Runcang Sun

Colloidal stability of negatively charged cellulose nanocrystalline in aqueous systems

Colloidal stability of negatively charged cellulose nanocrystalline (CNC) in the presence of inorganic and organic electrolytes was investigated by means of dynamic light scattering and atomic force microscopy. CNC could be well dispersed in distilled water due to the electrostatic repulsion among negatively charged sulfate ester groups. Increasing the concentration of inorganic cation ions (Na(+) and Ca(2+)) resulted in CNC aggregation. CNC in divalent cation ion Ca(2+) solution exhibited less stability than that in monovalent cation ion Na(+) solution. Organic low-molecular-weight electrolyte sodium dodecyl sulfate (SDS) favored the stability of CNC suspension, whereas organic high-molecular-weight electrolyte sodium carboxymethyl cellulose (CMC) induced CNC particle aggregation due to intermolecular bridging interaction or entanglement. Cationic polyacrylamide (CPAM) caused a serious aggregation of CNC particles even at low concentration of CPAM. At low ionic strength (Na(+), 1 mM), CNC were stable in aqueous solution at the pH range of 2-11.

Adsorption of heavy metals by a porous bioadsorbent from lignocellulosic biomass reconstructed in an ionic liquid.

A novel porous bioadsorbent for metal ion binding (Pd(2+) and Cd(2+)) was successfully prepared from lignocellulosic biomass in ionic liquid by homogeneous succinoylation and sequent chemical cross-linking. The morphology of the bioadsorbent and the interaction between bioadsorbent and metal ions was revealed by scanning electron microscopy and Fourier transform infrared spectroscopy. Results showed that the adsorption mechanism of the bioadsorbent was an ion exchange. A lower dose of cross-linker or higher carboxyl content increased the adsorption capacities of Pd(2+) and Cd(2+). The adsorption capacities of Pd(2+) and Cd(2+) remarkably increased as the pH of metal ion solutions increased. The pores in the bioadsorbent greatly favored the diffusion and adsorption of metal ions, and the adsorption equilibrium time was about 50 min. The adsorption of metal ions could be well explained by the Langmuir model, and the maximum adsorption capacities of Pd(2+) and Cd(2+) were 381.7 and 278.6 mg/g.

Long-chain anhydride modification: a new strategy for preparing xylan films.

Xylan, which is a widely abundant plant polymer, has been considered as an alternative for film preparation. Up to now, however, xylan films have suffered from brittleness, low mechanical strength, and humidity sensitivity. This paper describes a new and effective strategy to prepare xylan films with high mechanical strength and less moisture-sensitive properties by introducing long carbon chains into the xylan backbone. Furthermore, this work revealed some important details on the relationships between structure (molecular structure, aggregation behaviors, and surface morphology) and properties (film-forming performance, flexibility, tensile strength, and hydrophilicity) of xylan film. It was found that the hydrophobic carbon chains (2-octenylsuccinic anhydride half-ester groups) in the xylan backbone acted as steric hindrance and could effectively prevent xylan chains from aggregation. 2-Octenylsuccinic anhydride (2-OSA) modified xylan (2-OSA-X) demonstrated amorphous structure and had better film-forming performance than the unmodified xylan. 2-OSA-X films were smooth, flexible, and less moisture-sensitive and showed significantly increasing tensile strength at a low degree of substitution.

Hydrothermal conversion of xylose, glucose, and cellulose under the catalysis of transition metal sulfates.

Hydrothermal conversion (HTC) is an important thermochemical process to upgrade low-cost biomass into valuable chemicals or fuels. As compared with non-catalytic HTC, catalytic HTC shows high energy efficiency on biomass upgradation. In this work, the catalytic performances of various transition metal sulfates (Mn(2+), Fe(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), and Zn(2+)) in the HTCs of xylose, glucose, and cellulose under different conditions were explored. Among these catalysts, Zn(2+) and Ni(2+) showed obvious effects on the conversions of xylose, glucose, and cellulose into lactic acid, while Cu(2+) and Fe(3+), which could significantly accelerate the hydrolysis of cellulose into glucose at 200°C, displayed high efficiency on converting glucose and cellulose into levulinic acid and formic acid at high temperature. Additionally, significant positive correlative relationships among xylose, glucose, and cellulose degradations were observed. This study is helpful for screening appropriate catalysts for biomass upgradation through catalytic HTC of monosaccharide.

Rapid Synthesis of Cellulose Esters by Transesterification of Cellulose with Vinyl Esters under the Catalysis of NaOH or KOH in DMSO

Traditionally, a long reaction time was required in the synthesis of cellulose esters (CEs). In this work, dimethyl sulfoxide (DMSO)/aqueous NaOH or KOH was introduced as an efficient reaction system for rapidly synthesizing CEs by transesterification. Surprisingly, cellulose could react with vinyl acetate, vinyl propionate, and vinyl butyrate and synthesized cellulose acetate, cellulose propionate, and cellulose butyrate with a high degree of substitution (2.14-2.34) in 5 min, which was in sharp contrast to hours of existing methods. The effects of solvents, catalysts, and esterifying agents on the synthesis of CEs were comparatively investigated to better understand this method. The structure and thermal properties of obtained CEs were characterized by Fourier transform infrared (FTIR) and (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopies and differential scanning calorimetry. Results from these spectra confirmed the successful synthesis of these CEs. Furthermore, these CEs showed similar thermal properties compared to products obtained from other methods.

Conversion of xylose into furfural using lignosulfonic acid as catalyst in ionic liquid.

Preparation of biopolymer-based catalysts for the conversion of carbohydrate polymers to new energies and chemicals is a hot topic nowadays. With the aim to develop an ecological method to convert xylose into furfural without the use of inorganic acids, a biopolymer-derived catalyst (lignosulfonic acid) was successfully used to catalyze xylose into furfural in ionic acid ([BMIM]Cl). The characteristics of lignosulfonic acid (LS) and effects of solvents, temperature, reaction time, and catalyst loading on the conversion of xylose were investigated in detail, and the reusability of the catalytic system was also studied. Results showed that 21.0% conversion could be achieved at 100 °C for 1.5 h. The method not only avoids pollution from conventional mineral acid catalysts and organic liquids but also maked full use of a byproduct (lignin) from the pulp and paper industry, thus demonstrating an environmentally benign process for the conversion of carbohydrates into furfural.

Synthesis and characterization of cyanoethyl hemicelluloses and their hydrated products

A novel type of hemicellulosic derivative, cyanoethyl hemicelluloses (CEH), derived from xylan-rich hemicelluloses and acrylonitriles was successfully prepared in aqueous sodium hydroxide. The reaction was performed under various reaction conditions such as temperature, time, the amount of sodium hydroxide, and the molar ratio of acrylonitrile to anhydroxylose units in hemicelluloses, and the relationship between reaction condition and DS of the CEH was investigated in detail. A series of CEH with degree of substitution of cyanoethyl (DSC≡N) ranging from 0.23 to 1.64 were obtained. Importantly, CEH can undergo various reactions and convert into other macromolecules with functional groups like carboxylic acids, amine, aldehyde etc. In this work, H2O2/K2CO3/DMSO was used to hydrate CEH into carbamoylethyl hemicelluloses at room temperature. FT-IR, 1H and 13C NMR spectra confirmed the introduction of cyanoethyl groups into the hemicelluloses backbone and the presence of carbamoylethyl groups in the hydrated product. In addition, in the nucleophilic addition reaction, the hydroxyl groups at C-3 position of the anhydroxylose units were more active than these at C-2. TGA/DTG showed that CEH had lower thermal stability than hemicelluloses. This work provided a new macromolecule which can be used as a versatile platform for producing other functional macromolecules.

Microwave synthesis of cellulose/CuO nanocomposites in ionic liquid and its thermal transformation to CuO.

The purpose of this study is to develop a green strategy to synthesize the cellulose-based nanocomposites and open a new avenue to the high value-added applications of biomass. Herein, we reported a microwave-assisted ionic liquid route to the preparation of cellulose/CuO nanocomposites, which combined three major green chemistry principles: using environmentally friendly method, greener solvents, and sustainable resources. The influences of the reaction parameters including the heating time and the ratio of cellulose solution to ionic liquid on the products were discussed by X-ray powder diffraction, Fourier transform infrared spectrometry, and scanning electron microscopy. The crystallinity of CuO increased and the CuO shape changed from nanosheets to bundles and to particles with increasing heating time. The ratio of cellulose solution to ionic liquid also affected the shapes of CuO in nanocomposites. Moreover, CuO crystals were obtained by thermal treatment of the cellulose/CuO nanocomposites at 800 °C for 3 h in air.

Effects of pretreatments on crystalline properties and morphology of cellulose nanocrystals

Cellulose nanocrystals (CNCs) have drawn tremendous attention because of their extraordinary physical and chemical properties as well as renewability and sustainability. In this work, after a range of pretreatments, such as freeze-drying, ball-milling, mercerization, N-methylmorpholine-N-oxide dissolution and ionic liquid dissolution, various CNCs with different crystalline properties and morphologies were obtained by hydrolysis or oxidation. XRD and AFM were used to determine the influences of pretreatments on the crystalline properties and morphologies of CNCs. New methods, i.e., specific pretreatments followed by sulfuric acid hydrolysis or 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidation, were developed to obtain sphere-like CNCs. It was found that sphere-like CNCs were more likely to be obtained from cellulose materials possessing high accessibility. Pretreatments produced cellulose with various crystallinities and polymorphs, and therefore changed the yields of CNCs and influenced their morphology. CNCs prepared by TEMPO oxidation generally had smaller size than the corresponding products obtained by sulfuric acid hydrolysis. In addition, for the dissolved/regenerated cellulose, TEMPO oxidation was a better method to yield sphere-like CNCs than sulfuric acid hydrolysis.

The Microwave-Assisted Ionic-Liquid Method: A Promising Methodology in Nanomaterials

In recent years, the microwave-assisted ionic-liquid method has been accepted as a promising methodology for the preparation of nanomaterials and cellulose-based nanocomposites. Applications of this method in the preparation of cellulose-based nanocomposites comply with the major principles of green chemistry, that is, they use an environmentally friendly method in environmentally preferable solvents to make use of renewable materials. This minireview focuses on the recent development of the synthesis of nanomaterials and cellulose-based nanocomposites by means of the microwave-assisted ionic-liquid method. We first discuss the preparation of nanomaterials including noble metals, metal oxides, complex metal oxides, metal sulfides, and other nanomaterials by means of this method. Then we provide an overview of the synthesis of cellulose-based nanocomposites by using this method. The emphasis is on the synthesis, microstructure, and properties of nanostructured materials obtained through this methodology. Our recent research on nanomaterials and cellulose-based nanocomposites by this rapid method is summarized. In addition, the formation mechanisms involved in the microwave-assisted ionic-liquid synthesis of nanostructured materials are discussed briefly. Finally, the future perspectives of this methodology in the synthesis of nanostructured materials are proposed.