Cellulose Nanocrystals In Water Research Articles

Solvent-Dependent Dynamics of Cellulose Nanocrystals in Process-Relevant Flow Fields.

Flow-assisted alignment of anisotropic nanoparticles is a promising route for the bottom-up assembly of advanced materials with tunable properties. While aligning processes could be optimized by controlling factors such as solvent viscosity, flow deformation, and the structure of the particles themselves, it is necessary to understand the relationship between these factors and their effect on the final orientation. In this study, we investigated the flow of surface-charged cellulose nanocrystals (CNCs) with the shape of a rigid rod dispersed in water and propylene glycol (PG) in an isotropic tactoid state. In situ scanning small-angle X-ray scattering (SAXS) and rheo-optical flow-stop experiments were used to quantify the dynamics, orientation, and structure of the assigned system at the nanometer scale. The effects of both shear and extensional flow fields were revealed in a single experiment by using a flow-focusing channel geometry, which was used as a model flow for nanomaterial assembly. Due to the higher solvent viscosity, CNCs in PG showed much slower Brownian dynamics than CNCs in water and thus could be aligned at lower deformation rates. Moreover, CNCs in PG also formed a characteristic tactoid structure but with less ordering than CNCs in water owing to weaker electrostatic interactions. The results indicate that CNCs in water stay assembled in the mesoscale structure at moderate deformation rates but are broken up at higher flow rates, enhancing rotary diffusion and leading to lower overall alignment. Albeit being a study of cellulose nanoparticles, the fundamental interplay between imposed flow fields, Brownian motion, and electrostatic interactions likely apply to many other anisotropic colloidal systems.

Dispersion Characteristics of Cellulose Nanocrystals in Water and Ethanol Using Small-Angle X-Ray Scattering and Scanning Probe Microscopy

Dispersion Characteristics of Cellulose Nanocrystals in Water and Ethanol Using Small-Angle X-Ray Scattering and Scanning Probe Microscopy

Obtaining electrospun mats from waterborne polyurethanes containing cellulose nanocrystals

Cellulose nanocrystals (CNC) have attracted great interest as nanoreinforcement due to their excellent mechanical properties. Furthermore, their dispersibility in water makes them suitable for their incorporation in many aqueous systems such as waterborme polyurethanes (WBPU). WBPUs ​​have gained attention due to their versatility and ability to ajust their properties to a wide range of applications, in addition to their non-toxicity, non-flammability and environmental sustainability. Therefore, in this work a waterborne polyurethane has been synthesized for the preparation of nanocomposites with different contents of cellulose nanocrystals, incorporated by different routes, the classical mixing by sonication once the waterborne polyurethane has been synthesized, and the alternative in-situ by adding the CNCs in water during the WBPU synthesis, just in the phase inversion step. The obtained dispersions have been used in the preparation of films by casting and mats by electrospinning. The films and mats have been characterized from the point of view of their physical-chemical, morphological and superficial properties.

Rheological insights on the evolution of sonicated cellulose nanocrystal dispersions

Cellulose nanocrystals (CNCs) are promising biomaterials, but their tendency to agglomerate when dried limits their use in several applications. Ultrasonication is commonly used to disperse CNCs in water, bringing enough energy to the suspension to break agglomerates. While the optimized parameters for sonication are now well defined for small volumes of low concentration CNC suspensions, a deeper understanding of the influence of the dispersing process is needed to work with larger volumes, at higher concentrations. Herein, rheology is used to define the distribution and dispersion states upon ultrasonication of a 3.2 wt% CNC suspension. After considering the importance of the measurement sampling volume, the behavior of a more concentrated suspension (6.4 wt%) is examined and compared with a never-dried suspension of the same concentration to validate the dispersion state.

Moisture sensitivity and compressive performance of 3D-printed cellulose-biopolyester foam lattices

Abstract Biobased, foam-like polyester composite materials were 3D-printed from a thermoset paste formulation. This paste formulation was composed of sebacic acid, glycerol, citric acid, and cellulose nanocrystals in water and ethanol with potassium chloride as a salt porogen. Thin walls and lattices were 3D-printed with geometry selected to facilitate post-printing processes such as water removal during polyester curing and the post-curing removal of the salt porogen. The compressive performance of these moisture-sensitive lattice structures was investigated after conditioning at different humidity levels and by water immersion. Finite element analysis was used to simulate the compressive performance of these porous lattice structures using a crushable foam material model. Addition of plant triglyceride oils from sunflower and coconut were trialled to modify the compressive performance and moisture sensitivity. Addition of 5 wt% coconut oil to the formulation prior to 3D-printing was found to lower the cured material’s stiffness under dry conditions while increasing the compressive plateau strength of the lattice structures after water immersion.

Bioinspired Thermoresponsive Xyloglucan–Cellulose Nanocrystal Hydrogels

Thermoresponsive hydrogels present unique properties, such as tunable mechanical performance or changes in volume, which make them attractive for applications including wound healing dressings, drug delivery vehicles, and implants, among others. This work reports the implementation of bioinspired thermoresponsive hydrogels composed of xyloglucan (XG) and cellulose nanocrystals (CNCs). Starting from tamarind seed XG (XGt), thermoresponsive XG was obtained by enzymatic degalactosylation (DG-XG), which reduced the galactose residue content by ∼50% and imparted a reversible thermal transition. XG with native composition and comparable molar mass to DG-XG was produced by an ultrasonication treatment (XGu) for a direct comparison of behavior. The hydrogels were prepared by simple mixing of DG-XG or XGu with CNCs in water. Phase diagrams were established to identify the ratios of DG-XG or XGu to CNCs that yielded a viscous liquid, a phase-separated mixture, a simple gel, or a thermoresponsive gel. Gelation occurred at a DG-XG or XGu to CNC ratio higher than that needed for the full surface coverage of CNCs and required relatively high overall concentrations of both components (tested concentrations up to 20 g/L XG and 30 g/L CNCs). This is likely a result of the increase in effective hydrodynamic volume of CNCs due to the formation of XG-CNC complexes. Investigation of the adsorption behavior indicated that DG-XG formed a more rigid layer on CNCs compared to XGu. Rheological properties of the hydrogels were characterized, and a reversible thermal transition was found for DG-XG/CNC gels at 35 °C. This thermoresponsive behavior provides opportunities to apply this system widely, especially in the biomedical field, where the mechanical properties could be further tuned by adjusting the CNC content.

Photonic composite materials from cellulose nanorods and clay nanolayers

Cellulose nano crystals (CNCs) are promising materials for energy efficient buildings related to the control of reflectivity and heat absorption/reflection of light. In this sense it is important to improve CNCs films fire retardant properties, which can be achieved by adding clays. Cellulose nanocrystals (CNCs) and nanolayers obtained from Sodium Fluorohectorite (NaFh) synthetic clay are both known to form liquid crystalline phases in aqueous suspensions. CNCs form cholesteric phases, which structure is preserved after water evaporation, while dry NaFh nanolayers aligned films collapse. In this initial work, it is shown that CNCs are compatible with NaFh clay. We demonstrate that the liquid crystalline phase of CNCs in water is not destroyed by the presence of NaFh nanolayers. The NaFh nanolayers act as planar anchoring surfaces to the cellulose nanorods and, after evaporation of the water coloured films are obtained. The precursor solutions and the photonic films were investigated by Describe several techniques.

Characterization of the redispersibility of cellulose nanocrystals by particle size analysis using dynamic light scattering

Cellulose nanocrystals (CNCs), which are derived from the most abundant and inexhaustible natural polymer, cellulose, have received significant interest owing to their mechanical, optical, chemical, and rheological properties. In order to transport CNC products conveniently and efficiently, they are ideally dried and stored as powders using freeze-drying or spray-drying technologies. The redispersibility of CNC powders is quite important for their end use; hence, a convenient method is required to characterize the redispersibility of CNC powders. In this paper, the possibility of characterizing the redispersibility of CNC powders by particle size analysis using dynamic light scattering (DLS) was investigated by comparing the results from transmission electron microscopy (TEM) and DLS. The particle size obtained with DLS approximately matched that obtained with TEM. Compared with TEM, DLS is a quick and convenient method to measure the particle size distribution of CNCs in water. Two kinds of dispersing methods, sonication and high-speed shearing, and two kinds of CNCs prepared by different methods, sulfuric acid hydrolysis and the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) oxidization method, were used to study the redispersibility of CNCs. Sonication was more efficient than the high-speed shearing method for nanoscale dispersion of CNC powders in water. CNCs prepared by sulfuric acid hydrolysis could be more easily redispersed in water than those prepared by TEMPO oxidation.

Aqueous suspensions of cellulose nanocrystals as water-based lubricants

The tribological tests were performed on a pin on cylinder tribometer, in order to investigate the application of cellulose nanocrystals (CNC) as additives in water-based lubricants. The coefficient of friction and wear between a stainless steel shaft and chrome steel ball were measured in the presence of CNC lubricant with different concentrations. The effect of the normal force, the rotational speed and the shaft diameter on the coefficient of friction and wear were studied as well. It was found that adding 2 wt% of CNC in water improved lubrication and provided a very low friction coefficient of approximately 0.09. The wear depth and width were reduced by more than 50%. The improvement of the coefficient of friction and wear was mainly due to the high strength and alignment of CNC rods.

Ultrasonication of spray- and freeze-dried cellulose nanocrystals in water

The structural and rheological properties of aqueous suspensions of spray-dried cellulose nanocrystals (CNCs) were investigated and compared to those of freeze-dried. The cellulose nanocrystals were obtained from sulfuric acid hydrolysis of wood pulp. Ultrasonication was used to disperse cellulose nanocrystals in Milli-Q water and the power applied during ultrasonication was shown to be the controlling parameter for their dispersion, more than total energy. Dynamic light scattering measurements showed a decrease of the average hydrodynamic diameter down to the same limiting value, i.e. ∼75 nm, for both spray and freeze-dried cellulose nanocrystals. Since the same maximum dispersion state was reached for both CNC types, it indicated that the spray drying process did not limit dispersion, provided that sufficient ultrasonication was provided. Moreover, no desulfation occurred during ultrasonication at ambient temperature. Strong ultrasonication also caused a decrease of intrinsic viscosity, along with an increase in maximum packing concentration. These properties were correlated to agglomerates break-up, which released both ions and water in suspension. The ionic strength increase may lead to a thinner electrostatic double layer surrounding the cellulose nanocrystals, reducing their apparent concentration.

Order and gelation of cellulose nanocrystal suspensions: an overview of some issues.

Cellulose nanocrystals (CNCs) are polydisperse rod-shaped particles of crystalline cellulose I, typically prepared by sulfuric acid hydrolysis of natural cellulose fibres to give aqueous colloidal suspensions stabilized by sulfate half-ester groups. Sufficiently dilute suspensions are isotropic fluids, but as the concentration of CNC in water is increased, a critical concentration is reached where a spontaneously ordered phase is observed. The (equilibrium) phase separation of the ordered chiral nematic phase is in competition with a tendency of the CNC suspension to form a gel. Qualitatively, factors that reduce the stability of the CNC suspension favour the onset of gelation. The chiral nematic structure is preserved, at least partially, when the suspension dries. Solid chiral nematic films of cellulose are of interest for their optical and templating properties, but the preparation of the films requires improvement. The processes that govern the formation of solid chiral nematic films from CNC suspensions include phase separation, gelation and also the effects of shear on CNC orientation during evaporation. Some insight into these processes is provided by polarized light microscopy, which indicates that the relaxation of shear-induced orientation to give a chiral nematic structure may occur via an intermediate twist-bend state.This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.

Effect of Surface Charge on Surface-Initiated Atom Transfer Radical Polymerization from Cellulose Nanocrystals in Aqueous Media

Cellulose nanocrystals (CNCs) with different charge densities were utilized to examine the role of electrostatic interactions on surface-initiated atom transfer radical polymerization (SI-ATRP) in aqueous media. To this end, growth of hydrophilic uncharged poly(N,N-dimethylacrylamide) (PDMAM) brushes was monitored by electrophoresis, (1)H NMR spectroscopy, and dynamic light scattering (DLS). Molecular weight and polydispersity of PDMAM brushes was determined by GPC analysis of hydrolytically cleaved polymers. Initiator and polymer brush grafting densities, and thus, initiator efficiencies were derived from elemental analysis. Higher initiator efficiency of polymer brush growth was observed for CNCs with higher anionic surface sulfate half-ester group density, but at the expense of high polydispersity caused by inefficient deactivation. PDMAM grafts with number-average molecular weights up to 530 kDa and polydispersity indices <1.5 were obtained under highly diluted monomer concentrations. The role of surface chemistry on the growth of neutral polymer brushes from CNCs in water is emphasized and a model of the interfacial region at the onset of polymerization is proposed. The results presented here could have implications for other substrates that present surface charges and for the assumption that the kinetics of Cu-mediated SI-CRP are analogous to those conducted in solution.

Two different incorporation routes of cellulose nanocrystals in waterborne polyurethane nanocomposites

The renewability, availability and low-cost of eco-friendly cellulose nanocrystals (CNC), have gaining attention for nanocomposites preparation due to their unique properties in the nanoscale and their water dispersibility, becoming a suitable reinforcement in waterborne polyurethane (WBPU) dispersions. Thereby, a WBPU matrix with a high hard segment content (about 48wt%) was synthesized resulting in a dispersion of low particle size with a narrow distribution analyzed by means of dynamic light scattering and visually stable over 6months. The CNC reinforcement isolated from microcrystalline cellulose via acid hydrolysis lead to CNC with a high length/diameter aspect ratio of about 31, determined by atomic force microscopy. In the nanocomposites preparation, two incorporation routes were designed for analyzing the influence of CNC disposition in the nanocomposites films: the classical mixing by sonication or in-situ adding CNC in water during particles formation step. The influence of CNC addition route and their disposition in the final properties of nanocomposites were analyzed by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, atomic force microscopy and dynamic water contact angle, observing considerable variations by adding 1 and 3wt% of CNC. The reinforcement addition route influenced the WBPU–CNC interactions, which resulted more effective by the alternative in-situ incorporation method. The CNC incorporation restricted the crystallization of soft domains, in a higher extend in nanocomposites prepared by in-situ route, and improved the thermomechanical stability. The studied CNC incorporation routes lead to different dispositions of CNC in the matrix, resulting in different mechanical performance, providing a suitable stress transfer in the nanocomposite and diverse hydrophilic behavior, comparing with the WBPU matrix.

Adsorption of polyethylene glycol (PEG) onto cellulose nano-crystals to improve its dispersity

In this work, the adsorption of polyethylene glycol (PEG) onto cellulose nano-crystals (CNC) was investigated for preparing re-dispersible dried CNC. Results showed that the re-dispersity of CNC in water can be significantly enhanced using a PEG1000 dosage of 5wt% (based on the dry weight of CNC). The elemental analysis confirmed the adsorption of PEG onto the CNC surface. Transmission electron microscopy (TEM) was used to characterize the dry powder and indicated that the irreversible agglomeration of CNC after drying was essentially eliminated based on the PEG adsorption concept. Thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD) suggested that CNC crystallinity and thermal stability were not affected by the adsorption of PEG. Thus, the adsorption of PEG has great potential for producing re-dispersible powder CNC.

Cellulose nanocrystals and carboxymethyl cellulose from olive stones and their use to improve paper sheets properties

Olive stones wastes were used to prepare cellulose nanocrystals (CNC) and carboxymethyl cellulose (CMC). Transmission electron microscopy images showed that the prepared nanocrystals had width and length of about 5–7 nm and 174–234 nm, respectively. Mixtures containing CMC and CNC in water were prepared and the effect of CNC ratio (from 2.5–10 wt.% based on CMC) on viscosity of CMC solution was studied. Films casted from CMC/CNC mixtures were characterised regarding their crystallinity, tensile strength, and dynamic mechanical thermal properties. In addition, the prepared mixtures were used for coating of paper sheets and the effect of coating on mechanical properties (breaking length and tear factor), water absorption, and air permeability of paper sheets was studied. Presence of CNC in the coating mixtures resulted in improving mechanical properties and decreasing water absorption and air permeability of paper sheets as compared to paper sheets coated with neat CMC coating mixture.