Rod-like Cellulose Nanocrystals Research Articles

Physical Modification of Cellulose Nanocrystals with a Synthesized Triblock Copolymer and Rheological Thickening in Silicone Oil/Grease.

This study investigates the rheological thickening effect of surface-modified cellulose nanocrystals (mCNCs) with a triblock copolymer on silicone oil. An amphipathic copolymer comprising hydrophilic methoxypolyethylene glycols and hydrophobic polydimethylsiloxane segments is synthesized and introduced in silicone oil by physical adsorption of rodlike cellulose nanocrystals (CNCs). The surface-modified copolymer acts as a "bridge" to enhance the compatibility between CNCs and base oil, which produces the hybrid oils/greases containing homogeneously dispersed mCNCs at varied loading levels of 5-20 wt %. The presence of this rigid additive remarkably increases the viscosity of silicone oil, accompanied with the transition from flowable to nonflowable behavior with a gradual increase of mCNC loading levels. Furthermore, the change of storage and loss modulus of the fabricated hybrid oils/greases indicates the formation of a three-dimensional network by the chain entanglement and interactions between the copolymer and silicone oil (at a critical loading level of 15 wt % mCNC), which promotes the rigid CNCs to act as the physical cross-linking point for the significant transition from liquid to quasi-solid state.

Effect of the geometry of cellulose nanocrystals on morphology and mechanical performance of dynamically vulcanized PLA/PU blend

Effects of the addition of single but geometrically different cellulose nanocrystals (CNCs) namely cylindrical CNCs (ultrasonic treated), spherical CNCs (chemically treated) and rod-like CNCs (commercial) on microstructural development and mechanical performance of the thermoplastic vulcanizates (TPVs) based on polylactic acid/polyurethane prepolymer (80/20) were studied. It was shown that a fraction of PLA molecules reacted with PU molecules during the dynamic crosslinking process. This was confirmed by the results of gel content measurements which showed an appreciable amount of additional gel content. This phenomenon together with the dynamic vulcanization process facilitated the development of a dual-continuous morphology in the TPV sample which was confirmed by the melt viscoelastic results and TEM micrographs. Interestingly, the addition of spherical CNCs to the TPV led to a remarkable enhancement in its toughness. A similar effect but to a lesser extent was observed in the TPV sample filled with cylindrical CNCs. These results could be explained in terms of a 3D percolated or interconnected network microstructure formed between finely dispersed CNCs localized in PLA and/or between CNCs and the PLA matrix. This fact was evidenced by observation of strong liquid–solid transition in the melt viscoelastic results, as well as TEM and AFM micrographs. On contrary to other counterparts, the rod-like CNCs had a weakening effect on toughness of the TPV which was attributed to their poor dispersion and/or formation of their aggregates which could act as stress concentrators. Moreover, DMTA results showed an almost similar reinforcing effect for the three CNCs on increasing the modulus of the TPV below Tg of the PU and partially compensated the PU reducing effect on modulus in the temperature range between the Tg of PU and PLA.

Preparation and liquid crystal phase properties of discotic cellulose nanoparticles

Understanding the behavior of fluids with inhomogeneous structural properties is critical for many industrial and biological materials. Sulfuric acid hydrolysis of cotton with ultrasonic treatment and low-speed centrifugation during purification yields “spiky” discotic cellulose particles. Amorphous cellulose remained in solution and forms discotic units which may be nucleated by crystalline rods. Scanning electron microscope and transmission electron microscope images confirm the discotic nature of the cellulose. High speed centrifugation could recover rod-like cellulose nanocrystals from the discotic cellulose nanoparticle solution. 3.6 wt% discotic cellulose nanoparticles formed the typical nematic phase and the liquid crystal texture became more structured with increasing concentration. Our results showed that spontaneous structuring of amorphous cellulose can lead to phase behavior that cannot be achieved using just rod-like cellulose nanocrystals. Mixtures containing amorphous and crystalline cellulose can form discotic cellulose nanoparticles. These solutions can form nematic phase (A), a structured columnar-like phase (B), and a glassy phase (C). Scanning electron microscope characterization (D, E) confirms a discotic structure with some spikes and network formation

Citrate-based fluorophore-modified cellulose nanocrystals as a biocompatible fluorescent probe for detecting ferric ions and intracellular imaging

In this contribution, citrate-based fluorophore (CF)-modified cellulose nanocrystals (CNCs) were prepared in a facile manner using sulfuric acid hydrolysis of citric acid/cysteine-treated microcrystalline celluloses. These rod-like CNCs have an average length of 156 nm and an average width of 7.9 nm. Because of conjugated CFs, these CNCs exhibit typical fluorescence characteristics, including a maximum excitation wavelength at 350 nm, maximum emission wavelength at 435 nm, high quantum yield of 83%, and good photostability. More importantly, these fluorescent CNCs exhibit a selective quenching effect toward Fe3+ ions; meanwhile, these CNCs exhibit negligible cytotoxicity and were internalized by cells. Therefore, these CNCs can be used as a fluorescence probe for detecting Fe3+ ions in living cells.

Optimization of homogenization-sonication technique for the production of cellulose nanocrystals from cotton linter

Recently, cellulose nanocrystals (CNCs) have attracted a significant interest in different fields including drug delivery, biomedical, and food applications. In this study, homogenization-ultrasonication as a non-hazardous, time-saving, and organic solvent free technique was applied for fabrication of CNCs from cotton linter, containing over 90% cellulose. First, acid hydrolysis was applied on raw cellulose using sulfuric acid at 55, 60 and 65% for 3, 5 and 7 min and at various homogenization speeds. Final CNCs were produced by ultrasonication (350 W) for 3 min. The physicochemical properties of CNCs, particle size, X-ray diffraction (XRD) pattern, Fourier Transform Infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), atomic force microscopy (AFM) and transmission electron microscopy (TEM) were studied. Production yield of CNCs was 59–72%, and their water holding capacity was two times higher than raw cellulose. The average length of CNCs was 133 nm with a width of 10 nm and the XRD pattern revealed a 82% crystallinity degree. The FTIR spectrum detected almost similar frequencies in the raw and crystalline cellulose, while intensity of CNC peaks was reduced. TEM results showed rod-like CNCs with a length of 229 nm. TGA results also showed that thermal stability of CNCs was reduced compared to raw cellulose.

In vitro toxicity assessment of hydrogel patches obtained by cation-induced cross-linking of rod-like cellulose nanocrystals.

With the purpose of designing active patches for photodynamic therapy of melanoma, transparent and soft hydrogel membranes (HMs) have been fabricated by cation-induced gelation of rod-like cellulose nanocrystals (CNCs) bearing negatively charged carboxylic groups. Na+ , Ca2+ , Mg2+ have been used as cross-linkers of cellulose nanocrystal (CNC). The biosafety of this material and of its precursors has been evaluated in vitro in cell cultures. Morphological changes, cell organelles integrity, and cell survival with the tetrazolium salt reduction (MTT) assay were utilized as tests of cytotoxicity. Preliminary investigation was performed by addition of the hydrogel components to the cell culture medium and by incubations of the CNC-HM in direct and indirect contact with a confluent monolayer of A375 melanoma cells. Direct contact assays suffered from interference of physical stress. Careful evaluation of cytotoxicity was obtained considering the overall picture provided by microscopy and biochemical tests performed with the CNC-HM in indirect contact with two melanoma cell lines (A375, M14) and human fibroblasts. CNCs have been demonstrated to be a safe precursor material and CNC-HMs have a good biocompatibility provided that the excess of cations, in particular of Ca2+ is removed. These results indicate that CNC and can be safely used to fabricate biomedical devices such as transparent hydrogel patches, although attention must be paid to the fabrication procedure.

Hierarchically spacing DNA probes on bio-based nanocrystal for spatial detection requirements

Sterically spacing and locating functional matters at the nanoscale exert critical effects on their application, especially for the fluorescence probes whose aggregation causes emission quenching. Here we achieved a hierarchical spacing strategy of DNA fluorescence probes for ion detection via locating them separately on rod-like cellulose nanocrystals (CNCs) and further isolating CNCs by pre-grafting long molecular chains. Controlling chemical structure of CNC and location degree could adjust the inter-space of DNA probes (with a molecular length of ca. 3.6 nm) in a range of 3.5–6.5 nm with a gradient about 0.2 nm. A length up to micrometer scale of the CNC nanorods was necessary to provide DNA probes with well-separated grafting locations and enough freedom, which brought a vast linear detection range from 10 nmol/L to 5 μmol/L of Hg2+ concentration. The abundant reactive sites on CNC allowed a grafting pre-location of poly (tert-butyl acrylate) (PtBA) to promote the isolation of DNA probes. Controlled radical polymerization was employed to adjust the length of PtBA molecular chains, which increased the linear sensitivity coefficient of Hg2+ detection by ca. 2.5 times. This hierarchical nanoscale spacing concept based on chemical design can hopefully conduce to the development of biosensor and medical diagnosis. A hierarchical spacing strategy was applied to separate DNA fluorescent probes on CNCs and detect ion concentration linearly. The first-level spacing was to locate probes uniformly on CNCs, obtaining a wide linear range; and the second-level spacing was to isolate CNCs with polymer, obtaining an increased linear coefficient.

Deconstruction of microfibrillated cellulose into nanocrystalline cellulose rods and mesogenic phase formation in concentrated low-modulus sodium silicate solutions

This work demonstrates for the first time the deconstruction of microfibrillated cellulose (MFC) into rod-like cellulose nanocrystals (CNCs) in concentrated low modulus sodium silicate solutions. To this aim, MFC suspensions at different concentrations were first treated in sodium hydroxide solutions and then amorphous silica powder was added. Optical microscopy and transmission electron microscopy observation showed how MFC was efficiently deconstructed into CNCs, evidencing the occurrence of a phase separation into an isotropic and mesogenic phase. The extracted CNCs were characterized by a remarkably higher length (600–1200 nm) in comparison with the plant-derived ones commonly reported in literature. FT-IR spectroscopy and 29Si MAS NMR confirmed that the Qn equilibrium of the suspended silicate species was affected, proportionally to the amount of MFC. It was also shown, that due to the excluded volume effect exerted by silicate anions, nematic or smectic ordering could be achieved for CNC concentrations far below the critical rod concentration predicted by the Doi-Edwards model.

Anisotropic Diffusion and Phase Behavior of Cellulose Nanocrystal Suspensions.

In this paper, we use dynamic light scattering in polarized and depolarized modes to determine the translational and rotational diffusion coefficients of concentrated rodlike cellulose nanocrystals in aqueous suspension. Within the range of studied concentrations (1-5 wt %), the suspension starts a phase transition from an isotropic to an anisotropic state as shown by polarized light microscopy and viscosity measurements. Small-angle neutron scattering measurements also confirmed the start of cellulose nanocrystal alignment and a decreasing distance between the cellulose nanocrystals with increasing concentration. As expected, rotational and translational diffusion coefficients generally decreased with increasing concentration. However, the translational parallel diffusion coefficient was found to show a local maximum at the onset of the isotropic-to-nematic phase transition. This is attributed to the increased available space for rods to move along their longitudinal axis upon alignment. This increased parallel diffusion coefficient thus confirms the general idea that rodlike particles gain translational entropy upon alignment while paying the price for losing rotational degrees of freedom. Once the concentration increases further, diffusion becomes more hindered even in the aligned regions due to a reduction in the rod separation distance. This leads once again to a decrease in translational diffusion coefficients. Furthermore, the relaxation rate for fast mode translational diffusion (parallel to the long particle axis) exhibited two regimes of relaxation behavior at concentrations where significant alignment of the rods is measured. We attribute this unusual dispersive behavior to two length scales: one linked to the particle length (at large wavevector q) and the other to a twist fluctuation correlation length (at low wavevector q) along the cellulose nanocrystal rods that is of a larger length when compared to the actual length of rods and could be linked to the size of aligned domains.

Microstructural development and mechanical performance of PLA/TPU blends containing geometrically different cellulose nanocrystals

Microstructural development and mechanical performance of poly(lactic acid) (PLA)/thermoplastic polyurethane (TPU) (80/20) blends containing single but geometrically different cellulose nanocrystals (CNCs) were investigated. The CNCs used in this study include cylindrical CNCs (ultrasonic treated), spherical CNCs (chemical treated) and rod-like CNCs (commercial), all characterized by particle size analyzer, atomic force microscopy (AFM) and X-ray diffraction. The melt viscoelastic results obtained for the melt compounded CNCs with PLA/TPU blend have implied a fine dispersion of both spherical and cylindrical CNCs which are preferentially localized in the PLA matrix and/or interface, while poorly dispersed rod-like CNCs were mostly accumulated in the TPU phase. These results were supported by AFM micrographs. More evidence was provided by scanning electron microscope micrographs which showed a decrease in TPU particle size in the blends filled with spherical and cylindrical CNCs, as a result of the nanoparticles’ localization in the PLA matrix and/or interface. The results of dynamic mechanical thermal analysis have revealed that the addition of spherical and cylindrical CNCs into the blends not only has compensated the reducing effect of TPU on the storage modulus but also has enhanced the modulus up to values even higher than that of PLA matrix. In contrast, the rod-like CNCs did not enhance the storage modulus of the blend significantly. More interestingly, the blend nanocomposite containing 3 wt% spherical CNCs exhibited a highly enhanced yield stress as well as significant elongation at break. This behavior could be explained by the induction of an interconnected type microstructure of spherical CNCs in which the nanoparticles are localized in PLA matrix, allowing the overlapping of stress counters around TPU particles and facilitating the stress transformation throughout the loaded sample. A similar enhancing effect but to a lesser extent, was obtained for those blend nanocomposites filled with cylindrical CNCs. In contrast to the other two types of CNCs, rod-like CNCs have weakened the mechanical performance of the blends. The results of fracture toughness obtained from single edge notch bending experiments have shown almost similar enhancing effect of the three types of CNCs on toughening. However, the sensitivity of the fracture test was not high enough to distinguish the effect of different CNCs on mechanical behavior of CNCs-filled blend nanocomposites.

Rheological properties of cellulose nanocrystal-polymeric systems

Rod-like cellulose nanocrystals (CNC) were incorporated into different systems containing polymers (most of them are soluble polysaccharides, such as chitosan, gum arabic, sodium alginate, hydroxypropyl methylcellulose and sodium carboxylmethyl cellulose) of varying charge properties and molecular structures. The dependence of the thickening and rheological behavior of CNC dispersion with concentration were compared with classic models for spheres. It is evident that rod-like particles are more effective in achieving viscosity enhancement at lower particle loading. By varying the concentrations of each polymeric system, the phase diagrams of non-absorbing and absorbing polymers were determined. The gelation behavior of anisotropic CNC dispersion in the presence of various kinds of polymers was investigated, and the thickening effect has the following trends: cationic > anionic > nonionic. In addition, the molecular weight and conformation of the polymer chains had an impact on the viscosity. Hydroxypropyl methylcellulose is the most effective in promoting gelation of 3 wt% CNC dispersion. Understanding the rheological properties of various CNC-polymer complexes will be critical for their application in oil and gas, food and consumer goods.

Tunable d-Limonene Permeability in Starch-Based Nanocomposite Films Reinforced by Cellulose Nanocrystals.

In order to control d-limonene permeability, cellulose nanocrystals (CNC) were used to regulate starch-based film multiscale structures. The effect of sphere-like cellulose nanocrystal (CS) and rod-like cellulose nanocrystal (CR) on starch molecular interaction, short-range molecular conformation, crystalline structure, and micro-ordered aggregated region structure were systematically discussed. CNC aspect ratio and content were proved to be independent variables to control d-limonene permeability via film-structure regulation. New hydrogen bonding formation and increased hydroxypropyl starch (HPS) relative crystallinity could be the reason for the lower d-limonene permeability compared with tortuous path model approximation. More hydrogen bonding formation, higher HPS relative crystallinity and larger size of micro-ordered aggregated region in CS0.5 and CR2 could explain the lower d-limonene permeability than CS2 and CR0.5, respectively. This study provided new insight for the control of the flavor release from starch-based films, which favored its application in biodegradable food packaging and flavor encapsulation.

Nanocrystals of cellulose allomorphs have different adsorption of cellulase and subsequent degradation

Suspensions of cellulose nanocrystals (CNCs) having different allomorphs were prepared from pulp and microcrystalline cellulose. Comparison found varying particle features. In situ observation of cellulose enzymes interacting with CNC I, II and III by atomic force microscopy (AFM) and transmission electron microscopy (TEM) found diverse adsorption of the enzymes on the CNC. Greater degradation to glucose was revealed for short rod-like CNC II and thin needle-like CNC III than CNC I, which were mainly due to their greater d-spacings for the (110) (CNC II) and (1–10) (CNC III) planes compared to the (200) spacing for CNC I. According to the model crystal structures, the surface areas for those planes where the enzymes would adsorb were also lager for CNC II and III. However, CNC III had significantly enhanced adsorption capability compared to the low affinity of CNC II. Enzymes tended to gather near hydrophobic surfaces that correspond to planes with small crystallite sizes on CNC III, and the enzymes caused breaks of nanocrystals during the degradation. Understanding the interactions between CNC allomorphs and cellulase would provide deep insights into biodegradation of crystalline cellulose as well as extensive application of CNCs.

Polymer brush guided templating on well-defined rod-like cellulose nanocrystals

Precisely grafted polymer brushes on cellulose nanocrystals guide the formation of silica and yield uniform CNC-based hybrid nanomaterials which are subsequently used in the fabrication of hollow and highly porous silica nanorods.

From Cellulose Nanospheres, Nanorods to Nanofibers: Various Aspect Ratio Induced Nucleation/Reinforcing Effects on Polylactic Acid for Robust-Barrier Food Packaging.

The traditional approach toward improving the crystallization rate as well as the mechanical and barrier properties of poly(lactic acid) (PLA) is the incorporation of nanocelluloses (NCs). Unfortunately, little study has been focused on the influence of the differences in NC morphology and dimensions on the PLA property enhancement. Here, by HCOOH/HCl hydrolysis of lyocell fibers, microcrystalline cellulose (MCC), and ginger fibers, we unveil the preparation of cellulose nanospheres (CNS), rod-like cellulose nanocrystals (CNC), and cellulose nanofibers (CNF) with different aspect ratios, respectively. All the NC surfaces were chemically modified by Fischer esterification with hydrophobic formate groups to improve the NC dispersion in the PLA matrix. This study systematically compared CNS, CNC, and CNF as reinforcing agents to induce different kinds of heterogeneous nucleation and reinforce the effects on the properties of PLA. The incorporation of three NCs can greatly improve the PLA crystallization ability, thermal stability, and mechanical strength of nanocomposites. At the same NC loading level, the PLA/CNS showed the highest crystallinity (19.8 ± 0.4%) with a smaller spherulite size (33 ± 1.5 μm), indicating that CNS, with its high specific surface area, can induce a stronger heterogeneous nucleation effect on the PLA crystallization than CNC or CNF. Instead, compared to PLA, the PLA/CNF nanocomposites gave the largest Young's modulus increase of 350 %, due to the larger aspect ratio/rigidity of CNF and their interlocking or percolation network caused by filler-matrix interfacial bonds. Furthermore, taking these factors of hydrogen bonding interaction, increased crystallinity, and interfacial tortuosity into account, the PLA/CNC nanocomposite films showed the best barrier property against water vapor and lowest migration levels in two liquid food simulates (well below 60 mg kg-1 for required overall migration in packaging) than CNS- and CNF-based films. This comparative study was very beneficial for selecting reasonable nanocelluloses as nucleation/reinforcing agents in robust-barrier packaging biomaterials with outstanding mechanical and thermal performance.

Simultaneous enhancement of elasticity and strength of Al2O3-based ceramics body from cellulose nanocrystals via gel-casting process

A green gel-casting method was developed by the combination of rod-like cellulose nanocrystals (CNC) and low toxicity monomer N, N-dimethylacrylamide (DMAA), which was proved to be a promising substitute of traditional neurotoxin monomer acrylamide (AM). The hydrophilic nature and homogeneous dispersion of CNC in aqueous suspension ensured the essential compatibility with the hydrosoluble polymerization system, and therefore provided remarkable mechanical enhancement of green body. The bending strength of the green body was highly increased by 68% with the introduction of 0.9 wt‰ CNC. Meanwhile, the fabricated green body exhibited significant improvement in flexibility and elasticity, with the unique bendable and recovery performances after drying treatment at room temperature for 1h. The computer stimulation by the COMSOL Multiphysics confirmed the special mechanical enhancement effect induced by the presence of highly-crystalline and rigid CNC.

Liquid Tubule Formation and Stabilization Using Cellulose Nanocrystal Surfactants.

Structured liquids, generated by the interfacial formation, assembly, and jamming of nanoparticle (NP)-surfactants at liquid/liquid interfaces, maintain all the desirable characteristics of each liquid, while providing a spatially structured framework. Herein, we show that rod-like cellulose nanocrystal (CNC)-based NP-surfactants, termed CNC-surfactants, are formed rapidly at the liquid/liquid interface, assemble into a monolayer, and, when jammed, offer a robust assembly with exceptional mechanical properties. Plateau-Rayleigh (PR) instabilities of a free-falling jet of an aqueous medium containing the CNCs into a toluene solution of amine end-functionalized polystyrene are completely suppressed, allowing the jetting of aqueous tubules that are stabilized when the CNC-surfactants are jammed at the interface. These results open a new platform for the additive manufacturing techniques, for example, three-dimensional (3D) printing, of all-liquid constructs.

Enhanced Toughness and Thermal Stability of Cellulose Nanocrystal Iridescent Films by Alkali Treatment

Iridescent films constructed by self-assembly of rod-like cellulose nanocrystals (CNCs) are mechanically brittle and of poor thermal stability. Herein, we demonstrate that the toughness and thermal stability of vacuum filtered CNC iridescent films could be significantly improved by a simple alkali treatment. The results reveal that the NaOH treatment can simultaneously alter the condensed physical structure and surface chemical structure of CNCs in their liquid crystal state while the self-assembled CNC chiral nematic structure still well retained. To be specific, the CNC was transformed from a higher crystallinity of form I to a lower crystallinity of form II, and the sulfate groups of CNCs were erased by alkali treatment, resulting in the remarkable enhancement in mechanical and thermal properties of CNC iridescent films. Of note, the unprecedented improvements in both tensile strength and toughness of CNC iridescent film have been achieved by alkali treatment. A sandwiched model with interdigitated mol...

Structural Transition in Liquid Crystal Bubbles Generated from Fluidic Nanocellulose Colloids.

The structural transition in micrometer-sized liquid crystal bubbles (LCBs) derived from rod-like cellulose nanocrystals (CNCs) was studied. The CNC-based LCBs were suspended in nematic or chiral nematic liquid-crystalline CNCs, which generated topological defects and distinct birefringent textures around them. The ordering and structure of the LCBs shifted from a nematic to chiral nematic arrangement as water evaporation progressed. These packed LCBs exhibited a specific photonic cross-communication property that is due to a combination of Bragg reflection and bubble curvature and size.

A Self-Healing Cellulose Nanocrystal-Poly(ethylene glycol) Nanocomposite Hydrogel via Diels–Alder Click Reaction

Self-healing hydrogels are particularly desirable for increased safety and functional lifetimes because of stress-induced deformation and propagation of cracks. In this paper, we report a tough, highly resilient, fast self-recoverable, and self-healing nanocomposite hydrogel, which builds an interpenetrated network encapsulating rod-like cellulose nanocrystals (CNCs) by flexible polymer chains of poly(ethylene glycol) (PEG). A thermally reversible covalent Diels–Alder click reaction between furyl-modified CNCs and maleimide-end-functionalized PEG was confirmed by Fourier transform infrared spectroscopy. Uniaxial tensile tests and unconfined compression tests displayed outstanding mechanical properties of the hydrogels with a high fracture elongation up to 690% and a fracture strength up to 0.3 MPa at a strain of 90%. Cyclic loading–unloading tests showed excellent self-recovery and antifatigue properties of the nanocomposite hydrogels. The self-healing capability of nanocomposite hydrogels assessed by ten...