 73 Monoclinic

(a form)�9.9 0.022 64.5

PP-g-GMA4 90 MeV Ni8+

ion + BPO3 � 1011 3.9 75 Monoclinic

(a form)�13.2 0.016 112.5

PP-g-GMA5 120 MeV Ag11+

ion + BPO1 � 1010 5.0 61 Monoclinic

(a form)�12.4 0.019 �30.9

PP-g-GMA6 120 MeV Ag11+

ion + BPO3 � 1010 4.0 74 Monoclinic

(a form)�6.7 0.019 �54.9

PP-g-GMA7 120 MeV Ag11+

ion + BPO1 � 1011 2.2 76 Monoclinic

(a form)�22.6 0.021 1.0

PP-g-GMA9 BPO – 17.9 43 Monoclinic(a form)

�6.3 0.020 �56.3

PP-g-GMA10 120 MeV Ag9+ ion 3 � 1011 5.3 59 Monoclinic(a form)

�25.7 0.026 35.7

Fig. 4. Change of crystallite size as a function of the grafting percent for swift nickeland swift-silver-ions, respectively.

Fig. 5. Change in average crystallite size as a function of the fluence of swift-nickel-ions and swift-silver-ions irradiated and GMA-grafted BOPP using BPO initiator.

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ing number of macro-radicals propagate simultaneously, graftingpercent (Gp) increases, and the grafted chains grow to shorterlengths. As a result, only the spectrum of the graft is observed(Fig. 7(b)–(e)). With Gp increasing, some globular grains appeared.Moreover, the size and the number of the grains increase continu-ally. At last, the grains connected together and formed a new layer.The GMA-grafted BOPP was also prepared using BPO as the onlychemical initiator. It resulted in maximum Gp and the SEM(Fig. 7(f)) shows that grafted GMA forms a new layer. Usingswift-silver-ions at higher fluences, the latent tracks intersect eachother and the core or deactivated zone of one latent track can elim-inate the activated zone of the other latent track, consequently lessPP radicals are involved in propagation steps so the length of thegrafted chains gets bigger (Fig. 7(g)) and Gp decreases, even if theinitial GMA concentration is kept constant. Thus, SHI grafting is un-

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ique in the respect that it generates surface with micro domains ofmodified and unmodified polymers.

3.4. Grafting percent of grafting polymerization

3.4.1. Grafting system containing monomer (GMA) and polymer (swiftheavy ions irradiated BOPP films)

The obtained results as summarized in Table 4 indicate thatwhen SHI is used alone only Ag ions are suitable for the graftingof GMA on BOPP. This can be due to the fact that part of the dam-age induced in BOPP using Ag ions, having comparatively higherelectronic stopping power and smaller velocity than swift Ni ions,and subsequent exposure to air produced active sites (peroxidesand hydro peroxides) needed to initiate grafting reactions of glyc-idyl methacrylate (GMA) on BOPP. Mechanism of this grafting sys-tem is published elsewhere [27].

Fig. 6. Change in crystallinity as a function of the fluence of swift-nickel-ions andswift-silver-ions irradiated and GMA-grafted BOPP using BPO initiator.

Fig. 7. SEM photographs: (a) virgin BOPP, (b) Ni8+ (U = 1010) irradiated and GMA-grafted BOPP using BPO initiator (Gp = 4.396%), (c) Ni8+ (U = 3 � 1010) irradiated andGMA-grafted BOPP using BPO initiator (Gp = 4.412%), (d) Ag11+ (U = 3 � 1010)irradiated and GMA-grafted BOPP using BPO initiator (Gp = 4.00%), (e) Ag11+

(U = 1 � 1011) irradiated and GMA-grafted BOPP using BPO initiator (Gp = 2.22%),(f) GMA-grafted BOPP using benzoyl peroxide as initiator (Gp = 17.86%) and (g) Ag9+

(U = 3 � 1011) irradiated and GMA-grafted BOPP (Gp = 5.26%).

Fig. 8. Grafting percent as a function of the fluence for peroxide-initiated graftingsystem containing monomer (GMA) and polymer (swift Ni and Ag ions irradiatedindustrial polypropylene films).

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3.4.2. Peroxide-initiated grafting system containing monomer (GMA)and polymer (BOPP films)

Generally, in grafting systems like the present work, the forma-tion of significant amounts of homo-polymer is inevitable. Theo-retically, surface grafting polymerization is equivalent to chaintransfer reaction to polymer in ordinary polymerization systems,and the competition of grafting polymerization and homo-poly-merization is indeed the competition of chain transfer and propa-gation. According to the literature [40], the values of transferconstant to polymer are about 10�4 at 60 �C, which is to say thatthe rate of homo-polymerization is 104 times higher than the rateof grafting polymerization under the same experimental condi-tions. Furthermore, according to well-known Arrhenius equation,the increase of temperature can increase the rate of grafting poly-merization and homo-polymerization simultaneously. But the acti-

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vation energy of grafting polymerization is much greater that thatof homo-polymerization, so the increase of temperature cangreatly increase grafting efficiency. The increase in temperaturealso increases the decomposition rate of BPO, and the mobility ofthe GMA monomer. All these effects cause the increase in graftingrate. In addition to these factors, a more important point in thepresent work is that the increase in temperature increases theactivity of hydrogen atom on the PP backbone, which enables pri-mary radicals to abstract hydrogen atoms more easily and thuscreates more surface radicals. At low temperature, it is difficultfor the primary radicals to abstract hydrogen atoms from PP back-bone, so graft percent is very low. On the other hand, at a too hightemperature, the rate of formation of surface radicals is too rapid,which makes the termination to occur predominantly. Therefore, alower graft percent is obtained. In our system, we worked at inter-mediate temperature of 85 �C. To minimize the homo-polymeriza-tion of GMA, an aqueous solution of 1 wt.% Mohr’s salt was alsoadded. Moreover, the monomer concentration was kept constantand for avoiding degradation of polypropylene, BPO concentrationwas kept very low (0.5%). Under these conditions, the grafting per-cent was found to be 17.9%.

3.4.3. Peroxide-initiated grafting system containing monomer (GMA)and polymer (swift heavy ions irradiated BOPP films)

Influence of fluence of SHI on Grafting percent (Gp):The evolution of grafting percent as a function of the fluency of

swift Ni and Ag ions in peroxide-initiated grafting system is shownin Fig. 8. Initially, with an increase in the fluence, grafting percentincreases. At higher fluences, the Gp decreases, even if the initialGMA concentration is kept constant. The obtained results are inagreement with the previously reported results [41].

The obtained results (Table 4) indicate that the Gp was lesswhen grafting was done using benzoyl peroxide (BPO) on the swiftheavy ion irradiated industrial PP film. This is because in this sys-tem the BPO initiator is inefficiently used. There is wastage of BPOinitiator due to its induced decomposition by the attack of propa-gating radicals on the BPO initiator. This reaction is termed aschain transfer to initiator [40]. The induced decomposition of initi-

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ator does not change the radical concentration during the polymer-ization, since the newly formed radical (C6H5COO�) will initiate anew polymer chain. However, the reaction does result in wastageof initiator. A molecule of initiator is decomposed without an in-crease in the number of propagating radicals or the amount ofmonomer (GMA) being converted to graft copolymer (PPgGMA).This results in a decrease in Gp. The mechanism of grafting poly-merization reactions of such system is not clear and certainly de-serves further research.

3.5. Studies of the wetting properties

The dependence of the water contact angle versus content ofgrafted GMA in the modified PP film is given in Table 4. The watercontact angle on the virgin hydrophobic PP film surface is high andhas the value 78�. The value of contact angle was found to decreasewith raising content of grafted GMA. These results indicate that theincrease of the grafted GMA content causes significant increase inhydrophilicity in GMA-grafted PP film.

4. Conclusion

This article concerns with the synthesis of functional polymersby grafting of glycidyl methacrylate onto swift Ni and Ag ions irra-diated BOPP films using benzoyl peroxide as chemical initiator.FTIR, SEM and WAXD results provided evidence of the modificationof the PP surface on GMA grafting. Exposure of industrial PP film toSHI results in wastage of BPO initiator by chain transfer to initiator.Consequently, we observe a reduction in the effect of the BPO forgraft copolymerization. When the fluence of swift Ni and Ag ionsin BPO initiated grafting system increases, the evolution of thegrafting yield can be explained in terms of elimination of the acti-vated zone of one latent track by the deactivated zone of the otherlatent track, as the latent tracks intersect each other. Furthermore,the evolution of the change in average crystallite size and changein percentage crystallinity with respect to fluence can be explainedin terms of the effect of the length of graft chains on the crystalli-zation process. The hydrophilicity of PP film was improved bygrafting of GMA on it.

Acknowledgements

The authors thank the Inter University Accelerator Centre, NewDelhi, India for financial support and facilitating WAXD and AFMstudies through IRPHA project of DST. Shashi Chawla gratefullyacknowledges the blessings of Dr. Ashok K. Chauhan, Founder Pres-ident of RBEF and Amity University. He is also obliged to Prof. B.P.Singh, Senior Director, and Prof. P. Prakash, Director of the AmitySchool of Engineering and Technology, and Prof. Kishwar Saleem,Head of the Department of Chemistry of Jamia Millia Islamia (In-dia) for their guidance and encouragement.

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References

[1] D.C. Sherrington, Reactions of polymers, in: H.R. Mark, N.M. Bikales, C.G.Overberger, J.I. Kroschwitz (Eds.), Encyclopaedia of Polymer Science andEngineering, Vol. 14, John Wiley, New York, 1988, p. 101.

[2] J. Zhu, J. Deng, S. Cheng, W. Yang, Macromol. Chem. Phys. 207 (2006) 75.[3] P. Apel, Nucl. Instr. and Meth. B 208 (2003) 11.[4] A. Chapiro, Nucl. Instr. and Meth. B 32 (1988) 111.[5] R.L. Fleisher, P.B. Price, R.M. Walker, Nuclear Tracks in Solids, University of

California Press, 1975.[6] E.H. Lee, Nucl. Instr. and Meth. B 151 (1999) 29.[7] N. Betz, Nucl. Instr. and Meth. B 105 (1995) 55.[8] M.M. Nasef, E.S.A. Hegazy, J. Polym. Sci. 29 (2004) 499.[9] R.L. Fleischer, P.B. Price, R.W. Walker, Nuclear Tracks in Solids: Principles and

Applications, University of California Berkeley, 1975.[10] R. Mazzei, Radiat. Meas. 26 (1996) 577.[11] R. Spohr, Ions Tracks and Microtechnology, Principles and Applications, in: K.

Bethge (Ed.), Fried, Vieweg and Sohn Verlagsgesellschaft mb, Braunschweig,1990, p. 144.

[12] H. Omichi, Nucl. Instr. and Meth. B 105 (1995) 302.[13] R. Mazzei, G. Garcia Bermudez, N. Betz, E. Cabanillas, Nucl. Instr. and Meth. B

226 (2004) 575.[14] R. Mazzei, G. Garcia Bermudez, V.C. Chappa, M.F. del Grosso, A. Fernandez,

Nucl. Instr. and Meth. B 251 (2006) 99.[15] R. Mazzei, A. Fernandez, G. Garcia Bermudez, A. Torres, M.C. Gutierrez, M.

Magni, G. Celma, D. Tadey, Nucl. Instr. and Meth. B 266 (2008) 3170.[16] N. Betz, S. Dapz, M.J. Guittet, Nucl. Instr. and Meth. B 131 (1997) 252.[17] N.I. Shtanko, V.Ya. Kabanov, M. Yoshida, Nucl. Instr. and Meth. B 151 (1999)

416.[18] M.C.P. Durrieu, C.A. Chodur, N. Betz, J. Biomed. Mater. Res. 52 (2000) 119.[19] I. Kaetsu, Nucl. Instr. and Meth. B 105 (1995) 294.[20] N.I. Shtanko, V.Ya. Kabanov, P.Y. Apel, M. Yoshida, A.I. Vilenskii, J. Membr. Sci.

179 (2000) 155.[21] L.Y. Chu, S.H. Park, T. Yamaguchi, S.I. Nakao, J. Membr. Sci. 192 (2001) 27.[22] R. Mazzei, E. Smolko, A. Torres, D. Tadey, L. Gizzi, Nucl. Instr. and Meth. B 170

(2000) 419.[23] R.O. Mazzei, E. Smolko, A. Torres, D. Tadey, C. Rocco, L. Gizzi, S. Strangis, Radiat.

Phys. Chem. 64 (2002) 149.[24] G. Xu, S. Lin, Macromol. Sci. Rev. Macromol. Chem. Phys. 34 (1994) 555.[25] M. Kim, S. Kiyohara, K. Satoshi, T. Satoshi, K. Saito, T. Sugo, J. Membr. Sci. 33

(1996) 117.[26] Y.C. Nho, J.S. Park, J.H. Jin, J. Mat. Sci. Part A: Pure Appl. Chem. 34 (1997) 831.[27] S. Chawla, A.K. Ghosh, S. Ahmad, D.K. Avasthi, J. Appl. Polym. Sci. 105 (6)

(2007) 3578.[28] P. Scherrer, Gott. Nachar 2 (1918) 98.[29] Y. Shangguan, Y. Song, M. Peng, B. Li, Q. Zheng, Eur. Polym. J. 41 (2005) 1766.[30] E. Balanzat, N. Betz, S. Bouffard, Nucl. Instr. and Meth. B 105 (1995) 46.[31] G. Parthasarthy, R.M. Kannan, J. Polym. Sci: Part B: Polym. Phys. 40 (2002)

2539.[32] C. Aymes-Chodur, N. Betz, M.C. Porte-Durrieu, C. Baquey, A. Le Moel, Nucl.

Instr. and Meth. B 151 (1999) 377.[33] S. Chawla, A.K. Ghosh, S. Ahmad, D.K. Avasthi, Nucl. Instr. and Meth. B 244

(2006) 48.[34] J. Li, C. Zhou, W. Gang, Polym. Test. 22 (2003) 217.[35] Y. Pan, J. Ruan, J. Zhou, J. Appl. Polym. Sci. 65 (1997) 1905.[36] E. Smolko, Nucl. Instr. and Meth. B 132 (1997) 452.[37] V.C. Chappa, M.F. del Grosso, G. Garcia Bermudez, R.O. Mazzei, Nucl. Instr. and

Meth. B 243 (2006) 58.[38] M.F. del Grosso, V.C. Chappa, G. Garcia Bermudez, R.O. Mazzei, Nucl. Instr. and

Meth. B 245 (2006) 281.[39] G. Garcia Bermudez, V.C. Chappa, F. del Grosso, R.O. Mazzei, Nucl. Instr. and

Meth. B 266 (2008) 3063.[40] G. Odian, Principles of Polymerization, third ed., J. Wiley and Sons Inc.,

Hoboken, New Jersey, 2004.[41] N. Betz, A. Le Moel, J.P. Duraud, E. Balanzat, Macromolecules 25 (1992) 213.

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