direct current (de) electrical conductivity, ultraviolet-visible (UV-Vis) ... from aqueous solutions with conductivity close to the conducting polymer, yet with the ...
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Journal of Nanoscience and Nanotechnology Vol. 8, 1-6. 2008
Vol. 9 (5), 2917-2922, 2009
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Electrically Conductive Nanocomposites Made from Cellulose Nanofibrils and Polyaniline L. H. C. Mattoso1.2·*, E. S. Medeiros1.2, D. A. Baker2, J. Avloni 3, D. F. Wood 2, and W. J. Orts2 1
Laborat6rio Nacional de Nanotecnologia Aplicada ao Agroneg6cio. Embrapa lnstrumentafao Agropecuaria, Rua XV de Novembro, 1452, Sao Carlos-SP. 13560-970, Brazil 2Bioproducts Chemistry and Engineering Unit, Western Regional Research Center, Agricultural Research Center, USDA, Albany, CA. 94710, USA 3 Eeonyx Corporation, Pinole, CA. 94564, USA
Electrically conductive nanocomposites from cellulose nanofibrils (CN F) were successfully produced by in situ polymerization of aniline onto CNF, and studied by open circuit potential (Voc), four probe direct current (de) electrical conductivity, ultraviolet-visible (UV-Vis) spectroscopy and scanning electron microscopy (SEM). The oxidative polymerization of aniline using ammonium peroxydisulfate in hydrochloric acid aqueous solutions was realized by the addition of nanofibrils leading to an aqueous suspension of CNF coated with polyaniline (PANI). This procedure lead to stable, green suspensions of CNF coated with PANI in the emeraldine oxidation state as demonstrated by Voc and UV-Vis analyses. Electrically conductive films of this cellulose nanocomposite could be cast from aqueous solutions with conductivity close to the conducting polymer, yet with the potential for more useful flexible films.
Keywords: Nanocomposites, Conducting Polymers, Polyaniline, Cellulose Nanofibrils.
1. INTRODUCTION Nanotechnology has received great attention from the scientific community and an enormous investment from private and publ ic companies. universities and research institutes because of the great worldwide benefits it can generate.' Due to its interdisciplinary character. multiple fields have merged to create new materials with new propenies and appl i cation~: as a result. nanotechnology impacts have already been profound in many long-established areas including agriculture.2 Cellulose is one of the most abundant materials in nature and it naturally form s nanowhiskers that can be extracted from different plants. Cotton in particular possesses a high cellulose content. leading to nanofibrils with diameters in the range of 5 to 20 nm and aspect ratio of abom I to 100 times. Couon-derived nanofibril s possess several advantages such as low cost. low density. non-toxicity, renewable nature. biodegradability, formation of stable aqueous suspension and remarkab le mechanical properties. being capable of improving the mechanical performance of polymers at quite low fiber concentrations.3.4 • Amhor to "hom corre,pondence under different doping condition•. Doping condition
Conductivity (S/cm)
< 10- 7 1.0 X 10 -~ 1.0 X 10 -~
Dedoped (0.1 M aqueous NH,OH) As prepared (washed with distilled water) HCI (I M aqueou' 'olution) TSA ( I M aqueou• solution) LSA ( I M aqueous ~ol ut ion)
1.-1 x 10 -~ 2. 1 X 10_.
which are reasonably flexible and strong. can now be produced i n either dedoped or doped state using different dopants, HCL TSA and LSA as presented in Figure 5. There is no need for the polymeri zation to be carried out at elevated temperatures in order to confer stabili ty. again an advantage of previous reports in the literature.37 · 38 SEM analysis presented in Figures 7(a). (b) corroborates our hypothesis thm only a thin layer of PAN I is deposited on the surface of the cellu lose nanofibrils. as can be seen in the micrographs showing films that appear homogeneous. with no precipitate or aggregate formation present. One can also observe the presence of CNF w ith average diameters i n the range of 15-20 nm in both i mages. The depositi on of a very thin layer of PANI is consistent with the aqueous water suspension stabi lity obtained for the CNFIPANI. Furthermore. freeze-dried samples have the same appearance as the uncoated cellulose nanofi brils. while maintaining the green color of doped polyaniline as can be seen i n Figure 7(c). Previous work on CNF/PPY l ead to the formation of larger stntctures, i.e.. spherical polypyrrole aggregates with dimension in the range of 200 nm or CNF/PPY sticks with 70 nm in diameter. which it was reported to depend on the rate of oxidant/monomer used.34 Electrical conductivity as high as I 2 S/cm were obtained for the CNF/PANI nanocomposite films, which is at least two orders of magnitude higher than previ ously reported work for CNF/PPY fi lms34 compared at the same conducting poly mer content ( 18%). It is believed that conductivi ties in the order of polyaniline can be obtained by i ncreasing the PANI content within the composite; essemially by increasing the ani line content used in the polymerization. The type of dopant used influenced the electrical conductivity achieved for these composites. as indicated in Table I. Higher conducti vity was obtained for HCI and TSA (10-2 S/cm). as compared to LSA ( I 4 S/cm). M oreover. the film prepared with the assynthesized CNF/PANI showed lower conductivity due to an incomplete doping in agreement with the UV-Vis data previously presented. We should poin t out that these new nanocomposites might fi nd interesti ng uses in chemical sensors or paint formulations for antistatic applications. as well as in the development of electrically conductive nanocomposites wi th betrer mechanical properties due to the high mechanical strength of the CNF.
o-
(b)
o-
(c) Fig. 7. SEM image; of (a) CNF and (b) PANI coated CNF aqueous >olutiom and (c) PANt coated CNF freeze-dried.
J. Nanosci. Nanotechnol. 8, 1-6, 2008
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4. CONCLUSIONS Electrically conductive nanocomposites made from cellulose nanofibri Is and polyaniline were successfully produced by the in situ polymeri zation of aniline onto CNF. Reacti on induction period was si gnificantly increased indicating that there is a possible interaction between cellulose nanofibril s and aniline in acidic medium as a consequence of the positive charges of aniline and negative charges of cellulose nanofibril s. The use of CNF in highly stable aqueous medium lead to the possibi lity of obtaining stable !>uspensions of electrically conductive PANI coated onto CNF. UV-Vis results are consistent with PAN! being in the doped emeraldine salt form which could be achieved using different types of dopants. Shining nanocomposite films w ith electrical conductivi ties as high as 10- 2 S/cm were also obtained. These film s might find interesting uses in sensors. antistatic and anti-corrosive nanocoatings. as well as in the development of electrically conductive nanocomposi tes with superior mechanical properties.
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Acknowledgments: The financial support given by ARSIUSDA (USA). CNPq. FINEP and the EMBRAPALABEX program ( Brazil) are gratefully acknowledged.
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Received: 17 April 2008. Accepted: 12 July 2008.
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