RAMAN SPECTROSCOPY FOR EVALUATING THE DEGREE OF CRYSTALLINITY OF NANOCRYSTALLINE CELLULOSE

Preparation and characterization of hexadecyl trimethyl ammonium bromide (HDTMA-Br)-modified cellulose nanocrystals (CNCs) derived from South African waste agricultural residue (Corncobs)

Cellulosic materials have varying amounts of crystalline and amorphous domains, influenced by their source and processing history. The degree of crystallinity in cellulose significantly affects the properties and behaviour of cellulosic materials. Therefore, understanding and controlling cellulose crystallinity is vital for optimising the properties and performance of these materials. However, measuring the crystalline nature of synthesized cellulose nanocrystals is challenging due to inconsistent results from various analytical techniques such as XRD, NMR, FTIR, etc. Hence, developing an optimal method for predicting the crystalline nature of cellulose nanocrystals is promising. Herein, a machine learning model to predict the crystalline nature of CNCs is developed using a dataset created from the published literature. This model uses various cellulose sources and reaction conditions as input descriptors. The K-Nearest Neighbors (KNN) classifier, Support Vector classifier, Decision Tree classifier, RandomForest classifier and HistGradient boost classifier are trained on the dataset, and KNN was identified as the best machine learning model for crystalline nature prediction (accuracy = 95%). Using a KNN regressor, a crystallinity index predictor is also developed (R2 score = 0.82, RMSE = 1.59). Cellulose sources are identified as the major factors influencing cellulose nanocrystals' crystalline nature. The developed model can bypass the need for trial-and-error synthesis to obtain a highly crystalline nature.

Optimization of homogenization-sonication technique for the production of cellulose nanocrystals from cotton linter

Solid-state 13C NMR spectroscopy was used to determine the degree of cellulose crystallinity (CrI) in kraft, flow-through kraft and polysulphide–anthraquinone (PS–AQ) pulps of pine and birch containing various amounts of hemicelluloses. The applicability of acid hydrolysis and the purely spectroscopic proton spin-relaxation based spectral edition (PSRE) method to remove the interfering hemicellulose signals prior to the determination of CrI were also compared. For softwood pulps, the spectroscopic removal of hemicelluloses by PSRE was found to be more efficient than the removal of hemicelluloses by acid hydrolysis. In addition to that, the PSRE method also provides information on the associations between cellulose and hemicelluloses. On the basis of the incomplete removal of xylan from the cellulose subspectra by PSRE, the deposition of xylan on cellulose fibrils and therefore an ordered ultrastructure of xylan in birch pulps was suggested. The ordered structure of xylan in birch pulps was also supported by the observed change of xylan conformation after regeneration. Similarly, glucomannan in pine pulps may have an ordered structure. According to the 13C CPMAS measurements conducted after acid hydrolysis, the degree of cellulose crystallinity was found to be slightly lower in birch pulps than in the pine pulps. Any significant differences in cellulose crystallinity were not found between the pulps obtained by the various pulping methods. Only in pine PS–AQ pulp, the degree of cellulose crystallinity may be slightly lower than in the kraft pulps containing less hemicelluloses.

Comparative extraction and characterisation of cellulose nanostructures from sawdust and maize stalk biomass.

One commonly cited factor that contributes to the recalcitrance of biomass is cellulose crystallinity. The present study aims to establish the effect of several pretreatment technologies on cellulose crystallinity, crystalline allomorph distribution, and cellulose ultrastructure. The observed changes in the cellulose ultrastructure of poplar were also related to changes in enzymatic hydrolysis, a measure of biomass recalcitrance. Hot-water, organo-solv, lime, lime-oxidant, dilute acid, and dilute acid-oxidant pretreatments were compared in terms of changes in enzymatic sugar release and then changes in cellulose ultrastructure measured by 13C cross polarization magic angle spinning nuclear magnetic resonance and wide-angle X-ray diffraction. Pretreatment severity and relative chemical depolymerization/degradation were assessed through compositional analysis and high-performance anion-exchange chromatography with pulsed amperometric detection. Results showed minimal cellulose ultrastructural changes occurred due to lime and lime-oxidant pretreatments, which at short residence time displayed relatively high enzymatic glucose yield. Hot water pretreatment moderately changed cellulose crystallinity and crystalline allomorph distribution, yet produced the lowest enzymatic glucose yield. Dilute acid and dilute acid-oxidant pretreatments resulted in the largest increase in cellulose crystallinity, para-crystalline, and cellulose-Iβ allomorph content as well as the largest increase in cellulose microfibril or crystallite size. Perhaps related, compositional analysis and Klason lignin contents for samples that underwent dilute acid and dilute acid-oxidant pretreatments indicated the most significant polysaccharide depolymerization/degradation also ensued. Organo-solv pretreatment generated the highest glucose yield, which was accompanied by the most significant increase in cellulose microfibril or crystallite size and decrease in relatively lignin contents. Hot-water, dilute acid, dilute acid-oxidant, and organo-solv pretreatments all showed evidence of cellulose microfibril coalescence.

Green-in-green biohybrids as transient biotriboelectric nanogenerators

Atomic force microscopy reveals how relative humidity impacts the Young’s modulus of lignocellulosic polymers and their adhesion with cellulose nanocrystals at the nanoscale

To investigate the effect of ultrafine grinding pretreatment on the isolation of wheat straw cellulose fibers and nanocrystals, wheat straw at cellular scale (50–30 m) were produced with different ultrafine grinding time prior to extract cellulose fibers and nanocrystals. Cellulose fibers were obtained by 4% sodium hydroxide and alkaline hydrogen peroxide treatment from ultrafine ground wheat straw. Morphological changes were observed using scanning electron microscopy (SEM). Fourier transform infrared (FTIR) spectroscopy showed the removal of non-cellulosic components and the rearrangement of hydrogen bonds in cellulose. X-ray diffraction (XRD) analysis revealed the decrease of crystalline index with grinding time prolonged and the formation of cellulose II in alkali treated 8.0 h ultrafine ground wheat straw. Cellulose nanocrystals were produced from these cellulose fibers using 64% sulfuric acid hydrolysis treatment. Morphological examination through atomic force microscope (AFM) showed that the length of rod-like CNCs decreased with prolonged ultrafine grinding time in 2.0 h and then increased due to the formation of cellulose II.

Surface-modified nano-cellulose as reinforcement in poly(lactic acid) to conform new composites

In this study, cellulose nanocrystals (CNC) were produced from untreated and pretreated sugarcane fibers through enzymatic hydrolysis using a crude cellulolytic extract produced by the fungus Aspergillus fumigatus CCT 7873 using semi-solid fermentation (SSF). The fibers were characterized in terms of cellulose, hemicellulose, and lignin contents and crystallinity index. The CNC generated during the enzymatic hydrolysis using a sugarcane fiber pretreated with 4% NaOH and an enzymatic loading of 7.5 FPU g−1 of bagasse were characterized by atomic force microscopy (AFM). The results showed that after the hydrolysis time of 48 h, spherical-like particles with a good size distribution and a mean diameter of 61 nm were obtained. In this study, we produced cellulose nanocrystals (CNC) from untreated and pretreated sugarcane fibers through enzymatic hydrolysis using a crude cellulolytic extract produced by the fungus Aspergillus fumigatus CCT 7873 using semi-solid fermentation (SSF). In fact, the main novelty of this manuscript is the fact that it accompanies the formation of CNC, by means of atomic force microscopy (AFM). It is noteworthy that there are few manuscripts with this approach in the literature. In addition, this was performed during the cultivation of a fermentation broth containing cellulases produced by an enzymatic extract of the fungus Aspergillus fumigatus CCT 7873 using SSF. Thus, CNC, a highly added value product, can be obtained from lignocellulosic residues, which is a renewable and low-cost source. The results showed that, during the cultivation, there is a variation in the size distribution of the CNC and that, for the hydrolysis time of 48 h, a good size distribution was obtained for the CNC with about 61 nm in diameter, presenting a spherical shape.

Active films containing curcumin exhibit outstanding antioxidant and antibacterial properties. Because of curcumin’s poor solubility in water, cetyltrimethylammonium chloride (CTAC) brush-TEMPO-oxidized cellulose nanocrystal (TCN) colloidal systems were prepared to be used as a delivery excipient to modulate the hosting of curcumin. The curcumin-loaded cellulose nanocrystals were incorporated in a tara gum/PVA blend film to prepare antioxidant and antibacterial films. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) measurements, transmission electron microscope (TEM), and solid-state 13C NMR spectroscopy were performed to characterize the products. The results indicate the synthesis of TCN with a carboxyl content of 1.1878 mmol/g and 0.71 degree of substitution of CTAC based on carboxyl groups. There was 26.57% of the curcumin bound in the brush. The mechanical properties and barrier properties of the films were characterized. DPPH and ABTS+ assays were used to measure the antioxidant properties. The activities against Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria were also evaluated. The release of curcumin from the films into food simulants were also characterized to determine whether the antioxidants could provide intermediate protection from lipid oxidation. The results show that the mechanical and barrier properties of the films improved although water the vapor permeability slightly decreased. The film possessed desirable antioxidant and antibacterial properties. The release test revealed that curcumin was initially released rapidly into 50% ethanol solution and then released more slowly into the bulk. This suggests that the film could provide short-term protection from food oxidation. The films can be used for prolonging the shelf life of packed fat-rich foods.

The X-ray crystal structure-based models of Iα cellulose nanocrystals (CNC), both pristine and containing surface sulfate groups with negative charge 0-0.34 e/nm(2) produced by sulfuric acid hydrolysis of softwood pulp, feature a highly polarized "crystal-like" charge distribution. We perform sampling using molecular dynamics (MD) of the structural relaxation of neutral pristine and negatively charged sulfated CNC of various lengths in explicit water solvent and then employ the statistical mechanical 3D-RISM-KH molecular theory of solvation to evaluate the solvation structure and thermodynamics of the relaxed CNC in ambient aqueous NaCl solution at a concentration of 0.0-0.25 mol/kg. The MD sampling induces a right-hand twist in CNC and rearranges its initially ordered structure with a macrodipole of high-density charges at the opposite faces into small local spots of alternating charge at each face. This surface charge rearrangement observed for both neutral and charged CNC significantly affects the distribution of ions around CNC in aqueous electrolyte solution. The solvation free energy (SFE) of charged sulfated CNC has a minimum at a particular electrolyte concentration depending on the surface charge density, whereas the SFE of neutral CNC increases linearly with NaCl concentration. The SFE contribution from Na(+) counterions exhibits behavior similar to the NaCl concentration dependence of the whole SFE. An analysis of the 3D maps of Na(+) density distributions shows that these model CNC particles exhibit the behavior of charged nanocolloids in aqueous electrolyte solution: an increase in electrolyte concentration shrinks the electric interfacial layer and weakens the effective repulsion between charged CNC particles. The 3D-RISM-KH method readily treats solvent and electrolyte of a given nature and concentration to predict effective interactions between CNC particles in electrolyte solution. We provide CNC structural models and a modeling procedure for studies of effective interactions and the formation of ordered phases of CNC suspensions in electrolyte solution.

Sulfuric acid solvolysis of cellulose in a butanol-1/benzene mixture for isolating cellulose nanocrystals

Nanocrystals of cellulose allomorphs have different adsorption of cellulase and subsequent degradation