Preparation Of Multi-walled Carbon Nanotube/polyaniline Nanocomposites And Their Application In Electro-conductive Cellulosic Paper

Cellulosic paper imparted with electro-conductivity, known as electro-conductive paper,inheriting its intrinsic properties such as flexibility, biocompatibility, light weight, low cost andrecycling possibilities, has received considerable attention and shown great promise in suchapplication areas as electronic device and energy material. In fact, cellulosic fiber itself isnon-conductive. The electro-conductivity of cellulosic paper heavily depends on the nature of theelectro-conductive fillers used, which are strongly associated with the production process.Generally, the fillers used to impart electro-conductivity to cellulosic materials may includecarbon black, carbon fiber, carbon nanotubes and grapheme, as well as polypyrrole andpolyaniline. Among these electro-conductive fillers, the combination of multi-walled carbonnanotube (MWCNTs) and polyaniline (PANI) to produce highly electro-conductivenanocomposites has aroused wide concern. However, there has been limited study regarding theapplication of MWCNT/PANI nanocomposites as electro-conductive fillers for the production ofhigh-value added cellulosic paper. In the current work, the concept of using MWCNT/PANInanocomposites from in-situ oxidation polymerization process in the presence of MWCNTs andAN monomer as wet-end filler was demonstrated for producing electro-conductive paper.Moreover, the eletro-conductivity, mechanical properties, thermal stability and mictrostructure ofthe obtained electro-conductive paper were studied.Due to their large specific surface area and strong van der waals forces, MWCNTs are proneto agglomerate in aqueous and organic solvents, which would largely limit their potentialapplication. For this reason, it is rather essential to modify the surface of MWCNTs prior to thetargeted application. Here, surface modification of MWCNTs was conducted using mixture acids(H2SO4/HNO3=1/1), and the typical MWCNTs samples before and after modification werecharacterized. In comparision, the dispersion stability of modified MWCNTs in water wassignificantly improved. According to FT-IR result, characteristic peaks of MWCNTs samples occurred at3433cm-1,1637cm-1and1595cm-1, mainly assigned to the vibration absorption of–OH, C=O and C=C bonds, respectively. Furthermore, the number of hydroxyl and carboxylgroups of modified MWCNTs was significantly increased as compared to raw MWCNTs. TGcurves revealed that modified MWCNTs exhibited higher weight loss rate, which may be relatedto the increased amount of hydroxyl and carboxuyl groups of MWCNTs imparted by surfacemodification. Moreover, as shown in SEM images, modified MWCNTs were found to containsignificantly lower amounts of amorphous carbon and impurities.Subsequently, the synthesis of MWCNT/PANI nanocomposites through in-situ oxidationpolymerization was designed and performed. The optimum process conditions associated withMWCNT/PANI nanocomposites were systematically discussed, involving the mass ratios ofMWCNTs to AN, the mass ratio of oxidizing agent (APS) to AN, and the polymerization time.The optimum results derived from single factor optimization method in this study were asfollows: m (MWCNTs): m (AN)=1/1, m (APS): m (AN)=5/4, the polymerization time of6h.Afterwards, the obtained MWCNT/PANI nanocomposites were characterized by FT-IR, TEM,XRD and TGA. According to FT-IR spectra, it can be seen that the characteristic peaks of PANIwere found in MWCNT/PANI nanocomposites. TEM images showed that the as-obtainednanocomposites exhibited a core-shell structure. It was apparent that MWCNTs acted as the coreand PANI served as the shell, indicating the ideal combination of MWCNTs and PANI. PANIwas existed as nanocrystals in MWCNT/PANI nanocomposites according to XRD results.Furthermore, TG curves confirmed that the MWCNT/PANI nanocomposites showed animprovement in thermal stability properties in comparision with pure PANI.Eventually, the electro-conductive paper was produced via wet-end formation process usingMWCNT/PANI nanocomposites as electro-conductive fillers, and the related properties, i.e.,electro-conductivity, mechanical properties, thermal stability and microstructure of the obtainedsamples were investigated. It was found that the conductivity of electro-conductive paper wasincreased with the increased amount of MWCNT/PANI nanocomposites; while the mechanicalproperties of eletro-conductive paper exhibited a trend of first increase and then decrease withthe increased electro-conductive fillers. Moreover, modified MWCNTs provided significantadvantage in imparting improved conductivity and mechnical properties to MWCNT/PANI nanocomposites, and therefore offer opportunities to improve the related properties of theobtained electro-conductive cellulosic paper. Besides, TG curves showed that the thermalstability of electro-conductive paper was improved with the addition of MWCNT/PANInanocomposites. Additionly, SEM images demonstrated that modified MWCNT/PANInanocomposites were uniformly distributed on the surface of and/or between pulp fibers ofelectro-conductive paper, while the surface of electro-conductive paper containing unmodifiedMWCNT/PANI nanocomposites appeared to be an agglomerated state.