Filament spinning of unbleached birch kraft pulps: Effect of pulping intensity on the processability and the fiber properties

A Biodegradable, Waterproof, and Thermally Processable Cellulosic Bioplastic Enabled by Dynamic Covalent Modification

The growing environmental concern over petrochemical-based plastics continuously promotes the exploration of green and sustainable substitute materials. Compared with petrochemical products, cellulose has overwhelming superiority in terms of availability, cost, and biodegradability; however, cellulose's dense hydrogen-bonding network and highly ordered crystalline structure make it hard to be thermoformed. A strategy to realize the partial disassociation of hydrogen bonds in cellulose and the reassembly of cellulose chains via constructing a dynamic covalent network, thereby endowing cellulose with thermal processability as indicated by the observation of a moderate glass transition temperature (T_g  = 240 °C), is proposed. Moreover, the cellulosic bioplastic delivers a high tensile strength of 67 MPa, as well as excellent moisture and solvent resistance, good recyclability, and biodegradability in nature. With these advantageous features, the developed cellulosic bioplastic represents a promising alternative to traditional plastics.

Highly regioselective surface acetylation of cellulose and shaped cellulose constructs in the gas-phase

Gas-phase acylation is an attractive and sustainable method for modifying the surface properties of cellulosics. However, little is known concerning the regioselectivity of the chemistry, i.e., which cellulose hydroxyls are preferentially acylated and if acylation can be restricted to the surface, preserving crystallinities/morphologies. Consequently, we reexplore simple gas-phase acetylation of modern-day cellulosic building blocks - cellulose nanocrystals, pulps, dry-jet wet spun (regenerated cellulose) fibres and a nanocellulose-based aerogel. Using advanced analytics, we show that the gas-phase acetylation is highly regioselective for the C6-OH, a finding also supported by DFT-based transition-state modelling on a crystalloid surface. This contrasts with acid- and base-catalysed liquid-phase acetylation methods, highlighting that gas-phase chemistry is much more controllable, yet with similar kinetics, to the uncatalyzed liquid-phase reactions. Furthermore, this method preserves both the native (or regenerated) crystalline structure of the cellulose and the supramolecular morphology of even delicate cellulosic constructs (nanocellulose aerogel exhibiting chiral cholesteric liquid crystalline phases). Due to the soft nature of this chemistry and an ability to finely control the kinetics, yielding highly regioselective low degree of substitution products, we are convinced this method will facilitate the rapid adoption of precisely tailored and biodegradable cellulosic materials.

Evaluation of Keratin-Cellulose Blend Fibers as Precursors for Carbon Fibers

One main challenge to utilize cellulose-based fibers as the precursor for carbon fibers is their inherently low carbon yield. This study aims to evaluate the use of keratin in chicken feathers, a byproduct of the poultry industry generated in large quantities, as a natural charring agent to improve the yield of cellulose-derived carbon fibers. Keratin-cellulose composite fibers are prepared through direct dissolution of the pulp and feather keratin in the ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) and subsequent dry jet wet spinning (so-called Ioncell process). Thermogravimetric analysis reveals that there is an increase in the carbon yield by ∼53 wt % with 30 wt % keratin incorporation. This increase is comparable to the one observed for lignin-cellulose composite fibers, in which lignin acts as a carbon booster due to its higher carbon content. Keratin, however, reduces the mechanical properties of cellulose precursor fibers to a lesser extent than lignin. Keratin introduces nitrogen and induces the formation of pores in the precursor fibers and the resulting carbon fibers. Carbon materials derived from the keratin-cellulose composite fiber show potential for applications where nitrogen doping and pores or voids in the carbon are desirable, for example, for low-cost bio-based carbons for energy harvest or storage.

Fast and quantitative compositional analysis of hybrid cellulose-based regenerated fibers using thermogravimetric analysis and chemometrics

Cellulose can be dissolved with another biopolymer in a protic ionic liquid and spun into a bicomponent hybrid cellulose fiber using the Ioncell^® technology. Inside the hybrid fibers, the biopolymers are mixed at the nanoscale, and the second biopolymer provides the produced hybrid fiber new functional properties that can be fine-tuned by controlling its share in the fiber. In the present work, we present a fast and quantitative thermoanalytical method for the compositional analysis of man-made hybrid cellulose fibers by using thermogravimetric analysis (TGA) in combination with chemometrics. First, we incorporated 0-46 wt.% of lignin or chitosan in the hybrid fibers. Then, we analyzed their thermal decomposition behavior in a TGA device following a simple, one-hour thermal treatment protocol. With an analogy to spectroscopy, we show that the derivative thermogram can be used as a predictor in a multivariate regression model for determining the share of lignin or chitosan in the cellulose hybrid fibers. The method generated cross validation errors in the range 1.5-2.1 wt.% for lignin and chitosan. In addition, we discuss how the multivariate regression outperforms more common modeling methods such as those based on thermogram deconvolution or on linear superposition of reference thermograms. Moreover, we highlight the versatility of this thermoanalytical method-which could be applied to a wide range of composite materials, provided that their components can be thermally resolved-and illustrate it with an additional example on the measurement of polyester content in cellulose and polyester fiber blends. The method could predict the polyester content in the cellulose-polyester fiber blends with a cross validation error of 1.94 wt.% in the range of 0-100 wt.%. Finally, we give a list of recommendations on good experimental and modeling practices for the readers who want to extend the application of this thermoanalytical method to other composite materials.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10570-021-03923-6.

Recent progress in the conversion of biomass wastes into functional materials for value-added applications

The amount of biomass wastes is rapidly increasing, which leads to numerous disposal problems and governance issues. Thus, the recycling and reuse of biomass wastes into value-added applications have attracted more and more attention. This paper reviews the research on biomass waste utilization and biomass wastes derived functional materials in last five years. The recent research interests mainly focus on the following three aspects: (1) extraction of natural polymers from biomass wastes, (2) reuse of biomass wastes, and (3) preparation of carbon-based materials as novel adsorbents, catalyst carriers, electrode materials, and functional composites. Various biomass wastes have been collected from agricultural and forestry wastes, animal wastes, industrial wastes and municipal solid wastes as raw materials with low cost; however, future studies are required to evaluate the quality and safety of biomass wastes derived products and develop highly feasible and cost-effective methods for the conversion of biomass wastes to enable the industrial scale production.

Solubility and spinnability of cellulose-lignin blends in aqueous NMMO

The direct dissolution and joint spinning of cellulose and lignin from NMMO-water were investigated by using dissolving pulp and purified KRAFT lignin. Compared to the rather narrow dissolution window of cellulose in the NMMO-water system, lignin with concentrations up to 15 wt.-% was shown to dissolve in a range from 30 % NMMO to 70 % NMMO at room temperature. The quasi-ternary phase diagram of cellulose-lignin-(NMMO-monohydrate) is represented by a cross section at 95 °C. Dry-jet wet spinning was realized for the cellulose-lignin compound up to 50 % lignin loading. The spinnability decreases with increasing lignin content. SEM and TEM investigations of the fibers exhibit a core-shell structure with a dense core and a porous shell with lower lignin content. In accordance with the X-ray fiber diagrams, it can be concluded that cellulose governs fiber formation and fiber properties while lignin acts mainly as a filler in the core region.

Freeze Concentration of Aqueous [DBNH][OAc] Ionic Liquid Solution

In the present work, freeze crystallization studies, as a novel concentration method for aqueous 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]) ionic liquid solution, were conducted. In order to find the appropriate temperature and composition range for freeze crystallization, the solid–liquid equilibrium of a binary [DBNH][OAc]–water compound system was investigated with differential scanning calorimetry (DSC). Results of this analysis showed that the melting temperature of the pure ionic liquid was 58 ℃, whereas the eutectic temperature of the binary compound system was found to be −73 ℃. The activity coefficient of water was determined based on the freezing point depression data obtained in this study. In this study, the lowest freezing point was −1.28 ℃ for the aqueous 6 wt.% [DBNH][OAc] solution. Ice crystal yield and distribution coefficient were obtained for two types of aqueous solutions (3 wt.% and 6 wt.% [DBNH][OAc]), and two freezing times (40 min and 60 min) were used as the main parameters to compare the two melt crystallization methods: static layer freeze and suspension freeze crystallization. Single-step suspension freeze crystallization resulted in higher ice crystal yields and higher ice purities when compared with the single-step static layer freeze crystallization. The distribution coefficient values obtained showed that the impurity ratios in ice and in the initial solution for suspension freeze crystallization were between 0.11 and 0.36, whereas for static layer freeze crystallization these were between 0.28 and 0.46. Consequently, suspension freeze crystallization is a more efficient low-energy separation method than layer freeze crystallization for the aqueous-ionic liquid solutions studied and, therefore, this technique can be applied as a concentration method for aqueous-ionic liquid solutions.