Presence Of Cellulose Nanofibrils Research Articles

Polyester–melamine coil coating formulation reinforced with surface-modified cellulose nanofibrils

In light of the need to redesign industrially produced materials by utilizing renewable resources, nanoscopic forms of cellulose are regarded as a valuable asset. In this work, the potential of cellulose nanofibrils (CNFs) as an unconventional nanoadditive for a polyester–melamine coil coating formulation is explored. CNFs, hydrophilic nanomaterials with high aspect ratios, were successfully incorporated in the solvent-borne formulation. Coatings were prepared with extremely low loadings of the nanoadditive (0.5 and 0.7 wt%). At these concentrations, the volume fraction of the nanofibrils in the coatings was calculated to be close to their percolation threshold. Two different pathways of CNF surface modification were applied to allow for a good compatibilization in the resin matrix, and the formulations were cured in two different settings. The effective compatibilization of the nanoadditive led to a significant variation of the viscoelastic properties in the coatings containing CNFs. The results from dynamic mechanical analysis (DMA) highlighted the effect of CNFs on the crosslinked network at the nanoscale, resulting in an increase in Tg. Additionally, an increase in the stress at break and Young's modulus was determined by tensile testing, while satisfactory elongation at break was preserved. Other relevant effects induced by the presence of CNFs on the properties of the coatings were highlighted, such as a significant matt effect, increased surface roughness and lower scratch resistance. A preliminary evaluation of the water barrier properties by electrochemical impedance spectroscopy (EIS) is also presented, suggesting that the incorporation of a hydrophilic nanoadditive did not lead to a deterioration of the coatings' performance.

Composite electrospun membranes based on polyacrylonitrile and cellulose nanofibrils: Relevant properties for their use as active filter layers

Electrospun membranes comprising polyacrylonitrile (PAN) and 0.2 to 0.6 wt% cellulose nanofibrils (CNF) were prepared and characterized for their use as active layers of Filtering Facepiece Respirators (FFRs) and medical masks. Composite membranes with up to 0.4 wt% of CNF exhibited storage modulus values up to approximately 5 times higher and tensile strength and elastic modulus about 2 times and 6 times higher, respectively, compared to neat PAN. All membranes presented filtration efficiencies (FE) superior to 90% for aerosols with a median count diameter of 75 ± 20 nm and geometric standard deviation less than 1.86. For most membranes produced from an equal volume of solution, the increase in CNF content decreased the pressure drop (Δp, up to approximately five times) and increased the quality factor (QF, up to about 4 times) of the composite membranes, compared to neat PAN, due to the formation of more heterogeneous fibers, larger pores, a trend of increasing porosity and lower packing density. The presence of CNF also increased the air permeability (permeability coefficients, k1 and k2) of the composite materials. Following a yet not explored approach, it was demonstrated that the presence of CNF in the composition of PAN composite electrospun membranes led to materials with better performance as active filter layers than neat PAN.

ZnO microrods sandwiched between layered CNF matrix: Fabrication, stress transfer, and mechanical properties

Functional metal oxide particles are often added to the polymers to prepare flexible functional polymer composites with adequate mechanical properties. ZnO and cellulose nanofibrils (CNF) outstand among these metal oxides and the polymer matrices respectively due to their various advantages. Herein, we in situ prepare ZnO microrods in the presence of CNF, which resultes in a layered composite structure. The ZnO microrods are sandwiched between the CNF layers and strongly bind to highly charged CNF, which provides a better stress transfer during mechanical activity. Digital image correction (DIC) and finite element analysis-based computational homogenization methods are used to investigate the relationship between mechanical properties and composite structure, and the stress transfer to the ZnO microrods. Full-field strain measurements in DIC reveal that the in situ ZnO microrods preparation leads to their homogenous distribution in the CNF matrix unlike other methods, which require external means such as ultrasonication. The computational homogenization technique provides a fairly good insight into the stress transfer between constituents in microstructure as well as a good prediction of macroscopic mechanical properties, which otherwise, would be challenging to be assessed by any ordinary mechanical testing in the layered composites. Finally, we also demonstrate that these composites could be used as physiological motion sensors for human health monitoring.

Stabilization of the emulsion of Alkenyl Succinic Anhydride (ASA) in water using cellulose nanofibrils

Alkenyl Succinic Anhydride (ASA) is sizing agent that is applied as an aqueous emulsion during the papermaking process to improve paper’s hydrophobicity. However, its application becomes difficult as the emulsion quickly destabilizes due to the coalescence phenomenon and the high reactivity of ASA with water. In this work, we used cellulose nanofibrils (CNFs) to increase the stability of the ASA emulsion over time. Small amounts of CNFs added to the emulsion helps to increase its storage life by almost 3 times, by means of stabilizing the average droplet size and reducing the amount of hydrolyzed ASA. The time extension allows higher flexibility of the sizing processes. In this work, we identify the negative impact that the temperature and the presence of metal ions in water have on the quality on the optimal ASA emulsion, resulting in a reduction in their effects for both factors with the presence of cellulose nanofibrils.

Nanocellulose/LiCl systems enable conductive and stretchable electrolyte hydrogels with tolerance to dehydration and extreme cold conditions

Ionically-conductive and stretchable hydrogels are ideally suited for the synthesis of flexible electronic devices. However, conventional hydrogels undergo dehydration at ambient conditions and freeze at subzero temperatures, limiting their functions. As an alternative to counteract these limitations, we propose double network hydrogels that are easily synthesized by a one-step acrylamide (AM) polymerization in the presence of cellulose nanofibrils (CNF) and LiCl. Following molecular dynamics simulation, thermogravimetric and spectroscopic (Raman and low-field nuclear magnetic resonance) analyses, we show that LiCl increases the interactions between the colloidal phase and water molecules, ensuring water holding capability at atmospheric conditions and endowing the hydrogels with freezing tolerance over a wide range of temperatures, from −80 to 25 °C. The synergy between CNF and LiCl is critical in maintaining the mechanical strength of the system, which simultaneously displays high stretchability (~748%) and ionic conductivity (2.25 S/m) at low temperatures (−40 °C). As a proof of concept, a flexible supercapacitor comprising the proposed electrolyte hydrogel is demonstrated as a reliable, low-temperature electrochemical device. Our results provide the basis for simple and universally applicable systems that fulfill the requirements of flexible electronics under extreme cold conditions.

Effects of cationic starch in the presence of cellulose nanofibrils on structural, optical and strength properties of paper from soda bagasse pulp

The effects of widely available bio-based additives, cellulose nanofibrils (CNFs) (0.1, 0.5, 1, and 2 wt%, based on dry weight of pulp) in combination with high degree of substitution cationic starch (CS) (0.2, 0.4, and 0.6 wt%, based on dry weight of pulp) on the structural, optical and strength properties of handsheet paper made from soda bagasse pulp were studied. Obtained results indicated that both the type and loading level of the additives had meaningful effects (99% confidence level) on the evaluated properties. Scanning electron microscope (SEM) images showed the retention and reinforcing effects of the additives on the paper network. Tensile and burst strengths increased continuously with increasing levels of the bio-additives up to 33% and 23% (0.6 CS/2% CNFs), respectively. However, the cellulose nanofibrils improved retention and drainage of the pulp at the lower levels (0.5 CS/0.1 CNFs), presumably due to complex interaction between CNFs and CS. Moreover, for the handsheet papers made of semi-bleached soda bagasse pulp, higher addition of CNFs improved the brightness of paper.

In Situ Synthesized Hydroxyapatite—Cellulose Nanofibrils as Biosorbents for Heavy Metal Ions Removal

The synthesis of hydroxyapatite (HAp) in the presence of cellulose nanofibrils (CNF) or TEMPO-oxidized CNF (TCNF) was performed in situ by wet chemical precipitation process, using chemical precursors, to hybrid a low-cost biosorbents for removal of Co2+ as a model heavy metal ion. The removal is investigated by batch adsorption method depending on the pH value, the dosage of adsorbent, initial Co2+ concentration and the contact time of adsorption. The removal of Co2+ reached the maximum (87%) at pH 6 by using a dosage of 0.5 g L−1. The TCNFs is shown to increase the nucleation and growth of the HAp synthesized, providing higher surface area (138 m2 g−1) with lower pore diameter (11.89 nm), compared to the CNFs based hybrid (135 m2 g−1, 14.42 nm) or pure HAp (118 m2 g−1, 13.32 nm), however, both resulting to a higher adsorption capacity (25 mg g−1) of Co2+ compared to HAp or TCNF (20–22 mg g−1). The adsorption is follows primarily by pseudo-first and Elovic order kinetic models which is due to the physisorption of Co2+ and surface ionic interactions with available negative phosphate (from HAp) and/or carboxylic (from TCNF) groups, fitting well with the Freundlich adsorption isotherm, and secondly due to the ion-exchange mechanism of Co2+ with Ca2+ from HAp. Both hybrid adsorbents show good adsorption (≥40%) capacity even after third reusing cycle, and high temperature stability (weight loss of 14%) up to 1000 °C, however, the CNF-HAp hybrid represent a high-value alternative to relatively costly TCNF.

Waterborne acrylic–cellulose nanofibrils nanocomposite latexes via miniemulsion polymerization

Abstract Waterborne acrylic–cellulose nanofibrils (CNFs) nanocomposite latexes have been successfully synthesized via one-pot miniemulsion polymerization. A cationic copolymer and a low amount of anionic surfactant were used to promote the stabilization process and prevent the aggregation during storage. The effect of the CNFs content and the amount of added copolymer on the particle size and the stability of the dispersion were studied. Evidence of the binding of CNFs onto the polymer particles was supported by FE-SEM observation. Transparent nanocomposite films were obtained by casting after water evaporation and film-formation process. Investigation of the mechanical properties by dynamic mechanical analysis (DMA) and tensile testing revealed an enhancement in both the stiffness and strength of the nanocomposites, which is indicative that the in-situ polymerization in presence of CNFs did not compromise the strong reinforcing potential of CNFs. The synthesized acrylic–CNFs latexes are able to form films with promising properties for application as waterborne coatings.

Poly (acrylic acid-co-acrylamide)/cellulose nanofibrils nanocomposite hydrogels: effects of CNFs content on the hydrogel properties

Nanocomposite hydrogels based on cellulose nanofibrils (CNFs) and poly(acrylic acid-co-acrylamide) were synthesized via in situ free radical polymerization in an aqueous suspension of CNFs. Effects of the inclusion of CNFs with content up to 10 wt% on the swelling properties at different pH and on the compression strength were investigated. The presence of CNFs was shown to strongly reinforce the hydrogel without deteriorating its elasticity. Nanocomposite hydrogel with a content of 10 % CNF supported respectively a strength and deformation about 13 and 2 times higher than that of the neat hydrogel. This effect was explained by the grafting of polymers on the CNFs surface, contributing to an increase in the effective crosslinking density, and improving the interfacial adhesion between polymer chains and CNFs. Moreover, the addition of CNF enhanced the water holding capacity of the hydrogel and caused the system to release urea simulating a fertilizer in a more controlled manner than that with neat hydrogel.

Southern pine impregnated with silicate solution containing cellulose nanofibrils

Abstract A drying process has been tested to impregnate southern pine (Pinus spp.) samples with sodium silicate solution. The effect of adding cellulose nanofibrils in the treating solution was also studied. The mechanical tests show that the flexural modulus of rupture (MOR) and modulus of elasticity (MOE) increased significantly with increasing concentration of sodium silicate. The highest MOR and MOE of the treated samples were 170±13 MPa and 19±1 GPa, respectively, while the corresponding data of the control sample were 98±8 MPa and 11±1 GPa respectively. Deposition of polymerized silicate in the wood cell lumina was observed. The compression strength was improved by the incorporation of polymerized silicate to increase the measured flexural properties. The presence of cellulose nanofibrils in the sodium silicate solution had no effect.

DMA analysis and wood bonding of PVAc latex reinforced with cellulose nanofibrils

Suspensions of commercial refined beech pulp (RBP) were further processed through mechanical disintegration (MD-RBP), chemical modification (CM-RBP) and through chemical modification followed by mechanical disintegration (CM-MD-RBP). Nanocomposites were prepared by compounding a poly(vinyl acetate) (PVAc) latex adhesive with increasing contents of the different types of nanofibrils, and the resulting nanocomposites were analyzed by dynamic mechanical analysis (DMA). Also, the suitability of using the CM-RBP fibrils to formulate PVAc adhesives for wood bonded assemblies with improved heat resistance was studied. The presence of cellulose nanofibrils had a strong influence on the viscoelastic properties of PVAc latex films. For all nanocomposites, increasing amounts of cellulose nanofibrils (treated or untreated) led to increasing reinforcing effects in the glassy state, but especially in the PVAc and PVOH glass transitions. This reinforcement primarily resulted from interactions between the cellulose fibrils network and the hydrophilic PVOH matrix that led to the complete disappearance of the PVOH glass transition (tan δ peak) for some fibril types and contents. At any given concentration in the PVOH transition, the CM-MD-RBP nanofibrils provided the highest reinforcement, followed by the MD-RBP, CM-RBP and the untreated RBP. Finally, the use of the CM-RBP fibrils to prepare PVAc reinforced adhesives for wood bonding was promising since, even though they generally performed worse in dry and wet conditions, the boards showed superior heat resistance (EN 14257) and passed the test for durability class D1.