Core-Shell Filament with Excellent Wound Healing Property Made of Cellulose Nanofibrils and Guar Gum via Interfacial Polyelectrolyte Complexation Spinning.

Natural polymer-based sutures have attractive cytocompatibility and degradability in surgical operations. Herein, anionic cellulose nanofibrils (ACNF) and cationic guar gum (CGG) are employed to produce nontoxic CGG/ACNF composite filament with a unique core-shell structure via interfacial polyelectrolyte complexation (IPC) spinning. The comprehensive characterization and application performance of the resultant CGG/ACNF filament as a surgical suture are thoroughly investigated in comparison with silk and PGLA (90% glycolide and 10% l-lactide) sutures in vitro and in vivo, respectively. Results show that the CGG/ACNF filament with the typical core-shell structure and nervation pattern surface exhibits a high orientation index (0.74) and good mechanical properties. The tensile strength and knotting strength of CGG/ACNF suture prepared by twisting CGG/ACNF filaments increase by 69.5%, and CGG/ACNF suture has a similar friction coefficient to silk and PGLA sutures. Moreover, CGG/ACNF suture with antibiosis and cytocompatibility exhibits better growth promotion of cells than silk suture, similar to PGLA suture in vitro. In addition, the stitching experiment of mice with the CGG/ACNF suture further confirms better healing properties and less inflammation in vivo than silk and PGLA sutures do. Hence, the CGG/ACNF suture with a simple preparation method and excellent application properties is promising in surgical operations.

Potential issues specific to cytotoxicity tests of cellulose nanofibrils.

Cellulose nanofibrils (also called cellulose nanofibers or nanofibrillated cellulose [CNFs]) are novel polymers derived from biomass with excellent physicochemical properties and various potential applications. However, the introduction of such new materials into the market requires thorough safety studies to be conducted. Recently, toxicity testing using cultured cells has attracted attention as a safety assessment that does not rely on experimental animals. This article reviews recent information regarding the cytotoxicity testing of CNFs and highlights the issues relevant to evaluating tests. In the literature, we found that a variety of cell lines and CNF exposure concentrations was evaluated. Furthermore, the results of cytotoxicity results tests differed and were not necessarily consistent. Numerous reports that we examined had not evaluated endotoxin/microbial contamination or the interaction of CNFs with the culture medium used in the tests. The following potential specific issues involved in CNF in vitro testing, were discussed: (1) endotoxin contamination, (2) microbial contamination, (3) adsorption of culture medium components to CNFs, and (4) changes in aggregation/agglomeration and dispersion states of CNFs resulting from culture medium components. In this review, the available measurement methods and solutions for these issues are also discussed. Addressing these points will lead to a better understanding of the cellular effects of CNFs and the development of safer CNFs.

Surface functionalization and size modulate the formation of reactive oxygen species and genotoxic effects of cellulose nanofibrils.

BACKGROUND: Cellulose nanofibrils (CNFs) have emerged as a sustainable and environmentally friendly option for a broad range of applications. The fibrous nature and high biopersistence of CNFs call for a thorough toxicity assessment, but it is presently unclear which physico-chemical properties could play a role in determining the potential toxic response to CNF. Here, we assessed whether surface composition and size could modulate the genotoxicity of CNFs in human bronchial epithelial BEAS-2B cells. We examined three size fractions (fine, medium and coarse) of four CNFs with different surface chemistry: unmodified (U-CNF) and functionalized with 2,2,6,6-tetramethyl-piperidin-1-oxyl (TEMPO) (T-CNF), carboxymethyl (C-CNF) and epoxypropyltrimethylammonium chloride (EPTMAC) (E-CNF). In addition, the source fibre was also evaluated as a non-nanosized material. RESULTS: The presence of the surface charged groups in the functionalized CNF samples resulted in higher amounts of individual nanofibrils and less aggregation compared with the U-CNF. T-CNF was the most homogenous, in agreement with its high surface group density. However, the colloidal stability of all the CNF samples dropped when dispersed in cell culture medium, especially in the case of T-CNF. CNF was internalized by a minority of BEAS-2B cells. No remarkable cytotoxic effects were induced by any of the cellulosic materials. All cellulosic materials, except the medium fraction of U-CNF, induced a dose-dependent intracellular formation of reactive oxygen species (ROS). The fine fraction of E-CNF, which induced DNA damage (measured by the comet assay) and chromosome damage (measured by the micronucleus assay), and the coarse fraction of C-CNF, which produced chromosome damage, also showed the most effective induction of ROS in their respective size fractions. CONCLUSIONS: Surface chemistry and size modulate the in vitro intracellular ROS formation and the induction of genotoxic effects by fibrillated celluloses. One cationic (fine E-CNF) and one anionic (coarse C-CNF) CNF showed primary genotoxic effects, possibly partly through ROS generation. However, the conclusions cannot be generalized to all types of CNFs, as the synthesis process and the dispersion method used for testing affect their physico-chemical properties and, hence, their toxic effects.

Synthesis of Silver Nanoparticles and Detection of Glucose via Chemical Reduction with Nanocellulose as Carrier and Stabilizer.

The application of silver nanoparticles (AgNPs) in antibacterial materials, glucose detection, etc., is of broad interest for researchers around the world. Nanocellulose with many excellent properties can be used as a carrier and stabilizer to assist in the synthesis of AgNPs. In this study, cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) were used to assist in the synthesis of AgNPs under the reduction of glucose and detection of glucose concentration under different conditions. Transmission electron microscopy (TEM) analysis showed that the AgNPs in the nanocellulose-AgNPs (NC-AgNPs) system were roughly spherical and randomly distributed on the nanocellulose. In the whole reaction system, when the concentration of nanocellulose is 0.11 mg/mL, the concentration of silver ammonia solution is 0.6 mM, and the mixing time is 2.5 h, according to the UV-Vis analysis, the absorbance of CNF-AgNPs at 425 nm exhibited a good linear relationship (R2 = 0.9945) with the glucose concentration range (5-50 µM), while the absorbance of CNC-AgNPs at 420 nm showed a good linear relationship (R2 = 0.9956) with the glucose concentration range (5-35 µM). The synthesis of NC-AgNPs can be further developed into a sensor with higher sensitivity and higher stability for detecting glucose concentration and a material with antibacterial effects.

Polyoxometalate/Cellulose Nanofibrils Aerogels for Highly Efficient Oxidative Desulfurization.

Polyoxometalate (POM) presents great potential in oxidative desulfurization (ODS) reaction. However, the high dissolubility of POM in common solvents makes it difficult to recycle. Besides, the small specific surface area of POM also limits the interaction between them and the substrate. Depositing polyoxometalates onto three-dimensional (3D) network structured materials could largely expand the application of POM. Here, the surfaces of cellulose nanofibrils (CNFs) were modified with very few (3-Aminopropyl) trimethoxysilane (APTS) to endow positive charges on the surfaces of CNFs, and then phosphotungstic acid (PTA) was loaded to obtain the aerogel A-CNF/PTA as the ODS catalyst. FT-IR indicated the successful deposition of PTA onto aminosilane modified CNF surfaces. UV-VIS further suggested the stability of PTA in the aerogels. BET and SEM results suggested the increased specific surface area and the relatively uniform 3D network structure of the prepared aerogels. TGA analysis indicated that the thermal stability of the aerogel A-CNF/PTA50% was a little higher than that of the pure CNF aerogel. Most importantly, the aerogel A-CNF/PTA50% showed good catalytic performance for ODS. Catalysis results showed that the substrate conversion rate of the aerogel A-CNF/PTA50% reached 100% within 120 min at room temperature. Even after five cycles, the substrate conversion rate of the aerogel A-CNF/PTA50% still reached 91.2% during the dynamic catalytic process. This work provides a scalable and facile way to stably deposit POM onto 3D structured materials.

Wood Ionic Cable.

The combination of good stability, biocompatibility, and high mechanical strength is attractive for bio-related material applications, but it remains challenging to simultaneously achieve these properties in a single, ionically conductive material. Here a "wood" ionic cable, made of aligned wood nanofibrils, demonstrating a combination of biocompatibility, high mechanical strength, high ionic conductivity, and excellent stability is reported. The wood ionic cable possesses excellent flexibility and exhibits high tensile strength up to 260 MPa (in the dry state) and ≈80 MPa (in the wet state). The nanochannels within the highly aligned cellulose nanofibrils and the presence of negative charges on the surfaces of these nanochannels, originating from the cellulose hydroxyl groups, provide new opportunities for ion regulation at low salt concentrations. Ion regulation in turn enables the wood ionic cable to have unique nanofluidic ionic behaviors. The Na+ ion conductivity of the wood ionic cable can reach up to ≈1.5 × 10-4 S cm-1 at low Na+ ion concentration (1.0 × 10-5 mol L-1 ), which is an order of magnitude higher than that of bulk NaCl solution at the same concentration. The scalable, biocompatible wood ionic cable enables novel ionic device designs for potential ion-regulation applications.

Aqueous Polymer Modification of Cellulose Nanofibrils by Grafting-Through a Reactive Methacrylate Group.

Modifying the surface of cellulose nanofibrils (CNFs) produced by mechanical refinement with a variety of polymer functional groups in an entirely water-based system is challenging because only surface hydroxyl groups are accessible. To address this limitation, an entirely water-based, polymer modification scheme is developed. CNFs are functionalized with a reactive methacrylate functional group followed by subsequent grafting-through polymerization. This modification worked with a variety of water-soluble and water-insoluble (meth)acrylates and (meth)acrylamides, grafting up to 45 wt% polymer on to the CNFs. The reaction conditions introducing the methacrylate functional group are adjusted to vary the degree of functionality. Soxhlet extraction of modified samples demonstrates that the reactive methacrylate group is necessary to facilitate polymer grafting. The degree of functionalization of the polymers is studied via quantitative transmission IR spectroscopy and the morphology of the resulting cellulose nanofibrils is studied via a combination of optical, scanning electron, and atomic force microscopy. High levels of polymer modification do not significantly affect the micrometer-scale fibril morphology.

Pulmonary toxicity and RNA sequencing analyses of mouse in response to exposure to cellulose nanofibrils.

OBJECTIVE: The growing applications of nanocelluloses in the fields of advanced nanocomposites, electronics, and medical devices necessitate investigation of their potential adverse effects on human health. The lungs are the primary and the most important route for the entry of nanocelluloses into the human body in occupational settings. However, data on the pulmonary toxicity of cellulose nanofibrils (CNFs) and its molecular mechanism are limited. This study investigated the pulmonary toxicity of CNFs and its genomic expression using the RNA sequencing approach. MATERIALS AND METHODS: Female C57BL/6 mice were administered CNFs at 50 µg/mouse by oropharyngeal aspiration. Samples were collected at 3 and 14 days after exposure to CNFs (DAEC). RESULTS: At three DAEC, the microscopic sections of lungs revealed a significant inflammatory response. In terms of gene expression alterations, 94 genes were up-regulated, and 107 genes were down-regulated. Most of these differentially expressed genes were involved in the inflammatory and immune responses, including chemokines, NK cells, killer cell lectin-like receptors, CD antigens, T cell-specific GTPases, immunity-related GTPase family M members, and interferon-induced proteins encoding genes. However, only 9 and 26 genes at 14 DAEC were significantly up- and down-regulated, respectively. CONCLUSIONS: The pathological analysis of lung sections and the analysis of sequencing data suggested that the homeostasis of mice lungs was restored at 14 DAEC. The findings of this study provide insights into the pulmonary toxicity, and underlying toxicological mechanisms, caused by exposure to CNFs, and are useful for the assessment of the potential toxicity of nanocelluloses.

Fabrication and Performance of Self-Supported Flexible Cellulose Nanofibrils/Reduced Graphene Oxide Supercapacitor Electrode Materials.

With the rapid development of portable and wearable electronic devices, self-supporting flexible supercapacitors have attracted much attention, and higher requirements have been put forward for the electrode of the device, that is, it is necessary to have good mechanical properties while satisfying excellent electrochemical performance. In this work, a facile method was invented to obtain excellent self-supported flexible electrode materials with high mechanical properties and outstanding electrochemical performance by combining cellulose nanofibrils (CNFs) and reduced graphene oxide (RGO). We focused on the effect of the ratio of the addition of CNFs and the formation process of the film on the electrochemical and mechanical properties. The results show that the CNFs/RGO12 (where the ratio of CNFs to GO is 1:2) film displayed outstanding comprehensive properties; its tensile strength and conductivity were up to 83 MPa and 202.94 S/m, respectively, and its CA value was as high as 146 mF cm-2 under the current density of 5 mA cm-2. Furthermore, the initial retention rate of the specific capacitance was about 83.7% when recycled 2000 times; moreover, its capacitance did not change much after perpendicular bending 200 times. Therefore, the films prepared by this study have great potential in the field of flexible supercapacitors.

Cellulose Nanofibrils Filled Poly(Lactic Acid) Biocomposite Filament for FDM 3D Printing.

As direct digital manufacturing, 3D printing (3DP) technology provides new development directions and opportunities for the high-value utilization of a wide range of biological materials. Cellulose nanofibrils (CNF) and polylactic acid (PLA) biocomposite filaments for fused deposition modeling (FDM) 3DP were developed in this study. Firstly, CNF was isolated by enzymatic hydrolysis combined with high-pressure homogenization. CNF/PLA filaments were then prepared by melt-extrusion of PLA as the matrix and CNF as the filler. Thermal stability, mechanical performance, and water absorption property of biocomposite filaments and 3D-printed objects were analyzed. Findings showed that CNF increased the thermal stability of the PLA/PEG600/CNF composite. Compared to unfilled PLA FDM filaments, the CNF filled PLA biocomposite filament showed an increase of 33% in tensile strength and 19% in elongation at break, suggesting better compatibility for desktop FDM 3DP. This study provided a new potential for the high-value utilization of CNF in 3DP in consumer product applications.

Nanocellulose Hybrids with Metal Oxides Nanoparticles for Biomedical Applications.

Cellulose is one of the most affordable, sustainable and renewable resources, and has attracted much attention especially in the form of nanocellulose. Bacterial cellulose, cellulose nanocrystals or nanofibers may serve as a polymer support to enhance the effectiveness of metal nanoparticles. The resultant hybrids are valuable materials for biomedical applications due to the novel optical, electronic, magnetic and antibacterial properties. In the present review, the preparation methods, properties and application of nanocellulose hybrids with different metal oxides nanoparticles such as zinc oxide, titanium dioxide, copper oxide, magnesium oxide or magnetite are thoroughly discussed. Nanocellulose-metal oxides antibacterial formulations are preferred to antibiotics due to the lack of microbial resistance, which is the main cause for the antibiotics failure to cure infections. Metal oxide nanoparticles may be separately synthesized and added to nanocellulose (ex situ processes) or they can be synthesized using nanocellulose as a template (in situ processes). In the latter case, the precursor is trapped inside the nanocellulose network and then reduced to the metal oxide. The influence of the synthesis methods and conditions on the thermal and mechanical properties, along with the bactericidal and cytotoxicity responses of nanocellulose-metal oxides hybrids were mainly analyzed in this review. The current status of research in the field and future perspectives were also signaled.

Structure and Properties of Polylactic Acid Biocomposite Films Reinforced with Cellulose Nanofibrils.

Polylactic acid (PLA) is one of the most promising biodegradable and recyclable thermoplastic biopolymer derived from renewable feedstock. Nanocellulose reinforced PLA biocomposites have received increasing attention in academic and industrial communities. In the present study, cellulose nanofibrils (CNFs) was liberated by combined enzymatic pretreatment and high-pressure homogenization, and then subsequently incorporated into the PLA matrix to synthesize PLA/CNF biocomposite films via solution casting and melt compression. The prepared PLA/CNF biocomposite films were characterized in terms of transparency (UV-Vis spectroscopy), chemical structure (attenuated total reflectance-Fourier transform infrared, ATR-FTIR; X-ray powder diffraction, XRD), thermal (thermogravimetric analyzer, TGA; differential scanning calorimetry, DSC), and tensile properties. With 1.0-5.0 wt % additions of CNF to the PLA matrix, noticeable improvements in thermal and physical properties were observed for the resulting PLA/CNF biocomposites. The 2.5 wt % addition of CNF increased the tensile strength by 8.8%. The Tonset (initial degradation temperature) and Tmax (maximum degradation temperature) after adding 5.0 wt % CNF was increased by 20 °C, and 10 °C, respectively in the nitrogen atmosphere. These improvements were attributed to the good dispersibility and improved interfacial interaction of CNF in the PLA matrix.

Paper-Based Oil Barrier Packaging using Lignin-Containing Cellulose Nanofibrils.

Environmental and health concerns are driving the need for new materials in food packaging to replace poly- or perfluorinated compounds, aluminum layers, and petroleum-based polymers. Cellulose nanofibrils (CNF) have been shown by a number of groups to form excellent barrier layers to oxygen and grease. However, the influence of lignin-containing cellulose nanofibrils (LCNF) on film barrier properties has not been well reported. Herein, thin films (16 g/m2) from LCNF and CNF were formed on paper substrates through a filtration technique that should mimic the addition of material at the wet end of a paper machine. Surface, barrier and mechanical attributes of these samples were characterized. The analysis on the surface free energy and water contact angle pointed to the positive role of lignin distribution in inducing a certain degree of water repellency. The observed oxygen transmission rate (OTR) and water vapor permeability (WVP) values of LCNF-coated samples were nearly similar to those with CNF. However, the presence of lignin improved the oil proof performance; these layered designs exhibited an excellent resistance to grease (kit No. 12). The attained papers with LCNF coat were formed into bowl-like containers using metal molds and a facile oven drying protocol to evaluate their resistance to oil penetration over a longer period. The results confirmed the capability of LCNF layer in holding commercially available cooking oils with no evidence of leakage for over five months. Also, an improvement in the tensile strength and elongation at break was observed in the studied papers. Overall, the proposed packaging material possesses viable architecture and can be considered as a fully wood-based alternative for the current fluorocarbon systems.

The Crystallinity and Aspect Ratio of Cellulose Nanomaterials Determine Their Pro-Inflammatory and Immune Adjuvant Effects In Vitro and In Vivo.

Nanocellulose is increasingly considered for applications; however, the fibrillar nature, crystalline phase, and surface reactivity of these high aspect ratio nanomaterials need to be considered for safe biomedical use. Here a comprehensive analysis of the impact of cellulose nanofibrils (CNF) and nanocrystals (CNC) is performed using materials provided by the Nanomaterial Health Implications Research Consortium of the National Institute of Environmental Health Sciences. An intermediary length of nanocrystals is also derived by acid hydrolysis. While all CNFs and CNCs are devoid of cytotoxicity, 210 and 280 nm fluorescein isothiocyanate (FITC)-labeled CNCs show higher cellular uptake than longer and shorter CNCs or CNFs. Moreover, CNCs in the 200-300 nm length scale are more likely to induce lysosomal damage, NLRP3 inflammasome activation, and IL-1ß production than CNFs. The pro-inflammatory effects of CNCs are correlated with higher crystallinity index, surface hydroxyl density, and reactive oxygen species generation. In addition, CNFs and CNCs can induce maturation of bone marrow-derived dendritic cells and CNCs (and to a lesser extent CNFs) are found to exert adjuvant effects in ovalbumin (OVA)-injected mice, particularly for 210 and 280 nm CNCs. All considered, the data demonstrate the importance of length scale, crystallinity, and surface reactivity in shaping the innate immune response to nanocellulose.

Zwitterionic Acetylated Cellulose Nanofibrils.

A strategy is devised to synthesize zwitterionic acetylated cellulose nanofibrils (CNF). The strategy included acetylation, periodate oxidation, Schiff base reaction, borohydride reduction, and a quaternary ammonium reaction. Acetylation was performed in glacial acetic acid with a short reaction time of 90 min, yielding, on average, mono-acetylated CNF with hydroxyl groups available for further modification. The products from each step were characterized by FTIR spectroscopy, ζ-potential, SEM-EDS, AFM, and titration to track and verify the structural changes along the sequential modification route.

A General Aqueous Silanization Protocol to Introduce Vinyl, Mercapto or Azido Functionalities onto Cellulose Fibers and Nanocelluloses.

The effective and straight-forward modification of nanostructured celluloses under aqueous conditions or as "never-dried" materials is challenging. We report a silanization protocol in water using catalytic amounts of hydrogen chloride and then sodium hydroxide in a two-step protocol. The acidic step hydrolyzes the alkoxysilane to obtain water-soluble silanols and the subsequent addition of catalytic amounts of NaOH induces a covalent reaction between cellulose surficial hydroxyl groups and the respective silanols. The developed protocol enables the incorporation of vinyl, thiol, and azido groups onto cellulose fibers and cellulose nanofibrils. In contrast to conventional methods, no curing or solvent-exchange is necessary, thereby the functionalized celluloses remain never-dried, and no agglomeration or hornification occurs in the process. The successful modification was proven by solid state NMR, ATR-IR, and EDX spectroscopy. In addition, the covalent nature of this bonding was shown by gel permeation chromatography of polyethylene glycol grafted nanofibrils. By varying the amount of silane agents or the reaction time, the silane loading could be tuned up to an amount of 1.2 mmol/g. Multifunctional materials were obtained either by prior carboxymethylation and subsequent silanization; or by simultaneously incorporating both vinyl and azido groups. The protocol reported here is an easy, general, and straight-forward avenue for introduction of anchor groups onto the surface of never-dried celluloses, ready for click chemistry post-modification, to obtain multifunctional cellulose substrates for high-value applications.

Cellulose Nanomaterials-Binding Properties and Applications: A Review.

Cellulose nanomaterials (CNs) are of increasing interest due to their appealing inherent properties such as bio-degradability, high surface area, light weight, chirality and the ability to form effective hydrogen bonds across the cellulose chains or within other polymeric matrices. Extending CN self-assembly into multiphase polymer structures has led to useful end-results in a wide spectrum of products and countless innovative applications, for example, as reinforcing agent, emulsion stabilizer, barrier membrane and binder. In the current contribution, after a brief description of salient nanocellulose chemical structure features, its types and production methods, we move to recent advances in CN utilization as an ecofriendly binder in several disparate areas, namely formaldehyde-free hybrid composites and wood-based panels, papermaking/coating processes, and energy storage devices, as well as their potential applications in biomedical fields as a cost-effective and tissue-friendly binder for cartilage regeneration, wound healing and dental repair. The prospects of a wide range of hybrid materials that may be produced via nanocellulose is introduced in light of the unique behavior of cellulose once in nano dimensions. Furthermore, we implement some principles of colloidal and interfacial science to discuss the critical role of cellulose binding in the aforesaid fields. Even though the CN facets covered in this study by no means encompass the great amount of literature available, they may be regarded as the basis for future developments in the binder applications of these highly desirable materials.

Emulsion Stabilization with Functionalized Cellulose Nanoparticles Fabricated Using Deep Eutectic Solvents.

In this experiment, the influence of the morphology and surface characteristics of cellulosic nanoparticles (i.e., cellulose nanocrystals [CNCs] and cellulose nanofibers [CNFs]) on oil-in-water (o/w) emulsion stabilization was studied using non-modified or functionalized nanoparticles obtained following deep eutectic solvent (DES) pre-treatments. The effect of the oil-to-water ratio (5, 10, and 20 wt.-% (weight percent) of oil), the type of nanoparticle, and the concentration of the particles (0.05⁻0.2 wt.-%) on the oil-droplet size (using laser diffractometry), o/w emulsion stability (via analytical centrifugation), and stabilization mechanisms (using field emission scanning electron microscopy with the model compound-i.e., polymerized styrene in water emulsions) were examined. All the cellulosic nanoparticles studied decreased the oil droplet size in emulsion (sizes varied from 22.5 µm to 8.9 µm, depending on the nanoparticle used). Efficient o/w emulsion stabilization against coalescence and an oil droplet-stabilizing web-like structure were obtained only, however, with surface-functionalized CNFs, which had a moderate hydrophilicity level. CNFs without surface functionalization did not prevent either the coalescence or the creaming of emulsions, probably due to the natural hydrophobicity of the nanoparticles and their instability in water. Moderately hydrophilic CNCs, on the other hand, distributed evenly and displayed good interaction with both dispersion phases. The rigid structure of CNCs meant, however, that voluminous web structures were not formed on the surface of oil droplets; they formed in flat, uniform layers instead. Consequently, emulsion stability was lower with CNCs, when compared with surface-functionalized CNFs. Tunable cellulose nanoparticles can be used in several applications such as in enhanced marine oil response.

Improvement of the Thermal Stability of TEMPO-Oxidized Cellulose Nanofibrils by Heat-Induced Conversion of Ionic Bonds to Amide Bonds.

Improving thermal stability of TEMPO-oxidized cellulose nanofibrils (TOCNs) is a major challenge for the development and preparation of new nanocomposites. However, thermal degradation of TOCNs occurs at 220 °C. The present study reports a simple way to improve thermal stability of TOCNs by the heat-induced conversion of ionic bonds to amide bonds. Coupling amine-terminated polyethylene glycol to the TOCNs is performed through ionic bond formation. Films are produced from the dispersions by the casting method. Infrared spectroscopy and thermogravimetric analysis confirm conversion of ionic bonds to amide bonds for the modified TOCN samples after heating. As a result, improvement of TOCNs' thermal stability by up to 90 °C is successfully achieved.

Tung oil-based waterborne UV-curable coatings via cellulose nanofibril stabilized Pickering emulsions for self-healing and anticorrosion application.

In this study, waterborne UV-curable coatings with self-healing properties based on transesterification were prepared using renewable biomass resources for anti-corrosion application. Tung oil (TO)-based oligomer (TMHT) was synthesized through Diels-Alder reaction of TO with maleic anhydride, subsequent ring opening reaction with hydroxyethyl acrylate (HEA), and final neutralize reaction with triethylamine. A series of waterborne UV-curable coatings were prepared from cellulose nanofibrils (CNF) stabilized TMHT-based Pickering emulsions after drying and UV light-curing processes. It is suggested that CNF significantly improved the storage stability of Pickering emulsions. The obtained waterborne UV-curable coatings with CNF of 1-3 wt% exhibited remarking coating and mechanical performance (pencil hardness up to 5 H, adhesion up to 2 grade, flexibility of 2 mm, tensile strength up to 11.6 MPa, etc.), great transmittance (82.3 %-80.8 %) and great corrosion resistance (|Z|0.01Hz up to 5.4 × 106 Ω·cm2). Because of the presence of the dynamic ester bonds in TMHT, the coatings exhibited excellent self-healing performance (78.05 %-56.34 %) at 150 °C without catalyst and external force. More importantly, the |Z|0.01Hz of the self-healing coating was higher than that of the scratched coating, indicating that the self-healing performance could extend the service life of the coating in corrosion resistant application.