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Preparation of Polyaniline Composites Based on Cellulose Nanofibers

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Tutor: LiuYiXing
School: Northeast Forestry University
Course: Wood Science and Technology
Keywords: cellulose nanofibers,polyaniline,conductive composites
CLC: TB33
Type: Master's thesis
Year:  2013
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Abstract:
Cellulose nanofibers (CNF) appear as very promising support materials for conductive comosites because of its sustainability, biodegradability, broad chemical modification and assembly capacity. Cellulose based conductive composites with properties of lightweight, low pollution and desirable performance, have been attracted more scientific interest due to the increasing demand of electronic devices. In this thesis, CNF was disintegrated from poplar wood powers by chemical pretreatment combined with ultrosonication and polyaniline (PANI) deposited on CNF was synthesized through the in situ polymerization process. Change for morphology, crystallinity, dynamic rheological behavior, chemical compostion and conductivity of CNF/PANI conductive composits during the synthesis process were characterized by field emission scanning electron microscope, transmission electron microscope, X-ray diffraction, rotational rheometer, fourier transform infrared spectroscopy and four-probe meter. The effects of ultrosonic condition on isolation and dynamic rheologyical behavior of CNF were analized. And optimum technological condition combination for polyaniline content and conductivity of CNF/PANI conductive composits was also confirmed. The main conclusions are as follows:(1) CNF consists of1-3elementary fibrils were successfully prepared by chemical pretreatment combined with ultrosonication. As ultrasonic time, output power of ultrasonication and fiber content in suspension increaed, the diamenter of obtained CNF became finer. However, when fiber content exceed1.2wt%, due to the poor flowability of the suspension, the CNF showed an uneven diameter distribution.(2) The typical crystalline I form of the native cellulose remained after ultrasoniction, although the crystalline region of cellulose was slightly damaged. The decrement of relative crystallinity of CNF exhibited a positive correlation with the time and output power of ultrasonication, and a nagetive correlation with fiber content in suspension.(3) when ultrasonic time, output power of ultrasonication and concentration of suspension improved, the network structure constructed by CNF got more stable, result in the increase of storage modulus (G¡¯) and loss modulus (G"). The range of G¡¯and G"of the suspensions prepared at varity ultrasonic time or output power was100¡«102Pa and100¡«101Pa, respectively. And the suspention maintained elastic behavior though the frequency and temperature sweeps. However, CNF suspensions prepared at varity fiber content exhibit G¡¯between10-1and102Pa, G" between10-2and101Pa. what¡¯s more, the suspensions with fiber content less than0.8wt%showed a visco-fluid and-elastic transition during the frequency and temperature sweeps. I.e. fiber content has more significant effect on dynamic rheologyical behavior of CNF suspension than ultrasonic time or output power of ultrasonication.(4) The PANI content in CNF/PANI conductive composite was seriously influenced by the mass ratio of aniline and CNF, concentration of CNF suspension, and reaction temperature during the in situ polymerization process. When in situ polymerization was conducted at following condition:concentration of CNF suspension was0.5wt%, the mass ratio of aniline and CNF was2:1, the molar ratio of (NH4)2S2O8and aniline was1.5:1, the HCl concentration in reaction medium was0.5mol/L, reaction temperature was0¡æ, CNF/PANI conductive composite with higher PANI content (69.1%) was obtained.(5) During the process of in situ polymerization, the mass ratio of aniline and CNF, concentration of CNF suspension exhibited a significant effect on conductivity of CNF/PANI conductive composits. When in situ polymerization was conducted at following condition: concentration of CNF suspension was0.5wt%, the mass ratio of aniline and CNF was2:1, the molar ratio of (NH4)2S2O8and aniline was1.25:1, the HCl concentration in reaction medium was1.5mol/L, reaction temperature was0¡æ, the obtained CNF/PANI conductive composite showed a higher conductivity as4.67S/cm;(6) During the process of in situ polymerization, PANI grew along the fiber direction of CNF to form a core-shell structure, and finally organized a network structure under the induction of CNF. This was benefit for the conductivity and film-forming property of PANI. In addition, the CNF/PANI conductive composite showed a similar chemical structure with PANI, meaning the composite was suitable in the most applications of PANI.(7) With the formation of PANI on CNF, the conductivity of CNF/PANI conductive composite was improved due to the increasing charge channel (intrachain transport and interchain hopping). Once the PANI on CNF formed a continuous phase, the formation of PANI had a slight effect on the conductivity of the composite. When PANI was further oxidated by (NH4)2S2O8, the charge channel was damaged and the the conductivity of CNF/PANI conductive composite decreased.
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