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Cellulose nanopaper (CNP) has been considered as a promising material with great application potential in diverse fields. However, the hydrophilic nature of CNP significantly limits its practical application. In order to improve its water resistance, we demonstrate a facile approach to functionalize CNP by impregnating it with chitosan (CS), followed by in situ polymerization of polypyrrole (PPy). The results indicate that the obtained CNP/CS/PPy shows excellent water resistance with the wet tensile strength of up to 80 MPa, which is more than 10 times higher than that of the pure CNP. Intriguingly, new features (e.g., electrical conductivity, antibacterial activity, and so forth) are achieved at the same time. The functionalized CNP/CS/PPy shows a high conductivity of 6.5 S cm-1, which can be used for electromagnetic interference shielding applications with a high shielding performance of around 18 dB. In addition, the CNP/CS/PPy exhibits good antibacterial activity toward Staphylococcus aureus and Escherichia coli, with the bacterial reductions of 99.28 and 95.59%, respectively. Thus, this work provides a simple and versatile approach to functionalize CNP for achieving multifunctional properties.

We present a one-step route for the preparation of nickel phosphide/carbon nanotube (Ni2P@CNT) nano-composites for supercapacitor applications using a facile, ultrafast (90 s) microwave-based approach. Ni2P nanoparticles could grow uniformly on the surface of CNTs under the optimized reaction conditions, namely, a feeding ratio of 30:50:25 for CNT, Ni(NO3)2 · 6H2O, and red phosphorus and a microwave power of 1000 W for 90 s. Our study demonstrated that the single-step microwave synthesis process for creating metal phosphide nanoparticles was faster and simpler than all the other existing methods. Electrochemical results showed that the specific capacitance of the optimal Ni2P@CNT-nanocomposite electrode displayed a high specific capacitance of 854 F · g−1 at 1 A · g−1 and a superior capacitance retention of 84% after 5000 cycles at 10 A·g−1. Finally, an asymmetric supercapacitor was assembled using the nanocomposite with activated carbon as one electrode (Ni2P@CNT//AC), which showed a remarkable energy density of 33.5 W · h · kg−1 and a power density of 387.5 W·kg−1. This work will pave the way for the microwave synthesis of other transition metal phosphide materials for use in energy storage systems.

As a weak tricarboxylic acid, citric acid (CA) has been proposed for the preparation of cellulose nanocrystals (CNCs) due to its innocuous and easily recyclable nature. However, the yield of the ob...

Over the past few years, wearable electronics and smart textiles have seen tremendous growth in both academia and industries. However, it is still a challenge to prepare robust, flexible, wearable, and multiresponsive textile electronics. A newly blooming two-dimensional (2D) transition-metal carbide/nitride (MXene) is regarded as an ideal active material to build multifunctional electronics due to its intriguing properties. Herein, a hydrophobic and multifunctional textile composite (Si-MAP) was prepared by decoration of conductive MXene nanosheets onto air-laid paper, followed by wrapping with poly(dimethylsiloxane) (PDMS). These obtained smart textiles exhibited excellent electronic/photonic/mechanical triresponsive properties: Si-MAPs could reach high equilibrium temperatures (104.9 and 118.7 °C) under quite low power illumination (1.25 W cm-2) and working voltage (4 V). The Si-MAP pressure sensor exhibited high sensitivity and rapid response time (30-40 ms), which can capture a wide range of human movements. Moreover, the thin PDMS layer not only rendered the textile composites hydrophobic but also improved the stability and adaptation for daily use. Remarkably, the hydrophobic Si-MAPs have maintained the advantages of breathability and washability, which make them suitable for wearing. Thus, this smart Si-MAP textile provides a reference for the study of the next generation of light, portable, and wearable textile-based electronic devices.

Bacterial cellulose (BC), with non-toxicity, high purity, and biocompatibility, has been considered as a versatile candidate for various biomedical applications. Recently, the fabrication of BC-bas...

In this work, tension and fracture behaviors of cellulose nanopaper (CNP) made from two different preparation approaches are comparatively studied. The CNP are prepared by casting (or C-CNP) and filtration (or F-CNP) of CNF suspension. The resulting CNP are mechanically characterized using the vision-based full-field optical method of Digital Image Correlation. Tension tests show that F-CNP has a higher strength and greater nonlinearity than the C-CNP. The crack initiation and growth characteristics of the two types of CNP are investigated using optical measurements. The data are analyzed under small-scale-yielding conditions to quantify the fracture parameters such as stress intensity factors and energy release rates at crack initiation as well as during crack growth. The results indicate that both C-CNP and F-CNP show significant crack growth resistance in the post-crack initiation regime. The F-CNP particularly offers substantial resistance to crack growth relative to the C-CNP demonstrating that filtration is the preferred method to make CNP with higher tensile strength and better fracture properties.

Herein, we demonstrated a one-step route for the manufacturing of polypyrrole (PPy)/zinc nanohybrids with tunable elemental composition and nanoscale component mixing resolution by using an ultrafast (within tens of seconds) microwave approach for ultrasensitive DNA biosensors. The zinc-based nanoparticles (i.e., MWPPy/ZnO and MWPPy/ZnS) were produced by loading zinc acetate (ZnAc

Cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) are of great interest to researchers due to their outstanding properties and wide application potentials. However, green and sustainab...

The production of cellulose nanomaterials from lignocellulosic biomass opens an opportunity for the development and application of new materials in nanotechnology. Over the last decade, cellulose nanomaterials based hydrogels have emerged as promising materials in the field of biomedical applications due to their low toxicity, biocompatibility, biodegradability, as well as excellent mechanical stability. In this review, recent progress on the preparation of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) based hydrogels and their biomedical applications is summarized and discussed based on the analyses of the latest studies (especially for the reports in the past five years). We begin with a brief introduction of the differences in preparation methods and properties of two main types of cellulose nanomaterials: CNCs and CNFs isolated from lignocellulosic biomass. Then, various processes for the fabrication of CNCs based hydrogels and CNFs based hydrogels were elaborated, respectively, with the focus on some new methods (e.g. 3D printing). Furthermore, a number of biomedical applications of CNCs and CNFs based hydrogels, including drug delivery, wound dressings and tissue engineering scaffolds were highlighted. Finally, the prospects and ongoing challenges of CNCs and CNFs based hydrogels for biomedical applications were summarized. This work demonstrated that the CNCs and CNFs based hydrogels have great promise in a wide range of biomedical applications in the future.

With the increasing demand for wearable electronics (such as smartwatch equipment, wearable health monitoring systems, and human-robot interface units), flexible energy storage systems with eco-friendly, low-cost, multifunctional characteristics, and high electrochemical performances are imperative to be constructed. Nanocellulose with sustainable natural abundance, superb properties, and unique structures has emerged as a promising nanomaterial, which shows significant potential for fabricating functional energy storage systems. This review is intended to provide novel perspectives on the combination of nanocellulose with other electrochemical materials to design and fabricate nanocellulose-based flexible composites for advanced energy storage devices. First, the unique structural characteristics and properties of nanocellulose are briefly introduced. Second, the structure-property-application relationships of these composites are addressed to optimize their performances from the perspective of processing technologies and micro/nano-interface structure. Next, the recent specific applications of nanocellulose-based composites, ranging from flexible lithium-ion batteries and electrochemical supercapacitors to emerging electrochemical energy storage devices, such as lithium-sulfur batteries, sodium-ion batteries, and zinc-ion batteries, are comprehensively discussed. Finally, the current challenges and future developments in nanocellulose-based composites for the next generation of flexible energy storage systems are proposed.

As a kind of biomass waste, enzymatic hydrolysis residues (EHRs) are conventionally burned or just discarded, resulting in environmental pollution and low economic benefits. In this study, EHRs of corncob residues (CCR) were used to produce high lignin-containing cellulose nanofibrils (LCNFs) and lignin nanoparticles (LNPs) through a facile approach. The LCNFs and LNPs with controllable chemical compositions and properties were produced by tuning the enzymolysis time of CCR and the followed homogenization. The morphology, thermal stability, chemical and crystalline structure, and dispersibility of the resultant LCNFs and LNPs were further comprehensively investigated. This work not only promotes the production of lignocellulose-based nanomaterials but also provides a promising utilization pathway for EHRs.

Developing green and simple methods for the preparation of cellulose nanofibrils (CNFs) is of great significance. Herein, a green deep eutectic solvent (DES) system based on choline chloride (ChCl) and citric acid (CA) is employed to pretreat cellulose fibers for the preparation of CNFs. The effect of the pretreatment temperature on the chemo-physical properties of the CNFs is comprehensively investigated. A high CNFs yield of up to 84.19% can be achieved under optimized conditions. The optimal CNFs show a narrow diameter distribution and length up to several microns, high crystallinity and thermal stability, as well as excellent dispersibility in water. Furthermore, semi-transparent and flexible cellulose nanopaper (CNP) was fabricated through a facile vacuum filtration process. The optimal CNP shows high tensile strength (175.15 MPa) and toughness (7.51 MJ/m3). Therefore, this work provides a sustainable and facile approach to fabricate CNFs and CNP, which can be potentially used for various high-tech applications.

The purpose of this review is to summarize and discuss the recent developments in exploring cellulose and its derivatives in the applications of oilfield chemicals for petroleum drilling and exploiting. We begin with a brief introduction of cellulose and its common water-soluble derivatives, such as the carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, and amphoteric cellulose. Afterwards, the applications of cellulose derivatives in different petroleum exploitation processes, such as drilling, cementing, and fracturing, are set out in detail. Finally, the application perspectives and challenges of cellulose derivatives for oilfield applications are presented. This work demonstrates that cellulose derivatives have wide application prospects in oilfield industry in the future.

γ-Valerolactone (GVL), derived from renewable lignocellulosic biomass, has been considered as a cost-competitive and green platform chemical. With the increasingly prominent environmental problems, a deep understanding of the preparation and transformation of GVL is highly needed. Based on the latest progress made with GVL, preparation and applications of GVL are summarized and discussed in this Review. In particular, the state-of-the-art in catalytic production of GVL is described based on the use of noble-metal and non-noble-metal catalysts. The application of GVL for the valorization of lignocellulose would improve the yield of target products such as sugar monomers and furfural. Thus, GVL can be produced from lignocellulose and simultaneously it can also be used for the valorization of lignocellulose, just as in the sustainable and renewable cycle, "the falling leaves returns to their roots". This Review is expected to provide valuable reference and new proposal for the further development and better utilization of GVL.

Herein, we present an ultrafast microwave approach for fabricating MoS2/MoO2@CNT nanocomposites toward supercapacitor electrodes with excellent cycle stability. The surface chemistry, crystalline structure and morphology of the as-produced nanocomposites were characterized by FTIR, XRD, XPS, EDS and SEM. It was found that MoS2/MoO2 nanoparticles could grow uniformly on the surface of CNTs, and the CNTs can provide a transport path for ions in electrolytes and reduce energy loss, thus leading to enhanced electrochemical performance of the resultant nanocomposites. Electrochemical results showed that the capacitance of the nanocomposite electrode was increased by 187.1% after 25 000 cycles at a current density of 5 A g−1, indicating outstanding cycling stability. Also, the maximum capacitance of the optimized MoS2/MoO2@CNT electrode can reach 228.4 F g−1 at 0.5 A g−1. Moreover, an asymmetric supercapacitor (MoS2/MoO2@CNT//AC) was assembled which exhibited a maximum energy density of 11.88 W h kg−1 and a power density of 2 kW kg−1, respectively. Intriguingly, the asymmetric supercapacitors could successfully light three LED lights for 5 minutes, showing their great practical application potential in portable supercapacitors.

Corn husk is usually burned and discarded, resulting in environment pollution and a waste of resources. To make better use of corn husk, in this work, corn husk filament (CHF) and corn husk powder (CHP) were first separated and then the comparative evaluation of efficient conversion of CHF and CHP to valuable materials was carried out via a sustainable route [i.e., one-step formic acid (FA) hydrolysis]. After FA fractionation, over 90% hemicellulose could be removed (mainly converted to xylose), about 80% lignin with high purity could be isolated, and the fractionated cellulose solid residue was used to fabricate cellulose nanofibrils (CNFs) and functional cellulose nanopaper (CNP). Results showed that, compared to CHP, the CHF with lower density, longer fibers, and higher crystallinity could be easier to hydrolyze, and the resulting CNFs had a smaller diameter and higher crystallinity, leading the final CNP to have better mechanical properties. The maximum tensile strength and toughness of the resultant ...

With the increase of global energy consumption and serious environmental pollution, green and sustainable electrode materials are urgently needed for energy storage devices. Cellulose foams and aerogels have the advantages of low density, and biodegradability, which have been considered as versatile scaffolds for various applications. Recently, rational design and fabrication of cellulose based composite foams and aerogels for energy storage devices have received extensive attention which gradually becomes a hot spot in the research of sustainable electrode materials. In this review, we begin with a brief summary of the category and preparation strategies of cellulose foams and aerogels. Then, the fabrication methods of cellulose-based composite foams and aerogels compounded with various kinds of active materials are introduced, and their performances as electrode materials for supercapacitors and batteries were comprehensively elaborated, respectively. Finally, we proposed the current challenges and future prospects of the cellulose based composite foams and aerogels for advanced energy storage devices.

Cellulose nanopaper (CNP) is of great interest to researchers mainly due to its renewability, excellent mechanical properties and optical properties. However, CNP is usually sensitive to water, resulting in the loss of strength and durability. To overcome this issue, in this work, an efficient and sustainable route, which involved ammonium sulfite cooking and formic acid hydrolysis, was reported to isolate lignin-containing cellulose nanofibrils (CNFs) from tobacco stalk. The resultant CNFs were directly used to fabricate strong, flexible, and water resistant CNP without any complex chemical modification. The residual lignin was found to act as a reinforcing agent between CNFs in CNP. The tensile strength and toughness of the lignin-containing CNP (255 MPa and 19.7 MJ m−3) were much higher compared with those of the one without lignin (179 MPa and 12.8 MJ m−3). The water-resistance of the CNP was also improved extraordinarily, and its maximum wet tensile strength reached up to 83 MPa which is the highest value in comparison with the reported CNP. Compared to the lignin-free CNP, the lignin-containing CNP also showed the better thermal stability and excellent UV-blocking properties. The present work designed a new route to prepare lignin-containing CNFs and CNP, which are potential candidates to replace petroleum-based materials in many advanced applications.

In this study, different nanocellulose (NC) products were manufactured from corncob residue (CCR) through sulfuric acid hydrolysis, formic acid hydrolysis, and TEMPO-mediated oxidation methods (the products were referred as SCN, FCN, and TCN, respectively). The properties of NC products and their impact on rheological behavior of paper coatings were comparatively studied. Results showed that compared to SCN and TCN, FCN exhibited large dimensions, limited negative surface charge, and poor stability in their aqueous suspensions, while the FCN aqueous suspension displayed the highest viscoelastic modulus due to the formation of highly entangled network. In paper coatings, SCN exhibited superior thickening and promoted rheological function due to their highly charged surface and strong interactions with pigments and immobilized water molecules, in comparison with other NC products. This study verified that the NC derived from CCR could be utilized as green and renewable additives to improve rheological prope...

In this work, a sustainable and highly efficient approach for preparing bifunctional cellulose nanocrystals (CNCs) was proposed through a mixed acid system of sulfuric acid and formic acid (FA). It was found that low-concentration (5–10 wt%) sulfuric acid can significantly improve the hydrolysis efficiency of FA (65–80 wt%), which enabled the highly efficient preparation of CNCs, i.e., the maximum yield of CNCs reached up to 70.65%. The obtained CNCs exhibited a rod-like shape with high crystallinity, and good dispersibility in both water and some organic phases. Moreover, the as-prepared CNCs exhibited high thermal stability, which is much higher than that of the traditionally sulfuric acid hydrolyzed ones. In addition, it was demonstrated that the bifunctional CNCs were able to stabilize various oils to form stable Pickering emulsion gels. Thus, this work provides a promising approach for sustainable preparation of bifunctional CNCs, which may find high-end applications in diverse fields.

As the second most abundant organic polymers in nature, lignin demonstrates advantages of low cost, high carbon content, plentiful functional groups. In recent years, lignin and its derivatives, as well as lignin-derived porous carbon have emerged as promising electrode materials for energy storage application. In this review, recent progress on the design and fabrication of lignin-based electrode materials for energy storage application is summarized. We begin with a brief summary of the separation process and basic chemistry of lignin. Then, the latest development on the fabrication of lignin-based electrodes for supercapacitors and batteries is elaborated separately. Finally, we propose the current challenges and future prospects of the lignin-based electrodes for advanced energy storage devices.

Polyaniline (PANI), as one of the most promising electrode materials for flexible supercapacitors, faces the problems of limited capacitive behavior and poor cycling stability. Herein, we demonstrated that dopants have a great effect on the electrochemical performance of PANI. Selecting a suitable dopant can be used as an effective way for enhancing the electrochemical performance of PANI electrodes. All PANI electrodes were synthesized by electropolymerization method using hydrochloric acid (HCl), perchloric acid (HClO4), sulfuric acid (H2SO4), p-toluenesulfonic acid (p-TSA), phosphoric acid (H3PO4) and phytic acid (PA) as dopants, respectively. The influence of dopants on morphology, doping level, redox sites accessibility and electrochemical performance of PANI electrodes were studied systematically. The results show that, PANI/HClO4 has the best capacitive behavior with a maximum specific capacity of 1341 C g−1 at 5 mV s−1 along with a 57% capacity retention after 2000 cycles. Moreover, PANI/p-TSA shows the best cycling stability with 70% of capacity retention after 2000 cycles accompanied with a relatively high specific capacity (722 C g−1 at 5 mV s−1). Furthermore, PANI/HClO4 and PANI/p-TSA were used as electrodes for the fabrication of flexible all-solid-state symmetric supercapacitors. Results indicate that PANI/HClO4 device has higher energy density (12.57 Wh kg−1 at 283 W kg−1) than that of PANI/p-TSA (8.86 Wh kg−1 at 199 W kg−1). In contrast, PANI/p-TSA device with a capacity retention over 80% after 3000 cycles has better stability than PANI/HClO4 device which maintains 73% capacity after 3000 cycles. This fundamental study provides a much easier route in achieving high performance flexible PANI-based electrodes and opens new opportunities for facilitating PANI-based electrodes as promising candidates for wearable electronics.

This article described a sustainable route, which combined relatively mild formic acid (FA) hydrolysis pretreatment of bleached softwood pulp with high-pressure homogenization, to prepare cellulose nanofibrils (F-CNFs). Results showed that the prepared F-CNFs had high thermal stability (e.g. the onset decomposition temperature was over 290 °C). Also, it was found that the prepared F-CNFs were more homogeneous and the length of the F-CNFs became shorter with the increase of hydrolysis time in FA hydrolysis, and a maximum crystallinity index of about 52.9% could be achieved when the hydrolysis time was 6 h. Compared to H-CNFs (prepared by HCl pretreatment), F-CNFs showed better dispersibility in DMSO, DMF and DMAC respectively because of the introduction of ester groups on the surface of F-CNFs. This high compatibility leads to that the F-CNFs may have great potential in reinforcing polymeric matrix materials. In addition, FA could be easily recovered. Thus, FA hydrolysis pretreatment plus high-pressure homogenization could be a sustainable and economically feasible process for the production of CNFs.

In this work, nanocellulose was extracted from bleached corncob residue (CCR), an underutilized lignocellulose waste from furfural industry, using four different methods (i.e. sulfuric acid hydrolysis, formic acid (FA) hydrolysis, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation, and pulp refining, respectively). The self-assembled structure, morphology, dimension, crystallinity, chemical structure and thermal stability of prepared nanocellulose were investigated. FA hydrolysis produced longer cellulose nanocrystals (CNCs) than the one obtained by sulfuric acid hydrolysis, and resulted in high crystallinity and thermal stability due to its preferential degradation of amorphous cellulose and lignin. The cellulose nanofibrils (CNFs) with fine and individualized structure could be isolated by TEMPO-mediated oxidation. In comparison with other nanocellulose products, the intensive pulp refining led to the CNFs with the longest length and the thickest diameter. This comparative study can help to provide an insight into the utilization of CCR as a potential source for nanocellulose production.

Cellulose nanocrystals (CNCs) can be used as building blocks for the production of many renewable and sustainable nanomaterials. In this work, CNCs were produced from bleached eucalyptus kraft pulp with a high yield over 75 % via FeCl3-catalyzed formic acid (FA) hydrolysis process. It was found that the particle size of resultant CNC products (F-CNC) decreased with the increase of FeCl3 dosage in FA hydrolysis, and a maximum crystallinity index of about 75 % could be achieved when the dose of FeCl3 was 0.015 M (i.e. about 7 % based on the weight of starting material). Thermogravimetric analyses revealed that F-CNC exhibited a much higher thermal stability (the decomposition temperature was over 260 °C) than S-CNC prepared by typical sulfuric acid hydrolysis. In the FeCl3-catalyzed FA hydrolysis process, FA could be easily recovered and reused, and FeCl3 could be transferred to Fe(OH)3 as a high value-added product. Thus, the FeCl3-catalyzed FA hydrolysis process could be sustainable and economically feasible. In addition, F-CNC could be well dispersed in DMSO and its dispersibility in water could be improved by a cationic surface modification.

The present study is aimed at providing a mechanistic insight into the influence of acid dopants on electrochemical performance of polypyrrole (PPy) film based flexible supercapacitor. PPy films were electrochemically deposited on carbon cloth using different kinds of acid dopants: hydrochloric acid (HCl), perchloric acid (HClO4), sulfuric acid (H2SO4), p-toluenesulfonic acid (p-TSA), phosphoric acid (H3PO4) and phytic acid (PA). Results show that both the size and type of dopants have a great influence on the doping level, mass ratio of counterions, accessibility of redox sites and the electrochemical performance of the PPy film electrodes. Among the obtained electrodes, PPy/HCl exhibits the highest specific capacitance of 960 F g−1 at 5 mV s−1, yet with inferior cycling stability. Interestingly, PPy/p-TSA shows the best cycling stability with more than 75% of capacitance retention after 2000 cycles, also with a relatively high specific capacitance (572 F g−1 at 5 mV s−1). Moreover, the PPy/p-TSA is used to fabricate a flexible all-solid-state supercapacitor device which exhibits a maximum energy density of 6.2 Wh kg−1 and a power density of 2.64 KW kg−1, respectively. Intriguingly, the assembled PPy/p-TSA devices exhibit excellent cycling stability with 88% capacitance retention after 6000 cycles. This fundamental study provides new prospects for developing PPy-based electrode materials for future flexible and wearable supercapacitors.

In this paper, a series of monomers (M1-M7) were facilely synthesized by Passerini reaction and the subsequent in-situ polymerization led to the formation of the conductive poly(indole/thiophene)s (P1-P7). Among P1-P7, it was found through the comparison that P7-P with a higher conjugated system exhibits an outstanding specific capacitance of 1170 F g−1 (scan rate 1 mV s−1), power density of 2614.4 W kg−1 and energy density of 56.5 Wh kg−1 (5 A g−1). The capacitance performance of P7-P complexed with Fe3+ system is further increased by 130 F g−1 because of the redox reaction of Fe3+. Using the chronoamperometry, the minimum detection limit of polymer P7-P for Fe3+ is 3 × 10−5 M. In summary, the facile synthesis of the conductive poly(indole/thiophene) polymers, their excellent energy storage and Fe3+ detection performance, open an opportunity for functional polymers in the energy storage and sensor applications.

Polypyrrole (PPy) and cellulose nanofiber (CNF) based conducting composite films were synthesized using two new approaches, in-situ polymerization of pyrrole onto cellulose nanopaper (PPy/CNP) and polyvinyl alcohol coated cellulose nanopaper (PPy/PVA-CNP). Significant improvement in the conductivity, tensile strength, water resistance, and electromagnetic shielding effectiveness (SE) was observed for these composite films compared to commonly used in-situ nanofiber (ISF) approach, where PPy is coated on nanofibers prior to film preparation. Maximum improvement in conductivity, SE and tensile strength of PPy/PVA-CNP compared to ISF films was attributed to highly uniform and compact PPy coating and reduced porosity. SE of -23 dB (thickness upto 138.4 μm) and tensile strength of 103.8 MPa for PPy/PVA-CNP films are the highest values found in the literature for PPy and CNF based composite films at a comparable thickness. These new approaches could enable a scalable preparation of flexible conducting composite films with superior physical and electrical properties for EMI shielding applications.

A highly efficient and sustainable strategy for the production of functional and thermostable cellulose nanocrystals (CNCs) was developed in this work. In which, the acid hydrolysis system composed with small doses of H2SO4 (5-10%) and large amounts of easily recoverable acetic acid (70-90%) was used to hydrolyze cellulose pulp at 80 °C for several hours. The rod-like CNCs were obtained with the length of 150-500 nm and diameter of 5-20 nm in high yield (Ymax = 81%). The resulted CNCs showed high thermal stability and excellent dispersion stability in both aqueous and organic phases. The acetic acid in the hydrolysis system can be completely recovered by vacuum distillation, and the dosage of sulfuric acid can be reduced significantly compared with the traditional sulfuric acid hydrolysis. Thus, this approach is promising for the large-scale and sustainable preparation of CNCs with excellent water dispersibility and good thermal stability, with less environmental issues.

The recent strategies in preparation of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) were described. CNCs and CNFs are two types of nanocelluloses (NCs), and they possess various superior properties, such as large specific surface area, high tensile strength and stiffness, low density, and low thermal expansion coefficient. Due to various applications in biomedical engineering, food, sensor, packaging, and so on, there are many studies conducted on CNCs and CNFs. In this review, various methods of preparation of CNCs and CNFs are summarized, including mechanical, chemical, and biological methods. The methods of pretreatment of cellulose are described in view of the benefits to fibrillation.

A mild and efficient approach for the preparation of cellulose nanocrystals (CNCs) was developed by using mixed H2SO4/Oxalic acid hydrolysis. In this process, the mixed acid of sulfuric acid, oxalic acid and H2O in an optimal mass ratio of 1:5:4 was used to produce CNCs from bleached eucalyptus kraft pulp (BEKP) at 80 °C for 2–5 h. The CNCs with a diameter range of 5–20 nm and a length range of 150–400 nm were obtained at a high yield (>70%) and showed excellent dispersion stability in water and good thermal stability. Moreover, the dosage of sulfuric acid can reduce to 2.4 g/g CNCs in this mixed acid hydrolysis, which is far lower than that of the typical 64% sulfuric acid hydrolysis (55 g/g CNCs, tested in this work). In addition, 91±2% of oxalic acid could be recovered by a simple recrystallization operation.