A comparative study on the preparation and characterization of cellulose nanocrystals with various polymorphs

Nanocellulose: The Ultimate Green Aqueous Dispersant for Nanomaterials

Nanocellulose, a nanoscale derivative from renewable biomass sources, possesses remarkable colloidal properties in water, mechanical strength, and biocompatibility. It emerges as a promising bio-based dispersing agent for various nanomaterials in water. This mini-review explores the interaction between cellulose nanomaterials (nanocrystals or nanofibers) and water, elucidating how this may enable their potential as an eco-friendly dispersing agent. We explore the potential of nanocellulose derived from top-down processes, nanocrystals, and nanofibers for dispersing carbon nanomaterials, semiconducting oxide nanoparticles, and other nanomaterials in water. We also highlight its advantages over traditional methods by not only effectively dispersing those nanomaterials but also potentially eliminating the need for further chemical treatments or supporting stabilizers. This not only preserves the exceptional properties of nanomaterials in aqueous dispersion, but may even lead to the emergence of novel hybrid functionalities. Overall, this mini-review underscores the remarkable versatility of nanocellulose as a green dispersing agent for a variety of nanomaterials, inspiring further research to expand its potential to other nanomaterials and applications.

Advancements in Hybrid Cellulose-Based Films: Innovations and Applications in 2D Nano-Delivery Systems

This review paper delves into the realm of hybrid cellulose-based materials and their applications in 2D nano-delivery systems. Cellulose, recognized for its biocompatibility, versatility, and renewability, serves as the core matrix for these nanomaterials. The paper offers a comprehensive overview of the latest advancements in the creation, analysis, and application of these materials, emphasizing their significance in nanotechnology and biomedical domains. It further illuminates the integration of nanomaterials and advanced synthesis techniques that have significantly improved the mechanical, chemical, and biological properties of hybrid cellulose-based materials.

Cinnamaldehyde-enriched Pickering emulsions stabilized by modified cellulose I and II nanocrystals recycled from maple leaves for shrimp preservation

The utilization of biomass waste has attracted much interest, but such attention hasn't been paid to the abundant fallen maple leaves in Canada. Herein, we aim to obtain cellulose nanocrystals (CNCs) from maple leaves and explore their potential applications as sustainable stabilizers of Pickering emulsions for the preservation of food products with complicated structures. The results reveal that two types of CNCs were extracted from maple leaves at different alkaline conditions. Octenyl succinic anhydride was selected to modify rod-like CNCs, and the CNC-stabilized oil-in-water Pickering emulsions showed excellent stability. Cinnamaldehyde, a model antibacterial compound, was incorporated in the Pickering emulsions, which exhibited the improved storage stability and sustained antibacterial capacity towards both Gram-positive and Gram-negative bacteria. Shrimp was chosen as an example that has complicated surface structure and is hard to disinfect, and the CNC-stabilized Pickering emulsions could be easily sprayed on the surface of shrimp to inhibit the proliferation of bacteria and inactivate the psychrophilic bacteria responsible for shrimp spoilage at refrigerated condition, so as to preserve the quality of shrimp. Therefore, the current work suggests the possibility to utilize fallen maple leaves as a promising source of CNCs and the applications of CNC-stabilized Pickering emulsions in seafood preservation.

Mechanical Properties and Non-Isothermal Crystallization Kinetics of Polylactic Acid Modified by Polyacrylic Elastomers and Cellulose Nanocrystals

In this paper, a polyacrylic elastomer latex with butyl acrylate (BA) as the core and methyl methacrylate (MMA) copolymerized with glycidyl methacrylate (GMA) as the shell, named poly(BA-MMA-GMA) (PBMG), was synthesized by seeded emulsion polymerization. Cellulose nanocrystal (CNC) was dispersed in the polyacrylic latex to prepare PBMG/CNC dispersions with different CNC contents. The dried product was mixed with polylactic acid (PLA) to fabricate PLA/PBMG/CNC blends. The addition of PBMG and PBMG/CNC improved the mechanical properties of the PLA matrix. Differential scanning calorimetry (DSC) was used to investigate the non-isothermal crystallization kinetics. The Avrami equation modified by the Jeziorny, Ozawa and Mo equations was used to analyze the non-isothermal crystallization kinetics of PLA and its blends. Analysis of the crystallization halftime of non-isothermal conditions indicated that the overall rate of crystallization increased significantly at 1 wt% content of CNC. This seemed to result from the increase of nucleation density and the acceleration of segment movement in the presence of the CNC component. This phenomenon was verified by polarizing microscope observation.

Self-assembly of porous cellulose fibers and the incorporation of graphene carbon quantum dots for stable luminescence

Porous fibers as excellent carriers can be used to prepare photoluminescence materials. Herein, cellulose nanocrystals (CNCs) were derived from microcrystalline cellulose (MCC) by sulfuric acid hydrolysis. After CNCs were squeezed into a coagulating bath containing silicon precursors obtained by the hydrolysis of tetraethyl orthosilicate, porous cellulose fibers were constructed through self-assembly and then incorporated with graphene carbon quantum dots (GQDs) to prepare porous photoluminescence cellulose fibers. The silicon precursor amount, self-assembly time, and corrosion time were optimized. In addition, the morphology, structure and optical properties of the products were investigated. These results showed that as-prepared porous cellulose fibers with mesopores presented loose and porous mesh. Interestingly, the porous photoluminescence cellulose fibers exhibited blue fluorescence, and the maximum emission peak appeared at 430 nm under the excitation wavelength of 350 nm. Furthermore, the relative fluorescence intensity of the porous photoluminescence cellulose fibers was significantly enhanced compared with nonporous photoluminescence cellulose fibers. This work provided a new method to prepare environmentally and stably photoluminescence fibers, which had potential applications in anti-counterfeit packaging and smart packaging.

Effect of Acetylation of Two Cellulose Nanocrystal Polymorphs on Processibility and Physical Properties of Polylactide/Cellulose Nanocrystal Composite Film

Polylactide (PLA) has become a popular alternative for petroleum-based plastics to reduce environmental pollution. The broader application of PLA is hampered by its brittle nature and incompatibility with the reinforcement phase. The aim of our work was to improve the ductility and compatibility of PLA composite film and investigate the mechanism by which nanocellulose enhances PLA polymer. Here, we present a robust PLA/nanocellulose hybrid film. Two different allomorphic cellulose nanocrystals (CNC-I and CNC-III) and their acetylated products (ACNC-I and ACNC-III) were used to realize better compatibility and mechanical performance in a hydrophobic PLA matrix. The tensile stress of the composite films with 3% ACNC-I and ACNC-III increased by 41.55% and 27.22% compared to pure PLA film, respectively. Compared to the CNC-I or CNC-III enhanced PLA composite films, the tensile stress of the films increased by 45.05% with 1% ACNC-I and 56.15% with 1% ACNC-III. In addition, PLA composite films with ACNCs showed better ductility and compatibility because the composite fracture gradually transitioned to a ductile fracture during the stretching process. As a result, ACNC-I and ACNC-III were found to be excellent reinforcing agents for the enhancement of the properties of polylactide composite film, and the replacement some petrochemical plastics with PLA composites would be very promising in actual life.

Preparation of Cellulose Nanocrystals: Controlling the Crystalline Type by One-Pot Acid Hydrolysis

Cellulose nanocrystals (CNCs) have aroused increasing interest owing to their renewable origin and excellent properties derived from their size and morphology. Based on their chain orientation, CNCs can be prepared as two main allomorphs (I or II). However, achieving pure CNC allomorphs still requires enhanced control on the CNCs synthesis process and improved understanding of the involved reaction parameters. In this work, we study in detail a set of parameters for CNC synthesis using one-pot acid hydrolysis and evaluate their influence on the outcome with respect to yield, purity, and repeatability. We also demonstrate that a fast, nondestructive, and accurate methodology based on dynamic light scattering is an efficient alternative to the usual structural analysis of the synthesis outcome. Finally, we provide an improved protocol to reliably obtain each allomorph with mass yields of 25% for type I and 40% for type II. Emphasis is put on the reduction of the environmental impact and the overall preparation time.

Bacterial nanocellulose production using Cantaloupe juice, statistical optimization and characterization

The bacterial nanocellulose has been used in a wide range of biomedical applications including carriers for drug delivery, blood vessels, artificial skin and wound dressing. The total of ten morphologically different bacterial strains were screened for their potential to produce bacterial nanocellulose (BNC). Among these isolates, Bacillus sp. strain SEE-3 exhibited potent ability to produce the bacterial nanocellulose. The crystallinity, particle size and morphology of the purified biosynthesized nanocellulose were characterized. The cellulose nanofibers possess a negatively charged surface of - 14.7 mV. The SEM images of the bacterial nanocellulose confirms the formation of fiber-shaped particles with diameters of 20.12‒47.36 nm. The TEM images show needle-shaped particles with diameters of 30‒40 nm and lengths of 560‒1400 nm. X-ray diffraction show that the obtained bacterial nanocellulose has crystallinity degree value of 79.58%. FTIR spectra revealed the characteristic bands of the cellulose crystalline structure. The thermogravimetric analysis revealed high thermal stability. Optimization of the bacterial nanocellulose production was achieved using Plackett-Burman and face centered central composite designs. Using the desirability function, the optimum conditions for maximum bacterial nanocellulose production was determined theoretically and verified experimentally. Maximum BNC production (20.31 g/L) by Bacillus sp. strain SEE-3 was obtained using medium volume; 100 mL/250 mL conical flask, inoculum size; 5%, v/v, citric acid; 1.5 g/L, yeast extract; 5 g/L, temperature; 37 °C, Na₂HPO₄; 3 g/L, an initial pH level of 5, Cantaloupe juice concentration of 81.27 percent and peptone 11.22 g/L.

Ultrasonic cavitation: An effective cleaner and greener intensification technology in the extraction and surface modification of nanocellulose

With rising consumer demand for natural products, a greener and cleaner technology, i.e., ultrasound-assisted extraction, has received immense attention given its effective and rapid isolation for nanocellulose compared to conventional methods. Nevertheless, the application of ultrasound on a commercial scale is limited due to the challenges associated with process optimization, high energy requirement, difficulty in equipment design and process scale-up, safety and regulatory issues. This review aims to narrow the research gap by placing the current research activities into perspectives and highlighting the diversified applications, significant roles, and potentials of ultrasound to ease future developments. In recent years, enhancements have been reported with ultrasound assistance, including a reduction in extraction duration, minimization of the reliance on harmful chemicals, and, most importantly, improved yield and properties of nanocellulose. An extensive review of the strengths and weaknesses of ultrasound-assisted treatments has also been considered. Essentially, the cavitation phenomena enhance the extraction efficiency through an increased mass transfer rate between the substrate and solvent due to the implosion of microbubbles. Optimization of process parameters such as ultrasonic intensity, duration, and frequency have indicated their significance for improved efficiency.

Lignocellulosic Nanocrystals from Sawmill Waste as Biotemplates for Free-Surfactant Synthesis of Photocatalytically Active Porous Silica

This work presents a new approach for more effective valorization of sawmill wastes (Beech and Cedar sawdusts), which were used as new sources for the extraction of lignin-containing and lignin-free cellulose II nanocrystals (L-CNCs and CNCs). It was shown that the properties of the extracted nanocrystals depend on the nature of the used sawdust (softwood or hardwood sawdusts). L-CNCs and CNCs derived from Beech fibers were long and thin and also had a higher crystallinity, compared with those obtained from Cedar fibers. Thanks to their interesting characteristics and their high crystallinity, these nanocrystals have been used without changing their surfaces as template cores for nanostructured hollow silica-free-surfactant synthesis for photocatalysis to degrade methylene blue (MB) dye. The synthesis was performed with a simple and efficient sol-gel method using tetraethyl orthosilicate as the silica precursor followed by calcination at 650 °C. The obtained materials were denoted as B/L-CNC/nanoSiO2, B/CNC/nanoSiO2, C/L-CNC/nanoSiO2, and C/CNC/nanoSiO2, when the used L-CNC and CNC cores are from Beech and Cedar, respectively. By comprehensive analysis, it was demonstrated that the nanostructured silica were quite uniform and had a similar morphology as the templates. Also, the pore sizes were closely related to the dimensions of L-CNC and CNC templates, with high specific surface areas. The photocatalytic degradation of MB dye was about 94, 98, 74, and 81% for B/L-CNC/nanoSiO2, B/CNC/nanoSiO2, C/L-CNC/nanoSiO2, and C/CNC/nanoSiO2, respectively. This study provides a simple route to extract L-CNCs and CNCs as organic templates to prepare nanostructured silica. The different silica structures showed excellent photodegradation of MB.

In vitro gastrointestinal digestibility of corn oil-in-water Pickering emulsions stabilized by three types of nanocellulose

The effect of three nanocellulose (various in crystalline allomorph and morphology) on lipid in vitro gastrointestinal digestibility was investigated. Corn oil-in-water emulsions were prepared by CNCs-I, CNCs-II and CNFs respectively. The variations of droplets diameter D[4,3], zeta potential, and microstructure were measured during gastrointestinal digestion (mouth, stomach and small intestine), and the free fatty acid (FFA) released in the small intestine phase were examined. The FFA-released test results indicated that both crystalline allomorph and morphology of nanocellulose affected the degree of lipid digestion, especially the morphology. FFA released amount was ranked in the order of CNCs-I (56.60%), CNCs-II (48.67%) and CNFs (28.21%). This is mainly due to the difference in the self-assembly behavior of nanocellulose at the interface. Our findings provide an innovative solution that using nanocellulose as food-grade particle stabilizer to modulate the digestion of Pickering emulsified lipids, which would benefit the development of given functional foods.

A comprehensive investigation on cellulose nanocrystals with different crystal structures from cotton via an efficient route

The crystal structures of cellulose nanomaterials play an important role in their morphologies and applications, however, there was still lacking systematic research on preparing various crystalline allomorphs of cellulose nanocrystals with high thermal stability. Herein, the efficient synthesis route was presented to design various crystalline allomorphs of cellulose from cotton. And then, cellulose nanocrystals with different crystal structures (CNC-I, CNC-II, CNC-III_II, CNC-IV_II) were prepared by hydrogen peroxide hydrolysis of resultant cellulose. Overall, needle-like CNC-I (length of 180 ± 25 nm, diameter of 12 ± 2 nm), near-spherical CNC-II (diameter of 101 ± 12 nm), and spherical CNC-III_II (diameter of 22 ± 3 nm) and CNC-IV_II (diameter of 21 ± 2 nm) all exhibited remarkable dispersibility and thermal stability (T_max > 357 °C). This work provides a simple and low-cost synthesis route for various crystalline allomorphs of CNCs with high thermal stability from the same raw materials (cotton).

Effect of nanocellulose polymorphism on electrochemical analytical performance in hybrid nanocomposites with non-oxidized single-walled carbon nanotubes

Two cellulose nanocrystals/single-walled carbon nanotube (CNC/SW) hybrids, using two cellulose polymorphs, were evaluated as electrochemical transducers: CNC type I (CNC-I/SW) and CNC type II (CNC-II/SW). They were synthesized and fully characterized, and their analytical performance as electrochemical sensors was carefully studied. In comparison with SWCNT-based and screen-printed carbon electrodes, CNC/SW sensors showed superior electroanalytical performance in terms of sensitivity and selectivity, not only in the detection of small metabolites (uric acid, dopamine, and tyrosine) but also in the detection of complex glycoproteins (alpha-1-acid glycoprotein (AGP)). More importantly, CNC-II/SW exhibited 20 times higher sensitivity than CNC-I/SW for AGP determination, yielding a LOD of 7 mg L^-1.These results demonstrate the critical role played by nanocellulose polymorphism in the electrochemical performance of CNC/SW hybrid materials, opening new directions in the electrochemical sensing of these complex molecules. In general, these high-active-surface hybrids smartly exploited the preserved non-oxidized SW conductivity with the high aqueous dispersibility of the CNC, avoiding the use of organic solvents or the incorporation of toxic surfactants during their processing, making the CNC/SW hybrids promising nanomaterials for electrochemical detection following greener approaches.

Crystalline polysaccharides: A review

The biodegradability and mechanical properties of polysaccharides are dependent on their architecture (linear or branched) as well as their crystallinity (size of crystals and crystallinity percent). The amount of crystalline zones in the polysaccharide significantly governs their ultimate properties and applications (from packaging to biomedicine). Although synthesis, characterization, and properties of polysaccharides have been the subject of several review papers, the effects of crystallization kinetics and crystalline domains on the properties and application have not been comprehensively addressed. This review places focus on different aspects of crystallization of polysaccharides as well as applications of crystalline polysaccharides. Crystallization of cellulose, chitin, chitosan, and starch, as the main members of this family, were discussed. Then, application of the aforementioned crystalline polysaccharides and nano-polysaccharides as well as their physical and chemical interactions were overviewed. This review attempts to provide a complete picture of crystallization-property relationship in polysaccharides.

Biosynthesis of Polyhydroxybutyrate with Cellulose Nanocrystals Using Cupriavidus necator

Polyhydroxybutyrate (PHB) is a natural polyester synthesized by several microorganisms. Moreover, it has excellent biodegradability and is an eco-friendly material because it converts water and carbon dioxide as final decomposition products. However, the applications of PHB are limited because of its stiffness and brittleness. Because cellulose nanocrystals (CNCs) have excellent intrinsic mechanical properties such as high specific strength and modulus, they may compensate for the insufficient physical properties of PHB by producing their nanocomposites. In this study, natural polyesters were extracted from Cupriavidus necator fermentation with CNCs, which were well-dispersed in nitrogen-limited liquid culture media. Fourier-transform infrared spectroscopy results revealed that the additional O-H peak originating from cellulose at 3500-3200 cm-1 was observed for PHB along with the C=O and -COO bands at 1720 cm-1. This suggests that PHB-CNC nanocomposites could be readily obtained using C. necator fermented in well-dispersed CNC-supplemented culture media.

A review of nanocellulose as a new material towards environmental sustainability

Synthetic polymers, commonly referred to as plastics, are anthropogenic contaminants that adversely affect the natural ecosystems. The continuous disposal of long lifespan plastics has resulted in the accumulation of plastic waste, leading to significant pollution of both marine and terrestrial habitats. Scientific pursuit to seek environment-friendly materials from renewable resources has focused on cellulose, the primary reinforcement component of the cell wall of plants, as it is the most abundantly available biopolymer on earth. This paper provides an overview on the current state of science on nanocellulose research; highlighting its extraction procedures from lignocellulosic biomass. Literature shows that the process used to obtain nanocellulose from lignocellulosic biomass greatly influences its morphology, properties and surface chemistry. The efficacy of chemical methods that use alkali, acid, bleaching agents, ionic liquids, deep eutectic solvent for pre-treatment of biomass is discussed. There has been a continuous endeavour to optimize the pre-treatment protocol as it is specific to lignocellulosic biomass and also depends on factors such as nature of the biomass, process and environmental parameters and economic viability. Nanofibers are primarily isolated through mechanical fibrillation while nanocrystals are predominantly extracted using acid hydrolysis. A concise overview on the ways to improve the yield of nanocellulose from cellulosic biomass is also presented in this review. This work also reviews the techniques used to modify the surface properties of nanocellulose by functionalizing surface hydroxyl groups to impart desirable hydrophilic-hydrophobic balance. An assessment on the emerging application of nanocellulose with an emphasis on development of nanocomposite materials for designing environmentally sustainable products is incorporated. Finally, the status of the industrial production of nanocellulose presented, which indicates that there is a continuously increased demand for cellulose nanomaterials. The demand for cellulose is expected to increase further due to its increasing and broadening applications.

Cellulose nanocrystals in cancer diagnostics and treatment

Cancer is currently a major threat to public health, being among the principal causes of death to the global population. With carcinogenesis mechanisms, cancer invasion, and metastasis remaining blurred, cancer diagnosis and novel drug delivery approaches should be developed urgently to enable management and treatment. A dream break-through would be a non-invasive instantaneous monitoring of cancer initiation and progression to fast-track diagnosis for timely specialist treatment decisions. These innovations would enhance the established treatment protocols, unlimited by evasive biological complexities during tumorigenesis. It is therefore contingent that emerging and future scientific technologies be equally biased towards such innovations by exploiting the apparent properties of new developments and materials especially nanomaterials. CNCs as nanomaterials have undisputable physical and excellent biological properties that enhanced their interest as biomedical materials. This article therefore highlights CNCs utility in cancer diagnosis and therapy. Their extraction, properties, modification, in-vivo/in-vitro medical applications, biocompatibility, challenges and future perspectives are precisely discussed.

Temperature-triggered formation of a cellulose II nanocrystal network through regioselective derivatization

The two ends of rodlike cellulose II nanocrystals (CNC-II) were regioselectively functionalized either with gold nanoparticles or thermosensitive polymer chains. In the first case, after the introduction of sulfur atoms at both ends of the rods, CNC-II were labelled using a method based on the in situ nucleation and growth of gold nanoparticles (AuNPs) from soluble derivatives. Transmission electron microscopy (TEM) images showed that such a method resulted in the grafting of one monodisperse AuNP at each extremity of the CNC-II, i.e. to the formation of hybrid dumbbell-shaped objects. No AuNP was detected on the lateral surfaces of the CNC-II and almost all observed CNC-II exhibited this dual labeling. This result confirmed with a good statistics when compared to previous works the possibility to derivatize only the two ends of the CNC-II, thanks to the antiparallel arrangement of cellulose chains in these nanoparticles. In the second case, the localized grafting of temperature-sensitive macromolecules onto the ends of the CNC-II was performed using an oxidation reaction followed by a peptide coupling. This end-specific grafting of thermosensitive chains onto CNC-II enhanced their colloidal stability when the temperature was below the lower critical solution temperature (LCST) of the polymer. Above the LCST, the TEM images revealed the formation of a network extending to tens of microns resulting from end-to-end associations of the derivatized rods through attractive interactions between collapsed polymer chains. Rheology experiments further evidenced a temperature-induced sol-gel transition from a liquid-like (sol) behavior below the LCST to solid-like (gel) behavior above the LCST, in agreement with a change from purely repulsive interactions to interconnections via the hydrophobic collapsed chains. Importantly, all results concurred with a full reversibility of the phenomena upon cooling and reproducibility when samples were subjected to temperature cycles around the LCST. This work reveals that the dual site-specific derivatization of CNC-II can provide symmetric hybrid particles with innovative assembling and macroscopic properties that cannot be obtained through homogeneous chemical modifications.

Valorization of khat (Catha edulis) waste for the production of cellulose fibers and nanocrystals

Cellulose fibers (C40 and C80) were extracted from khat (Catha edulis) waste (KW) with chlorine-free process using 40% formic acid/40% acetic acid (C40), and 80% formic acid/80% acetic acid (C80) at the pretreatment stage, followed by further delignification and bleaching stages. Cellulose nanocrystals (CNCs40 and CNCs80) were then isolated from C40 and C80 with sulfuric acid hydrolysis, respectively. Thus, the current study aims to isolate cellulose fibers and CNCs from KW as alternative source. The KW, cellulose fibers, and CNCs were investigated for yield, chemical composition, functionality, crystallinity, morphology, and thermal stability. CNCs were also evaluated for colloidal stability, particle size, and their influence on in vitro diclofenac sodium release from gel formulations preliminarily. The FTIR spectra analysis showed the removal of most hemicellulose and lignin from the cellulose fibers. The XRD results indicated that chemical pretreatments and acid hydrolysis significantly increased the crystallinity of cellulose fibers and CNCs. The cellulose fibers and CNCs exhibited Cellulose Iβ crystalline lattice. TEM analysis revealed formation of needle-shaped nanoscale rods (length: 101.55-162.96 nm; aspect ratio: 12.84-22.73). The hydrodynamic size, polydispersity index, and zeta potential of the CNCS ranged from 222.8-362.8 nm; 0.297-0.461, and -45.7 to -75.3 mV, respectively. CNCs40 exhibited superior properties to CNCs80 in terms of aspect ratio, and colloidal and thermal stability. Gel formulations containing high proportion of CNCs sustained diclofenac sodium release (< 50%/cm2) over 12 h. This study suggests that cellulose fibers and nanocrystals can be successfully obtained from abundant and unexploited source, KW for value-added industrial applications.

Crystalline stability of cellulose III nanocrystals in the hydrothermal treatment and NaOH solution

To better understand the system and conversion of cellulose allomorphs, cellulose III nanocrystals (CNC-III) were used to investigate the crystalline stability of cellulose III in the hydrothermal condition and a lower concentrated NaOH-water system. It was shown that H₂O or alkali played an important role in the process of polymorphic transformation. The CNC-III allomorph turned back to cellulose I with an extremely low crystallinity (∼4.18 %) during hydrothermal process at 90-95 °C, or cellulose II when the temperature excessed boiling point (≥100 °C). Furthermore, CNC-III could be rapidly dissolved in an aqueous NaOH (∼7 wt.%) without a pre-cooled treatment to obtain its stable solution. Afterwards, cellulose II with a steady average crystallite size (∼34) was acquired after the regeneration process via dialysis with distilled water. The polymorphic transformation was also analyzed by X-ray diffraction (XRD), solid-state ¹³C nuclear magnetic resonance (¹³C NMR).

Residual lignin in cellulose nanofibrils enhances the interfacial stabilization of Pickering emulsions

Lignocellulose nanofibrils (LCNF) were used to prepare oil-in-water Pickering emulsions and to assess the role residual lignin in interfacial stabilization. Two LCNF fractions of similar morphology (length ∼700 nm and width ∼8 nm) and structure (polymorphism and crystallinity) were obtained by microfluidization of fibers obtained by hydrothermal treatment of wood with a recyclable organic acid. The LCNF with higher residual lignin was less hydrophilic and, correspondingly, performed better as Pickering stabilizer, producing emulsions of smaller droplet size and higher resistance to creaming. Long-term emulsion stabilization (over 40 days) was achieved with LCNF at concentrations as low as 0.24 (w/v)% based on emulsion volume. We conclude that LCNF-stabilized Pickering emulsions can be finely tuned by varying the residual lignin content, providing a rationale for LCNF selection according to lignin type and concentration as variables affecting stabilization. Complementary considerations include the possible benefits of the residual lignin in LCNF, including antioxidant and UV absorption properties.

Quantitative and qualitative characterization of dual scale mechanical enhancement on cellulosic and crystalline-structural variation of NaOH treated wheat straw

In order to explore the effects of different mechanical fragmentation on cellulose separation and cellulose polymorphic transformation of wheat straw during alkali treatment, one coarse milled (CM) and two ball milled wheat straw samples (BM30 and BM120) were treated with different NaOH concentrations (1%-10%), and the lignocellulosic compositions and crystalline-structural various were quantitative and qualitative characterized. The quantitative equations between cellulose content and NaOH concentration of different mechanical treated samples were Y_CM = 69.8-35.1exp(-0.64X)), Y_BM30 = 71.3-35.1exp(-0.86X)) and Y_BM120 = 73.5-35.1exp(-1.82X)). The enhancement effect of cellulose separation with the increasing mechanical fragmentation intensity is mainly due to the increasing hemicellulose solubilization. X-ray diffraction results reveals that the NaOH concentration required for cellulose crystalline transformation of CM, BM30 and BM120 is 10%, 8% and 2%, respectively. In conclusion, mechanical fragmentation contributes to cellulose separation and cellulose crystalline transformation under lower NaOH concentration.

Patience is a virtue: self-assembly and physico-chemical properties of cellulose nanocrystal allomorphs

Cellulose nanocrystals (CNCs) are bio-based rod-like nanoparticles with a quickly expanding market. Despite the fact that a variety of production routes and starting cellulose sources are employed, all industrially produced CNCs consist of cellulose I (CNC-I), the native crystalline allomorph of cellulose. Here a comparative study of the physico-chemical properties and liquid crystalline behavior of CNCs produced from cellulose II (CNC-II) and typical CNC-I is reported. CNC-I and CNC-II are isolated by sulfuric acid hydrolysis of cotton and mercerized cotton, respectively. The two allomorphs display similar surface charge densities and ζ-potentials and both have a right-handed twist, but CNC-II have a slightly smaller average length and aspect ratio, and are less hygroscopic. Interestingly, the self-assembly behavior of CNC-I and CNC-II in water is different. Whilst CNC-I forms a chiral nematic phase, CNC-II initially phase separates into an upper isotropic and a lower nematic liquid crystalline phase, before a slow reorganization into a large-pitch chiral nematic texture occurs. This is potentially caused by a combination of factors, including the inferred faster rotational diffusion of CNC-II and the different crystal structures of CNC-I and CNC-II, which are responsible for the presence and absence of a giant dipole moment, respectively.

Extraction and characterization of celluloses from various plant byproducts

Celluloses were extracted from teff straw (TS), enset fiber (EF), sugarcane bagasse (SB) and coffee hull (CH) agro-industrial byproducts generated in large quantities in Ethiopia. The present study aimed to explore these plant byproducts as alternative sources of cellulose for potential industrial applications, using various eco-friendly chlorine-free treatment conditions to obtain an optimum cellulose extraction condition. The byproducts and the as-extracted celluloses were analyzed for chemical compositions, yield, chemical functionality, crystallinity, thermal stability and morphology. EF yielded the highest cellulose content (60.0%), whereas CH the least (35.5%). FTIR spectra and ESEM morphological studies of the celluloses indicated progressive removal of non-cellulosic constituents. XRD analyses showed EF cellulose had the highest crystallinity index (CrI) (85.56%), crystallite size (5.52 nm), and proportion of crystallite interior chains of 200 plane (0.629), exhibiting unique physicochemical properties. The byproducts and the as-extracted celluloses showed Cellulose Iβ crystal lattice, while celluloses from EF and SB also displayed (partial) polymorphic transition into Cellulose II. TGA studies revealed enhanced stability of the as-extracted celluloses. On the basis of the physicochemical characteristics of the celluloses, all the byproducts studied could be considered as alternative sources of cellulose for potential value-added industrial applications.

Effect of Different Concentration of Cellulose Nanocrystals Comprising Hydroxyethyl Cellulose / Poly(Vinyl Alcohol) as a Bone Tissue Engineering Scaffold

In this study, biodegradable scaffolds based on hydroxyethyl cellulose (HEC) (5 wt%) and poly (vinyl alcohol) (PVA) (15 wt%) with different percentages of celullose nanocrystal (CNC) (1 and 7 wt%) were fabricated by lyophilization method to get highly porous scaffolds. These scaffolds were made water insoluble by cross-linking via heat treatment. The morphology and thermal properties of HEC/PVA/CNCs scaffolds were characterized by using Scanning Electron Microscope (SEM) and Thermogravimetric Analysis (TGA). The morphological study showed that both prepared scaffold have highly porous structures with good pore interconnected structure. It was observed that thermal properties of scaffolds increased significantly as the concentration of CNCs increased. Cytotoxicity studies on scaffolds were carried out by utilizing human fetal osteoblast (hFOB) cells using DAPI nuclear stain and then confirmed using SEM. hFOB cells were able to attach and spread on all scaffolds. Incorporated CNCs as reinforcing nanofiller on scaffolds promising a superior functionality in bone tissue engineering.

A Comparative Study on the Characterization of Nanofibers with Cellulose I, I/II, and II Polymorphs from Wood

Polymorphic changes in cellulose nanofibers (CNFs) are closely related to their properties and applications, and it is of interest to investigate how polymorphic changes influence their properties. A comparative study on the properties of CNFs with cellulose I, I/II, and II polymorphs from wood was conducted herein. CNFs were obtained by chemical extraction combined with a simple and efficient mechanical treatment (one pass through a grinder). This process resulted in a relatively high yield of 80⁻85% after a simple grinding treatment. The polymorphic changes in the CNFs and the chemical composition, morphology, tensile performances, and thermal properties were systematically characterized and compared. The X-ray diffraction and FTIR analyses verified the existence of three types of purified pulps and CNFs with cellulose I, cellulose I/II, and cellulose II polymorphs (CNF-I, CNF-I/II, CNF-II). Morphological observations presented that these three types of CNFs all exhibited high aspect ratios and entangled structures. Tensile testing showed that the CNF films all exhibited high tensile strengths, and the fracture strains of the CNF-I/II (11.8%) and CNF-II (13.0%) films were noticeably increased compared to those of the CNF-I film (6.0%). If CNF-II is used as reinforcing material, its larger fracture strain can improve the mechanical performance of the CNF composites, such as fracture toughness and impact strength. In addition, CNF-I, CNF-I/II, and CNF-II films showed very low thermal expansion in the range 20⁻150 °C, with the coefficient of thermal expansion values of 9.4, 17.1, and 17.3 ppm/K, respectively. Thermogravimetric analysis (TGA) revealed that the degradation temperature of CNF-I and CNF-II was greater than that of CNF-I/II, which was likely due to increased α-cellulose content. This comparative study of the characterization of CNF-I, CNF-I/II, and CNF-II provides a theoretical basis for the application of CNFs with different polymorphs and could broaden the applications of CNFs.

Eco-friendly waterborne polyurethane reinforced with cellulose nanocrystal from office waste paper by two different methods

Focusing on eco-friendly materials, cellulose nanocrystal (CNC) extracted from office waste paper was used to reinforce waterborne polyurethane (WPU) with varying content by two incorporation routes including blending method by sonication after WPU synthesis (BCNC/WPU) and the alternative in-situ during the WPU synthesis process (CNC/WPU). The results showed that new interaction between CNC and WPU through hydrogen bonds in the interfacial area was formed and CNC reinforced hard segments effectively. However, the interaction in BCNC/WPU was not as stronger as that in CNC/WPU. Besides, CNC improved thermal stability of WPU remarkably, especially BCNC/WPU. The addition of CNC caused a delay around 50 °C in the start of the degradation process, and a delay of 5-18 °C and 2-20 °C in the temperatures at 10 and 50 wt% weight loss, respectively. These eco-friendly and biodegradable novel materials have potential applications in medical and biologic fields.