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The fabrication of commercial cellulose nanofibrils (CNFs) into arrays with long-range ordering is of great significance for their extended applications, which, however, is severely hindered by their high disorder, aggregation, and hornified features. Herein, sub-nanoscale anionic metal oxide clusters (phosphotungstic acid, H 3 PW 12 O 40 , PTA) are applied to complex with commercial CNFs (dried powder DCNF and aqueous suspension WCNF) in aqueous media, and a long-range ordered layer structure can be facilely fabricated via typical unidirectional freezing. The surface complexation of the commercial CNFs and PTA can be confirmed through the small-angle scattering studies of the complex hydrogels. The hydrogels present similar correlation lengths in small-angle X-ray and neutron scattering measurements, suggesting the homogeneous distribution of PTA along the commercial CNFs. This gives rise to the negatively charged surface feature and further leads to strong repulsion among the commercial CNFs. Due to the disparity in sizes, the influence of PTA on the density of hydrogel networks is suppressed, and the network density is mainly dependent on the mass content of CNFs. The studies provide guidance to fabricate hydrogels with catalytic and photosensitive properties and also to design and stabilize long-range ordered structured aerogels during the removal of the nonfreezing bound water absorbed by the commercial CNFs after unidirectional freezing. This facile strategy shows great potential to broaden the application of commercial CNFs in thermal insulators, super-adsorbent materials, and supercapacitors in electrical devices.

Cellulose nanocrystals (CNC) are green, safe, and renewable nanomaterials with a variety of excellent performances but their morphologies are notoriously difficult to control as this is unfavorable to the diversification of the end products. Allomorphic conversion plays an important role in diversifying the morphology of CNC. However, this further complicates the prediction, design, and control of the geometric dimensions of CNC. Herein, allomorphically modified cellulose (mercerized cellulose, ethylenediamine (EDA)-treated cellulose, and ball-milled cellulose) is designed and used as the starting material for CNC isolation. Subsequently, the morphological evolution of cellulose particles during acid hydrolysis is traced by scanning electron microscopy observations. A mechanism that facilitates further understanding of CNC shaping during sulfuric acid hydrolysis is proposed. According to the CNC shaping mechanism, precise prediction, design, and efficient control of the morphology of CNC (needle-like, ribbon-like, ellipsoid, and spherical) can be realized. CNC with various morphologies are favorable for their applications, such as templating synthesis of porous materials and Pickering emulsion dispersion.

Cellulose-water interactions are crucial to understand biological processes as well as to develop tailor made cellulose-based products. However, the main challenge to study these interactions is the diversity of natural cellulose fibers and alterations in their supramolecular structure. Here, we study the humidity response of different, well-defined, ultrathin cellulose films as a function of industrially relevant treatments using different techniques. As treatments, drying at elevated temperature, swelling, and swelling followed by drying at elevated temperatures were chosen. The cellulose films were prepared by spin coating a soluble cellulose derivative, trimethylsilyl cellulose, onto solid substrates followed by conversion to cellulose by HCl vapor. For the highest investigated humidity levels (97%), the layer thickness increased by ca. 40% corresponding to the incorporation of 3.6 molecules of water per anhydroglucose unit (AGU), independent of the cellulose source used. The aforementioned treatments affected this ratio significantly with drying being the most notable procedure (2.0 and 2.6 molecules per AGU). The alterations were investigated in real time with X-ray reflectivity and quartz crystal microbalance with dissipation, equipped with a humidity module to obtain information about changes in the thickness, roughness, and electron density of the films and qualitatively confirmed using grazing incidence small angle X-ray scattering measurements using synchrotron irradiation.

Bioactive substances, displaying excellent biocompatibility, chemical stability, and processability, could be extensively applied in biomedicine and tissue engineering. In recent years, plant-based bioactive substances such as flavonoids, vitamins, terpenes, and lignin have received considerable attention due to their human health benefits and pharmaceutical/medical applications. Among them is lignin, an amorphous biomacromolecule mainly derived from the combinatorial radical coupling of three phenylpropane units ( p -hydroxypenyl, guaiacyl, and syringyl) during lignification. Lignin possesses intrinsic bioactivities (antioxidative, antibacterial, anti-UV activities, etc.) against phytopathogens. Lignin also enhances the plant resistance (adaptability) against environmental stresses. The abundant structural features of lignin offer other significant bioactivities including antitumor and antivirus bioactivities, regulation of plant growth, and enzymatic hydrolysis of cellulose. This Review reports the latest research results on the bioactive potential of lignin and lignin-based substances in biomedicine, agriculture, and biomass conversion. Moreover, the interfacial reactions and bonding mechanisms of lignin with biotissue/cells and other constituents were also discussed, aiming at promoting the conversion or evolution of lignin from industrial wastes to value-added bioactive materials.

The fabrication of biomimetic photonic materials with environmental stimuli-responsive functions from entirely biobased materials is becoming increasingly challenging with the growing demand for biodegradable materials. Herein, the effect of glucan with different molecular weights on the mechanical performance and tunable structural color of iridescent CNC composite films was investigated. The existence of glucan did not influence the self-assembly performance of CNCs, but rather led to an improvement in the mechanical performance, enabling cholesteric CNC composite films with an adjustable structural color. Simultaneously, the iridescent films showed a conspicuous redshift and enlarged initial pitch without obstruction of the chiral structure. In response to environmental humidity, the structural colors of the iridescent composite films can be changed by regulating their chiral nematic structure. In particular, the films demonstrate a reversible structural color change between blue and red at RH between 50 and 98%. The resulting biobased iridescent composite films have potential applications in decorative coating, optical and humidity sensing, and anticounterfeiting.

Lignin/tannin/ZnONP composite coatings were designed for paper-based green packaging. Multiple functions, such as high strength, moisture resistance, low air permeance, heat endurance, UV aging resistance, and antibacterial/mold properties, were successfully integrated into one biobased coating. Prepolymerization improved the physical properties of coatings at high lignin contents. The best ingredient ratio was: 40% lignin, 15% tannin, and 10% ZnONPs (based on tannin weight), and the as-prepared biocoating was labeled LTZn-10. After coated with LTZn-10, the tensile strength and bursting strength of the packaging were efficiently enhanced by more than 3 times and were dramatically increased by 51.6 and 5.6 times at the wet state, respectively, which reveals that the packaging has favorable moisture resistance and it can be used in high humidity environments. Scanning electron microscopy (SEM) proved that most of the pores on the paper were blocked by the coatings, which helped to decrease the air permeance by 10.3 times. Meanwhile, ZnONPs were evenly spread on the coatings, which endowed the packaging with excellent antibacterial/mold performance. No colony or mycelium was found in the test against Gram-negative/positive bacteria and eight common molds. Besides, antibacterial activity is only available while the bacteria come in contact with the coating and no active substances were released into the culture medium, which is a good property that can keep the cargo from contamination of antibacterial agents. In addition, the coated paper presented an improved T and thermal degradation temperature, indicating that the coated package has favorable thermostability and can maintain its outstanding physical properties in a wider temperature range. Lignin and tannin promoted the UV stability and service life of the coated paper, as a rare physical decrease was observed after UV aging for 72 h. The function-integrated biobased coating with favorable sustainability is a good candidate to be widely used in paper-based green packaging fields.g and thermal degradation temperature, indicating that the coated package has favorable thermostability and can maintain its outstanding physical properties in a wider temperature range. Lignin and tannin promoted the UV stability and service life of the coated paper, as a rare physical decrease was observed after UV aging for 72 h. The function-integrated biobased coating with favorable sustainability is a good candidate to be widely used in paper-based green packaging fields.

Cellulose nanofibrils, which attract extensive attention as a bio-based, sustainable, high-performance nanofibril, are believed to be predominantly hydrophilic. This study aimed to prove the presence of an amphiphilic "Janus-type fiber surface" in water with hydrophobic and hydrophilic faces in a cellulose nanofibril (ACC-CNF) that was prepared by the aqueous counter collision method. We clarified the surface characteristics of the ACC-CNF by confocal laser scanning microscopy with a carbohydrate-binding module and congo red probes for the hydrophobic planes on the cellulose fiber surfaces and calcofluor white as hydrophilic plane probes. The results indicated the presence of both characteristic planes on a single ACC-CNF surface, which verifies an amphiphilic Janus-type structure. Both hydrophobic probes adsorbed onto ACC-CNFs for the quantitative evaluation of the degree of ACC-CNF surface hydrophobicity by Langmuir's adsorption theory based on the optimal maximum adsorption amounts for various starting raw material types.

Biopolymer cellulose is investigated in terms of the crystallographic order within thin films. The films were prepared by spin-coating of a trimethylsilyl cellulose precursor followed by an exposure to HCl vapors; two different source materials were used. Careful precharacterization of the films was performed by infrared spectroscopy and atomic force microscopy. Subsequently, the films were investigated by grazing incidence X-ray diffraction using synchrotron radiation. The results showed broad diffraction peaks, indicating a rather short correlation length of the molecular packing in the range of a few nanometers. The analysis of the diffraction patterns was based on the known structures of crystalline cellulose, as the observed peak pattern was comparable to cellulose phase II and phase III. The dominant fraction of the film is formed by two different types of layers, which are oriented parallel to the substrate surface. The stacking of the layers results in a one-dimensional crystallographic order with a defined interlayer distance of either 7.3 or 4.2 Å. As a consequence, two different preferred orientations of the polymer chains are observed. In both cases, polymer chain axes are aligned parallel to the substrate surface, and the orientation of the cellulose molecules are concluded to be either edge-on or flat-on. A minor fraction of the cellulose molecules form nanocrystals that are randomly distributed within the films. In this case, the molecular packing density was found to be smaller in comparison to the known crystalline phases of cellulose.

Stretchable and compressible hydrogels based on natural polymers have received immense considerations for electronics. The feasibility of using pure natural polymer-based hydrogels could be improved if their mechanical behaviors satisfy the requirements of practical applications. Herein, we report highly stretchable (tensile strain ∼126%) and compressible (compression strain ∼80%) cellulose ionic hydrogels (CIHs) among pure natural polymer-based hydrogels including cellulose, chitin, and chitosan via chemical cross-linking based on free radical polymerization of allyl cellulose in NaOH/urea aqueous solution. In addition, the hydrogels have good transparency (transmittance of ∼89% at 550 nm) and ionic conductivity (∼0.16 mS cm -1 ) and can be worked at -20 °C without freezing and visual loss of transparency. Moreover, the CIHs can serve as reliable and stable strain sensors and have been successfully used to monitor human activities. Significantly, the various properties of hydrogel can be controlled through rationally adjusting the chemically cross-linked density. Our methodology will prove useful in developing the satisfied mechanical and transparent CIHs for a myriad of applications in flexible electronics.

Nanotechnology has been identified as having great potential for improving the efficiency of water prevention and purification while reducing costs. In this field, two applications of nanocellulose have generated attention and have proven to be a sound strategy as an adsorbent and as a membrane for the removal of contaminants. This potential is attributed to its high aspect ratio, high specific surface area, high capacity retention, and environmental inertness. In addition to the aforementioned advantages, the presence of active sites allows the incorporation of chemical moieties that may enhance the binding efficiency of pollutants to the surface. This review paper intends to understand how nanocellulose affects the adsorption behavior of water pollutants, e.g., heavy metal ions, microbes, dyes, and organic molecules, and is divided in two parts. First, a general overview of the different strategies for the preparation of nanocellulose is described, and its specific properties are reported. The second section reports some of its application as adsorbent nanomaterial or separation membrane. It appears that the use of nanocellulose for these applications is very promising for wastewater treatment industries.

Knowledge gaps in the biosafety data of the nanocellulose (NC) for biomedical use through various routes of administration call for closer look at health and exposure evaluation. This work evaluated the potentially immunogenic contaminants levels, for example, endotoxin and (1,3)-β-d-glucan, in four representative NCs, that is, wood-based NCs and bacterial cellulose (BC). The hot-water extracts were analyzed with ELISA assays, HPSEC-MALLS, GC, and NMR analysis. Varying levels of endotoxin and (1,3)-β-d-glucan contaminats were found in these widely used NCs. Although the β-(1,3)-d-glucan was not detected from the NMR spectra due to the small extract samples amount (2-7 mg), the anomerics and highly diastereotopic 6-CH 2 signals may suggest the presence of β-(1,4)-linkages with β-(1,6) branching in the polysaccharides of NCs' hot-water extracts, which were otherwise not detectable in the enzymatic assay. In all, the article highlights the importance of monitoring various water-soluble potentially immunogenic contaminants in NC for biomedical use.

We present an approach to construct biocompatible and photoluminescent hybrid materials comprised of carbon quantum dots (CQDs) and TEMPO-oxidized cellulose nanocrystals (TO-CNCs). First, the amino-functionalized carbon quantum dots (NH 2 -CQDs) were synthesized using a simple microwave method, and the TO-CNCs were prepared by hydrochloric acid (HCl) hydrolysis followed by TEMPO-mediated oxidation. The conjugation of NH 2 -CQDs and TO-CNCs was conducted via carbodiimide-assisted coupling chemistry. The synthesized TO-CNC@CQD hybrid nanomaterials were characterized using X-ray photoelectron spectroscopy, cryo-transmittance electron microscopy, confocal microscopy, and fluorescence spectroscopy. Finally, the interactions of TO-CNC@CQD hybrids with HeLa and RAW 264.7 macrophage cells were investigated in vitro. Cell viability tests suggest the surface conjugation with NH 2 -CQDs not only improved the cytocompatibility of TO-CNCs, but also enhanced their cellular association and internalization on both HeLa and RAW 264.7 cells after 4 and 24 h incubation.

The current study aims to demonstrate the influence of the surface chemistry of wood-derived cellulose nanofibril (CNF) hydrogels on fibroblasts for tissue engineering applications. TEMPO-mediated oxidation or carboxymethylation pretreatments were employed to produce hydrogels with different surface chemistry. This study demonstrates the following: first, the gelation of CNF with cell culture medium and formation of stable hydrogels with improved rheological properties; second, the response of mouse fibroblasts cultured on the surface of the hydrogels or sandwiched within the materials with respect to cytotoxicity, cell attachment, proliferation, morphology, and migration. Indirect cytotoxicity tests showed no toxic effect of either hydrogel. The direct contact with the carboxymethylated hydrogel adversely influenced the morphology of the cells and limited their spreading, while typical morphology and spreading of cells were observed with the TEMPO-oxidized hydrogel. The porous fibrous structure may be a key to cell proliferation and migration in the hydrogels.

The state of dispersion and the interactions between a polymer and a filler in a nanocomposite crucially define its properties and performance. The affinity of polylactide (PLA) with vegetable and animal proteins (casein, gelatin, soy protein isolate, and hydrolysate) is investigated and their role as eco-friendly dispersants and compatibilizers of cellulose nanofibrils (CNF) is elucidated. The affinity of the proteins with PLA is determined by using sensograms acquired by electroacoustic (quartz crystal microgravimetry) and optical (surface plasmon resonance) techniques. The surface energy of PLA increases upon protein adsorption while the opposite effect is observed for CNF, under identical experimental conditions. A significant improvement in the thermodynamic work of adhesion for PLA/CNF systems is predicted by application of the denatured proteins at low concentrations (∼20% and ∼15% enhancement with soy protein and casein at pH 3 and pH 8, respectively). We offer a robust method to screen denatured proteins and to tailor the wettability and material compatibility in the synthesis of bionanocomposites based on CNF and PLA.

We present an efficient approach to develop cellulose nanocrystal (CNC) hybrids with magnetically responsive Fe 3 O 4 nanoparticles that were synthesized using the (Fe 3+ /Fe 2+ ) coprecipitation. After 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-catalyzed oxidation of CNC, carbodiimide (EDC/NHS) was used for coupling amine-containing iron oxide nanoparticles that were achieved by dopamine ligand exchange (NH 2 -Fe 3 O 4 NPs). The as-prepared hybrids (Fe 3 O 4 @CNC) were further complexed with Cu(II) ions to produce specific protein binding sites. The performance of magnetically responsive Cu-Fe 3 O 4 @CNC hybrids was assessed by selectively separating lysozyme from aqueous media. The hybrid system displayed a remarkable binding capacity with lysozyme of 860.6 ± 14.6 mg/g while near full protein recovery (∼98%) was achieved by simple elution. Moreover, the regeneration of Fe 3 O 4 @CNC hybrids and efficient reutilization for protein separation was demonstrated. Finally, lysozyme separation from matrices containing egg white was achieved, thus revealing the specificity and potential of the presented method.

The temperature-dependence of xyloglucan (XG) adsorption onto smooth cellulose model films regenerated from N-methylmorpholine N-oxide (NMMO) was investigated using surface plasmon resonance spectroscopy, and it was found that the adsorbed amount increased with increasing temperature. This implies that the adsorption of XG to NMMO-regenerated cellulose is endothermic and supports the hypothesis that the adsorption of XG onto cellulose is an entropy-driven process. We suggest that XG adsorption is mainly driven by the release of water molecules from the highly hydrated cellulose surfaces and from the XG molecules, rather than through hydrogen bonding and van der Waals forces as previously suggested. To test this hypothesis, the adsorption of XG onto cellulose was studied using cellulose films with different morphologies prepared from cellulose nanocrystals (CNC), semicrystalline NMMO-regenerated cellulose, and amorphous cellulose regenerated from lithium chloride/dimethylacetamide. The total amount of high molecular weight xyloglucan (XGHMW) adsorbed was studied by quartz crystal microbalance and reflectometry measurements, and it was found that the adsorption was greatest on the amorphous cellulose followed by the CNC and NMMO-regenerated cellulose films. There was a significant correlation between the cellulose dry film thickness and the adsorbed XG amount, indicating that XG penetrated into the films. There was also a correlation between the swelling of the films and the adsorbed amounts and conformation of XG, which further strengthened the conclusion that the water content and the subsequent release of the water upon adsorption are important components of the adsorption process.

Cellulose nanofibrils (CNFs) are produced and commonly used in the form of aqueous suspensions or gels. A number of studies have focused lately on rheological properties of CNF suspensions, which gives insight into properties of such materials and can reflect their behavior during handling. This Review summarizes the recent progress in rheological studies on CNF aqueous suspensions using rotational rheometry. Here, we discuss linear viscoelastic properties, i.e., frequency-dependent storage and loss moduli; shear flow behavior, i.e., apparent viscosity and shear stress as a function of shear rate; local flow characteristics, etc. In this Review, we point out that the rheological behavior of at least two types of CNF suspensions should be distinguished: (i) ones produced using mechanical fibrillation with or without enzymatic pretreatment (no surface chemical modification), which possess highly flocculated structure, and (ii) ones produced involving chemical modification pretreatments, e.g., carboxylation, carboxymethylation, quaternization, or sulfonation, which possess better colloidal stability and do not evidently flocculate.

In this work, we take advantage of the rod-like structure of electrosterically stabilized nanocrystalline cellulose (ENCC, with a width of about 7 nm and a length of about 130 nm), which has dicarboxylated cellulose (DCC) chains protruding from both ends, providing electrosterical stability for ENCC particles, to chemically end-to-end assemble these particles into nanocellulose fibers. ENCC with shorter DCC chains can be obtained by a mild hydrolysis of ENCC with HCl, and subsequently the hydrolyzed ENCC (HENCC, with a width of about 6 nm and a length of about 120 nm) is suitable to be assembled into high aspect ratio nanofibers by chemically cross-linking HENCC from one end to another. Two sets of HENCC were prepared by carbodiimide-mediated formation of an alkyne and an azide derivative, respectively. Cross-linking these two sets of HENCC was performed by a click reaction. HENCCs were also end-to-end cross-linked by a bioconjugation reaction, with a diamine. From atomic force microscopy (AFM) images, about ten HENCC nanoparticles were cross-linked and formed high aspect ratio nanofibers with a width of about 6 nm and a length of more than 1 μm.

Toward our goal of scalable, antimicrobial materials based on photodynamic inactivation, paper sheets comprised of photosensitizer-conjugated cellulose fibers were prepared using porphyrin and BODIPY photosensitizers, and characterized by spectroscopic (infrared, UV-vis diffuse reflectance, inductively coupled plasma optical emission) and physical (gel permeation chromatography, elemental, and thermal gravimetric analyses) methods. Antibacterial efficacy was evaluated against Staphylococcus aureus (ATCC-2913), vancomycin-resistant Enterococcus faecium (ATCC-2320), Acinetobacter baumannii (ATCC-19606), Pseudomonas aeruginosa (ATCC-9027), and Klebsiella pneumoniae (ATCC-2146). Our best results were achieved with a cationic porphyrin-paper conjugate, Por((+))-paper, with inactivation upon illumination (30 min, 65 ± 5 mW/cm(2), 400-700 nm) of all bacterial strains studied by 99.99+% (4 log units), regardless of taxonomic classification. Por((+))-paper also inactivated dengue-1 virus (>99.995%), influenza A (∼ 99.5%), and human adenovirus-5 (∼ 99%). These results demonstrate the potential of cellulose materials to serve as scalable scaffolds for anti-infective or self-sterilizing materials against both bacteria and viruses when employing a photodynamic inactivation mode of action.

The properties of paper sheets can be tuned by adjusting the surface or bulk chemistry using functional polymers that are applied during (online) or after (offline) papermaking processes. In particular, polymers are widely used to enhance the mechanical strength of the wet state of paper sheets. However, the mechanical strength depends not only on the chemical nature of the polymeric additives but also on the distribution of the polymer on and in the lignocellulosic paper. Here, we analyze the photochemical attachment and distribution of hydrophilic polydimethylacrylamide-co-methacrylate-benzophenone P(DMAA-co-MABP) copolymers with defined amounts of photoreactive benzophenone moieties in model paper sheets. Raman microscopy was used for the unambiguous identification of P(DMAA-co-MABP) and cellulose specific bands and thus the copolymer distribution within the cellulose matrix. Two-dimensional Raman spectral maps at the intersections of overlapping cellulose fibers document that the macromolecules only partially surround the cellulose fibers, favor to attach to the fiber surface, and connect the cellulose fibers at crossings. Moreover, the copolymer appears to accumulate preferentially in holes, vacancies, and dips on the cellulose fiber surface. Correlative brightfield, Raman, and confocal laser scanning microscopy finally reveal a reticular three-dimensional distribution of the polymer and show that the polymer is predominately deposited in regions of high capillarity (i.e., in proximity to fine cellulose fibrils). These data provide deeper insights into the effects of paper functionalization with a copolymer and aid in understanding how these agents ultimately influence the local and overall properties of paper.

In this work, flexible and free-standing composite films of nanofibrillated cellulose/polypyrrole (NFC/PPy) and NFC/PPy-silver nanoparticles (NFC/PPy-Ag) have been synthesized for the first time via in situ one-step chemical polymerization and applied in potential biomedical applications. Incorporation of NFC into PPy significantly improved its film formation ability resulting in composite materials with good mechanical and electrical properties. It is shown that the NFC/PPy-Ag composite films have strong inhibition effect against the growth of Gram-positive bacteria, e.g., Staphylococcus aureus. The electrical conductivity and strong antimicrobial activity makes it possible to use the silver composites in various applications aimed at biomedical treatments and diagnostics. Additionally, we report here the structural and morphological characterization of the composite materials with Fourier-transform infrared spectroscopy, atomic force microscopy, and scanning and transmission electron microscopy techniques.

This article focuses on the formation of the surface tension torque (STT) phenomenon close to the dry-line boundary layer during evaporation of the liquid phase of a solution casted shape-anisotropic nanoparticle suspension (here, cellulose nanowhisker (CNW)) or dissolved polymer (here, polyvinyl alcohol (PVA)) and its effects on self-assembly of the cellulose nanocrystals and polymer chains. The results confirm that the STT tends to align both the CNWs and the PVA chains tangential to the dry-line boundary layer. By careful control of the advancement of the dry-line, achieving special linear and curved patterns of both the CNWs and the PVA chains proportional to the mold position and geometry is possible. The STT phenomenon is explained and simplified in terms of a physical model. Understanding of the STT phenomenon and its effects on the alignment and self-assembly of the CNWs and PVA chains is necessary especially when achieving alignment using a modulated external magnetic or electric field is desired. The STT is safe, inexpensive, easy, and efficient, and can be a good alternative to the magnetic and electric field orientation methods.

When grafted β-cyclodextrin is used as targeting sites, Pluronic polymers have been introduced on the surface of cellulose nanocrystals by means of inclusion interaction between β-cyclodextrin and hydrophobic segment of the polymer. Because of the steric stabilization effect, surface poly(ethylene glycol) chains facilitate the dispersion and compatibility of nanocrystals, which also enhance the loading levels of nanocrystals in the hydrogel system. Meanwhile, uncovered poly(ethylene glycol) segments render the participating inclusion of α-cyclodextrin for the architecture of in situ hydrogels. Surface grafting and inclusion reactions were proved by solid (13)C NMR and FTIR. Grafting efficiency of β-cyclodextrin and inclusion efficiency of Pluronic on the surface of nanocrystals were confirmed by UV spectroscopy and elemental analysis. A significant enhancement of the structural and thermal stability of in situ hydrogels with high loading levels of modified nanocrystals (>5.77 wt %) was observed by rheological analysis. Further study reveals the performance and behavior of hydrogels under a different pH environment. Finally, in situ hydrogels were used as drug carrier for in vitro release of doxorubicin and exhibit the behavior of prolonged drug release with special release kinetics.

The present study reports for the first time a method to obtain water redispersible dried NFC using freeze-drying. No chemical surface modification was required to get this kind of product. Salt addition (sodium chloride: NaCl) strategy has been selected to block and then to regenerate hydrogen bonds during the drying and the redispersion steps, respectively. Several samples were produced at different pH (i.e., 4, 6, 8, and 10). All the redispersed NFC were characterized by different techniques (e.g., FE-SEM, XRD, EPMA-EDX) to check the effect of salt on NFC aggregation. The interactions between NFC and NaCl at different pH conditions have been discussed and the rheology of the redispersed NFC suspension has been performed. All the results prove a perfect water redispersion at pH 8 and exactly similar suspension is obtained after water dispersion of dried NFC following our procedure. These results are very promising for increasing application of NFC.

Adsorption of oligonucleotides onto model cellulose surfaces was investigated by comparing the Boese and Breaker's cellulose binding oligonucleotide (CBO) with a nonspecific oligonucleotide control (NSO). Measurements using the quartz crystal microbalance with dissipation technique confirmed that CBO adsorbed onto cellulose more than NSO, particularly at high ionic strengths (100 mM CaCl(2)). CBO showed a higher maximum adsorption on nanofibrillated and nanocrystalline cellulose than on regenerated cellulose, indicating a preference for the native cellulose I crystal structure under conditions that favored specific adsorption over calcium-mediated electrostatically driven adsorption. In addition, an anionic polyacrylamide (A-PAM) with grafted CBO also adsorbed onto the surface of cellulose in CaCl(2), whereas the unmodified A-PAM did not. This work shows that CBO performs as a "sticker", facilitating the adsorption of polyacrylamide onto cellulose, even under high ionic strength conditions where the adsorption of conventional polyelectrolytes is inhibited.

All-cellulose nanocomposite was directly fabricated using nanowelding of cellulose microfibers as a starting material, in 1-butyl-3-methylimidazolium chloride (BMIMCl) as a solvent, for the first time. The average diameter of the reinforcing component (undissolved nanofibrils) in the nanocomposite made directly from cellulose microfibers (NC-microfiber) was 53 ± 16 nm. Owing to its high mechanical properties (tensile strength of 208 MPa and Young's modulus of 20 GPa), high transparency (76% at a wavelength of 800 nm), and complete barrier to air and biodegradability, the NC-microfiber is regarded as a high multiperformance material. The NC-microfiber made directly from cellulose microfibers showed similar macro-, micro-, and nanostructures and the same properties as those made from solvent-based welding of ground cellulose nanofibers (NC-nanofiber). Omitting the step of cellulose nanofiber production makes the direct production of all-cellulose nanocomposite from cellulose microfibers easier, shorter, and cheaper than using cellulose nanofibers as starting material. The direct nanowelding of macro/micrometer-sized materials is theorized to be a fundamental approach for making nanocomposites.

Nanocomposites were developed by cross-linking cellulose nanowhiskers with poly(methyl vinyl ether-co-maleic acid) and polyethylene glycol. Nuclear magnetic resonance (NMR) studies showed cross-linking occurs between the matrix and cellulose nanowhiskers via an esterification reaction. Proton NMR T(2) relaxation experiments provided information on the mobility of the polymer chains within the matrix, which can be related to the structure of the cross-linked nanocomposite. The nanocomposite was found to consist of mobile chain portions between cross-linked junction points and immobilized chain segments near or at those junction points, whose relative fraction increased upon further incorporation of cellulose nanowhiskers. Atomic force microscopy images showed a homogeneous dispersion of nanowhiskers in the matrix even at high nanowhisker content, which can be attributed to cross-linking of the nanowhiskers in the matrix. Relative humidity conditions were found to affect the mechanical properties of the composites negatively while the nanowhiskers content had a positive effect. It is expected that the cross-links between the matrix and the cellulose nanowhiskers trap the nanowhiskers in the cross-linked network, preventing nanowhisker aggregation subsequently producing cellulose nanocomposites with unique mechanical behaviors. The results show that in situ cross-linking of cellulose nanowhiskers with a matrix polymer is a promising route to obtain nanocomposites with well dispersed nanowhiskers, tailored nanostructure, and mechanical performance.

In the present work, nanowhiskers and microfibrillated cellulose (MFC) both extracted from sisal were used to reinforce polycaprolactone (PCL). We report the influence of the nanoparticle's nature on the mechanical and thermal properties of the ensuing nanocomposites. The surface of both the nanoparticles was chemically modified to improve their compatibilization with the polymeric matrix. N-Octadecyl isocyanate (C18H37NCO) was used as the grafting agent. PCL nanocomposite films reinforced with sisal whiskers or MFC (raw or chemically modified) were prepared by film casting. The thermal behavior (Tg, Tm, Tc, and degree of crystallinity) and the mechanical properties of the nanocomposites in both the linear and the nonlinear range were determined using differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), and tensile tests, respectively. Significant differences were reported according to the nature of the nanoparticle and amount of nanofillers used as reinforcement. It was also proved that the chemical treatment clearly improves the ultimate properties of the nanocomposites.

Aqueous layer-by-layer (LbL) processing was used to create polyelectrolyte multilayer (PEM) nanocomposites containing cellulose nanocrystals and poly(allylamine hydrochloride). Solution-dipping and spin-coating assembly methods gave smooth, stable, thin films. Morphology was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and film growth was characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry, and optical reflectometry. Relatively few deposition cycles were needed to give full surface coverage, with film thicknesses ranging from 10 to 500 nm. Films prepared by spin-coating were substantially thicker than solution-dipped films and displayed radial orientation of the rod-shaped cellulose nanocrystals. The relationship between film color and thickness is discussed according to the principles of thin film interference and indicates that the iridescent properties of the films can be easily tailored in this system.

The adhesion of polyvinylamine to wet cellulose was significantly enhanced by the presence of pendant phenylboronic acid groups. It is proposed that adhesion results from boronate ester formation with cellulose at pH > 8. Experiments with phenol derivatized polyvinylamine gave low adhesion supporting the fact that the boronate moiety was responsible for strong adhesion to never-dried cellulose surfaces.

Sulfuric acid hydrolysis of native cellulose fibers produces stable suspensions of cellulose nanocrystals. Above a critical concentration, the suspensions spontaneously form an anisotropic chiral nematic liquid crystal phase. We have examined the effect of reaction time and acid-to-pulp ratio on nanocrystal and suspension properties for hydrolyzed black spruce acid sulfite pulp. Longer hydrolysis times produced shorter, less polydisperse black spruce cellulose nanocrystals and slightly increased the critical concentration for anisotropic phase formation. Increased acid-to-pulp ratio reduced the dimensions of the nanocrystals thus produced; the critical concentration was increased and the biphasic range became narrower. A suspension made from a bleached kraft eucalyptus pulp gave very similar properties to the softwood nanocrystal suspension when prepared under similar hydrolysis conditions.

When used as fillers in polymer composites, the thermostability of cellulose crystals is important. Sulfate groups, introduced during hydrolysis with sulfuric acid, are suspected to diminish the thermostability. To elucidate the relationship between the hydrolysis conditions, the number of sulfate groups introduced, and the thermal degradation behavior of cellulose crystals, bacterial cellulose was hydrolyzed with sulfuric acid under different hydrolysis conditions. The number of sulfate groups in the crystals was determined by potentiometric titration. The thermal degradation behavior was investigated by thermogravimetric analysis. The sulfate group content increased with acid concentration, acid-to-cellulose ratio, and hydrolysis time. Even at low levels, the sulfate groups caused a significant decrease in degradation temperatures and an increase in char fraction confirming that the sulfate groups act as flame retardants. Profile analysis of the derivative thermogravimetric curves indicated thermal separation of the degradation reactions by the sulfate groups into low- and high-temperature processes. The Broido method was used to determine activation energies for the degradation processes. The activation energies were lower at larger amounts of sulfate groups suggesting a catalytic effect on the degradation reactions. For high thermostability in the crystals, low acid concentrations, small acid-to-cellulose ratios, and short hydrolysis times should be used.