Characterization of CNF, BC, and conductive nanopapers

(0.1, 0.3, 0.5 and 0.7 mL) were used in this experiment, and the molar ratios of Pyrrole/0.5 M HCl, FeCl3/Pyrrole and FeCl3/0.5 M HCl were 0.4, 2.4 and 1, respectively. The reaction was 20, 40, and 60 min for 0.1 mL of pyrrole at 4ºC were coded as BC-PPy_1, BC-PPy_2, and BC-PPy_3, and was 60 min for 0.3, 0.5, and 0.7 mL, which were coded as BC-PPy_4, BC- PPy_5, and BC-PPy_6. The membrane turned from white to grey and finally to black within a few minute. After finishing the reaction, BC-PPy membrane was washed thoroughly with distilled water to extract the byproducts and remain reagents of the reaction. Afterwards, the mechanical pressing was applied for 5 min to remove excess water. BC-PPy nanopaper was finally obtained by drying for approximately 25 min.

supplier. The weight fractions of nanocellulose, PPy, MWCNT, and PH500 are represented by !!!"", !_!!",!_!"#$%, and !!"!"", respectively.

The percentages of carbon, hydrogen, and nitrogen were determined by elemental analysis by means of a Perkin Elmer EA2400 series II. The measured amount of nitrogen was used to determine the PPy content in the formulation. The samples (3 mg) were pyrolyzed in helium (He) at a combustion temperature of 925–930°C. Acetanilide powder (C8H9NO) was used as reference.

3.7.3 Fourier transform infrared (FTIR) (Paper I-IV)

The chemical compositions of nanopapers were characterized by Fourier transform infrared spectroscopy (FT-IR) from Bruker with a PLATINUM attenuated total reflectance mode (ART) under transmittance mode in range between 4000 cm^-1 and 500 cm^-1 using 24 scans at a resolution of 4 cm^-1.

3.7.4 Tensile properties (Paper I-IV)

Mechanical properties of nanopapers were evaluated using tensile test under control conditions of 50% relative humidity at room temperature. The rectangle specimens of nanopaper (50×5) mm with various thickness were tested using a Universal Testing Machine HOUNSFIELD, equipped with a 250 N load cell with a cross-head speed of 5 mm/min. These parameters were set according to previous work (Hamedi et al., 2014). The statistical error for each sample type was taken from at least five different specimens according to ISO 527 standard.

3.7.5 Field emission scanning electron microscopy (FE-SEM) (Paper I-IV)

The cross section surfaces of nanopapers, as well as the PPy platelet, were observed under a field emission scanning electron microscope (FE-SEM) HITACHI S-4100. The samples from tensile test were coated with gold using a sputter. The images were taken using secondary electron detector at different voltages.

3.7.6 Transmission electron microscopy (TEM) (Paper III)

Transmission electron microscopy (TEM) images of CNF, CNF-PH500_50, and CNF- PH500-PPy were recorded using a ZEISS EM-910 JEOL-2100F (1993) and an internal

charge-coupled device (CCD) camera gatan orius SC200W1. The samples were diluted to 1:50 in distilled water, and only 8 µL of each sample was drop in a cupper 400 mesh grid with formvar film for 3 min minutes. 8 µL of contrast solution uranyl acetate 1% was dropped on the solution above and kept for 3 min before testing.

3.7.7 Thermogravimetric analysis (TGA) (Paper I, III, and IV)

Thermogravimetric analysis (TGA) was used to determine the lost weight with the temperature and the degradation temperatures of nanopapers. The samples were heated from 30 to 600°C at the heating rate of 10°C min^-1 using a METTLER TOLEDO ultra-micro balance, TGA/DSC. The purge gas was nitrogen with a flowing rate of 40 mL/min.

3.7.8 Electrical conductivity measurement (Paper I-IV)

The electrical conductivity of the obtained nanopapers was determined based on the measurement of the resistance (R) over the length of the specimens using an Agilent 34461A digital multimeter. The sample were cut were cut into (5×20) mm rectangular shape. Silver paint was applied at room temperature at the end of both sides of each sample to ensure good electrical contact with the clip probes. The measurement was done 16 h after the application of silver paint. Equation 2 calculated the conductivity:

!^! = !

!×!×! (2)

Where L, w, and d are length, width, and thickness of the sample, respectively.

In the cases of CNF-MWCNT and CNF-PEDOT:PSS, the prediction of percolation threshold was determined to describe the insulator-to-conductor transitions in composites made of conductive filler and an insulating matrix. Above the percolation threshold, the conductivity occurs, whereas below this concentration the composites are very resistant to electrical flow.

According to Equation 3, the conductive fillers networks that follow classical geometrical percolation theory (where filler bonding occurs) obey a universal conductivity-loading relationship above the percolation threshold was carried out (Hermant, 2009; Koga et al., 2014).

!=!_! !−!_! ^! (3)

Where ! is the theoretical conductivity, !_!the ultimate conductivity, ! the volume fraction of the conductive filler, and !_! is the percolation threshold. To determine the percolation threshold (!_!) experimental results are fitted by plotting log σ versus log (!−!_!), and the value of !_! was incrementally varied until the best linear fit is obtained.

3.7.9 Cyclic voltammetry measurement (Paper I-IV)

Cyclic voltammetry (CV) was carried out with a standard three-electrode electrochemical cell (working electrode), a platinum wire (counter electrode), and a 2 M NaCl-saturated Ag/AgCl electrode (reference electrode) by using a Potentistat/Galvanostat Model 273A Princeton equipment. Cyclic voltammograms were recorded in the potential window of −0.9 to +0.9 V vs Ag/AgCl at different scan rate of 5, 20, 50, 100, and 200 mV s^-1. CView and originPro software were used to plot the graphs. The sample dimensions were (7×15) mm. Equation 4 calculates the specific capacitance.

!!"=!/!.!.∆! 4

Where !_!" (F g^-1) is the specific capacitance, ! the integration in the CV curve, ! the scan rate in V s^-1, ! the mass (g) of the electrode material, and ∆! = 1.8 V is the potential window.