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Preparation, Characterization and Properties ofFlexible Magnetic Nanocomposites of NiFe2O4-polybenzoxazine-LLDPEAmit B. Rajput a , Seikh J. Rahaman b , Gautam Sarkhel b , Manoj K. Patra c , Sampat R.Vadera c & Narendra N. Ghosh aa Nano-materials Lab, Department of Chemistry , Birla Institute of Technology and Science,Pilani KK Birla Goa Campus , Goa , Indiab Department of Chemical and Polymer Engineering , Birla Institute of Technology , Mesra ,Jharkhand , Indiac Defense Lab , Jodhpur , Rajasthan , IndiaAccepted author version posted online: 24 Jun 2013.Published online: 02 Aug 2013.

To cite this article: Amit B. Rajput , Seikh J. Rahaman , Gautam Sarkhel , Manoj K. Patra , Sampat R. Vadera & Narendra N.Ghosh (2013) Preparation, Characterization and Properties of Flexible Magnetic Nanocomposites of NiFe2O4-polybenzoxazine-LLDPE, Polymer-Plastics Technology and Engineering, 52:11, 1097-1105, DOI: 10.1080/03602559.2013.763378

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Preparation, Characterization and Propertiesof Flexible Magnetic Nanocompositesof NiFe2O4-polybenzoxazine-LLDPE

Amit B. Rajput1, Seikh J. Rahaman2, Gautam Sarkhel2, Manoj K. Patra3,Sampat R. Vadera3, and Narendra N. Ghosh11Nano-materials Lab, Department of Chemistry, Birla Institute of Technology and Science, PilaniKK Birla Goa Campus, Goa, India2Department of Chemical and Polymer Engineering, Birla Institute of Technology, Mesra,Jharkhand, India3Defense Lab, Jodhpur, Rajasthan, India

A simple method for the preparation of magnetic nanocompositesconsisting of NiFe2O4 nanoparticles, polybenzoxazine (PB), linearlow-density polyethylene (LLDPE) and LLDPE-g- Maleic anhy-dride (LgM) is described. Composites were prepared by formingbenzoxazine- NiFe2O4 nanocomposites followed by melt blendingwith LLDPE and thermal curing of benzoxazine. The compositeswere characterized by XRD, DSC and TGA, FT-IR, SEM, UTMand VSM. The saturation magnetization of the composites contain-ing 33.25 wt% NiFe2O4 was 7.72 emu/g and it decreased withdecreasing amount of NiFe2O4 in the composite. The compositefilms exhibited mechanical flexibility as well as magnetic properties.

Keywords Composite; Ferrite; LLDPE; Magnetic property;Mechanical property; Polybenzoxazine; Synthesisand processing

INTRODUCTION

In recent years, there has been considerable interest inpolymer-ceramic nanocomposites due to their novel mech-anical, thermal and physicochemical properties. In poly-mer- ceramic composites it is possible to manipulate theirproperties (e.g., mechanical, thermal, electrical, magnetic,etc) by controlling the size and weight ratio of ceramic par-ticles in the composition[1–7]. These materials are capable ofexhibiting multifunctional performance, based on theproperties of individual constituents.

NiFe2O4 is one of the important members of magneticferrite family because of its plethora of applications inhigh-density magnetic recording media, magnetic refriger-ation, magnetic liquids, etc.[8,9]. Some other less traditionalbut interesting applications include its use as microwave or

radar absorbing stealth materials, which is very importantin defense technology[10,11]. Though, NiFe2O4 possessinteresting magnetic and electrical properties, theirinherent brittleness and lack of structural flexibility limittheir usage in complex structured devices and fabricationof flexible microwave or radar shielding sheets or coating.Apart from that, high sintering temperature (>1200�C) isgenerally required to prepare sintered NiFe2O4 bodies[12].One of the solutions to this problem is the hybridizationof NiFe2O4 nanoparticles with a flexible material (such aspolymer) to form composites which can possess goodmechanical flexibility and easy processibility.

The objective of our present work is to prepareNiFe2O4-polymer composites in the form of sheets andfilms, which can exhibit magnetic property as well asimproved mechanical properties (particularly structuralflexibility) and thermal stability. Here, NiFe2O4 (NF)nanoparticles have been used as magnetic material and ablend of polybenzoxazine (PB) and linear low-density ofpolyethylene (LLDPE) as polymeric matrix. Polybenzoxa-zine was deliberately chosen as one of the components inthe composites because it offers various advantages suchas near zero shrinkage upon curing, very low water absorp-tion, and good thermal stability, etc. Polybenzoxazines areformed by thermally activated ring opening polymerizationof the corresponding monomers without using any cata-lysts[13–17]. Varieties of polybenzoxazine based materials,their preparation, properties and applications have beenreported in the literature[18–26].

However, polybenzoxazine based magnetic nanocom-posites have scarcely been investigated. Only somestudies[27–29] concerned the preparation of polybenzoxa-zine-magnetic nanocomposites. Yet, the inherent brittle-ness of polybenzoxazine[30] needs to be improved for itsuse in fabrication of flexible films and complex structures.

Address correspondence to Narendra N. Ghosh,Nano-materials Lab, Department of Chemistry, Birla Instituteof Technology and Science, Pilani KK Birla Goa Campus, Goa403726, India. E-mail: naren70@yahoo.com

Polymer-Plastics Technology and Engineering, 52: 1097–1105, 2013

Copyright # Taylor & Francis Group, LLC

ISSN: 0360-2559 print=1525-6111 online

DOI: 10.1080/03602559.2013.763378

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Therefore, in this study polybenzoxazine was blended withlinear low-density polyethylene (LLDPE), because LLDPEpossesses excellent low-temperature flexibility, extraordi-nary processibility, better environmental stress crackingresistance, mechanical flexibility, more elongation at breakand puncture resistance[31]. In this article, we report thepreparation of flexible sheets and films of NiFe2O4-PB-LLDPE based magnetic nanocomposites with variouscompositions. The variation of mechanical and magneticproperties of these composites with changing compositionswas also investigated.

EXPERIMENTAL

Materials

The chemicals used were Fe(NO3)3 � 9H2O,Ni(NO3)2 � 6H2O, ethylene diamine tetra acetic acid(EDTA) (99.9%, Merck, India), aniline, paraformaldehydeand bisphenol-A (99%, s.d. fine-chem limited, India),CHCl3 (99.7%, Qualigens Fine Chemicals, India). Linearlow-density polyethylene (LLDPE, R35A042) having adensity of 0.935 gm=cm3 and melt flow index (MFI) of4.2 gm=10min, was obtained from GAIL (India) Ltd. andLLDPE-g-Maleic anhydride (LgM) (OPTIM E-126) with0.73% maleic anhydride content and MFI 2.16 gm=10min, from Pluss Polymers Pvt, Ltd., India. All chemicalswere used without further purification.

Synthesis

Synthesis of NiFe2O4(NF) Nanoparticles

NiFe2O4 nanoparticles, with �23 nm average particlesize, were synthesized by using a simple aqueous solutionbased EDTA precursor method, developed by us. Detailedsynthetic procedure and characterization of NiFe2O4 nano-powders have been reported elsewhere[32]. In a typical syn-thesis, nickel nitrate, iron (III) nitrate and EDTA wereused as starting compounds. A fluffy, brown colored pre-cursor was obtained by reacting stoichiometric amount ofaqueous solutions of metal nitrates with EDTA, followedby evaporating the reaction mixture to dryness at

�125�C. Calcination of precursor powder at 550�C for 4 hin air resulted in the formation of NiFe2O4 nanopowders.

Synthesis of Benzoxazine (BA) Monomer

Benzoxazine monomer (bis (3-phenyl-3, 4-dihydro-2H-1, 3-benzoxazinyl) isopropane) was synthesized using a sol-ventless method by reacting bisphenol-A, aniline, and par-aformaldehyde[33]. In a typical synthesis, bisphenol-A(0.02mol, 4.48 gm), aniline (0.04mol, 3.68ml) and parafor-maldehyde (0.08mol, 2.4 gm) were mixed in a round bot-tom flask and heated slowly at 90�C in an oil bath for90min. After cooling, benzoxazine monomer was extractedfrom reaction mixture by dissolving in CHCl3 followed byfiltration. Pure benzoxazine monomer was finally obtainedby evaporating CHCl3. Benzoxazine monomer was thendried in a vacuum oven for 24 h at 55�C to remove tracesof chloroform.

Preparation of Benzoxazine-NiFe2O4 (BA-NF)Nanocomposite

For synthesis of benzoxazine-NiFe2O4 nanocomposite,a solvent casting method was employed. Various composi-tions of nanocomposites, prepared by using BA andLLDPE are listed in Table 1. BA monomer was first dis-solved in CHCl3, followed by stepwise addition of NiFe2O4

nanopowder in desired weight ratio. During mixing, themixture was ultrasonicated. After completion of mixing,the mixture was dried in a vacuum oven at 80�C for 12 h.Dynamic light scattering studies showed the averageparticle sizes of these benzoxazine coated NiFe2O4

nanoparticles were in the range of 111 to 134 nm. Thebenzoxazine-NiFe2O4 nanocomposite powders thusobtained were used for further composite preparation.

Preparation ofLLDPE-LgM-PB-NiFe2O4(L-LgM-PB-NF)Composites

To prepare NiFe2O4-PB-LLDPE composite sheets,benzoxazine-NiFe2O4 nanocomposite powders (BA-NF)were blended with LLDPE with various weight ratios.

TABLE 1Compositions of prepared composites

Sample code LLDPE (wt%) LgM (wt%) PB (wt%) NiFe2O4 (wt%)

BA-NF (70:30) – – 70 30BA-NF (50:50) – – 50 50BA-NF (30:70) – – 30 7047.5L-5LgM-47.5PB 47.5 5 47.5 –47.5L-5LgM-33.25PB-14.25NF 47.5 5 33.25 14.2547.5L-5LgM-23.75PB-23.75NF 47.5 5 23.75 23.7547.5L-5LgM-14.25PB-33.25NF 47.5 5 14.25 33.25

BA¼Benzoxazine; NF¼NiFe2O4; L¼LLDPE; LgM¼LLDPE-g-Maleic anhydride; PB¼ polybenzoxazine.

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5wt% LgM was used as compatibilizer between LLDPEand PB. 5wt% LgM was chosen to prepare compositesbecause we have observed that mixing of 5wt% LgM withLLDPE and PB helps to achieve best mechanical propertyof LLDPE-PB composite[34]. Nanocomposites having dif-ferent compositions of NiFe2O4, PB and LLDPE were pre-pared as listed in Table 1. The blending of LLDPE, LgMand BA-NF was carried out in a custom made cylindricalmixing chamber (65mm diameter� 65mm height) using atwo sided blade stirrer. The temperature of mixing wasset at 180�C and the stirrer speed was 80 rpm. A mixtureof LLDPE and LgM was first melted for 10min thenBA-NF was added and mixed for 20min. The hot masswas then taken out from the mixing chamber and trans-ferred into a pot and heated at 200�C for 30min in an ovenfor the polymerization of BA monomer. The hotsemi-viscous mixture thus obtained was immediatelypoured into a closed mold under hydraulic pressurethrough a 5mm gate. The material inside the mold cavitywas allowed to cool to room temperature and then moldwas opened to take out the final product. As per ASTMD638 standard specification Type I dog bone shaped speci-mens (with over all dimension 165mm� 19mm� 3.2mm)of the composites were prepared by this method for mech-anical testing.

Sample Characterization

Room temperature X-Ray diffraction spectra of the cal-cined powder and cured composites were recorded by usinga wide angle powder X-Ray diffractometer (Mini Flex II,Rigaku, Japan) with Cu Ka (k¼ 0.15405 nm) radiation.Thermogravimetric analysis (TGA) and differential scan-ning calorimetric (DSC) analysis were carried out for neatpolymer and composites by using DTG-60 and DSC-60(Shimadzu, Japan), respectively. Thermal analysis was per-formed at a constant heating rate of 10�C=min in airatmosphere.

Fourier transform infrared (FT-IR) spectra of the sam-ples were recorded using a Shimadzu IR Prestige-21 Spec-trometer, equipped with a potassium bromide (KBr)beam-splitter. All spectra were recorded with 50 scans atresolution of 4 cm�1and spectral range between 4000 to400 cm�1. Tensile measurements were performed accordingto ASTM D638 standard using an INSTRON 3366 univer-sal testing machine (USA). Type I dog bone specimenswere tested for polybenzoxazine, LLDPE and composites.Room temperature tensile measurements were carried outat a constant crosshead speed of 5mm=min. The flexuralproperties of polybenzoxazine, LLDPE and compositeswere determined in accordance with ASTM D790 usingan INSTRON 3366 universal testing machine (USA) with10 kN load cell. Specimens were tested in a three pointloading with 50mm support span at crosshead speed of5mm=min at room temperature. The morphology of the

fractured surfaces of the composites was studied using aScanning electron microscopy (SEM) (JSM-6390LV,JEOL, Japan). Room temperature magnetization measure-ment was performed for pure NiFe2O4 nanopowder as wellas the composites using a Vibrating sample magnetometer(VSM) (EV5, ADE Technology, USA).

RESULTS AND DISCUSSIONS

In this study, we have combined the useful properties ofNiFe2O4, PB and LLDPE to prepare flexible magneticnanocomposites. The method of composite preparationconsists of three steps:

Step 1: preparation of NiFe2O4 nanoparticles;Step 2: mixing of benzoxazine monomers with NiFe2O4

nanoparticles; and,Step 3: blending of NiFe2O4-benzoxazine with LLDPE fol-

lowed by thermal curing of benzoxazine.

SEM micrograph of the surface of a cross-section of thecomposites (Figure 1) shows that polybenzoxazine coatedNiFe2O4 nanoparticles are embedded within the polymericmatrix.

X-Ray Diffraction Analysis

The room temperature wide angle powder X-Ray dif-fraction spectra were recorded for pure NiFe2O4 nanopow-ders, BA-NF nanocomposites and L-LgM-PB-NFcomposites. In the XRD spectra of pure NiFe2O4 nano-powder, presence of peaks corresponding to (111), (220),(311), (222), (400), (422), (511) and (440) diffraction planesof NiFe2O4 [ICDD 54-0964] confirmed the formation ofsingle-phase NiFe2O4 (Fig. 2(a)). In case of BA-NF

FIG. 1. SEMmicrograph of the composites showing that NiFe2O4 nano-

particles are dispersed within the polymeric matrix. Polybenzoxazine-coated

NiFe2O4 nanoparticles are marked within the circle. (Color figure available

online.)

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nanocomposite samples, all the XRD peaks of NiFe2O4

were present and no additional peaks were detected(Fig. 2 (b)). For L-LgM-PB-NF nanocomposite samples,XRD peaks of NiFe2O4 were present along with additionalpeaks at 2h¼ 21.6� and 23.8�. These two peaks correspondto the (110) and (200) diffraction planes of LLDPE[31,35,36]

and indicated that the crystalline structure of LLDPEremained unchanged upon blending in the nanocomposites(Fig. 2(c-e)). However, the intensity of the crystallite peaksof LLDPE varied with compositions. These XRD spectraof the composite conformed that the pure crystallinephases of NiFe2O4 remained preserved in the compositewith no impurity phase generation during melt blendingprocess.

Thermal Analysis

Thermogravimetric (TGA) and differential scanningcalorimetric (DSC) analysis of pure benzoxazine monomer,polybenzoxazine, LLDPE, PB-NF and L-LgM-PB-NFcomposites were performed to evaluate their thermal stab-ility. In the DSC thermogram of pure benzoxazine mono-mer an exothermic peak at 205�C was observed, whichwas attributed to the ring opening polymerization of ben-zoxazine ring (Fig. 3(a))[37–39]. In case of PB-NF nanocom-posites, this exothermic curing peak of benzoxazine shiftedfrom 205 to 194�C (Fig. 3 (b)). This decrease in curing tem-perature of benzoxazine might be due to the catalytic effectof NiFe2O4 towards the thermal curing of benzoxazinemonomer[40–43]. In DSC thermogram of pure LLDPE anendothermic peak at 124�C due to its melting[35] and an

exothermic peak at 224�C for its thermal oxidativedecomposition[44,45] were observed (Fig. 3(c)).

In case of L-LgM-PB-NF composite samples, an endo-thermic peak at 124�C, corresponding to the melting tem-perature of LLDPE was observed. It was observed thatfor composite samples the exothermic peak for thermaldegradation shifted to higher temperature (�254�C) com-pare to pure LLDPE (224�C), indicating that the presenceof PB enhances the thermal stability of composites.Another important observation was that, the exothermicpeak for ring opening polymerization of benzoxazine ringwas absent in the thermograms of final composite samples(Fig. 3(d)). This result confirmed that, all benzoxazinemonomers were fully polymerized to polybenzoxazineduring composite preparation at 200�C. From TGA ofpure PB, LLDPE and composites, temperatures for 5%weight loss (T5%), 10% weight loss (T10%) and char yield(%) at 800�C in air were determined (Fig. 4) and listedin Table 2. These thermograms also revealed that, pres-ence of more thermally stable PB in L-LgM-PB-NFcomposites enhances the overall thermal stability of thecomposites. However, as the melting temperature ofLLDPE is 124�C, the composites should be used belowthis temperature.

FT-IR Analysis

In the FT-IR spectra of pure benzoxazine monomer(BA) (Fig. 5(a)), the peaks at 949 cm�1 and 1496 cm�1

assigned to the tri-substituted benzene ring and absorptionat 1235 cm�1 for asymmetric stretching of C-O-C wereobserved[30,46]. In case of BA-NF samples (Fig. 5(b)), all

FIG. 2. XRD spectra of (a) NiFe2O4 powder, (b) PB-NF(50:50) nanocom-

posite, (c) 47.5L-5LgM-14.25PB-33.25NF composite, (d) 47.5L-5LgM-

23.75PB-23.75NF composite, (e) 47.5L-5LgM-33.25PB-14.25NF

composite. (� NiFe2O4 and # LLDPE).

FIG. 3. DSC thermogram of (a) benzoxazine monomer, (b)

BA-NF(70:30) nanocomposite, (c) LLDPE, (d) 47.5L-5LgM-23.75PB-

23.75NF composite.

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the characteristic bands of benzoxazine were present alongwith a peak at 586 cm�1, which corresponded to M-Ostretching vibration mode of NiFe2O4

[47–49]. In the FT-IRspectra of L-LgM-PB-NF composites (Fig. 5(c)), followingfeatures were observed (i) the disappearance of peaks at949 cm�1and 1496 cm�1 peak (assigned for tri-substitutedbenzene ring of BA) and appearance of a peak at1482 cm�1 (correspond to the tetra-substituted benzenering of PB) indicated that the ring opening polymerizationof BA occurred during preparation of composites at200�C[39]. (ii) characteristic peaks of LLDPE at 1364 cm�1

(-CH3 symmetric vibration) and peaks around 2907 and2849 cm�1, associated with the C-H stretching vibration[31],(iii) a peak around 549 cm�1 for NiFe2O4.

Mechanical Properties and SEM Analysis

To evaluate the mechanical properties of the L-LgM-PB-NF composites tensile tests and three-point bendingflexural tests were performed. The morphology of the frac-tured surfaces of the samples was investigated by SEM.

From tensile tests it was observed that, pure polybenzox-azine possessed high tensile strength (47.05MPa) and lesselongation at break (2.2%), while LLDPE showed low ten-sile strength (16.75MPa) and significantly more elongationat break (57%). The blend, composed of LLDPE, PB and5wt% compatibilizer LgM (47.5L-5LgM-47.5PB), exhib-ited higher tensile strength (23.81MPa) than pure LLDPEand more elongation at break (6.11%) than pure polyben-zoxazine (Fig. 6). This might be due to the binding roleof compatibilizer (LgM), which enhanced chemical andphysical interaction among the two separate phases (i.e.,PB and LLDPE) and ultimately improved their interfacialadhesion by reducing the interfacial tension[34,50]. SEMmicrograph of the composite (Fig. 7 (a)) also showed thehomogeneous polymeric matrix of the composite and nophase separation between PB and LLDPE in presence ofLgM compatibilizer.

From the tensile stress-strain graph (Fig. 6) it wasobserved that due to loading of 14.25wt% NiFe2O4 nano-particle in polymeric blend (47.5L-5LgM-47.5PB) tensilestrength decreased from 23.81MPa to 19.45MPa but %of elongation at break increased from 6.11% to 15.5%.However, variation of NiFe2O4 nanoparticles loading(14.25 to 33.25wt%) did not affect much in the tensilestrength and tensile module of the composite. But, elonga-tion at break was found to be decreased from 15.5 to 8.52%

FIG. 4. Thermograms (TGA) of (a) LLDPE, (b) polybenzoxazine, (c)

47.5L-5LgM-33.25PB-14.25NF composite, (d) 47.5L-5LgM-23.75PB-

23.75NF composite, (e) 47.5L-5LgM-14.25PB-33.25NF composite, (f)

PB-NF(50:50) nanocomposite.

FIG. 5. FT-IR spectra of (a) benzoxazine monomer, (b) BA-NF (70-30)

nanocomposite, (c) 47.5L-5LgM-33.25PB-14.25NF composite.

TABLE 2Thermal properties of neat polymer and composite

Sample codeT5%

(�C)T10%

(�C)Char yield

(%) at 800 �C

Polybenzoxazine 350 400 0LLDPE 267 305 0PB-NF (70:30) 319 381 29PB-NF (50:50) 261 348 43PB-NF (30:70) 222 338 6047.5L-5LgM-33.25PB-14.25NF 258 296 947.5L-5LgM-23.75PB-23.75NF 255 318 1747.5L-5LgM-14.25PB-33.25NF 254 303 25

T5%- temperature at 5% weight loss.T10%- temperature at 10% weight loss.

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with increasing NiFe2O4 loading in the composite. Themorphology of the fractured surfaces of the compositesafter tensile testing was investigated by SEM and is shownin Figure 7(b-d). It was observed that, delamination of thenanoparticles from polymeric matrix occurred under ten-sile strain and formation of voids during breaking. Thiseffect was pronounced for the composites having higherNiFe2O4 loading and large voids were observed in theirfractured surfaces (Figs.7(c), (d)). This might be due tothe formation of large NiFe2O4 agglomerates in the

composites with high NiFe2O4 loading, as nanoparticlestend to form agglomerates.

From the flexural stress-strain curves of PB, LLDPE,47.5L-5LgM-47.5PB blend and L-LgM-PB-NF composite(Fig. 8), it was observed that L-LgM-PB-NF compositespossessed greater flexural strength than that of pureLLDPE but lesser than 47.5L-5LgM-47.5PB blend. How-ever, it is important to note that the toughness (area underthe stress-strain curve) of the composites was higherthan that of pure polybenzoxazine, pure LLDPE, and47.5L-5LgM-47.5PB blends. Mechanical properties of thepure LLDPE, polybenzoxazine and composites are sum-marized in Table 3.

Magnetic Properties

The variation of magnetic properties, in terms ofsaturation magnetization (Ms) and coercivity (Hc), withthe composition of composites were investigated by usinga VSM at room temperature with an applied field of2000Oe. Figure 9 shows the hysteresis loops of the assynthesized pure NiFe2O4 nanoparticles, BA-NF, L-LgM-PB-NF composite and the values of Ms and Hc are summar-ized in Table 4. The saturation magnetization (Ms) andcoericivity (Hc) values of NiFe2O4 nanoparticles were foundto be 30.70 emu=g and 158.30Oe, respectively[32]. It wasobserved that, when NiFe2O4 nanoparticles were mixed withbenzoxazine (BA-NF), the Ms value of the samples weredecreased with increasing PB content. In the L-LgM-PB-NF composites the same trend was also observed.

This decrease of Ms value with decreasing NiFe2O4

loading in the composition of composite is quite obviousbecause the composite is composed of magnetic NiFe2O4

nanoparticles and non-magnetic polymer. Coercivity (Hc)

FIG. 6. Tensile stress-strain curves of neat polymer, blend, L-LgM-PB-

NF composites.

FIG. 7. SEM micrographs of (a) surface of 47.5L-5LgM-23.75PB-23.75-

NF composite before tensile testing, and fractured surfaces of composites

after tensile testing (b) 47.5L-5LgM- 33.25PB-14.25NF, (c) 47.5L-5LgM-

23.75PB-23.75NF, (d) 47.5L-5LgM-14.25PB-33.25NF. (Color figure

available online.)

FIG. 8. Flexural stress-strain curves of neat polymer, blend, L-LgM-PB-

NF composites.

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value of the composites was found to be higher than that ofpure NiFe2O4 nanoparticles. This might be due to theincreased inter particle distance in the composite as

compared to the close contact of the pure NiFe2O4

nanoparticles[51–53] Similar trend of change of Hc valueswas also reported by Zhanhu et al.[54] for iron oxide nano-particle reinforced vinyl ester resin nanocomposites.

Figure 10 demonstrates that a film of L-LgM-PB-NFcomposite is attached with a bar magnet indicating its mag-netic nature and both ends of the film can be gripped by atweezer by bending it easily due to its mechanical flexibility.This shows that the composites reported here possessmagnetic property as well as mechanical flexibility.

CONCLUSION

In this article, we have reported the preparation of com-posites, composed of NiFe2O4 nanoparticles, PB andLLDPE, which possess magnetic property as well as mech-anical flexibility. X-Ray diffraction analysis showed thatspinel phase of NiFe2O4 was present in the cured compo-sites. The mechanical properties of composites have beenassessed by using tensile and flexural testing. Tensile testing

TABLE 3Tensile and flexural properties of the composites

Sample code

Tensilestrength(MPa)

Tensilemodulus(GPa)

Elongationat break

(%)

Flexuralstrength(MPa)

Flexuralmodulus(GPa)

Toughness(MPa)

LLDPE 16.75 0.236 57 16.33 0.403 0.274Polybenzoxazine 47.05 3.6 2.2 54.06 1.928 0.43947.5L-5LgM-47.5PB 23.81 1.071 6.11 35.75 1.236 0.24447.5L-5LgM-33.25PB-14.25NF 19.45 0.997 15.5 30.01 1.369 0.53047.5L-5LgM-23.75PB-23.75NF 19.20 0.956 9.06 28.22 1.139 0.51247.5L-5LgM-14.25PB-33.25NF 19.00 0.900 8.52 25.04 0.998 0.502

FIG. 9. Magnetization curves for (a) NiFe2O4powder, (b) PB-NF

(50:50) nanocomposite, (c) 47.5L-5LgM-14.25PB-33.25NF composite,

(d) 47.5L-5LgM-23.75PB-23.75NF composite, (e) 47.5L-5LgM-33.25PB-

14.25NF composite.

TABLE 4Magnetic properties of composite

Sample codeMs

(emu=g) Hc (Oe)

NiFe2O4 30.70 158.30PB-NF (70:30) 7.53 187.35PB-NF (50:50) 12.57 210.55PB-NF (30:70) 18.05 205.1447.5L-5LgM-33.25PB-14.25NF 3. 51 253.1447.5L-5LgM-23.75PB-23.75NF 6.44 230.4647.5L-5LgM-14.25PB-33.25NF 7.72 210.32

FIG. 10. NiFe2O4-polybenzoxazine-LLDPE composite films exhibiting

(a) magnetic nature, (b) mechanical flexibility. (Color figure available

online.)

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of the samples reveled that pure polybenzoxazine possesseshigher tensile strength and less elongation at break com-pare to LLDPE, having low tensile strength and signifi-cantly more elongation at break. Composite consists ofLLDPE, PB and 5wt% LgM compatibilizer exhibitedhigher tensile strength than pure LLDPE and more elonga-tion at break than pure polybenzoxazine. Note, though,loading of NiFe2O4 nanoparticle (14.25wt%) in polymericblend (47.5L-5LgM-47.5PB) tensile strength decreasedslightly but variation of NiFe2O4 nanoparticles loading(14.25 to 33.25wt%) did not affect much in the tensilestrength and tensile module of the composite.

L-LgM-PB-NF composites possessed higher flexuralstrength than that of pure LLDPE but less flexural strengththan 47.5L-5LgM 47.5PB. However, toughness of theL-LgM-PB-NF composites was higher than that of purepolybenzoxazine, pure LLDPE, and 47.5L-5LgM-47.5PBblend. Incorporation of NiFe2O4 nanoparticles introducedmagnetic property in the composites and composites hav-ing 33.25wt% NiFe2O4 nanoparticles possess saturationmagnetization of 7.72 emu=g and coercivity of 210.32Oe.

The method reported here for composite preparation isvery simple and does not require any elaborate set up. Themechanical and magnetic properties of these compositescan be tailored by judiciously choosing compositions. Asthe sheets and films of these composites showed structuralflexibility as well as magnetic properties, so thesecomposites have capability to be used in complex deviceapplications and coatings.

ACKNOWLEDGMENT

N. N. Ghosh gratefully acknowledges the financialsupport from DRDO (ERIP=ER=0904500=M=01=1240).

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