2.5.1. Morphology

Morphologies of the prepared ChNF as well as ChNF–CNF composites were investigated by using a field emission scanning electron microscopy (FE-SEM, S-4,000, Hitachi, Japan) and an atomic force microscopy (AFM, Veeco 3100, USA). Since the morphologies of CNF are well reported [21–25], they are not repeated in this paper.

## 2.5.2. FTIR Spectra

FTIR spectra of the ChNF–CNF composites and ChNF were determined using a FTIR spectroscopy (Cary 630, Agilent Technol. Santa Clara, CA, USA) with a diamond crystal that has the wavelength range from 650 to 4000 cm<sup>−</sup>1. The specimens were tested for the absorbance between 650 and 4000 cm−<sup>1</sup> with accumulation of 32 scans and the data were collected at a resolution of 4 cm<sup>−</sup>1.

## 2.5.3. X-ray Diffraction (XRD)

The crystallinity index (CrI) of ChNF and ChNF–CNF composites were measured using an X-ray diffractometer (XRD, X'Pert PRO MRD, Malvern). It is hard to make chitosan particles into a thin film of 45–70 g/m2. Thus, the pure chitosan was used in powder form. A thin ChNF film of 40–45 μm was cast on a polycarbonate substrate by using the doctor blade, and 2 <sup>×</sup> 2 cm2 specimens were prepared to evaluate the CrI. The CrI of chitosan was calculated using the following equation [7].

$$\text{CrI} \left(\% \right) = (\text{I}\_{002} - \text{I}\_{\text{arm}}) / \text{I}\_{002} \* 100 \text{ (\%)}\tag{1}$$

where I002 is XRD peak at 2θ = 19.7◦ and Iam is diffraction pattern of amorphous area at 2θ = 15◦. The prepared ChNF–CNF composites were directly used for XRD.
