DOI: 10.15125/bath-00930
title: Dataset for "Microstructural, thermal, crystallization and water absorption properties of films prepared from never-dried and freeze-dried cellulose nanocrystals"

description: Self-assembled cellulose film was prepared from a stable aqueous dispersion of ND CNCs using the air-drying process at room temperature. For comparison, another pure cellulose film was prepared from the FD CNCs (which also produced from the same ND CNC suspension after quickly freezing using liquid nitrogen followed by freeze-drying) via casting from their aqueous suspension. The dataset contains the raw data highlighting the influence of the microstructures created during the air and freeze-drying processes on nanoscale structure (measured by small-angle x-ray scattering (SAXS)), light transparency (UV-visible), chemical (FTIR), thermal (TGA, DSC), crystallization (XRD) and water contact angle properties of the cellulose nanocrystal films.
description: Small angle x-ray scattering (SAXS) analysis
SAXS measurements on the ND and FD CNC suspensions with various concentrations (0.05, 0.1, 0.5 and 1.0 wt%) in DI water were conducted at Diamond Light Source (Didcot, Oxfordshire, UK), on the I22 beamline (x-ray wavelength of 1 Å and beam energy of E = 12.4 keV) equipped with a PILATUS P3-2M detector (Silicon hybrid pixel detector, DECTRIS). The FD CNC suspension was dispersed using a sonication probe (1 s on, 1 s off pulsed mode for a net time of 10 min at 30 % amplitude, Ultrasonic Processor, FB-505) and then loaded in special glass capillary tubes (nominal diameter 1.5 mm, Capillary Tube Supplies Ltd, Bodmin, UK) and sealed. The scattering pattern from an empty capillary and a capillary containing DI water were also recorded for solvent background subtraction. The probed q-range was 0.005–0.2 Å−1. Data are provided in absolute scaling. 
The intensity I(q) can be written as follows:
I(q)∝P(q)S(q)…………(1)
with P(q) the form factor of the objects studied, giving information about their shape and S(q) the structure factor associated with the interactions between the objects probed.

SAXS measurements of the film samples were performed on an Anton-Paar SAXSpoint 2.0 provided by the Material and Chemical Characterisation Facility (MC²) equipped with a copper source (Cu K-α, λ=1.542 Å) and a 2D EIGER R series Hybrid Photon Counting (HPC) detector. The distance between the film sample holder (containing ND and FD CNC films) and the detector was 556.9 mm and the data were collected at 25°C in one frame, with 900 s exposure covering the q range of about 0.07-1.8 Å-1. SASView software (version 4.1.2) was used to fit the SAXS data using a rigid elliptical cylindrical and mass fractal models.

Light Transmittance:

Light transparency properties of the ND CNC and FD CNC films were determined by measuring the light transmittance using a UV-Vis spectrometer (PerkinElmer, Lambda-25) over the wavelength range of 200 to 800 nm.

Fourier transform infrared spectroscopy (FTIR):

The principal chemical groups present in ND CNC and FD CNC films were identified using an FTIR spectroscopy (PerkinElmer, Spectrum 100, USA) equipped with a standard attenuated total reflectance (ATR) cell. The films were scanned in transmittance mode over the wavenumber range from 4000 to 650 cm-1, and the obtained spectra were analyzed using OPUS™ software (version 5.5). 

Thermogravimetric analysis (TGA):

TGA was performed on a TGA Q500 (TA Instruments) from 25oC to 500oC with a heating rate of 10oC min-1 under airflow. TA Universal Analysis 2000 software was used to calculate the weight loss (%) and the derivative weight loss of the films with temperature from the TGA scans. 

Differential scanning calorimetry (DSC):

DSC analysis was conducted utilizing a DSC Q20 (V24.10 Build 122) from TA Instruments over a temperature range from 25 to 300oC at a heating rate of 10°C min-1 under argon gas flow (18 mL min 1). A blank pan measurement was conducted for background, and at least two tests were done for each film (~5 mg) to ensure repeatability.

X-ray diffraction (XRD) analysis:

X-ray diffraction patterns for ND CNC and FD CNC films at different temperatures (25, 150, 200, 300 and 400oC) were determined using a Bruker D8 Advanced diffractometer equipped with a Cu-Kα radiation source (λ= 0.15406 nm) at 35 mA and 40 kV. The film samples were heated from room temperature to 400oC at a heating rate of 10oC min-1 and were equilibrated at a specific temperature for 1 min prior to scan from 7o to 30o diffraction angle (2θ) with a step size of 0.04o and 2 s time interval. 
The crystallinity index (CI%) of the films was calculated according to the following Equation:
CI [%]=(I_((Crys+am) )-I_((am) ))/I_((Crys+am) ) ×100
Where  ) denotes the most intense peak attributed to the combined crystalline (Crys) and amorphous (am) parts of cellulose (peak intensity at 2θ=22.8o), whereas I(am) represents the amorphous portion of cellulose (peak intensity usually appearing at 2θ=18o).

Water contact angle:
The water contact angles of the films were measured using a drop tensiometer (OCA 20, Dataphysics Co., Germany) at ambient temperature. A 10 μl of DI water drop was deposited via a microsyringe on the CNC film surface, and the contact angles were measured at different time points. The reported contact angle value was taken from an average of 5 measurements.
description: This work benefited from the use of the SasView software (developed under NSF Award DMR-0520547) containing code developed under the EU Horizon 2020 programme (the SINE2020 project Grant 654000).