Influence Of Cellulose Nanofibers Research Articles

Influence of cellulose nanofibers on the behavior of Pickering emulsions. Part II: Thixotropy and dynamic-mechanical tests

Nonlinear rheology of Pickering emulsions is used to further investigate the nonlinear and unrecoverable transformation of inner structures, which is beyond the linear viscoelastic regime of tiny structural disturbances. Exploring various rheological methods plays a vital role in emulsion applications, such as simulating the macroscopic structural transformation between static and liquidlike flow states, strain overshoot, and regeneration for broken structures. According to our previous studies, cellulose nanofibers (CNFs) Pickering emulsions are a typical system for investigating polymer-based emulsions with the auxiliary surfactant [didodecyldimethylammonium bromide (DDAB)] for enhancing CNF absorption. To further study different rheological properties by varying CNF or DDAB contents, multiple interval thixotropic test, large amplitude oscillatory shear, and concentration-time-dependent superposition are employed to study the linear viscoelasticity and structural transformation of nonlinear range. This research was conducted based on the previous published works [Cui et al., Materials 15, 8285 (2022)] as a further characterization for the same sample series.

Influence of Cellulose Nanofibers on the Behavior of Pickering Emulsions. Part 1. Microscopy and Startup Flow Test

The dispersibility of flexible polymer chains present at the emulsion's interface between the dispersed and continuous phase has obvious effects on rheology and dielectric properties of the whole emulsion. Cellulose nanofiber (CNF)-based Pickering emulsions are good systems to research these properties with respect to their microscopic phase structure, dielectric, and rheological properties by using CNF as a water-dispersible Pickering emulsifier, liquid paraffin as an oil phase, and didodecyldimethylammonium bromide (DDAB) as a cationic auxiliary surfactant. The CNF and DDAB contents were systematically varied while the water-to-paraffin oil ratio was kept constant to discern the influence of the Pickering emulsifiers. Polarized optical microscopic images reveal that the droplets tend to shrink at higher CNF content but grow bigger when increasing the DDAB content, which is proved by fluorescence analysis of the CNF dispersibility with varying DDAB content. The dielectric damping exhibits a minimum, whose value decreases with increasing DDAB and CNF content. Increasing the DDAB content promotes the solubilization of CNF in the aqueous phase, which will increase the overall viscosity and yield points. Similarly, a higher CNF content leads to a higher viscosity and yield point, but at high DDAB contents, the viscosity function exhibits an S-shape at intermediate CNF contents. To evaluate the results further, they were compared with CNF dispersions (without oil phase), which showed a surfactant effect slightly on maximum stress but strongly on yield stress τy, indicating that DDAB can promote the formation of a CNF network rather than the viscosity of the whole system. This paper provides information on how a systematical variation of the composition influences morphology and physico-chemical interactions as detected by broadband dielectric spectroscopy and rheological behavior.

Structural and mechanical characterisation of cellulose nanofibers (CNF) from Pennisetum Purpureum reinforced with polylactic acid (PLA)

This study aims to develop a composite scaffold based on polylactic acid reinforced with cellulose nanofibers from Pennisetum purpureum (PLA/CNF). The composite scaffolds were prepared via solvent casting and particulate leaching technique; sodium chloride (NaCl) was used as the porogen material. The influence of CNF on PLA is investigated; scaffolds were fabricated with different content of CNF (5%, 10% and 15%). The prepared composite scaffold was characterised using porosity measurements, Fourier-transform infrared spectroscopy (FTIR) and the compression strength and modulus were also evaluated in this study. The PLA/CNF scaffolds were highly porous with porosity higher than 80%. It was also shown that the porosity had a slight decrease with increasing CNF contents due to the compact arrangement of CNF within the scaffolds. Compression strength and modulus also show an increase in value as the CNF content increases. The results also show that introducing CNF to the PLA matrix can be considered beneficial for cartilage regeneration, cell attachment, and extracellular matrix (ECM) production.

Removal of Cu2+ ions by cellulose nanofibers-assisted starch-g-poly(acrylic acid) superadsorbent hydrogels

Removal of pollutants by bio-superadsorbent is currently in the limelight due to their low cost and biocompatibility with the environment. This research, we investigated the potential of cellulose nanofibers (CNFs) treated starch-g-poly(acrylic acid) (St-g-PAA) superadsorbent hydrogels in removing Cu2+ ions from water. It was found that CNFs-incorporated starch-g-poly(acrylic acid) hydrogel exhibit the highest amount of Cu2+ uptake in a solution containing 0.1 g/L Cu2+ ions, and that adsorption capacity rises significantly with the increase in Cu2+ concentration from 0.1 to 0.6 g/L. The influence of CNFs on the adsorption of Cu2+ ions was studied by Langmuir and Freundlich adsorption isotherm models, the graphs verged on linearity in Langmuir model while the maximum monolayer adsorption capacity was found to be 0.736 g/g for the untreated St-g-PAA hydrogels and 0.957 g/g for the CNFs-treated hydrogels in 0.6 g/L Cu2+ solution at pH 5. In this study, the adsorption capacity was enhanced by increasing the contact time between the bio-adsorbent and solution up to 5 h while longer contact time resulted in reduced adsorption and desorption phenomenon. In addition, desorption results showed that maximum adsorbent recovery for pH near to 1–2. This study confirms that the starch-based hydrogel is promising to be used for removal of pollutants from water efficiently.

Influence of cellulose nanofibers on the rheological behavior of silica-based shear-thickening fluid

In this work, the influence of cellulose nanofibers (CNFs) on the rheological behavior of silica-based shear-thickening fluid (STF) is investigated. CNFs of 150–200 nm in diameter were extracted from cotton fibers using a supermasscolloider. CNF-reinforced STF of different concentrations (0.1–0.3 wt.%) was prepared via an ultrasonication technique. The presence of CNFs and their interaction with the silica nanoparticles in the STF were analyzed using SEM and FTIR. The addition of a minute quantity of CNF to the STF (0.3% CNF-reinforced STF) caused a marked increase in the peak viscosity, from 36.8 (unmodified STF) to 139.0 Pa s (0.2% CNF-reinforced STF), and a concomitant decrease in the critical shear rate from 33.45 to 14.8 s−1 . The presence of a large number of hydroxyl groups on the CNFs enhanced their interaction with the nanoparticles via hydrogen bonding, which induced shear thickening. The mechanism of the interaction between silica nanoparticles and CNF was also demonstrated. Oscillatory dynamic rheological analysis showed that the addition of even a small amount of CNF led to higher elastic behavior in the system at lower shear rates. In contrast, a more viscous nature was demonstrated at higher angular frequencies. As the concentration of nanofibers in the STFs increased, the crossover point between storage and loss modulus shifted to higher angular frequencies, implying stronger interaction between the constituents of the STF. The dynamic viscosity profile of all samples also exhibited shear-thickening behavior.

Mechanical Properties of Injection Molded Poly(lactic) Acid—<i>Luffa</i> Fiber Composites

The influence of cellulose nano fibers extracted from the fruit of luffa cylindrica (LC) on the tensile, flexural and impact properties of composite materials using poly lactic acid (PLA) processed by micro compounding and injection molding was studied. Preliminary results suggested promising mechanical properties. The impact strength, tensile strength and flexural strength of the composites increased with incorporation of very low content of LC fiber up to 2 wt%. But when the wt of LC fiber in the composite increased (5 wt% and 10 wt%), mechanical strength of the composites reduced probably due to agglomeration of cellulose fibers. However, modulus of composites was enhanced with increase in wt of fiber content in the composites. Before reinforcement, the LC fibers were modified with calcium phosphate in order to explore the possibilities of using these composites in biomedical industries. The novelty of this work is that there is no use of compatiblizer and coupling agent during the processing so that the cost of processing is reduced.

Influence of cellulose nanofibers on the curing behavior of epoxy/amine systems

Epoxy composites were prepared using diglycidyl ether bisphenol F and water-dilutable diglycidyl ether bisphenol A with curing agents, polyoxypropylenediamine and diethylmethylbenzenediamine, in water or dimethylformamide as a solvent. The influence of cellulose nanofibers and solvents on curing kinetics of epoxy composites was investigated. Curing kinetic parameters were calculated using the model-fitting methods and the isoconversional method. Among these, the Sestak–Berggren equation best fit the experimental data. Results indicated that dimethylformamide decreased the reaction rate, whereas water revealed the opposite pattern. Cellulose nanofibers catalyzed the reaction between bisphenol F resins and the aromatic curing agent.

Influence of cellulose nanofibers on the morphology and physical properties of poly(lactic acid) foaming by supercritical carbon dioxide

The foaming process of poly(lactic acid) (PLA)/cellulose nanofiber (CNF) nanocomposites using supercritical CO2 as a foaming agent was studied with various CNF contents. CNFs were obtained by sonication, and their morphology was examined by transmission electron microscopy. According to the CNF content, the changes in the rheological and the thermal properties of the nanocomposites were studied through viscometry and differential scanning calorimetry. The viscosity of the composites increased with increasing CNF content. The effects of the CNF content on the foam properties and morphologies were evaluated. Compared to neat PLA foam, the PLA/CNF nanocomposite foams exhibited decreased cell size as well as increased cell density and foam density due to the improved viscous properties. Open image in new window