A molecular dynamics study of cellulose inclusion complexes in NaOH/urea aqueous solution

Regenerated cellulose films with controllable microporous structure for enhanced seed germination

In this work, the preparation of high-performance and porous regenerated cellulose (RCNH) films for seed germination application were investigated. The films were prepared from bamboo-based cellulose carbamate-NaOH/ZnO/urea and coagulated using environmentally friendly aqueous solution of (NH4)2SO4. The results showed that the pore size of the films could be efficiently controlled by changing the concentration and temperature of the coagulation bath. In a mild environment, the system remains undisturbed, resulting in slow diffusion between the solvent and coagulation bath. This allows for the cellulose molecular chains to align in parallel and self-aggregate, forming a three-dimensional network structure. Therefore, the best mechanical properties were demonstrated by a film coagulated using 5 wt% (NH4)2SO4 solution at 10 °C. This film showed excellent tensile strength of 108 MPa and high elongation at break (35 %). As compared to a plastic wrap, the film demonstrated higher permeability for oxygen, and a moisture retaining ability. Due to these properties, it could be used as an agricultural film to encase and promote the growth of mung bean seeds. Moreover, the film was biodegradable with a short decomposition time, losing 90.75 % of its original mass after 63 days. In a summary, this work provides a route for robust, biodegradable, and permeable regenerated cellulose films with potential applications as biodegradable agricultural mulches.

Accumulation of Hydrogen Bonds and van der Waals Interactions Determines Force Response between Two Parallel Cellulose Chains: Steered Molecular Dynamics Simulations

We investigated the response forces between two parallel cellulose chains during the shearing and tearing processes by using steered molecular dynamics simulations. It was found that there are two logarithmic dependencies between response force and pulling speed in shearing processes but only one in tearing, according to Bell's equation by fitting the f-ln v curve. The mechanism is that there are 2-fold interactions determining the force response between two parallel cellulose chains resisting chain separation during a shearing process. Our results indicate that hydrogen bonds dominate the interchain interactions in the fast pull mode (FPM) for shearing, while van der Waals interactions dominate in the slow pull mode (SPM). For tearing, the one-by-one breaking of hydrogen bonds and van der Waals interactions plays a main role.

Molecular mechanism of cellulose dissolution in N-methyl morpholine-N-oxide: A molecular dynamics simulation study

N-methyl morpholine-N-oxide (NMMO) is the only commercialised solvent to dissolve cellulose and produce lyocell. However, the molecular mechanism of NMMO-induced cellulose solubilisation is unknown which limits further process development. In this work, and for the first time the complete dissolution process of a large cellulose bunch was simulated in NMMO monohydrate using long microsecond molecular dynamic simulations. The dissolution process was also simulated in 1-ethyl-3-methylimidazolium acetate (EmimAc) as an efficient ionic liquid in cellulose dissolution and the results were compared with the aqueous conditions. While the cellulose bunch showed a stable and insoluble structure in pure water, it was completely and efficiently dissolved in both NMMO monohydrate and EmimAc. It was shown that the dissolution time of cellulose in NMMO monohydrate is almost twice that in EmimAc, which is in agreement with the experimental observations. Although it is revealed that hydrogen bonding is the main driving force of cellulose dissolution in NMMO monohydrate, one cannot explain the complete molecular mechanism of NMMO-induced cellulose dissolution only by considering hydrogen bonds. A straightforward molecular mechanism was proposed, in which the interactions of NMMO molecules, not with cellulose, but with the other NMMO molecules play a critical role in the dissolution process.

Waste Reutilization in Polymeric Membrane Fabrication: A New Direction in Membranes for Separation

In parallel to the rapid growth in economic and social activities, there has been an undesirable increase in environmental degradation due to the massively produced and disposed waste. The need to manage waste in a more innovative manner has become an urgent matter. In response to the call for circular economy, some solid wastes can offer plenty of opportunities to be reutilized as raw materials for the fabrication of functional, high-value products. In the context of solid waste-derived polymeric membrane development, this strategy can pave a way to reduce the consumption of conventional feedstock for the production of synthetic polymers and simultaneously to dampen the negative environmental impacts resulting from the improper management of these solid wastes. The review aims to offer a platform for overviewing the potentials of reutilizing solid waste in liquid separation membrane fabrication by covering the important aspects, including waste pretreatment and raw material extraction, membrane fabrication and characterizations, as well as the separation performance evaluation of the resultant membranes. Three major types of waste-derived polymeric raw materials, namely keratin, cellulose, and plastics, are discussed based on the waste origins, limitations in the waste processing, and their conversion into polymeric membranes. With the promising material properties and viability of processing facilities, recycling and reutilization of waste resources for membrane fabrication are deemed to be a promising strategy that can bring about huge benefits in multiple ways, especially to make a step closer to sustainable and green membrane production.

Solvent Regulation Approach for Preparing Cellulose-Nanocrystal-Reinforced Regenerated Cellulose Fibers and Their Properties

An electrolyte and aprotic solvent mixture were used to prepare cellulose solutions containing cellulose nanocrystals (CNCs). All-cellulose composite fibers were then produced by dry-wet spinning these solutions. The presence of CNC in the all-cellulose fibers was demonstrated, and the effects of the CNC on the fiber properties were investigated. The all-cellulose fibers were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and electronic tensile measurements. These results showed that CNCs were present in the mixture and that their structure was maintained in the all-cellulose fibers. No compatibility problems between the CNC and cellulose II matrix were observed. Introducing CNC enhanced the crystallinity, thermal stability, and mechanical properties of the composite fibers.