Understanding the Drying Behavior of Regenerated Cellulose Gel Beads: The Effects of Concentration and Nonsolvents

Insights into the assembly process and properties of regenerated cellulose beads prepared in alkali/urea aqueous solutions

Taking the perspective of cellulose molecular chain assembly via the "bottom-top" route, we delve into the influence of both the cellulose solution and the coagulation bath on the assembly process and structure of regenerated cellulose beads (RCBs). The results show that cellulose molecular weight, mass fraction, and the presence of surfactant have an impact on RCBs. Contrary to traditional views where the structures of material are determined by solvent-nonsolvent exchange rate, ion-cellulose binding capacity also affects RCBs. Overall, the influence of ions follows the Hofmeister sequence. Kosmotropes promote the assembly of cellulose chains and elementary fibers, leading to "salting out" effects, reduced pore size of RCBs, increased crystallinity, and enhanced mechanical properties. In contrast, chaotropes induce "salting in" effects, resulting in opposite outcomes. The average pore size of RCBs coagulated in NaSCN solution was approximately 15-folds larger than those prepared in sodium citrate solution. Anions have a greater impact than cations, and both "salting out" and "salting in" effects strengthen with concentration. Temperature variations primarily affect solvent and nonsolvent exchange speed during cellulose regeneration. These findings provide new insights into regulating RCBs, enabling tailored performance for different applications.

Structuring restricted amorphous molecular chains in the reinforced cellulose film by uniaxial stretching

The construction of the preferred orientation structure by stretching is an efficient strategy to fabricate high-performance cellulose film and it is still an open issue whether crystalline structure or amorphous molecular chain is the key factor in determining the enhanced mechanical performance. Herein, uniaxial stretching with constant width followed by drying in a stretching state was carried out to cellulose hydrogels with physical and chemical double cross-linking networks, achieving high-performance regenerated cellulose films (RCFs) with an impressive tensile strength of 154.5 MPa and an elastic modulus of 5.4 GPa. The hierarchical structure of RCFs during uniaxial stretching and drying was systematically characterized from micro- to nanoscale, including microscopic morphology, crystalline structure as well as relaxation behavior at a molecular level. The two-dimensional correlation spectra of dynamic mechanical analysis and Havriliak-Negami fitting results verified that the enhanced mechanical properties of RCFs were mainly attributed to the stretch-induced tight packing and restricted relaxation of amorphous molecular chains. The new insight concerning the contribution of molecular chains in the amorphous region to the enhancement of mechanical performance for RCFs is expected to provide valuable guidance for designing and fabricating high-performance eco-friendly cellulose-based films.

Engineering High-Performance Composite Cellulose Materials for Fast Hemostasis

The development of an effective hemostatic agents is of vital importance for saving wounded individuals from uncontrolled hemorrhage, which is the main reason for preventable death after accidental injury. However, current high-performance hemostatic agents suffer from a cumbersome preparation procedures and poor biocompatibility. Here, we engineered a cellulosic-derived aerogel material by simply controlling the drying process of cellulose regeneration for fast hemostasis. Four different freeze-drying pretreatments were investigated. As compared with the other three, the cellulosic aerogel material prepared without freezing pretreatment exhibited the lowest crystallinity (21.3%) and the highest body fluid absorption capacity (20.3 times that of its own weight) due to its super hierarchical porous structure, which led to an excellent hemostatic performance in vitro blood coagulation (≈100 s). Moreover, the addition of gelatin and diatomite in the material could tune the functional groups and electrostatic properties of the aerogel and further enhance its hemostatic performance. Various characterizations, including X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), X-ray nanocomputed tomography (CT), scanning electron microscopy (SEM), and zeta potential analysis, were carried out to probe the structure-function relationship of the prepared material, and its mechanism of fast hemostasis was thereafter revealed. The results indicate that the developed aerogel is a cost-effective and feasibly scalable hemostatic material suitable for practical use in industry.

Multiporous ZIF-8 carbon/cellulose composite beads: Highly efficient and scalable adsorbents for water treatment

Metal-organic framework (MOF) particles are one of the most promising adsorbents for removing organic contaminants from wastewater. However, powder-type MOF particles face challenges in terms of utilization and recovery. In this study, a novel bead-type adsorbent was prepared using activated carbon based on the zeolitic imidazolate framework-8 (AC-ZIF-8) and a regenerated cellulose hydrogel for dye removal. AC-ZIF-8 particles with a large surface area were obtained by carbonization and chemical activation with KOH. The AC-ZIF-8 powders were efficiently immobilized in hydrophilic cellulose hydrogel beads via cellulose dissolution/regeneration. The prepared AC-ZIF-8/cellulose hydrogel (AC-ZIF-8/CH) composite beads exhibit a large specific surface area of 1412.8 m2/g and an excellent maximum adsorption capacity of 565.13 mg/g for Rhodamine B (RhB). Moreover, the AC-ZIF-8/CH beads were effective over a wide range of pH, temperatures and for different types of dyes. These composite beads also offer economic benefits through desorption of dyes for recycling. The AC-ZIF-8/CH beads can be produced in substantial amounts and used as fillers in a fixed-bed column system, which can purify the continuous inflow of dye solutions. These findings suggest that our simple approach for preparing high-performance adsorbent beads will broaden the application of dye adsorbents, oil-water separation, and catalysts.

Reevaluation of the adhesion between cellulose materials using macro spherical beads and flat model surfaces

Interactions between dry cellulose were studied using model systems, cellulose beads, and cellulose films, using custom-built contact adhesion testing equipment. Depending on the configuration of the substrates in contact, Polydimethylsiloxane (PDMS) film, cellulose films spin-coated either on PDMS or glass, the interaction shows three distinct processes. Firstly, molecular interlocking is formed between cellulose and cellulose when there is a soft PDMS thin film backing the cellulose film. Secondly, without backing, no initial attraction force between the surfaces is observed. Thirdly, a significant force increase, ∆F, is observed during the retraction process for cellulose on glass, and there is a maximum in ∆F when the retraction rate is increased. This is due to the kinetics of a contacting process occurring in the interaction zone between the surfaces caused by an interdigitation of a fine fibrillar structure at the nano-scale, whereas, for the spin-coated cellulose surfaces on the PDMS backing, there is a more direct adhesive failure. The results have generated understanding of the interaction between cellulose-rich materials, which helps design new, advanced cellulose-based materials. The results also show the complexity of the interaction between these surfaces and that earlier mechanisms, based on macroscopic material testing, are simply not adequate for molecular tailoring.

Metal-Assisted Injection Spinning of Ultra Strong Fibers from Megamolecular LC Polysaccharides

The molecular orientation of liquid crystalline (LC) hydrogels has the potential to induce a range of functionalities that can deliver great mechanical strength. Sacran is a supergiant LC polysaccharide isolated from the cyanobacterium Aphanothece sacrum with a high amount of anionic functional groups such as sulfates and carboxylates. In this article, ultra-strong sacran hydrogels and their dried fibers were produced by cross-linking under injection flow with trivalent metal ions such as Al3+, Cr3+, Fe3+, In3+, and rare-earth metal ions such Er3+ and Sr3+. Crossed-polarizing microscopy and X-ray diffraction imaging revealed a uniaxial molecular orientation in the LC gel fiber, resulting in outstanding mechanical characteristics.

Synthesis and Characterization of Biodegradable Poly(vinyl alcohol)-Chitosan/Cellulose Hydrogel Beads for Efficient Removal of Pb(II), Cd(II), Zn(II), and Co(II) from Water

Globally, water contamination by heavy metals is a serious problem that affects the environment and human health. Adsorption is the most efficient way of water treatment for eliminating heavy metals. Various hydrogels have been prepared and used as adsorbents to remove heavy metals. By taking advantage of poly(vinyl alcohol) (PVA), chitosan (CS), cellulose (CE), and the process for physical crosslinking, we propose a simple method to prepare a PVA-CS/CE composite hydrogel adsorbent for the removal of Pb(II), Cd(II), Zn(II) and Co(II) from water. Structural analyses of the adsorbent were examined by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis, and X-ray diffraction (XRD). PVA-CS/CE hydrogel beads had a good spherical shape together with a robust structure and suitable functional groups for the adsorption of heavy metals. The effects of adsorption parameters such as pH, contact time, adsorbent dose, initial concentration of metal ions, and temperature on the adsorption capacity of PVA-CS/CE adsorbent were studied. The adsorption characteristics of PVA-CS/CE for heavy metals may be completely explained by pseudo-second-order adsorption and the Langmuir adsorption model. The removal efficiency of PVA-CS/CE adsorbent for Pb(II), Cd(II), Zn(II), and Co(II) was 99, 95, 92, and 84%, respectively, within 60 min. The heavy metal's hydrated ionic radius may be crucial in determining the adsorption preference. After five consecutive adsorption-desorption cycles, the removal efficiency remained over 80%. As a result, the outstanding adsorption-desorption properties of PVA-CS/CE can potentially be extended to industrial wastewater for heavy metal ion removal.

A Numerical Model for Understanding the Development of Adhesion during Drying of Cellulose Model Surfaces

Adhesion is crucial for the development of mechanical properties in fibre-network materials, such as paper or other cellulose fibre biocomposites. The stress transfer within the network is possible through the fibre-fibre joints, which develop their strength during drying. Model surfaces are useful for studying the adhesive strength of joints by excluding other parameters influencing global performance, such as geometry, fibre fibrillation, or surface roughness. Here, a numerical model describes the development of adhesion between a cellulose bead and a rigid surface using an axisymmetric formulation, including moisture diffusion, hygroexpansion, and cohesive surfaces. It is useful for studying the development of stresses during drying. A calibration of model parameters against previously published contact and geometry measurements shows that the model can replicate the observed behaviour. A parameter study shows the influence of cohesive and material parameters on the contact area. The developed model opens possibilities for further studies on model surfaces, with quantification of the adhesion during pull-off measurements.