All-cellulose composites from unbleached hardwood kraft pulp reinforced with nanofibrillated cellulose

In the present work, nanofibrillated cellulose (NFC) from bleached eucalyptus pulp was prepared, characterized and used as reinforcement in an unbleached eucalyptus fiber matrix. First, the NFC was fabricated through TEMPO-mediated oxidation and characterized for the degree of polymerization, water retention value, cationic demand and carboxyl content. Intrinsic mechanical properties were also calculated by applying the rule of mixtures, which determines the coupling (f _c) and efficiency factor (η _e) of cellulose nanofibrils within the matrix. The results showed that the average intrinsic tensile strength and Young’s modulus of NFC are estimated to be 6,919 MPa and 161 GPa, respectively. After characterization, the NFC was used as reinforcement in the preparation of biocomposites in the form of paper handsheets, which were physically and mechanically analyzed. The presence of NFC induced an increase in the density of biocomposites and significant enhancement of the mechanical properties as well as an important reduction in porosity. Finally, f _c and η _e were determined from the mean intrinsic properties.     

Carboxymethylated nanofibrillated cellulose: rheological studies

The rheological properties of carboxymethylated nanofibrillated cellulose (NFC), investigated with controlled shear rate- and oscillatory measurements, are reported for the first time. It was shown that the rheological properties of the studied system are similar to those reported for other NFC systems. The carboxymethylated NFC systems showed among other things high elasticity and a shear thinning behaviour when subjected to increasing shear rates. Further, the shear viscosity and storage modulus of the system displayed power-law relations with respect to the dry content of the NFC suspension. The exponential values, 2 and 2.4 respectively, were found to be in good agreement with both theoretical predictions and published experimental work. Furthermore, it was found that the pulp consistency at which NFC is produced affects the properties of the system. The rheological studies imply that there exists a critical pulp concentration below which the efficiency of the delamination process diminishes; the same adverse effect is also observed when the critical concentration is significantly exceeded due to a lower energy input during delamination.     

Carboxymethylated nanofibrillated cellulose: effect of monovalent electrolytes on the rheological properties

The effect of the ionic strength on the properties of a carboxymethylated nanofibrillated cellulose (NFC) system was investigated through rheological studies. It was shown that homogenization of pulp suspensions containing a high amount of a monovalent electrolyte leads to the production of NFC systems displaying a lower magnitude in the rheological response as compared with systems prepared at lower ionic strengths conditions. It was further shown that increasing the ionic strength of NFC suspensions after their manufacturing also results in a lowering of the rheological response. The decreased rheological response in the former case was postulated to be caused by a lowering of the delamination deficiency of the homogenization process, due to decreased swelling of the carboxymethylated pulp, caused by the screening of the charges. In the latter case (post-addition of the electrolyte), the lowering of the rheological response was postulated to be due to the compression of the electrostatic double layer, when the electrostatic repulsion between the charged fibrils diminished in the presence of the electrolyte.     

Rheology and rheokinetics of triethanolamine modified carboxymethyl hydroxyethyl cellulose

To meet requirements of fracturing fluid thickener, triethanolamine was used to modify carboxymethyl hydroxyethyl cellulose (CMHEC) to obtain product called T-CMHEC of high viscosity. Rheological properties of CMHEC and T-CMHEC solutions were investigated to compare its structure and rheological performance, including viscosity, flow curve, thixotropy, and viscoelasticity. Viscosities of CMHEC and T-CMHEC solutions are, respectively, 19.0 and 63.2?mPa?·?s for the same concentration of 0.3%. Viscosity of T-CMHEC solutions is 3.3 times of CMHEC ones. Besides, the thixotropy and viscoelasticity of T-CMHEC system are both getting stronger than before. In summary, the T-CMHEC system shows better rheological performance after modification. Crosslinking process of T-CMHEC system is investigated under steady shear under different conditions, containing shear rates, concentrations of crosslinking agent, concentrations of pH adjuster, and temperature. Viscosity curves changing with time are obtained during crosslinking process. Four-parameter crosslinking rheokinetics equation is suitable to fit the viscosity curves under different conditions. Study on crosslinking process of T-CMHEC solutions is helpful to deepen the understanding on gel formation, and provides a theoretical basis for its application.     

Rheological properties of hexadecyl dimethyl amine modified carboxymethyl hydroxyethyl cellulose solutions and its gelling process

To obtain a new fracturing fluid viscosifier, hexadecyl dimethyl amine was used to modify carboxymethyl hydroxyethyl cellulose (CMHEC) to obtain a product called HD-CMHEC with high viscosity. The rheological properties of HD-CMHEC solutions and CMHEC solutions were studied. For the concentration of 0.3%, the viscosity of CMHEC and HD-CMHEC solutions is, respectively, 19.0?mPa?·?s and 73.6?mPa?·?s, respectively. The viscosity of HD-CMHEC solution increases 2.8 times than before. The thixotropy and viscoelasticity of HD-CMHEC solutions become stronger. As a typical viscoelastic fluid, HD-CMHEC solutions show better rheological performance than that of CMHEC solutions. The gelling process of HD-CMHEC solutions under steady shear was studied in detail. The concentrations of HD-CMHEC solutions, shear rates, and crosslinking agent were investigated. Viscosity versus time curves during the crosslinking process were obtained. The four-parameter crosslinking rheokinetics equation can describe the gelling process of HD-CMHEC solutions under different conditions well. Study on the gelling process of HD-CMHEC solutions under steady shear contributes to the understanding of gel formation, and provides theoretical guidance for exploration and exploitation of the system.     

Water redispersible cellulose nanofibrils adsorbed with carboxymethyl cellulose

Cellulose nanofibrils (CNFs) are difficult to redisperse in water after they have been completely dried due to the irreversible agglomeration of cellulose during drying. Here, we have developed a simple process to prepare water-redispersible dried CNFs by the adsorption of small amounts of carboxymethyl cellulose (CMC) and oven drying. The adsorption of CMC onto CNFs in water suspensions at 22 and 121 °C was studied, and the adsorbed amount of CMC was measured via conductimetric titration. The water-redispersibility of dried CNFs adsorbed with different amounts of CMC was characterized by sedimentation test. Above a critical threshold of CMC adsorption, i.e. 2.3 wt%, the oven dried CNF–CMC sample was fully redispersible in water. The morphology, rheological, and mechanical properties of water-redispersed CNF–CMC samples were investigated by field emission scanning electron microscopy, viscosity measurement, and tensile test, respectively. The water-redispersed CNFs preserved the original properties of never dried CNFs. This new method will facilitate the production, transportation and storage, and large-scale industrial applications of CNFs.     

Rheological properties of polycomplex gels of carboxymethyl cellulose with urea-formaldehyde oligomers

Structural and rheological properties of polycomplex gels of sodium carboxymethyl cellulose (Na-CMC) with urea-formaldehyde oligomers were studied at various component ratios at 298–343 K. The polycomplexes were examined by IR spectroscopy. Mechanical characteristics of solutions of Na-CMC and its complexes with urea-formaldehyde oligomers and the size of structural units of these solutions were determined.     

Homogeneous and porous modified bacterial cellulose achieved by in situ modification with low amounts of carboxymethyl cellulose

To improve the rehydration ability of bacterial cellulose (BC), many macromolecules have been used as modifiers in previous reports. However, the aggregation of additives in the BC matrix appears to be inevitable. We investigated different parts of a BC pellicle, which was achieved by in situ modification with carboxymethyl cellulose (CMC) in culture with Gluconacetobacter xylinus ATCC53582 or Enterobacter sp. FY-07. We observed a concentration gradient of CMC in the BC pellicle from G. xylinus ATCC53582, but not with Enterobacter sp. FY-07. Low concentrations of CMC (0.01 %, m/v) are sufficient to modify BC in situ in culture with Enterobacter sp. FY-07, in which CMC could sufficiently contact with the newly formed BC. The crystallinity of the modified BC decreased by more than 39.8 %, and its rehydration ability and water holding capacity increased by 43.3 and 31.0 %, respectively. Unlike the pellicle of modified BC achieved from obligate aerobes, such as G. xylinus ATCC53582, that produced by Enterobacter sp. FY-07 exhibited better homogeneity and porosity.     

Grinding process for the production of nanofibrillated cellulose based on unbleached and bleached bamboo organosolv pulp

Nanofibrillated cellulose (NFC) is a type of nanomaterial based on renewable resources and produced by mechanical disintegration without chemicals. NFC is a potential reinforcing material with a high surface area and high aspect ratio, both of which increase reinforcement on the nanoscale. The raw materials used were unbleached and bleached bamboo organosolv pulp. Organosolv pulping is a cleaner process than other industrial methods (i.e. Kraft process), as it uses organic solvents during cooking and provides easy solvent recovery at the end of the process. The NFC was produced by treating unbleached and bleached bamboo organosolv pulps for 5, 10, 15 and 20 nanofibrillation cycles using the grinding method. Chemical, physical and mechanical tests were performed to determine the optimal condition for nanofibrillation. The delamination of the S2 layer of the fibers during nanofibrillation contributed to the partial removal of amorphous components (mainly lignin), which have low polarity and improved the adhesion of the fibers, particularly the unbleached cellulose. The transverse modulus of elasticity of the unbleached NFC was highest after 10 nanofibrillation cycles. Further treatment cycles decreased the modulus due to the mechanical degradation of the fibers. The unbleached NFC produced by 10 cycles have a greater transverse modulus of elasticity, the crystallite size showed increase with the nanofibrillation, and after 5 nanofibrillation cycles, no differences are observed in the morphology of the fibers.     

Characterization on conduction properties of carboxymethyl cellulose/kappa carrageenan blend-based polymer electrolyte system

The present work deals with the development of carboxymethyl cellulose (CMC) blended with kappa carrageenan (KC) as a host-based polymer electrolyte (PE) system. The CMC/KC films were successfully prepared using solution casting method and were characterized through electrical impedance spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) methods, respectively. The FTIR spectrum revealed that the significant region of interaction transpires at wave number 1,057, 1,326, 1,584, and 3,387?cm^?1 which correspond to the bending of C–O–C, bending of –OH, asymmetric of –COO^? as well as the stretching of –OH, respectively. It has also been demonstrated that the complexation process occurred between CMC and KC. The CMC/KC blend PE system with a ratio of 80:20 achieved an optimum conductivity of 3.91?×?10^?7?S?cm^?1 and had the lowest crystallinity percentage as suggested by the XRD analysis.     

Rheological properties of carboxymethyl cellulose (CMC) solutions

In this study, we investigated the way of predicting two critical concentrations of sodium carboxymethyl cellulose (CMC) solutions using simple experimental procedures with a rotational rheometer. It was found that, above a critical shear rate, all CMC solutions (0.2 to 7 wt.%) exhibit shear-thinning behavior and the flow curves could be described by the Cross model. A first critical CMC concentration c*, transition to semidilute network solution, was determined using the following methods (1) study of the flow curve shapes, (2) Cross model parameters, (3) plot of the specific viscosity vs the overlap parameter, and (4) empirical structure–properties relationships. Furthermore, both creep and frequency-sweep measurements showed that the solutions behaved as viscoelastic materials above a second critical CMC concentration c** (transition to concentrated solution). The characterization of CMC solutions was completed with a time-dependent viscosity study that showed that the CMC solutions exhibited strong thixotropic behavior, especially at the highest CMC concentrations.     

Adsorption of carboxymethyl cellulose on polymer surfaces: evidence of a specific interaction with cellulose

The adsorption of carboxymethyl cellulose (CMC), one of the most important cellulose derivatives, is crucial for many scientific investigations and industrial applications. Especially for surface modifications and functionalization of materials, the polymer is of interest. The adsorption properties of CMC are dependent not only on the solutions state, which can be influenced by the pH, temperature, and electrolyte concentration, but also on the chemical composition of the adsorbents. We therefore performed basic investigation studies on the interaction of CMC with a variety of polymer films. Thin films of cellulose, cellulose acetate, deacetylated cellulose acetate, polyethylene terephthalate, and cyclo olefin polymer were therefore prepared on sensors of a QCM-D (quartz crystal microbalance) and on silicon substrates. The films were characterized with respect to the thickness, wettability, and chemical composition. Subsequently, the interaction and deposition of CMC in a range of pH values without additional electrolyte were measured with the QCM-D method. A comparison of the QCM-D results showed that CMC is favorably deposited on pure cellulose films and deacetylated cellulose acetate at low pH values. Other hydrophilic surfaces such as silicon dioxide or polyvinyl alcohol coated surfaces did not adsorb CMC to a significant extent. Atomic force microcopy confirmed that the morphology of the adsorbed CMC layers differed depending on the substrate. On hydrophobic polymer films, CMC was deposited in the form of larger particles in lower amounts whereas hydrophilic cellulose substrates were to a high extent uniformly covered by adsorbed CMC. The chemical similarity of the CMC backbone seems to favor the irreversible adsorption of CMC when the molecule is almost uncharged at low pH values. A selectivity of the cellulose CMC interaction can therefore be assumed. All CMC treated polymer films exhibited an increased hydrophilicity, which confirmed their modification with the functional molecule.     

Functionalization of nanofibrillated cellulose with silver nanoclusters: fluorescence and antibacterial activity

Native cellulose nanofibers are functionalized using luminescent metal nanoclusters to form a novel type of functional nanocellulose/nanocluster composite. Previously, various types of cellulose fibers have been functionalized with large, non-luminescent metal nanoparticles. Here, mechanically strong native cellulose nanofibers, also called nanofibrillatedcellulose (NFC), microfibrillatedcellulose (MFC) ornanocellulose, disintegrated from macroscopic cellulose pulp fibers are used as support for small and fluorescent silver nanoclusters. The functionalization occurs in a supramolecular manner, mediated by poly(methacrylic acid) that protects nanoclusters while it allows hydrogen bonding with cellulose, leading to composites with fluorescence and antibacterial activity.     

Aspects on nanofibrillated cellulose (NFC) processing,rheology and NFC-film properties

This communication summarizes the salient features and mechanisms in high-pressure homogenization of wood fibres in order to make nanofibrillar cellulose (NFC).The energy-efficiency of delamination of fibres and the clogging tendency of fibres in high-pressure homogenizers/microfluidizers during delamination are critical and ways to alleviate these problems are reviewed.It is shown that the mechanical properties of NFC-films can be estimated from the Page equation. Usually, the evolution of the tensile strength properties of NFC-films increases with the extent of film delamination to reach a saturation value, which can be deduced from first principles using the Page equation.Finally, the evolution of the rheological features of NFC-gels and the barrier properties are reviewed and the estimation the nanofraction content in NFC-gels is being discussed.     

Influence of drying restraint on physical and mechanical properties of nanofibrillated cellulose films

Nanofibrillated cellulose (NFC) is a renewable and biodegradable fibril that possesses high strength and stiffness resulting from high level hydrogen bonding. Films made from NFC shrink and distort as they transition from a wet state (20 wt% solids) to a state of moisture equilibrium (90 wt% solids at 50 % RH, 23 °C). Material distortions are driven by development of moisture gradients within the fibril network and effectively reduce mechanical performance. For this study, NFC was extracted from softwood holocellulose by first employing a chemical pretreatment [(2,2,6,6-tetramethylpiperidin-1-yl)oxyl catalyzed oxidation] followed by mechanical fibrillation using ultrasound energy. To assess the problem of film distortion, neat NFC films were dried at 50 % RH, 23 °C under one of the following three restraint conditions: fully restrained, partially restrained, and uniaxially drawn. The influence of restraint condition on the resulting physical and mechanical properties was evaluated. Raman and X-ray results showed that fibrils in the uniaxially drawn specimens tended to align with the drawing axis, whereas no in-plane orientation effects were observed for the fully or partially restrained specimens. Fully restrained specimens had a respective strength and stiffness of 222 MPa and 14 GPa in every (in-plane) direction. However, samples that were wet-drawn to a 30 % strain level had a respective strength and stiffness of 474 MPa and 46 GPa in the direction of draw. Mechanical properties for axially drawn specimens had both fibril alignment and fibril straightening contributions.     

Effect of fiber modification with carboxymethyl cellulose on the efficiency of a microparticle flocculation system

Carboxymethyl cellulose (CMC) has been used widely to enhance dry strength of paper and uniformity of sheet in the papermaking industry. Besides these positive effects, it may affect the fines retention and dewatering processes negatively. These negative effects are mainly seen when fiber modifications with high CMC dosages are studied in laboratory scale. In this paper, the effect of fiber modification with CMC on the deposition of precipitated calcium carbonate (PCC) and on the dewatering process in the presence of cationic polyacrylamide (CPAM)/bentonite microparticle flocculation system is examined. It was determined that fiber modification with 10 mg g⁻¹ of CMC decreased PCC deposition at the initial addition of CPAM and gave better PCC deposition at 2 mg g⁻¹ of CPAM. It was also observed that PCC deposition on unmodified fibers is higher at lower CPAM concentration. PCC deposition was found as almost stable after a maximum value obtained at 0.5 mg g⁻¹ of bentonite concentration for fiber modified with 40 mg g⁻¹ of CMC. This indicates that interaction between CPAM and bentonite particles changed due to higher surface charge and CMC conformation on fibers. Results of the dewatering experiments showed that CMC modification increased the drainage time due to a denser and more plugged sheet. This negative effect was compensated with higher concentrations of CPAM and bentonite. On the other hand, dewatering is also affected by the mass ratio of CMC and CPAM, which was not the optimum one in this study at lower of CPAM. Thus, the increase in the drainage time in the presence of CMC on the fiber surface could be also caused by incorrect ratios of chemicals because the effect of CMC on the drainage time was not observed at higher concentrations of CPAM.     

Processing of wood-based microfibrillated cellulose and nanofibrillated cellulose,and applications relating to papermaking: a review

As an emerging cellulosic nanomaterial, microfibrillated cellulose (MFC) and nanofibrillated cellulose (NFC) have shown enormous potential in the forest products industry. The forest products industry and academia are working together to realise the possibilities of commercializing MFC and NFC. However, there are still needs to improve the processing, characterisation and material properties of nanocellulose in order to realise its full potential. The annual number of research publications and patents on nanocellulose with respect to manufacturing, properties and applications is now up in the thousands, so it is of the utmost importance to review articles that endeavour to research on this explosive topic of cellulose nanomaterials. This review examines the past and current situation of wood-based MFC and NFC in relation to its processing and applications relating to papermaking.     

Physical properties of sodium carboxymethyl cellulose molecules adsorbed on a polyacrylonitrile ultrafiltration membrane

Ultrafiltration experiments showed that the graphical relationship between flux and pressure was a straight line through the origin, provided that the wall shear rate of the bulk fluid was higher than a certain critical value or the pressure was below a critical value. A higher critical shear rate corresponded to a higher critical pressure. For these conditions the total hydrodynamic resistance was only slightly greater than the resistance of a clean membrane for pure water. This additional resistance is attributed to a (mono-) molecular layer of macromolecules which is adsorbed on the membrane in the absence of both a concentration polarization layer and a conventional gel layer.At steady state ultrafiltration conditions, an increase of the flux was obtained after replacing the bulk solution by distilled water at constant experimental conditions, which is attributed to the removal of the concentration polarization layer whereas a mono-molecular layer of macromolecules remained adsorbed on the membrane. For these conditions the flux vs. pressure relationship showed a qualitatively similar behaviour as for ultrafiltration conditions.At a constant shear rate the flux vs. pressure relationship was a straight line through the origin for pressures below the critical pressure, the value of which increased with the shear rate. This linear relationship was reversible, showing no hysteresis. However, if the pressure was higher than its critical value, the flux vs. pressure relationship was no longer a straight line as a consequence of the occurrence of an additional hydrodynamic resistance which did not disappear entirely upon lowering the pressure below its critical value. For the explanation of these phenomena it is assumed that freely moveable parts of the adsorbed macromolecules can block the entrance region of the pores in the membrane if the pressure is beyond its critical value.On the other hand, for pressures below the critical pressure or shear rates beyond the critical shear rate, the pores of the membrane are deblocked. This blocking and deblocking of pores by parts of adsorbed macromolecules apparently takes place in a partly reversible way.