Cellulosic nanocomposite membranes from hydroxypropyl cellulose reinforced by cellulose nanocrystals

Cellulosic nanocomposite membranes were prepared by incorporation of cellulose nanocrystals (CNCs) into a hydroxypropyl cellulose (HPC) matrix using a mixing/evaporation technique. CNCs were obtained from filter paper using the sulfuric acid hydrolysis method with the aid of ultrasonication. The relationship between the microstructure and mechanical properties of the CNCs/HPC nanocomposite membranes was studied. Scanning electron microscopy showed that the CNCs were well dispersed in the HPC matrix, and the fracture surface demonstrated a fibrous characteristic. With increasing CNCs content, the tensile strength and Young’s modulus of the CNCs/HPC nanocomposite membranes gradually increased. At 5 wt% content of CNCs, the strength was increased by 525 % and the Young’s modulus by 124 % compared with pure HPC membrane. Moreover, the effect of the phase change of HPC on the mechanical properties of the CNCs_5wt%/HPC nanocomposite membranes and the corresponding mechanism were also studied.     

Cellulose nanocrystal extraction from rice straw using a chlorine-free bleaching process

Cellulose nanocrystals (CNCs) have attracted tremendous attention because of their excellent chemical and physical properties and due to their renewability and sustainability. This material can be extracted from agricultural by-products such as rice straw, banana tree, or bagasse. Rice straw was selected as the raw material in this study. Initially, a large amount of lignin must be removed by an alkaline process to obtain a slurry. Thereafter, a green bleaching process can be used to remove the remaining lignin in the slurry. An UV-emitting diode with 365 nm wavelength assisted the oxidation reaction of the H₂O₂ solution without the use of chlorine-containing chemical bleach. The reaction required only 2.5 h to obtain high-purity cellulose and successfully enhanced the yield. Transmission electron microscopy images showed that the CNCs from rice straw were?~?100 nm long and 10–15 nm wide. The crystalline index and degradation temperature of CNCs were 83.8% and 257 °C, respectively.

     

Porous electrospun nanocomposite mats based on chitosan–cellulose nanocrystals for wound dressing: effect of surface characteristics of nanocrystals

Randomly oriented fiber mats of chitosan–polyethylene oxide matrix reinforced with cellulose nanocrystals (CNCs) were prepared by electrospinning technique. The cellulose nanocrystals used were isolated using hydrochloric acid (CNC_HCl) or sulphuric acid (\({\text{CNC}}_{{{\text{H}}_{ 2} {\text{SO}}_{ 4} }}\)) and the concentration of CNCs was 50 wt% in the electrospun mats. The surface characteristics of the nanocrystals were found to affect the dispersion, viscosity, conductivity and zeta-potential of the respective spinning solutions and resulted in better spinnability, homogeneity as well as crosslinking of CNC_HCl based nanocomposite fiber mats compared to \({\text{CNC}}_{{{\text{H}}_{ 2} {\text{SO}}_{ 4} }}\) ones. The microscopy studies showed that the diameter of the electrospun fibers decreased with the inclusion of both types of nanocrystals and that crosslinking decreased the porosity of the mats. The tensile strength and tensile modulus of the mats increased with the addition of nanocrystals and increased further for the CNC_HCl based mats (58 MPa, 3.1 GPa) after crosslinking. The as-spun CNC_HCl based mats had average pore diameters of 1.6 μm and porosity of 38 %. The water vapor permeability and the O₂/CO₂ transmission increased with the addition of CNC_HCl. The used nanocrystals as well as electrospun mats showed non-cytotoxic impact on adipose derived stem cells (ASCs), which was considered favorable for wound dressing.     

One-pot preparation of hydrophobic cellulose nanocrystals in an ionic liquid

The facile one-pot preparation of hydrophobic cellulose nanocrystals (CNCs) from wood pulpboard in an ionic liquid is reported in the present paper. This process employed a so-called amorphous cellulose solvent system capable of dissolving the majority of the amorphous regions in cellulose while maintaining the crystalline domains essentially intact, and consisting of tetrabutylammonium acetate with dimethylacetamide. These solvents were mixed at a mass ratio of 1:9 in conjunction with acetic anhydride to prepare CNCs via surface acetylation. The rod-like morphology and nanometer-scale dimensions of the resulting CNCs were ascertained by atomic force microscopy and transmission electron microscopy. Successful surface acetylation while maintaining an intact crystalline core was confirmed by Fourier transform infrared, ¹³C CP/MAS NMR and X-ray photoelectron spectroscopy in addition to X-ray diffraction. Finally, the thermal stability and hydrophobic behavior of the hydrophobic CNCs were characterized using thermal gravimetric analysis and water contact-angle measurements, respectively.     

Structure Selectivity of Alkaline Periodate Oxidation on Lignocellulose for Facile Isolation of Cellulose Nanocrystals

Reported here for the first time is the alkaline periodate oxidation of lignocelluloses for the selective isolation of cellulose nanocrystals (CNCs). With the high concentrations as a potassium salt at pH 10, periodate ions predominantly exist as dimeric orthoperiodate ions (H₂I₂O₁₀^4?). With reduced oxidizing activity in alkaline solutions, dimeric orthoperiodate ions preferentially oxidized non‐ordered cellulose regions. The alkaline surroundings promoted the degradation of these oxidized cellulose chains by β‐alkoxy fragmentation and generated CNCs. The obtained CNCs were uniform in size and generally contained carboxy groups. Furthermore, the reaction solution could be reused after regeneration of the periodate with ozone gas. This method allows direct production of CNCs from diverse sources, in particular lignocellulosic raw materials including sawdust (European beech and Scots pine), flax, and kenaf, in addition to microcrystalline cellulose and pulp.     

Poly(lactic acid)-based biocomposites reinforced with modified cellulose nanocrystals

This work investigates reinforcing poly(lactic acid) (PLA) nanocomposites using triazine derivative-grafted cellulose nanocrystals (CNCs). A hydrophobic triazine derivative was synthesized and applied to modify CNCs to improve their thermal stability and diminish the hydrophilicity of the nanoparticles. CNCs before and after modification were used to reinforce PLA nanocomposites by a hot compression process. The results of thermogravimetric analysis indicated that the initial thermal decomposition temperature of modified nanocrystals was improved by approximately 100 °C compared to the original CNCs. That is, the thermal stability of modified cellulose nanocrystals was improved due to the shielding effect of CNCs by a hydrophobic aliphatic amine layer on the surface of the nanoparticles. The results of dynamic contact angle measurements revealed a decrease of hydrophilicity of the modified CNCs. The results from scanning electron microscopy and a UV–Vis spectrophotometer revealed that the compatibility between the modified nanocrystals and the PLA was improved. Finally, the results of tensile tests indicated a significant improvement in terms of breaking strength and elongation at the break point.     

Facile one-step extraction and oxidative carboxylation of cellulose nanocrystals through hydrothermal reaction by using mixed inorganic acids

A facile and efficient approach to prepare carboxylated cellulose nanocrystals (CCNCs) is presented through a novel one-step hydrothermal procedure by using a mixed acid system of hydrochloric acid and nitric acid (HCl/HNO₃). The as-prepared cellulose nanoparticles were characterized by scanning electron microscopy, wide angle X-ray diffraction, conductometric titrations, Fourier transform infrared spectrometry and thermal gravimetric analysis. The results showed that the combination of the mixed acid and hydrothermal reaction can speed up the process of CCNC preparation, and then high quality of the product could be obtained at relatively low acid concentration. It is found that the addition of nitric acid could not only promote the conversion of surface groups on the cellulose nanocrystals (CNCs), but also have significant influences on the yield, particle size and microstructure of CNCs. For the volume ratio of HCl/HNO₃ of 7:3, the as-prepared CCNCs exhibited the largest length to diameter ratio and narrowest dimension distributions as well as maximum degree of oxidation of 0.12. In addition, high dispersion stability for the CCNCs could be observed due to the existence of negative carboxyl groups. This approach based on one-step oxidative carboxylation greatly simplified the preparation of CCNCs with high yield and high crystallinity under mild hydrothermal condition.     

Effects of pretreatments on crystalline properties and morphology of cellulose nanocrystals

Cellulose nanocrystals (CNCs) have drawn tremendous attention because of their extraordinary physical and chemical properties as well as renewability and sustainability. In this work, after a range of pretreatments, such as freeze-drying, ball-milling, mercerization, N-methylmorpholine-N-oxide dissolution and ionic liquid dissolution, various CNCs with different crystalline properties and morphologies were obtained by hydrolysis or oxidation. XRD and AFM were used to determine the influences of pretreatments on the crystalline properties and morphologies of CNCs. New methods, i.e., specific pretreatments followed by sulfuric acid hydrolysis or 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidation, were developed to obtain sphere-like CNCs. It was found that sphere-like CNCs were more likely to be obtained from cellulose materials possessing high accessibility. Pretreatments produced cellulose with various crystallinities and polymorphs, and therefore changed the yields of CNCs and influenced their morphology. CNCs prepared by TEMPO oxidation generally had smaller size than the corresponding products obtained by sulfuric acid hydrolysis. In addition, for the dissolved/regenerated cellulose, TEMPO oxidation was a better method to yield sphere-like CNCs than sulfuric acid hydrolysis.     

Electrospun hyperbranched polylactic acid–modified cellulose nanocrystals/polylactic acid for shape memory membranes with high mechanical properties

The polylactic acid (PLA) nanofiber membranes reinforced with hyperbranched PLA‐modified cellulose nanocrystals (H‐PLA‐CNCs) were prepared by electrospinning. The H‐PLA‐CNCs and the nanofiber membranes were researched by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The outcomes embodied that the cellulose nanocrystals (CNCs) could be successfully improved by the hyperbranched PLA, which would offer powerful CNCs/matrix interfacial adhesion. Thus, the mechanical and shape memory properties of PLA can be improved by adding the H‐PLA‐CNCs. In particular, when the addition of H‐PLA‐CNCs was 7 wt%, the tensile strength and an ultimate strain of PLA composite nanofiber membranes was 15.56 MPa and 25%, which was 228% and 72.4% higher than that of neat PLA, respectively. In addition, the shape recovery rate of the PLA/5 wt% H‐PLA‐CNCs composite nanofiber membrane was 93%, which was 37% higher than that of neat PLA. We expected that this present study would provide unremitting efforts for the development of more effective approaches to prepare biology basic shape memory membranes with high mechanical properties.     

Preparation and characterization of cellulose nanocrystals via ultrasonication-assisted FeCl3-catalyzed hydrolysis

Cellulose nanocrystals (CNC) was obtained from bamboo pulp via ultrasonication-assisted FeCl₃-catalyzed hydrolysis process, with parameters optimized by response surface methodology. The optimal parameters were reaction temperature: 107 °C, reaction time: 58 min, ultrasonication time: 186 min. The morphological, crystal structural, chemical structural and thermal features of the prepared cellulose nanocrystals were analyzed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), Fourier transfer infrared (FTIR) and thermogravimetric analysis. The results showed that the cellulose nanocrystals formed an interconnected network structure and CNC was rod-like with the length of 100–200 nm and the width of 10–20 nm. XRD result revealed that, compared with cellulose pulp, the crystallinity index of CNC increased from 69.5 to 79.4 %, while the cellulose I crystal structure remained. FTIR analysis demonstrated that CNC had the similar chemical structures to that of cellulose pulp, which indicated that the chemical structures of CNC remained unchanged in the presence of FeCl₃-catalyzed hydrolysis process and ultrasonication treatment. Thermogravimetric analysis revealed that the resulting CNC exhibited relatively high thermal stability. The research shows that ultrasonication-assisted FeCl₃-catalyzed hydrolysis could be a highly efficient method for preparing CNC.     

One-pot functionalization of cellulose nanocrystals with various cationic groups

After successful cationization of cellulose nanocrystals (CNCs) to produce pyridinium-grafted-CNCs, a variety of different cationic CNCs were prepared using a similar procedure, thus unlocking access to a wide variety of cationized cellulose nanocrystals through a simple one-pot reaction. In this study, cationic CNCs were prepared through the use of 4-(1-bromoethyl)benzoic acid or 4-bromomethylbenzoic acid, p-toluenesulfonyl chloride, CNCs, and two different amines, 1-methylimidazole and 4-dimethylaminopyridine. The amines acted as both the base catalyst for the esterification and the nucleophile to form the cationic charge. This method offers a versatile and straightforward route to prepare a variety of different cationic nanocrystals and therefore tailor their interaction with their environment.     

Isolation of a novel,crystalline cellulose material from the spent liquor of cellulose nanocrystals (CNCs)

We have modified the standard sulphuric acid hydrolysis method for the production of cellulose nanocrystals (CNCs) to successfully isolate a novel, highly crystalline cellulose material from the spent liquor of CNCs. The novel material has a cellulose II crystal structure that is distinctly different from the cellulose I crystal structure of CNCs. The modified method uses a shorter time for the hydrolysis, followed by maintaining a high residual acid concentration for the separation of the spent liquor and CNCs, and by adding the spent liquor to water. The modified method offers an opportunity to concurrently produce CNCs in up to ~40 % yield and the novel, highly crystalline, sulphated cellulose II in ~15 % yield in separate and pure forms from sulphuric acid hydrolysis of a commercial northern bleached softwood kraft pulp. It can potentially reduce the production cost of CNCs, allow easier downstream processing of CNCs and recovery of sulphuric acid, and generate a new cellulose bio-material for product development.     

The influence of chitin nanocrystals on structural evolution of ultra-high molecular weight polyethylene/chitin nanocrystal fibers in hot-drawing process

Ultra-high molecular weight polyethylene (UHMWPE)/chitin nanocrystal (CNC) fibers were prepared. Compared with the pure UHMWPE fibers, the ultimate tensile strength and Young’s modulus of UHMWPE/CNC fibers are improved by 15.7% and 49.6%, respectively, with the addition of chitin nanocrystals (CNCs) of 1 wt%. The melting temperature (T _m) of UHMWPE/CNC fibers was higher than that of pure UHMWPE fibers. Pure UHMWPE fibers and UHMWPE/CNC fibers were characterized with respect to crystallinity, orientation and kebab structure by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). It is found that the CNCs act as the shish structure in UHMWPE/CNC fibers and the kebab crystals are grown around the CNCs. There was almost no difference between pure UHMWPE fibers and UHMWPE/CNC fibers in orientation. But the degree of crystallinity of various stages of UHMWPE/CNC fibers was respectively higher than the corresponding stage of pure UHMWPE fibers. Moreover, the addition of 1 wt% CNCs improved the thickness of kebab crystals and accelerated the transformation of kebab to shish.     

Inside Cover: Uniform Growth of Nanocrystalline ZIF-8 on Cellulose Nanocrystals: Useful Template for Microporous Organic Polymers (Angew. Chem. Int. Ed. 24/2023)

Zeolitic imidazolate framework (ZIF-8) nanocrystals were uniformly grown on the surface of cellulose nanocrystals (CNCs) to give a hybrid material, ZIF@CNCs. By varying the stoichiometry of the components, it was possible to control the size of the ZIF-8 crystals grown on the CNC surface. Optimized ZIF@CNC ( ZIF@CNC-2 ) was used as a template to synthesize a microporous organic polymer (MOP), ZIF@MOP@CNC . After etching the ZIF-8 with 6 M HCl solution, a MOP material with encapsulated CNCs ( MOP@CNC ) was formed. Zinc coordination into the porphyrin unit of the MOP yielded the ship-in-a-bottle structure, Zn MOP@CNC , comprised of CNCs encapsulated within the Zn-MOP. In comparison to ZIF@CNC-2 , Zn MOP@CNC showed better catalytic activity and chemical stability for CO₂ fixation, converting epichlorohydrin to chloroethylene carbonate. This work demonstrates a novel approach to create porous materials through CNC templating.     

Cellulose nanocrystals obtained from microcrystalline cellulose by p-toluene sulfonic acid hydrolysis,NaOH and ethylenediamine treatment

Cellulose nanocrystals (CNCs) were first isolated from microcrystalline cellulose (MCC) by p-toluene sulfonic acid (p-TsOH) hydrolysis. Cellulose II nanocrystal (CNC II) and cellulose III nanocrystal (CNC III) were then formed by swelling the obtained cellulose I nanocrystal (CNC I) in concentrated sodium hydroxide solutions and ethylenediamine (EDA) respectively. The properties of CNC I, CNC II and CNC III were subjected to comprehensive characterization by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The results indicated that CNC I, CNC II and CNC III obtained in this research had high crystallinity index and good thermal stability. The degradation temperatures of the resulted CNC I, CNC II and CNC III were 300 °C, 275 °C and 242 °C, respectively. No ester bonds were found in the resulting CNCs. CNCs prepared in this research also had large aspect ratio and high negative zeta potential.

     

Tailoring the morphology and properties of waterborne polyurethanes by the procedure of cellulose nanocrystal incorporation

Polyurethane waterborne synthesis was performed using a two-step method, commonly referred to as a prepolymer method. Nanocomposites based on waterborne polyurethane and cellulose nanocrystals were prepared by the prepolymer method by altering the mode and step in which the nanofillers were incorporated during the polyurethane formation. The morphology, structural, thermal, and mechanical properties of the resulting nanocomposite films were evaluated by Fourier transform infrared spectroscopy (FTIR), small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and tensile tests. FTIR results indicated that the degree of interaction between the nanofillers and the WPU through hydrogen bonds could be controlled by the method of cellulose nanocrystal incorporation. Data obtained from SAXS experiments showed that the cellulose nanocrystals as well as the step of the reaction in which they are added influenced the morphology of the polyurethane. The reinforcing effect of CNCs on the nanocomposites depends on their morphology.     

Liquid crystalline thermosets based on anisotropic phases of cellulose nanocrystals

A new class of liquid crystalline thermosets (LCTs) was successfully produced containing lyotropic cellulose nanocrystals (CNCs) as the primary mesogenic component (up to 72 wt%) by the addition of non-mesogenic epoxy monomers. Cellulose-based LCTs were produced by totally aqueous processing methods and ultimately cured at elevated temperatures to produce ordered networks of ‘frozen’ liquid crystalline (LC) phases. Various degrees of birefringence were obtained via self-assembly of CNCs into oriented phases as observed by polarized optical microscopy and transmission electron microscopy. X-ray diffraction measurements highlighted the effects of texture of CNCs within LCT films compared to lyophilized CNCs. Cellulose-based LCT films uniquely exhibited thermo-mechanical properties of both traditional LCTs and LC elastomers, such as high elastic modulus (~1 GPa) under ambient conditions and low glass transition temperature (~?25 °C), respectively. The development of LCTs based on CNCs and aqueous processing methods provides a renewable pathway for designing high performance composites with ordered network structures and unique optical properties.     

Structure and properties of regenerated cellulose/tourmaline nanocrystal composite films

Nanocomposite films were successfully prepared from cellulose and tourmaline nanocrystals with mean diameters of 70 nm in a 1.5 M NaOH/0.65 M thiourea aqueous solution by coagulation with 5 wt % CaCl₂ and then a 3 wt % HCl aqueous solution for 2 min. The structure and properties of the composite films were characterized by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and tensile testing. The results indicated that the tourmaline nanocrystals were dispersed in a cellulose matrix, maintaining the original structure of the nanocrystals in the composite films. The loss peaks (tan δ) in the DMA spectra and the decomposition temperatures in the DSC curves of the composite films were significantly shifted toward low temperatures, suggesting that the nanocrystals broke the partial intermolecular hydrogen bonds of cellulose, and this led to a reduction in the thermal stability. However, the nanocomposite films exhibited a homogeneous structure and dispersion of the nanocrystals. When the tourmaline content was in the range of 4–8 wt %, the composite films possessed good tensile strength (92–107 MPa) and exhibited obvious antibacterial action against Staphylococcus aureus. This work provides a potential way of preparing functional composite films or fibers from cellulose and nanoinorganic particles with NaOH/thiourea aqueous solutions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 367–373, 2004     

Preparation and Properties of Poly（vinyl alcohol）/Chitosan Blend Bio-nanocomposites Reinforced by Cellulose Nanocrystals

The aim of this paper is to report the effect of the addition of cellulose nanocrystals（CNCs） on the mechanical, thermal and barrier properties of poly（vinyl alcohol）/chitosan（PVA/Cs） bio-nanocomposites films prepared through the solvent casting process. The characterizations of PVA/Cs/CNCs films were carried out in terms of X-ray diffraction（XRD）, transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, thermogravimetric analysis（TGA and DTG）, oxygen transmission rate（OTR）, and tensile tests. TEM and SEM results showed that at low loading levels, CNCs were dispersed homogenously in the PVA/Cs matrix. The tensile strength and modulus in films increased from 55.1 MPa to 98.4 MPa and from 395 MPa to 690 MPa respectively, when CNCs content went from 0 wt% to 1.0 wt%. The thermal stability and oxygen barrier properties of PVA/Cs matrix were best enhanced at 1.0 wt% of CNCs loading. The enhanced properties attained by incorporating CNCs can be beneficial in various applications.     

Gas‐Sensing Properties of Needle‐Shaped Ni‐Doped SnO2 Nanocrystals Prepared by a Simple Sol–Gel Chemical Precipitation Method

The preparation of needle‐shaped SnO₂ nanocrystals doped with different concentration of nickel by a simple sol–gel chemical precipitation method is demonstrated. By varying the Ni‐dopant concentration from 0 to 5 wt %, the phase purity and morphology of the SnO₂ nanocrystals are significantly changed. Powder XRD results reveal that the SnO₂ doped with a nickel concentration of up to 1 wt % shows a single crystalline tetragonal rutile phase, whereas a slight change in the crystallite structure is observed for samples with nickel above 1 wt %. High resolution scanning electron microscopy (HRSEM) results reveal the change in morphology of the materials from spherical, for SnO₂, to very fine needle‐like nanocrystals, for Ni‐doped SnO₂, annealed at different temperatures. The gas sensing properties of the SnO₂ nanocrystals are significantly enhanced after the nickel doping.