07) 3269–3272www.elsevier.com/locate/matlet

Materials Letters 61 (20

Synthesis and performances of Fe2O3/PA-6 nanocomposite fiber

Ying Liang a,b,⁎, Xiaohong Xia a, Yongsong Luo a, Zhijie Jia a

a Center of Nano-Science and Technology, College of Physics, Central China Normal University, Wuhan 430079, People's Republic of Chinab Department of Chemistry and Biologic Science, Xiangfan University, Xiangfan 441003, People's Republic of China

Received 5 September 2006; accepted 9 November 2006Available online 28 November 2006

Abstract

A novel fiber consisted of nano-Fe2O3 particles/polyamide-6 (PA-6) nanocomposite has been prepared successfully. The thermal stability of thecomposite material was enhanced about 16 °C (from 440 °C to 456 °C) by the addition of Fe2O3 nanoparticles with 15.0% content (part per hundredparts of resin). In situ polymerization can make the materials possess homogeneously dispersed nanoparticles. The Fe2O3 reinforced materialsprocessed by melt spinning displayed improved tensile modulus compared to similarly processed pure polyamide-6, the improvements of tensilestrength and modulus were 21.22% and 112%, respectively. Moreover, this fiber has the property of ultraviolet and visible light absorption.© 2006 Elsevier B.V. All rights reserved.

Keywords: Nano-Fe2O3; Nanocomposite; Melt spinning; Mechanical properties

1. Introduction

Modification of polymers using nanometer particles as fillerto enhance the polymer performance has gained considerableattention over the last few years. This interest was createdinitially by reports of significant mechanical property improve-ments in PA-6 that was reinforced with naturally occurringsmectite clays [1]. These polymer nanocomposites usuallyexhibit significant improvements in the modulus, the glasstransition, melting and thermal decomposition temperatures atrelatively low levels of filler inclusion. Therefore, there hasbeen considerable experimental [1–5] and theoretical [6]interest in these materials for various polymers [7–11].However, the wide practical applications are not possiblecases due to lacking low cost and multi-function materials orpossessing a relatively complex experimental technique.

In recent years, the polymer nanocomposites based on a widevariety of nanometer fillers including aluminum particles [12],TiO2 particles [13], carbon nanotubes [14], etc. have beeninvestigated. Among various nanomaterials, those based onnano-Fe2O3 are a promising candidate for practical applications

⁎ Corresponding author. Center of Nano-Science and Technology, College ofPhysics, Central China Normal University, Wuhan 430079, People's Republicof China. Tel./fax: +86 276 786 1185.

E-mail address: xfliangy@163.com (Y. Liang).

0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.matlet.2006.11.051

because these Fe2O3 particles are readily available and cheaperthan other nano-scale fillers and also exhibit multi-functionalproperties. For example, the nanocrystalline Fe2O3 would havepotential applications in the fields [15–18] such as solar energyconversion, electrochromism, optical and magnetic materials.Fe2O3 based gas sensors have been fabricated and used to detectethanol, methane, isobutane, and some other gases. In this work,a reinforced Fe2O3/PA-6 fiber was prepared by melt spinning.The structure, thermal, and mechanical properties and ultravio-let and visible light absorption of fiber have been characterizedwhen the nano-Fe2O3 content is 15.0% (wt.%).

2. Experimental

2.1. Fabrication of nano-Fe2O3/PA-6 composites by in situprocess [19]

Polymerization was carried out in 250 ml round-bottomedthree-necked flask equipped with a stirrer, an inlet of argon.Typically, an appropriate amount of nano-Fe2O3 (prepared byour laboratory) aqueous solution was placed into the flask,stirred for 15 min, 60 g of caprolactam was added, stirred for30 min. The pre-polymerization was allowed by adding 4.8 gamino–hexanoic acid at 120 °C for 1 h. Then polymerizationlasted for 5 h at 250 °C under stirring. The products were driedunder vacuum at 80 °C for 24 h.

Fig. 1. Thermal degradation curves of Fe2O3/PA-6 and pure PA-6. (a) TGA of purePA-6; (b) TGA of Fe2O3/PA-6; (c) DTA of Fe2O3/PA-6.

3270 Y. Liang et al. / Materials Letters 61 (2007) 3269–3272

2.2. Fiber spinning

Nanocomposites chip was processed in an extruder with ascrew diameter of 25 mm and a length to diameter ratio of 25. Around single-hole spinneret having 0.6 mm/1.0 mm diameterwas used to produce the as-spun filament. Spinning temperatureranged from 210 to 240 °C, and spinline length, between thespinneret face and take-up godet, varied from 2.6 to 4.4 m. Theirinfluence on the spinnability and properties of the resultant fibersamples were determined. Unless otherwise mentioned, how-ever, a temperature of 220 °C, a spinline length of 2.6 m andspinneret of 0.6 mm were used in most experiments.

2.3. Measurements

Surface morphologies of nano-Fe2O3 particles and nano-composites were investigated by scanning electronic micro-scope (SEM) (JEOL 6700F, Japan).Fiber alignment, dispersionand porosity were studied using the fracture surfaces of tensilespecimens.

Thermal degradation stability of the fibers was determinedusing a thermogravimetric analyzer (TGA) (WCT-2A). Theexperiments were run from room temperature to 800.0 °C at aheating rate of 10 °C/min in a nitrogen atmosphere.

Mechanical properties of the as-spun fibers were measuredon an Instron tensile strength microtester 1122 at roomtemperature. Based on ASTM D3822, fiber samples weretested at a gage length of 100 mm and a constant cross-headspeed of 50 mm/min. An average of 5 individual tensiledeterminations was reported for each specimen.

UV–Vis absorption spectra of the nanocomposite wereobtained on a Shimadzu UV-2550 spectrophotometer at roomtemperature in the wavelength ranging from 200 to 800 nm.

3. Results and discussion

3.1. Thermal degradation properties of nano-Fe2O3/PA-6 composite

Fig. 1 presents the thermal degradation behavior of pure PA-6 andnano-Fe2O3/PA-6 composite. The thermal degradation temperatures ofnano-Fe2O3/PA-6 composite and pure PA-6 at maximumweight loss rateare 456.0 °C and 440.0 °C, respectively. Fig. 1(c) is the DTA curve ofnano-Fe2O3/PA-6 composite, which shows two peaks. One peak (about220.0 °C) may correspond to the H2O evaporation and smaller molecularpolymer decomposition, another peak (about 456.0 °C) may correspondto the decomposition of bigger molecular polymer. The results indicatedthat adding nano-Fe2O3 increased the temperature of maximum thermaldegradation and the thermal stability of the nanocomposite.

3.2. Morphological properties

The SEM image of the product Fe2O3 synthesized by the typicalprocedure is shown in Fig. 2(a). The size of the particles is 10–50 nm;Fe2O3 nanoparticles are well dispersed in the solution. Furthermore, thenanoparticles can't aggregate at the reaction temperature (250 °C).Fig. 2(b and c) shows the SEM images of the Fe2O3/PA-6 matrix afterremoving PA-6 from the surface (matrix was immerged in acetic acid).Fe2O3 were wrapped by the polymer, it was not easy to create anaggregation of the nanoparticles, so it was helpful to form the uniform

dispersion of the particles. Fig. 2(d) shows the SEM image of thefracture surface of tensile test specimens with Fe2O3 content of 15.0%.The exposed matrix displayed an alignment which was consistent withthe extrusion direction. Fe2O3 can be effectively dispersed via theinterfacial interaction between the Fe2O3 and the PA-6 though not achemical bonding formation in nature.

3.3. Tensile properties

The tensile strength and modulus to break of the Fe2O3/PA-6composite fiber are 21.22% (from 1.79 GPa to 2.17 GPa) and 112%(from 18.0 GPa to 38.2 GPa) higher than the pure PA-6 fiber,respectively. Svahlova [20] and Mareri [21] have shown that uniformfiller dispersion leads to a large modulus. A stress concentration affectsthe matrix zone around each particle. Because the nano-Fe2O3 particlesare so small and evenly dispersed that the distance between the nano-Fe2O3 particles becomes shorter; these zones around each particle jointogether and form a percolation network, which increase the modulus.

The inclusion of nano-Fe2O3 particles in the polyamide-6 matrixleads to a significant increase in the tensile strength. The influence ofFe2O3 nanoparticle on the mechanical property of nanocomposites canbe attributed to two factors. First, Fe2O3 nanoparticles are uniformlydispersed in the matrix. The nano-Fe2O3 is in intimate contact with thematrix, with no obvious gaps at nano-scales, indicating the goodinterfacial adhesion between Fe2O3 and PA-6. The binding force infiller–polymer is formed. Moreover, when the binding force is stronger,the interfacial adhesion can bear more load. This enables the interfacialstructure to bear part of the tensile strength inside the nanocomposites[22]. Second, the local non-uniformity of nanoparticles embedded in thegaps of the polymer matrix may result in the “nail or anchor wrapping”[23]. In fact, the size matching between nanoparticles and the PAmolecule chain is more efficient, the interfacial adhesion in thecomposites would be enhanced. The effect is similar to the physicaljunction in the PA-6,whichmeans the physical cross-linking (twisting ofeach other) of PA-6 molecular chain. When the outside force affects thesystem of the filler–polymer, these physical junctions would be firstlybroken, the energies would be absorbed. Consequently, the tensilestrength of the composites would be enhanced.

3.4. Property of ultraviolet and visible light absorption

Fig. 3 shows optical transmittance of the membrane of Fe2O3–PA-6and PA-6 over 200–800 nm wavelength range. Fig. 3(a) shows that

Fig. 2. SEM microphotograph of Fe2O3 and composite (15.0% Fe2O3) (a) Fe2O3 on preferable reaction conditions. (b) The composite surface extracted PA-6(1⁎33,000). (c) The composite surface extracted PA-6 (1⁎50,000). The Fe2O3 are wrapped by the polymer to create an uniform dispersion. (d) Fracture surfaces oftensile test specimens.

3271Y. Liang et al. / Materials Letters 61 (2007) 3269–3272

Fe2O3–PA-6 composite has an excellent UV-absorption capacity andhigh transparency in visible light. The absorption edge of Fe2O3–PA-6wavelength is shorter than 600 nm, the absorption increases slowly upto the peak at the range of about 550–200 nm and two sharps increasesappear at about 290 nm and 367 nm, respectively. The UV–Visabsorption investigation (Fig. 3(b)) shows that the pure PA-6membrane has an absorption threshold in the range 250–460 nm, theabsorption peak is flatter and the intensity is weaker. These data suggest

Fig. 3. Optical absorption spectrum of the membrane of (a) Fe2O3–PA-6; (b)pure PA-6.

that nano-Fe2O3 doped PA-6 results in a large increase in absorption atabout 290–367 nm and makes nano-Fe2O3/PA-6 nanocompositeacquire UV-shielding ability and transparency in the visible lightregion. So nano-Fe2O3/PA-6 nanocomposite can act as an ultravioletresistant fiber.

4. Conclusions

Nano-Fe2O3 particles/polyamide-6 composite fiber has beenprepared successfully. The thermal stability of the compositematerial was improved about 16 °C (from 440 °C to 456 °C) bythe addition of Fe2O3 nanoparticles with 15.0% content. SEMimages showed that ferric oxide could be effectively dispersedby in situ polymerization and melt spinning. Tensile propertytests showed that adding ferric oxide enhanced the tensilestrength and modulus very significantly. Meanwhile, nano-Fe2O3/PA-6 composite took on a UV-shielding ability. Sub-sequent work on a different polyamide system where theprocessing conditions were better optimized will be reported infuture publications.

Acknowledgements

This work was supported by the Hubei Provincial Depart-ment of Education and the Important Program for nanomaterialscience of Hubei Province, China (No. 20041003068-09).

3272 Y. Liang et al. / Materials Letters 61 (2007) 3269–3272

References

[1] Y. Kojima, A. Usuki, M. Kawasumi, A. Okada, Y. Fukushima, T. Kurauchi,O. Kamigaito, J. Mater. Res. 8 (1992) 1185.

[2] A.B. Morgan, J.W. Gilman, R.H. Harris, C.L. Jackson, C.H. Wilkie,J. Zhu, Polym. Mater. Sci. Eng. 83 (2000) 53.

[3] R. Krishnamoorti, R.A. Vaia, E.P. Giannelis, Chem. Mater. 8 (1996) 1728.[4] R.A. Vaia, E.P. Giannelis, Macromolecules 30 (1997) 7990.[5] S. Thomas, Ellis, Polymer 44 (2003) 6443.[6] V.V. Ginzburg, A.C. Balazs, Macromolecules 32 (1999) 5681.[7] M.U. Fawn, Q. Yao, H. Nakajima, E. Manias, A.W. Charles, Polym.

Degrad. Stab. 89 (2005) 70.[8] A. Usuki, Y. Kojima, A. Okada, Y. Fukushima, T. Kurauchi, O. Kamigaito,

J. Mater. Res. 8 (1993) 1179.[9] M. Alexandre, P. Dubois, Mater. Sci. Eng., R 28 (2000) 1.[10] PC. LeBaron, Z. Wang, T.J. Pinnavaia, Appl. Clay Sci. 15 (1999) 11.

[11] J.W. Cho, D.R. Paul, Polymer 42 (2001) 1083.[12] R.P. Singh, M. Zhang, D. Chan, J. Mater. Sci. 37 (2002) 781.[13] C.B. Ng, L.S. Schadler, R.W. Siegel, Nanostruct. Mater. 12 (1999) 507.[14] A. Allaoui, S. Bai, H.M. Cheng, J.B. Bai, Compos. Sci. Technol. 62 (2002)

1993.[15] G. Zotti, G. Schiavon, S. Zechin, J. Electrochem. Soc. 145 (1998) 385.[16] T. Schmidt, H. Wendt, Electrochim. Acta 39 (1994) 1763.[17] F.V. Kupovich, A.M.Virnik, V.I. Eberil, Russ. J. Electrochem. 37 (2001) 907.[18] Y. Nakatani, S. Matsuoka, Jpn. J. Appl. Phys. 21 (1982) L758.[19] Z.J. Jia, Z. Wang, C. Xu, J. Tsinghua Univ. 14 (2000) 40.[20] V. Svehlova, Angew. Makromol. Chem. 214 (1994) 91.[21] P. Mareri, S. Bastide, N. Binda, A. Crespy, Compos. Sci. Technol. 58

(1998) 747.[22] Z. Wang, G. Li, H. Peng, Z. Zhang, J. Mater. Sci. 40 (2005) 433.[23] S.X. Wang, M.T. Wang, Y. Lei, J. Inorg. Mater. 15 (2000) 45.