Microstructural, Thermal, Crystallization, and Water Absorption Properties of Films Prepared from Never‐Dried and Freeze‐Dried Cellulose Nanocrystals

Abstract

In this paper, the microstructural, optical, thermal, crystallization, and water absorption properties of films prepared from never‐dried (ND) and freeze‐dried (FD) cellulose nanocrystals (CNCs) are reported. Morphology of the ND CNCs reveals a needle‐like structure, while after freeze‐drying, they show a flake‐like morphology. Microstructural analysis of ND and FD CNCs are further studied via small angle X‐ray scattering to probe interactions. ND CNCs yield a transparent film with a low surface roughness (14 ± 4 nm), while the FD CNC film evidence a significant reduction of their transparency due to their higher surface roughness (134 ± 20 nm). Although Fourier transform infrared spectroscopy and energy‐dispersive X‐ray spectroscopy analyses reveal no chemical change occurs during the freeze‐drying process, yet a more intense thermal degradation profile is observed for FD CNC film, probably due to the higher oxygen ingress within the gaps created between the stacked flakes. This, in turn, results in a greater loss of crystallinity at a higher temperature (300 °C) compared to the ND CNC film. A rapid decrease in water contact angle of the FD CNC film proves that the morphology of flakes and their orientation within the film has a strong influence in increasing water absorption capacity.

Effect of bonding on the structure and properties of nanocellulose films

“…The water molecules introduced by the rehydration and hot-press drying treatment allowed the formation of a large number of hydrogen bonds in the network structure of the fibril assembly. At the same time, the pressure helped the cellulose to overcome its inherent spatial resistance, while the temperature provided by the hot pressing process softened the cellulose and promoted interfibrillar entanglement under capillary pressure, forming an increasingly "strong" three-dimensional network (Hossain et al 2021). Table 1 shows that regardless of the drying method used, the density and porosity changed considerably during hot-pressing.…”

Recent progress in Pickering emulsions stabilised by bioderived particles

“…[19][20][21] Fig. 3 Transmission electron microscopy (TEM) images of (a) cellulose nanocrystals (CNCs isolated from cotton via a sulphuric acid hydrolysis process), 29 (b) cellulose nanofibrils (CNFs obtained from wood pulp utilising a high-pressure homogenisation process) 30 CNCs with comparatively shorter length have better emul-sication efficiency as the smaller sized CNCs are favourable for high coverage of oil droplets. 22 The high coverage is probably obtained via side by side stacking of these particles, as well as longitudinal alignment of the self-assembled CNC particles at a relatively higher concentration.…”

Influence of cellulose nanocrystal surface chemistry and dispersion quality on latex nanocomposite stability, film formation and adhesive properties

“…15 Never-dried cCNCs which were not ultrasonicated prior to their incorporation into latex nanocomposites were reported to have a higher “apparent” aspect ratio which translated to improved PSA properties. 14 It has also been reported that the never-dried sCNCs have a needle-like structure (with a particle length in the nm range), whereas the structure of dried sCNCs are more flake-like (with a particle length in the μm range), 32 which highlights that sometimes the drying process can permanently alter the morphology of the nanoparticles. The storage method of commercial CNCs, never-dried in suspension versus dried powder, and how this translates to their behaviour and dispersion quality within latex nanocomposites has yet to be explored.…”