Fast Production of Cellulose Nanocrystals by Hydrolytic-Oxidative Microwave-Assisted Treatment

Abstract

In contrast to conventional approaches, which are considered to be energy- and time-intensive, expensive, and not green, herein, we report an alternative microwave-assisted ammonium persulfate (APS) method for cellulose nanocrystals (CNCs) production, under pressurized conditions in a closed reaction system. The aim was to optimize the hydrolytic-oxidative patented procedure (US 8,900,706), replacing the conventional heating with a faster process that would allow the industrial scale production of the nanomaterial and make it more appealing to a green economy. A microwave-assisted process was performed according to different time–temperature programs, varying the ramp (from 5 to 40 min) and the hold heating time (from 60 to 90 min), at a fixed reagent concentration and weight ratio of the raw material/APS solution. Differences in composition, structure, and morphology of the nanocrystals, arising from traditional and microwave methods, were studied by several techniques (TEM, Fourier transform infrared spectroscopy (FTIR)-attenuated total reflectance (ATR), dynamic light scattering (DLS), electrophoretic light scattering (ELS), thermogravimetric analysis (TGA), X-ray diffraction (XRD)), and the extraction yields were calculated. Fine tuning the microwave treatment variables, it was possible to realize a simple, cost-effective way for faster materials’ preparation, which allowed achieving high-quality CNCs, with a defined hydrodynamic diameter (150 nm) and zeta potential (−0.040 V), comparable to those obtained using conventional heating, in only 90 min instead of 16 h.

Active natural-based films for food packaging applications: The combined effect of chitosan and nanocellulose

“…The XRD pattern of CNC powder revealed the characteristic peaks of crystalline cellulose I at 2θ = 15.1°, 16.5°, 22.5°and a weak peak at 34.4°. These peaks correspond to the (1 1 0), ( 110), ( 200) and (0 0 4) crystallographic planes, respectively, which are in agreement with different studies [19,34,35,40,42]. Chitosan films exhibited four diffraction peaks at 2θ = 8.12°, 11.4°, 18.0°, and a broad peak around 22.5°due to its semi-crystalline nature [9,19].…”

“…The bands observed in the range 1030-1161 cm −1 correspond to C\ \O stretching and C\ \H rocking vibrations of the pyranose ring [31]. Finally, the bands at 897 and 557 cm −1 are from β-glycosidic linkages in cellulose structure and O\ \H out of plane bending vibrations, respectively [18,23,35].…”

“…The band at 1645 cm −1 is attributed to O\ \H bending of the adsorbed water, the band at 1429 cm −1 is from symmetric bending of CH 2 and the band at 1369 cm −1 corresponds to CH deformation vibration [31][32][33]. Moreover, the bands at 1335 and 1315 cm −1 arise from the rocking of OH and the bending vibrations of the C\ \H and C\ \O groups of the rings in polysaccharides, respectively [31,35]. The bands observed in the range 1030-1161 cm −1 correspond to C\ \O stretching and C\ \H rocking vibrations of the pyranose ring [31].…”

Relationship between Structural Characteristics of Cellulose Nanocrystals Obtained from Kraft Pulp

“…This observation can be verified in Figure 6 b, where crystallites size versus fractional variation in their interplanar distance (Δ d / d ) showed a significant but negative Pearson correlation of r = −0.99; p < 0.01. In literature, the importance of the potential variation between the distances of the crystalline planes in CNCs has been discussed, which affect properties in materials developed using these CNCs [ 52 ]. On the other hand, in the case of our data, the CNC yield may be related to the mechanical compression on the microfibrils during hydrolysis, and for this reason, the crystallite size decreases with increasing CNC yield ( Figure 6 c).…”

Preparation and Surface Functionalization of Carboxylated Cellulose Nanocrystals

“…Amoroso et al examined the use of a microwave-assisted process to overcome the inefficiencies of heating currently used in the conventional APS process [ 39 ]. They found that controlling the heating ramp time and holding the heating time were important parameters to allow for sufficient time for the APS to convert to the active radical oxidant reacting with the biomass.…”