Lirong Tang

Ultrasonication-assisted manufacture of cellulose nanocrystals esterified with acetic acid

Esterified cellulose nanocrystals (E-CNCs) are cellulose derivatives that could be applied in biomedical and chemical industries. E-CNCs were prepared with cellulose pulp using a mixture of 17.5M acetic and 18.4M sulfuric acid with the aid of ultrasonication. The effects of esterification time (3-7h), ultrasonication time (with a frequency of 40 kHz, 0 to 6h) and temperature (68-75 °C) on the yield and degree of substitution (DS) of E-CNCs were evaluated. The sample obtained without ultrasonication had the lowest yield and DS value of 48.16% and 0.22, respectively, whereas ultrasonication for 5h at 70 °C resulted in a yield of 85.38% and a DS value of 0.46. Characterization indicated the successful esterification of hydroxyl groups of cellulose, and the width of rod-shaped E-CNCs was from 10 to 100 nm. The study provides a simple and convenient method to manufacture E-CNCs.

Manufacture of cellulose nanocrystals by cation exchange resin-catalyzed hydrolysis of cellulose

Cellulose nanocrystals (CNC) were prepared from microcrystalline cellulose (MCC) by hydrolysis with cation exchange resin (NKC-9) or 64% sulfuric acid. The cation exchange resin hydrolysis parameters were optimized by using the Box-Behnken design and response surface methodology. An optimum yield (50.04%) was achieved at a ratio of resin to MCC (w/w) of 10, a temperature of 48 °C and a reaction time of 189 min. Electron microscopy (EM) showed that the diameter of CNCs was about 10-40 nm, and the length was 100-400 nm. Regular short rod-like CNCs were obtained by sulfuric acid hydrolysis, while long and thin crystals of cellulose were obtained with the cation exchange resin. X-ray diffraction (XRD) showed that, compared with MCC, the crystallinity of H2SO4-CNC and resin-CNC increased from 72.25% to 77.29% and 84.26%, respectively. The research shows that cation exchange resin-catalyzed hydrolysis of cellulose could be an excellent method for manufacturing of CNC in an environmental-friendly way.

Organic solvent-free and efficient manufacture of functionalized cellulose nanocrystals via one-pot tandem reactions

An environmentally benign approach for the manufacture of maleic anhydride functionalized cellulose nanocrystals (MA-CNCs) via one-pot tandem reactions with H2SO4 as a catalyst under organic solvent-free conditions was put forward. The effects of ball milling time, ultrasonication temperature and time on the yield and degree of substitution (DS) have been explored.

One-pot tandem reactions for the preparation of esterified cellulose nanocrystals with 4-dimethylaminopyridine as a catalyst

An efficient approach for the manufacture of esterified cellulose nanocrystals (E-CNCs) via one-pot tandem reactions with 4-dimethylaminopyridine (DMAP) as a catalyst under mild operating conditions is put forward. The effects of ball milling time, reaction temperature and ultrasonication time on the yield and degree of substitution (DS) are explored. Characterization indicates the successful esterification of the hydroxyl groups of cellulose. The micromorphology and microstructure of the prepared E-CNCs are studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results show that the E-CNCs are short rod-like particles 130–230 nm in length and 20–40 nm in width, forming an interconnected network structure. X-ray diffraction (XRD) results indicate that the crystallinity index increases from 63.5% to 77.2%. The thermal properties of the E-CNCs are investigated by thermogravimetric analysis (TGA) and the results show that the E-CNCs exhibit higher thermal stability than cellulose pulp.

One-pot construction of cellulose-gelatin supramolecular hydrogels with high strength and pH-responsive properties

Inspired by the supramolecular structure of cellulose, cellulose-gelatin supramolecular hydrogels with high strength and pH-sensitivity were constructed in a basic-based solvent system, ethylene diamine/potassium thiocyanate (EDA/KSCN) with the aid of cyclic freezing-thawing. The investigation on the characteristics of supramolecular hydrogels revealed that repeated freezing-thawing cycles played an important role in the formation of the physical cross-linked supramolecular network structure between cellulose and gelatin. The mechanical properties of supramolecular hydrogels were much higher than pure cellulose and gelatin hydrogel, and the compressive strength was 9.6 times higher than that of pure gelatin hydrogel. The synergistic effect between hydrogen-bonding interaction and the reinforcement of regenerated cellulose nanofibrils (CNF) contributed to the superior mechanical performance. Furthermore, the swelling kinetics tests showed that the supramolecular hydrogels exhibited excellent pH-responsibility, indicating potential applications in biomedical fields. Thus, a straightforward route to construct natural polymer-based hydrogels with supramolecular structure through physical crosslinking strategy without employing hazardous crosslinking agents was developed, paving the way for the design of new types of hydrogels.

Diaqua­bis­(2-hy­droxy-5-meth­oxy­benzoato-κO 1)zinc

The title compound, [Zn(C8H7O4)2(H2O)2], has been synthesized by hydrothermal methods. The ZnII atom, whose symmetry element is a twofold axis, is four coordinated by two O atoms from 5-methoxysalicylate anions and two aqua O atoms in a distorted tetrahedral geometry. In the crystal, molecules are linked into a layer by O—H⋯O hydrogen bonds, which stabilize the packing.

1-Cyclo­propyl-6-fluoro-7-(4-nitro­so­piperazin-1-yl)-4-oxo-1,4-dihydro­quinoline-3-carboxylic acid

The title compound, C17H17FN4O4, is a derivative of ciprofloxacin [1-cyclopropyl-6-fluoro-4-oxo-7-(1-piperazinyl)-1,4-dihydroquinoline-3-carboxylic acid]. The crystal packing is stabilized by intermolecular C—H⋯O hydrogen bonds together with π–π electron ring interactions [centroid–centroid separations between quinoline rings of 3.5864 (11) and 3.9339 (13) Å]. A strong intramolecular O—H⋯O hydrogen bonds is present as well as an intramolecular C—H⋯F interaction.