Cellulose Nanofibrils Concentrations Research Articles

Direct-ink-writable nanocellulose ternary hydrogels via one-pot gelation with alginate and calcium montmorillonite

Nanocellulose hydrogels are promising to replace synthetic ones for direct ink writing (DIW)-based 3D printing biobased applications. However, less gelation strength and low solid content of the hydrogels limit the printability and subsequent fidelity of the dried object. Herein, a biobased, ternary DIW hydrogel ink is developed by one-pot gelation of cellulose nanofibrils (CNF), sodium alginate (SA), and Ca-montmorillonite (Ca-MMT) via in situ ionic crosslinking. The addition of Ca-MMT into CNF/SA formulation simultaneously increases the solid content and gelation strength of the hydrogel. The resultant hydrogels exhibit shape recovery after compression. The optimal CNF concentration in the hydrogel is 1.2 wt%, enabling the highest compressive mechanical performance of the scaffolds. A series of complex, customized shapes with different curvatures and three-dimensional structures (e.g., high-curvature letters, pyramids, human ears, etc.) can be printed with high fidelity before and after drying. This study opens an avenue on preparing nanocellulose-based DIW hydrogel inks using one-pot gelation of the components, which offers a solution to combine DIW-based 3D printing with biobased hydrogel inks, towards diverse biobased applications.

Sustainable Production of Stable Lignin Nanoparticle-Stabilized Pickering Emulsions via Cellulose Nanofibril-Induced Depletion Effect

Spherical lignin nanoparticles (SLNs) are able to formulate Pickering emulsions with various applications. However, SLN-stabilized emulsions commonly comprise droplets in the micron range, resulting in inevitable instability upon storage. Herein, nonadsorbing cellulose nanofibrils (CNF) are shown to induce stabilization of the diluted SLN-stabilized Pickering emulsions via concentration-dependent depletion effects. Two regimes for such depletion interactions are established, including depletion flocculation-induced droplet aggregation at intermediate CNF concentrations and depletion stabilization of micron-sized droplets over critical CNF concentrations (0.2 wt %). The long-term stability of the SLN-based emulsions against creaming is over two months. The universality of the findings is tested with different initial oil volume fractions and droplet diameters. Overall, this study unveils the depletion effects in SLN-stabilized Pickering emulsions induced by renewable CNF, offering a simple, sustainable route for tailoring their phase behavior and creating ultrastable systems that are available for formulating green products.

Cellulose nanofibrils/polydimethylsiloxane double-layer coating for fabrication of high barrier and excellent water- and oil-resistance paper

Paper-based packaging materials have attracted much attention due to their biodegradability, non-toxicity and renewability. However, traditional paper with poor water- and oil-repellency limits its application in food packaging. In this study, the traditional paper coated with cellulose nanofibrils (CNF) and a mixture of polydimethylsiloxane (PDMS) & CNF microparticles (CNFmp) became a hydrophobic and oleophobic paper-based material. The layer of CNF coated on paper can fill the porous on surface to improve the barrier, and the hydrophilicity of this layer contributed to resistance to oil. The coatings of PDMS@CNFmp provided the paper with good hydrophobicity. The effects of CNF concentration, coated thickness, and the second layer of PDMS@CNFmp on thermal stability, mechanical properties, water- and oil-resistance, and air barrier of the paper were investigated. When the concentration of CNF suspension for coating reached 2 wt%, the CNF layer's thickness was 16 μm and the coatings' thickness was 18 μm, the paper exhibited excellent tensile strength (35.02 ± 2 MPa), high hydrophobicity (WCA of 141° ± 3.2°), oil-resistance (91.8° ± 1.9°, kit rating 12/12) and gas barrier (1.38 ± 0.2 mL/min). The present work has great potential for preparing high barrier, fluorine-free, and water- and oil-resistant materials in the food packaging field.

Dewatering of cellulose nanofibrils using ultrasound

Although cellulose nanomaterials have promising properties and performance in a wide application space, one hinderance to their wide scale industrial application has been associated with their economics of dewatering and drying and the ability to redisperse them back into suspension without introducing agglomerates or lose of yield. The present work investigates the dewatering of aqueous suspensions of cellulose nanofibrils (CNFs) using ultrasound as a potentially low-cost, non-thermal, and scalable alternative to traditional heat-based drying methods such as spray drying. Specifically, we use vibrating mesh transducers to develop a direct-contact mode ultrasonic dewatering platform to remove water from CNF suspensions in a continuous manner. We demonstrate that the degree of dewatering is modulated by the number of transducers, their spatial configuration, and the flow rate of the CNF suspension. Water removal of up to 72 wt.% is achieved, corresponding to a final CNF concentration of 11 wt.% in 30 min using a two-transducer configuration. To evaluate the redispersibility of the dewatered CNF material, we use a microscopic analysis to quantify the morphology of the redispersed CNF suspension. By developing a custom software pipeline to automate image analysis, we compare the histograms of the dimensions of the redispersed dewatered fibrils with the original CNF samples and observe no significant difference, suggesting that no agglomeration is induced due to ultrasonic dewatering. We also perform SEM analysis to evaluate the nanoscale morphology of these fibrils showing a width range of 20 nm–4 um. We estimate that this ultrasound dewatering technique is also energy-efficient, consuming up to 36% less energy than the enthalpy of evaporation per kilogram of water. Together with the inexpensive cost of transducers (< $1), the potential for scaling up in parallel flow configurations, and excellent redispersion of the dewatered CNFs, our work offers a proof-of-concept of a sustainable CNF dewatering system, that addresses the shortcomings of existing techniques.

A Flexible Triboelectric Nanogenerator Based on Cellulose‐Reinforced MXene Composite Film

AbstractA flexible triboelectric nanogenerator (TENG) is an indispensable part in future flexible self‐powered system. However, it is still a great challenge to establish a balance among the robust mechanical property, strong triboelectrification effect, and high conductivity of electrode materials. A flexible and enhanced‐performance TENG based on cellulose nanofibrils (CNFs)/transition metal carbides and nitrides (MXene) composite films is developed here for harvesting human movement energy. By introducing CNFs, the mechanical strength, flexibility of the composite film, and sensitive to the temperature change and strain are improved. The effect of CNFs concentration, working force, and frequency on the output performance of TENG is also demonstrated. At the optimized CNFs/MXene ratio of 2/5, the transferred charges and output voltage reach the maximum value of 7.4 nC and 24.9 V, respectively. The maximum instantaneous output power density of the as‐prepared TENG is 1.2 mW m−2. Moreover, a self‐powered flexible display system is demonstrated by integrating the TENG with a flexible alternating current electroluminescence. The flexible TENG based on cellulose nanofibrils‐reinforced MXene composite film is promising as a flexible energy source for self‐powered system.

Structure and rheological studies of phosphorylated cellulose nanofibrils suspensions

Cellulose nanofibrils (CNFs) are normally handled in the form of aqueous suspensions. Therefore, their rheology and intrinsic flow features in an aqueous state also fascinated the researchers. However, understanding the structure-rheology relationship remains a profound challenge to design CNFs with desirable properties. For that purpose, jute fibers were used as source material (Corchorus olitorius) to produce CNFs, and pretreatment using phosphorylation was applied to facilitate the fibrillation during ultra-sonication. This study aims to investigate the relationship between the microstructure and their rheology for CNF aqueous suspensions as influenced by the temperature and concentration of CNF. The surface chemistry, fiber diameter distribution, crystalline structure, thermal stability, and rheological properties of the obtained CNFs were characterized and compared. The grafting of phosphorous moieties on the surface of the fibers was confirmed by the FTIR, XPS analyses, elemental analyses, and zeta potential. Despite influencing crystallinity, phosphorylation enhanced the diameter of nanofibers. The results demonstrated that phosphorylation did not alter the main chemical structure of cellulose. The crystallographic form of the obtained CNFs remained cellulose I. The resulting fibers have nanometric dimensions (<100 nm) with high absolute zeta potential values (>30 mV). A substantial improvement in flame retardancy has also been noted for CNF due to the presence of phosphate groups. Both steady-state and dynamic rheological measurements were improved significantly upon increasing concentration from 0.5 to 2.5 wt%. All the CNF suspensions demonstrated typical shear-thinning behavior and gel-like viscoelastic character even at low concertation (0.5 wt%) due to the construction of a wire-like matrix structure. The frequency and temperature alteration, however, do not affect the viscoelastic gel-like properties of the CNF suspensions.

Genotoxicity assessment of cellulose nanofibrils using a standard battery of in vitro and in vivo assays

Cellulose nanofibrils (CNFs) are identified as novel nanomaterials with many potential applications. Since CNFs are fibrous manufactured nanomaterials, their potential carcinogenic effects and mesothelial toxicity raise some concerns. In this study, we conducted a standard battery of in vitro and in vivo assays to evaluate the genotoxicity of two CNF types using different manufacturing methods and physicochemical properties. Namely, one was CNF produced via chemical modification by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation, while the other was CNF produced via mechanical defibrillation using needle bleached kraft pulp. A bacterial reverse mutation test and a mouse lymphoma TK assay revealed that CNFs at 100 μg/mL did not induce bacterial reverse mutations and in vitro mammalian cell gene mutation. Further, in vitro chromosomal aberration tests demonstrated that CNFs at 100 μg/mL did not induce chromosomal aberration in Chinese hamster lung fibroblasts. From the mammalian erythrocyte micronucleus test, no statistically significant increase was observed in the proportion of micronucleated polychromatic erythrocytes in the bone marrow cells of rats intratracheally instilled with any concentration of CNFs (0.25–1.0 mg/kg) compared with values from respective negative control groups. Therefore, this battery of in vitro and in vivo assays illustrated that the CNFs examined in this study did not induce genotoxicity, suggesting our results provide valuable insight on the future use of these materials in various industrial applications.

Combining cellulose nanofibrils and galactoglucomannans for enhanced stabilization of future food emulsions

The use of wood-derived cellulose nanofibrils (CNFs) or galactoglucomannans (GGM) for emulsion stabilization may be a way to obtain new environmentally friendly emulsifiers. Both have previously been shown to act as emulsifiers, offering physical, and in the case of GGM, oxidative stability to the emulsions. Oil-in-water emulsions were prepared using highly charged (1352 ± 5 µmol/g) CNFs prepared by TEMPO-mediated oxidation, or a coarser commercial CNF, less charged (≈ 70 µmol/g) quality (Exilva forte), and the physical emulsion stability was evaluated by use of droplet size distributions, micrographs and visual appearance. The highly charged, finely fibrillated CNFs stabilized the emulsions more effectively than the coarser, lower charged CNFs, probably due to higher electrostatic repulsions between the fibrils, and a higher surface coverage of the oil droplets due to thinner fibrils. At a constant CNF/oil ratio, the lowest CNF and oil concentration of 0.01 wt % CNFs and 5 wt % oil gave the most stable emulsion, with good stability toward coalescence, but not towards creaming. GGM (0.5 or 1.0 wt %) stabilized emulsions (5 wt % oil) showed no creaming behavior, but a clear bimodal distribution with some destabilization over the storage time of 1 month. Combinations of CNFs and GGM for stabilization of emulsions with 5 wt % oil, provided good stability towards creaming and a slower emulsion destabilization than for GGM alone. GGM could also improve the stability towards oxidation by delaying the initiation of lipid oxidation. Use of CNFs and combinations of GGM and CNFs can thus be away to obtain stable emulsions, such as mayonnaise and beverage emulsions.

Addition of wheat straw nanofibrils to improve the mechanical and barrier properties of cassava starch–based bionanocomposites

Cellulose nanofibrils (CNFs) were obtained from wheat straw, and different concentrations (0 %, 10 %, 20 %, 30 % and 50 %) of the CNFs were incorporated into cassava starch-based films. Thirty passages through a microfibrillator allowed us to obtain well-dispersed CNFs with reduced thickness (34.26 nm). The addition of CNFs promoted an average increase in tensile strength values on the order of 126.69 %. The treatments with higher CNF addition percentages (30 % and 50 %) presented higher Young's modulus values (566.68 and 585.72 MPa, respectively), which indicates an increase in stiffness. The elongation and puncture force decreased with the addition of CNFs, presenting average reductions of 83.72 % and 56.66 %, respectively. A significant decrease in water vapour permeability was observed for the treatments with higher percentages of CNFs added, with a drop from 2.15 × 10−6 in the control film to 1.39 × 10−6 g mm/KPa−1 day−1 m2 in the film with the maximum addition percentage. The contact angle values increased from 43.45° in the control film to 68.66° in the sample with the maximum CNF concentration. The lower hydrophilicity of the treatments with 30 % and 50 % CNF additions is evidenced by the lower values presented for the Cobb test (99.84 and 99.31 g m2), polar surface free energy (0.41 and 0.19 mN m-1) and polarity (0.01 and 0.007). In these treatments, there were stronger interactions between the CNF and starch molecules. Thus, the addition of 30–50 % wheat straw CNFs is recommended to strengthen the structure and improve the barrier properties of cassava starch-based films.

Hydration and Early Age Properties of Cement Pastes Modified with Cellulose Nanofibrils

In this work, the effects of cellulose nanofibrils (CNFs) on workability, hydration reaction, microstructure, early age shrinkage, fracture properties, flexural strength, and compressive strength of cement paste were investigated. Six batches with variable CNF concentrations with the same water-to-cement (w/c) ratio (0.35) were tested. Flow table test showed a reduction in the workability as CNF dosage increased. Isothermal calorimetry (IC) tests showed that after 3 days, degree of hydration (DOH) improved up to 8% because of the addition of CNFs. Thermogravimetric analysis (TGA) tests at 7 and 28 days showed no significant changes in DOH for all pastes. After 7 days, mixture with 0.15% CNF resulted in up to 31% improvement in compressive strength. For 0.09% CNF addition, cement paste showed 26% increase in compressive strength after 28 days. Tests revealed that adding a small quantity of CNF (0.06%) along with entraining 0.05 extra water reduces autogenous shrinkage by 49% at a cement paste with w/c = 0.30. For interpreting the results, a tunnels, reservoirs, and bridges (TR&amp;B) model is proposed. This model suggests that, as proposed by others, CNFs can modify microstructure by providing tunnels for transporting water to unhydrated cement grain. Because of their hydrophilicity, CNFs retain water and work as reservoirs (internal curing), which explains the improvement in properties at low w/c ratios. Significant increases in fracture energy (up to 60%) and flexural strength (up to 116%) suggest that CNFs are an effective toughening mechanism, acting as bridges that increase the energy required for crack propagation.

Fluorescently labeled cellulose nanofibrils for detection and loss analysis

Fluorescently labeled cellulose nanofibrils (CNFs) were used to evaluate CNF leaching from paper according to standard safety assays for food contact materials. Enzymatically pretreated pulp was first labeled with 5-([4,6-Dichlorotriazin-2-yl]amino)fluorescein hydrochloride (DTAF), followed by homogenization to produce fluorescent CNFs of varying degrees of fibrillation. Labeling at the μmolar DTAF/g cellulose level imparted quantitative ppb fluorescence detection of CNFs (LOD of approximately 20 ppb), without significantly altering other material properties, suggesting that DTAF-labeled CNFs are an appropriate mimic for native CNFs and that this approach can be used to detect low CNF concentrations. Cold and hot-water extractions of laboratory papers (100 % CNFs and CNF-fiber blended papers) showed loss values below 3 wt% CNFs, with the finest CNF quality showing the least loss overall and with greater loss experienced under hot water conditions compared with cold water. DTAF-labeled CNFs can be used to address questions related to CNF distribution, localization, and loss.

Structure-property relationships of cellulose nanofibril hydro- and aerogels and their building blocks.

As abundant and renewable materials with excellent mechanical and functional properties, cellulose nanomaterials are utilized in advanced structural, optical and electronic applications. However, in order to further improve and develop new cellulose nanomaterials, a better understanding of the interplay between the self-assembled materials and their building blocks is crucial. This paper describes the structure–property relationships between cellulose nanofibrils (CNFs) and their resulting self-assembled structures in the form of hydrogels and aerogels. Rheological experiments revealed that the transition from viscous to elastic state with the corresponding evolution of the properties of the CNF dispersion depends on the aspect ratio and can be described in terms of the dynamic overlap concentration. The elastic shear modulus was dependent on the aspect ratio at very low CNF concentrations, reaching a plateau, where only the concentration of CNFs was relevant. This transition point in shear modulus was exploited to determine the mesh size of the fibril network, which was found to be in excellent agreement with predictions from scaling arguments. These findings highlight the possibility to tune the self-assembled materials response directly from the bottom-up by the CNF particle structure and thus, suggest new assembly routes starting directly from the CNF design.

Superamphiphobic nanocellulose aerogels loaded with silica nanoparticles

Superamphiphobic aerogels of cellulose nanofibrils (CNF) were successfully fabricated based on their porous rough structure via the chemical vapor deposition of fluorosilane reagent. FE-SEM images show the protruding nano-filaments, micron fibrils and sheet-like layers in the nanocellulose aerogel constitute the micro–nano hierarchical structure, which is critically important for the superamphiphobic performance. The lyophobicity increases with an increase in the nanocellulose concentration within the range of 0.5–2.0 wt%. For the fluorinated aerogel with CNF concentration of 2.0 wt%, the contact angles of water, castor oil, and hexdecane reach 163°, 154° and 143°, respectively. In addition, the loading of SiO2 nanoparticles in the CNF aerogels was conducted to increase the proportion of the nanoscale protuberance on the aerogel surface. The combination of nanocellulose and the loaded SiO2 nanoparticles optimizes the micro–nano hierarchical structure, which further improves the superamphiphobic performance with the contact angle of hexdecane reaching 150°. The superamphiphobic CNF-based composite aerogels with excellent liquid repellency for both water and oil can be used as potential self-cleaning substrates in the fields of gas sensors, catalysis, supercapacitor, and etc.

Transparent and strong polymer nanocomposites generated from Pickering emulsion gels stabilized by cellulose nanofibrils

We report here the development of transparent and strong polymer composites reinforced by unmodified cellulose nanofibrils (CNFs) with a Pickering emulsion gelation strategy. The CNFs entangle and firmly stabilize on the surface of emulsion droplets containing polymethyl methacrylate (PMMA) solution, leading to the gelation of the emulsions. CNFs/PMMA composites were generated via vacuum filtration and solvent washing of the gel and a subsequent two-step hot pressing. The composites contained a unique self-assembled two-tier hierarchy of CNFs networks and demonstrate promising transparency, tensile strength, flexibility, and an extremely low thermal expansion. Remarkably, these properties are highly tunable with varying the concentration of CNFs and the volume ratio of the water to oil phase. This work offers a facile route to realize the well dispersion of unmodified CNFs in hydrophobic polymer matrix and achieve high performance of polymeric materials reinforced by CNFs.

The potential of TEMPO-oxidized cellulose nanofibrils as rheology modifiers in food systems

Cellulose nanofibrils (CNFs) have been proposed for use in low-fat food products due to their availability and excellent viscosifying and gel forming abilities. As the CNFs are negatively charged, the presence of other components in foods, such as electrolytes and food additives such as xanthan gum is likely to affect their rheological properties. Hence, the study of these interactions can contribute valuable information of the suitability of CNFs as rheology modifiers and fat replacers. Rheological measurements on aqueous dispersions of TEMPO-oxidized CNFs were performed with variations in concentration of CNFs, concentration of electrolytes and with varying CNF/xanthan ratios. UV–Vis Spectroscopy was used to evaluate the onset of CNF flocculation/aggregation in the presence of electrolytes. The CNF dispersions followed a power-law dependency for viscosity and moduli on CNF concentration. Low electrolyte additions strengthened the CNF network by allowing for stronger interactions, while higher additions led to fibril aggregation, and loss of viscosity, especially under shear. The CNF/xanthan ratio, as well as the presence of electrolytes were shown to be key factors in determining whether the viscosity and storage modulus of CNF dispersions increased or decreased when xanthan was added.

Structure and rheology of aqueous suspensions and hydrogels of cellulose nanofibrils: Effect of volume fraction and ionic strength

The structure and rheology of TEMPO-oxidized cellulose nanofibrils (CNF) suspensions and hydrogels, used as precursors in the elaboration of bio-based aerogels for thermal insulation applications, were studied as a function of CNF volume fraction and ionic strength. The CNF geometry and rigidity were evaluated using AFM observations. Viscometric measurements, performed at very low CNF concentrations, highlighted the prominent role played by electroviscous effects, which can be modulated by ionic strength. Oscillatory measurements on semi-dilute CNF suspensions revealed the formation of a three-dimensional hydrogel network above a percolation fraction, which was shown to depend on the ionic strength. The rheological properties of CNF hydrogels were shown to depend on CNF fraction and ionic strength. In deionized water, the existence of two different concentration regimes was discussed in terms of network structural characteristics and CNF interactions.

An Investigation on the Effects of Cellulose Nanofibrils on the Performance of Cement Paste and Concrete

AbstractCellulose nanofibrils (CNFs) have the potential to enhance cement and concrete properties because of the way they change both how water is distributed during mixing and how they modify the hydration process. In this work, the effects of CNFs on certain properties of cement paste and concrete were investigated. For the cement paste, workability, shrinkage properties, and compressive strength were investigated. In the cement paste study, 32 batches with variable CNF concentrations in 4 groups with different water-to-cement (w/c) ratios (0.35, 0.40, 0.45, and 0.50) were prepared and tested. Two rheological tests were performed; one used an ammeter to measure torque versus rotational speed, and a second used a standard flow table. Both tests showed a decrease in the workability of cement pastes that was due to the increase in CNF volume for all pastes, which suggests that CNF retains mix water in the fresh state. Thus, the water held in the CNF is not available during initial mixing of the cement paste. The results of the free shrinkage tests for all 32 cement pastes were collected for up to 90 days. Additional results showed that at a low w/c ratio (0.35), adding a small quantity of CNF (0.05 %) can reduce free shrinkage by 13 %. In compressive strength tests, a small dosage of CNF (0.05 %) improved compressive strength (up to 28 %), but higher dosages reduced strength. Results suggest that CNF has a good potential to be considered as a new natural plant-based internal curing agent in cement paste and concrete. For the concrete specimens, the primary focus was on workability effects and compressive strength. In the concrete study, twelve batches with different CNF volumes were prepared, and the corresponding slump results were measured. Results showed that to preserve the slump values, extra water content of 5–8 % should be added for every 0.1 % of CNF incorporated in the concrete mixture. Based on compressive strength tests, it has been shown that CNF is the weakest link in concrete microstructures and controls the compressive strength.

Evaluating the genotoxicity of cellulose nanofibrils in a co-culture of human lung epithelial cells and monocyte-derived macrophages

Cellulose nanofibrils (CNF) are manufactured nanofibres that hold impressive expectations in forest, food, pharmaceutical, and biomedical industries. CNF production and applications are leading to an increased human exposure and thereby it is of utmost importance to assess its safety to health. In this study, we screened the cytotoxic, immunotoxic and genotoxic effects of a CNF produced by TEMPO-mediated oxidation of an industrial bleached Eucalyptus globulus kraft pulp on a co-culture of lung epithelial alveolar (A549) cells and monocyte-derived macrophages (THP-1 cells). The results indicated that low CNF concentrations can stimulate A549 cells proliferation, whereas higher concentrations are moderately toxic. Moreover, no proinflammatory cytokine IL-1β was detected in the co-culture medium suggesting no immunotoxicity. Although CNF treatment did not induce sizable levels of DNA damage in A549 cells, it leaded to micronuclei formation at 1.5 and 3 μg/cm2. These findings suggest that this type of CNF is genotoxic through aneugenic or clastogenic mechanisms. Noteworthy, cell overgrowth and genotoxicity, which are events relevant for cell malignant transformation, were observed at low CNF concentration levels, which are more realistic and relevant for human exposure, e.g., in occupational settings.

Effect of Cellulose Nanofibrils on the Bond Strength of Polyvinyl Acetate and Starch Adhesives for Wood

Nanocellulose is a competitive reinforcement material for use in biocomposite structures and fibrous products. In this study, adhesive mixtures of dicarboxylic acid cellulose nanofibrils (CNF) were dispersed into commercial polyvinyl acetate (PVAc) and starch adhesives, which were applied to Norway spruce (Picea abies) to assess their performance in wood joining. Single-lap joints were prepared and tested with PVAc mixtures with 0 to 0.64 wt% CNF and starch glue mixtures containing 0 to 1.07 wt% CNF. CNF suspensions having three concentrations (0.64, 0.96, and 1.28%) were compared. The results showed that the optimum amount of CNF, 0.48% suspensions, added to PVAc increased the average lap joint strength (EN 205:2003) by 74.5% when compared to control specimens with pure PVAc. Correspondingly, 0.96% CNF suspensions also enhanced the strength of starch adhesive by 34.5%. Lower and higher CNF concentrations showed clearly inferior performance.

Enhanced Swelling, Mechanical and Thermal Properties of Cellulose Nanofibrils (CNF)/Poly(vinyl alcohol) (PVA) Hydrogels with Controlled Porous Structure.

In this work, novel porous cellulose nanofibrils (CNF)/poly(vinyl alcohol) (PVA) hydrogels were prepared using the hybrid solvent of dimethyl sulfoxide (DMSO)/water, followed by freezing/thawing process. Structure, swelling, mechanical and thermal properties of CNF/PVA were explored. The results revealed that porous hydrogels were formed by using the hybrid solvent of DMSO/water, and the pore sizes of hydrogels were controlled by the concentration of CNF. The porous structure of the composite hydrogels can strongly enhance the swelling properties as expected. Compared with pure PVA hydrogels, a 150% improvement in compressive strength were achieved by the hybrid solvent. And the increment of compressive strength depended on the concentration of the CNF. Moreover, the addition of CNF improved the thermal stability of the PVA hydrogels significantly. The low cost, nontoxic and high-performance nanoreinforced hydrogels may have a promising application in tissue engineering fields.