Investigation of accessibility and reactivity of cellulose pretreated by ionic liquid at high loading

Biodegradable films from the lignocellulosic fibers of wheat straw biomass and the effect of calcium ions

Plastics are hazardous to human health, and plastic waste results in environmental pollution and ecological catastrophe. Biobased polymers from renewable sources have recently become promising for developing biodegradable packaging films. Among them, lignocellulosic residue from agricultural biomass is inexpensive, renewable, and biodegradable. This study aims to develop biodegradable films using lignocellulosic residue from wheat straw biomass. The methodology is a green process that solubilizes lignocellulosic chains using Zn2+ ions and crosslinks with Ca2+ ions of different concentrations (200-800 mM). The results reveal that the increase of Ca2+ ions significantly decreases moisture content, water solubility, water vapor permeability, transparency, and elongation of films. The tensile strength is recorded as 6.61 ± 0.07 MPa with the addition of 800 mM of CaCl2, which is approximately 2.5 times higher than commercial polyethylene films. Around 90 % of films biodegrade within a month in soil containing 20 % moisture content. Overall, lignocellulosic residue from wheat straw biomass could be an excellent replacement for synthetic polymer to fabricate strong, transparent, and biodegradable plastic films.

Spectroscopic and Chemical Properties of Ionic Liquids: Computational Study

A brief account is given of highlights of our computational efforts - often in collaboration with experimental groups - to understand spectroscopic and chemical properties of ionic liquids (ILs). Molecular dynamics, including their inhomogeneous character, responsible for key spectral features observed in dielectric absorption, infra-red (IR) and fluorescence correlation spectroscopy (FCS) measurements are elucidated. Mechanisms of chemical processes involving imidazolium-based ILs are illustrated for CO2 capture and related reactions, transesterification of cellulose, and Au nanocluster-catalyzed Suzuki cross-coupling reaction with attention paid to differing roles of IL ions. A comparison with experiments is also made.

Alkalization of Kraft Pulps from Pine and Eucalyptus and Its Effect on Enzymatic Saccharification and Viscosity Control of Cellulose

Bleached kraft pulps from eucalyptus and pine were subjected to cold caustic extraction (CCE) with NaOH (5, 10, 17.5, and 35%) for hemicelluloses removal and to increase cellulose accessibility. The effect of these changes was evaluated in enzymatic saccharification with the multicomponent Cellic CTec3 enzyme cocktail, and in viscosity reduction of pulps with the monocomponent Trichoderma reesei endoglucanase (EG). After CCE with 10% NaOH (CCE10) and 17.5% NaOH (CCE17.5), hemicellulose content lower than 1% was achieved in eucalyptus and pine pulps, respectively. At these concentrations, cellulose I started to be converted into cellulose II. NaOH concentrations higher than 17.5% decreased the intrinsic viscosity (from 730 to 420 mL/g in eucalyptus and from 510 to 410 mL/g in pine). Cellulose crystallinity was reduced from 60% to 44% in eucalyptus and from 71% to 44% in pine, as the NaOH concentration increased. Enzymatic multicomponent saccharification showed higher glucose yields in all CCE-treated eucalyptus samples (up to 93%) while only CCE17.5 and CCE35 pine pulps achieved 90% after 40 h of incubation. Untreated bleached pulps of both species presented saccharification yields lower than 70%. When monocomponent EG was used to treat the same pulps, depending on enzyme charge and incubation time, a wide range of intrinsic viscosity reduction was obtained (up to 74%). Results showed that eucalyptus pulps are more accessible and easier to hydrolyze by enzymes than pine pulps and that the conversion of cellulose I to cellulose II hydrate only has the effect of increasing saccharification of CCE pine samples. Viscosity reduction of CCE pulps and EG treated pulps were obtained in a wide range indicating that pulps presented characteristics suitable for cellulose derivatives production.

Polar zwitterion/saccharide-based deep eutectic solvents for cellulose processing

Liquid zwitterions are biocompatible cellulose solvents and have enabled successive ethanol production from plant biomass in the same reaction pot. However, only a few carboxylate-type liquid zwitterions have been reported since almost all zwitterions are solid. Here, we propose zwitterion-based deep eutectic solvents (DESs) to expand the choices of zwitterionic solvents for cellulose dissolution and the subsequent processing. Zwitterion-based DESs were prepared by mixing four types of saccharide at various ratios. Twenty-two combinations of zwitterion/saccharide mixtures formed DESs, that is, liquid state below 100 °C. Two of them, whose saccharide ratio were 5 wt%, successfully dissolved cellulose because the low saccharide load was sufficient for liquefaction but did not disrupt the intrinsic cellulose dissolution ability of zwitterions.

Effect of Regenerated Cellulose Fibers Derived from Black Oat on Functional Properties of PVA-Based Biocomposite Film

In this study, agricultural residue from black oat, a cover crop usually grown to improve soil nutrients between the periods of regular crop production, was used as a source of cellulose fibers. Concentrations of 1, 3, and 5 wt. % of regenerated cellulose (RC) fibers blended in poly(vinyl alcohol) (PVA) solution were used to prepare the reinforced composite films (CFs) by the solvent cast method. Compared to neat PVA film (control), the effects of RC addition on functional properties of CFs, such as water absorption, transparency, thermal stability, and mechanical property were investigated. All CFs with different RC concentrations exhibited improved mechanical property and thermal stability while the swelling property was decreased, and no significant changes were observed in the film transparency as compared with the control film. Among the CFs, films with 3% RC significantly decreased water vapor transmission rate, swelling, and soluble fraction (p < 0.05). In addition, Young’s modulus and tensile strength were increased by 40 MPa and 3 MPa, respectively, while elongation at break was decreased by 4%, compared to the control film. The results indicate that RC from black oat might be feasible as potential bio fillers to improve film properties in a bio-based composite matrix.

Coupled Pretreatment with Liquid Nitrogen and Ball Milling for Enhanced Cellulose Hydrolysis in Water

A key problem in the conversion of cellulose into chemicals and fuels is the low product yield from cellulose due to its robust structure. In this work, for the first time, cellulose was pretreated with coupling of liquid nitrogen and ball milling (LN-BM) for cellulose hydrolysis. After the LN-BM treatment, the glucose yield from cellulose by HCl in water increased by almost 2 times and yield of formic acid catalyzed by H₂SO₄-NaVO₃ was more than 3-fold that obtained from untreated cellulose. The yields were also much higher than that from the individually ball-milled cellulose. The structure variation of cellulose indicated that reduction of both crystallinity index and molecular weight contributed to improving the conversion efficiency, but the former was the dominant factor. The combination of liquid nitrogen and ball milling developed in this work is an effective and environment-friendly approach for cellulose pretreatment.

Solubility of Cellulose in Binary Mixtures of 1-Alkyl-3-methylimidazolium Acetate and Dimethyl Sulfoxide: Influence of Alkyl Chain Length in the Cation

The influence of alkyl chain length of cations on cellulose solubility in a neat imidazolium (MIM)-based ionic liquid (IL) [CnMIM][OAc] and [CnMIM][OAc]–DMSO binary system (n=0–6) was investigated. The correlation between cellulose solubility and Kamlet–Taft hydrogen bond basicity (β) was also examined. Cellulose solubility (g per mol IL) in neat [CnMIM][OAc] increased as the cation alkyl chain length decreased from 6 to 2. However, alkyl chain lengths of 1 and 0 resulted in extremely poor cellulose solubility, indicating that a chain length of 2 was optimal for dissolution of cellulose in the system. Cellulose solubility in the [CnMIM][OAc]–DMSO binary system (n=1–6) was greater than that in neat IL, with maximum solubility occurring at an IL mole fraction of ~0.2. Maximum cellulose solubility in the [CnMIM][OAc]–DMSO binary system was slightly better at even alkyl chain lengths (n=2, 4, or 6) than at odd chain lengths (n=1, 3, or 5), with the best solubility at n=4. More interestingly, maximum cellulose solubility and specific IL mole fraction in the IL-DMSO binary system were related with the β values of neat ILs, even with ILs containing different anionic species or cation alkyl chain lengths. This indicates that solubility information in IL-DMSO binary systems is influenced by the characteristics of neat ILs.

CS2 capture in the ionic liquid 1-alkyl-3-methylimidazolium acetate: reaction mechanism and free energetics

Reaction pathways for CS2 and COS in the ionic liquid, 1-ethyl-3-methylimidazolium (EMI+) acetate (OAc-), are studied using the ab initio self-consistent reaction field theory (SCRF) and molecular dynamics (MD) computer simulations. It is found that while CS2 converts to COS nearly at the 100% level through S/O exchange with acetate, both conversion and capture processes are kinetically possible for COS, yielding CO2/thioacetate and 1-ethyl-3-methylimidazole-2-thiocarboxylate (EMI-COS)/acetic acid as reaction products, respectively. These findings are in excellent agreement with recent experimental observations in the closely related 1-butyl-3-methylimidazolium acetate (BMI+OAc-) ionic liquid system. Constrained ab initio MD indicates that the capture reaction of COS (and CS2 if allowed) proceeds in a concerted fashion; viz., proton transfer from EMI+ to OAc- and carboxylation of EMI+ by COS (and CS2) occur concurrently, analogous to the concerted pathway proposed recently for CO2 capture in the imidazolium acetate ionic liquid family. As N-heterocyclic carbene (NHC) is not required, the concerted mechanism is fully consistent with the experimental fact that NHC has not been detected directly in this ionic liquid family. Computational analysis further predicts that if NHC would be present in the ionic liquid, it would react with CS2 and produce 1-ethyl-3-imidazole-2-dithiocarboxylate, prior to the conversion of CS2 to COS. Since such a dithiocarboxylate compound was not detected experimentally, the present analysis lends support to the view that NHC is not formed in the pure imidazolium acetate ionic liquid family.